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draft-ietf-sigtran-m3ua-03

Description: Request For Comments

You can download source copies of the file as follows:

draft-ietf-sigtran-m3ua-03.txt in text format.

Listed below is the contents of file draft-ietf-sigtran-m3ua-03.txt.


Network Working Group                G. Sidebottom, L. Ong, Guy Mousseau
INTERNET-DRAFT                                           Nortel Networks
                                                              Ian Rytina
                                                                Ericsson
                                              Hanns-Juergen Schwarzbauer
                                                                 Siemens
                                                           Ken Morneault
                                                                   Cisco
                                                           Mallesh Kalla
                                                               Telcordia
                                                          Normand Glaude
                                                Performance Technologies

Expires in six months                                          June 2000

                SS7 MTP3-User Adaptation Layer (M3UA)
                  <draft-ietf-sigtran-m3ua-03.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/ietf/1id-abstracts.txt

     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).

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 1]

Internet Draft         SS7 MTP3-User Adaptation Layer          June 2000

                        TABLE OF CONTENTS

1. Introduction.......................................................3
    1.1 Scope.........................................................3
    1.2 Terminology...................................................3
    1.3 M3UA Overview.................................................5
    1.4 Functional Areas.............................................10
    1.5 Sample Configurations........................................18
    1.6 Definition of M3UA Boundaries................................21
2. Conventions.......................................................22
3. M3UA Protocol Elements............................................22
    3.1 Common Message Header........................................22
    3.2 Transfer Messages............................................24 
    3.3 SS7 Signalling Network management (SSNM) Messages............26
    3.4 Application Server Process Maintenance Messages..............32
    3.5 Management Messages..........................................40
4. Procedures........................................................44
    4.1 Procedures to Support the Services of the M3UA Layer.........44
    4.2 Procedures to Support the M3UA Services in Section 1.4.2.....44
    4.3 Procedures to Support the M3UA Services in Section 1.4.4.....45
    4.4 Procedures to Support the M3UA Services in Section 1.4.3.....52 
5. Examples of M3UA Procedures.......................................54
    5.1 Establishment of Association and Traffic 
        Between SGs and ASPs.........................................54
    5.2 ASP traffic Fail-over Examples...............................56
    5.3 M3UA/MTP3-User Boundary Examples.............................57
6. Security..........................................................61
    6.1 Introduction.................................................61
    6.2 Threats......................................................61
    6.3 Protecting Confidentiality...................................62
7. IANA Considerations...............................................62
8. Acknowledgements..................................................62
9. References........................................................62
10. Author's Addresses...............................................65

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Internet Draft         SS7 MTP3-User Adaptation Layer          June 2000

1.  Introduction

1.1 Scope

There is a need for 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 fail-over 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 
protocols and deliver ISUP, SCCP and/or any other MTP3-User protocol 
messages 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 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.

Application Server Process (ASP) - A process instance of an Application 
Server. An Application Server Process serves as an active or standby 
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 end-
point and may be configured to process signalling traffic within more 
than one Application Server. 

Association - An association refers to an SCTP association.  The 
association provides the transport for 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 

Sidebottom et al                                              [Page 3]

Internet Draft       SS7 MTP3-User Adaptation Layer         June 2000

uses MU3A in a peer-to-peer 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, 
standby or load-sharing process of a Signalling Gateway.

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

Routing Key: A Routing Key describes a set of SS7 parameter and 
parameter values that uniquely define the range of signalling traffic to 
be handled by a particular Application Server. For example, where all 
traffic directed to an SS7 DPC, OPC and ISUP CIC_range(s) or SCCP SSN is 
to be sent to a particular Application Server, that SS7 data defines the 
associated Routing Key.  Routing Keys are unique in the sense that a 
received SS7 signalling message cannot be directed to more than one 
Routing Key.   Also, a Routing Key cannot extend across more than a 
single SS7 DPC, in order to more easily support SS7 Management 
procedures.  It is not necessary for the parameter range values within a 
particular Routing Key to be contiguous.  For example, an ASP could be 
configured to support call processing for multiple ranges of PSTN trunks 
that are not represented by contiguous CIC values.

Routing Context  An Application Server Process may be configured to 
process traffic related to more than one Application Server, over a 
single SCTP Association.  At an ASP, the Routing Context parameter 
uniquely identifies the traffic associated with each Application Server 
that the ASP is configured to support.  There is a 1:1 relationship 
between a received Routing Context value and a Routing Key entry at the 
sending node.  Therefore the Routing Context can be viewed as an index 
into a sending node's Message Distribution Table containing the Routing 
Key entries. 

Fail-over - The capability to re-route 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.  Fail-back may apply upon the 
return to service of a previously unavailable Application Server 
Process.

Signalling Point Management Cluster (SPMC) - A complete set of 
Application Servers represented to the SS7 network under the same SS7 
Point Code.  SPMCs are used to sum the availability / congestion / 
User_Part status of an SS7 destination point code that is distributed in 
the IP domain, for the purpose of supporting MTP3 management procedures 
at an SG.  In some cases, the SG itself may also be a member of the 
SPMC.  In this case, the SG availability / congestion / User_Part status 
must also be taken into account when considering any supporting MTP3 
management actions.  

MTP  The Message Transfer Part of the SS7 protocol

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Internet Draft       SS7 MTP3-User Adaptation Layer         June 2000

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 identifies an SS7 network 
context for the purposes of logically separating the signalling traffic 
between the SG and the Application Server Processes over a common SCTP 
Association.  An example is where an SG is logically partitioned to 
appear as an element in four separate national SS7 networks.  A Network 
Appearance implicitly defines the SS7 Point Code(s), Network Indicator 
and MTP3 protocol type/variant/version used within a specific SS7 
network partition.  A physical SS7 route-set or link-set at an SG can 
appear in only one network appearance. The Network Appearance is not 
globally significant and requires coordination only between the SG and 
the ASP.

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 ASP process is running on.

Stream - A stream refers to an SCTP stream.

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 layer, in SS7 
terms, as a user part.  The list of these protocol layers include, but 
is not limited 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 as SCCP payload, as they are SCCP-User protocols.  

It is recommended that the 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:

Sidebottom et al                                              [Page 5]

Internet Draft       SS7 MTP3-User Adaptation Layer         June 2000

   - 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 may not be necessary.  
In these cases, it is acceptable to use TCP as the underlying common 
transport protocol.  

1.3.2 Services Provided by the M3UA Layer

The M3UA Layer at an ASP provides the equivalent set of primitives at 
its upper layer to the MTP3-Users as provided by the MTP Level 3 to its 
local users at an SS7 SEP.  In this way, the ISUP and/or SCCP layer at 
an ASP is unaware that the expected MTP3 services are offered remotely 
from an MTP3 Layer at an SG, and not by a local MTP3 layer.  The MTP3 
layer at an SG 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 does not 
itself provide the MTP3 services.

The M3UA Layer may also be used for point-to-point signalling between 
two IP Server Processes (IPSPs).  In this case, the M3UA 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 SG.  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.

1.3.2.1 Support for the transport of MTP3-User Messages

The M3UA provides the transport of MTP-TRANSFER primitives across an 
established SCTP association between an SG and an ASP and between IPSPs. 
The MTP-TRANSFER primitives are encoded as MTP3-User messages with 
attached MTP3 Routing Labels as described in the message format sections 
of the SCCP and ISUP recommendations.  In this way, the SCCP and ISUP 
messages received from the SS7 network are not re-encoded into a 
different format for transport to/from the server processes.  As well, 
all the required MTP3 Routing Label information (OPC, DPC, SIO) is 
available at the ASP and the IPSP as is expected by the MTP3-User 
protocol layer.  

The M3UA does not impose a 272-octet user information block limit as 
specified by the SS7 MTP Level 3 protocol.  Larger information blocks

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Internet Draft       SS7 MTP3-User Adaptation Layer         June 2000

can be accommodated directly by M3UA/SCTP, without the need for an upper 
layer segmentation/re-assembly 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 inter-working 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 SG.  However, if the SS7 network is provisioned to 
support the Broadband MTP [20] to the final SS7 destination, the 
information block size limit may be increased past 272 octets.  

1.3.2.2 Native Management Functions

The M3UA provides management of the underlying SCTP transport protocol 
to ensure that SG-ASP and IPSP-IPSP transport is available to the degree 
called for by the MTP3-User signalling applications.

The M3UA 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 Inter-working with MTP3 Network Management Functions

At the SG, the M3UA must also provide inter-working 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 remote 
destination in the SS7 network is not reachable.

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

  - Providing an indication to MTP3-Users at an ASP that messages to a 
remote MTP3-User peer in the SS7 network are experiencing SS7 
congestion

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

The M3UA layer at an ASP may initiate an audit of the availability or 
the congested state of remote SS7 destinations.  This information is 
requested from the M3UA at the SG. 

1.3.2.4 Support for the management of SCTP associations between the SG 
and ASPs.

The M3UA layer at the SG maintains the availability state of all 
configured remote ASPs, in order to manage the SCTP Associations and the 
traffic between the SG and ASPs.  As well, the active/inactive state of

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Internet Draft       SS7 MTP3-User Adaptation Layer         June 2000

remote ASPs is also maintained - Active ASPs are those currently 
receiving traffic from the SG.

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 primitive to request, indicate and confirm the 
establishment of an SCTP association with a peer M3UA node.

The M3UA layer may also need to inform local management of the status of 
the underlying SCTP associations using the M-SCTP STATUS request and 
indication primitive. For example, the M3UA may 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 need to inform the local management of the 
change in status of an ASP or AS.  This can be achieved using the M-ASP 
STATUS or M-AS STATUS primitives.

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 
description is not designed to meet any performance and reliability 
requirements for such transport.  However, the conjunction of 
distributed architecture and redundant networks does allow 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, these 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 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 within 
the available Hosts must also be considered.  As an example, for a 
particular Application Server, the related ASPs should be distributed 
over at least two Hosts.

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

Sidebottom et al                                              [Page 8]

Internet Draft       SS7 MTP3-User Adaptation Layer         June 2000

               SG                                     MGC

  Host#1 **************                          ************** Host#1
     =   *  ********__*__________________________*__********  *   =
    SG1  *  * SGP1 *__*_____      _______________*__* ASP1 *  *  MGC1
         *  ********  *     \    /               *  ********  *
         *  ********__*______\__/________________*__********  *
         *  * SGP2 *__*_______\/______      _____*__* ASP2 *  *
         *  ********  *       /\      |    |     *  ********  *
         *      :     *      /  \     |    |     *      :     *
         *  ********  *     /    \    |    |     *  ********  *
         *  * SGPn *  *     |    |    |    |     *  * ASPn *  *
         *  ********  *     |    |    |    |     *  ********  *
         **************     |    |    |    |     **************
                            |    |    \    /
  Host#2 **************     |    |     \  /      ************** Host#2
     =   *  ********__*_____|    |______\/_______*__********  *   =
    SG2  *  * SGP1 *__*_________________/\_______*__* ASP1 *  *  MGC2
         *  ********  *                /  \      *  ********  *
         *  ********__*_______________/    \_____*__********  *
         *  * SGP2 *__*__________________________*__* ASP2 *  *
         *  ********  *                          *  ********  *
         *      :     *     SCTP Associations    *      :     *
         *  ********  *                          *  ********  *
         *  * SGPn *  *                          *  * ASPn *  *
         *  ********  *                          *  ********  *
         **************                          **************

                    Figure 1  Physical Model

In this model, each host has many application processes.  In the case of 
the MGC, an ASP may provide service to one or more application server, 
and is identified as an SCTP end point.  In the case of the SG, a pair 
of signalling gateway processes may represent, as an example, a single 
network appearance, serving a signalling point management cluster.

This example model can also be applied to IPSP-IPSP signalling.  In this 
case, each IPSP would 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 many 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 availability of signalling 
points in the SS7 network, and the redundancy model (active-standby, 
load-sharing, n+k) of the remote signalling processes.

For carrier grade networks, Operators should ensure that under failure 
or isolation of a particular signalling process, stable calls or

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Internet Draft       SS7 MTP3-User Adaptation Layer         June 2000

transactions are not lost.  This implies that signalling processes need, 
in some cases, to share the call or transaction state information with 
other signalling processes.  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 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

Within an SS7 network, a Signalling Gateway is charged with representing 
a set of nodes in the IP domain into the SS7 network for routing 
purposes.  The SG itself, as a physical node in the SS7 network, must be 
addressable with an SS7 Point Code for MTP3 Management purposes. The SG 
Point Code will also be used for addressing any local MTP3-Users at the 
SG such as an SG-resident SCCP function.  

An SG may be logically partitioned to operate in multiple SS7 network 
Appearances.  In such a case, the SG must be addressable with a Point 
Code in each network appearance, and must represent a set of nodes in 
the IP domain into each SS7 network.  Alias PCs may also be used within 
an SG network appearance, but SG MTP3 management messages to/from the 
SS7 network will not use the alias PCs. 

The M3UA places no restrictions on the SS7 Point Code representation of 
an AS.  Application servers can be represented under the same PC of the 
SG, their own individual Point Codes or grouped with other applications 
for Point Code preservation purposes.  A single Point Code may be used 
to represent the SG and all the ASPs 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) can be represented by a 
Point Code that is separate from any SG Point Code.  This allows these 
SGs to be viewed from the SS7 network as "STPs", each having an ongoing  
"route" to the same ASP(s).  Under failure conditions where an ASP 
becomes unavailable from one of the SGs, this approach enables MTP3 
route management messaging between the SG and SS7 network, allowing 
simple SS7 re-routing through an alternate SG without changing the 
Destination Point Code Address of SS7 traffic to the ASPs. 

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Internet Draft       SS7 MTP3-User Adaptation Layer         June 2000

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

Note: there is no SG to SG communication shown, so each SG can be 
reached only via the direct Linkset from the SS7 network.

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 Message Distribution

1.4.2.1 Address Translation and Mapping at the SG

In order to direct messages received from the SS7 MTP3 network to the 
appropriate IP destination, the SG must perform address translation and 
mapping functions using information from the received MTP3-User message.

To support this message distribution, the SG must 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 is accomplished by comparing 
elements of the incoming SS7 message to provisioned Routing Keys in the 
SG.  These Routing Keys in turn make reference to an Application Server 
that is enabled by one or more ASP.  These ASPs provide dynamic status 
information to the SG using various management messages defined in the 
M3UA protocol.  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 other MTP3-User specific fields such as the ISUP 
CIC, SCCP subsystem number, or TCAP transaction ID. Some example routing 
keys are: the DPC alone, the DPC/OPC combination, the DPC/OPC/CIC 

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Internet Draft       SS7 MTP3-User Adaptation Layer         June 2000

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 contains a list of one or more ASPs that are 
capable of processing the traffic.  This list is assumed to be dynamic, 
taking into account the availability status of the individual ASPs in 
the list, configuration changes, and possible fail-over mechanisms. The 
M3UA protocol includes messages to convey the availability status of the 
individual ASPs as input to a fail-over mechanism.

Normally, one or more ASPs is active in the ASP (i.e., currently 
processing traffic) but in certain failure and transition cases it is 
possible that there may not be an active ASP available.  Both load-
sharing and backup scenarios are supported.

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

1.4.2.2 Address Translation and Mapping at the ASP

In order to direct messages to the SS7 network, the ASP must also 
perform an address translation and mapping function in order to choose 
the proper SGP for a given message.  This is accomplished by observing 
elements of the outgoing message, SS7 network status, SGP availability 
and network appearance configuration tables.

A Signalling Gateway contains a list of one or more SGPs that are 
capable of routing SS7 traffic.  As is the case with ASPs, this list can 
be dynamic, taking into account the availability status of the 
individual SGPs, configuration changes and fail-over mechanisms.

1.4.3 SS7 and M3UA Interworking

In the case of SS7 and M3UA inter-working, 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 (SG) 
transmits and receives SS7 Message Signalling Units (MSUs) to and from 
the PSTN over a standard SS7 network interface, using the SS7 Message

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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].  It is possible for IP-based links to be present, using the 
services of the MTP2-User Adaptation Layer (M2UA) [19].  These SS7 
datalinks may be terminated at a Signalling Transfer Point (STP) or at a 
Signalling End Point (SEP).  Using the services of MTP3, the SG may 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.

Where ATM-based High Speed Links are used in the SS7 network, it is 
possible for the SG to use the services of the MTP-3b [20] for reliable 
transport to and from an SS7 SEP or STP. The maximum Service Data Unit 
(SDU) supported by the MTP-3b is 4096 octets compared to the 272-octet 
maximum of the MTP3.  However, for MTP3-Users to take advantage of the 
larger SDU between MTP3-User peers, network architects should ensure 
that MTP3-b is used end-to-end between the SG and the SS7-resident peer.  

1.4.3.2 SS7 and M3UA Inter-Working at the SG

The SG provides a functional inter-working 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.

The Signalling Gateway must maintain knowledge of SS7 node and 
Signalling Point Management Cluster (SPMC) status in their respective 
domains in order to perform a seamless inter-working of the IP-based 
signalling and the SS7 domains.  For example, SG knowledge of the 
availability and/or congestion status of the SPMC and SS7 nodes must be 
maintained and disseminated in the respective networks, in order to 
ensure that end-to-end operation is transparent to the communicating SCN 
protocol peers at the SS7 node and ASP.

When the SG determines that the transport of SS7 messages to an SPMC is 
encountering congestion, the SG may optionally inform the MTP3 route 
management function (by an implementation-dependent mechanism).  This 
information is used by the MTP3 to mark the route to the affected 
destination as congested and to trigger MTP Transfer Controlled (TFC) 
messages to any SS7 SEPs generating traffic to the congested DPC, as per 
current MTP3 procedures.

When the SG determines that the transport of SS7 messages to all ASPs in 
a particular SPMC is interrupted, then it may similarly optionally 
inform the MTP3 route management function.  This information is used by 
the MTP3 to mark the route to the affected destination as unavailable, 

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and in the case of a signalling transfer point, to send MTP Transfer 
Prohibited (TFP) messages to the relevant adjacent SS7 nodes, according 
to the local SS7 network procedures. 

When the SG determines that the transport of SS7 messages to an ASP in a 
particular SPMC can be resumed, the SG may similarly optionally inform 
the MTP3 route management function.  This information is used by the 
MTP3 to mark the route to the affected destination as available, and in 
the case of a signalling transfer point, to send MTP Transfer Allowed 
(TFA) messages to the relevant adjacent SS7 nodes, according to the 
local SS7 network procedures.  In some SS7 network architectures, 
sending TFP and TFA messages from the SG into the SS7 network should be 
suppressed.  As an example, in the case where the SG is seen by the 
adjacent SS7 nodes as an SEP (i.e., in ANSI MTP terms the SG is 
connected via A-links or F-links), TFP or TFA messages would not 
normally be expected by the adjacent SS7 node.

In the case of 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 User Part availability as would 
be expected 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 made propagated to the remote MTP3-
User lower layer interface at the ASP. These indication primitives are 
also made available to any existing local MTP3-Users at the SG, if 
present.

It is important to clarify that MTP3 management messages such as TFPs or 
TFAs received from the SS7 network are not "encapsulated" and sent 
blindly to the ASPs.  Rather, the existing MTP3 management procedures 
are followed within the MTP3 function of the SG to re-calculate the MTP3 
route set status and initiate any required signalling-route-set-test 
procedures into the SS7 network.  Only when an SS7 destination status 
changes are MTP-PAUSE or MTP-RESUME primitives invoked.  These 
primitives can also be invoked due to local SS7 link set conditions as 
per existing MTP3 procedures.

1.4.3.2 Application Server

A cluster of application servers is responsible for providing the 
overall support for one or many SS7 upper layers.  From an SS7 
standpoint, a signalling point management cluster (SPMC) must provide 
complete support for the upper layer service for a given point code.  As 
an example, such a SPMC providing MGC capabilities must provide complete 
support for ISUP for a given point code, according to the local SS7 
network specifications.

This measure is necessary to allow the SG to accurately represent the 
signalling point on the local SS7 network.

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1.4.3.3 IPSP

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 
inter-working is not necessary for this model.

1.4.4 Redundancy Models

The network address translation and mapping function of the M3UA layer 
supports signalling process fail-over functions in order to support a 
high availability of call and transaction processing capability.

1.4.4.1 Application Server Redundancy

All MTP3-User messages (e.g., ISUP, SCCP) incoming to an SG from the SS7 
network are assigned to a unique Application Server, based on the 
information in the message and the provisioned Routing Keys.

The Application Server is, in practical terms a list of all ASPs 
actively configured to process a range of MTP3-User traffic defined by 
Routing Keys.  One or more ASPs in the list are normally active (i.e., 
handling traffic) while any others may be unavailable or inactive, to be 
possibly used in the event of failure or unavailability of the active 
ASP(s).  

The fail-over 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/standby redundancy is a subset of this model. A simplex 
"1+0" model is also supported as a subset, with no ASP redundancy.

At the SG, an Application Server list contains active and inactive ASPs 
to support ASP load-sharing and fail-over procedures.  The list of ASPs 
within a logical Application Server is kept updated in the SG to reflect 
the active Application Server Process(es).

To avoid a single point of failure, it is recommended that a minimum of 
two ASPs be in the list, resident in separate hosts, and therefore 
available over different SCTP Associations.  For example, in the network 
shown in Figure 1, all messages to DPC x could be sent to ASP1 in Host1 
or ASP1 in Host2.  The AS list at SG1 might look like this:

    Routing Key {DPC=x) - "Application Server #1"
        ASP1/Host1   State=Up, Active
        ASP1/Host2   State=Up, Inactive

In this "1+1" redundancy case, ASP1 in Host1 would be sent any incoming 
message with DPC=x.  ASP1 in Host2 would normally be brought to the 
active state upon failure of, or loss of connectivity to, ASP1/Host1. In 
this example, both ASPs are Up, meaning that the related SCTP 
association and far-end M3UA peer is ready.

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The AS List at SG1 might also be set up in load-share mode:

    Routing Key {DPC=x) - "Application Server #1"
        ASP1/Host1  State = Up, Active
        ASP1/Host2  State = Up, 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 must 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.  Similarly, within an AS, 
if a load-balancing algorithm were to use CIC values to balance the load 
across the ASPs, the span of circuit contol assigned to particular ASPs 
must also be weighed against the ISUP circuit group management 
procedures.  

In the process of fail-over or fail-back, 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.

1.4.4.2 Signalling Gateway Redundancy

Signalling Gateways may also be distributed over multiple hosts.  Much 
like the AS model, SGs are comprised of one or more SG processes (SGP), 
distributed over one or more hosts, using an active/standby or a load-
sharing model.  An SGP is viewed as a remote SCTP end-point from an ASP 
perspective.

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/back-up redundancy model is possible, where the 
unavailability of the SCTP association to a primary SGP, or the 
unavailability of the SS7 destination node from the primary SGP, could 
be used to reroute affected traffic to an alternate SGP.  A load-sharing 
model is possible, where the signalling messages are load-shared between 
multiple SGPs.

It may also be possible for an AS 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 load-
shared between them.  Other models are also possible, subject to the 
limitations of the local SS7 network provisioning guidelines.

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>From the perspective of an ASP, a particular SG is capable of 
transferring traffic to an SS7 destination if an SCTP association with 
the SGP is established, the SGP has received an indication from the ASP 
that it is actively handling traffic for that destination, and the SG 
has not indicated that the destination is inaccessible.  When an ASP is 
configured to use multiple SGPs or SGs for transferring traffic to the 
SS7 network, the ASP must maintain knowledge of the current capability 
of the SG to handle traffic to destinations of interest.  This 
information is crucial to the overall reliability of the service, for 
both active/standby and load-sharing model, in the event of failures, 
recovery and maintenance activities.  The ASP may also use this 
information for congestion avoidance purposes.

1.4.5 Management Inhibit/Uninhibit

Local Management at an ASP or SG may wish to stop traffic across an SCTP 
association in order 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). When an SG 
determines that the transport of SS7 messages to a Signalling Point 
Management Cluster (SPMC) is encountering congestion, the SG may 
optionally trigger SS7 MTP3 Transfer Controlled management messages to 
originating SS7 nodes. The triggering of SS7 MTP3 Management messages 
from an SG is an implementation-dependent function.  

At an ASP, congestion is indicated to local MTP3-Users by means of an 
MTP-Status primitive indicating congestion, to invoke appropriate upper 
layer responses, as per current MTP3 procedures.

1.4.7 SCTP Stream Mapping.  

The M3UA at both the SG and ASP also supports the assignment of 
signalling traffic into streams within an SCTP association.  Traffic 
that requires sequencing must be assigned to the same stream.  To 
accomplish this, MTP3-User traffic may be assigned to individual streams 
based on 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.  

The use of SCTP streams within M3UA is recommended in order to minimize 
transmission and buffering delays, therefore improving the overall 
performance and reliability of the signalling elements.  The 
distribution of the MTP3 user messages over the various streams should 
be done in such

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a way to minimize message mis-sequencing, as required by the SS7 User 
Parts.

1.4.8 Client/Server Model

The SG takes on the role of server while the ASP is the client. ASPs 
must initiate the SCTP association to the SG.

The SCTP (and UDP/TCP) Registered User Port Number Assignment for M3UA 
is 2905.

1.5 Sample Configurations

1.5.1 Example 1: ISUP message transport

  ********   SS7   *****************   IP   ********
  * SEP  *---------*      SG       *--------* 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 Inter-working Function

In this example, the SG provides an implementation-dependent nodal 
inter-working function (NIF) that allows the MGC to exchange SS7 
signalling messages with the SS7-based SEP.  The NIF within the SG 
serves to transport messages within the SG between the MTP3 and M3UA.  
This nodal inter-working 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 SG 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 and are 
sent to the local M3UA-resident message distribution function for 
ongoing routing to the final IP destination.  MTP-TRANSFER primitives 
received from the local M3UA network address translation and mapping 
function are sent to the MTP Level 3 upper layer interface as MTP- 

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TRANSFER request primitives for on-going 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.

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 inter-working is not required, therefore there is 
no MTP3 network management status information for the SCCP and SCCP-User 
protocols to consider.  Any MTP-PAUSE, -RESUME or -STATUS indications 
from the M3UA to the SCCP should consider only the status of the SCTP 
Association and underlying IP network.    

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1.5.3 Example 3: SG resident SCCP layer, with remote ASP

  ********   SS7   *****************   IP   ********
  * SEP  *---------*               *--------*      *
  *  or  *         *      SG       *        * 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

In this example, the SG 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 
result 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 SG can perform the SCCP GTT service 
for messages logically addressed to it from SCCP peers in the IP domain.  
In this case, MTP-TRANSFER messages 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 is given to the 
MTP3 for delivery to an SS7-resident node.

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

For internal SG modeling purposes, this may be accomplished with the use 
of an implementation-dependent nodal inter-working function within the 
SG that effectively sits below the SCCP and routes MTP-TRANSFER messages 
to/from both the MTP3 and the M3UA, based on the SS7 DPC or DPC/SSN 

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address information.  This nodal inter-working function has no visible 
peer protocol with either the ASP or SEP.

Note that the services and interface provided by the M3UA are the same 
as in Example 1 and the functions taking place in the SCCP entity are 
transparent to M3UA.  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 [2]:

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

1.6.2 Definition of the boundary between M3UA and SCTP

The upper layer primitives provided by the SCTP are provided in [13]

1.6.3 Definition of the Boundary between M3UA and Layer Management

   M-SCTP ESTABLISH request
   M-SCTP ESTABLISH indication
   M-STCP ESTABLISH confirm

   M-SCTP RELEASE request
   M-SCTP RELEASE indication
   M-SCTP RELEASE confirm

   M-SCTP STATUS request
   M-SCTP STATUS indication

   M-ASP STATUS request
   M-ASP STATUS indication 

   M-AS-STATUS request
   M-AS-STATUS indication

   M-NOTIFY indication
   M-ERROR indication

   M-ASP-INHIBIT request
   M-ASP-UNINHIBIT request

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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].

3.0 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 
structure that contains a version, message type, message length, and 
message contents.  This message header is common among all signalling 
protocol adaptation layers:

    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.

M3UA Protocol Version: 8 bits (unsigned integer)

   The version field contains the version of the M3UA adaptation layer.  
   The supported versions are:

       Value    Version
       -----    -------
         1      Release 1.0

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Message Class: 8 bits (unsigned integer)

   The following list contains the Message Type Classes for the defined 
   messages.

         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 to 255    Reserved

Message Type: 8 bits (unsigned integer)

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

     Management (MGMT) Message

         0        Error (ERR)
         1        Notify (NTFY)
       2 to 255   Reserved for Management Messages     

     Transfer Messages

         0        Reserved
         1        Payload Data (DATA)
       2 to 255   Reserved for Transfer Messages

     SS7 Signalling Network Management (SSNM) Messages

         0        SS7 Network Isolation (S7ISO)
         1        Destination Unavailable (DUNA)
         2        Destination Available (DAVA)
         3        Destination State Audit (DAUD)
         4        SS7 Network Congestion State (SCON)
         5        Destination User Part Unavailable (DUPU)
       6 to 255   Reserved for SSNM Messages            

     ASP State Maintenance (ASPSM) Messages

         0        Reserved
         1        ASP Up (UP)
         2        ASP Down (DOWN)         3        Heartbeat (HEARTBEAT)
         4        ASP Up Ack (UP ACK)
         5        ASP Down Ack (DOWN ACK)
       6 to 255   Reserved for ASPSM Messages

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     ASP Traffic Maintenance (ASPTM) Messages

         0        Reserved
         1        ASP Active (ACTIVE)
         2        ASP Inactive (INACTIVE)
         3        ASP Active Ack (ACTIVE ACK) 
         4        ASP Inactive Ack (INACTIVE ACK)
       5 to 255   Reserved for ASPTM Messages

Reserved: 5 bits

   Should be set to all '0's and ignored by the receiver.

Message Length: 32-bits (unsigned integer)

   The Message Length defines the length of the message in octets, not 
   including the header.

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.  The 
variable-length 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                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Parameter Tag: 16 bits (unsigned integer)

   Tag field is a 16-bit identifier of the type of parameter. It takes a 
   value of 0 to 65534. 

   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.

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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 NEVER pad with more than 3 bytes. The 
   receiver MUST ignore the padding bytes.

3.2 Transfer Messages

The following section describes the Transfer messages and parameter 
contents. 

3.2.1 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
     Protocol Data         Mandatory

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 = 1            |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Network Appearance*                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 3            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                        Protocol Data                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 

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   signalling traffic between the SG and the Application Server Process 
   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 defines the SS7 Point Codes 
   used, the SS7 Network Indicator value and MTP3/MTP3-User protocol 
   type/variant/version used within the SS7 network partition.  Where an 
   SG operates in the context of a single SS7 network, or individual 
   SCTP associations are dedicated to each SS7 network context, or the 
   Network Indicator in the SIO of the MTP-Transfer primitive is 
   sufficient, the Network Appearance parameter is not required.

   The Network Appearance parameter value assigned according to network 
   operator policy.  The values used are of local significance only, 
   coordinated between the SG and ASP.

   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.

Protocol Data: variable length

   The Protocol Data field contains the MTP3-User application message, 
   which is in effect an MTP-TRANSFER primitive.  As defined for a 
   specific value of the Protocol Identifier, this will include the MTP-
   User Data and includes the MTP Routing Label (SS7 OPC, DPC, SLS), and 
   the SIO (Service Indicator, Network Indicator & optional Message 
   Priority codes).  Note: in the case of ISUP messages, the Circuit 
   Identification Code is also included. 

3.3 SS7 Signalling Network Management (SSNM) Messages

3.3.1 Destination Unavailable (DUNA)

The DUNA message is sent from the SG to all concerned ASPs to indicate 
that the SG has determined that one or more SS7 destinations are 
unreachable.  The MTP3-User at the ASP is expected to stop traffic to 
the affected destination through the SG initiating the DUNA as per the 
defined MTP3-User procedures. 

The DUNA message contains the following parameters:

     Network Appearance      Optional
     Affected Destination    Mandatory
     Info String             Optional

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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 = 1            |           Length =8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Network Appearance*                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 5            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask      |                 Affected DPC 1                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                              ...                              |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask      |                 Affected DPC n                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Tag = 4           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                          INFO String*                         |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Network Appearance: 32-bit 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 SG and the Application Server Process 
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 an SSNM message, the Network Appearance parameter defines the format 
of the Affected DPC(s) in the Affected Destination parameter.  The DPC 
point code length (e.g., 14-, 16-, or 24-bit) and sub-field definitions 
(e.g., ANSI 24-bit network/cluster/member, ITU-international 14-bit 
zone/region/signal_point, many national field variants, ...) are fixed 
within a particular Network Appearance.  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 and the format of the Affected DPC(s) is understood 
implicitly.

The format of the Network Appearance parameter is an integer, the values 
of which are assigned according to network operator policy. The values 
used are of local significance only, coordinated between the SG and ASP.

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Where the optional Network Appearance parameter is present, it must be 
the first parameter in the message as it defines the format of the 
Affected DPCs in the Affected Destination parameter.

Affected Destination: 24-bits

The Affected Destination parameter contains one or more Affected 
Destination Point Codes, 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 Destination parameter with more than 
one Affected DPC but it is mandatory to receive it.  All the Affected 
DPCs included must be within the same Network Appearance.  Including 
multiple Affected DPCs 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.  

Mask: 8-bits

The Mask parameter is 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.  For example, if all DPCs in an ANSI cluster are 
determined to be unavailable due to local linkset unavailability, the 
DUNA could identify potentially 256 Affected DPCs in a single Affected 
DPC field. 

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

Info String: variable length

The optional INFO String parameter can carry any meaningful 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.

3.3.2 Destination Available (DAVA)   

The DAVA message is sent from the SG to all concerned ASPs to indicate 
that the SG has determined that one or more SS7 destinations are now 
reachable. The ASP MTP3-User protocol is expected to resume traffic to 
the affected destination through the SG initiating the DUNA. 

The DAVA message contains the following parameters:

     Network Appearance      Optional
     Affected Destination    Mandatory
     Info String             Optional

The format and description of DAVA Message parameters is the same as for 
the DUNA message (See Section 3.3.2.1.)  

3.3.3 Destination State Audit (DAUD)

The DAUD message can be sent from the ASP to the SG to audit the 
availability/congestion state of SS7 routes to one or more affected 
destinations.  See Section 3.4.3 for the audit procedures.

The DAUD message contains the following parameters:

     Network Appearance      Optional
     Affected Destination    Mandatory
     Info String             Optional

The format and description of DAUD Message parameters is the same as for 
the DUNA message (See Section 3.3.2.1.)

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Multiple Affected Destination Point Codes parameters may optionally be 
included in a DAUD message.  However all the Affected Destination Point 
Codes must be part of the same Network Appearance.

3.3.4 SS7 Network Congestion (SCON)

The SCON message can be sent from the SG to all concerned ASPs to 
indicate that the congestion level in the SS7 network to one or more 
destinations has changed.

The SCON message contains the following parameters:

     Network Appearance       Optional
     Affected Destination     Mandatory
     Congestion Level         Mandatory           
     Info String              Optional

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 = 1            |           Length =8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                       Network Appearance*                     | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 5            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Cong. Level 1 |                 Affected DPC 1                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                              ...                              |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Cong. Level n |                 Affected DPC n                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 4            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                         INFO String*                          |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the Network Appearance, Affected 
Destination and Info String parameters is the same as for the DUNA 
message (See Section 3.3.2.1.)

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Congestion Level: 8-bits (unsigned integer)

The valid values for the optional Congestion Level parameter are shown 
in the following table.

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

The congestion levels are as defined in the national congestion method 
in the ITU MTP recommendation [14] or in the ANSI MTP standard [15].  
For MTP congestion methods that do not employ congestion levels (e.g., 
the ITU international method, the parameter is always "Undefined".

3.3.5 Destination User Part Unavailable (DUPU)

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

The DUPU message contains the following parameters:

     Network Appearance       Optional
     Affected Destination     Mandatory
     Unavailability Cause     Mandatory
     MTP3-User Identity       Mandatory
     Info String              Optional

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 = 1            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                      Network Appearance*                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 5            |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Cause | User  |              Affected Destination             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 4            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                          INFO String*                         |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the Network Appearance, Affected 
Destination and Info String parameters is the same as for the DUNA 

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message (See Section 3.3.2.1.) One exception is that the Affected 
Desination parameter in the DUPU message can only contain one Affected 
DPC. 

Unavailability Cause: 4-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 context, 
additional values may be used  the specification of the relevant MTP3 
protocol variant/version is definitive.

         0         Unknown
         1         Unequipped Remote User
         2         Inaccessible Remote User

MTP3-User Identity: 4-bits (unsigned integer)

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

         Value       Description
        00 - 02       Reserved
           03         SCCP
           04         TUP
           05         ISUP
        06  08       Reserved
           09         Broadband ISUP
           10         Satellite ISUP           
 

3.4 Application Server Process Maintenance (ASPM) Messages

3.4.1 ASP Up (ASPUP)

The ASP UP (ASPUP) message is used to indicate to a remote M3UA peer 
that the Adaptation layer is ready to receive traffic or maintenance 
messages.

The ASPUP message contains the following parameters:

     Adaptation Layer Identifer    Optional
     Protocol Identifier           Optional
     INFO String                   Optional
     
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The format for ASPUP 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 = 2            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Adaptation Layer Identifier*                  |   
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 4            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                          INFO String*                         |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional Info String parameter is the 
same as for the DUNA message (See Section 3.3.2.1.)

Adaptation Layer Identity: 32-bits ()

The optional Adaptation Layer Identifier (ALI) is a string that 
identifies the adaptation layer.  This string must be set to "M3UA" 
which results in a length of 8.  The ALI would normally only be used in 
the initial ASP Up message across a new SCTP association to ensure both 
peers are assuming the same adaptation layer protocol.

3.4.2 ASP Up Ack

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

The ASPUP Ack message contains the following parameters:

     Adaptation Layer Identifier (optional)
     Protocol Identifier (optional)
     INFO String (optional)
     

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The format for ASPUP 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 =2             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                 Adaptation Layer Identifier*                  |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag =4            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                          INFO String*                         |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional Info String parameter is the 
same as for the DUNA message (See Section 3.3.2.1.)

The format and description of the optional Adaptation Layer Identifier 
(ALI) parameter is the same as for the ASP-UP message. (See Section 
3.4.1)

3.4.3 ASP Down (ASPDN)

The ASP Down (ASPDN) message is used to indicate to a remote M3UA peer 
that the adaptation layer is not ready to receive traffic or maintenance 
messages.

The ASPDN message contains the following parameters:

     Reason         Mandatory
     INFO String    Optional

The format for the ASPDN 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Reason                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag =4             |            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 3.3.2.1.)

Reason: 32-bit (unsigned integer)

The Reason parameter indicates the reason that the remote M3UA 
adaptation layer is unavailable.  The valid values for Reason are shown 
in the following table.

         1        Processor Outage
         2        Management Inhibit

3.4.4 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:

     Reason       Mandatory
     INFO String  Optional

The format for the ASPDN 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Reason                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 4            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   \                                                               \
   |                         INFO String*                          |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional Info String parameter is the 
same as for the DUNA message (See Section 3.3.2.1.)

The format of the Reason parameter is the same as for the ASP-Down 
message. (See Section 3.4.3)

3.4.5 ASP Active (ASPAC)

The ASPAC message is sent by an ASP to indicate to a remote M3UA peer  
that it is Active and ready to process signalling traffic for a 
particular Application Server

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The ASPAC message contains the following parameters:

     Type               Mandatory
     Routing Context    Optional
     INFO String        Optional

The format for the ASPAC 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                             Type                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag =6             |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                       Routing Context*                        | 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |          Tag = 4              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                          INFO String*                         |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type: 32-bit (unsigned integer)

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

         1         Over-ride
         2         Load-share

Within a particular Routing Context, only one Type can be used.  The 
Over-ride value indicates that the ASP is operating in Over-ride mode, 
where the ASP takes over all traffic in an Application Server (i.e., 
primary/back-up operation), over-riding any currently active ASP in the 
AS.  In Load-share mode, the ASP will share in the traffic distribution 
with any other currently active ASPs.  

A node that receives an ASPAC with an incorrect Type for a particular 
Routing Context will respond with an Error Message (Cause: Invalid 
Traffic Handling Mode.

Routing Context: 

The optional Routing Context parameter contains (a list of) integers 
indexing the Application Server traffic that the sending ASP is

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configured/registered to receive.  There is one-to-one relationship 
between an index entry and an SG Routing Key or AS Name.  Because an AS 
can only appear in one Network Appearance, the Network Appearance 
parameter is not required in the ASPAC 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 SG.  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 3.3.2.1.)

3.4.6 ASP Active Ack

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

The ASPAC Ack message contains the following parameters:

     Type               Mandatory
     Routing Context    Optional
     INFO String        Optional

The format for the ASPAC 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                             Type                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 6            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                       Routing Context*                        | 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |            Tag = 4            |             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 3.3.2.1.)

The format of the Type and Routing Context parameters is the same as for 
the ASP-Active message. (See Section 3.4.5).

3.4.7  ASP Inactive (ASPIA)

The ASPIA message is sent by an ASP to indicate to a remote M3UA peer 
that it is no longer processing signalling traffic within a particular 
Application Server.  

The ASPIA message contains the following parameters:

     Type                 Mandatory
     Routing Context      Optional
     INFO String          Optional

The format for the ASPIA 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                             Type                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 6            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                       Routing Context*                        | 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |            Tag = 4            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                          INFO String*                         |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

    Value          Description
     0x1            Over-ride
     0x2            Load-share
Within a particular Routing Context, only one Type can be used.  The 
Over-ride value indicates that the ASP is operating in Over-ride mode, 

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and will no longer handle traffic within an Application Server (i.e., it 
is now a backup in a primary/back-up arrangement).  The Load-share value 
indicates that the ASP is operating in Load-share mode and will no 
longer share in the traffic distribution with any other currently active 
ASPs.

A node that receives an ASPIA with an incorrect Type for a particular 
Routing Context will respond with an Error Message (Cause: Invalid 
Traffic Handling Mode.

The format and description of the optional Routing Context and Info 
String parameters is the same as for the ASPAC message (See Section 
2.3.3.3.)

3.4.8 ASP Inactive Ack

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

The ASPIA Ack message contains the following parameters:

     Type               Mandatory
     Routing Context    Optional
     INFO String        Optional

The format for the ASPIA 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                             Type                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 6            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                       Routing Context*                        | 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |            Tag = 4            |             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 3.3.2.1.)

The format of the Type and Routing Context parameters is the same as for 
the ASP-Inctive message. (See Section 3.4.7).

3.4.9 Heartbeat (BEAT)

The Heartbeat 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 no parameters.

3.5  Management Messages

3.5.1  Error (ERR)

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 ERR message contains the following parameters:

     Error Code                 Mandatory
     Diagnostic Information     Optional

The format for the ERR 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Error Code                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 7            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                     Diagnostic Information*                   |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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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:

     Invalid Version                        0x1
     Invalid Network Appearance             0x2
     Invalid Adaptation Layer Identifier    0x3
     Invalid Message Type                   0x4
     Invalid Traffic Handling Mode          0x5
     Unexpected Message Type                0x6
     Protocol Error                         0x7

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, 
Adaptation Layer Identifier or Traffic Handling Mode, the Diagnostic 
information includes the received parameter.  In the other cases, the 
Diagnostic information may be the first 40 bytes of the offending 
message.

In the case of an Invalid Version Error Code, the Common Header contains 
the supported Version.

Error messages are not generated in response to other Error messages.

3.5.2 Notify (NTFY)

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

The NTFY message contains the following parameters:

     Status Type                Mandatory
     Status Identification      Mandatory
     Routing Context            Optional
     INFO String                Optional

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The format for the NTFY 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |        Status Type            |    Status Identification      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 6              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                       Routing Context*                        | 
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |          Tag = 4              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   |                          INFO String*                         |
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Status Type: 16-bits (unsigned integer)

The Status Type parameter identifies the type of the Notify message.  
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.  

If the Status Type is AS_State_Change the following Status Information 
values are used:

         1    Application Server Down (AS_Down)
         2    Application Server Up (AS_Up)
         3    Application Server Active (AS_Active)
         4    Application Server Pending (AS_Pending)
         5    Alternate ASP Active
         6    Insufficient ASPs

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

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

         1    Insufficient ASP resources active in AS

This notification is not based on the SG reporting the state change of 
an ASP or AS.  For the value defined the SG is indicating to an ASP(s) 
in the AS that another ASP is required in order to handle the load of 
the AS. 

The format and description of the optional Routing Context and Info 
String parameters is the same as for the ASPAC message (See Section 
3.4.6.)

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4.0 Procedures

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

4.1 Procedures to support the services of the M3UA layer

4.1.1 Receipt of primitives from the M3UA-User

On receiving an MTP-Transfer primitive from an upper layer, or the nodal 
inter-working function at an SG, the M3UA layer will send a 
corresponding Data message (see Section 2) to its M3UA peer.  The M3UA 
layer must fill in various fields of the common and specific headers 
correctly.  

At an SG, the M3UA address translation and mapping function determines 
the Application Server (AS) based on the information in the incoming 
message.  From an ordered list of ASPs within the AS table, an Active 
ASP is selected and a Data message is constructed and issued on the 
corresponding SCTP Association.  If more than one ASP is active (i.e., 
traffic is to be load-shared across all the active ASPs), one of the 
active ASPs from the list is selected.  The selection algorithm is 
implementation dependent but could be roud-robin or based on, for 
example, the SLS or ISUP CIC.  The appropriate selection algorithm must 
be chosen carefully as it is dependent on application assumptions and 
understanding of the degree of state coordination between the 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. 

4.1.2 Receipt of primitives from the Layer Management

On receiving these primitives from the local Layer Management, the M3UA 
layer will send the corresponding management message (Error) to its 
peer.  The M3UA layer must fill in the various fields of the common and 
specific headers correctly.

4.2 Receipt of Peer Management messages

Upon receipt of Management messages, the M3UA layer must invoke the 
corresponding Layer Management primitive indications (M-ERROR ind.) to 
the local layer management.

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4.3 Procedures to support the M3UA services in Section 1.4.4

These procedures support the M3UA management of SCTP Associations 
between SGs and ASPs.

4.3.1 State Maintenance

The M3UA layer on the SG maintains the state of each AS, in each 
Application Server that it is configured to receive traffic, as input to 
the M3UA address translation and mapping function.

4.3.1.1  ASP States

The state of each ASP, in each AS that it is configured, is maintained 
in the M3UA layer in the SG. 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
   * Reception of indications from the SCTP layer
   * Switch-over Time triggers

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

ASP-DOWN: The remote M3UA peer at the ASP is unavailable and/or the SCTP 
association is down.  Initially all ASPs will be in this state.

ASP-UP: The remote M3UA peer at the ASP is available (and the SCTP 
association is up) but application traffic is stopped.

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).

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                 Figure 4: ASP State Transition Diagram

                                  +-------------+
           +----------------------|             |      
           |   Alternate  +-------| ASP-ACTIVE  |<------------+
           |       ASP    |       +-------------+             |
           |    Takeover  |           ^     |                 | 
           |              |    ASP    |     | ASP             |
           |              |    Active |     | Inactive        | ASP
           |              |           |     v                 |Takeover
           |              |       +-------------+             |  
           |              |       |             |-------------+
           |              +------>|   ASP-UP    |-------------+
           |                      +-------------+             |
           |                          ^    |                  |
 ASP Down/ |                     ASP  |    | ASP Down /       | ASP
 SCTP CDI  |                     Up   |    | SCTP CDI         | Down/
           |                          |    v                  | SCTP
           |                      +-------------+             | CDI
           |                      |             |             |
           +--------------------->|             |<------------+
                                  |  ASP-DOWN   |
                                  +-------------+

SCTP CDI: The local SCTP layer's Communication Down Indication to the 
Upper Layer Protocol (M3UA) on an SG. The local SCTP will send this 
indication when it detects the loss of connectivity to the ASP's peer 
SCTP layer.

Ts: Switch-over Time Triggers.  This timer is configurable by the 
0perator on a per AS basis.

4.3.1.2  AS States

The state of the AS is maintained in the M3UA layer on the SG.

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.

AS-UP: The Application Server is available but no application traffic is 
active (i.e., one or more related ASPs are in the ASP-UP state, but none 
in the ASP-Active state).

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

AS-PENDING: An active ASP has transitioned from active to inactive or 
down and it was the last remaining active ASP in the AS. A recovery 
timer T(r) will be started and all incoming SCN messages will be queued 
by the SG. If an ASP becomes active before T(r) expires, the AS will 
move to AS-ACTIVE state and all the queued messages will be sent to the 
active ASP. 

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

                 Figure 5: AS State Transition Diagram

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

    Tr = Recovery Timer

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4.3.2 ASPM procedures for primitives

Before the establishment of an SCTP association the ASP state at both 
the SG and ASP is assumed to be "Down".  

As the ASP is responsible for initiating the setup of an SCTP 
association to an SG, the M3UA layer at an ASP receives an M-SCTP 
ESTABLISH request primitive from the Layer Management, the M3UA layer 
will try to establish an SCTP association with the remote M3UA peer at 
an SG.  Upon reception of an eventual SCTP-Communication Up confirm 
primitive from the SCTP, the M3UA layer will invoke the primitive M-SCTP 
ESTABLISH confirm to the Layer Management.

The M3UA layers at the SG will receive an SCTP-Communication_Up 
indication primitive from the SCTP when the association is successfully 
set up.  The M3UA layer will then invoke the primitive M-SCTP ESTABLISH 
indication to the Layer Management. 

Once the SCTP association is established and assuming that the local 
M3UA-User is ready, the local ASP M3UA Application Server Process 
Maintenance (ASPM) function will initiate the ASPM procedures, using the 
ASP-Up/-Down/-Active/-Inactive messages to convey the ASP-state to the 
SG - see Section 4.3.3. 

If the M3UA layer subsequently receives an SCTP-Communication Down 
indication from the underlying SCTP layer, it will inform the Layer 
Management by invoking the M-SCTP STATUS indication primitive. The state 
of the remote ASP will be moved to "Down".

At an ASP, the Layer Management may try to re-establish the SCTP 
association using M-SCTP ESTABLISH request primitive. 

4.3.3 ASPM procedures for peer-to-peer messages

All ASPM messages are sent on a sequenced stream to ensure ordering.  
SCTP stream '0' is used.

4.3.3.1 ASP-Up

After an ASP has successfully established an SCTP association to an SG, 
the SG 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 exchange.  

When an ASP-Up message is received at an SG and internally the ASP is 
not considered locked-out for local management reasons, the SG marks the 
remote ASP as 'Up'.  The SG responds with an ASP-Up Ack message in 
acknowledgement.  The SG sends an-Up Ack message in response to a 
received ASP-Up message even if the ASP is already marked as "Up" at the 
SG.  

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If for any local reason the SG cannot respond with an ASP-Up Ack, the SG 
responds to an ASP-Up with a ASP-Down message.  

At the ASP, the ASP-Up Ack message received from the SG is not 
acknowledged by the ASP.  If the ASP does not receive a response from 
the SG, or an ASP-Down is received, the ASP may resend ASP-Up messages 
every 2 seconds until it receives an ASP-Up Ack message from the SG.  
The ASP may decide to reduce the frequency (say to every 5 seconds) if 
an ASP-Up Ack is not received after a few tries.

The ASP must wait for the ASP-Up Ack message from the SG before sending 
any ASP traffic control messages (ASPAC or ASPIA) or Data messages or it 
will risk message loss.  If the SG receives Data messages before an ASP 
Up is received, the SG should discard.

4.3.3.2 ASP-Down

The ASP will send an ASP-Down to an SG when the ASP is to be removed 
from the list of ASPs in all Application Servers that it is a member.

The SG marks the ASP as "Down" and returns an ASP-Down Ack message to 
the ASP if one of the following events occur:

    - an ASP-Down message is received from the ASP,
    - another ASPM message is received from the ASP and the SG has  
      locked out the ASP for management reasons.

The SG sends an ASP-Down Ack message in response to a received ASP-Down 
message from the ASP even if the ASP is already marked as "Down" at the 
SG.  

If the ASP does not receive a response from the SG, the ASP may send 
ASP-Down messages every 2 seconds until it receives an ASP-Down Ack 
message from the SG or the SCTP association goes down.  The ASP may 
decide to reduce the frequency (say to every 5 seconds) if an ASP-Down 
Ack is not received after a few tries.

4.3.3.3 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.

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 SG.

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4.3.3.4 ASP-Active

Anytime after the ASP has received an ASP-Up Ack from the SG, the ASP 
sends an ASP-Active (ASPAC) to the SG indicating that the ASP is ready 
to start processing traffic.  In the case where an ASP is 
configured/registered to process the traffic for more than one 
Application Server across an SCTP association, the ASPAC contains one or 
more Routing Contexts to indicate for which Application Servers the 
ASPAC applies. 

When an ASP Active (ASPAC) message is received, the SG responds to the 
ASP with a ASPAC Ack message acknowledging that the ASPAC was received 
and starts sending traffic for the associated Application Server(s) to 
that ASP.

There are two modes of Application Server traffic handling in the SG 
M3UA - Over-ride and Load-share.  The Type parameter in the ASPAC 
message indicates the traffic handling mode used in a particular 
Application Server. If the SG determines that the mode indicated in an 
ASPAC is incompatible with the mode currently used in the AS, the SG 
responds with an Error message indicating "Invalid Traffic Handling 
Mode".

In the case of an Over-ride mode AS, reception of an ASPAC message at an 
SG causes the redirection of all traffic for the AS to the ASP that sent 
the ASPAC.  The SG responds to the ASPAC with an ASP-Active Ack message 
to the ASP.  Any previously active ASP in the AS is now considered 
Inactive and will no longer receive traffic from the SG within the AS.  
The SG sends a Notify (Alternate ASP-Active) to the previously active 
ASP in the AS, after stopping all traffic to that ASP.

In the case of a Load-share mode AS, reception of an ASPAC message at an 
SG causes the direction of traffic to the ASP sending the ASPAC, in 
addition to all the other ASPs that are currently active in the AS.  The 
algorithm at the SG for load-sharing traffic within an AS to all the 
active ASPs is application and network dependent.  The algorithm could, 
for example be round-robin or based on information in the Data message 
(e.g, such as the SLS, SCCP SSN, ISUP CIC value), depending on the 
requirements of the application and the call/transaction state handling 
assumptions of the collection of ASPs in the AS. The SG responds to the 
ASPAC with an ASP-Active Ack message to the ASP.

4.3.3.5 ASP Inactive

When an ASP wishes to withdraw from receiving traffic within an AS, the 
ASP sends an ASP Inactive (ASPIA) to the SG.  In the case where an ASP 
is configured/registered to process the traffic for more than one 
Application Server across an SCTP association, the ASPIA contains one or 
more Routing Contexts to indicate for which Application Servers the 
ASPIA applies.

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There are two modes of Application Server traffic handling in the SG 
M3UA when withdrawing an ASP from service - Over-ride and Load-share.  
The Type parameter in the ASPIA message indicates the mode used in a 
particular Application Server.  If the SG determines that the mode 
indicates in an ASPAC is incompatible with the traffic handling mode 
currently used in the AS, the SG responds with an Error message 
indicating "Invalid Traffic Handling Mode".

In the case of an Over-ride mode AS, where normally another ASP has 
already taken over the traffic within the AS with an Over-ride ASPAC, 
the ASP that sends the ASPIA is already considered by the SG to be 
"Inactive" (i.e., in the "Up" state).  An ASPIA Ack message is sent to 
the ASP, after ensuring that all traffic is stopped to the ASP.  

In the case of a Load-share mode AS, the SG moves the ASP to the "Up" 
state and the AS traffic is re-allocated across the remaining "active" 
ASPs per the load-sharing algorithm currently used within the AS.  An 
ASPIA Ack message is sent to the ASP after all traffic is halted to the 
ASP.

If no other ASPs are "Active" in the Application Server, the SG either 
discards all incoming messages for the AS or starts buffering the 
incoming messages for T(r)seconds, after which messages will be 
discarded.  T(r) is configurable by the network operator.  If the SG 
receives an ASPAC from 
an ASP in the AS before expiry of T(r), the buffered traffic is directed 
to the ASP and the timer is cancelled.

4.3.3.6 NotifyIn the case where a Notify (AS-Up) message is sent by an 
SG that now has no ASPs active to service the traffic, the Notify does 
not force the ASP(s) receiving the message to become active. The ASPs 
remain in control of what (and when) action is taken.

4.3.3.7 Heartbeat

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 the SCTP).  

Once the ASP sends an ASP-Up message to the SG, the ASP sends Beat 
messages periodically, subject to a provisionable timer T(beat).  The SG 
M3UA, upon receiving a BEAT message from the ASP, responds with a BEAT
message.  If no BEAT message (or any other M3UA message), is received 
from the ASP within the timer 2*T(beat), the ASP will consider the 
remote M3UA as 'Down".

At the ASP, if no BEAT message (or any other M3UA message) is received 
from the SG within 2*T(beat), the SG is considered unavailable. 

 
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Transmission of BEAT messages is stopped and ASP-Up procedures are used 
to re-establish communication with the SG M3UA peer.

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

4.4 Procedures to support the M3UA services in Section 1.4.3

4.4.1 At an SG

On receiving an MTP-PAUSE, MTP-RESUME, or MTP-STATUS indication 
primitive from the nodal inter-working function at an SG, the SG M3UA 
layer will send a corresponding SSNM DUNA, DAVA, SCON, or DUPU message 
(see Section 2) 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 SG M3UA determines the set of concerned ASPs to be informed based on 
the SS7 network partition 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 SG operates 
within a single SS7 network appearance, then all ASPs are informed.  

Optionally, the SG M3UA may filter further based on the Affected Point 
Code in the MTP-PAUSE, MTP-Resume, or MTP-Status indication primitives.  
In this way ASPs can be informed only of affected destinations to which 
they actually communicate.  The SG M3UA may also suppress DUPU messages 
to ASPs that do not implement an MTP3-User protocol peer for the 
affected MTP3-User.

DUNA, DAVA, SCON messages must be sent on a sequenced stream as these 
primitives should arrive in order.  Stream 0 is used.  Sequencing is not 
required for the DUPU or DAUD message, which may optionally be sent un-
sequenced.

4.4.2 At an ASP

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

4.4.3 ASP Auditing

An ASP may optionally initiate an audit procedure in order to enquire of 
an SG the availability or congestion status of an SS7 destination or set 
of destinations.  A Destination Audit (DAUD) message is sent from the 
ASP to the SG requesting the current availability or congestion status 
of one or more SS7 Destination Point Codes.

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The DAUD may be sent by the ASP in the following cases.  The DAUD may be 
sent unsequenced.

   - Periodic.  A Timer originally set upon reception of DUVA or SCON 
     message has expired without a subsequent DAVA, DUVA or SCON  
     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 SG that originally sent the  
     SSNM message.
 
   - the ASP is newly "Up" or "Active" or has been isolated from an SG  
     for an extended period.  The SG can request the  
     availabilty/congestion status of one or more SS7 destinations to  
     which it expects to communicate.

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

The SG must respond to a DAUD with the MTP3 status of the routeset 
associated with each Destination Point Code(s) in the DAUD.  The status 
of each SS7 destination requested is indicated in a DUNA (if 
unavailable), DAVA (if available/uncongested) or an SCON (if 
available/congested).  Optionally, any DUNA or DAVA in response to a 
DAUD may contain more than one Affected Point Code. 

Note that from the point of view of an ASP sending an DAUD, the 
subsequent reception of an SCON implies that the Affected Destination is 
available.  The reception of a DAVA implies that the routeset to the 
Affected Destination are not congested.  Obviously with the reception of 
an DUNA, the routeset to the Affected Destination can not also be 
congested.

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5.0 Examples of M3UA Procedures

5.1 Establishment of Association and Traffic between SGs and ASPs

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

This scenario shows the example M3UA message flows for the establishment 
of traffic between an SG and an ASP, where only one ASP is configured 
within an AS (no backup).  It is assumed that the SCTP association is 
already set-up.

             SG                       ASP1
              |
              |<---------ASP Up----------| 
              |-------ASP-Up Ack-------->|
              |                      -   | 
              |<-------ASP Active--------| 
              |-----ASP Active Ack------>|
              |                          |

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

This scenario shows the example M3UA message flows for the establishment 
of traffic between an SG and two ASPs in the same Application Server, 
where ASP1 is configured to be "active" and ASP2 a "standby" in the 
event of communication failure or the withdrawal from service of ASP1.  
ASP2 may act as a hot, warm, or cold standby depending on the extent to 
which ASP1 and ASP2 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 are Over-ride or Load-share mode 
although typically this example would use an Over-ride mode.

       SG                        ASP1                        ASP2
        |                         |                          |
        |<--------ASP Up----------|                          | 
        |-------ASP-Up Ack------->|                          |
        |                         |                          |
        |<-----------------------------ASP Up----------------|
        |-----------------------------ASP-Up Ack------------>|
        |                         |                          | 
        |                         |                          |
        |<-------ASP Active-------|                          | 
        |------ASP-Active Ack---->|                          | 
        |                         |                          |

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5.1.3 Two ASPs in an Application Server ("1+1" sparing, load-sharing 
case)

This scenario shows a similar case to Section 4.1.2 but where the two 
ASPs are brought to "active" and load-share the traffic load.  In this 
case, one ASP is sufficient to handle the total traffic load.

       SG                       ASP1                       ASP2
        |                         |                          |
        |<---------ASP Up---------|                          | 
        |--------ASP-Up Ack------>|                          |
        |                         |                          |
        |<------------------------------ASP Up---------------|
        |-----------------------------ASP Up Ack------------>|
        |                         |                          | 
        |                         |                          |
        |<--ASP Active (Ldshr)----|                          | 
        |-----ASP-Active Ack----->|                          | 
        |                         |                          |
        |<----------------------------ASP Active (Ldshr)-----| 
        |-------------------------------ASP-Active Ack------>| 
        |                         |                          |

5.1.4 Three ASPs in an Application Server ("n+k" sparing, load-sharing 
case) 

This scenario shows the example M3UA message flows for the establishment 
of traffic between an SG and three ASPs in the same Application Server, 
where two of the ASPs are brought to "active" and share the load. In 
this case, a minimum of two ASPs are required to handle the total 
traffic load (2+1 sparing).

   SG                  ASP1                 ASP2                 ASP3 
    |                    |                   |                   |
    |<------ASP Up-------|                   |                   | 
    |-----ASP-Up Ack---->|                   |                   |
    |                    |                   |                   |
    |<--------------------------ASP Up-------|                   |
    |-------------------------ASP-Up Ack)--->|                   |
    |                    |                   |                   |
    |<---------------------------------------------ASP Up--------|
    |---------------------------------------------ASP-Up Ack---->|
    |                    |                   |                   | 
    |                    |                   |                   |
    |<--ASP Act (Ldshr)--|                   |                   | 
    |----ASP-Act Ack---->|                   |                   | 
    |                    |                   |                   |
    |<--------------------ASP Act. (Ldshr)---|                   | 
    |-----------------------ASP-Act Ack----->|                   | 
    |                    |                   |                   |

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5.2 ASP Traffic Fail-over Examples

5.2.1 (1+1 Sparing, withdrawal of ASP, Back-up Over-ride) 

Following on from the example in Section 4.1.2, and ASP withdraws from 
service:

       SG                       ASP1                       ASP2 
        |                         |                          |
        |<-----ASP Inactive-------|                          |
        |----ASP Inactive Ack---->|                          |
        |-------------------------NTFY(AS-Down) (Optional)-->| 
        |                         |                          | 
        |<------------------------------ ASP Active----------| 
        |------------------------------ASP-Active Ack)------>| 
        |                                                    |

Note: If the SG detects loss of the M3UA peer (M3UA heartbeat loss or 
detection of SCTP failure), the initial SG-ASP1 ASP Inactive message 
exchange would not occur.

5.2.2 (1+1 Sparing, Back-up Over-ride)

Following on from the example in Section 4.1.2, and ASP2 wishes to over-
ride ASP1 and take over the traffic:

       SG                       ASP1                       ASP2 
        |                         |                          | 
        |<------------------------------ ASP Active----------| 
        |-------------------------------ASP-Active Ack------>|
        |----NTFY(Alt ASP-Act)--->| 
        |                         |                          | 

5.2.3 (n+k Sparing, Load-sharing case, withdrawal of ASP)

Following on from the example in Section 4.1.4, and ASP1 withdraws from 
service:

   SG                  ASP1                 ASP2                 ASP3 
    |                    |                   |                   |
    |<----ASP Inact.-----|                   |                   | 
    |---ASP-Inact Ack--->|                   |                   |
    |                    |                   |                   | 
    |---------------------------------NTFY(Ins. ASPs)(Optional)->| 
    |                    |                   |                   |
    |<-----------------------------------------ASP Act (Ldshr)---| 
    |-------------------------------------------ASP Act (Ack)--->|
    |                    |                   |                   |

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The Notify message to ASP3 is optional, as well as the ASP-Active from 
ASP3.  The optional Notify can only occur if the SG maintains knowledge 
of the minimum ASP resources required  for example if the SG knows that 
"n+k" = "2+1" for a load-share AS and "n" currently equals "1". 

Note: If the SG detects loss of the ASP1 M3UA peer (M3UA heartbeat loss 
or detection of SCTP failure), the first SG-ASP1 ASP Inactive message 
exchange would not occur.  

5.3  M3UA/MTP3-User Boundary Examples

5.3.1 At an ASP

This section describes the primitive mapping from the MTP3 User to M3UA 
at an ASP.  

5.3.1.1 Support for MTP-Transfer on the ASP

5.3.1.1.1 Support for MTP-Transfer Request
When the MTP3-User on the ASP has data to send into the SS7 network, it 
will use the MTP-Transfer Request primitive.  The M3UA on the ASP will 
do the following when it receives an MTP-Transfer Request primitive from 
the M3UA user:

  - Determine the correct SG

  - Determine the correct association to the chosen SG

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

  - Determine whether to complete the optional fields of the Data  
    message

  - Map the MTP-Transfer Request primitive into the Protocol Data  
    field of an m3ua Data message

  - Send the Data message to the remote M3UA peer in the SG, over the  
    SCTP association

        SG                       ASP   
        |                         |                  
        |<-----Data Message-------|<--MTP-Transfer req. 
        |                         | 

        

             
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5.3.1.1.2 Support for MTP Transfer Indication

When the M3UA on the ASP has received Data messages from the remote M3UA 
peer in the SG it will do the following:

  - Evaluate the optional fields of the Data message if present

  - Map the Payload 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.

        SG                       ASP   
        |                         |
        |------Data Message------>|---MTP-Transfer ind.
        |                         |          

5.3.1.1.3 Support for ASP Querying of SS7 Destination States

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

The M3UA on the ASP normally sends Destination State Audit (DAUD) 
messages for each of the destinations that the ASP supports.

       SG                        ASP   
        |                         |                  
        |<-----DAUD Message ------| 
        |<-----DAUD Message ------| 
        |<-----DAUD Message ------| 
        |                         |                     
        |                         |             

5.3.2 At an SG 

This section describes the MTP3 upper layer primitive mapping to the 
M3UA at the SG.

5.3.2.1 Support for MTP-Transfer Request at the SG

When the M3UA on the SG has received Data messages from its peer 
destined to the SS7 network it will do the following:

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  - Evaluate the optional fields of the Data message if present to  
    determine the network appearance

  - Map the Protocol data of the Data message into an MTP-Transfer  
    Request primitive

  - Pass the MTP-Transfer Request primitive to the MTP3 of the  
    concerned network appearance.

                            SG                        ASP
                             |                         |
        <---MTP-Transfer req.|<------Data Message------|
                             |                         |

5.3.2.2 Support for MTP-Transfer Indication at the SG

When the MTP3 on the SG has data to pass its user parts, it will use the 
MTP-Transfer Indication primitive.  The M3UA on the S>G will do the 
following when it receives an MTP-Transfer Indication:

  - Determine the correct ASP

  - Determine the correct association to the chosen ASP

  - Determine the correct stream in the 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 an M3UA Data message

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

                           SG                        ASP
                            |                         |
       --MTP-Transfer ind.->|------Data Message------>|
                            |                         |

5.3.2.3 Support for MTP-PAUSE, MTP-RESUME, MTP-STATUS

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

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5.3.2.3.1 Destination Unavailable 

The MTP3 on the SG will generate an MTP-PAUSE primitive when it 
determines locally that an SS7 destination is unreachable.  The M3UA 
will map this primitive to a Destination Unavailable (DUNA) message.  It 
will determine which ASP(s) to send the DUNA based on the Network 
Appearance information.

                   SG                       ASP   
                    |                         |
 --MTP-PAUSE ind.-->|------DUNA Message ----->|--MTP-PAUSE ind.-->
                    |                         |

5.3.2.3.2 Destination Available

The MTP3 on the SG will generate an MTP-RESUME primitive when it 
determines locally that an SS7 destination that was previously 
unreachable is now reachable.  The M3UA will map this primitive to a 
Destination Unavailable (DAVA) message.  It will determine which ASP(s) 
to send the DUNA based on the Network Appearance information.

                   SG                       ASP   
                    |                         |
--MTP-RESUME ind.-->|------DAVA Message ----->|--MTP-RESUME ind.-->
                    |                         |

5.3.2.3.3  SS7 Network Congestion 

The MTP3 on the SG will generate an MTP-STATUS primitive when it 
determines locally that the route to an SS7 destination is congested.  
The M3UA will map this primitive to a SS7 Network Congestion State 
(SCON) message.  It will determine which ASP(s) to send the DUPU to 
based on the intended Application Server.
 
                     SG                       ASP   
                       |                         |                  
   --MTP-STATUS ind.-->|------SCON Message ----->|--MTP-STATUS ind.--> 
                       |                         |

 
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5.3.2.3.4 Destination User Part Unavailable

The MTP3 on the SG will generate an MTP-STATUS primitive when it 
determines locally that an SS7 destination User Part is unavailable.  
The M3UA will map this primitive to a Destination User Part Unavailable 
(DUPU) message.  It will determine which ASP(s) to send the DUPU based 
on the intended Application Server.

                      SG                       ASP   
                       |                         |                  
   --MTP-STATUS ind.-->|------DUPU Message ----->|--MTP-STATUS ind.--> 
                       |                         | 

6.0 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 runs on top of SCTP.  SCTP [6] provides certain transport related
security features, such as some protection against:

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

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

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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 should be used instead.  
Regardless of which level performs the encryption, the IPSEC ISAKMP 
service should be used for key management.

7.0 IANA Considerations

A request will be made to IANA to assign an M3UA value for the Payload 
Protocol Identifier in SCTP Payload Data chunk.  The following SCTP 
Payload Protocol Identifier will be registered:

        M3UA    tbd

The SCTP Payload Protocol Identifier is included in each SCTP Data 
chunk, to indicate which protocol the SCTP is carrying. 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.

8.0 Acknowledgements

The authors would like to thank John Loughney, Neil Olson, Michael 
Tuexen, Nikhil Jain, Steve Lorusso, Dan Brendes, Heinz Prantner, Barry 
Nagelberg for their valuable comments and suggestions.

9.0  References

[1] RFC 2719, "Framework Architecture for Signaling Transport"

[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"

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[5] ITU-T Recommendations Q.711-715, '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 Recommendations Q.720, 'Telephone User Part'

[9] ITU-T Recommendation Q.771-775 '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);  
     Signalling System No.7; Transaction Capabilities (TC) version 2; 
     Part 1: Protocol specification"

[12] 3G TS 25.410 V3.1.0 (2000-01) Technical Specification  3rd  
     Generation partnership Project; Technical Specification Group  
     Radio Access Network; UTRAN Iu Interface: General Aspects and  
     Principles (3G TS 25.410 Version 3.1.0 Release 1999) 

[13] Stream Control Transport Protocol <draft-ietf-sigtran-sctp- 
     13.txt>, July 2000, Work in Progress
 
[14] ITU-T Recommendations Q.701-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] MTP2-User Adaptation Layer <draft-ietf-sigtran-m2ua-01.txt>, Nov.  
     1999, Work in Progress

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[20] ITU-T Recommendation Q.2210 'B-ISDN MTP'

[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.

10.0  Author's Addresses

Lyndon Ong
Nortel Networks
4401 Great America Pkwy
Santa Clara, CA, USA  95054
long@nortelnetworks.com

Greg Sidebottom
Nortel Networks
3685 Richmond Rd,
Nepean, Ontario, Canada  K2H 5B7
gregside@nortelnetworks.com

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

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

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

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

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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

This draft expires December 2000.



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