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draft-ietf-sigtran-m3ua-09

Description: Request For Comments

You can download source copies of the file as follows:

draft-ietf-sigtran-m3ua-09.txt in text format.

Listed below is the contents of file draft-ietf-sigtran-m3ua-09.txt.


Network Working Group                                   Greg Sidebottom
INTERNET-DRAFT                                      gregside consulting
                                                   Javier Pastor-Balbs
                                                             Ian Rytina
                                                               Ericsson
                                                           Guy Mousseau
                                                        Nortel Networks
                                                             Lyndon Ong
                                                                  Ciena
                                             Hanns Juergen Schwarzbauer
                                                                Siemens
                                                      Klaus Gradischnig
                                                                NeuStar
                                                          Ken Morneault
                                                                  Cisco
                                                          Mallesh Kalla
                                                              Telcordia
                                                         Normand Glaude
                                               Performance Technologies
                                                         Brian Bidulock
                                                                OpenSS7
                                                          John Loughney 
                                                                  Nokia  
                                                    

Expires in six months                                         Oct 2001

                SS7 MTP3-User Adaptation Layer (M3UA)
                  <draft-ietf-sigtran-m3ua-09.txt>

Status of This Memo

This document is an Internet-Draft and is in full conformance with all 
provisions of Section 10 of RFC 2026. Internet-Drafts are working 
documents of the Internet Engineering Task Force (IETF), its areas, and 
its working groups.  Note that other groups may also distribute working 
documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months 
and may be updated, replaced, or obsoleted by other documents at any 
time.  It is inappropriate to use Internet-Drafts as reference material 
or to cite them other than as 'work in progress.'

     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/1id-abstracts.html

     The list of Internet-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html

To learn the current status of any Internet-Draft, please check the 
'1id-abstracts.txt' listing contained in the Internet- Drafts Shadow 
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), 
munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or 
ftp.isi.edu (US West Coast).

Sidebottom et al                                              [Page 1]

Internet Draft         SS7 MTP3-User Adaptation Layer         Oct 2001

Abstract

This Internet Draft defines a protocol for supporting the transport of 
any SS7 MTP3-User signalling (e.g., ISUP and SCCP messages) over IP 
using the services of the Stream Control Transmission Protocol.  Also, 
provision is made for protocol elements that enable a seamless 

operation of the MTP3-User peers in the SS7 and IP domains. This 
protocol would be used between a Signalling Gateway (SG) and a Media 
Gateway Controller (MGC) or IP-resident Database.  It is assumed that 
the SG receives SS7 signalling over a standard SS7 interface using the 
SS7 Message Transfer Part (MTP) to provide transport. 

Sidebottom et al                                              [Page 2]

Internet Draft         SS7 MTP3-User Adaptation Layer         Oct 2001

                        TABLE OF CONTENTS

1. Introduction.......................................................4
    1.1 Scope.........................................................4
    1.2 Terminology...................................................4
    1.3 M3UA Overview.................................................6
    1.4 Functional Areas.............................................12
    1.5 Sample Configurations........................................20
    1.6 Definition of M3UA Boundaries................................23
2. Conventions.......................................................28
3. M3UA Protocol Elements............................................28
    3.1 Common Message Header........................................28
    3.2 Variable Length Parameter....................................31
    3.3 Transfer Messages............................................33
    3.4 SS7 Signalling Network management (SSNM) Messages............36
    3.5 ASP State Maintenance (ASPM) Messages........................45
    3.6 Routing Key Management (RKM) Messages........................48
    3.7 ASP Traffic Maintenance (ASPTM) Messages.....................58
    3.8 Management(MGMT) Messages....................................62
4. Procedures........................................................66
    4.1 Procedures to Support the M3UA-User .........................66
    4.2 Procedures to Support the Management of SCTP Associations ...69
    4.3 AS and ASP State Maintenance.................................69
    4.4 Routing Key Management Procedures............................81
    4.5 Procedures to Support the Availability or Congestion Status
        of SS7 Destination...........................................83
    4.6 MTP3 Restart.................................................86
5. Examples of M3UA Procedures.......................................86
    5.1 Establishment of Association and Traffic 
        Between SGs and ASPs.........................................86
    5.2 ASP traffic Failover Examples................................91
    5.3 Normal Withdrawal of an ASP from an Application Server 
        and Teardown of an Association...............................92
    5.4.M3UA/MTP3-User Boundary Examples.............................93
6. Security..........................................................97
    6.1 Introduction.................................................97
    6.2 Threats......................................................97
    6.3 Protecting Confidentiality...................................98
7. IANA Considerations...............................................98
    7.1 SCTP Payload Protocol Identifier.............................98
    7.2 M3UA Port Number.............................................98
    7.3 M3UA Protocol Extensions.....................................99
8. Acknowledgements.................................................100
9. References.......................................................100
11.  Author's Addresses.............................................102

Sidebottom et al                                              [Page 3]

Internet Draft         SS7 MTP3-User Adaptation Layer         Oct 2001

1.  Introduction

1.1 Scope

There is a need for Switched Circuit Network (SCN) signalling protocol 
delivery from an SS7 Signalling Gateway (SG) to a Media Gateway 
Controller (MGC) or IP-resident Database as described in the Framework 
Architecture for Signalling Transport [1].  The delivery mechanism 
SHOULD meet the following criteria: 

*  Support for the transfer of all SS7 MTP3-User Part messages (e.g., 
   ISUP, SCCP, TUP, etc.)
*  Support for the seamless operation of MTP3-User protocol peers
*  Support for the management of SCTP transport associations and 
   traffic between an SG and one or more MGCs or IP-resident Databases 
*  Support for MGC or IP-resident Database process failover and load
   sharing
*  Support for the asynchronous reporting of status changes to 
   management 

In simplistic transport terms, the SG will terminate SS7 MTP2 and MTP3 
protocol layers and deliver ISUP, SCCP and/or any other MTP3-User 
protocol messages, as well as certain MTP network management events, 
over SCTP transport associations to MTP3-User peers in MGCs or IP-
resident Databases.

1.2 Terminology

Application Server (AS) - A logical entity serving a specific Routing 
Key. An example of an Application Server is a virtual switch element 
handling all call processing for a unique range of PSTN trunks, 
identified by an SS7 SIO/DPC/OPC/CIC_range.  Another example is a 
virtual database element, handling all HLR transactions for a 
particular SS7 DPC/OPC/SCCP_SSN combination.  The AS contains a set of 
one or more unique Application Server Processes, of which one or more 
is normally actively processing traffic.  Note that there is a 1:1 
relationship between an AS and a Routing Key.

Application Server Process (ASP) - A process instance of an Application 
Server. An Application Server Process serves as an active or backup 
process of an Application Server (e.g., part of a distributed virtual 
switch or database). Examples of ASPs are processes (or process 
instances) of MGCs, IP SCPs or IP HLRs.  An ASP contains an SCTP 
endpoint and may be configured to process signalling traffic within 
more than one Application Server. 

Sidebottom et al                                              [Page 4]

Internet Draft       SS7 MTP3-User Adaptation Layer         Oct 2001

Association - An association refers to an SCTP association.  The 
association provides the transport for the delivery of MTP3-User 
protocol data units and M3UA adaptation layer peer messages.

IP Server Process (IPSP) - A process instance of an IP-based 
application.  An IPSP is essentially the same as an ASP, except that it
uses M3UA in a point-to-point fashion.  Conceptually, an IPSP does not 
use the services of a Signalling Gateway.

Signalling Gateway Process (SGP) - A process instance of a Signalling 
Gateway.  It serves as an active, backup, loadsharing or broadcast 
process of a Signalling Gateway.

Signalling Gateway - An SG is a signaling agent that receives/sends SCN 
native signaling at the edge of the IP network [1].  An SG appears to 
the SS7 network as an SS7 Signalling Point.  An SG contains a set of 
one or more unique Signalling Gateway Processes, of which one or more 
is normally actively processing traffic.  Where an SG contains more 
than one SGP, the SG is a logical entity and the contained SGPs are 
assumed to be coordinated into a single management view to the SS7 
network and to the supported Application Servers.

Signalling Process - A process instance that uses M3UA to communicate 
with other signalling processes.  An ASP, an SGP and an IPSP are all 
signalling processes.

Routing Key: A Routing Key describes a set of SS7 parameters and 
parameter values that uniquely define the range of signalling traffic 
to be handled by a particular Application Server. Parameters within the 
Routing Key cannot extend across more than a single Signalling Point 
Management Cluster.

Routing Context - A value that uniquely identifies a Routing Key.
Routing Context values are either configured using a configuration 
management interface, or by using the routing key management procedures 
defined in this document.

Failover - The capability to reroute signalling traffic as required 
to an alternate Application Server Process, or group of ASPs, within an 
Application Server in the event of failure or unavailability of a 
currently used Application Server Process.  Failover also applies upon 
the return to service of a previously unavailable Application Server 
Process.

Signalling Point Management Cluster (SPMC) - The complete set of 
Application Servers represented to the SS7 network under a single MTP 
entity (Signalling Point) in one specific Network Appearance.  SPMCs 
are used to aggregate the availability, congestion, and user part status 
of an MTP entity (Signalling Point) that is distributed in the IP domain, 
for the purpose of supporting MTP3 management procedures 

Sidebottom et al                                              [Page 5]

Internet Draft       SS7 MTP3-User Adaptation Layer         Oct 2001

towards the SS7 network.  In some cases, the SG itself may also be a 
member of the SPMC.  In this case, the SG availability /congestion 
/User_Part status should also be taken into account when considering any 
supporting MTP3 management actions.  

MTP - The Message Transfer Part of the SS7 protocol.

MTP3 - MTP Level 3, the signalling network layer of SS7

MTP3-User - Any protocol normally using the services of the SS7 MTP3 
(e.g., ISUP, SCCP, TUP, etc.).

Network Appearance - The Network Appearance is a M3UA local reference 
shared by SG and AS (typically an integer) that together with an 
Signaling Point Code uniquely identifies an SS7 node by indicating 
the specific SS7 network it belongs to. It can be used to distinguish 
between signalling traffic associated with different networks being 
sent between the SG and the ASP over a common SCTP association. An 
example scenario is where an SG appears as an element in multiple 
separate national SS7 networks and the same Signaling Point Code 
value may be reused in different networks.

Network Byte Order: Most significant byte first, a.k.a Big Endian.

Layer Management - Layer Management is a nodal function that handles 
the inputs and outputs between the M3UA layer and a local management 
entity.

Host - The computing platform that the process (SGP, ASP or IPSP) is 
running on.

Stream - A stream refers to an SCTP stream; a unidirectional logical 
channel established from one SCTP endpoint to another associated SCTP 
endpoint, within which all user messages are delivered in-sequence 
except for those submitted to the unordered delivery service.

1.3 M3UA Overview

1.3.1 Protocol Architecture.  

The framework architecture that has been defined for SCN signalling 
transport over IP [1] uses multiple components, including a common 
signalling transport protocol and an adaptation module to support the 
services expected by a particular SCN signalling protocol from its 
underlying protocol layer.  

Within the framework architecture, this document defines an MTP3-User 
adaptation module suitable for supporting the transfer of messages of 
any protocol layer that is identified to the MTP Level 3 as an MTP 
User.  The list of these protocol layers include, but is not limited 

Sidebottom et al                                              [Page 6]

Internet Draft       SS7 MTP3-User Adaptation Layer         Oct 2001

to, ISDN User Part (ISUP) [2,3,4], Signalling Connection Control Part 
(SCCP) [5,6,7] and Telephone User Part (TUP) [8].  TCAP [9,10,11] or 
RANAP [12] messages are transferred transparently by the M3UA protocol 
as SCCP payload, as they are SCCP-User protocols.  

It is recommended that M3UA use the services of the Stream Control 
Transmission Protocol (SCTP) [13] as the underlying reliable common 
signalling transport protocol. This is to take advantage of various 
SCTP features such as:

   - Explicit packet-oriented delivery (not stream-oriented),
   - Sequenced delivery of user messages within multiple streams,
     with an option for order-of-arrival delivery of individual
     user messages, 
   - Optional multiplexing of user messages into SCTP datagrams, 
   - Network-level fault tolerance through support of multi-homing
     at either or both ends of an association,
   - Resistance to flooding and masquerade attacks, and   
   - Data segmentation to conform to discovered path MTU size. 

Under certain scenarios, such as back-to-back connections without 
redundancy requirements, the SCTP functions above might not be a 
requirement and TCP MAY be used as the underlying common transport 
protocol.  

1.3.2 Services Provided by the M3UA Layer

The M3UA Layer at an ASP or IPSP provides the equivalent set of 
primitives at its upper layer to the MTP3-Users as provided by the MTP 
Level 3 to its local MTP3-Users at an SS7 SEP.  In this way, the ISUP 
and/or SCCP layer at an ASP or IPSP is unaware that the expected MTP3 
services are offered remotely from an MTP3 Layer at an SGP, and not by 
a local MTP3 layer.  The MTP3 layer at an SGP may also be unaware that 
its local users are actually remote user parts over M3UA.  In effect, 
the M3UA extends access to the MTP3 layer services to a remote IP-based 
application.  The M3UA layer does not itself provide the MTP3 services.  
However, in the case where an ASP is connected to more than one SG, 
the M3UA layer at an ASP should maintain the status of configured SS7 
destinations and route messages according to the availability and 
congestion status of the routes to these destinations via each SG.

The M3UA layer may also be used for point-to-point signalling between 
two IP Server Processes (IPSPs).  In this case, the M3UA layer provides 
the same set of primitives and services at its upper layer as the MTP3. 
However, in this case the expected MTP3 services are not offered 
remotely from an SGP.  The MTP3 services are provided but the 
procedures to support these services are a subset of the MTP3 
procedures due to the simplified point-to-point nature of the IPSP to 
IPSP relationship.

Sidebottom et al                                             [Page 7]

Internet Draft       SS7 MTP3-User Adaptation Layer         Oct 2001

1.3.2.1 Support for the Transport of MTP3-User Messages

The M3UA layer provides the transport of MTP-TRANSFER primitives across 
an established SCTP association between an SGP and an ASP or between 
IPSPs.

At an ASP, in the case where a destination is reachable via multiple 
SGPs, the M3UA layer must also choose via which SGP the message is to 
be routed or support load balancing across the SGPs, minimizing 
missequencing.

The M3UA layer does not impose a 272-octet signalling information field 
(SIF) length limit as specified by the SS7 MTP Level 2 protocol [14] 
[15] [16].  Larger information blocks can be accommodated directly by 
M3UA/SCTP, without the need for an upper layer segmentation/reassembly 
procedure as specified in recent SCCP or ISUP versions.  However, in 
the context of an SG, the maximum 272-octet block size must be followed 
when interworking to a SS7 network that does not support the transfer 
of larger information blocks to the final destination.  This avoids 
potential ISUP or SCCP fragmentation requirements at the SGPs.  The 
provisioning and configuration of the SS7 network determines the 
restriction placed on the maximum block size.  Some configurations 
(e.g., Broadband MTP [20]) may permit larger block sizes.

1.3.2.2 Native Management Functions

The M3UA layer provides the capability to indicate errors associated 
with received M3UA messages and to notify, as appropriate, local 
management and/or the peer M3UA.

1.3.2.3 Interworking with MTP3 Network Management Functions

At the SGP, the M3UA layer provides interworking with MTP3 
management functions to support seamless operation of the user SCN 
signalling applications in the SS7 and IP domains.  This includes:
 
  - Providing an indication to MTP3-Users at an ASP that a destination 
    in the SS7 network is not reachable.

  - Providing an indication to MTP3-Users at an ASP that a destination 
    in the SS7 network is now reachable.

  - Providing an indication to MTP3-Users at an ASP that messages to a 
    destination in the SS7 network are experiencing SS7 congestion.

  - Providing an indication to the M3UA layer at an ASP that the routes 
    to a destination in the SS7 network are restricted.

Sidebottom et al                                             [Page 8]

Internet Draft       SS7 MTP3-User Adaptation Layer         Oct 2001

  - Providing an indication to MTP3-Users at an ASP that a MTP3-User 
    peer is unavailable.  

The M3UA layer at an ASP keeps the state of the routes to remote SS7 
destinations and may initiate an audit of the availability, the 
restricted or the congested state of remote SS7 destinations.  This 
information is requested from the M3UA layer at the SGP. 

The M3UA layer at an ASP may also indicate to the SG that the M3UA 
layer itself or the ASP or the ASP's Host is congested.

1.3.2.4 Support for the Management of SCTP Associations between the SGP 
and ASPs.

The M3UA layer at the SGP maintains the availability state of all 
configured remote ASPs, to manage the SCTP Associations and 
the traffic between the M3UA peers.  As well, the active/inactive and 
congestion state of remote ASPs is maintained.

The M3UA layer MAY be instructed by local management to establish an 
SCTP association to a peer M3UA node.  This can be achieved using the 
M-SCTP_ESTABLISH primitives to request, indicate and confirm the 
establishment of an SCTP association with a peer M3UA node.  In order 
to avoid redundant SCTP associations between two M3UA peers, one side 
(client) SHOULD be designated to establish the SCTP association, or 
M3UA configuration information maintained to detect redundant 
associations (e.g., via knowledge of the expected local and remote SCTP 
endpoint addresses).

Local management MAY request from the M3UA layer the status of the 
underlying SCTP associations using the M-SCTP_STATUS request and 
confirm primitives.  Also, the M3UA MAY autonomously inform local 
management of the reason for the release of an SCTP association, 
determined either locally within the M3UA layer or by a primitive from 
the SCTP.

Also the M3UA layer MAY inform the local management of the change in 
status of an ASP or AS.  This MAY be achieved using the M-ASP_STATUS 
request or M-AS_STATUS request primitives.

1.3.2.5 Support for the Management of Connections to Multiple SGPs

As shown in Figure 1 an ASP may be connected to multiple SGPs. In such 
a case a particular SS7 destination may be reachable via more than one 
SGP and/or SG, i.e., via more than one route. As MTP3 users only 
maintain status on a destination and not on a route basis, the M3UA 
layer must maintain the status (availability, restriction, and/or 
congestion of route to destination) of the individual routes, derive 
the overall availability or congestion status of the destination 

Sidebottom et al                                              [Page 9]

Internet Draft       SS7 MTP3-User Adaptation Layer         Oct 2001

from the status of the individual routes, and inform the MTP3 users 
of this derived status whenever it changes.

1.3.3 Signalling Network Architecture

A Signalling Gateway is used to support the transport of MTP3-User 
signalling traffic received from the SS7 network to multiple 
distributed ASPs (e.g., MGCs and IP Databases).  Clearly, the M3UA 
protocol is not designed to meet the performance and reliability 
requirements for such transport by itself.  However, the conjunction 
of distributed architecture and redundant networks provides support 
for reliable transport of signalling traffic over IP.  The M3UA 
protocol is flexible enough to allow its operation and management 
in a variety of physical configurations, enabling Network Operators 
to meet their performance and reliability requirements.  

To meet the stringent SS7 signalling reliability and performance 
requirements for carrier grade networks, Network Operators SHOULD 
ensure that no single point of failure is present in the end-to-end 
network architecture between an SS7 node and an IP-based application.  
This can typically be achieved through the use of redundant SGPs or 
SGs, redundant hosts, and the provision of redundant QOS-bounded IP 
network paths for SCTP Associations between SCTP End Points. Obviously, 
the reliability of the SG, the MGC and other IP-based functional 
elements also needs to be taken into account.  The distribution of ASPs 
and SGPs within the available Hosts MAY also be considered.  As an 
example, for a particular Application Server, the related ASPs could 
be distributed over at least two Hosts.

One example of a physical network architecture relevant to SS7 carrier-
grade operation in the IP network domain is shown in Figure 1 below:

Sidebottom et al                                              [Page 10]

Internet Draft       SS7 MTP3-User Adaptation Layer         Oct 2001

          SG                                     MGC

  Host#1 **************                          ************** Host#3
     =   *  ********__*__________________________*__********  *   =
         *  * SGP1 *__*_____      _______________*__* ASP1 *  *  MGC1
         *  ********  *     \    /               *  ********  *
         *  ********__*______\__/________________*__********  *
         *  * SGP2 *__*_______\/______      _____*__* ASP2 *  *
         *  ********  *       /\      |    |     *  ********  *
         *      :     *      /  \     |    |     *      :     *
         *  ********  *     /    \    |    |     *  ********  *
         *  * SGPn *  *     |    |    |    |     *  * ASPn *  *
         *  ********  *     |    |    |    |     *  ********  *
         **************     |    |    |    |     **************
                            |    |    \    /
  Host#2 **************     |    |     \  /      ************** Host#4
     =   *  ********__*_____|    |______\/_______*__********  *   =
         *  * SGP1 *__*_________________/\_______*__* ASP1 *  *  MGC2
         *  ********  *                /  \      *  ********  *
         *  ********__*_______________/    \_____*__********  *
         *  * SGP2 *__*__________________________*__* ASP2 *  *
         *  ********  *                          *  ********  *
         *      :     *     SCTP Associations    *      :     *
         *  ********  *                          *  ********  *
         *  * SGPn *  *                          *  * ASPn *  *
         *  ********  *                          *  ********  *
         **************                          **************

                      Figure 1 - Physical Model

In this model, each host MAY have many application processes.  In the 
case of the MGC, an ASP may provide service to one or more Application 
Servers, and is identified as an SCTP end point. One or more 
Signalling Gateway Processes make up a single Signalling Gateway.

This example model can also be applied to IPSP-IPSP signalling.  In 
this case, each IPSP MAY have its services distributed across 2 hosts 
or more, and may have multiple server processes on each host.

In the example above, each signalling process (SGP, ASP or IPSP) is the 
end point to more than one SCTP association, leading to more than one 
other signalling processes.  To support this, a signalling process must 
be able to support distribution of M3UA messages to many simultaneous 
active associations.  This message distribution function is based on 
the status of provisioned Routing Keys, the status of the signalling 
routes to signalling points in the SS7 network , and the redundancy 
model (active-standby, load sharing, broadcast, n+k) of the remote 
signalling processes.

Sidebottom et al                                             [Page 11]

Internet Draft       SS7 MTP3-User Adaptation Layer         Oct 2001

For carrier grade networks, the failure or isolation of a particular 
signalling process should not cause stable calls or transactions to be 
lost.  This implies that signalling processes need, in some cases, to 
share the call/transaction state or be able to pass the call state 
information between each other.  In the case of ASPs performing call 
processing, coordination may also be required with the related Media 
Gateway to transfer the MGC control for a particular trunk termination.  
However, this sharing or communication of call/transaction state 
information is outside the scope of this document.

This model serves as an example.  M3UA imposes no restrictions as to 
the exact layout of the network elements, the message distribution 
algorithms and the distribution of the signalling processes.  Instead, 
it provides a framework and a set of messages that allow for a flexible 
and scalable signalling network architecture, aiming to provide 
reliability and performance.

1.4 Functional Areas

1.4.1 Signalling Point Code Representation

For example, within an SS7 network, a Signalling Gateway might be 
charged with representing a set of nodes in the IP domain into the SS7 
network for routing purposes.  The SG itself, as a signalling point in 
the SS7 network, might also be addressable with an SS7 Point Code for 
MTP3 Management purposes. The SG Point Code might also be used for 
addressing any local MTP3-Users at the SG such as a local SCCP layer.

An SG may be logically partitioned to operate in multiple SS7 network 
appearances.  In such a case, the SG could be addressable with a Point 
Code in each network appearance, and represents a set of nodes in the 
IP domain into each SS7 network.  Alias Point Codes [15] may also be 
used within an SG network appearance. 

Where an SG contains more than one SGP, the MTP3 routeset, SPMC and 
remote AS/ASP states of each SGP SHOULD be coordinated across all the 
SGPs.  Rerouting of traffic between the SGPs SHOULD also be supported.

Application Servers can be represented under the same Point 
Code of the SG, their own individual Point Codes or grouped with other 
Application Servers for Point Code preservation purposes.  A single 
Point Code may be used to represent the SG and all the Application 
Servers together, if desired. 

If an ASP or group of ASPs is available to the SS7 network via more 
than one SG, each with its own Point Code, the ASP(s) will typically be 
represented by a Point Code that is separate from any SG Point Code.  
This allows, for example, these SGs to be viewed from the SS7 network 
as "STPs", each 

Sidebottom et al                                             [Page 12]

Internet Draft       SS7 MTP3-User Adaptation Layer         Oct 2001

having an ongoing "route" to the same ASP(s).  Under failure conditions 
where the ASP(s) become(s) unavailable from one of the SGs, this 
approach enables MTP3 route management messaging between the SG and SS7 
network, allowing simple SS7 rerouting through an alternate SG without 
changing the Destination Point Code Address of SS7 traffic to the 
ASP(s). 

Where a particular AS can be reached via more than one SGP, the 
corresponding Routing Keys in the SGPs should be identical.  (Note: 
It is possible for the SGP Routing Key configuration data to be 
temporarily out-of-synch during configuration updates).

                           +--------+ 
                           |        | 
              +------------+  SG 1  +--------------+ 
  +-------+   |  SS7 links | "STP"  |  IP network  |     ---- 
  |  SEP  +---+            +--------+              +---/      \ 
  |   or  |                    |*                      | ASPs  | 
  |  STP  +---+            +--------+              +---\      / 
  +-------+   |            |        |              |     ---- 
              +------------+  SG 2  +--------------+ 
                           | "STP"  | 
                           +--------+

* Note:.  SG-to-SG communication (i.e., "C-links") is recommended for 
carrier grade networks, using an MTP3 linkset or an equivalent, to 
allow rerouting between the SGs in the event of route failures.  
Where SGPs are used, inter-SGP communication might be used.  
Inter-SGP protocol is outside of the scope of this document.

The following example shows a signalling gateway partitioned into two 
network appearances.

                               SG
  +-------+              +---------------+
  |  SEP  +--------------| SS7 Ntwk |M3UA|              ----
  +-------+   SS7 links  |   "A"    |    |            /      \
                         |__________|    +-----------+  ASPs  |
                         |          |    |            \      /
  +-------+              | SS7 Ntwk |    |              ----
  |  SEP  +--------------+   "B"    |    |
  +-------+              +---------------+

1.4.2 Routing Contexts and Routing Keys

1.4.2.1 Overview

The distribution of SS7 messages between the SGP and the Application 
Servers is determined by the Routing Keys and their associated Routing
Contexts. A Routing Key is essentially a set of SS7 parameters used to 

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filter SS7 messages, whereas the Routing Context parameter is a 4-byte 
value (integer) that is associated to that Routing Key in a 1:1 
relationship. The Routing Context therefore can be viewed as an index 
into a sending node's Message Distribution Table containing the Routing 
Key entries.

Possible SS7 address/routing information that comprise a Routing Key 
entry includes, for example, the OPC, DPC, SIO found in the MTP3 
routing label, or MTP3-User specific fields (such as the ISUP CIC, SCCP 
subsystem number).  Some example Routing Keys are: the DPC alone, the 
DPC/OPC combination, the DPC/OPC/CIC combination, or the DPC/SSN 
combination.  The particular information used to define an M3UA 
Routing Key is application and network dependent, and none of the 
above examples are mandated.  

An Application Server Process may be configured to process signalling 
traffic related to more than one Application Server, over a single SCTP 
Association.  In ASP Active and ASP Inactive management messages, the 
signalling traffic to be started or stopped is discriminated by the 
Routing Context parameter.  At an ASP, the Routing Context parameter 
uniquely identifies the range of signalling traffic associated with 
each Application Server that the ASP is configured to receive.

1.4.2.2 Routing Key Limitations

Routing Keys SHOULD be unique in the sense that each received SS7 
signalling message SHOULD have a full or partial match to a single 
routing result. It is not necessary for the parameter range values 
within a particular Routing Key to be contiguous.  For example, an 
AS could be configured to support call processing for multiple ranges 
of PSTN trunks that are not represented by contiguous CIC values. 

1.4.2.3 Managing Routing Contexts and Routing Keys

There are two ways to provision a Routing Key at an SGP. A Routing Key 
may be configured statically using an implementation dependent 
management interface, or dynamically using the M3UA Routing Key 
registration procedure. 

When using a management interface to configure Routing Keys, the 
message distribution function within the SGP is not limited to the set 
of parameters defined in this document.  Other implementation dependent 
distribution algorithms may be used.

1.4.2.4 Message Distribution at the SGP

To direct messages received from the SS7 MTP3 network to the 
appropriate IP destination, the SGP must perform a message distribution 
function using information from the received MTP3-User message.

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To support this message distribution, the SGP might, for example, 
maintain the equivalent of a network address translation table, mapping 
incoming SS7 message information to an Application Server for a 
particular application and range of traffic.  This could be accomplished 
by comparing elements of the incoming SS7 message to currently defined 
Routing Keys in the SGP.  These Routing Keys could in turn map directly 
to an Application Server that is enabled by one or more ASPs.  These 
ASPs provide dynamic status information regarding their availability, 
traffic handling capability and congestion to the SGP using various 
management messages defined in the M3UA protocol.  

The list of ASPs in an AS is assumed to be dynamic, taking into account 
the availability, traffic handling capability and congestion status of 
the individual ASPs in the list, as well as configuration changes and 
possible failover mechanisms. 

Normally, one or more ASPs are active (i.e., currently processing 
traffic) in the AS but in certain failure and transition cases it is 
possible that there may be no active ASP available.  Broadcast, 
loadsharing and backup scenarios are supported.

When there is no matching Routing Key entry for an incoming SS7 
message, a default treatment MAY be specified.  Possible solutions are 
to provide a default Application Server at the SGP that directs all 
unallocated traffic to a (set of) default ASP(s), or to drop the 
message and provide a notification to layer management.  The treatment 
of unallocated traffic is implementation dependent.

1.4.2.5 Message Distribution at the ASP

The ASP must choose an SGP to direct a message to the SS7 network.  
This is accomplished by observing the Destination Point Code (and 
possibly other elements of the outgoing message such as the SLS value).  

Implementation Note: Where more than one route (or SGP) is 
possible for routing to the SS7 network, the ASP could, for example, 
maintain a dynamic table of available SGP routes for the SS7 
destinations, taking into account the SS7 destination 
availability/restricted/congestion status received from the SGP(s), the 
availability status of the individual SGPs and configuration changes 
and failover mechanisms. There is, however, no M3UA messaging to manage 
the status of an SGP (e.g., SGP-Up/Down/Active/Inactive messaging).  

Whenever an SCTP association to an SGP exists, the SGP is assumed to 
be ready for the purposes of responding to M3UA ASPSM messages 
(Refer to Section 3).  

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1.4.3 SS7 and M3UA Interworking

In the case of SS7 and M3UA interworking, the M3UA adaptation layer is 
designed to provide an extension of the MTP3 defined user primitives.

1.4.3.1 Signalling Gateway SS7 Layers

The SG is responsible for terminating MTP Level 3 of the SS7 protocol, 
and offering an IP-based extension to its users.

>From an SS7 perspective, it is expected that the Signalling Gateway 
transmits and receives SS7 Message Signalling Units (MSUs) to and 
from the PSTN over a standard SS7 network interface, using the SS7 
Message Transfer Part (MTP) [14,15,16] to provide reliable transport of 
the messages.

As a standard SS7 network interface, the use of MTP Level 2 signalling 
links is not the only possibility.  ATM-based High Speed Links can also 
be used with the services of the Signalling ATM Adaptation Layer (SAAL) 
[17,18].  

Note: It is also possible for IP-based interfaces to be present, using 
the services of the MTP2-User Adaptation Layer (M2UA) [26] or M2PA [27].  

These could be terminated at a Signalling Transfer Point (STP) or 
Signalling End Point (SEP).  Using the services of MTP3, the SG could 
be capable of communicating with remote SS7 SEPs in a quasi-associated 
fashion, where STPs may be present in the SS7 path between the SEP and 
the SG.

1.4.3.2 SS7 and M3UA Interworking at the SG

The SGP provides a functional interworking of transport functions 
between the SS7 network and the IP network by also supporting the M3UA 
adaptation layer.  It allows the transfer of MTP3-User signalling 
messages to and from an IP-based Application Server Process where the 
peer MTP3-User protocol layer exists.

For SS7 user part management, it is required that the MTP3-User 
protocols at ASPs receive indications of SS7 signalling point 
availability, SS7 network congestion, and remote User Part 
unavailability as would be expected in an SS7 SEP node.  To accomplish 
this, the MTP-PAUSE, MTP-RESUME and MTP-STATUS indication primitives 
received at the MTP3 upper layer interface at the SG need to be 
propagated to the remote MTP3-User lower layer interface at the ASP. 

MTP3 management messages (such as TFPs or TFAs received from the SS7 
network) MUST NOT be encapsulated as Data message Payload Data and sent 
either from SG to ASP or from ASP to SG.  The SG MUST terminate these 
messages and generate M3UA messages as appropriate. 

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1.4.3.3 Application Server

A cluster of application servers is responsible for providing the 
overall support for one or more SS7 upper layers.  From an SS7 
standpoint, a Signalling Point Management Cluster (SPMC) provides 
complete support for the upper layer service for a given point code.  
As an example, an SPMC providing MGC capabilities could provide 
complete support for ISUP (and any other MTP3 user located at the 
point code of the SPMC) for a given point code.

In the case where an ASP is connected to more than one SGP, the M3UA 
layer must maintain the status of configured SS7 destinations and route 
messages according to availability/congestion/restricted status of the 
routes to these SS7 destinations.

1.4.3.4 IPSP Considerations

Since IPSPs use M3UA in a point-to-point fashion, there is no concept 
of routing of messages beyond the remote end.  Therefore, SS7 and M3UA 
interworking is not necessary for this model.  

1.4.4 Redundancy Models

1.4.4.1 Application Server Redundancy

All MTP3-User messages (e.g., ISUP, SCCP) which match a provisioned 
Routing Key at an SGP are mapped to an Application Server.

The Application Server is the set of all ASPs associated with a 
specific Routing Key. Each ASP in this set may be active inactive or 
unavailable.  Active ASPs handle traffic; inactive ASPs might be used 
when active ASPs become unavailable.

The failover model supports an "n+k" redundancy model, where "n" ASPs 
is the minimum number of redundant ASPs required to handle traffic and 
"k" ASPs are available to take over for a failed or unavailable ASP.  A 
"1+1" active/backup redundancy is a subset of this model. A simplex 
"1+0" model is also supported as a subset, with no ASP redundancy.

At the SGP, an Application Server list contains active and inactive 
ASPs to support ASP broadcast, loadsharing and failover procedures.  
The list of ASPs within a logical Application Server is kept updated in 
the SGP to reflect the active Application Server Process(es).

For example, in the network shown in Figure 1, all messages to DPC x 
could be sent to ASP1 in Host3 or ASP1 in Host4.  The AS list at SGP1 
in Host 1 might look like the following:

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    Routing Key {DPC=x) - "Application Server #1"
        ASP1/Host3  - State = Active
        ASP1/Host4  - State = Inactive

In this "1+1" redundancy case, ASP1 in Host3 would be sent any incoming 
message with DPC=x.  ASP1 in Host4 would normally be brought to the 
"active" state upon failure of, or loss of connectivity to, ASP1/Host1. 

The AS List at SGP1 in Host1 might also be set up in loadshare mode:

    Routing Key {DPC=x) - "Application Server #1"
        ASP1/Host3 - State = Active
        ASP1/Host4 - State = Active

In this case, both the ASPs would be sent a portion of the traffic.  
For example the two ASPs could together form a database, where incoming 
queries may be sent to any active ASP.

Care might need to be exercised by a Network Operator in the selection 
of the routing information to be used as the Routing Key for a 
particular AS.  

For example, where Application Servers are defined using ranges of ISUP 
CIC values, the Operator is implicitly splitting up control of the 
related circuit groups.  Some CIC value range assignments may interfere 
with ISUP circuit group management procedures.  

In the process of failover, it is recommended that in the case of ASPs 
supporting call processing, stable calls do not fail.  It is possible 
that calls in "transition" MAY fail, although measures of communication 
between the ASPs involved can be used to mitigate this.  For example, 
the two ASPs MAY share call state via shared memory, or MAY use an ASP 
to ASP protocol to pass call state information.  Any ASP-to-ASP 
protocol to support this function is outside the scope of this 
document.

1.4.4.2 Signalling Gateway Redundancy

Signalling Gateways MAY also be distributed over multiple hosts.  Much 
like the AS model, SGs may comprise one or more SG Processes (SGPs), 
distributed over one or more hosts, using an active/backup or a 
loadsharing model.  Should an SGP lose all or partial SS7 
connectivity and other SGPs exist, the SGP MUST terminate the SCTP 
associations to the concerned ASPs.

It is therefore possible for an ASP to route signalling messages 
destined to the SS7 network using more than one SGP.  In this model, a 
Signalling Gateway is deployed as a cluster of hosts acting as a single 
SG.  A primary/backup redundancy model is possible, where the 

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unavailability of the SCTP association to a primary SGP could be used 
to reroute affected traffic to an alternate SGP.  A loadsharing model 
is possible, where the signalling messages are loadshared between 
multiple SGPs.  A broadcast model is also possible, where signalling 
messages are sent to each active SGP in the SG. The distribution of the 
MTP3-user messages over the SGPs should be done in such a way to 
minimize message missequencing, as required by the SS7 User Parts.  
 
It may also be possible for an ASP to use more than one SG to access a 
specific SS7 end point, in a model that resembles an SS7 STP mated 
pair.  Typically, SS7 STPs are deployed in mated pairs, with traffic 
loadshared between them.  Other models are also possible, subject to 
the limitations of the local SS7 network provisioning guidelines.

>From the perspective of the M3UA layer at an ASP, a particular SG is 
capable of transferring traffic to a provisioned SS7 destination X if 
an SCTP association with at least one SGP of the SG is established, 
the SGP has returned an acknowledgement to the ASP to indicate that 
the ASP is actively handling traffic for that destination X, the SGP 
has not indicated that the destination X is inaccessible and the SGP 
has not indicated MTP Restart.  When an ASP is configured to use 
multiple SGPs for transferring traffic to the SS7 network, the ASP 
must maintain knowledge of the current capability of the SGPs to 
handle traffic to destinations of interest.  This information is 
 

crucial to the overall reliability of the service, for active/backup, 
loadsharing and broadcast models, in the event of failures, recovery 
and maintenance activities.  The ASP M3UA may also use this 
information for congestion avoidance purposes.  The distribution of 
the MTP3-user messages over the SGPs should be done in such a way to 
minimize message missequencing, as required by the SS7 User Parts.

1.4.5 Flow Control

Local Management at an ASP may wish to stop traffic across an SCTP 
association to temporarily remove the association from service 
or to perform testing and maintenance activity.  The function could 
optionally be used to control the start of traffic on to a newly 
available SCTP association.

1.4.6 Congestion Management

The M3UA layer is informed of local and IP network congestion by means 
of an implementation-dependent function (e.g., an implementation-
dependent indication from the SCTP of IP network congestion). 

At an ASP or IPSP, the M3UA layer indicates congestion to local MTP3-
Users by means of an MTP-STATUS primitive, as per current MTP3 
procedures, to invoke appropriate upper layer responses.  

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When an SG determines that the transport of SS7 messages to a 
Signalling Point Management Cluster (SPMC) is encountering congestion, 
the SG MAY trigger SS7 MTP3 Transfer Controlled management messages 
to originating SS7 nodes, per the congestion procedures of the relevant 
MTP3 standard. The triggering of SS7 MTP3 Management messages from an 
SG is an implementation-dependent function.

The M3UA layer at an ASP or IPSP MAY indicate local congestion to an 
M3UA peer with an SCON message.  When an SG receives a congestion 
message (SCON) from an ASP, and the SG determines that an SPMC is now 
encountering congestion, it MAY trigger SS7 MTP3 Transfer Controlled 
management messages to concerned SS7 destinations according to 
congestion procedures of the relevant MTP3 standard.

1.4.7 SCTP Stream Mapping.  

The M3UA layer at both the SGP and ASP also supports the assignment of 
signalling traffic into streams within an SCTP association.  Traffic 
that requires sequencing SHOULD be assigned to the same stream.  To 
accomplish this, MTP3-User traffic may be assigned to individual 
streams based on, for example, the SLS value in the MTP3 Routing Label 
or the ISUP CIC assignment, subject of course to the maximum number of 
streams supported by the underlying SCTP association.  

1.4.8 Client/Server Model

It is recommended that the SGP and ASP be able to support both client 
and server operation. The peer endpoints using M3UA SHOULD be 
configured so that one always takes on the role of client and the 
other the role of server for initiating SCTP associations. The default 
orientation would be for the SGP to take on the role of server while 
the ASP is the client. In this case, ASPs SHOULD initiate the
SCTP association to the SGP.

In the case of IPSP to IPSP communication, the peer endpoints using 
M3UA SHOULD be configured so that one always takes on the role of 
client and the other the role of server for initiating SCTP 
associations.

The SCTP Registered User Port Number Assignment for M3UA is 2905.

1.5 Sample Configurations

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1.5.1 Example 1: ISUP Message Transport

  ********   SS7   *****************   IP   ********
  * SEP  *---------*      SGP      *--------* ASP  *
  ********         *****************        ********

  +------+         +---------------+        +------+
  | ISUP |         |     (NIF)     |        | ISUP |
  +------+         +------+ +------+        +------+
  | MTP3 |         | MTP3 | | M3UA |        | M3UA |
  +------|         +------+-+------+        +------+
  | MTP2 |         | MTP2 | | SCTP |        | SCTP |
  +------+         +------+ +------+        +------+
  |  L1  |         |  L1  | |  IP  |        |  IP  |
  +------+         +------+ +------+        +------+ 
      |_______________|         |______________|

    SEP - SS7 Signalling End Point
    SCTP - Stream Control Transmission Protocol
    NIF - Nodal Interworking Function

In this example, the SGP provides an implementation-dependent nodal 
interworking function (NIF) that allows the MGC to exchange SS7 
signalling messages with the SS7-based SEP.  The NIF within the SGP 
serves as the interface within the SGP between the MTP3 and M3UA.  This 
nodal interworking function has no visible peer protocol with either 
the MGC or SEP.  It also provides network status information to one or 
both sides of the network.

For internal SGP modeling purposes, at the NIF level, SS7 signalling 
messages that are destined to the MGC are received as MTP-TRANSFER 
indication primitives from the MTP Level 3 upper layer interface, 
translated to MTP-TRANSFER request primitives, and sent to the local 
M3UA-resident message distribution function for ongoing routing to the 
final IP destination.  Messages received from the local M3UA network 
address translation and mapping function as MTP-TRANSFER indication 
primitives are sent to the MTP Level 3 upper layer interface as MTP-
TRANSFER request primitives for ongoing MTP Level 3 routing to an SS7 
SEP.  For the purposes of providing SS7 network status information the 
NIF also delivers MTP-PAUSE, MTP-RESUME and MTP-STATUS indication 
primitives received from the MTP Level 3 upper layer interface to the 
local M3UA-resident management function. In addition, as an 
implementation and network option, restricted destinations are 
communicated from MTP network management to the local M3UA-resident 
management function.

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1.5.2  Example 2: SCCP Transport between IPSPs

        ********    IP    ********
        * IPSP *          * IPSP *
        ********          ********
  
        +------+          +------+
        |SCCP- |          |SCCP- |
        | User |          | User |
        +------+          +------+
        | SCCP |          | SCCP |
        +------+          +------+
        | M3UA |          | M3UA |
        +------+          +------+
        | SCTP |          | SCTP |
        +------+          +------+
        |  IP  |          |  IP  |
        +------+          +------+
            |________________|

This example shows an architecture where no Signalling Gateway is used.  
In this example, SCCP messages are exchanged directly between two IP-
resident IPSPs with resident SCCP-User protocol instances, such as 
RANAP or TCAP.  SS7 network interworking is not required, therefore 
there is no MTP3 network management status information for the SCCP and 
SCCP-User protocols to consider.  Any MTP-PAUSE, MTP-RESUME or MTP-
STATUS indications from the M3UA layer to the SCCP layer should 
consider the status of the SCTP Association and underlying IP network 
and any congestion information received from the remote site.    

1.5.3 Example 3: SGP Resident SCCP Layer, with Remote ASP

  ********   SS7   *****************   IP   ********
  * SEP  *---------*               *--------*      *
  *  or  *         *      SGP      *        * ASP  *
  * STP  *         *               *        *      *
  ********         *****************        ********

  +------+         +---------------+        +------+
  | SCCP-|         |     SCCP      |        | SCCP-|
  | User |         +---------------+        | User |
  +------+           |   _____   |          +------+
  | SCCP |           |  |     |  |          | SCCP |
  +------+         +------+-+------+        +------+
  | MTP3 |         | MTP3 | | M3UA |        | M3UA |
  +------|         +------+ +------+        +------+
  | MTP2 |         | MTP2 | | SCTP |        | SCTP |
  +------+         +------+ +------+        +------+
  |  L1  |         |  L1  | |  IP  |        |  IP  |
  +------+         +------+ +------+        +------+
      |_______________|         |______________|

    STP - SS7 Signalling Transfer Point

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In this example, the SGP contains an instance of the SS7 SCCP protocol 
layer that may, for example, perform the SCCP Global Title Translation 
(GTT) function for messages logically addressed to the SG SCCP.  If the 
result of a GTT for an SCCP message yields an SS7 DPC or DPC/SSN 
address of an SCCP peer located in the IP domain, the resulting MTP-
TRANSFER request primitive is sent to the local M3UA-resident network 
address translation and mapping function for ongoing routing to the 
final IP destination.  

Similarly, the SCCP instance in an SGP can perform the SCCP GTT service 
for messages logically addressed to it from SCCP peers in the IP 
domain.  In this case, MTP-TRANSFER indication primitives are sent from 
the local M3UA-resident network address translation and mapping 
function to the SCCP for GTT.  If the result of the GTT yields the 
address of an SCCP peer in the SS7 network then the resulting MTP-
TRANSFER request primitive is given to the MTP3 for delivery to an SS7-
resident node.

It is possible that the above SCCP GTT at the SGP could yield the 
address of an SCCP peer in the IP domain and the resulting MTP-TRANSFER 
request primitive would be sent back to the M3UA layer for delivery to 
an IP destination.

For internal SGP modeling purposes, this may be accomplished with the 
use of an implementation-dependent nodal interworking function within 
the SGP that effectively sits below the SCCP and routes MTP-TRANSFER
request/indication messages to/from both the MTP3 and the M3UA layer, 
based on the SS7 DPC or DPC/SSN address information.  This nodal 
interworking function has no visible peer protocol with either the 
ASP or SEP.

Note that the services and interface provided by the M3UA layer are the 
same as in Example 1 and the functions taking place in the SCCP entity 
are transparent to the M3UA layer.  The SCCP protocol functions are not 
reproduced in the M3UA protocol.

1.6 Definition of M3UA Boundaries

1.6.1 Definition of the Boundary between M3UA and an MTP3-User.

>From ITU Q.701 [14]:

   MTP-TRANSFER request
   MTP-TRANSFER indication
   MTP-PAUSE indication
   MTP-RESUME indication
   MTP-STATUS indication  

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1.6.2 Definition of the Boundary between M3UA and SCTP

An example of the upper layer primitives provided by the SCTP are 
provided in Reference [13] Section 10.

1.6.3 Definition of the Boundary between M3UA and Layer Management

   M-SCTP_ESTABLISH request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to establish an SCTP association with its 
            peer.

   M-STCP_ESTABLISH confirm 
   Direction: M3UA -> LM
   Purpose: ASP confirms to LM that it has established an SCTP 
            association with its peer.

   M-SCTP_ESTABLISH indication 
   Direction: M3UA -> LM
   Purpose: M3UA informs LM that a remote ASP has established an SCTP 
            association.

   M-SCTP_RELEASE request 
   Direction: LM -> M3UA
   Purpose: LM requests ASP to release an SCTP association with its 
            peer.

   M-SCTP_RELEASE confirm
   Direction: M3UA -> LM
   Purpose: ASP confirms to LM that it has released SCTP association 
            with its peer.

   M-SCTP_RELEASE indication
   Direction: M3UA -> LM
   Purpose: M3UA informs LM that a remote ASP has released an SCTP 
            Association or the SCTP association has failed.

   M-SCTP RESTART indication
   Direction: M3UA -> LM
   Purpose: M3UA informs LM that an SCTP restart indication has been 
            received.

   M-SCTP_STATUS request 
   Direction: LM -> M3UA
   Purpose: LM requests M3UA to report the status of an SCTP 
            association.

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   M-SCTP_STATUS confirm 
   Direction: M3UA -> LM
   Purpose: M3UA responds with the status of an SCTP association.

   M-SCTP STATUS indication
   Direction: M3UA -> LM
   Purpose: M3UA reports the status of an SCTP association.

   M-ASP_STATUS request 
   Direction: LM -> M3UA
   Purpose: LM requests M3UA to report the status of a local or remote 
            ASP.

   M-ASP_STATUS confirm 
   Direction: M3UA -> LM
   Purpose: M3UA reports status of local or remote ASP.

   M-AS_STATUS request 
   Direction: LM -> M3UA
   Purpose: LM requests M3UA to report the status of an AS.

   M-AS_STATUS confirm 
   Direction: M3UA -> LM
   Purpose: M3UA reports the status of an AS.

   M-NOTIFY indication 
   Direction: M3UA -> LM
   Purpose: M3UA reports that it has received a Notify message 
            from its peer.

   M-ERROR indication 
   Direction: M3UA -> LM
   Purpose: M3UA reports that it has received an Error message from 
            its peer or that a local operation has been unsuccessful.

   M-ASP_UP request 
   Direction: LM -> M3UA
   Purpose: LM requests ASP to start its operation and send an ASP Up
            message to its peer.

   M-ASP_UP confirm
   Direction: M3UA -> LM
   Purpose: ASP reports that is has received an ASP UP Ack message from 
            its peer.

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   M-ASP_UP indication
   Direction: M3UA -> LM
   Purpose: M3UA reports it has successfully processed an incoming ASP 
            Up message from its peer.

   M-ASP_DOWN request 
   Direction: LM -> M3UA
   Purpose: LM requests ASP to stop its operation and send an ASP Down 
            message to its peer.

   M-ASP_DOWN confirm
   Direction: M3UA -> LM
   Purpose: ASP reports that is has received an ASP Down Ack message 
            from its peer.

   M-ASP_DOWN indication
   Direction: M3UA -> LM
   Purpose: M3UA reports it has successfully processed an incoming ASP 
            Down message from its peer, or the SCTP association has 
            been lost/reset.

   M-ASP_ACTIVE request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to send an ASP Active message to its peer.

   M-ASP_ACTIVE confirm
   Direction: M3UA -> LM
   Purpose: ASP reports that is has received an ASP Active
            Ack message from its peer.

   M-ASP_ACTIVE indication
   Direction: M3UA -> LM
   Purpose: M3UA reports it has successfully processed an incoming ASP 
            Active message from its peer.

   M-ASP_INACTIVE request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to send an ASP Inactive message to its 
            peer.

   M-ASP_INACTIVE confirm
   Direction: LM -> M3UA
   Purpose: ASP reports that is has received an ASP Inactive
            Ack message from its peer.

   M-ASP_INACTIVE indication
   Direction: M3UA -> LM
   Purpose: M3UA reports it has successfully processed an incoming ASP 
            Inactive message from its peer.

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   M-AS_ACTIVE indication
   Direction: M3UA -> LM
   Purpose: M3UA reports that an AS has moved to the AS-ACTIVE state.

   M-AS_INACTIVE indication
   Direction: M3UA -> LM
   Purpose: M3UA reports that an AS has moved to the AS-INACTIVE state.

   M-AS_DOWN indication
   Direction: M3UA -> LM
   Purpose: M3UA reports that an AS has moved to the AS-DOWN state.

If dynamic registration of RK is supported by the M3UA layer, the layer 
MAY support the following additional primitives:

   M-RK_REG request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to register RK(s) with its peer by sending 
            REG REQ message

   M-RK_REG confirm
   Direction: M3UA -> LM
   Purpose: ASP reports that it has received REG RSP message with 
            registration status as successful from its peer.

   M-RK_REG indication
   Direction: M3UA -> LM
   Purpose: M3UA informs LM that it has successfully processed an 
            incoming REG REQ message.

   M-RK_DEREG request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to deregister RK(s) with its peer by 
            sending DEREG REQ message.

   M-RK_DEREG confirm
   Direction: M3UA -> LM
   Purpose: ASP reports that it has received DEREG REQ message with 
            deregistration status as successful from its peer.

   M-RK_DEREG indication
   Direction: M3UA -> LM
   Purpose: M3UA informs LM that it has successfully processed an 
            incoming DEREG REQ from its peer.

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2.0 Conventions

The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD 
NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they appear 
in this document, are to be interpreted as described in [RFC2119].

3. M3UA Protocol Elements

The general M3UA message format includes a Common Message Header 
followed by zero or more parameters as defined by the Message Type.  
For forward compatibility, all Message Types may have attached 
parameters even if none are specified in this version.

3.1 Common Message Header

The protocol messages for MTP3-User Adaptation require a message header 
which contains the adaptation layer version, the message type, and 
message length.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Version    |   Reserved    | Message Class | Message Type  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Message Length                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                                                               /

All fields in an M3UA message MUST be transmitted in the network byte 
order, unless otherwise stated.

3.1.1 M3UA Protocol Version: 8 bits (unsigned integer)

   The version field contains the version of the M3UA adaptation layer.  

   The supported versions are the following:

         1      Release 1.0

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3.1.2  Message Classes and Types

The following list contains the valid Message Classes:

Message Class: 8 bits (unsigned integer)

   The following list contains the valid Message Type Classes:

     0     Management (MGMT) Message
     1     Transfer Messages
     2     SS7 Signalling Network Management (SSNM) Messages
     3     ASP State Maintenance (ASPSM) Messages
     4     ASP Traffic Maintenance (ASPTM) Messages
     5     Reserved for Other Sigtran Adaptation Layers
     6     Reserved for Other Sigtran Adaptation Layers
     7     Reserved for Other Sigtran Adaptation Layers
     8     Reserved for Other Sigtran Adaptation Layers
     9     Routing Key Management (RKM) Messages
  10 to 127 Reserved by the IETF
 128 to 255 Reserved for IETF-Defined Message Class extensions

Message Type: 8 bits (unsigned integer)

   The following list contains the message types for the defined 
   messages.

     Management (MGMT) Messages (See Section 3.6)

         0        Error (ERR)
         1        Notify (NTFY)
      2 to 127    Reserved by the IETF
    128 to 255    Reserved for IETF-Defined MGMT extensions

     Transfer Messages (See Section 3.3)

         0        Reserved
         1        Payload Data (DATA)      
      2 to 127    Reserved by the IETF
    128 to 255    Reserved for IETF-Defined Transfer extensions

     SS7 Signalling Network Management (SSNM) Messages (See Section 
     3.4)

         0        Reserved
         1        Destination Unavailable (DUNA)
         2        Destination Available (DAVA)
         3        Destination State Audit (DAUD)
         4        Signalling Congestion (SCON)
         5        Destination User Part Unavailable (DUPU)
         6        Destination Restricted (DRST)      
      7 to 127    Reserved by the IETF
    128 to 255    Reserved for IETF-Defined SSNM extensions

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  ASP State Maintenance (ASPSM) Messages (See Section 3.5)

         0        Reserved
         1        ASP Up (ASPUP)
         2        ASP Down (ASPDN)         
         3        Heartbeat (BEAT)
         4        ASP Up Acknowledgement (ASPUP ACK)
         5        ASP Down Acknowledgement (ASPDN ACK)
         6        Heartbeat Acknowledgement (BEAT ACK)
      7 to 127    Reserved by the IETF
    128 to 255    Reserved for IETF-Defined ASPSM extensions

  ASP Traffic Maintenance (ASPTM) Messages (See Section 3.5)

         0        Reserved
         1        ASP Active (ASPAC)
         2        ASP Inactive (ASPIA)
         3        ASP Active Acknowledgement (ASPAC ACK) 
         4        ASP Inactive Acknowledgement (ASPIA ACK)
      5 to 127    Reserved by the IETF
    128 to 255    Reserved for IETF-Defined ASPTM extensions

  Routing Key Management (RKM) Messages (See Section 3.7)

         0        Reserved
         1        Registration Request (REG REQ)
         2        Registration Response (REG RSP)
         3        Deregistration Request (DEREG REQ) 
         4        Deregistration Response (DEREG RSP)
      5 to 127    Reserved by the IETF
    128 to 255    Reserved for IETF-Defined RKM extensions

3.1.3  Reserved: 8 bits

   The Reserved field SHOULD be set to all '0's and ignored by the 
   receiver.

3.1.4  Message Length: 32-bits (unsigned integer)

   The Message Length defines the length of the message in octets, 
   including the Common Header.  For messages with a final parameter 
   containing padding, the parameter padding MUST be included in the 
   Message Length. 

   Note: A receiver SHOULD accept the message whether or not the final 
   parameter padding is included in the message length.  

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3.2 Variable Length Parameter Format

M3UA messages consist of a Common Header followed by zero or more 
variable length parameters, as defined by the message type.  All the 
parameters contained in a message are defined in a Tag Length-Value 
format as shown below.  

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Parameter Tag        |       Parameter Length        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  \                                                               \
  /                       Parameter Value                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where more than one parameter is included in a message, the parameters 
may be in any order, except where explicitly mandated.  A receiver 
SHOULD accept the parameters in any order. 

Parameter Tag: 16 bits (unsigned integer)

   The Tag field is a 16-bit identifier of the type of parameter. It 
   takes a value of 0 to 65534.  Common parameters used by adaptation 
   layers are in the range of 0x00 to 0x3f.   M3UA-specific parameters 
   have Tags in the range 0x0200 to 0x02ff.  The parameter Tags defined 
   are as follows:

   Common Parameters.  These TLV parameters are common across the 
   different adaptation layers:

   Parameter Name                     Parameter ID 
   ==============                     ============ 
   Reserved                              0x0000
   Not Used in M3UA                      0x0001
   Not Used in M3UA                      0x0002
   Not Used in M3UA                      0x0003
   INFO String                           0x0004   
   Not Used in M3UA                      0x0005
   Routing Context                       0x0006
   Diagnostic Information                0x0007
   Not Used in M3UA                      0x0008
   Heartbeat Data                        0x0009
   Not Used in M3UA                      0x000a
   Traffic Mode Type                     0x000b
   Error Code                            0x000c
   Status                                0x000d
   Not Used in M3UA                      0x000e
   Not Used in M3UA                      0x000f
   Not Used in M3UA                      0x0010
   ASP Identifier                        0x0011
   Affected Point Code                   0x0012

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   M3UA-Specific parameters.  These TLV parameters are specific to the 
   M3UA protocol:

   Network Appearance                    0x0200
   Reserved                              0x0201
   Reserved                              0x0202
   Reserved                              0x0203
   User/Cause                            0x0204
   Congestion Indications                0x0205
   Concerned Destination                 0x0206
   Routing Key                           0x0207
   Registration Result                   0x0208
   Deregistration Result                 0x0209
   Local_Routing Key Identifier          0x020a
   Destination Point Code                0x020b
   Service Indicators                    0x020c
   Subsystem Numbers                     0x020d
   Originating Point Code List           0x020e
   Circuit Range                         0x020f
   Protocol Data                         0x0210
   Correlation Id                        0x0211
   Registration Status                   0x0212
   Deregistration Status                 0x0213

   Reserved by the IETF             0x0214 to 0xffff
 
   The value of 65535 is reserved for IETF-defined extensions.  Values 
   other than those defined in specific parameter description are 
   reserved for use by the IETF. 

Parameter Length: 16 bits (unsigned integer)

   The Parameter Length field contains the size of the parameter in 
   bytes, including the Parameter Tag, Parameter Length, and Parameter 
   Value fields. The Parameter Length does not include any padding 
   bytes.

Parameter Value: variable length.

   The Parameter Value field contains the actual information to be 
   transferred in the parameter. 

   The total length of a parameter (including Tag, Parameter Length and 
   Value fields) MUST be a multiple of 4 bytes. If the length of the 
   parameter is not a multiple of 4 bytes, the sender pads the 
   Parameter at the end (i.e., after the Parameter Value field) with 
   all zero bytes. The length of the padding is NOT included in the 
   parameter length field. A sender SHOULD NOT pad with more than 3 
   bytes. The receiver MUST ignore the padding bytes.

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3.3 Transfer Messages

The following section describes the Transfer messages and parameter 
contents. 

3.3.1 Payload Data Message (DATA)

The DATA message contains the SS7 MTP3-User protocol data, which is an 
MTP-TRANSFER primitive, including the complete MTP3 Routing Label. The 
DATA message contains the following variable length parameters:

     Network Appearance       Optional
     Routing Context          Optional
     Protocol Data            Mandatory
     Correlation Id           Optional

3.3 Transfer Messages

The following section describes the Transfer messages and parameter 
contents. 

3.3.1 Payload Data Message (DATA)

The DATA message contains the SS7 MTP3-User protocol data, which is an 
MTP-TRANSFER primitive, including the complete MTP3 Routing Label. The 
DATA message contains the following variable length parameters:

     Network Appearance       Optional
     Routing Context          Optional
     Protocol Data            Mandatory
     Correlation Id           Optional

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The following format MUST be used for the Data Message:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x0200           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Network Appearance                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x0006           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Routing Context                        | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x0210           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                        Protocol Data                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x0211           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Correlation Id                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Network Appearance: 32-bits (unsigned integer)

   The optional Network Appearance parameter identifies the SS7 network 
   context for the message, for the purposes of logically separating 
   the signalling traffic between the SGP and the ASP over a common 
   SCTP association.  An example is where an SG is logically 
   partitioned to appear as an element in four different national SS7 
   networks.

   In a DATA message, the Network Appearance implicitly defines the SS7 
   Point Code format used, the SS7 Network Indicator value, and the 
   MTP3 and possibly the MTP3-User protocol type/variant/version used 
   within the specific SS7 network.  Where an SG operates in the 
   context of a single SS7 network, or individual SCTP associations 
   are dedicated to each SS7 network context, the Network Appearance 
   parameter is not required.  In other cases the parameter MUST be 
   included.

   The Network Appearance parameter value is of local significance 
   only, coordinated between the SGP and ASP. Therefore, in the case 
   where an ASP is connected to more than one SGP, the same SS7 network 
   context may be identified by different Network Appearance values 
   depending over which SGP a message is being transmitted/received.

   Where the optional Network Appearance parameter is present, it must 
   be the first parameter in the message as it defines the format of 
   the Protocol Data field.

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Routing Context: 32-bits (unsigned integer)

   The optional Routing Context parameter contains the Routing Context 
   value associated with the DATA message.   Where multiple Routing 
   Keys and Routing Contexts are used across a common association, the 
   Routing Context may identify to the receiver the traffic flow, 
   assisting in the internal distribution of Data messages.

Protocol Data 1 or 2: variable length
 
   The Protocol Data parameter contains the original SS7 MTP3 
   message, including the Service Information Octet and Routing Label. 

   The Protocol Data parameter contains the following fields:

       Service Indicator, 
       Network Indicator,
       Message Priority.

       Destination Point Code,
       Originating Point Code,
       Signalling Link Selection Code (SLS).

       User Protocol Data.  Includes:
            MTP3-User protocol elements (e.g., ISUP, SCCP, or TUP 
               parameters).

   The Protocol Data parameter is encoded as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Originating Point Code                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Destination Point Code                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       SI      |       NI      |      MP       |      SLS      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      \                                                               \
      /                        Protocol Data                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Originating Point Code: 32 bits (unsigned integer)
Destination Point Code: 32 bits (unsigned integer)

   The Originating and Destination Point Code fields contains the OPC 
   and DPC from the   routing label of the original SS7 message in 
   Network Byte Order, justified to the least significant bit.  Unused 
   bits are coded `0'.

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Service Indicator: 8 bits (unsigned integer)

   The Service Indicator field contains the SI field from the original 
   SS7 message justified to the least significant bit.   Unused bits 
   are coded `0'.

Network Indicator: 8-bits (unsigned integer)

   The Network Indicator contains the NI field from the original SS7 
   message justified to the least significant bit.  Unused bits are 
   coded `0'.

Message Priority: 8 bits (unsigned integer)

   The Message Priority field contains the MP bits (if any) from the 
   original SS7 message, both for ANSI-style and TTC-style message 
   priority bits. The MP bits are aligned to the least significant 
   bit. Unused bits are coded `0'.

Signalling Link Selection: 8 bits (unsigned integer)

   The Signalling Link Selection field contains the SLS bits from 
   the routing label of the original SS7 message justified to the 
   least significant bit and in Network Byte Order.  Unused bits are 
   coded `0'.

Protocol Data: (variable)

   The Protocol Data field contains a byte string of MTP-User 
   information from the original SS7 message starting with the 
   first byte of the original SS7 message following the Routing Label.

Correlation Id: 32-bits (unsigned integer)

   The Correlation Id parameter uniquely identifies the MSU carried in 
   the Protocol Data within an AS.  This Correlation Id parameter is 
   assigned by the sending M3UA.

3.4 SS7 Signalling Network Management (SSNM) Messages

3.4.1 Destination Unavailable (DUNA)

The DUNA message is sent from an SGP in an SG to all concerned ASPs 
to indicate that the SG has determined that one or more SS7 
destinations are unreachable.  It is also sent by an SGP in response 
to a message from the ASP to an unreachable SS7 destination.  As an 
implementation option the SG may suppress the sending of subsequent 
"response" DUNA messages regarding a certain unreachable SS7 

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destination for a certain period to give the remote side time 
to react. If there is no alternate route via another SG, the 
MTP3-User at the ASP is expected to stop traffic to the 
affected destination via the SG as per the defined MTP3-User 
procedures. 

The DUNA message contains the following parameters:

     Network Appearance      Optional
     Routing Context         Optional
     Affected Point Code   Mandatory
     INFO String             Optional

The format for DUNA Message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |         Tag = 0x0200          |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Network Appearance                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x0006           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         / 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0012          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Mask      |                 Affected PC 1                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Mask      |                 Affected PC n                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0004         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Network Appearance: 32-bit unsigned integer

   See Section 3.3.1

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Routing Context: n x 32-bits (unsigned integer)

   The optional Routing Context parameter contains the Routing Context 
   values associated with the DUNA message.  Where multiple Routing 
   Keys and Routing Contexts are used across a common association, the 
   Routing Context(s) may identify to the receiver the concerned 
   traffic flows for which the DUNA message applies, assisting in 
   outgoing traffic management and internal distribution of MTP-PAUSE 
   indications to MTP3-Users at the receiver.

Affected Point Code: n x 32-bits

   The Affected Point Code parameter contains up to sixteen Affected 
   Destination Point Code fields, each a three-octet parameter to allow 
   for 14-, 16- and 24-bit binary formatted SS7 Point Codes.  Affected 
   Point Codes that are less than 24-bits, are padded on the left to 
   the 24-bit boundary.  The encoding is shown below for ANSI and ITU 
   Point Code examples.

ANSI 24-bit Point Code:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |     Mask      |    Network    |    Cluster    |     Member    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      |MSB-----------------------------------------LSB|

   ITU 14-bit Point Code:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |     Mask      |0 0 0 0 0 0 0 0 0 0|Zone |     Region    | SP  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                           |MSB--------------------LSB|

   It is optional to send an Affected Point Code parameter with more 
   than one Affected PC but it is mandatory to receive it.  All the 
   Affected PCs included must be within the same Routing Context.  
   Including multiple Affected PCs may be useful when reception of an 
   MTP3 management message or a linkset event simultaneously affects 
   the availability status of a list of destinations at an SG.  

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Mask: 8-bits (unsigned integer)

   The Mask field can be used to identify a contiguous range of 
   Affected Destination Point Codes, independent of the point code 
   format.  Identifying a contiguous range of Affected DPCs may be 
   useful when reception of an MTP3 management message or a linkset 
   event simultaneously affects the availability status of a series of 
   destinations at an SG.   

   The Mask parameter is an integer representing a bit mask that can be 
   applied to the related Affected PC field.  The bit mask identifies 
   how many bits of the Affected PC field are significant and which are 
   effectively "wildcarded".  For example, a mask of "8" indicates that 
   the last eight bits of the PC is "wildcarded".  For an ANSI 24-
   bit Affected PC, this is equivalent to signalling that all PCs in 
   an ANSI Cluster are unavailable.  A mask of "3" indicates that the 
   last three bits of the PC is "wildcarded".  For a 14-bit ITU 
   Affected PC, this is equivalent to signaling that an ITU 

   Region is unavailable. A mask value equal (or greater than) the 
   number of bits in the PC indicates that the entire network 
   appearance is affected - this is used to indicate network isolation 
   to the ASP.

INFO String: variable length

   The optional INFO String parameter can carry any 8-bit ASCII 
   character string along with the message.  Length of the INFO 
   String parameter is from 0 to 255 characters.  No procedures are 
   presently identified for its use but the INFO String MAY be used by 
   Operators to identify in text form the location reflected by the 
   Affected DPC for debugging purposes.

3.4.2 Destination Available (DAVA)   

The DAVA message is sent from an SGP to all concerned ASPs to indicate 
that the SG has determined that one or more SS7 destinations are now 
reachable (and not restricted), or in response to a DAUD message if 
appropriate. If the ASP M3UA layer previously had no routes to the 
affected destinations the ASP MTP3-User protocol is informed and may 
now resume traffic to the affected destination.  The ASP M3UA layer 
now routes the MTP3-user traffic through the SG initiating the DAVA 
message. 

The DAVA message contains the following parameters:

     Network Appearance       Optional
     Routing Context          Optional
     Affected Point Code    Mandatory
     INFO String              Optional

   

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The format and description of the Network Appearance, Routing Context, 
Affected Point Code and INFO String parameters is the same as for the 
DUNA message (See Section 3.4.1). 

3.4.3 Destination State Audit (DAUD)

The DAUD message MAY be sent from the ASP to the SGP to audit the 
availability/congestion state of SS7 routes from the SG to one 
or more affected destinations.  

The DAUD message contains the following parameters:

     Network Appearance      Optional
     Routing Context         Optional
     Affected Point Code     Mandatory
     INFO String             Optional

The format and description of DAUD Message parameters is the same as 
for the DUNA message (See Section 3.4.1).

3.4.4 Signalling Congestion (SCON)

The SCON message can be sent from an SGP to all concerned ASPs to 
indicate that an SG has determined that there is congestion in the 
SS7 network to one or more destinations, or to an ASP in response to 
a DATA or DAUD message as appropriate.  For 
some MTP protocol variants (e.g., ANSI MTP) the SCON message may be 
sent when the SS7 congestion level changes.  The SCON message MAY also 
be sent from the M3UA layer of an ASP to an M3UA peer indicating that 
the M3UA layer or the ASP is congested.

The SCON message contains the following parameters:

     Network Appearance       Optional
     Routing Context          Optional
     Affected Point Code      Mandatory
     Concerned Destination    Optional
     Congestion Indications   Optional           
     INFO String              Optional

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The format for SCON Message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0200          |           Length =8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                       Network Appearance                      | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x0006           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         / 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0012          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Mask     |                 Affected PC 1                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Mask     |                 Affected PC n                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0206          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    reserved   |                 Concerned DPC                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0205          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Reserved                    |  Cong. Level  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 0x0004       |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         INFO String                           /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the Network Appearance, Routing 
Context, Affected Point Code, and INFO String parameters is the same 
as for the DUNA message (See Section 3.4.1).

The Affected Point Code parameter can be used to indicate congestion 
of multiple destinations or ranges of destinations.  However, an 
SCON message MUST not be delayed to "collect" individual congested 
destinations into a single SCON message as any delay might affect 
the timing of congestion indications to the M3UA Users.  One use for 
including a range of Congested DPCs is when the SG supports an ANSI 
cluster route set to the SS7 network that becomes congested due to 
outgoing link set congestion. 

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Concerned Destination: 32-bits
   
   The optional Concerned Destination parameter is only used if the 
   SCON message is sent from an ASP to the SGP. It contains the point 
   code of the originator of the message that triggered the SCON 
   message. The Concerned Destination parameter contains one Concerned 
   Destination Point Code field, a three-octet parameter to allow for 
   14-, 16- and 24-bit binary formatted SS7 Point Codes.  A Concerned 
   Point Code that is less than 24-bits is padded on the left to the 
   24-bit boundary. Any resulting Transfer Controlled (TFC) message 
   from the SG is sent to the Concerned Point Code  using the single 
   Affected DPC contained in the SCON message to populate the 
  (affected) Destination field of the TFC message

Congested Indications: 32-bits

   The optional Congestion Indications parameter contains a Congestion 
   Level field.  This optional parameter is used to communicate 
   congestion levels in national MTP networks with multiple congestion 
   thresholds, such as in ANSI MTP3.  For MTP congestion methods 
   without multiple congestion levels (e.g., the ITU international 
   method) the parameter is not included.

Congestion Level field: 8-bits (unsigned integer)

   The Congestion Level field, associated with all of the Affected 
   DPC(s) in the Affected Destinations parameter, contains one of the 
   Following values:

         0     No Congestion or Undefined
         1     Congestion Level 1
         2     Congestion Level 2
         3     Congestion Level 3

   The congestion levels are defined in the congestion method in the 
   appropriate national MTP recommendations [14,15]. 

3.4.5 Destination User Part Unavailable (DUPU)

The DUPU message is used by an SGP to inform concerned ASPs that a 
remote peer MTP3-User Part (e.g., ISUP or SCCP) at an SS7 node is 
unavailable.

The DUPU message contains the following parameters:

     Network Appearance       Optional
     Routing Context          Optional
     Affected Point Code      Mandatory
     User/Cause               Mandatory
     INFO String              Optional

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The format for DUPU message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0200          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                      Network Appearance                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x0006           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         / 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0012          |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Mask = 0    |                  Affected PC                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0204          |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Cause             |            User               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0004          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

User/Cause: 32-bits

   The Unavailability Cause and MTP3-User Identity fields, associated 
   with the Affected PC in the Affected Point Code parameter, are 
   encoded as follows:

Unavailability Cause field: 16-bits (unsigned integer)

   The Unavailability Cause parameter provides the reason for the 
   unavailability of the MTP3-User.  The valid values for the 
   Unavailability Cause parameter are shown in the following table. 
   The values agree with those provided in the SS7 MTP3 User Part 
   Unavailable message.  Depending on the MTP3 protocol used in the 
   Network Appearance, additional values may be used - the 
   specification of the relevant MTP3 protocol variant/version 
   recommendation is definitive.

         0         Unknown
         1         Unequipped Remote User
         2         Inaccessible Remote User 

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MTP3-User Identity field: 16-bits (unsigned integer)

   The MTP3-User Identity describes the specific MTP3-User that is 
   unavailable (e.g., ISUP, SCCP, ...).  Some of the valid values for 
   the MTP3-User Identity are shown below.  The values align with those 
   provided in the SS7 MTP3 User Part Unavailable message and Service 
   Indicator.  Depending on the MTP3 protocol variant/version used in 
   the network appearance, additional values may be used.  The relevant 
   MTP3 protocol variant/version recommendation is definitive.

       0 to 2      Reserved
          3        SCCP
          4        TUP
          5        ISUP
       6 to 8      Reserved
          9        Broadband ISUP
         10        Satellite ISUP
         11        Reserved
         12        AAL type 2 Signalling
         13        Bearer Independent Call Control (BICC)
         14        Gateway Control Protocol 
         15        Reserved
                    
 
The format and description of the Affected Point Code parameter is 
the same as for the DUNA message (See Section 3.4.1.) except that 
the Mask field is not used and only a single Affected DPC is 
included.  Ranges and lists of Affected DPCs cannot be signalled in 
a DUPU message, but this is consistent with UPU operation in the 
SS7 network. The Affected Destinations parameter in an MTP3 User 
Part Unavailable message (UPU) received by an SGP from the SS7 
network contains only one destination.

The format and description of the Network Appearance, Routing 
Context,  and INFO String parameters is the same as for the DUNA 
message (See Section 3.4.1).

3.4.6 Destination Restricted (DRST)   

The DRST message is optionally sent from the SGP to all concerned ASPs 
to indicate that the SG has determined that one or more SS7  
destinations are now restricted from the point of view of the SG, or 
in response to a DAUD message if appropriate. The M3UA layer at the ASP 
is expected to send traffic to the affected destination via an 
alternate SG with route(s) of equal priority, but only if such an 
alternate route exists and is available. If the affected destination 
is currently considered unavailable by the ASP, The MTP3-User should 
be informed that traffic to the affected destination can be resumed.  
In this case, the M3UA layer should route the traffic through the SG 
initiating the DRST message.

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This message is optional for the SG to send and it is optional for the 
ASP to act on any information received in the message. It is for use in 
the "STP" case described in Section 1.4.1.

The DRST message contains the following parameters:

     Network Appearance       Optional
     Routing Context          Optional
     Affected Point Code      Mandatory
     INFO String              Optional

The format and description of the Network Appearance, Routing Context, 
Affected Point Code and INFO String parameters is the same as for the 
DUNA message (See Section 3.4.1).

3.5 ASP State Maintenance (ASPSM) Messages

3.5.1 ASP Up

The ASP Up message is used to indicate to a remote M3UA peer that the 
adaptation layer is ready to receive any SSNM or ASPSM/ASPTM messages 
for all Routing Keys that the ASP is configured to serve.

The ASP Up message contains the following parameters:

     ASP Identifier                Optional
     INFO String                   Optional

The format for ASP Up message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0011          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         ASP Identifier                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0004          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The optional ASP Identifier parameter contains a unique value that is 
locally significant among the ASPs that support an AS. The SGP should 
save the ASP Identifier to be used, if necessary, with the Notify 
message (see Section 3.8.2).

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The format and description of the optional INFO String parameter is the 
same as for the DUNA message (See Section 3.4.1).

3.5.2 ASP Up Acknowledgement (ASP Up Ack)

The ASP UP Ack message is used to acknowledge an ASP Up message 
received from a  remote M3UA peer.

The ASP Up Ack message contains the following parameters:

     INFO String (optional)

The format for ASP Up Ack message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag =0x0004             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional INFO String parameter is the 
same as for the DUNA message (See Section 3.4.1).  The INFO String in 
an ASP Up Ack message is independent from the INFO String in the ASP Up 
message (i.e., it does not have to echo back the INFO String received).

3.5.3 ASP Down

The ASP Down message is used to indicate to a remote M3UA peer that the 
adaptation layer is NOT ready to receive DATA, SSNM, RKM or ASPTM 
messages.

The ASP Down message contains the following parameters:

     INFO String    Optional

The format for the ASP Down message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag =0x0004           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   \                                                               \
   /                         INFO String                           /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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The format and description of the optional INFO String parameter is the 
same as for the DUNA message (See Section 3.4.1).

3.5.4 ASP Down Acknowledgement (ASP Down Ack)

The ASP Down Ack message is used to acknowledge an ASP Down message 
received from a remote M3UA peer.  

The ASP Down Ack message contains the following parameters:

     INFO String     Optional

The format for the ASP Down Ack message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0004          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   \                                                               \
   /                         INFO String                           /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional INFO String parameter is the 
same as for the DUNA message (See Section 3.4.1).

The INFO String in an ASP Down Ack message is independent from the INFO 
String in the ASP Down message (i.e., it does not have to echo back the 
INFO String received).

3.5.5 Heartbeat (BEAT)

The BEAT message is optionally used to ensure that the M3UA peers 
are still available to each other.  It is recommended for use when the 
M3UA runs over a transport layer other than the SCTP, which has its own 
heartbeat.

The BEAT message contains the following parameters:

     Heartbeat Data         Optional

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The format for the BEAT message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |         Tag = 0x0009          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Heartbeat Data                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 

The Heartbeat Data parameter contents are defined by the sending node.  
The Heartbeat Data could include, for example, a Heartbeat Sequence 
Number and/or Timestamp.  The receiver of a BEAT message does not 
process this field as it is only of significance to the sender.  The 
receiver MUST respond with a BEAT Ack message.
  

3.5.6 Heartbeat Acknowledgement (BEAT Ack)

The BEAT Ack message is sent in response to a received BEAT 
message.  It includes all the parameters of the received BEAT 
message, without any change.

3.6 Routing Key Management (RKM) Messages

3.6.1 Registration Request (REG REQ)

The REG REQ message is sent by an ASP to indicate to a remote M3UA peer
that it wishes to register one or more given Routing Keys with the 
remote peer.  Typically, an ASP would send this message to an SGP, and 
expects to receive a REG RSP message in return with an associated 
Routing Context value.

The REG REQ message contains the following parameters:

     Routing Key           Mandatory

One or more Routing Key parameters MAY be included.  The format for the 
REG REQ message is as follows:

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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0207         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         Routing Key 1                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0207         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         Routing Key n                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Routing Key: variable length

   The Routing Key parameter is mandatory. The sender of this message
   expects that the receiver of this message will create a Routing
   Key entry and assign a unique Routing Context value to it, if the 
   Routing Key entry does not already exist.

   The Routing Key parameter may be present multiple times in the same
   message. This is used to allow the registration of multiple Routing 
   Keys in a single message.

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The format of the Routing Key parameter is as follows.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Local-RK-Identifier                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Traffic Mode Type (optional)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Destination Point Code                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Network Appearance (optional)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Service Indicators (optional)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Originating Point Code List (optional)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Circuit Range List (optional)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Destination Point Code                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Network Appearance (optional)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Service Indicators (optional)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Originating Point Code List (optional)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Circuit Range List (optional)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Local-RK-Identifier: 32-bit integer

   The mandatory Local-RK-Identifier field is used to uniquely identify 
   the registration request. The Identifier value is assigned by the 
   ASP, and is used to correlate the response in an REG RSP message 
   with the original registration request. The Identifier value must 
   remain unique until the REG RSP message is received.

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   The format of the Local-RK-Identifier field is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x020a          |         Length = 8            |   
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Local-RK-Identifier value                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Traffic Mode Type: 32-bit (unsigned integer)

   The optional Traffic Mode Type parameter identifies the traffic mode 
   of operation of the ASP(s) within an Application Server.  The format 
   of the Traffic Mode Type Identifier is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x000b          |         Length = 8            |   
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Traffic Mode Type                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The valid values for Traffic Mode Type are shown in the 
   following table:

      1     Override
      2     Loadshare
      3     Broadcast

If the receiver of the REG REQ creates a new Routing Key entry, then 
the Traffic Mode Type sets the traffic mode for the new Application 
Server.  If the receiver of the REG REQ determines that a matching 
Routing Key already exists, the Traffic Mode Type MUST match the 
existing traffic mode for the AS.

Destination Point Code:

   The Destination Point Code parameter is mandatory, and identifies 
   the Destination Point Code of incoming SS7 traffic for which the ASP 
   is registering.  The format is the same as described for the 
   Affected Destination parameter in the DUNA message (See Section 
   3.4.1). Its format is:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x020b          |         Length = 8            |   
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |            Destination Point Code             |   
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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Network Appearance:

   The optional Network Appearance parameter field identifies the SS7 
   network context for the Routing Key, and has the same format as in 
   the DATA message (See Section 3.3.1).  The absence of the Network 
   Appearance parameter in the Routing Key indicates the use 
   of any Network Appearance value, Its format is:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0200          |         Length = 8            |   
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   
   |                     Network Appearance                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Service Indicators (SI): n X 8-bit integers

   The optional SI field contains one or more Service Indicators from 
   the values as described in the MTP3-User Identity field of the DUPU 
   message.  The absence of the SI parameter in the Routing Key 
   indicates the use of any SI value, excluding of course MTP 
   management.  Where an SI parameter does not contain a multiple of 
   four SIs, the parameter is padded out to 32-byte alignment.  An 
   SI value of zero is not valid in M3UA.  The SI format is:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x020c          |             Length            |   
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   
   |      SI #1    |     SI #2     |    SI #3      |    SI #4      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   
   /                              ...                              /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   
   |      SI #n    |             0 Padding, if necessary           |   
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

OPC List:

   The Originating Point Code List parameter contains one or more SS7 
   OPC entries, and its format is the same as the Destination Point 
   Code parameter.  The absence of the OPC List parameter in the 
   Routing Key indicates the use of any OPC value,

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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x020e          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #1            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #2            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #n            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Circuit Range:

   An ISUP controlled circuit is uniquely identified by the SS7 OPC, 
   DPC and CIC value.  For the purposes of identifying Circuit Ranges 
   in an M3UA Routing Key, the optional Circuit Range parameter 
   includes one or more circuit ranges, each identified by an OPC and 
   Upper/Lower CIC value.  The DPC is implicit as it is mandatory and 
   already included in the DPC parameter of the Routing Key.  The 
   absence of the Circuit Range parameter in the Routing Key indicates 
   the use of any Circuit Range values, in the case of ISUP/TUP 
   traffic.  The Origination Point Code is encoded the same as the 
   Destination Point Code parameter, while the CIC values are 16-bit 
   integers.

   The Circuit Range format is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x020f        |              Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #1            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Lower CIC Value #1      |      Upper CIC Value #1       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #2            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Lower CIC Value #2      |      Upper CIC Value #2       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #n            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Lower CIC Value #n      |      Upper CIC Value #n       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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3.6 2 Registration Response (REG RSP)

The REG RSP message is used as a response to the REG REQ message from a
remote M3UA peer.  It contains indications of success/failure for 
registration requests and returns a unique Routing Context value for 
successful registration requests, to be used in subsequent M3UA Traffic 
Management protocol.

The REG RSP message contains the following parameters:

     Registration Result   Mandatory

One or more Registration Result parameters MAY be included.  The format 
for the REG RSP message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0208         |              Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Registration Result 1                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0208        |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Registration Result n                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Registration Results:

   The Registration Result parameter contains the registration result 
   for a single Routing Key in an REG REQ message.  The number of 
   results in a single REG RSP message MAY be anywhere from one to the 
   total number of number of Routing Key parameters found in the 
   corresponding REG REQ message. Where multiple REG RSP messages are 
   used in reply to REG REQ message, a specific result SHOULD be in 
   only one REG RSP message. The format of each result is as follows:

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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Tag = 0x020a        |          Length = 8             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Local-RK-Identifier value                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Tag = 0x0212      |          Length = 8             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Registration Status                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Tag = 0x0006      |          Length = 8             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Routing Context                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Local-RK-Identifier: 32-bit integer

   The Local-RK-Identifier contains the same value as found in the
   matching Routing Key parameter found in the REG REQ message (See 
   Section 3.5.5.1).

Registration Status: 32-bit integer

   The Registration Result Status field indicates the success or the 
   reason for failure of a registration request.

   Its values may be:

        0           Successfully Registered
        1           Error - Unknown
        2           Error - Invalid DPC
        3           Error - Invalid Network Appearance
        4           Error - Invalid Routing Key
        5           Error - Permission Denied
        6           Error - Cannot Support Unique Routing
        7           Error - Routing Key not Currently Provisioned
        8           Error - Insufficient Resources
        9           Error - Unsupported RK parameter Field
       10           Error - Unsupported/Invalid Traffic Handling Mode

Routing Context: 32-bit integer

   The Routing Context field contains the Routing Context value for the
   associated Routing Key if the registration was successful. It is set
   to "0" if the registration was not successful.

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3.6.3 Deregistration Request (DEREG REQ)

The DEREG REQ message is sent by an ASP to indicate to a remote M3UA
peer that it wishes to deregister a given Routing Key. Typically, an 
ASP would send this message to an SGP, and expects to receive a DEREG 
RSP message in return with the associated Routing Context value.

The DEREG REQ message contains the following parameters:

     Routing Context       Mandatory

The format for the DEREG REQ message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         / 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Routing Context: n X 32-bit integers

   The Routing Context parameter contains (a list of) integers indexing 
   the Application Server traffic that the sending ASP is currently 
   registered to receive from the SGP but now wishes to deregister. 

3.6.4 Deregistration Response (DEREG RSP)

The DEREG RSP message is used as a response to the DEREG REQ message
from a remote M3UA peer.

The DEREG RSP message contains the following parameters:

     Deregistration Result    Mandatory

One or more Deregistration Result parameters MAY be included.  The 
format for the DEREG RSP message is as follows:

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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0209         |               Length          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Deregistration Result 1                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0209        |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Deregistration Result n                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Deregistration Results:

   The Deregistration Result parameter contains the deregistration 
   status for a single Routing Context in a DEREG REQ message. The 
   number of results in a single DEREG RSP message MAY be anywhere from 
   one to the total number of number of Routing Context values found in 
   the corresponding REG REQ message. Where multiple DEREG RSP messages 
   are used in reply to DEREG REQ message, a specific result SHOULD be 
   in only one DEREG RSP message.  The format of each result is as 
   follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Routing Context                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0213          |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Deregistration Status                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Routing Context: 32-bit integer

   The Routing Context field contains the Routing Context value of the
   matching Routing Key to deregister, as found in the DEREG REQ 
   message.

Deregistration Status: 32-bit integer

   The Deregistration Result Status field indicates the success or the 
   reason for failure of the deregistration.

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   Its values may be:
        0           Successfully Deregistered
        1           Error - Unknown
        2           Error - Invalid Routing Context
        3           Error - Permission Denied
        4           Error - Not Registered
        5           Error - ASP Currently Active for Routing Context

3.7 ASP Traffic Maintenance (ASPTM) Messages

3.7.1 ASP Active

The ASP Active message is sent by an ASP to indicate to a remote M3UA 
peer that it is ready to process signalling traffic for a particular 
Application Server.  The ASP Active message affects only the ASP state 
for the Routing Keys identified by the Routing Contexts, if present.

The ASP Active message contains the following parameters:

     Traffic Mode Type     Optional 
     Routing Context       Optional
     INFO String           Optional

The format for the ASP Active message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |         Tag = 0x000b          |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Traffic Mode Type                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         / 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |         Tag = 0x0004          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Traffic Mode Type: 32-bit (unsigned integer)

   The Traffic Mode Type parameter identifies the traffic mode of 
   operation of the ASP within an AS. The valid values for Traffic Mode 
   Type are shown in the following table:

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         1         Override
         2         Loadshare
         3         Broadcast

   Within a particular Routing Context, Override, Loadshare and 
   Broadcast MUST NOT be mixed.  The Override value indicates that the 
   ASP is operating in Override mode, and the ASP takes over all 
   traffic in an Application Server (i.e., primary/backup operation), 
   overriding any currently active ASPs in the AS.  In Loadshare mode, 
   the ASP will share in the traffic distribution with any other 
   currently active ASPs.  In Broadcast mode, the ASP will receive the 
   same messages as any other currently active ASP.  

Routing Context: n X 32-bit integers

   The optional Routing Context parameter contains (a list of) integers 
   indexing the Application Server traffic that the sending ASP is 
   configured/registered to receive.  

   There is one-to-one relationship between an index entry and an SGP 
   Routing Key or AS Name.  Because an AS can only appear in one 
   Network Appearance, the Network Appearance parameter is not required 
   in the ASP Active message.

   An Application Server Process may be configured to process traffic 
   for more than one logical Application Server.  From the perspective 
   of an ASP, a Routing Context defines a range of signalling traffic 
   that the ASP is currently configured to receive from the SGP.  For 
   example, an ASP could be configured to support call processing for 
   multiple ranges of PSTN trunks and therefore receive related 
   signalling traffic, identified by separate SS7 DPC/OPC/CIC ranges. 

The format and description of the optional INFO String parameter is the 
same as for the DUNA message (See Section 3.4.1).

3.7.2 ASP Active Acknowledgement (ASP Active Ack)

The ASP Active Ack message is used to acknowledge an ASP Active message 
received from a remote M3UA peer.  

The ASP Active Ack message contains the following parameters:

     Traffic Mode Type     Optional 
     Routing Context       Optional
     INFO String           Optional

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The format for the ASP Active Ack message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x000b        |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Traffic Mode Type                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 0x0006       |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         / 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |           Tag = 0x0004        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional INFO String parameter is the 
same as for the DUNA message (See Section 3.4.1).

The INFO String in an ASP Active Ack message is independent from the 
INFO String in the ASP Active message (i.e., it does not have to echo 
back the INFO String received).

The format of the Traffic Mode Type and Routing Context parameters is 
the same as for the ASP Active message. (See Section 3.5.5).

3.7.3  ASP Inactive

The ASP Inactive message is sent by an ASP to indicate to a remote M3UA 
peer that it is no longer an active ASP to be used from within a list of 
ASPs.  The ASP Inactive message affects only the ASP state in the 
Routing Keys identified by the Routing Contexts, if present. 

The ASP Inactive message contains the following parameters:

     Routing Context         Optional
     INFO String             Optional

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The format for the ASP Inactive message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         / 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |         Tag = 0x0004          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional Routing Context and INFO 
String parameters is the same as for the ASP Active message (See 
Section 3.5.5.)

3.7.4 ASP Inactive Acknowledgement (ASP Inactive Ack)

The ASP Inactive Ack message is used to acknowledge an ASP Inactive 
message received from a remote M3UA peer.

The ASP Inactive Ack message contains the following parameters:

     Routing Context       Optional
     INFO String           Optional

The format for the ASP Inactive Ack message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         / 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |         Tag = 0x0004          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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The format and description of the optional INFO String parameter is the 
same as for the DUNA message (See Section 3.4.1.)

The INFO String in an ASP Inactive Ack message is independent from the 
INFO String in the ASP Inactive message (i.e., it does not have to echo 
back the INFO String received).

The format of the Routing Context parameter is the same as for the ASP
Inactive message. (See Section 3.5.7).

3.8  Management (MGMT) Messages

3.8.1  Error

The Error message is used to notify a peer of an error event associated 
with an incoming message.  For example, the message type might be 
unexpected given the current state, or a parameter value might be 
invalid.  

The Error message contains the following parameters:

     Error Code                 Mandatory
     Diagnostic Information     Optional

The format for the Error message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x000c         |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Error Code                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0007         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                     Diagnostic Information                    /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Error Code: 32-bits (unsigned integer)

   The Error Code parameter indicates the reason for the Error Message. 
   The Error parameter value can be one of the following values:

     0x01      Invalid Version 
     0x02      Not Used in M3UA
     0x03      Unsupported Message Class

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     0x04      Unsupported Message Type 
     0x05      Unsupported Traffic Handling Mode 
     0x06      Unexpected Message
     0x07      Protocol Error
     0x08      Not used in M3UA
     0x09      Invalid Stream Identifier
     0x0a      Not used in M3UA
     0x0b      Not used in M3UA
     0x0c      Not used in M3UA
     0x0d      Refused - Management Blocking
     0x0e      ASP Identifier Required
     0x0f      Invalid ASP Identifier
     0x10      Invalid Routing Context
     0x11      Invalid Parameter Value
     0x12      Parameter Field Error
     0x13      Unexpected Parameter
     0x14      Destination Status Unknown
     0x15      Invalid Network Appearance          

The "Invalid Version" error is sent if a message was received with an 
invalid or unsupported version.  The Error message contains the 
supported version in the Common header.  The Error message could 
optionally provide the supported version in the Diagnostic Information 
area.

The "Invalid Network Appearance" error is sent by a SGP if an ASP sends 
a message with an invalid (unconfigured) Network Appearance value.

The "Unsupported Message Class" error is sent if a message with an 
unexpected or unsupported Message Class is received.

The "Unsupported Message Type" error is sent if a message with an 
unexpected or unsupported Message Type is received.

The "Unsupported Traffic Handling Mode" error is sent by a SGP 
if an ASP sends an ASP Active message with an unsupported Traffic Mode 
Type  or a Traffic Mode Type that is inconsistent with the presently 
configured mode for the Application Server.  An example would be a case 
in which the SGP did not support loadsharing.

The "Unexpected Message" error MAY be sent if a defined and recognized 
message is received that is not expected in the current state (in some 
cases the ASP may optionally silently discard the message and not send 
an Error message).  For example, silent discard is used by an ASP if it 
received a DATA message from an SGP while it was in the ASP-INACTIVE 
state. 

The "Protocol Error" error is sent for any protocol anomaly (i.e., 
reception of a parameter that is syntactically correct but unexpected 
in the current situation.

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The "Invalid Routing Context" error is sent if a message is received 
from a peer with an invalid (unconfigured) Routing Context value, or 
if a message is received from a peer without a Routing Context 
parameter and it is not known by configuration data which 
Application Servers are referenced.

The "Invalid Stream Identifier" error is sent if a message is received 
on an unexpected SCTP stream (e.g., a Management message was received 
on a stream other than "0").

The " Invalid Parameter Value " error is sent if a message is received 
with an invalid parameter value (e.g., a DUPU message was received with 
a Mask value other than "0").

The "Refused - Management Blocking" error is sent when an ASP Up or 
ASP Active message is received and the request is refused for 
management reasons (e.g., management lockout").

The "ASP Identifier Required" is sent by a SGP in response 
to an ASP Up message which does not contain an ASP Identifier 
parameter when the SGP requires one.  The ASP should resend the
ASP Up message with an ASP Identifier.

The "Invalid ASP Identifier" is send by a SGP in response
to an ASP Up message with an invalid (i.e., non-unique) ASP Identifier.

The "Destination Status Unknown" Error MAY be sent if a DAUD is 
received at an SG enquiring of the availability/congestion status of 
a destination, and the SG does not wish to provide the status (e.g., 
the sender is not authorized to know the status).

Diagnostic Information: variable length

   When included, the optional Diagnostic information can be any 
   information germane to the error condition, to assist in 
   identification of the error condition.  In the case of an Invalid 
   Network Appearance, Traffic Handling Mode, Routing Context or 
   Parameter Value, the Diagnostic information parameter MUST be added 
   and include the offending parameter.  In the case of Destination 
   Status Unknown, the Diagnostic information SHOULD include the Point 
   Code in the original DAUD request.  In the other cases, the 
   Diagnostic information MAY be the first 40 bytes of the offending 
   message.

Error messages MUST NOT be generated in response to other Error 
messages.

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3.8.2 Notify

The Notify message used to provide an autonomous indication of M3UA 
events to an M3UA peer.  

The Notify message contains the following parameters:

     Status                     Mandatory
     ASP Identifier             Optional
     Routing Context            Optional
     INFO String                Optional

The format for the Notify message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x000d           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Status Type            |       Status Information      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x0011           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        ASP Identifier                         | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x0006           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         / 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |         Tag = 0x0004          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Status Type: 16-bits (unsigned integer)

   The Status Type parameter identifies the type of the Notify message.  
   The following are the valid Status Type values:

         1     Application Server State Change (AS-State_Change)
         2     Other 

Status Information: 16-bits (unsigned integer)

   The Status Information parameter contains more detailed information 
   for the notification, based on the value of the Status Type.  

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   If the Status Type is AS-State_Change the following Status 
   Information values are used:

         1    reserved
         2    Application Server Inactive (AS-INACTIVE)
         3    Application Server Active (AS-ACTIVE)
         4    Application Server Pending (AS-PENDING)

   These notifications are sent from an SGP to an ASP upon a change in 
   status of a particular Application Server. The value reflects the 
   new state of the Application Server.

   If the Status Type is Other, then the following Status Information 
   values are defined:

         1    Insufficient ASP Resources Active in AS
         2    Alternate ASP Active
         3    ASP Failure

These notifications are not based on the SGP reporting the state change 
of an ASP or AS.  In the Insufficent ASP Resources case, the SGP is 
indicating to an ASP_INACTIVE ASP in the AS that another ASP is 
required to handle the load of the AS (Loadsharing or Broadcast mode).  
For the Alternate ASP Active case, an ASP is informed when an alternate 
ASP transitions to the ASP-ACTIVE state in Override mode.  

The format and description of the optional ASP Identifier, Routing 
Context and Info String parameters is the same as for the ASP Active 
message (See Section 3.5.5.)

4. Procedures

The M3UA layer needs to respond to various local primitives it receives 
from other layers as well as the messages that it receives from the 
peer M3UA layer.  This section describes the M3UA procedures in 
response to these events.

4.1 Procedures to Support the M3UA-User

4.1.1 Receipt of Primitives from the M3UA-User

On receiving an MTP-TRANSFER request primitive from an upper layer at 
an ASP/IPSP, or the nodal interworking function at an SGP, the M3UA 
layer sends a corresponding DATA message (see Section 3) to its M3UA 
peer.  The M3UA peer receiving the DATA message sends an MTP-TRANSFER 
indication primitive to the upper layer.

The M3UA message distribution function (see Section 1.4.2.1) determines 
the Application Server (AS) based on comparing the information in the 
MTP-TRANSFER request primitive with a provisioned Routing Key. 

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>From the list of ASPs within the AS table, an ASP in the ASP-ACTIVE 
state is selected and a DATA message is constructed and issued on the 
corresponding SCTP association.  If more than one ASP is in the ASP-
ACTIVE state (i.e., traffic is to be loadshared across more than one 
ASP), one of the ASPs in the ASP_ACTIVE state is selected from the 
list.  If the ASPs are in Broadcast Mode, all active ASPs will be 
selected and the message sent to each of the active ASPs.  The 
selection algorithm is implementation dependent but could, for 
example, be round-robin or based on the SLS or ISUP CIC.  The a
appropriate selection algorithm must be chosen carefully as it is 
dependent on application assumptions and understanding of the 
degree of state coordination between the ASP_ACTIVE ASPs in the AS. 

In addition, the message needs to be sent on the appropriate SCTP 
stream, again taking care to meet the message sequencing needs of the 
signalling application. DATA messages SHOULD be sent on an SCTP stream
other than stream '0'.

When there is no Routing Key match, or only a partial match, for an 
incoming SS7 message, a default treatment MUST be specified.  Possible 
solutions are to provide a default Application Server at the SGP that 
directs all unallocated traffic to a (set of) default ASP(s), or to 
drop the message and provide a notification to Layer Management in an 
M-ERROR indication primitive.  The treatment of unallocated traffic is 
implementation dependent.

4.1.2 Receipt of Primitives from the Layer Management

On receiving primitives from the local Layer Management, the M3UA layer 
will take the requested action and provide an appropriate response 
primitive to Layer Management.

An M-SCTP_ESTABLISH request primitive from Layer Management at an ASP 
or IPSP will initiate the establishment of an SCTP association.  The 
M3UA layer will attempt to establish an SCTP association with the 
remote M3UA peer by sending an SCTP-ASSOCIATE primitive to the local 
SCTP layer.  

When an SCTP association has been successfully established, the SCTP 
will send an SCTP-COMMUNICATION_UP notification primitive to the local 
M3UA layer.  At the SGP or IPSP that initiated the request, the M3UA 
layer will send an M-SCTP_ESTABLISH confirm primitive to Layer 
Management when the association setup is complete.  At the peer M3UA 
layer, an M-SCTP_ESTABLISH indication primitive is sent to Layer 
Management upon successful completion of an incoming SCTP association 
setup.

An M-SCTP_RELEASE request primitive from Layer Management initiates the 
teardown of an SCTP association.  The M3UA layer accomplishes a 
graceful shutdown of the SCTP association by sending an SCTP-SHUTDOWN 
primitive to the SCTP layer.

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When the graceful shutdown of the SCTP association has been 
accomplished, the SCTP layer returns an SCTP-SHUTDOWN_COMPLETE 
notification primitive to the local M3UA layer.  At the M3UA Layer that 
initiated the request, the M3UA layer will send an M-SCTP_RELEASE 
confirm primitive to Layer Management when the association shutdown 
is complete.  At the peer M3UA Layer, an M-SCTP_RELEASE indication 
primitive is sent to Layer Management upon abort or successful 
shutdown of an SCTP association.

An M-SCTP_STATUS request primitive supports a Layer Management query of 
the local status of a particular SCTP association.  The M3UA layer 
simply maps the M-SCTP_STATUS request primitive to an SCTP-STATUS 

primitive to the SCTP layer.  When the SCTP responds, the M3UA layer 
maps the association status information to an M-SCTP_STATUS confirm 
primitive.  No peer protocol is invoked.

Similar LM-to-M3UA-to-SCTP and/or SCTP-to-M3UA-to-LM primitive mappings 
can be described for the various other SCTP Upper Layer primitives in 
RFC2960 [13]  such as INITIALIZE, SET PRIMARY, CHANGE HEARTBEAT, 
REQUEST HEARTBEAT, GET SRTT REPORT, SET FAILURE THRESHOLD, SET PROTOCOL 
PARAMETERS, DESTROY SCTP INSTANCE, SEND FAILURE, AND NETWORK STATUS 
CHANGE.  Alternatively, these SCTP Upper Layer primitives (and Status 
as well) can be considered for modeling purposes as a Layer Management 
interaction directly with the SCTP Layer.  

M-NOTIFY indication and M-ERROR indication primitives indicate to Layer 
Management the notification or error information contained in a 
received M3UA Notify or Error message respectively.  These indications 
can also be generated based on local M3UA events.

An M-ASP_STATUS request primitive supports a Layer Management query of 
the status of a particular local or remote ASP.  The M3UA layer 
responds with the status in an M-ASP_STATUS confirm primitive.  No M3UA 
peer protocol is invoked.
 
An M-AS_STATUS request supports a Layer Management query of the status 
of a particular AS.  The M3UA responds with an M-AS_STATUS confirm 
primitive.  No M3UA peer protocol is invoked.

M-ASP_UP request, M-ASP_DOWN request, M-ASP_ACTIVE request and M-ASP_
INACTIVE request primitives allow Layer Management at an ASP to 
initiate state changes.  Upon successful completion, a corresponding 
confirm primitive is provided by the M3UA layer to Layer Management.  
If an invocation is unsuccessful, an Error indication primitive is 
provided in the primitive.  These requests result in outgoing ASP Up, 
ASP Down, ASP Active and ASP Inactive messages to the remote M3UA 
peer at an SGP or IPSP. 

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4.2 Procedures to Support the Management of SCTP Associations

4.2.1 Receipt of M3UA Peer Management Messages

Upon successful state changes resulting from reception of ASP Up, 
ASP Down, ASP Active and ASP Inactive messages from a peer M3UA, the 
M3UA layer SHOULD invoke corresponding M-ASP_UP, M-ASP_DOWN, M-
ASP_ACTIVE and M-ASP_INACTIVE, M-AS_ACTIVE, M-AS_INACTIVE, and M-
AS_DOWN indication primitives to the local Layer Management.

M-NOTIFY indication and M-ERROR indication primitives indicate to Layer 
Management the notification or error information contained in a 
received M3UA Notify or Error message.  These indications can also be 
generated based on local M3UA events.

All Non-Transfer messages, except BEAT and BEAT Ack, SHOULD be sent 
with sequenced delivery to ensure ordering.  All Non-Transfer 
messages, with the exception of ASPTM, BEAT and BEAT Ack messages, 
SHOULD be sent on SCTP stream '0'.  ASPTM messages MAY be sent on 
one of the streams used to carry the data traffic related to the 
Routing Context(s), to minimize possible message loss.  BEAT and 
BEAT Ack messages MAY be sent using out-of-order delivery, and MAY 
be sent on any stream.

4.3 AS and ASP State Maintenance

The M3UA layer on the SGP maintains the state of each remote ASP, in 
each Application Server that the ASP is configured to receive traffic, 
as input to the M3UA message distribution function.  Similarly, where 
IPSPs use M3UA in a point-to-point fashion, the M3UA layer in an IPSP 
maintains the state of remote IPSPs. For the purposes of the following 
procedures, only the SGP/ASP case is described but the SGP side of the 
procedures also apply to an IPSP sending traffic to an AS consisting of 
a set of remote IPSPs.

4.3.1 ASP States

The state of each remote ASP, in each AS that it is configured to 
operate, is maintained in the M3UA layer in the SGP. The state of a 
particular ASP in a particular AS changes due to events. The events 
include:

   * Reception of messages from the peer M3UA layer at the ASP;
   * Reception of some messages from the peer M3UA layer at other ASPs  
     in the AS (e.g., ASP Active message indicating "Override");
   * Reception of indications from the SCTP layer; or
   * Local Management intervention.

The ASP state transition diagram is shown in Figure 4.  The possible 
states of an ASP are:

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ASP-DOWN: The remote M3UA peer at the ASP is unavailable and/or the 
related SCTP association is down.  Initially all ASPs will be in this 
state.  An ASP in this state SHOULD NOT be sent any M3UA messages, 
with the exception of Heartbeat messages.

ASP-INACTIVE: The remote M3UA peer at the ASP is available (and the 
related SCTP association is up) but application traffic is stopped.  In 
this state the ASP MAY be sent any non-DATA M3UA messages.

ASP-ACTIVE: The remote M3UA peer at the ASP is available and 
application traffic is active (for a particular Routing Context or set 
of Routing Contexts).

                 Figure 4: ASP State Transition Diagram, per AS

                                   +--------------+ 
                                   |              |
            +----------------------|  ASP-ACTIVE  |
            |      Other   +-------|              |
            |   ASP in AS  |       +--------------+
            |   Overrides  |           ^     |
            |              |    ASP    |     | ASP
            |              |    Active |     | Inactive
            |              |           |     v
            |              |       +--------------+
            |              |       |              |
            |              +------>| ASP-INACTIVE |
            |                      +--------------+
            |                          ^     |
  ASP Down/ |                     ASP  |     | ASP Down /
  SCTP CDI/ |                     Up   |     | SCTP CDI/
  SCTP RI   |                          |     v SCTP RI
            |                      +--------------+
            |                      |              |
            +--------------------->|   ASP-DOWN   |
                                   |              |
                                   +--------------+

SCTP CDI: The SCTP CDI denotes the local SCTP layer's Communication 
Down Indication to the Upper Layer Protocol (M3UA) on an SGP. The local 
SCTP layer will send this indication when it detects the loss of 
connectivity to the ASP's peer SCTP layer.  SCTP CDI is understood as 
either a SHUTDOWN_COMPLETE notification or COMMUNICATION_LOST 
notification from the SCTP layer.

SCTP RI: The local SCTP layer's Restart indication to the upper layer 
protocol (M3UA) on an SG.  The local SCTP will send this indication 
when it detects a restart from the ASP's peer SCTP layer.

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4.3.2 AS States

The state of the AS is maintained in the M3UA layer on the SGP. The 
state of an AS changes due to events. These events include:

   * ASP state transitions
   * Recovery timer triggers

The possible states of an AS are:

AS-DOWN: The Application Server is unavailable.  This state implies 
that all related ASPs are in the ASP-DOWN state for this AS. Initially 
the AS will be in this state. An Application Server MUST be in the AS-
DOWN state before it can be removed from a configuration.

AS-INACTIVE: The Application Server is available but no application 
traffic is active (i.e., one or more related ASPs are in the ASP-
INACTIVE state, but none in the ASP-ACTIVE state).  The recovery 
timer T(r) is not running or has expired. 

AS-ACTIVE: The Application Server is available and application traffic 
is active.  This state implies that at least one ASP is in the ASP-
ACTIVE state.

AS-PENDING: An active ASP has transitioned to ASP-INACTIVE or ASP-DOWN  
and it was the last remaining active ASP in the AS.  A recovery timer 
T(r) SHOULD be started and all incoming signalling messages SHOULD be 
queued by the SGP. If an ASP becomes ASP-ACTIVE before T(r) expires, 
the AS is moved to the AS-ACTIVE state and all the queued messages 
will be sent to the ASP. 

If T(r) expires before an ASP becomes ASP-ACTIVE, the SGP stops queuing 
messages and discards all previously queued messages. The AS will move 
to the AS-INACTIVE state if at least one ASP is in ASP-INACTIVE state, 
otherwise it will move to AS-DOWN state.

Figure 5 shows an example AS state machine for the case where the 
AS/ASP data is preconfigured.  For other cases where the AS/ASP 
configuration data is created dynamically, there would be differences 
in the state machine, especially at creation of the AS.  

For example, where the AS/ASP configuration data is not created until 
Registration of the first ASP, the AS-INACTIVE state is entered 
directly upon the first successful REG REQ from an ASP.  Another 
example is where the AS/ASP configuration data is not created until the 
first ASP successfully enters the ASP-ACTIVE state.  In this case the 
AS-ACTIVE state is entered directly.

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                 Figure 5: AS State Transition Diagram

     +----------+   one ASP trans to ACTIVE   +-------------+
     |    AS-   |---------------------------->|     AS-     |      
     | INACTIVE |                             |   ACTIVE    |
     |          |<---                         |             |
     +----------+    \                        +-------------+
        ^   |         \ Tr Expiry,                ^    |
        |   |          \ at least one             |    |
        |   |           \ ASP in ASP-INACTIVE     |    |
        |   |            \                        |    |
        |   |             \                       |    |
        |   |              \                      |    |
one ASP |   | all ASP       \            one ASP  |    | Last ACTIVE
trans   |   | trans to       \           trans to |    | ASP trans to
to      |   | ASP-DOWN        -------\   ASP-     |    | ASP-INACTIVE
ASP-    |   |                         \  ACTIVE   |    | or ASP-DOWN
INACTIVE|   |                          \          |    |  (start Tr)
        |   |                           \         |    |
        |   |                            \        |    |
        |   v                             \       |    v         
     +----------+                          \  +-------------+
     |          |                           --|             |      
     | AS-DOWN  |                             | AS-PENDING  |
     |          |                             |  (queueing) |
     |          |<----------------------------|             |
     +----------+    Tr Expiry and no ASP     +-------------+
                     in ASP-INACTIVE state)

    Tr = Recovery Timer

4.3.3 M3UA Management Procedures for Primitives

Before the establishment of an SCTP association the ASP state at both 
the SGP and ASP is assumed to be in the state ASP-DOWN.  

Once the SCTP association is established (see Section 4.2.1) and 
assuming that the local M3UA-User is ready, the local M3UA ASP 
Maintenance (ASPM) function will initiate the relevant procedures, 
using the ASP Up/ASP Down/ASP Active/ASP Inactive messages to convey 
the ASP state to the SGP (see Section 4.4.3).

If the M3UA layer subsequently receives an SCTP-COMMUNICATION_DOWN 
or SCTP-RESTART indication primitive from the underlying SCTP layer, it 
will inform the Layer Management by invoking the M-SCTP_STATUS 
indication primitive. The state of the ASP will be moved to ASP-DOWN.  
At an ASP, the MTP3-User will be informed of the unavailability of any 
affected SS7 destinations through the use of MTP-PAUSE indication 
primitives.  In the case 

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of SS7 network isolation, the local MTP3-Users MAY be informed by 
implementation-dependent means, as there is currently no primitive 
defined for conveying this information.

In the case of SCTP-COMMUNICATION_DOWN, the SCTP client MAY try to re-
establish the SCTP Association.  This MAY be done by the M3UA layer 
automatically, or Layer Management MAY reestablish using the 
M-SCTP_ESTABLISH request primitive. 

In the case of an SCTP-RESTART indication at an ASP, the ASP is now 
considered by its M3UA peer to be in the ASP-DOWN state.  The ASP, if 
it is to recover, must begin any recovery with the ASP-Up procedure.

4.3.4 ASPM Procedures for Peer-to-Peer Messages

4.3.4.1 ASP Up Procedures

After an ASP has successfully established an SCTP association to an 
SGP, the SGP waits for the ASP to send an ASP Up message, indicating 
that the ASP M3UA peer is available.  The ASP is always the initiator 
of the ASP Up message.  This action MAY be initiated at the ASP by an 
M-ASP_UP request primitive from Layer Management or MAY be initiated 
automatically by an M3UA management function.

When an ASP Up message is received at an SGP and internally the remote 
ASP is in the ASP-DOWN state and not considered locked out for local 
management reasons, the SGP marks the remote ASP in the state ASP-
INACTIVE and informs Layer Management with an M-ASP_Up indication 
primitive.  If the SGP is aware, via current configuration data, which 
Application Servers the ASP is configured to operate in, the SGP 
updates the ASP state to ASP-INACTIVE in each AS that it is a member.  

Alternatively, the SGP may move the ASP into a pool of Inactive ASPs 
available for future configuration within Application Server(s), 
determined in a subsequent Registration Request or ASP Active 
procedure.  If the ASP Up message contains an ASP Identifier, the SGP 
should save the ASP Identifier for that ASP. The SGP MUST send an 
ASP Up Ack message in response to a received ASP Up message even if 
the ASP is already marked as ASP-INACTIVE at the SGP.  

If for any local reason (e.g., management lockout) the SGP cannot 
respond with an ASP Up Ack message, the SGP responds to an ASP Up 
message with an Error message with reason "Refused - Management 
Blocking".  

At the ASP, the ASP Up Ack message received is not acknowledged. Layer 
Management is informed with an M-ASP_UP confirm primitive.  When an ASP

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enters the ASP-Inactive state from the ASP-Down state towards an SGP 
the M3UA MUST mark all SS7 destinations configured to be reachable via 
this SGP as available.

When the ASP sends an ASP Up message it starts timer T(ack).  If the 
ASP does not receive a response to an ASP Up message within T(ack), the 
ASP MAY restart T(ack) and resend ASP Up messages until it receives an 
ASP Up Ack message.  T(ack) is provisionable, with a default of 2 
seconds.  Alternatively, retransmission of ASP Up messages MAY be put 
under control of Layer Management.  In this method, expiry of T(ack) 
results in an M-ASP_UP confirm primitive carrying a negative 
indication.  

The ASP must wait for the ASP Up Ack message before sending any other 
M3UA messages (e.g., ASP Active or REG REQ).  If the SGP receives any 
other M3UA messages before an ASP Up message is received, the SGP 
SHOULD discard them.

If an ASP Up message is received and internally the remote ASP is in 
the ASP-ACTIVE state, an ASP-Up Ack message is returned, as well as an 
Error message ("Unexpected Message), and the remote ASP state is 
changed to ASP-INACTIVE in all relevant Application Servers.

If an ASP Up message is received and internally the remote ASP is 
already in the ASP-INACTIVE state, an ASP Up Ack message is returned 
and no further action is taken.

4.3.4.1.1 M3UA Version Control

If an ASP Up message with an unsupported version is received, the 
receiving end responds with an Error message, indicating the version 
the receiving node supports and notifies Layer Management.

This is useful when protocol version upgrades are being performed in a 
network.  A node upgraded to a newer version should support the older 
versions used on other nodes it is communicating with.  Because ASPs 
initiate the ASP Up procedure it is assumed that the Error message 
would normally come from the SGP.

4.3.4.1.2 IPSP Considerations

In the case of peer-to-peer IPSPs, either of the IPSPs (IPSP_A) may 
start operations by sending an ASP Up message to the remote peer 
(IPSP_B).  When the ASP Up message is received at IPSP_B and internally 
the remote IPSP_A is in the ASP-DOWN state and not considered locked 
out for local management reasons, IPSP_B marks the remote IPSP_A in the 
state ASP-INACTIVE and informs Layer Management with an M-ASP_Up 
indication primitive.  IPSP_B returns an ASP Up Ack message to IPSP_A.  
IPSP_A moves IPSP_B to the ASP-INACTIVE state upon reception of an ASP 
Up Ack message, if is not already in the ASP_INACTIVE state, and 
informs Layer Management with an M-ASP_UP confirmation primitive.

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If for any local reason (e.g., management lockout) the IPSP_B cannot 
respond with an ASP Up Ack message, it responds to an ASP Up message 
with an Error message with reason "Refused - Management Blocking" and 
leaves IPSP_A in the ASP-DOWN state.  

4.3.4.2 ASP-Down Procedures

The ASP will send an ASP Down message to an SGP when the ASP wishes to 
be removed from service in all Application Servers that it is a 
member and no longer receive any DATA, SSNM or ASPTM messages.  
This action MAY be initiated at the ASP by an M-ASP_DOWN request 
primitive from Layer Management or MAY be initiated automatically 
by an M3UA management function.   

Whether the ASP is permanently removed from any AS is a function of 
configuration management.  In the case where the ASP previously used 
the Registration procedures (see Section 4.3.5) to register within 
Application Servers but has not deregistered from all of them prior to 
sending the ASP Down message, the SGP SHOULD consider the ASP as 
Deregistered in all Application Servers that it is still a member.

The SGP marks the ASP as ASP-DOWN, informs Layer Management with an M-
ASP_Down indication primitive, and returns an ASP Down Ack message to 
the ASP. 

The SGP MUST send an ASP Down Ack message in response to a received 
ASP Down message from the ASP even if the ASP is already marked as 
ASP-DOWN at the SGP.

At the ASP, the ASP Down Ack message received is not acknowledged. 
Layer Management is informed with an M-ASP_DOWN confirm primitive.  If 
the ASP receives an ASP Down Ack without having sent an ASP Down 
message, the ASP should now consider itself as in the ASP-DOWN state.  
If the ASP was previously in the ASP-ACTIVE or ASP-INACTIVE state, the 
ASP should then initiate procedures to return itself to its previous 
state.

When the ASP sends an ASP Down message it starts timer T(ack).  If the 
ASP does not receive a response to an ASP Down message within T(ack), 
the ASP MAY restart T(ack) and resend ASP Down messages until it 
receives an ASP Down Ack message.  T(ack) is provisionable, with a 
default of 2 seconds.  Alternatively, retransmission of ASP Down 
messages MAY be put under control of Layer Management.  In this method, 
expiry of T(ack) results in an M-ASP_DOWN confirm primitive carrying a 
negative indication. 

4.3.4.4 ASP Active Procedures

Anytime after the ASP has received an ASP Up Ack message from the SGP 
or IPSP, the ASP MAY send an ASP Active message to the SGP indicating 

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that the ASP is ready to start processing traffic.  This action MAY be 
initiated at the ASP by an M-ASP_ACTIVE request primitive from Layer 
Management or MAY be initiated automatically by an M3UA management 
function.  In the case where an ASP wishes to process the traffic for 
more than one Application Server across a common SCTP association, the 
ASP Active message(s) SHOULD contain a list of one or more Routing 
Contexts to indicate for which Application Servers the ASP Active 
message applies. It is not necessary for the ASP to include all Routing 
Contexts of interest in a single ASP Active message, thus requesting to 
become active in all Routing Contexts at the same time.  Multiple ASP 
Active messages MAY be used to activate within the Application Servers 
independently, or in sets.  In the case where an ASP Active message 
does not contain a Routing Context parameter, the receiver must know, 
via configuration data, which Application Server(s) the ASP is a 
member.

For the Application Servers that the ASP can be successfully activated, 
the SGP or IPSP responds with one or more ASP Active Ack messages, 
including the associated Routing Context(s) and reflecting any 
Traffic Mode Type value present in the related ASP Active message.  
The Routing Context parameter MUST be included in the ASP Active 
Ack message(s) if the received ASP Active message contained any 
Routing Contexts.  Depending on any Traffic Mode Type request in 
the ASP Active message, or local configuration data if there is no 
request, the SGP moves the ASP to the correct ASP traffic state 
within the associated Application Server(s). Layer Management is 
informed with an M-ASP_Active indication. If the SGP or IPSP 
receives any Data messages before an ASP Active message is 
received, the SGP or IPSP MAY discard them.  By sending an ASP 
Active Ack message, the SGP or IPSP is now ready to receive and 
send traffic for the related Routing Context(s).  The ASP SHOULD 
NOT send Data messages for the related Routing Context(s) before 
receiving an ASP Active Ack message, or it will risk message loss.

Multiple ASP Active Ack messages MAY be used in response to an ASP 
Active message containing multiple Routing Contexts, allowing the SGP 
or IPSP to independently acknowledge the ASP Active message for 
different (sets of) Routing Contexts.  The SGP or IPSP MUST send an 
Error message ("Invalid Routing Context") for each Routing Context 
value that the ASP cannot be successfully activated . 

In the case where an "out-of-the-blue" ASP Active message is received 
(i.e., the ASP has not registered with the SG or the SG has no static 
configuration data for the ASP), the message MAY be silently discarded. 

The SGP MUST send an ASP Active Ack message in response to a received 
ASP Active message from the ASP, if the ASP is already marked in the 
ASP-ACTIVE state at the SGP.  

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At the ASP, the ASP Active Ack message received is not acknowledged. 
Layer Management is informed with an M-ASP_ACTIVE confirm primitive.  
It is possible for the ASP to receive Data message(s) before the ASP 
Active Ack message as the ASP Active Ack and Data messages from an SG 
or IPSP may be sent on different SCTP streams.  Message loss is 
possible as the ASP does not consider itself in the ASP-ACTIVE state 
until reception of the ASP Active Ack message.

When the ASP sends an ASP Active message it starts timer T(ack).  If 
the ASP does not receive a response to an ASP Active message within 
T(ack), the ASP MAY restart T(ack) and resend ASP Active messages until 
it receives an ASP Active Ack message.  T(ack) is provisionable, with a 
default of 2 seconds.  Alternatively, retransmission of ASP Active 
messages MAY be put under control of Layer Management.  In this method, 
expiry of T(ack) results in an M-ASP_ACTIVE confirm primitive carrying 
a negative indication.  

There are three modes of Application Server traffic handling in the SGP 
M3UA layer: Override, Loadshare and Broadcast.  When included, the 
Traffic Mode Type parameter in the ASP Active message indicates the 
traffic handling mode to be used in a particular Application Server. 
If the SGP determines that the mode indicated in an ASP Active 
message is unsupported or incompatible with the mode currently 
configured for the AS, the SGP responds with an Error message 
("Unsupported / Invalid Traffic Handling Mode").  If the traffic 
handling mode of the Application Server is not already known via 
configuration data, then the traffic handling mode indicated in the 
first ASP Active message causing the transition of the Application 
Server state to AS-ACTIVE MAY be used to set the mode.

In the case of an Override mode AS, reception of an ASP Active message 
at an SGP causes the (re)direction of all traffic for the AS to the ASP 
that sent the ASP Active message.  Any previously active ASP in the AS 
is now considered to be in state ASP-INACTIVE and SHOULD no longer 
receive traffic from the SGP within the AS.  The SGP or IPSP then MUST 
send a Notify message ("Alternate ASP_Active") to the previously active 
ASP in the AS, and SHOULD stop traffic to/from that ASP.  The ASP 
receiving this Notify MUST consider itself now in the ASP-INACTIVE 
state, if it is not already aware of this via inter-ASP communication 
with the Overriding ASP.

In the case of a Loadshare mode AS, reception of an ASP Active message 
at an SGP or IPSP causes the direction of traffic to the ASP sending 
the ASP Active message, in addition to all the other ASPs that are 
currently active in the AS.  The algorithm at the SGP for loadsharing 
traffic within an AS to all the active ASPs is implementation 
dependent.  The algorithm could, for example, be round-robin or based 
on information in the Data message (e.g., the SLS, SCCP SSN, ISUP CIC 
value).  

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An SGP or IPSP, upon reception of an ASP Active message for the first 
ASP in a Loadshare AS, MAY choose not to direct traffic to a newly 
active ASP until it determines that there are sufficient resources to 
handle the expected load (e.g., until there are "n" ASPs in state ASP-
ACTIVE in the AS).

All ASPs within a loadsharing mode AS must be able to process any 
Data message received for the AS, to accommodate any potential 
failover or rebalancing of the offered load.

In the case of a Broadcast mode AS, reception of an ASP Active message 
at an SGP or IPSP causes the direction of traffic to the ASP sending 
the ASP Active message, in addition to all the other ASPs that are 
currently active in the AS. The algorithm at the SGP for broadcasting 
traffic within an AS to all the active ASPs is a simple broadcast 
algorithm, where every message is sent to each of the active ASPs. 
 
An SGP or IPSP, upon reception of an ASP Active message for the first 
ASP in a Broadcast AS, MAY choose not to direct traffic to a newly 
active ASP until it determines that there are sufficient resources to 
handle the expected load (e.g., until there are "n" ASPs in state 
ASP-ACTIVE in the AS). 

Whenever an ASP in a Broadcast mode AS becomes ASP-ACTIVE, the SGP 
MUST tag the first DATA message broadcast in each SCTP stream with 
a unique Correlation Id parameter.  The purpose of this 
 Id is to permit the newly active ASP to synchronize its processing 
of traffic in each ordered stream with the other ASPs in the 
broadcast group.
 
4.3.4.5 ASP Inactive Procedures

When an ASP wishes to withdraw from receiving traffic within an AS, the 
ASP sends an ASP Inactive message to the SGP or IPSP.  This action MAY 
be initiated at the ASP by an M-ASP_INACTIVE request primitive from 
Layer Management or MAY be initiated automatically by an M3UA 
management function.  In the case where an ASP is processing the 
traffic for more than one Application Server across a common SCTP 
association, the ASP Inactive message contains one or more Routing 
Contexts to indicate for which Application Servers the ASP Inactive 
message applies.  In the case where an ASP Inactive message does not 
contain a Routing Context parameter, the receiver must know, via

configuration data, which Application Servers the ASP is a member and 
move the ASP to the ASP-INACTIVE state in all Application Servers.  
In the case of an Override mode AS, where another ASP has already 
taken over the traffic within the AS with an ASP Active ("Override") 
message, the ASP that sends the ASP Inactive message is already 
considered by the SGP to be in state ASP-INACTIVE.  An ASP Inactive Ack 
message is sent to the ASP, after ensuring that all traffic is stopped 
to the ASP. 

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In the case of a Loadshare mode AS, the SGP moves the ASP to the ASP-
INACTIVE state and the AS traffic is reallocated across the remaining 
ASPs in the state ASP-ACTIVE, as per the loadsharing algorithm 
currently used within the AS.  A Notify message ("Insufficient ASP 
resources active in AS") MAY be sent to all inactive ASPs, if required.  
An ASP Inactive Ack message is sent to the ASP after all traffic 
is halted and Layer Management is informed with an M-ASP_INACTIVE 
indication primitive. 

In the case of a Broadcast mode AS, the SGP moves the ASP to the 
ASP-INACTIVE state and the AS traffic is broadcast only to the 
remaining ASPs in the state ASP-ACTIVE. A Notify message 
("Insufficient ASP resources active in AS") MAY be sent to all 
inactive ASPs, if required.  An ASP Inactive Ack message 
is sent to the ASP after all traffic is halted and Layer Management is 
informed with an M-ASP_INACTIVE indication primitive.

Multiple ASP Inactive Ack messages MAY be used in response to an ASP 
Inactive message containing multiple Routing Contexts, allowing the SGP 
or IPSP to independently acknowledge for different (sets of) Routing 
Contexts.  The SGP or IPSP sends an Error message ("Invalid Routing 
Context") message for each invalid or unconfigured Routing Context 
value in a received ASP Inactive message.

The SGP MUST send an ASP Inactive Ack message in response to a received 
ASP Inactive message from the ASP and the ASP is already marked as ASP-
INACTIVE at the SGP.  

At the ASP, the ASP Inactive Ack message received is not acknowledged.  
Layer Management is informed with an M-ASP_INACTIVE confirm primitive. 
If the ASP receives an ASP Inactive Ack without having sent an ASP 
Inactive message, the ASP should now consider itself as in the 
ASP-INACTIVE state.  If the ASP was previously in the ASP-ACTIVE 
state, the ASP should then initiate procedures to return itself to 
its previous state.  

When the ASP sends an ASP Inactive message it starts timer T(ack).  If 
the ASP does not receive a response to an ASP Inactive message within 
T(ack), the ASP MAY restart T(ack) and resend ASP Inactive messages  
until it receives an ASP Inactive Ack message.  T(ack) is 
provisionable, with a default of 2 seconds.  Alternatively, 
retransmission of ASP Inactive messages MAY be put under control of 
Layer Management.  In this method, expiry of T(ack) results in a M-
ASP_Inactive confirm primitive carrying a negative indication.  

If no other ASPs in the Application Server are in the state 
ASP-ACTIVE, the SGP MUST send a Notify message ("AS-Pending") to 
all of the ASPs in the AS which are in the state ASP-INACTIVE.  
The SGP SHOULD start buffering the incoming messages for T(r)
seconds, after which messages MAY be discarded.  T(r) is 

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configurable by the network operator.  If the SGP receives an ASP 
Active message from an ASP in the AS before expiry of T(r), the 
buffered traffic is directed to that ASP and the timer is cancelled. 
If T(r) expires, the AS is moved to the AS-INACTIVE state.

4.3.4.6 Notify Procedures

A Notify message reflecting a change in the AS state MUST be sent to 
all ASPs in the AS, except those in the ASP-DOWN state, with
appropriate Status Information and any ASP Identifier of the failed 
ASP.  At the ASP, Layer Management is informed with an M-NOTIFY 
indication primitive.  The Notify message must be sent whether the 
AS state change was a result of an ASP failure or reception of an 
ASP State management (ASPSM) / ASP Traffic Management (ASPTM) 
message.  In the second case, the Notify message MUST be sent after 
any related acknowledgement messages  (e.g., ASP Up Ack, ASP Down 
Ack, ASP Active Ack, or ASP Inactive Ack). 

In the case where a Notify message("AS-PENDING") message is sent by 
an SGP that now has no ASPs active to service the traffic, or where a 
Notify ("Insufficient ASP resources active in AS") message MUST be 
sent in the Loadshare or Broadcast mode, the Notify message does not 
explicitly compel the ASP(s) receiving the message to become 
active. The ASPs remain in control of what (and when) traffic action 
is taken.

In the case where a Notify message does not contain a Routing Context
parameter, the receiver must know, via configuration data, of which
Application Servers the ASP is a member and take the appropriate 
action in each AS.

4.3.4.7 Heartbeat Procedures

The optional Heartbeat procedures MAY be used when operating over 
transport layers that do not have their own heartbeat mechanism for 
detecting loss of the transport association (i.e., other than SCTP).  

Either M3UA peer may optionally send Heartbeat messages periodically, 
subject to a provisionable timer T(beat).  Upon receiving a Heartbeat 
message, the M3UA peer MUST respond with a Heartbeat Ack message.  

If no Heartbeat Ack message (or any other M3UA message) is received 
from the M3UA peer within 2*T(beat), the remote M3UA peer is 
considered unavailable.  Transmission of Heartbeat messages is 
stopped and the signalling process SHOULD attempt to reestablish 
communication if it is configured as the client for the 
disconnected M3UA peer.

The Heartbeat message may optionally contain an opaque Heartbeat Data 
parameter that MUST be echoed back unchanged in the related Heartbeat 

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Ack message.  The sender, upon examining the contents of the returned 
Heartbeat Ack message, MAY choose to consider the remote M3UA peer as 
unavailable.  The contents/format of the Heartbeat Data parameter is 
implementation-dependent and only of local interest to the original 
sender.  The contents may be used, for example, to support a Heartbeat 
sequence algorithm (to detect missing Heartbeats), and/or a timestamp 
mechanism (to evaluate delays).

Note: Heartbeat related events are not shown in Figure 4 "ASP state 
transition diagram".  

4.4 Routing Key Management Procedures

4.4.1 Registration

An ASP MAY dynamically register with an SGP as an ASP within an 
Application Server using the REG REQ message. A Routing Key parameter 
in the REG REQ message specifies the parameters associated with the 
Routing Key.  

The SGP examines the contents of the received Routing Key parameter and 
compares it with the currently provisioned Routing Keys.  If the 
received Routing Key matches an existing SGP Routing Key entry, and the 
ASP is not currently included in the list of ASPs for the related 
Application Server, the SGP MAY authorize the ASP to be added to the 
AS.  Or, if the Routing Key does not currently exist and the received 
Routing Key data is valid and unique, an SGP supporting dynamic 
configuration MAY authorize the creation of a new Routing Key and 
related Application Server and add the ASP to the new AS.  In either 
case, the SGP returns a Registration Response message to the ASP, 
containing the same Local-RK-Identifier as provided in the initial 
request, and a Registration Result "Successfully Registered".  A unique 
Routing Context value assigned to the SGP Routing Key is included. The 
method of Routing Context value assignment at the SGP is 
implementation dependent but must be guaranteed to be unique for each 
Application Server or Routing Key supported by the SGP.  
 
If the SGP determines that the received Routing Key data is invalid, or 
contains invalid parameter values, the SGP returns a Registration 
Response message to the ASP, containing a Registration Result "Error - 
Invalid Routing Key", "Error - Invalid DPC", "Error - Invalid Network 
Appearance" as appropriate.

If the SGP determines that a unique Routing Key cannot be created, the 
SGP returns a Registration Response message to the ASP, with a 
Registration Status of "Error - "Cannot Support Unique Routing"  An 
incoming signalling message received at an SGP should not match against 
more than one Routing Key.

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If the SGP does not authorize the registration request, the SGP returns 
a REG RSP message to the ASP containing the Registration Result "Error 
- Permission Denied".

If an SGP determines that a received Routing Key does not currently 
exist and the SGP does not support dynamic configuration, the SGP 
returns a Registration Response message to the ASP, containing a 
Registration Result "Error - Routing Key not Currently Provisioned".

If an SGP determines that a received Routing Key does not currently 
exist and the SGP supports dynamic configuration but does not have the 
capacity to add new Routing Key and Application Server entries, the SGP 
returns a Registration Response message to the ASP, containing a 
Registration Result "Error - Insufficient Resources".

If an SGP determines that one or more of the Routing Key parameters are 
not supported for the purpose of creating new Routing Key entries, the 
SGP returns a Registration Response message to the ASP, containing a 
Registration Result "Error - Unsupported RK parameter field".  This 
result MAY be used if, for example, the SGP does not support RK Circuit 
Range Lists in a Routing Key because the SGP does not support ISUP 
traffic, or does not provide CIC range granularity.

A Registration Response "Error - Unsupported Traffic Handling Mode" is 
returned if the Routing Key in the REG REQ contains an Traffic Handling 
Mode that is inconsistent with the presently configured mode for the 
matching Application Server.

An ASP MAY register multiple Routing Keys at once by including a number 
of Routing Key parameters in a single REG REQ message.  The SGP MAY 
respond to each registration request in a single REG RSP message, 
indicating the success or failure result for each Routing Key in a 
separate Registration Result parameter.  Alternatively the SGP MAY 
respond with multiple REG RSP messages, each with one or more 
Registration Result parameters.  The ASP uses the Local-RK-Identifier 
parameter to correlate the requests with the responses.

Upon successful registration of an ASP in an AS, the SGP can now send 
related SS7 Signalling Network Management messaging, if this did not 
previously start upon the ASP transitioning to state ASP-INACTIVE

4.4.2 Deregistration

An ASP MAY dynamically deregister with an SGP as an ASP within an 
Application Server using the DEREG REQ message.  A Routing Context 
parameter in the DEREG REQ message specifies which Routing Keys to 
deregister.  An ASP SHOULD move to the ASP-INACTIVE state for an 
Application Server before attempting to deregister the Routing Key 
(i.e., deregister after receiving an ASP Inactive Ack).  Also, an ASP 

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SHOULD deregister from all Application Servers that it is a member 
before attempting to move to the ASP-Down state.  

The SGP examines the contents of the received Routing Context parameter 
and validates that the ASP is currently registered in the Application 
Server(s) related to the included Routing Context(s).  If validated, 
the ASP is deregistered as an ASP in the related Application Server.  

The deregistration procedure does not necessarily imply the deletion of
Routing Key and Application Server configuration data at the SGP. Other 
ASPs may continue to be associated with the Application Server, in 
which case the Routing Key data MUST NOT be deleted.  If a  
Deregistration results in no more ASPs in an Application Server, an SGP 
MAY delete the Routing Key data.

The SGP acknowledges the deregistration request by returning a DEREG 
RSP message to the requesting ASP.  The result of the deregistration is 
found in the Deregistration Result parameter, indicating success or 
failure with cause.

An ASP MAY deregister multiple Routing Contexts at once by including a 
number of Routing Contexts in a single DEREG REQ message.  The SGP MAY 
respond to each deregistration request in a single DEREG RSP message, 
indicating the success or failure result for each Routing Context in a 
separate Deregistration Result parameter.  

4.5 Procedures to Support the Availability or Congestion Status of SS7 
Destination

4.5.1 At an SGP

On receiving an MTP-PAUSE, MTP-RESUME or MTP-STATUS indication 
primitive from the nodal interworking function at an SGP, the SGP M3UA 
layer will send a corresponding SS7 Signalling Network Management 
(SSNM) DUNA, DAVA, SCON, or DUPU message (see Section 3.4) to the M3UA 
peers at concerned ASPs.  The M3UA layer must fill in various fields of 
the SSNM messages consistently with the information received in the 
primitives.  

The SGP M3UA layer determines the set of concerned ASPs to be informed 
based on the specific SS7 network for which the primitive indication 
is relevant. In this way, all ASPs configured to send/receive traffic 
within a particular network appearance are informed.  If the SGP 
operates within a single SS7 network appearance, then all ASPs are 
informed. 

DUNA, DAVA, SCON, and DRST messages MUST be sent sequentially and 
processed at the receiver in the order sent.  SCTP stream "0" is 
used to provide the sequencing. The only exception to this is if the 

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international congestion method (see Q.704) is used.  If so, the 
Unordered bit in the SCTP DATA chunk MAY be used for the SCON message.

Sequencing is not required for the DUPU or DAUD messages, which MAY 
be sent unsequenced.  Again, SCTP stream 0 is used, with optional use 
of the Unordered bit in the SCTP DATA chunk.

4.5.2 At an ASP

4.5.2.1 Single SGP Configurations

At an ASP, upon receiving an SS7 Signalling Network Management (SSNM) 
message from the remote M3UA Peer, the M3UA layer invokes the 
appropriate primitive indications to the resident M3UA-Users.  Local 
management is informed.

In the case where a local event has caused the unavailability or 
congestion status of SS7 destinations, the M3UA layer at the ASP SHOULD
pass up appropriate indications in the primitives to the M3UA User, as 
though equivalent SSNM messages were received.  For example, the loss 
of an SCTP association to an SGP may cause the unavailability of a set 
of SS7 destinations.  MTP-PAUSE indication primitives to the M3UA User 
are appropriate.  

Implementation Note: To accomplish this, the M3UA layer at an ASP 
maintains the status of routes via the SG(P), much like an MTP3 layer 
maintains route-set status.

4.5.2.2 Multiple SGP Configurations

At an ASP, upon receiving a Signalling Network Management message from 
the remote M3UA Peer, the M3UA layer updates the status of the affected 
route(s) via the originating SG and determines, whether or not the 
overall availability or congestion status of the effected 
destination(s) has changed. If so, the M3UA layer invokes the 
appropriate primitive indications to the resident M3UA-Users.  Local 
management is informed.  

4.5.3 ASP Auditing

An ASP may optionally initiate an audit procedure to enquire 
of an SGP the availability and, if the national congestion method with 
multiple congestion levels and message priorities is used, congestion 
status of an SS7 destination or set of destinations.  A Destination 
Audit (DAUD) message is sent from the ASP to the SGP requesting the 
current availability and congestion status of one or more SS7 
Destination Point Codes.

The DAUD message MAY be sent unsequenced. The DAUD MAY be sent by the 
ASP in the following cases:  

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   - Periodic.  A Timer originally set upon reception of a DUNA, SCON 
                or DRST message has expired without a subsequent DAVA, 
                DUNA, SCON or DRST message updating the 
                availability/congestion status of the affected 
                Destination Point Codes.  The Timer is reset upon 
                issuing a DAUD.  In this case the DAUD is sent to the 
                SGP that originally sent the SSNM message.
 
   - Isolation. The ASP is newly ASP-INACTIVE or ASP-ACTIVE or has been 
                isolated from an SGP for an extended period.  The ASP 
                MAY request the availability/congestion status of one 
                or more SS7 destinations to which it expects to 
                communicate.

In the first of the cases above, the auditing  procedure must not be 
invoked for the case of a received SCON message containing a congestion 
level value of "no congestion" or undefined" (i.e., congestion Level = 
"0").  This is because the value indicates either congestion abatement 
or that the ITU MTP3 international congestion method is being used.  In 
the international congestion method, the MTP3 layer at the SGP does not 
maintain the congestion status of any destinations and therefore the 
SGP cannot provide any congestion information in response to the DAUD.  
For the same reason, in the second of the cases above a DAUD message 
cannot reveal any congested destination(s).

The SGP SHOULD respond to a DAUD message with the MTP3 
availability/congested status of the routeset associated with each 
Destination Point Code(s) in the DAUD message.  The status of each SS7 
destination requested is indicated in a DUNA message (if unavailable), 
a DAVA message (if available), or a DRST (if restricted and the SGP 
supports this feature).  Where the SGP maintains the congestion status 
of the SS7 destination, and the SS7 destination is congested, the SGP 
MUST additionally respond with an SCON message before the DAVA or DRST 
message.  If the SS7 destination is available and congested, the SGP 
MUST respond with an SCON message DAVA message.  If the SS7 
destination is restricted and congested, the SGP MUST respond with 
an SCON message immediately followed by a DRST message.  If the SGP 
has no information on the availability status of the SS7 destination, 
the SGP responds with a DUNA message, as it has no routing 
information to allow it to route traffic to this destination.

Any DUNA or DAVA message in response to a DAUD message MAY contain a 
list of up to sixteen Affected Point Codes. 

An SG MAY refuse to provide the availability or congestion status of 
a destination if, for example, the ASP is not authorized to know the 
status of the destination.  The SG MAY respond with an Error Message 
(Error Code = "Destination Status Unknown") 

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4.6 MTP3 Restart

In the case where the MTP3 in the SG undergoes an MTP restart, event 
communication SHOULD be handled as follows:

When the SG discovers SS7 network isolation, the SGPs send an 
indication to all concerned available ASPs (i.e., ASPs in the ASP-
ACTIVE state) using DUNA messages for the concerned destinations.

When the SG has completed the MTP Restart procedure, the M3UA 
layers at the SGPs inform all concerned ASPs in the ASP-ACTIVE state 
of any available/restricted SS7 destinations using the DAVA/DRST 
messages.  No message is necessary for those destinations still 
unavailable after the restart procedure.

When the M3UA layer at an ASP receives a DUNA message indicating SS7 
destination unavailability at an SG, MTP Users will receive an 
MTP-PAUSE indication and will stop any affected traffic to this 
destination.   When the M3UA receives a DAVA/DRST message, MTP Users 
will receive an MTP-RESUME indication and can resume traffic to the 
newly available SS7 destination, provided the ASP is in the 
ASP-ACTIVE state towards this SGP.

The ASP MAY choose to audit the availability of unavailable 
destinations by sending DAUD messages. This would be for example the 
case when an AS becomes active at an ASP and does not have current 
destination statuses.  If MTP restart is in progress at the 
SG, the SGP returns a DUNA message for that destination, even if it 
received an indication that the destination became available or 
restricted. 

In the IPSP case, MTP restart could be considered if the IPSP also has
connection to an SS7 network. In that case, the same behavior as 
described above for the SGP would apply to the restarting IPSP. This 
would also be the case if the IPSPs were perceived as exchanging MTP 
Peer PDUs, instead of MTP primitives between MTP User and MTP 
Provider. In other words, M3UA does not provide the equivalent to 
Traffic Restart Allowed messages indicating the end of the restart 
procedure between peer IPSPs that would also be connected to an SS7 
network.

5. Examples of M3UA Procedures

5.1 Establishment of Association and Traffic between SGPs and ASPs

These scenarios show the example M3UA message flows for the 
establishment of traffic between an SGP and an ASP or between two 
IPSPs.  In all cases it is assumed that the SCTP association is 
already set up.

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5.1.1 Single ASP in an Application Server ("1+0" sparing),

These scenarios show the example M3UA message flows for the 
establishment of traffic between an SGP and an ASP or between two 
IPSPs, where only one ASP/IPSP is configured within an AS/IPS 
(no backup).

5.1.1.1 Single ASP/IPSP in an Application Server/IPS ("1+0" sparing), 
No Registration

The sending of any DUNA/SCON messages by 
the SGP is not shown but is similar to the case described in Section 
5.1.2.

           SGP/IPSP                        ASP1/IPSP1
              |                                |
              |<-------------ASP Up------------|
              |-----------ASP Up Ack---------->|
              |                                | 
              |<------- ASP Active(RCn)--------|  RC: Routing Context 
              |-----ASP Active Ack (RCn)------>|      (optional)
              |                                |

Note: If the ASP Active message contains an optional Routing Context 
parameter, The ASP Active message only applies for the specified RC 
value(s). For an unknown RC value, the SGP responds with an Error 
message.

5.1.1.2 Single ASP/IPSP in Application Server/IPS ("1+0" sparing), 
Dynamic Registration

This scenario is the same as for 5.1.1.1 but with the optional exchange 
of registration information.  In this case the Registration is accepted 
by the SGP/IPSP.

           SGP/IPSP                        ASP1/IPSP1
              |                                |
              |<------------ASP Up-------------| 
              |----------ASP Up Ack----------->|
              |                                |
              |<----REGISTER REQ(LRCn,RKn)-----|  LRC: Local Routing                             
              |                                |       Context            
              |----REGISTER RESP(LRCn,RCn)---->|   RK: Routing Key        
              |                                |   RC: Routing Context    
              |                                | 
              |<------- ASP Active(RCn)--------| 
              |-----ASP Active Ack (RCn)------>|
              |                                |

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Note: In the case of an unsuccessful registration attempt (e.g., 
invalid RKn), the Register Response message will contain an 
unsuccessful indication and the ASP/IPSP will not subsequently send 
an ASP Active message.  

5.1.1.3 Single ASP/IPSP in Multiple Application Servers/IPSs (each 
with "1+0" sparing), Dynamic Registration (Case 1 - Multiple 
Registration Requests)

           SGP/IPSP                        ASP1/IPSP1
              |                                |
              |<------------ASP Up-------------| 
              |----------ASP Up Ack----------->|
              |                                |
              |<----REGISTER REQ(LRC1,RK1)-----|  LRC: Local Routing 
              |                                |       Context 
              |----REGISTER RESP(LRC1,RC1)---->|   RK: Routing Key 
              |                                |   RC: Routing Context 
              |                                | 
              |<------- ASP Active(RC1)--------| 
              |-----ASP Active Ack (RC1)------>|
              |                                |
              |                                |
              |<----REGISTER REQ(LRCn,RKn)-----|
              |                                |
              |----REGISTER RESP(LRCn,RCn)---->|
              |                                |
              |                                | 
              |<------- ASP Active(RCn)--------| 
              |-----ASP Active Ack (RCn)------>|
              |                                |

Note: In the case of an unsuccessful registration attempt (e.g., 
invalid RKn), the Register Response message will contain an 
unsuccessful indication and the ASP/IPSP will not subsequently send 
an ASP Active message. Each LRC/RK pair registration is considered 
independently. 

It is not necessary to follow a Registration Request/Response message 
pair with an ASP Active message before sending the next Registration 
Request. The ASP Active message can be sent at any time after the 
related successful registration. 

5.1.1.4 Single ASP/IPSP in Multiple Application Servers/IPSs (each 
with "1+0" sparing), Dynamic Registration (Case 2 - Single 
Registration Request)

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           SGP/IPSP                        ASP1/IPSP1
              |                                |
              |<------------ASP Up-------------| 
              |----------ASP Up Ack----------->|
              |                                |
              |<---REGISTER REQ({LRC1,RK1},----| 
              |                   ...,         |
              |                 {LRCn,RKn}),----|
              |                                |
              |---REGISTER RESP({LRC1,RC1},--->|   
              |                  ...,          |
              |                 (LRCn,RCn})    |   
              |                                | 
              |<------- ASP Active(RC1)--------| 
              |-----ASP Active Ack (RC1)------>|
              |                                |
              :                                :
              :                                :
              |                                | 
              |<------- ASP Active(RCn)--------| 
              |-----ASP Active Ack (RCn)------>|
              |                                |

Note: In the case of an unsuccessful registration attempt (e.g., 
Invalid RKn), the Register Response message will contain an 
unsuccessful indication and the ASP/IPSP will not subsequently 
send an ASP Active message. Each LRC/RK pair registration is 
considered independently. 

The ASP Active message can be sent at any time after the related 
successful registration, and may have more than one RC.

5.1.2 Two ASPs/IPSPs in Application Server/IPS ("1+1" sparing)

This scenario shows the example M3UA message flows for the 
establishment of traffic between an SGP and two ASPs in the same 
Application Server, or between an IPSP and two IPSPs in the same 
IPS, where ASP1/IPSP1 is configured to be in the ASP-ACTIVE 
state and ASP2/IPSP2 is to be a "backup" in the event of 
communication failure or the withdrawal from service of 
ASP1/IPSP1.  ASP2/IPSP2 may act as a hot, warm, or cold backup 
depending on the extent to which ASP1/IPSP1 and ASP2/IPSP2 
share call/transaction state or can communicate call state 
under failure/withdrawal events.  The example message flow is 
the same whether the ASP Active messages indicate "Override", 
"Loadshare" or "Broadcast" mode, although typically this example 
would use an Override mode. The SGP MAY start sending any 
relevant DUNA, DRST and SCON messages to ASPs as soon as they 
enter the ASP-INACTIVE state.

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     SGP/IPSP                 ASP1/IPSP1                 ASP2/IPSP2
        |                         |                          |
        |<--------ASP Up----------|                          | 
        |-------ASP Up Ack------->|                          |
        |                         |                          |
        |<-----------------------------ASP Up----------------|
        |-----------------------------ASP Up Ack------------>|
        |                         |                          | 
        |                         |                          |
        |<-------ASP Active-------|                          | 
        |------ASP Active Ack---->|                          | 
        |                         |                          |

5.1.3 Two ASPs/IPSPs in an Application Server/IPS ("1+1" sparing, 
loadsharing case)

This scenario shows a similar case to Section 5.1.2 but where the 
two ASPs/IPSPs are brought to the state ASP-ACTIVE and subsequently 
loadshare the traffic.  In this case, one ASP/IPSP is sufficient 
to handle the total traffic load. The sending of DUNA, DRST and 
SCON messages by the SGP is not shown but is similar to the case 
described in Section 5.1.2.

     SGP/IPSP                 ASP1/IPSP1                 ASP2/IPSP2
        |                         |                          |
        |<---------ASP Up---------|                          | 
        |--------ASP Up Ack------>|                          |
        |                         |                          |
        |<------------------------------ASP Up---------------|
        |-----------------------------ASP Up Ack------------>|
        |                         |                          | 
        |                         |                          |
        |<--ASP Active (Ldshr)----|                          | 
        |-----ASP-Active Ack----->|                          | 
        |                         |                          |
        |----------------------------NOTIFY (AS-ACTIVE------>|
        |                         |                          |
        |<----------------------------ASP Active (Ldshr)-----| 
        |-------------------------------ASP Active Ack------>| 
        |                         |                          |

5.1.4 Three ASPs/IPSPs in an Application Server/IPS ("n+k" sparing, 
loadsharing case) 

This scenario shows the example M3UA message flows for the 
establishment of traffic between an SGP and three ASPs in the same 
Application Server, or between an IPSP and three IPSPs in the same 

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IPS, where two of the ASPs/IPSPs are brought to the state 
ASP-ACTIVE and subsequently share the load. In this case, a minimum 
of two ASPs/IPSPs are required to handle the total traffic load 
(2+1 sparing). The  sending of DUNA, DRST and SCON messages by the 
SGP is not shown but is similar to the case described in Section 5.1.2.

 SGP/IPSP            ASP1/IPSP1          ASP2/IPSP2          ASP3/IPSP3 
    |                    |                   |                   |
    |<------ASP Up-------|                   |                   | 
    |-----ASP Up Ack---->|                   |                   |
    |                    |                   |                   |
    |<--------------------------ASP Up-------|                   |
    |-------------------------ASP Up Ack---->|                   |
    |                    |                   |                   |
    |<---------------------------------------------ASP Up--------|
    |---------------------------------------------ASP Up Ack---->|
    |                    |                   |                   | 
    |                    |                   |                   |
    |<--ASP Act (Ldshr)--|                   |                   | 
    |----ASP Act Ack---->|                   |                   | 
    |                    |                   |                   |
    -----------Notify (AS-ACTIVE)----------->|                   |
    |-----------------------Notify (AS-ACTIVE)------------------>|
    |                    |                   |                   |
    |<--------------------ASP Act. (Ldshr)---|                   | 
    |-----------------------ASP Act Ack----->|                   | 
    |                    |                   |                   |

5.2 ASP/IPSP Traffic Failover Examples

5.2.1 (1+1 Sparing, Withdrawal of ASP/IPSP, Backup Override) 

Following on from the example in Section 5.1.2, and ASP1/IPSP1 
withdraws from service:

     SGP/IPSP                 ASP1/IPSP1                 ASP2/IPSP2 
        |                         |                          |
        |<-----ASP Inactive-------|                          |
        |----ASP Inactive Ack---->|                          |
        |------------------------NTFY(AS-Pending)----------->| 
        |                         |                          | 
        |<------------------------------ ASP Active----------| 
        |------------------------------ASP Active Ack------->| 
        |                                                    |

Note: If the SGP/IPSP M3UA layer detects the loss of the M3UA peer 
(e.g., M3UA heartbeat loss or detection of SCTP failure), the 
initial ASP Inactive message exchange (i.e., between ASP1/IPSP1 
and SGP/IPSP) would not occur.

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5.2.2 (1+1 Sparing, Backup Override)

Following on from the example in Section 5.1.2, ASP2/IPSP2 wishes to 
Override ASP1/IPSP1 and take over the traffic:

     SGP/IPSP                 ASP1/IPSP1                 ASP2/IPSP2 
        |                         |                          | 
        |<------------------------------ ASP Active----------| 
        |-------------------------------ASP Active Ack------>|
        |----NTFY(Alt ASP-Act)--->| 
        |                         |                          | 

5.2.3 (n+k Sparing, Loadsharing case, Withdrawal of ASP/IPSP)

Following on from the example in Section 5.1.4, and ASP1/IPSP1 
withdraws from service:

 SGP/IPSP            ASP1/IPSP1          ASP2/IPSP2          ASP3/IPSP3 
    |                    |                   |                   |
    |<----ASP Inact.-----|                   |                   | 
    |---ASP Inact Ack--->|                   |                   |
    |                    |                   |                   | 
    |---------------------------------NTFY(Ins. ASPs)----------->| 
    |                    |                   |                   |
    |<-----------------------------------------ASP Act (Ldshr)---| 
    |-------------------------------------------ASP Act (Ack)--->|
    |                    |                   |                   |

For the Notify message to be sent, the SG/IPSP maintains knowledge of 
the minimum ASP/IPSP resources required (e.g., if the SG/IPSP knows 
that "n+k" = "2+1" for a Loadshare AS/IPS and "n" currently equals 
"1"). 

Note: If the SGP/IPSP detects loss of the ASP1/IPSP1 M3UA peer (e.g., 
M3UA heartbeat loss or detection of SCTP failure), the initial ASP 
Inactive message exchange (i.e., SGP/IPSP-ASP1/IPSP1) would not occur.  

5.3 Normal Withdrawal of an ASP/IPSP from an Application Server/IPS 
and Teardown of an Association

An ASP/IPSP which is now confirmed in the state ASP-INACTIVE (i.e., 
the ASP/IPSP has received an ASP Inactive Ack message) may now proceed 
to the ASP-DOWN state, if it is to be removed from service.  Following 
on from Section 5.2.1 or 5.2.3, where ASP1/IPSP1 has moved to the 
"Inactive" state:

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     SGP/IPSP                       ASP1/IPSP1 
        |                               |
        |<-----ASP Inactive (RCn)-------|    RC: Routing Context
        |----ASP Inactive Ack (RCn)---->|
        |                               |
        |<-----DEREGISTER REQ(RCn)------|    See Notes 
        |                               |        
        |---DEREGISTER RESP(LRCn,RCn)-->|
        |                               |   
        :                               :   
        |                               | 
        |<-----------ASP Down-----------| 
        |---------ASP Down Ack--------->|
        |                               |

Note: The Deregistration procedure MUST be used if the ASP/IPSP 
previously used the Registration procedures for configuration 
within the Application Server/IPS.  ASP Inactive and Deregister 
messages exchanges may contain multiple Routing Contexts.

The ASP/IPSP SHOULD be in the ASP-INACTIVE state and SHOULD have 
deregistered in all its Routing Contexts before attempting to move 
to the ASP-DOWN state.  

5.4  M3UA/MTP3-User Boundary Examples

5.4.1 At an ASP/IPSP

This section describes the primitive mapping between the MTP3 User and 
the M3UA layer at an ASP or IPSP.  

5.4.1.1 Support for MTP-TRANSFER Primitives at the ASP

5.4.1.1.1 Support for MTP-TRANSFER Request Primitive

When the MTP3-User on the ASP/IPSP has data to send to a remote 
MTP3-User, it uses the MTP-TRANSFER request primitive.  The M3UA 
layer at the ASP/IPSP will do the following when it receives an 
MTP-TRANSFER request primitive from the M3UA user:

  - Determine the correct SGP/IPSP;

  - Determine the correct association to the chosen SGP/IPSP;

  - Determine the correct stream in the association (e.g., based on  
    SLS);

  - Determine whether to complete the optional fields of the DATA  
    message;

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  - Map the MTP-TRANSFER request primitive into the Protocol Data  
    field of a DATA message;

  - Send the DATA message to the remote M3UA peer at the SGP/IPSP, over 
    the SCTP association.

     SGP/IPSP                  ASP/IPSP   
        |                         |                  
        |<-----DATA Message-------|<--MTP-TRANSFER req. 
        |                         | 

        
5.4.1.1.2 Support for the MTP-TRANSFER Indication Primitive

When the M3UA layer on the ASP/IPSP receives a DATA message from the 
M3UA peer at the remote SGP/IPSP, it will do the following:

  - Evaluate the optional fields of the DATA message, if present;

  - Map the Protocol Data field of a DATA message into the MTP-TRANSFER 
indication primitive;

  - Pass the MTP-TRANSFER indication primitive to the user part. In  
    case of multiple user parts, the optional fields of the Data
    message are used to determine the concerned user part.

     SGP/IPSP                  ASP/IPSP   
        |                         |
        |------Data Message------>|-->MTP-Transfer ind.
        |                         |          

5.4.1.1.3 Support for ASP Querying of SS7 Destination States

There are situations such as temporary loss of connectivity to the SGP 
that may cause the M3UA layer at the ASP to audit SS7 destination 
availability/congestion states.  Note: there is no primitive for the 
MTP3-User to request this audit from the M3UA layer as this is 
initiated by an internal M3UA management function.  

       SGP                        ASP   
        |                         |
        |<----------DAUD----------| 
        |<----------DAUD----------| 
        |<----------DAUD----------| 
        |                         | 
        |                         | 

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5.4.2 At an SGP 

This section describes the primitive mapping between the MTP3-User and 
the M3UA layer at an SGP.

5.4.2.1 Support for MTP-TRANSFER Request Primitive at the SGP

When the M3UA layer at the SGP has received DATA messages from its peer 
destined to the SS7 network it will do the following:

  - Evaluate the optional fields of the DATA message, if present, to  
    determine the Network Appearance;

  - Map the Protocol data field of the DATA message into an MTP-
    TRANSFER request primitive;

  - Pass the MTP-TRANSFER request primitive to the MTP3 of the  
    concerned Network Appearance.

                            SGP                        ASP
                             |                         |
        <---MTP-TRANSFER req.|<---------DATA ----------|
                             |                         |

5.4.2.2 Support for MTP-TRANSFER Indication Primitive at the SGP

When the MTP3 layer at the SGP has data to pass its user parts, it will 
use the MTP-TRANSFER indication primitive.  The M3UA layer at the SGP 
will do the following when it receives an MTP-TRANSFER indication 
primitive:

  - Determine the correct ASP using the distribution function;

  - Select an ASP in the ASP-ACTIVE state

  - Determine the correct association to the chosen ASP;

  - Determine the correct stream in the SCTP association (e.g., based 
    on SLS);

  - Determine whether to complete the optional fields of the DATA  
    message;

  - Map the MTP-TRANSFER indication primitive into the Protocol Data  
    field of a DATA message;

  - Send the DATA message to the remote M3UA peer in the ASP, over the  
    SCTP association 

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                           SGP                        ASP
                            |                         |
       --MTP-TRANSFER ind.->|----------DATA --------->|
                            |                         |

5.4.2.3 Support for MTP-PAUSE, MTP-RESUME, MTP-STATUS Indication 
Primitives

The MTP-PAUSE, MTP-RESUME and MTP-STATUS indication primitives from the 
MTP3 upper layer interface at the SGP need to be made available to the 
remote MTP3 User Part lower layer interface at the concerned ASP(s).

5.4.2.3.1 Destination Unavailable 

The MTP3 layer at the SGP will generate an MTP-PAUSE indication 
primitive when it determines locally that an SS7 destination is 
unreachable.  The M3UA layer will map this primitive to a DUNA message.  
The SGP M3UA layer determines the set of concerned ASPs to be informed 
based on internal SS7 network information associated with the MTP-PAUSE 
indication primitive indication.

                   SGP                       ASP   
                    |                         |
 --MTP-PAUSE ind.-->|---------DUNA----------->|--MTP-PAUSE ind.-->
                    |                         |

5.4.2.3.2 Destination Available

The MTP3 at the SGP will generate an MTP-RESUME indication primitive 
when it determines locally that an SS7 destination that was previously 
unreachable is now reachable.  The M3UA layer will map this primitive 
to a  DAVA message.  The SGP M3UA determines the set of concerned ASPs 
to be informed based on internal SS7 network information associated 
with the MTP-RESUME indication primitive.

                   SGP                       ASP   
                    |                         |
--MTP-RESUME ind.-->|-----------DAVA--------->|--MTP-RESUME ind.-->
                    |                         |

5.4.2.3.3 SS7 Network Congestion 

The MTP3 layer at the SGP will generate an MTP-STATUS indication 
primitive when it determines locally that the route to an SS7 
destination is congested.  The M3UA layer will map this primitive to a 
SCON message.  It will determine which ASP(s) to send the SCON message 
to, based on the intended Application Server.

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                     SGP                       ASP   
                       |                         |                  
   --MTP-STATUS ind.-->|-----------SCON--------->|--MTP-STATUS ind.--> 
                       |                         |

5.4.2.3.4 Destination User Part Unavailable

The MTP3 layer at the SGP will generate an MTP-STATUS indication 
primitive when it receives an UPU message from the SS7 network.  The 
M3UA layer will map this primitive to a DUPU message.  It will 
determine which ASP(s) to send the DUPU based on the intended 
Application Server.

                      SGP                       ASP   
                       |                         |                  
   --MTP-STATUS ind.-->|----------DUPU---------->|--MTP-STATUS ind.--> 
                       |                         | 

6. Security

6.1 Introduction

M3UA is designed to carry signalling messages for telephony services. 
As such, M3UA must involve the security needs of several parties: the 
end users of the services; the network providers and the applications 
involved.  Additional requirements may come from local regulation.  
While having some overlapping security needs, any security solution 
should fulfill all of the different parties' needs. 

6.2 Threats

There is no quick fix, one-size-fits-all solution for security.  As a 
transport protocol, M3UA has the following security objectives:

 * Availability of reliable and timely user data transport.
 * Integrity of user data transport.
 * Confidentiality of user data.

M3UA is recommended to be transported on SCTP.  SCTP [13] provides 
certain transport related security features, such as some protection 
against:

 * Blind Denial of Service Attacks
 * Flooding
 * Masquerade
 * Improper Monopolization of Services

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When M3UA is running in professionally managed corporate or service 
provider network, it is reasonable to expect that this network includes 
an appropriate security policy framework. The "Site Security Handbook" 
[21] should be consulted for guidance.

When the network in which M3UA runs in involves more than one party, it 
may not be reasonable to expect that all parties have implemented 
security in a sufficient manner.  In such a case, it is recommended 
that IPSEC is used to ensure confidentiality of user payload.  Consult 
[22] for more information on configuring IPSEC services.

6.3 Protecting Confidentiality 

Particularly for mobile users, the requirement for confidentiality may 
include the masking of IP addresses and ports.  In this case 
application level encryption is not sufficient; IPSEC ESP [23] SHOULD 
be used instead.  Regardless of which level performs the encryption, 
the IPSEC ISAKMP [24] service SHOULD be used for key management.

7. IANA Considerations

7.1 SCTP Payload Protocol Identifier

IANA has assigned an M3UA value for the Payload Protocol Identifier in 
the SCTP DATA chunk.  The following SCTP Payload Protocol Identifier is 
registered:

        M3UA    "3"

The SCTP Payload Protocol Identifier value "3" SHOULD be included in 
each SCTP DATA chunk, to indicate that the SCTP is carrying the M3UA 
protocol. The value "0" (unspecified) is also allowed but any other 
values MUST not be used.  This Payload Protocol Identifier is not 
directly used by SCTP but MAY be used by certain network entities to 
identify the type of information being carried in a DATA chunk.

The User Adaptation peer MAY use the Payload Protocol Identifier as a 
way of determining additional information about the data being 
presented to it by SCTP.

7.2 M3UA Port Number

IANA has registered SCTP (and UDP/TCP) Port Number 2905 for M3UA.  It 
is recommended that SGPs use this SCTP port number for listening for 
new connections.  SGPs MAY also use statically configured SCTP port 
numbers instead.

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7.3 M3UA Protocol Extensions

This protocol may also be extended through IANA in three ways:
 -- through definition of additional message classes,
 -- through definition of additional message types, and 
 -- through definition of additional message parameters

The definition and use of new message classes, types and parameters is 
an integral part of SIGTRAN adaptation layers.  Thus these extensions 
are assigned by IANA through an IETF Consensus action as defined in 
Guidelines for Writing an IANA Considerations Section in RFCs (25]

The proposed extension must in no way adversely affect the general 
working of the protocol.

7.3.1 IETF Defined Message Classes

The documentation for a new message class MUST include the following 
information:
(a) A long and short name for the new message class;
(b) A detailed description of the purpose of the message class.

7.3.2 IETF Defined Message Types

The documentation for a new message type MUST include the following 
information:

(a) A long and short name for the new message type;
(b) A detailed description of the structure of the message;. 
(c) A detailed definition and description of intended use for each 
    field within the message; 
(d) A detailed procedural description of the use of the new message 
    type within the operation of the protocol; 
(e) A detailed description of error conditions when receiving this 
    message type. 

When an implementation receives a message type which it does not 
support, it MUST respond with an Error (ERR) message ("Unsupported 
Message Type").

7.3.3 IETF Defined Parameter Extension

Documentation of the message parameter MUST contain the following 
information:

(a) Name of the parameter type;
(b) Detailed description of the structure of the parameter field.  This 
    structure MUST conform to the general type-length-value format 
    described in Section 3.2;
(c) Detailed definition of each component of the parameter value;
(d) Detailed description of the intended use of this parameter type, 
    and an indication of whether and under what circumstances multiple 

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    instances of this parameter type may be found within the same 
    message.

8. Acknowledgements

The authors would like to thank Antonio Roque Alvarez, Joyce Archibald, 
Tolga Asveren, Maria-Cruz Bartolome-Rodrigo, Dan Brendes, Nikhil Jain, 
Roland Jesske, Joe Keller, Kurt Kite, Ming Lin, Steve Lorusso, Naoto 
Makinae, Howard May, Francois Mouillaud, Barry Nagelberg, Neil Olson, 
Heinz Prantner, Shyamal Prasad, Mukesh Punhani, Selvam Rengasami, 
John Shantz, Ray Singh, Michael Tuexen, Nitin Tomar, Gery Verwimp, 
Tim Vetter, Kazuo Watanabe, Ben Wilson and many others for their 
valuable comments and suggestions.

9.  References

[1] RFC 2719, "Framework Architecture for Signaling Transport", L. Ong 
et al, October 1999

[2] ITU-T Recommendations Q.761 to Q.767, "Signalling System No.7 (SS7)  
    - ISDN User Part (ISUP)"

[3] ANSI T1.113 - "Signaling System Number 7 - ISDN User Part"

[4] ETSI ETS 300 356-1 "Integrated Services Digital Network (ISDN);  
    Signalling System No.7; ISDN User Part (ISUP) version 2 for the  
    international interface; Part 1: Basic services"

[5] ITU-T Recommendations Q.711 to Q.715, "Signalling System No. 7 
    (SS7) - Signalling Connection Control Part (SCCP)"

[6] ANSI T1.112 "Signaling System Number 7 - Signaling Connection 
    Control Part"

[7] ETSI ETS 300 009-1, "Integrated Services Digital Network (ISDN);  
    Signalling System No.7; Signalling Connection Control Part (SCCP)  
    (connectionless and connection-oriented class 2) to support  
    international interconnection; Part 1: Protocol specification"

[8] ITU-T Recommendation Q.720, "Telephone User Part"

[9] ITU-T Recommendations Q.771 to Q.775 "Signalling System No. 7 (SS7) 
    - Transaction Capabilities (TCAP)"

[10] ANSI T1.114 "Signaling System Number 7 - Transaction Capabilities 
     Application Part"

[11] ETSI ETS 300 287-1, "Integrated Services Digital Network (ISDN);  

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     Signalling System No.7; Transaction Capabilities (TC) version 2; 
     Part 1: Protocol specification"

[12] 3G TS 25.410 V4.0.0 (2001-04) "Technical Specification - 3rd  
     Generation partnership Project; Technical Specification Group  
     Radio Access Network; UTRAN Iu Interface: General Aspects and  
     Principles" 

[13] RFC 2960, "Stream Control Transport Protocol", R. Stewart et al, 
     October 2000. 
 
[14] ITU-T Recommendations Q.701 to Q.705, "Signalling System No. 7 
     (SS7) - Message Transfer Part (MTP)"

[15] ANSI T1.111 "Signaling System Number 7 - Message Transfer Part"

[16] ETSI ETS 300 008-1, "Integrated Services Digital Network (ISDN);  
     Signalling System No.7; Message Transfer Part (MTP) to support  
     international interconnection; Part 1: Protocol specification"

[17] ITU-T Recommendation Q.2140 "B-ISDN ATM Adaptation Layer - Service 
     Specific Coordination Function for signalling at the Network Node  
     Interface (SSCF at NNI)"

[18] ITU-T Recommendation Q.2110 "B-ISDN ATM Adaptation Layer - Service  
     Specific Connection Oriented Protocol (SSCOP)"

[19] RFC 2119, "Key words for use in RFCs to Indicate Requirement 
     Levels", S. Bradner, March 1997.

[20] ITU-T Recommendation Q.2210 "Message Transfer Part Level 3 
     functions and messages using the services of ITU Recommendation 
     Q.2140"

[21] RFC 2196, "Site Security Handbook", B. Fraser Ed., September 1997 

[22] RFC 2401, "Security Architecture for the Internet Protocol", S.
     Kent, R. Atkinson, November 1998.

[23] RFC 2406, "IP Encapsulating Security Payload (ESP)", S.Kent and 
     R. Atkinson, November 1998.

[24] RFC 2408, "Internet Security Association and Key Management
     Protocol", D. Maughan, M. Schertler, M. Schneider and J. Turner,
     November 1998.

[25] RFC 2434, "Guidelines for Writing an IANA Considerations Section 
     in RFCs", T. Narten and H. Alvestrand, October 1998

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[26] <draft-ietf-sigtran-m2ua-10.txt>, "MTP2-User Adaptation Layer",
     K. Morneault et al, Sept 2001 (Work in Progress)

[27] <draft-ietf-sigtran-m2pa-03.txt>, "SS7 MTP2-User Peer-to-Peer 
     Adaptation Layer", Tom George et al, July 2001 (Work in Progress)

10. Author's Addresses

Greg Sidebottom
gregside consulting
Kanata, Ontario, Canada
EMail: gregside@home.com

Javier Pastor-Balbs
Ericsson Espaa S.A.
C/ Omb 3
28045 Madrid - Spain
EMail: j.javier.pastor@ericsson.com

Guy Mousseau
Nortel Networks
3685 Richmond Rd
EMail: Nepean, Ontario, Canada  K2H 5B7

Lyndon Ong
Ciena
10480 Ridgeview Court
Cupertino, CA 95014
EMail: lyong@ciena.com

Ian Rytina
Ericsson Australia
37/360 Elizabeth Street 
Melbourne, Victoria 3000, Australia
EMail: ian.rytina@ericsson.com.au

Hanns Juergen Schwarzbauer
SIEMENS AG
Hofmannstr. 51
81359 Munich, Germany
EMail: HannsJuergen.Schwarzbauer@icn.siemens.de

Klaus D. Gradischnig
NeuStar, Inc
1120 Vermont Ave. N.W.Suite 400
Washington D.C 20005
EMail: klaus.gradischnig@neustar.com

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Ken Morneault
Cisco Systems Inc.
13615 Dulles Technology Drive
Herndon, VA, USA  20171
EMail: kmorneau@cisco.com

Malleswar Kalla
Telcordia Technologies
MCC 1J211R
445 South Street
Morristown, NJ, USA  07960
Email: kalla@research.telcordia.com

Normand Glaude
Performance Technologies
150 Metcalf Sreet, Suite 1300
Ottawa, Ontario, Canada  K2P 1P1
EMail: nglaude@microlegend.com

Brian Bidulock
OpenSS7 Corporation
c/o #424, 4701 Preston Park Blvd. 
Plano, TX, USA  75093 
EMail: bidulock@openss7.org 

John Loughney 
Nokia Research Center 
PO Box 407 
FIN-00045 Nokia Group 
Finland 
EMail: john.loughney@nokia.com 

This draft expires April 2002.

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