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Network Working Group Malleswar Kalla
INTERNET-DRAFT Selvam Rengasami
Telcordia Technologies
Ken Morneault
Cisco Systems
Greg Sidebottom
Nortel Networks
Expires in six months March 2000
ISDN Q.921-User Adaptation Layer
<draft-ietf-sigtran-iua-02.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
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Abstract
This Internet Draft defines a protocol for backhauling of ISDN Q.921
User messages over IP using the Simple Control Transmission Protocol
(SCTP). This protocol would be used between a Signaling Gateway (SG)
and Media Gateway Controller (MGC). It is assumed that the SG receives
ISDN signaling over a standard ISDN interface.
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Internet Draft ISDN Q.921 User Adaptation Layer Mar 2000
TABLE OF CONTENTS
1. Introduction.....................................................3
1.1 Scope.........................................................3
1.2 Terminology...................................................3
1.3 Signaling Transport Architecture..............................4
1.4 Services Provided by the IUA Layer............................8
1.5 Functions Implemented by the IUA Layer.......................10
1.6 Definition of IUA Boundaries.................................11
2. Protocol Elements...............................................12
2.1 Common Message Header........................................12
2.2 IUA Message Header...........................................13
2.3 Description of Messages......................................14
3. Procedures......................................................24
3.1 Procedures to Support Service in Section 1.4.1...............24
3.2 Procedures to Support Service in Section 1.4.2...............24
3.3 Procedures to Support Service in Section 1.4.3...............25
4. Examples.........................................................32
4.1 Establishment of associations between SG and MGC examples.....32
4.2 ASP Traffic Fail-over Examples................................34
4.3 Q.921/Q.931 primitives backhaul Examples......................36
4.4 Layer Management Communication Examples.......................37
5. Security........................................................37
5.1 Threats.......................................................37
5.2 Protecting Confidentiality ...................................38
6. IANA Considerations.............................................38
7. Acknowledgements................................................38
8. References......................................................39
9. Author's Addresses..............................................39
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Internet Draft ISDN Q.921 User Adaptation Layer Mar 2000
1. Introduction
In this document, the term Q.921 user refers to an upper layer which
uses the services of Q.921, not the user side of ISDN interface.
Examples of the upper layer would be Q.931 and QSIG.
This section describes the need for ISDN Q.921 User Adaptation (IUA)
layer protocol as well as how this protocol shall be implemented.
1.1 Scope
There is a need for Switched Circuit Network (SCN) signaling protocol
delivery from an ISDN Signaling Gateway (SG) to a Media Gateway
Controller (MGC). The delivery mechanism should meet the following
criteria
* Support for transport of the Q.921 / Q.931 boundary primitives
* Support for communication between Layer Management modules on SG
and MGC
* Support for management of active associations between SG and MGC
This draft supports both ISDN Primary Rate Access (PRA) as well as
Basic Rate Access (BRA) including the support for both point-to-point
mode and point-to-multipoint modes of communication. QSIG adaptation
layer requirements do not differ from Q.931 adaptation layer, hence
the procedures described in this draft are also applicable to QSIG
adaptation layer. For simplicity, only Q.931 will be mentioned in the
rest of this document.
1.2 Terminology
Interface - For the purposes of this document an interface supports the
relevant ISDN signalling channel. This signalling channel may be a
16 kbps D channel for an ISDN BRA as well as 64 kbps primary or backup
D channel for an ISDN PRA. For QSIG, the signalling channel is a Qc
channel.
Q.921-User - Any protocol normally using the services of the ISDN
Q.921 (e.g., Q.931, QSIG, etc.).
Backhaul - A SG terminates the lower layers of an SCN protocol and
backhauls the other layer to MGC for call processing. For the purposes
of this draft the SG terminates Q.921 and backhauls Q.931 to MGC.
Association - An association refers to a SCTP association. The
association will provide the transport for the delivery of Q.921-User
protocol data units and IUA adaptation layer peer messages.
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Stream - A stream refers to a SCTP stream. For the purposes of this
document, a stream will be mapped to an ISDN signalling channel.
Application Server (AS) - A logical entity serving a specific
application instance. An example of an Application Server is a MGC
handling the Q.931 and call processing for D channels terminated by
the Signaling Gateways. Practically speaking, an AS is modeled at
the SG as an ordered list of one or more related Application Server
Processes (e.g., primary, secondary, tertiary).
Application Server Process (ASP) - A process instance of an Application
Server. Examples of Application Server Processes are primary or backup
MGC instances.
Application Server Process Path (ASP Path or just Path) - A Path to a
remote Application Server Process instance. A Path maps 1:1 to an SCTP
association.
Fail-over - The capability to re-route signalling traffic as required
between related ASPs in the event of failure or unavailability of the
currently used ASP (e.g. from primary MGC to back-up MGC). Fail-over
also applies upon the return to service of a previously unavailable
process.
Network Byte Order: Most significant byte first, a.k.a Big Endian.
Host - The computing platform that the ASP process is running on.
Stream - A stream refers to an SCTP stream.
1.3 Signaling Transport Architecture
The architecture that has been defined [5] for SCN signaling transport
over IP uses multiple components, including an IP transport
protocol, a signaling common transport protocol and an adaptation
module to support the functions expected by a particular SCN signaling
protocol from its underlying protocol layer.
This document defines an adaptation module that is suitable for the
transport of ISDN Q.921 User (Q.931).
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1.3.1 Example - SG to MGC
In a Signaling Gateway, it is expected that the ISDN signaling is
received over a standard ISDN network termination. The SG then
provides interworking of transport functions with IP Signaling
Transport, in order to transport the Q.931 signaling messages to the
MGC where the peer Q.931 protocol layer exists, as shown below
****** ISDN ****** IP *******
* EP *---------------* SG *--------------* MGC *
****** ****** *******
+-----+ +-----+
|Q.931| (NIF) |Q.931|
+-----+ +----------+ +-----+
| | | | IUA| | IUA |
| | | +----+ +-----+
|Q.921| |Q.921|SCTP| |SCTP |
| | | +----+ +-----+
| | | |UDP | | UDP |
| | | +----+ +-----+
| | | | IP + | IP |
+-----+ +-----+----+ +-----+
NIF - Nodal Interworking Function
EP - ISDN End Point
SCTP - Simple Control Transmission Protocol (Refer to [3])
IUA - ISDN User Adaptation Layer Protocol
1.3.2 Signaling Network Architecture
A Signaling Gateway is used to support the transport of Q.921-User
signaling traffic to one or more distributed ASPs (e.g., MGCs).
Clearly, the IUA protocol description cannot in itself meet any
performance and reliability requirements for such transport. A
physical network architecture is required, with data on the
availability and transfer performance of the physical nodes involved
in any particular exchange of information. However, the IUA protocol
must be flexible enough allow its operation and management in a
variety of physical configurations that will enable Network Operators
to meet their performance and reliability requirements.
To meet the stringent ISDN signaling reliability and performance
requirements for carrier grade networks, these Network Operators
should ensure that there is no single point of failure provisioned
in the end-to-end network architecture between an ISDN node and an IP
ASP.
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Depending of course on the reliability of the SG and ASP functional
elements, this can typically be met by the provision of redundant
QOS-bounded IP network paths for SCTP Associations between SCTP End
Points, and redundant Hosts, and redundant SGs. The distribution of
ASPs within the available Hosts is also important. For a particular
Application Server, the related ASPs should be distributed over at
least two Hosts.
An example physical network architecture relevant to carrier-grade
operation in the IP network domain is shown in Figure 1 below:
Host1
******** **************
* *_________________________________________* ******** *
* * _________* * ASP1 * *
* SG1 * SCTP Associations | * ******** *
* *_______________________ | * *
******** | | **************
| |
******** | |
* *_______________________________|
* * |
* SG2 * SCTP Associations |
* *____________ |
* * | | Host2
******** | | **************
| |_________________* ******** *
|____________________________* * ASP1 * *
* ******** *
* *
**************
.
.
.
Figure 2 - Physical Model Example
For carrier grade networks, Operators should ensure that under failure
or isolation of a particular ASP, stable calls are not lost. This
implies that ASPs need, in some cases, to share the call state or be
able to pass the call state between each other. However, this sharing
or communication is outside the scope of this document.
1.3.3 ASP Fail-over Model and Terminology
The IUA supports ASP fail-over functions in order to support a high
availability of call processing capability. All Q.921-User messages
incoming to an SG are assigned to a unique Application Server, based
on the Interface Identifier of the message.
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The Application Server is in practical terms a list of all ASPs
currently registered to process Q.921-User messages from certain
Interface Identifiers. 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. Note that 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.
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 from a particular D Channel
could be sent to ASP1 in Host1 or ASP1 in Host2. The AS list at SG1
might look like this:
Interface Identifiers - 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 for the Interface Identifiers registered. 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 IUA peer
is ready.
The AS List at SG1 might also be set up in loadshare mode:
Interface Identifier {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.
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.
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1.3.4 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
IUA is 9900.
1.4 Services Provided by the IUA Layer
1.4.1 Support for transport of Q.921/Q.931 boundary primitives
In the backhaul scenario, the Q.921/Q.931 boundary primitives are
exposed. IUA layer needs to support all of the primitives of this
boundary to successfully backhaul Q.931.
This includes the following primitives [1]
DL-ESTABLISH
The DL-ESTABLISH primitives are used to request, indicate and confirm
the outcome of the procedures for establishing multiple frame
operation.
DL-RELEASE
DL-RELEASE primitives are used to request, indicate, and confirm the
outcome of the procedures for terminating a previously established
multiple frame operation, or for reporting an unsuccessful
establishment attempt.
DL-DATA
The DL-DATA primitives are used to request and indicate SDUs
containing Q.931 PDUs which are to be transmitted, or have been
received, by the Q.921 layer using the acknowledged information
transfer service.
DL-UNIT DATA
The DL-UNIT DATA primitives are used to request and indicate SDUs
containing Q.931 PDUs which are to be transmitted, by the Q.921 layer
using the unacknowledged information transfer service.
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1.4.2 Support for communication between Layer Management modules
on SG and MGC
It is envisioned that the IUA layer needs to provide some services
that will facilitate communication between Layer Management modules on
the SG and MGC. These primitives are pointed out in [2], which are
shown below
MIUA-TEI STATUS
The MIUA-TEI STATUS primitives are used to request, confirm and
indicate the status (in service/out of service) of a TEI.
To facilitate reporting of errors that arise because of backhauling
Q.931 scenario, the following primitive is defined
M-ERROR
The M-ERROR primitive is used to indicate an error with a received
IUA message (e.g., interface identifier value is not known to the SG).
1.4.3 Support for management of active associations between SG and MGC
The IUA layer on the SG keeps the state of various ASPs it is
associated with. A set of primitives between IUA layer and the Layer
Management are defined below to help the Layer Management manage the
association(s) between SG and MGC.
The IUA layer can be instructed by the Layer Management to establish
SCTP association to a peer IUA node. This can be achieved using the
following primitive
M-SCTP ESTABLISH
The M-SCTP ESTABLISH primitives are used to request, indicate, and
confirm the establishment of SCTP association to a peer IUA node.
The IUA layer may also need to inform the status of the SCTP
associations to the Layer Management. This can be achieved using the
following primitive
M-SCTP STATUS
The M-SCTP STATUS primitives are used to request and indicate the
status of the underlying SCTP association(s).
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The Layer Management may need to inform the IUA layer of a user status
(i.e., failure, active, etc.), so that messages can be exchanged
between IUA layer peers to stop traffic to the local IUA user. This
can be achieved using the following primitive.
M-ASP STATUS
The M-ASP STATUS primitives are used to request and indicate the
status of the Application Server Process.
1.5 Functions Implemented by the IUA Layer
1.5.1 Mapping
The IUA layer must maintain a map of the Interface ID to a physical
interface on the Signaling Gateway. A physical interface would
be a T1 line, E1 line, etc. In addition, for a given interface the SG
must be able to identify the associated signalling channel. IUA
layers on both SG and MGC need to maintain the status of TEIs, SAPIs.
1.5.2 Status of ASPs
The IUA layer on the SG must maintain the state of various ASPs it is
associated with. The state of an ASP changes because of reception of
peer-to-peer messages or reception of indications from the local SCTP
association. ASP state transition procedures are described in
section 3.3.1.
1.5.3 SCTP Stream Management
SCTP allows a user specified number of streams to be opened during the
initialization. It is the responsibility of the IUA layer to ensure
proper management of these streams. Because of the unidirectional
nature of streams, IUA layers are not aware of the stream information
from the peer IUA layers. For the purposes of this draft, it is
assumed that a separate stream will be used for each D channel.
1.5.4 Seamless Network Management Interworking
The IUA layer on the SG should pass an indication of unavailability of
the IUA-User (Q.931) to the local Layer Management, if the currently
active ASP moves from the ACTIVE state. The Layer Management could
instruct Q.921 to take some action, if it deems appropriate.
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1.5.5 Management Inhibit/Uninhibit
Local Management 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 manage the start of traffic on to a newly
available SCTP association.
1.5.6 Active Association Control
At an SG, an Application Server list may contain active and inactive
ASPs to support ASP loads-haring and fail-over procedures. When, for
example, both a primary and a back-up ASP are available, IUA peer
protocol is required to control which ASP is currently active. The
ordered list of ASPs within a logical Application Server is kept
updated in the SG to reflect the active Application Server
Process(es).
1.6 Definition of IUA Boundaries
1.6.1 Definition of IUA/Q.921 boundary
DL-ESTABLISH
DL-RELEASE
DL-DATA
DL-UNIT DATA
1.6.2 Definition of IUA/Q.931 boundary
DL-ESTABLISH
DL-RELEASE
DL-DATA
DL-UNIT DATA
1.6.3 Definition of SCTP/IUA Boundary
The upper layer primitives provided by SCTP are available in
Reference [3] section 9.
1.6.4 Definition of IUA/Layer-Management Boundary
M-ERROR
M-NOTIFY
M-SCTP ESTABLISH
M-SCTP STATUS
M-ASP STATUS
MIUA-TEI STATUS
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2. Protocol Elements
This section describes the format of various messages used in this
protocol.
2.1 Common Message Header
The protocol messages for Q.921 User Adaptation require a message
header which contains the adaptation layer version, the message type,
and message length. All types of messages contain this header. This
message header is common among all SCN signaling 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 | Spare | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 Common Header Format
All fields in an IUA message MUST be transmitted in the network byte
order, unless otherwise stated.
2.1.1 Version
The version field (vers) contains the version of the IUA adaptation
layer. The supported versions are:
0000 0001 Release 1.0 protocol
2.1.2 Message Types
The valid message types are defined in Section 2.2.2 and the message
contents are described in Section 2.3. Each message can contain
parameters.
The following list contains the message names for the defined
messages.
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Q.921/Q.931 Boundary Primitives Transport (QAUP) Messages
Data Request Message 0501
Data Indication Message 0502
Unit Data Request Message 0503
Unit Data Indication Message 0504
Establish Request 0505
Establish Confirm 0506
Establish Indication 0507
Release Request 0508
Release Confirm 0509
Release Indication 0510
Application Server Process Maintenance (ASPM) messages
ASP Up 0301
ASP Down 0302
ASP Active 0401
ASP Inactive 0402
Management (MGMT) Messages
Error Indication 0000
Notify 0001
TEI Status Request 0101
TEI Status Confirm 0102
TEI Status Indication 0103
2.1.3 Message Length
The Message length defines the length of the message in octets, not
including the common Message header.
2.2 IUA Message Header
In addition to the common message header, there will be a specific
message header for QAUP and TEI related MGMT messages. The IUA
message header will immediately follow the common message header in
these messages.
This message header will contain the Interface Identifier and Data
Link Connection Identifier(DLCI). The Interface Identifier identifies
the physical interface terminating the signalling channel at the SG
for which the signaling messages are sent/received. The format of the
Interface Identifier 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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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 (0x1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DLCI | Spare |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 IUA Message Header
The Tag value for Interface Identifier is 0x1. The length is always
set to a value of 4.
The DLCI format is shown below in Figure 3.
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+-----+-----+-----+-----+
| 0 | SPR | SAPI |
+-----------------------------------------------+
| 1 | TEI |
+-----------------------------------------------+
Figure 3 DLCI Format
SPR Spare, 2nd bit in octet 1
SAPI Service Access Point Identifier, 3rd thru 8th bits in octet 1
TEI Terminal Endpoint Identifier, 2nd thru 8th bits in octet 2
The DLCI field (including the SAPI and TEI) is coded in accordance
with Q.921.
2.3 IUA Messages
The following section defines the messages and parameter contents.
The IUA messages will use the common message header (Figure 2) and
the IUA message header (Figure 3).
2.3.1 Q.921-User Backhauled Messages
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2.3.1.1 Establish Messages (Request, Confirm, Indication)
The Establish Messages are used to establish a data link on the
signalling channel or to confirm that a data link on the signalling
channel has been established.
The Establish messages contain the common message header followed by
IUA message header. It does not contain any additional parameters.
2.3.1.2 Release Messages (Request, Indication, Confirmation)
The Release Request message is used to release the data link on the
signalling channel. The Release Confirm and Indication messages are
used to indicate that the data link on the signaling channel has
been released.
The Release messages contain the common message header followed by
IUA message header. The Release confirm message is in response to
a Release Request message and it does not contain any additional
parameters. The Release Request and Indication messages contain the
following parameters
REASON
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The valid values for Reason are shown in the following table.
Define Value Description
RELEASE_MGMT 0x0 Management layer generated release.
RELEASE_PHYS 0x1 Physical layer alarm generated release.
RELEASE_DM 0x2 Specific to a request. Indicates Layer 2
should release and deny all requests from
far end to establish a data link on the
signalling channel (i.e. if SABME is
received send a DM)
RELEASE_OTHER 0x3 Other reasons
Note Only RELEASE_MGMT, RELEASE_DM and RELEASE_OTHER are valid
reason codes for a Release Request message.
2.3.1.3 Data Messages (Request, Indication)
The Data message contains an ISDN Q.921-User Protocol Data Unit (PDU)
corresponding to acknowledged information transfer service.
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The Data messages contain the common message header followed by IUA
message header. The Data message contains the following parameters
PROTOCOL DATA
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The protocol data contains upper layer signalling message e.g.
Q.931, QSIG.
2.3.1.4 Unit Data Messages (Request, Indication)
The Unit Data message contains an ISDN Q.921-User Protocol Data Unit
(PDU) corresponding to unacknowledged information transfer service.
The Unit Data messages contain the common message header followed by
IUA message header. The Unit Data message contains the following
parameters
PROTOCOL DATA
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.3.2 Application Server Process Maintenance (ASPM) Messages
The ASPM messages will only use the common message header.
2.3.2.1 ASP UP (ASPUP)
The ASP UP (ASPUP) message is used to indicate to a remote IUA peer
that the Adaptation layer is ready to receive traffic or maintenance
messages.
The ASPUP message contains the following parameters:
Adaptation Layer 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 (0x2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Adaptation Layer Identifier* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Adaptation Layer Identifier (ALI) is a string that identifies the
adaptation layer. This string must be set to "IUA". 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.
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
for debugging purposes.
Note: Strings are padded to 32-bit boundaries. The length field
indicates the end of the string.
2.3.2.2 ASP Down (ASPDN)
The ASP Down (ASPDN) message is used to indicate to a remote IUA peer
that the adaptation layer is not ready to receive traffic or
maintenance messages.
The ASPDN message contains the following parameters:
Reason
INFO String (Optional)
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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 (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is
the same as for the ASP Up message (See Section 2.3.2.1.)
The Reason parameter indicates the reason that the remote IUA
adaptation layer is unavailable. The valid values for Reason are
shown in the following table.
Value Description
0x1 Management Inhibit
2.3.2.3 ASP Active (ASPAC)
The ASPAC message is sent by an ASP to indicate to an SG that it is
Active and ready to be used.
The ASPAC message contains the following parameters:
Type
Interface Identifier (Optional)
INFO String (Optional)
The format for the ASPAC message is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xx) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifiers* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | 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
0x3 New traffic
Within a particular Interface Identifier, 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
ASPs in the AS. In loadshare mode, the ASP will share in the
traffic distribution with any other currently active ASPs. In New
traffic mode the ASP wishes to take on traffic in the AS but does
not expect to receive messages related to calls that are pending
completion in another ASP
The optional Interface Identifiers parameter contains a list of
Interface Identifier integers indexing the Application Server traffic
that the sending ASP is configured/registered to receive. There is
one-to-one relationship between an Interface Identifier and an AS
Name.
An SG that receives an ASPAC with an incorrect type for a particular
Interface Identifier will respond with an Error Message.
The format and description of the optional Info String parameter is the
same as for the ASP Up message (See Section 2.3.2.1.)
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2.3.2.4 ASP Inactive (ASPIA)
The ASPIA message is sent by an ASP to indicate to an SG that it is no
longer an active ASP to be used from within a list of ASPs. The SG will
respond with an ASPIA message and either discard incoming messages or
buffer for a timed period and then discard.
The ASPIA message contains the following parameters:
Type
Interface Identifiers (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 (0xx) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifiers* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | 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
0x3 Graceful Withdrawal
The format and description of the optional Interface Identifiers and
Info String parameters is the same as for the ASP Active message (See
Section 2.3.2.3.)
2.3.3 Layer Management (MGMT) Messages
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2.3.3.1 Error (ERR)
The ERR message is sent when an invalid value is found in an incoming
message.
The ERR message contains the following parameters:
Error Code
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 (0xx) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Diagnostic Information* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 Interface Identifier 0x2
Invalid Adaptation Layer Identifier 0x3
Invalid Message Type 0x4
Invalid Stream Identifier 0x5
Invalid TEI 0x6
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 Version Error Code the
Diagnostic information includes the supported Version parameter. In
the other cases, the Diagnostic information may be the first 40 bytes
of the offending message.
2.3.3.2 Notify (NTFY)
The Notify message used to provide autonomous notification of IUA
events.
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The NTFY message contains the following parameters:
Status Type
Status Identification
Interface Identifiers (Optional)
INFO String (Optional)
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 (0xx) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifiers* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Status Type parameter identifies the type of the Notify message.
Following are the valid Status Type values:
Value Description
0x1 Application Server state change (AS_State_Change)
0x2 Application Server Process state change (ASP_State_Change)
0x3 Other
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:
Value Description
0x1 Application Server Down (AS_Down)
0x2 Application Server Up (AS_Up)
0x3 Application Server Active (AS_Active)
0x4 Application Server Pending (AS_Pending)
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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.
If the Status type is ASP_State_Change, the Status Information
values are:
Value Description
0x1 Application Server Process (ASP) Down
0x2 Application Server Process (ASP) Up
0x3 Application Server Process (ASP) Active
These notifications are sent from an SG to an ASP upon a change in
status of a particular Application Server process within the ASP
list of a particular Application Server. The value reflects the new
state of the Application Server Process.
If the Status Type is Other, then the following Status Information
values are defined:
Value Description
0x1 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 Interface Identifiers and
Info String parameters is the same as for the ASP Active message
(See Section 2.3.2.3.)
2.3.3.3 TEI Status Messages (Request, Confirm and Indication)
The TEI Status messages are exchanged between IUA layer peers to
request, confirm and indicate the status of a particular TEI.
The TEI Status messages contain the common message header followed by
IUA message header. The TEI Status Request message does not contain
any additional parameters.
The TEI Status Indication, and Confirm messages contain the following
parameters
STATUS
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The valid values for Status are shown in the following table.
Define Value Description
IN_SERVICE 0x0 TEI is in service
OUT_OF_SERVICE 0x1 TEI is out of service
3.0 Procedures
The IUA layers needs to respond to various primitives it receives from
other layers as well as messages it receives from the peer-to-peer
messages. This section describes various procedures involved in
response to these events.
3.1 Procedures to support service in section 1.4.1
These procedures achieve the IUA layer's "Transport of Q.921/Q.931
boundary" service.
3.1.1 Q.921 or Q.931 primitives procedures
On receiving these primitives from the local layer, the IUA layer will
send the corresponding QAUP message (Data, Unit Data, Establish,
Release) to its peer. While doing so, the IUA layer needs to fill
various fields of the common and specific headers correctly. In
addition the message needs to be sent on the SCTP stream that
corresponds to the D channel.
3.1.2 QAUP message procedures
On receiving QAUP messages from a peer IUA layer, the IUA layer on an
SG or MGC needs to invoke the corresponding layer primitives
(DL-ESTABLISH, DL-DATA, DL-UNIT DATA, DL-RELEASE) to the local Q.921
or Q.931 layer.
3.2 Procedures to support service in section 1.4.2
These procedures achieve the IUA layer's "Support for Communication
between Layer Managements" service.
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3.2.1 Layer Management primitives procedures
On receiving these primitives from the local layer, the IUA layer will
send the corresponding MGMT message (TEI Status, Error) to its peer.
While doing so, the IUA layer needs to fill various fields of the
common and specific headers correctly.
3.2.2 MGMT message procedures
On receiving MGMT messages the IUA layer needs to invoke the
corresponding Layer Management primitives (MIUA-TEI STATUS, M-ERROR)
to the local layer management.
3.3 Procedures to support service in section 1.4.3
These procedures achieve the IUA layer's "Support for management of
active associations between SG and MGC" service.
3.3.1 State Maintenance
The IUA layer on the SG needs to maintain the states of each ASP as
well as the state of the AS.
3.3.1.1 ASP States
The state of the each ASP, in each AS that it is configured, is
maintained in the IUA layer on the SG. The state of an ASP changes
due to events. The events include
* Reception of messages from peer IUA layer at that ASP
* Reception of some messages from the peer IUA layer at other
ASPs in the AS
* Reception of indications from 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: Application Server Process is unavailable and/or the SCTP
association is down. Initially all ASPs will be in this state.
ASP-UP: The remote IUA peer at the ASP is available (and the SCTP
association is up) but application traffic is stopped.
ASP-ACTIVE: The remote IUA peer at the ASP is available and
application traffic is active.
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ASP-ACT-OLD: The remote IUA peer at the ASP is available and
application traffic is active, but for draining of current
calls only (i.e., no new calls)
ASP-ACT-NEW: The remote IUA peer at the ASP is available and
application traffic is active, but for new calls only (i.e., not for
traffic related to completing calls in another ASP).
Figure 4: ASP State Transition Diagram
+-------------+
|----------------------| |
| ASPIA (GW)/ ____| ASP-ACTIVE |<--------\
| Some other / +-------------+ |
| ASPAC (NT) / ^ | | Ts
| / ASPAC | | ASPIA |
| / (LS,OR) | | (LS,OR) |
| V | v |
| +-------------+ +-------------+ +-------------+
| | | | | | |
| | ASP-ACT-OLD |----->| ASP-UP |------>| ASP-ACT-NEW |
| +-------------+ Ts / +-------------+ ASPAC +-------------+
| | ASPIA ^ | (NT) |
|<---| | | |
| | | |
ASPDN/ | ASPUP | | ASPDN/ |
SCTP CDI | | | SCTP CDI | ASPDN/
| | v | SCTP
| +-------------+ | CDI
| | | |
|------------------>| |<-------------|
| ASP-DOWN |
+-------------+
SCTP CDI: The local SCTP layer's Communication Down Indication to the
Upper Layer Protocol (IUA) 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
Operator on a per AS basis.
LS : Value of Type parameter in ASPIA and ASPAC messages is
equal to Load-share.
OR : Value of Type parameter in ASPIA and ASPAC messages is
equal to Over-ride.
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NT : Value of Type parameter in ASPAC message is equal to
New traffic.
GW : Value of Type parameter in ASPIA message is equal to
Graceful withdrawal.
3.3.1.2 AS States
The state of the AS is maintained in the IUA 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).
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.
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Figure 5: AS State Transition Diagram
+----------+ one ASP trans ACTIVE +-------------+
| |------------------------>| |
| AS-UP | | AS-ACTIVE |
| | | |
| |< -| |
+----------+ \ / +-------------+
^ | \ Tr Trigger / ^ |
| | \ at least one / | |
| | \ ASP in UP / | |
| | \ / | |
| | \ / | |
| | \ /---/ | |
one ASP | | \ / one ASP | | Last ACTIVE ASP
trans | | all ASP \-/----\ trans to | | trans to UP or
to UP | | trans to / \ ACTIVE | | DOWN
| | DOWN / \ | |
| | / \ | |
| | / \ | |
| | /all ASP \ | |
| v / trans to \ | v
+----------+ / DOWN \ +-------------+
| |<--/ -| |
| AS-DOWN | | AS-PENDING |
| | | (queueing) |
| |<------------------------| |
+----------+ Tr Trigger no ASP +-------------+
in UP state
Tr = Recovery Timer
3.3.2 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 IUA layer at an ASP receives an M-SCTP
ESTABLISH request primitive from the Layer Management, the IUA layer
will try to establish an SCTP association with the remote IUA peer at
an SG. Upon reception of an eventual SCTP-Communication Up confirm
primitive from the SCTP, the IUA layer will invoke the primitive
M-SCTP ESTABLISH confirm to the Layer Management.
At the SG, the IUA layer will receive an SCTP Communication Up
indication primitive from the SCTP. The IUA layer will then invoke
the primitive M-SCTP ESTABLISH indication to the Layer Management.
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Once the SCTP association is established, The IUA layer at an ASP
will then find out the state of its local IUA-user from the Layer
Management using the primitive M-ASP STATUS. Based on the status of
the local IUA-User, the local ASP IUA 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 3.3.3.
If the IUA 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 ASP will be moved to "Down" at both the SG and ASP.
At an ASP, the Layer Management may try to reestablish the SCTP
association using M-SCTP ESTABLISH request primitive.
3.3.3 ASPM procedures for peer-to-peer messages
All ASPM messages are sent on a sequenced stream to ensure ordering.
SCTP stream 0 is used.
3.3.3.1 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 IUA 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 locked-out for local management reasons, the SG marks the remote
ASP as Up. The SG responds with an Notify (ASP-Up) message to the
ASP in acknowledgement. The SG sends a Notify (ASP-Up) message in
response to a received ASP-Up message from the ASP even if the ASP is
already marked as Up at the SG.
If for any local reason the SG cannot respond with an ASP-Up, the SG
responds to a ASP-Up with a ASP-Down message.
At the ASP, the Notify (ASP-Up) 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 a Notify (ASP-Up) message from the
SG. The ASP may decide to reduce the frequency (say to every 5
seconds) if a Notify (ASP-Up) is not received after a few tries.
The ASP must wait for the Notify (ASP-Up) 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.
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3.3.3.1.1 IUA Version Control
If a 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.
3.3.3.2 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 Notify (ASP-Down) 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 a Notify (ASP-Down) 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 a ASP-Down 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 is not
received after a few tries.
3.3.3.3 ASP-Active
Any time after the ASP has received a Notify (ASP-Up) acknowledgement
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 Interface Identifiers 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 Notify message acknowledging that the ASPAC was received
and starts sending traffic for the associated Application Server(s)
to that ASP.
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There are three modes of Application Server traffic handling in the SG
IUA - Over-ride, Load-balancing and New Traffic. The Type parameter
in the ASPAC messge 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, reception of an ASPAC message at
an SG causes the redirection of all traffic for the AS to the ASP
which sent the ASPAC. Any previously active ASP in the AS is now
considered Inactive and will no longer receive traffic within the AS.
The SG responds to the ASPAC with a Notify (ASP-Active) message to
the ASP. The SG sends a Notify (ASP-Inactive) to any previously
active ASP in the AS.
In the case of a Loadshare 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 loadsharing 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, such as Interface ID, depending on the requirements of the
application and the call state handling assumptions of the collection
of ASPs in the AS. The SG responds to the ASPAC with a Notify
(ASP-Active) message to the ASP.
In the case of a New Traffic mode AS, reception of an ASPAC message
at an SG causes the direction of traffic to the ASP sending the ASPAC.
However, traffic related to completing calls in another ASP is not
sent to the new ASP (i.e., new calls only). How an SG accomplishes
the differentiation of old and new calls and any loadsharing of
traffic is application and implementation dependent. The SG responds
to the ASPAC with a Notify (ASP-Active_New) message to the ASP. After
a configurable time Ts, the ASP is moved to the ASP-Active state and
a Notify (ASP-Active) is sent to the ASP.
3.3.3.4 ASP Inactive
When an ASP wishes to withdraw from receiving traffic 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 Interface Ids to indicate for which Application Servers the
ASPIA applies.
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There are three modes of Application Server traffic handling in the SG
IUA when withdrawing an ASP from service - Over-ride, Load-balancing
and Graceful Withdrawal. The Type parameter in the ASPIA messge
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 which sent the ASPIA is already considered by the SG to be
Inactive. A Notify (ASP_Up) message is resent to the ASP.
In the case of a Loadshare mode AS, the SG moves the ASP to the
Inactive state and the AS traffic is re-allocated across the
remaining active ASPs per the loadsharing algorithm currently used
within the AS. A Notify (ASP-Up) message is sent to the ASP after the
traffic is halted to the ASP.
In the case of Graceful Withdrawal, the SG diverts all traffic related
to new calls to other active ASPs and therafter sends only traffic
related to incomplete calls to the ASP. A Notify (ASP-Act_Old) is
sent to the ASP and the ASP is moved to the Active_Old state. When
the outstanding calls are drained, or after a configurable time Ts,
the SG moves the ASP to the Up state and sends a Notify (ASP-Up)
message to the ASP.
If no other ASPs are Active in the Application Server, the SG either
discards all incoming messages (except messages related to an
Active_Old ASP) 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. Examples
4.1 Establishment of Association and Traffic between SGs and ASPs
4.1.1 Single ASP in an Application Server (1+0 sparing)
This scenario shows the example IUA 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.
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SG ASP1
|
|<---------ASP Up----------|
|------NTFY (ASP-Up)------>|
| - |
|<-------ASP Active--------|
|----NTFY (ASP_Active)---->|
| |
4.1.2 Two ASPs in Application Server (1+1 sparing)
This scenario shows the example IUA 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 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----------| |
|------NTFY (ASP-Up)----->| |
| | |
|<-----------------------------ASP Up----------------|
|----------------------------NTFY (ASP-Up)---------->|
| | |
| | |
|<-------ASP Active-------| |
|----NTFY(ASP-Active)---->| |
| | |
4.1.3 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 loadshare the traffic load. In this
case, one ASP is sufficient to handle the total traffic load.
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SG ASP1 ASP2
| | |
|<---------ASP Up---------| |
|-------NTFY(ASP-Up)----->| |
| | |
|<------------------------------ASP Up---------------|
|-----------------------------NTFY(ASP Up)---------->|
| | |
| | |
|<--ASP Active (Ldshr)----| |
|----NTFY(ASP-Active)---->| |
| | |
|<----------------------------ASP Active (Ldshr)-----|
|-----------------------------NTFY(ASP-Active)------>|
| | |
4.1.4 Three ASPs in an Application Server (n+k sparing, load-sharing
case)
This scenario shows the example IUA 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-------| | |
|----NTFY(ASP-Up)--->| | |
| | | |
|<--------------------------ASP Up-------| |
|------------------------NTFY(ASP-Up)--->| |
| | | |
|<---------------------------------------------ASP Up--------|
|--------------------------------------------NTFY(ASP-Up)--->|
| | | |
| | | |
|<-ASP Act. (Ldshr)--| | |
|---NTFY(ASP-Act.)-->| | |
| | | |
|<--------------------ASP Act. (Ldshr)---| |
|----------------------NTFY(ASP-Act.)--->| |
| | | |
4.2 ASP Traffic Fail-over Examples
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Internet Draft ISDN Q.921 User Adaptation Layer Mar 2000
4.2.1 (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-------| |
|---NTFY(ASP Inactive)--->| |
|--------------------NTFY(ASP-Inactive) (Optional)-->|
| | |
|<------------------------------ ASP Active----------|
|-----------------------------NTFY(ASP-Active)------>|
| |
Note: If the SG detects loss of the IUA peer (IUA heartbeat loss or
detection of SCTP failure), the initial SG-ASP1 ASP Inactive message
exchange would not occur.
4.2.2 (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----------|
|-----------------------------NTFY(ASP-Active)------>|
|----NTFY(ASP-Inactive)-->|
| | |
4.2.3 (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.-----| | |
|--NTFY(ASP-Inact.)->| | |
| | | |
|---------------------------------NTFY(Ins. ASPs)(Optional)->|
| | | |
|<-----------------------------------------ASP Act. (Ldshr)--|
|-------------------------------------------ASP Act. (Ack)-->|
| | | |
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Internet Draft ISDN Q.921 User Adaptation Layer Mar 2000
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 loadshare AS and n currently equals 1.
Note: If the SG detects loss of the ASP1 IUA peer (IUA heartbeat loss
or detection of SCTP failure), the first SG-ASP1 ASP Inactive message
exchange would not occur.
4.3 Q.921/Q.931 primitives backhaul Examples
An example of the message flows for establishing a data link on a
signalling channel, passing PDUs and releasing a data link on a
signalling channel is shown below. An active association between MGC
and SG is established (section 4.1) prior to the following message
flows.
SG MGC
<----------- Establish Request
Establish Response ---------->
<----------- Data Request
Data Indication ----------->
<----------- Data Request
Data Indication ----------->
<----------- Data Request
<----------- Data Request
Data Indication ----------->
<----------- Release Request (RELEASE_MGMT)
Release Confirm ---------->
An example of the message flows for a failed attempt to establish a
data link on the signalling channel is shown below. In this case, the
gateway has a problem with its physical connection (e.g. Red Alarm),
so it cannot establish a data link on the signalling channel.
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Internet Draft ISDN Q.921 User Adaptation Layer Mar 2000
SG MGC
<----------- Establish Request (ESTABLISH_START)
Release Indication ---------->
(RELEASE_PHYS)
4.4 Layer Management Communication Examples
An example of the message flows for communication between Layer
Management modules between SG and MGC is shown below. An active
association between MGC and SG is established (section 4.1) prior to
the following message flows.
SG MGC
<----------- Data Request
Error ---------->
(INVALID_TEI)
<----------- TEI Status
TEI Status ---------->
5.0 Security
IUA is designed to carry signaling messages for telephony services.
As such, IUA 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.
5.1 Threats
There is no quick fix, one-size-fits-all solution for security. As a
transport protocol, IUA has the following security objectives:
* Availability of reliable and timely user data transport.
* Integrity of user data transport.
* Confidentiality of user data.
IUA runs on top of SCTP. SCTP [3] provides certain transport related
security features, such as:
* Blind Denial of Service Attacks
* Flooding
* Masquerade
* Improper Monopolization of Services
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Internet Draft ISDN Q.921 User Adaptation Layer Mar 2000
When IUA 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" [6] should be consulted for guidance.
When the network in which IUA runs in involves more than one party,
it may not be reasonable to expect that all parties have implemented
security in a sufficient manner. In such a case, it is recommended
that IPSEC is used to ensure confidentiality of user payload.
Consult [7] for more information on configuring IPSEC services.
5.2 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.
6.0 IANA Considerations
A request will be made to IANA to assign an IUA value for the Payload
Protocol Identifier in SCTP Payload Data chunk. The following SCTP
Payload Protocol Identifier will be registered:
IUA 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.
7.0 Acknowledgements
The authors would like to thank Ming-te Chao, Keith Drage, Stephen
Lorusso, John Loughney, Neil Olson, Norm Glaude, Michael Tuexen,
Nikhil Jain, Dan Brendes and Heinz Prantner for their valuable
comments and suggestions.
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8.0 References
[1] ITU-T Recommendation Q.920, 'Digital Subscriber Signalling System
No. 1 (DSS1) - ISDN User-Network Interface Data Link Layer -
General Aspects'
[2] T1S1.7/99-220 Contribution, 'Back-hauling of DSS1 protocol in a
Voice over Packet Network'
[3] Simple Control Transmission Protocol,
draft-ietf-sigtran-sctp-07.txt, March 2000
[4] Media Gateway Control Protocol (MGCP),
draft-huitema-megaco-mgcp-v1-03.txt, August 1999
[5] Architectural Framework for Signaling Transport,
RFC 2719 , October 1999
[6] Site Security Handbook, RFC 2196, September 1997
[7] Security Architecture for the Internet Protocol, RFC 2401
9.0 Author's Addresses
Malleswar Kalla Tel +1-973-829-5212
Telcordia Technologies EMail kalla@research.telcordia.com
MCC 1J211R
445 South Street
Morristown, NJ 07960
USA
Selvam Rengasami Tel +1-732-758-5260
Telcordia Technologies EMail srengasa@telcordia.com
NVC-2Z439
331 Newman Springs Rd
Red Bank, NJ 07701
USA
Ken Morneault Tel +1-703-484-3323
Cisco Systems Inc. EMail kmorneau@cisco.com
13615 Dulles Technology Drive
Herndon, VA. 20171
USA
Greg Sidebottom Tel +1-613-763-7305
Nortel Networks EMail gregside@nortelnetworks.com
3685 Richmond Rd,
Nepean, Ontario
Canada K2H5B7
Kalla, Rengasami, Morneault, & Sidebottom [Page 39]
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