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rfc:rfc3331

Network Working Group K. Morneault Request for Comments: 3331 Cisco Systems Category: Standards Track R. Dantu

                                                               NetRake
                                                         G. Sidebottom
                                                 Signatus Technologies
                                                           B. Bidulock
                                                               OpenSS7
                                                              J. Heitz
                                                                Lucent
                                                        September 2002
     Signaling System 7 (SS7) Message Transfer Part 2 (MTP2) -
                       User Adaptation Layer

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

 This document defines a protocol for the backhauling of Signaling
 System 7 Message Transfer Part 2 (SS7 MTP2) User signalling messages
 over IP using the Stream Control Transmission Protocol (SCTP).  This
 protocol would be used between a Signalling Gateway (SG) and Media
 Gateway Controller (MGC).  It is assumed that the SG receives SS7
 signalling over a standard SS7 interface using the SS7 Message
 Transfer Part (MTP) to provide transport.  The Signalling Gateway
 would act as a Signalling Link Terminal.

Morneault, et. al. Standards Track [Page 1] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

Table of Contents

 1.  Introduction.............................................. 2
   1.1  Scope.................................................. 3
   1.2  Terminology............................................ 3
   1.3  M2UA Overview.......................................... 5
   1.4  Services Provided by the M2UA Adaptation Layer......... 7
   1.5  Functions Provided by the M2UA Layer................... 9
   1.6  Definition of the M2UA Boundaries..................... 12
 2.  Conventions.............................................. 16
 3.  Protocol Elements........................................ 16
   3.1  Common Message Header................................. 16
   3.2  M2UA Message Header................................... 22
   3.3  M2UA Messages......................................... 23
 4.  Procedures............................................... 58
   4.1  Procedures to Support the M2UA-User Layer............. 58
   4.2  Receipt of Primitives from the Layer Management....... 59
   4.3  AS and ASP State Maintenance.......................... 61
   4.4  Link Key Management Procedures........................ 73
 5.  Examples of MTP2 User Adaptation (M2UA) Procedures....... 75
   5.1  Establishment of associations between SGP and MGC..... 75
        examples
   5.2  ASP Traffic Fail-over Examples........................ 77
   5.3  SGP to MGC, MTP Level 2 to MTP Level 3 Boundary
        Procedures............................................ 78
 6.  Timer Values............................................. 85
 7.  Security Considerations.................................. 85
   7.1 Threats................................................ 85
   7.2 Protecting Confidentiality............................. 86
 8.  IANA Considerations...................................... 86
   8.1 SCTP Payload Protocol Identifier....................... 86
   8.2 M2UA Protocol Extensions............................... 86
 9.  Acknowledgements......................................... 87
 10. References............................................... 88
 Appendix A: Signalling Network Architecture.................. 90
 Authors' Addresses........................................... 92
 Full Copyright Statement..................................... 94

1. Introduction

 This document defines a protocol for the backhauling of SS7 [1] MTP2
 User [2] [3] [4] (i.e. MTP3) signalling messages over IP using the
 Stream Control Transmission Protocol (SCTP) [8].  This protocol would
 be used between a Signalling Gateway (SG) and Media Gateway
 Controller (MGC).

Morneault, et. al. Standards Track [Page 2] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

1.1 Scope

 There is a need for Switched Circuit Network (SCN) signalling
 protocol delivery from a Signalling Gateway (SG) to a Media Gateway
 Controller (MGC) [9].  The delivery mechanism addresses the following
 objectives:
  • Support for MTP Level 2 / MTP Level 3 interface boundary
  • Support for communication between Layer Management modules on SG

and MGC

  • Support for management of SCTP active associations between the SG

and MGC

 The SG will terminate up to MTP Level 2 and the MGC will terminate
 MTP Level 3 and above.  In other words, the SG will transport MTP
 Level 3 messages over an IP network to a MGC.

1.2 Terminology

 Application Server (AS) - A logical entity serving a specific
 application instance.  An example of an Application Server is a MGC
 handling the MTP Level 3 and call processing for SS7 links terminated
 by the Signalling 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
 active or standby MGC instances.
 Association - An association refers to a SCTP association.  The
 association will provide the transport for the delivery of protocol
 data units for one or more interfaces.
 Backhaul - Refers to the transport of signalling from the point of
 interface for the associated data stream (i.e., SG function in the
 MGU) back to the point of call processing (i.e., the MGCU), if this
 is not local [9].
 Fail-over - The capability to reroute signalling traffic as required
 to an alternate Application Server Process 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.
 Host - The computing platform that the ASP process is running on.

Morneault, et. al. Standards Track [Page 3] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 Interface - For the purposes of this document, an interface is a SS7
 signalling link.
 Interface Identifier - The Interface Identifier identifies the
 physical interface at the SG for which the signalling messages are
 sent/received.  The format of the Interface Identifier parameter can
 be text or 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.
 Layer Management - Layer Management is a nodal function in an SG or
 ASP that handles the inputs and outputs between the M2UA layer and a
 local management entity.
 Link Key - The link key is a locally unique (between ASP and SG)
 value that identifies a registration request for a particular
 Signalling Data Link and Signalling Terminal pair.
 MTP - The Message Transfer Part of the SS7 protocol
 MTP2 - MTP Level 2, the signalling data link layer of SS7
 MTP3 - MTP Level 3, the signalling network layer of SS7
 MTP2-User - A protocol that uses the services of MTP Level 2 (i.e.
 MTP3).
 Network Byte Order: Most significant byte first, a.k.a Big Endian.
 Signalling Data Link - An SDL refers to a specific communications
 facility that connects two Signalling Link Terminals.
 Signalling Gateway (SG) - An SG is a signalling agent at the edge of
 the IP network.  An SG appears to the SS7 as one or more Signalling
 Link Terminals that are connected to one or more Signalling Data
 Links in the SS7 network.  An SG contains a set of one or more unique
 Signalling Gateway Processes, on which one or more is normally
 actively processing traffic.  Where an SG contains more than one SGP,
 the SG is a logical entity.
 Signalling Gateway Process (SGP) - A process instance that uses M2UA
 to communicate to and from a Signalling Link Terminal.  It serves as
 an active, backup or load-sharing process of a Signalling Gateway.
 Signalling Link Terminal (SLT) - Refers to the means of performing
 all of the functions defined at MTP level 2 regardless of their
 implementation [2,3].

Morneault, et. al. Standards Track [Page 4] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

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

1.3 M2UA Overview

 The framework architecture that has been defined for SCN signalling
 transport over IP [9] uses two components: a signalling common
 transport protocol and an adaptation module to support the services
 expected by a particular SCN signalling protocol from its underlying
 protocol layer.
 Within this framework architecture, this document defines a SCN
 adaptation module that is suitable for the transport of SS7 MTP2 User
 messages.  The only SS7 MTP2 User is MTP3.  The M2UA uses the
 services of the Stream Control Transmission Protocol [8] as the
 underlying reliable signalling common transport protocol.
 In a Signalling Gateway, it is expected that the SS7 MTP2-User
 signalling is transmitted and received from the PSTN over a standard
 SS7 network interface, using the SS7 Message Transfer Part Level 1
 and Level 2 [2,3,4] to provide reliable transport of the MTP3-User
 signalling messages to and from an SS7 Signalling End Point (SEP) or
 Signalling Transfer Point (STP).  The SG then provides an
 interworking of transport functions with the IP transport, in order
 to transfer the MTP2-User signalling messages to and from an
 Application Server Process where the peer MTP2-User protocol layer
 exists.

Morneault, et. al. Standards Track [Page 5] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

1.3.1 Example - SG to MGC

 In a Signalling Gateway, it is expected that the SS7 signalling is
 received over a standard SS7 network termination, using the SS7
 Message Transfer Part (MTP) to provide transport of SS7 signalling
 messages to and from an SS7 Signalling End Point (SEP) or SS7
 Signalling Transfer Point (STP).  In other words, the SG acts as a
 Signalling Link Terminal (SLT) [2,3].  The SG then provides an
 interworking of transport functions with IP Signalling Transport, in
 order to transport the MTP3 signalling messages to the MGC where the
 peer MTP3 protocol layer exists, as shown below:
  • * SS7 IP *
  • SEP *———–* SG *————-* MGC *
  • * *
     +----+                              +----+
     |S7UP|                              |S7UP|
     +----+                              +----+
     |MTP +                              |MTP |
     | L3 |            (NIF)             |L3  |
     +----+         +----+----+          +----+
     |MTP |         |MTP |M2UA|          |M2UA|
     |    |         |    +----+          +----+
     |L2  |         |L2  |SCTP|          |SCTP|
     |L1  |         |L1  +----+          +----+
     |    |         |    |IP  |          |IP  |
     +----+         +---------+          +----+
     NIF  - Nodal Interworking Function
     SEP  - SS7 Signalling Endpoint
     IP   - Internet Protocol
     SCTP - Stream Control Transmission Protocol (Reference [8])
         Figure 1  M2UA in the SG to MGC Application
 Note: STPs MAY be present in the SS7 path between the SEP and the SG.
 It is recommended that the M2UA use the services of the Stream
 Control Transmission Protocol (SCTP) [8] as the underlying reliable
 common signalling transport protocol.  The use of SCTP provides the
 following features:
  1. explicit packet-oriented delivery (not stream-oriented)
  2. 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,

Morneault, et. al. Standards Track [Page 6] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

  1. network-level fault tolerance through the support of multi-homing

at either or both ends of an association,

  1. resistance to flooding and masquerade attacks, and
  2. data segmentation to conform to discovered path MTU size
 There are scenarios without redundancy requirements and scenarios in
 which redundancy is supported below the transport layer.  In these
 cases, the SCTP functions above MAY NOT be a requirement and TCP can
 be used as the underlying common transport protocol.

1.3.2 ASP Fail-over Model and Terminology

 The M2UA layer supports ASP fail-over functions in order to support a
 high availability of call and transaction processing capability.  All
 MTP2-User messages incoming to a SGP from the SS7 network are
 assigned to the unique Application Server, based on the Interface
 Identifier of the message.
 The M2UA layer supports a n+k redundancy model (active-standby, load
 sharing, broadcast) where n 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.

1.3.3 Client/Server Model

 It is recommended that the SGP and ASP be able to support both client
 and server operation.  The peer endpoints using M2UA SHOULD be
 configured so that one always takes on the role of client and the
 other the role of server for initiating SCTP associations.  The
 default orientation would be for the SGP to take on the role of
 server while the ASP is the client.  In this case, ASPs SHOULD
 initiate the SCTP association to the SGP.
 The SCTP and TCP Registered User Port Number Assignment for M2UA is
 2904.

1.4 Services Provided by the M2UA Adaptation Layer

 The SS7 MTP3/MTP2(MTP2-User) interface is retained at the termination
 point in the IP network, so that the M2UA protocol layer is required
 to provide the equivalent set of services to its users as provided by
 the MTP Level 2 to MTP Level 3.

Morneault, et. al. Standards Track [Page 7] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

1.4.1 Support for MTP Level 2 / MTP Level 3 interface boundary

 M2UA supports a MTP Level 2 / MTP Level 3 interface boundary that
 enables a seamless, or as seamless as possible, operation of the
 MTP2-User peers in the SS7 and IP domains.  An example of the
 primitives that need to be supported can be found in [10].

1.4.2 Support for communication between Layer Management modules on SG

     and MGC
 The M2UA layer needs to provide some messages that will facilitate
 communication between Layer Management modules on the SG and MGC.  To
 facilitate reporting of errors that arise because of the backhauling
 MTP Level 3 scenario, the following primitive is defined:
 M-ERROR
 The M-ERROR message is used to indicate an error with a received M2UA
 message (e.g., an interface identifier value is not known to the SG).

1.4.3 Support for management of active associations between SG and MGC

 The M2UA layer on the SG keeps the state of the configured ASPs.  A
 set of primitives between M2UA layer and the Layer Management are
 defined below to help the Layer Management manage the association(s)
 between the SG and the MGC.  The M2UA layer can be instructed by the
 Layer Management to establish a SCTP association to a peer M2UA node.
 This procedure can be achieved using the M-SCTP ESTABLISH primitive.
 M-SCTP_ESTABLISH
 The M-SCTP_ESTABLISH primitive is used to request, indicate and
 confirm the establishment of a SCTP association to a peer M2UA node.
 M-SCTP_RELEASE
 The M-SCTP_RELEASE primitives are used to request, indicate, and
 confirm the release of a SCTP association to a peer M2UA node.
 The M2UA layer MAY also need to inform the status of the SCTP
 association(s) to the Layer Management.  This can be achieved using
 the following primitive.
 M-SCTP_STATUS
 The M-SCTP_STATUS primitive is used to request and indicate the
 status of underlying SCTP association(s).

Morneault, et. al. Standards Track [Page 8] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The Layer Management MAY need to inform the M2UA layer of an AS/ASP
 status (i.e., failure, active, etc.), so that messages can be
 exchanged between M2UA layer peers to stop traffic to the local M2UA
 user.  This can be achieved using the following primitive.
 M-ASP_STATUS
 The ASP status is stored inside the M2UA layer on both the SG and MGC
 sides.  The M-ASP_STATUS primitive can be used by Layer Management to
 request the status of the Application Server Process from the M2UA
 layer.  This primitive can also be used to indicate the status of the
 Application Server Process.
 M-ASP_MODIFY
 The M-ASP_MODIFY primitive can be used by Layer Management to modify
 the status of the Application Server Process.  In other words, the
 Layer Management on the ASP side uses this primitive to initiate the
 ASPM procedures.
 M-AS_STATUS
 The M-AS_STATUS primitive can be used by Layer Management to request
 the status of the Application Server.  This primitive can also be
 used to indicate the status of the Application Server.

1.5 Functions Provided by the M2UA Layer

1.5.1 Mapping

 The M2UA layer MUST maintain a map of an Interface ID to a physical
 interface on the Signalling Gateway.  A physical interface would be a
 V.35 line, T1 line/time slot, E1 line/time slot, etc.  The M2UA layer
 MUST also maintain a map of the Interface Identifier to SCTP
 association and to the related stream within the association.
 The SGP maps an Interface Identifier to an SCTP association/stream
 only when an ASP sends an ASP Active message for a particular
 Interface Identifier.  It must be noted, however, that this mapping
 is dynamic and could change at any time due to a change of ASP state.
 This mapping could even temporarily be invalid, for example during
 fail-over of one ASP to another.  Therefore, the SGP MUST maintain
 the states of AS/ASP and reference them during the routing of any
 messages to an AS/ASP.
 Note that only one SGP SHOULD provide Signalling Link Terminal
 services to an SS7 link.  Therefore, within an SG, an Application
 Server SHOULD be active for only one SGP at any given point in time.

Morneault, et. al. Standards Track [Page 9] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 An example of the logical view of the relationship between an SS7
 link, Interface Identifier, AS and ASP in an SGP is shown below:
             /-------------------------------------------------+
            /   /----------------------------------------------|--+
           /   /                                               v  |
          /   /    +----+             act+-----+   +-------+ -+--+|-+-
 SS7 link1-------->|IID |-+          +-->| ASP |-->| Assoc |      v
            /      +----+ |  +----+  |   +-----+   +-------+ -+--+--+-
           /              +->| AS |--+                        Streams
          /        +----+ |  +----+   stb+-----+
 SS7 link2-------->|IID |-+              | ASP |
                   +----+                +-----+
 where IID = Interface Identifier
 A SGP MAY support more than one AS.  An AS MAY support more than one
 Interface Identifier.

1.5.2 Support for the management of SCTP associations between the SGPs

     and ASPs
 The M2UA layer at the SG maintains the availability state of all
 configured ASPs, in order to manage the SCTP associations and the
 traffic between the SG and ASPs.  As well, the active/inactive state
 of remote ASP(s) are also maintained.  The Active ASP(s) are the
 one(s) currently receiving traffic from the SG.
 The M2UA layer MAY be instructed by local management to establish an
 SCTP association to a peer M2UA 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 M2UA node.
 The M2UA layer MAY also need to inform local management of the status
 of the underlying SCTP associations using the M-SCTP_STATUS request
 and the indication primitive.  For example, the M2UA MAY inform local
 management of the reason for the release of an SCTP association,
 determined either locally within the M2UA layer or by a primitive
 from the SCTP.
 Also the M2UA layer may need to inform the local management of the
 change in status of an ASP or AS.  This may be achieved using the M-
 ASP STATUS request or M-AS_STATUS request primitives.

Morneault, et. al. Standards Track [Page 10] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

1.5.3 Status of ASPs

 The M2UA layer on the SG MUST maintain the state of the ASPs it is
 supporting.  The state of an ASP changes because of the reception of
 peer-to-peer messages (ASPM messages as described in Section 3.3.2)
 or the reception of indications from the local SCTP association.  The
 ASP state transition procedures are described in Section 4.3.1.
 At a SGP, an Application Server list MAY contain active and inactive
 ASPs to support ASP fail-over procedures.  When, for example, both a
 primary and a backup ASP are available, the M2UA 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
 SGP to reflect the active Application Server Process.
 Also the M2UA 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.

1.5.4 SCTP Specifics

1.5.4.1 SCTP Stream Management

 SCTP allows a user specified number of streams to be opened during
 initialization of the association.  It is the responsibility of the
 M2UA layer to ensure proper management of these streams.  Because of
 the unidirectional nature of streams, a M2UA layer is not aware of
 the stream information from its peer M2UA layer.  For this reason,
 the Interface Identifier is in the M2UA message header.
 The use of SCTP streams within M2UA is recommended in order to
 minimize transmission and buffering delay, thereby, improving the
 overall performance and reliability of the signalling elements.  A
 separate SCTP stream can be used for each SS7 link.  Or, an
 implementation may choose to split the SS7 link across several
 streams based on SLS.  This method may be of particular interest for
 high speed SS7 links (MTP3b) since high speed links have a 24-bit
 sequence number and the stream sequence number is 16-bits.
 SCTP Stream '0' SHOULD NOT be used for MTP2 User Adaptation (MAUP)
 messages (see Section 3) since stream '0' SHOULD only be used for ASP
 Management (ASPM) messages (see Section 4.3.3).

Morneault, et. al. Standards Track [Page 11] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

1.5.5 Seamless SS7 Network Management Interworking

 The M2UA layer on the SGP SHOULD pass an indication of unavailability
 of the M2UA-User (MTP3) to the local Layer Management, if the
 currently active ASP moves from the ACTIVE state.  The actions taken
 by M2UA on the SGP with regards to MTP Level 2 should be in
 accordance with the appropriate MTP specifications.

1.5.6 Flow Control / Congestion

 It is possible for the M2UA layer to be informed of the IP network
 congestion onset and abatement by means of an implementation
 dependent function (i.e. an indication from the SCTP).  The handling
 of this congestion indication by M2UA is implementation dependent.
 However, the actions taken by the SG should be in accordance with the
 appropriate MTP specification and should enable SS7 functionality
 (e.g. flow control) to be correctly maintained.

1.5.7 Audit of SS7 Link State

 After a fail-over of one ASP to another ASP, it may be necessary for
 the M2UA on the ASP to audit the current SS7 link state to ensure
 consistency.  The M2UA on the SGP would respond to the audit request
 with information regarding the current state of the SS7 link (i.e.
 in-service, out-of-service, congestion state, LPO/RPO state).

1.6 Definition of the M2UA Boundaries

1.6.1 Definition of the M2UA / MTP Level 3 boundary

 DATA
 ESTABLISH
 RELEASE
 STATE
 DATA RETRIEVAL
 DATA RETRIEVAL COMPLETE

1.6.2 Definition of the M2UA / MTP Level 2 boundary

 DATA
 ESTABLISH
 RELEASE
 STATE
 DATA RETRIEVAL
 DATA RETRIEVAL COMPLETE

Morneault, et. al. Standards Track [Page 12] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

1.6.3 Definition of the Lower Layer Boundary between M2UA and SCTP

 The upper layer and layer management primitives provided by SCTP are
 provided in Reference [8] Section 10.

1.6.4 Definition of Layer Management / M2UA Boundary

 M-SCTP_ESTABLISH request
 Direction: LM -> M2UA
 Purpose: LM requests ASP to establish an SCTP association with an
          SGP.
 M-SCTP_ESTABLISH confirm
 Direction: M2UA -> LM
 Purpose: ASP confirms to LM that it has established an
          SCTP association with an SGP.
 M-SCTP_ESTABLISH indication
 Direction: M2UA -> LM
 Purpose: SGP informs LM that an ASP has established an SCTP
          association.
 M-SCTP_RELEASE request
 Direction: LM -> M2UA
 Purpose: LM requests ASP to release an SCTP association with SGP.
 M-SCTP_RELEASE confirm
 Direction: M2UA -> LM
 Purpose: ASP confirms to LM that it has released SCTP association
          with SGP.
 M-SCTP_RELEASE indication
 Direction: M2UA -> LM
 Purpose: SGP informs LM that ASP has released an SCTP association.
 M-SCTP_RESTART indication
 Direction: M2UA -> LM
 Purpose: M2UA informs LM that a SCTP Restart indication has
          been received.
 M-SCTP_STATUS request
 Direction: LM -> M2UA
 Purpose: LM requests M2UA to report status of SCTP association.
 M-SCTP_STATUS indication
 Direction: M2UA -> LM
 Purpose: M2UA reports status of SCTP association.

Morneault, et. al. Standards Track [Page 13] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 M-ASP_STATUS request
 Direction: LM -> M2UA
 Purpose: LM requests SGP to report status of remote ASP.
 M-ASP_STATUS indication
 Direction: M2UA -> LM
 Purpose: SGP reports status of remote ASP.
 M-AS_STATUS request
 Direction: LM -> M2UA
 Purpose: LM requests SG to report status of AS.
 M-AS_STATUS indication
 Direction: M2UA -> LM
 Purpose: SG reports status of AS.
 M-NOTIFY indication
 Direction: M2UA -> LM
 Purpose: ASP reports that it has received a NOTIFY message
          from its peer.
 M-ERROR indication
 Direction: M2UA -> LM
 Purpose: ASP or SGP reports that it has received an ERROR
          message from its peer.
 M-ASP_UP request
 Direction: LM -> M2UA
 Purpose: LM requests ASP to start its operation and send an ASP UP
          message to the SGP.
 M-ASP_UP confirm
 Direction: M2UA -> LM
 Purpose: ASP reports that it has received an ASP UP Acknowledgment
          message from the SGP.
 M-ASP_DOWN request
 Direction: LM -> M2UA
 Purpose: LM requests ASP to stop its operation and send an ASP DOWN
          message to the SGP.
 M-ASP_DOWN confirm
 Direction: M2UA -> LM
 Purpose: ASP reports that is has received an ASP DOWN Acknowledgment
          message from the SGP.

Morneault, et. al. Standards Track [Page 14] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 M-ASP_ACTIVE request
 Direction: LM -> M2UA
 Purpose: LM requests ASP to send an ASP ACTIVE message to the SGP.
 M-ASP_ACTIVE confirm
 Direction: M2UA -> LM
 Purpose: ASP reports that is has received an ASP ACTIVE
          Acknowledgment message from the SGP.
 M-ASP_INACTIVE request
 Direction: LM -> M2UA
 Purpose: LM requests ASP to send an ASP INACTIVE message to the SGP.
 M-ASP_INACTIVE confirm
 Direction: M2UA -> LM
 Purpose: ASP reports that is has received an ASP INACTIVE
          Acknowledgment message from the SGP.
 M-LINK_KEY_REG Request
 Direction:  LM -> M2UA
 Purpose: LM requests ASP to register Link Key with SG by sending REG
          REQ message.
 M-LINK_KEY_REG Confirm
 Direction:   M2UA -> LM
 Purpose: ASP reports to LM that it has successfully received a REG
          RSP message from SG.
 M-LINK_KEY_REG Indication
 Direction:  M2UA -> LM
 Purpose:  SG reports to LM that it has successfully processed an
           incoming REG REQ message from ASP.
 M-LINK_KEY_DEREG Request
 Direction:  LM -> M2UA
 Purpose:  LM requests ASP to de-register Link Key with SG by sending
           DEREG REQ message.
 M-LINK_KEY_DEREG Confirm
 Direction:  M2UA -> LM
 Purpose:  ASP reports to LM that it has successfully received a
           DEREG RSP message from SG.
 M-LINK_KEY_DEREG  Indication
 Direction:  M2UA -> LM
 Purpose:  SG reports to LM that it has successfully processed an
           incoming DEREG REQ message from ASP.

Morneault, et. al. Standards Track [Page 15] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

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 Protocol Elements

 This section describes the format of various messages used in this
 protocol.

3.1 Common Message Header

 The protocol messages for MTP2-User Adaptation require a message
 structure that contains a version, message class, 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    |     Spare     | Message Class | Message Type  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Message Length                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 2  Common Message Header
 All fields in an M2UA message MUST be transmitted in the network byte
 order, unless otherwise stated.

3.1.1 Version

 The version field contains the version of the M2UA adaptation layer.
 The supported versions are:
       Value    Version
       -----    -------
         1      Release 1.0

3.1.2 Spare

 The Spare field is 8-bits.  It SHOULD be set to all '0's by the
 sender and ignored by the receiver.

Morneault, et. al. Standards Track [Page 16] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

3.1.3 Message Class

 The following List contains the valid Message Classes:
 Message Class: 8 bits (unsigned integer)
   0      Management (MGMT) Message [IUA/M2UA/M3UA/SUA]
   1      Transfer Messages [M3UA]
   2      SS7 Signalling Network Management (SSNM) Messages [M3UA/SUA]
   3      ASP State Maintenance (ASPSM) Messages [IUA/M2UA/M3UA/SUA]
   4      ASP Traffic Maintenance (ASPTM) Messages [IUA/M2UA/M3UA/SUA]
   5      Q.921/Q.931 Boundary Primitives Transport (QPTM)
          Messages [IUA]
   6      MTP2 User Adaptation (MAUP) Messages [M2UA]
   7      Connectionless Messages [SUA]
   8      Connection-Oriented Messages [SUA]
   9      Routing Key Management (RKM) Messages (M3UA)
  10      Interface Identifier Management (IIM) Messages (M2UA)

11 to 127 Reserved by the IETF 128 to 255 Reserved for IETF-Defined Message Class extensions

3.1.4 Message Type

 The following List contains the Message Types for the valid Message
 Classes:
 MTP2 User Adaptation (MAUP) Messages
      0      Reserved
      1      Data
      2      Establish Request
      3      Establish Confirm
      4      Release Request
      5      Release Confirm
      6      Release Indication
      7      State Request
      8      State Confirm
      9      State Indication
     10      Data Retrieval Request
     11      Data Retrieval Confirm
     12      Data Retrieval Indication
     13      Data Retrieval Complete Indication
     14      Congestion Indication
     15      Data Acknowledge
  16 to 127  Reserved by the IETF
 128 to 255  Reserved for IETF-Defined MAUP extensions

Morneault, et. al. Standards Track [Page 17] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 Application Server Process State Maintenance (ASPSM) messages
      0      Reserved
      1      ASP Up (UP)
      2      ASP Down (DOWN)
      3      Heartbeat (BEAT)
      4      ASP Up Ack (UP ACK)
      5      ASP Down Ack (DOWN ACK)
      6      Heartbeat Ack (BEAT ACK)
   7 to 127  Reserved by the IETF
 128 to 255  Reserved for IETF-Defined ASPSM extensions
 Application Server Process 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 127  Reserved by the IETF
 128 to 255  Reserved for IETF-Defined ASPTM extensions
 Management (MGMT) Messages
      0      Error (ERR)
      1      Notify (NTFY)
   2 to 127  Reserved by the IETF
 128 to 255  Reserved for IETF-Defined MGMT extensions
 Interface Identifier Management (IIM) Messages
      0        Reserved
      1        Registration Request (REG REQ)
      2        Registration Response (REG RSP)
      3        Deregistration Request (DEREG REQ)
      4        Deregistration Response (DEREG RSP)
   5 to 127    Reserved by the IETF
 128 to 255    Reserved for IETF-Defined IIM extensions

3.1.5 Message Length

 The Message Length defines the length of the message in octets,
 including the header.  The Message Length MUST include parameter
 padding bytes, if any.  The Message Length MUST NOT be longer than a
 MTP3 message [2,3,4,5] plus the length of the common and M2UA message
 headers.

Morneault, et. al. Standards Track [Page 18] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

3.1.6 Variable-Length Parameter Format

 M2UA 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                         /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Mandatory parameters MUST be placed before optional parameters in a
 message.
 Parameter Tag: 16 bits (unsigned integer)
 The Type field is a 16 bit identifier of the type of parameter.  It
 takes a value of 0 to 65534.  The common parameters used by the
 adaptation layers are in the range of 0x00 to 0xff.  The M2UA
 specific parameters have Tags in the range 0x300 to 0x3ff.

Morneault, et. al. Standards Track [Page 19] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The common parameter tags (used by all User Adaptation layers) that
 M2UA uses are defined below:
    Parameter Value     Parameter Name
    ---------------     --------------
          0 (0x00)       Reserved
          1 (0x01)       Interface Identifier (Integer)
          2 (0x02)       Unused
          3 (0x03)       Interface Identifier (Text)
          4 (0x04)       Info String
          5 (0x05)       Unused
          6 (0x06)       Unused
          7 (0x07)       Diagnostic Information
          8 (0x08)       Interface Identifier (Integer Range)
          9 (0x09)       Heartbeat Data
         10 (0x0a)       Unused
         11 (0x0b)       Traffic Mode Type
         12 (0x0c)       Error Code
         13 (0x0d)       Status Type/Information
         14 (0x0e)       Unused
         15 (0x0f)       Unused
         16 (0x10)       Unused
         17 (0x11)       ASP Identifier
         18 (0x12)       Unused
         19 (0x13)       Correlation Id
        18-255           Reserved

Morneault, et. al. Standards Track [Page 20] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The M2UA specific parameter Tags defined are as follows:
    Parameter Value     Parameter Name
    ---------------     --------------
      768 (0x0300)      Protocol Data 1
      769 (0x0301)      Protocol Data 2 (TTC)
      770 (0x0302)      State Request
      771 (0x0303)      State Event
      772 (0x0304)      Congestion Status
      773 (0x0305)      Discard Status
      774 (0x0306)      Action
      775 (0x0307)      Sequence Number
      776 (0x0308)      Retrieval Result
      777 (0x0309)      Link Key
      778 (0x030a)      Local-LK-Identifier
      779 (0x030b)      Signalling Data Terminal (SDT) Identifier
      780 (0x030c)      Signalling Data Link (SDL) Identifier
      781 (0x030d)      Registration Result
      782 (0x030e)      Registration Status
      783 (0x030f)      De-Registration Result
      784 (0x0310)      De-Registration Status
 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.  Thus, a parameter with a zero-length Parameter Value
 field would have a Length field of 4.  The Parameter Length does not
 include any padding bytes.
 Parameter Value: variable-length.
 The Parameter Value field contains the actual information to be
 transferred in the parameter.
 The total length of a parameter (including Tag, Parameter Length and
 Value fields) MUST be a multiple of 4 bytes.  If the length of the
 parameter is not a multiple of 4 bytes, the sender pads the Parameter
 at the end (i.e., after the Parameter Value field) with all zero
 bytes.  The length of the padding is NOT included in the parameter
 length field.  A sender MUST NOT pad with more than 3 bytes.  The
 receiver MUST ignore the padding bytes.

Morneault, et. al. Standards Track [Page 21] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

3.2 M2UA Message Header

 In addition to the common message header, there will be a M2UA
 specific message header.  The M2UA specific message header will
 immediately follow the common message header, but will only be used
 with MAUP messages.
 This message header will contain the Interface Identifier.  The
 Interface Identifier identifies the physical interface at the SG for
 which the signalling messages are sent/received.  The format of the
 Interface Identifier parameter can be text or 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.
 The integer formatted Interface Identifier MUST be supported.  The
 text formatted Interface Identifier MAY optionally be supported.
  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=8            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier (integer)                |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure 3  M2UA Message Header (Integer-based Interface Identifier)
 The Tag value for the Integer-based Interface Identifier is 0x1.  The
 length is always set to a value of 8.
  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 (0x3)           |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                   Interface Identifier (text)                 /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  Figure 4  M2UA Message Header (Text-based Interface Identifier)
 The Tag value for the Text-based Interface Identifier is 0x3.  The
 encoding of the Identifier is ANSI X3.4-1986 [7].  The maximum string
 length of the text-based Interface Identifier is 255 octets.  The tag
 length is equal to the string length of the Interface Identifier name
 plus four bytes for the Tag and Length fields.

Morneault, et. al. Standards Track [Page 22] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

3.3 M2UA Messages

 The following section defines the messages and parameter contents.
 The M2UA messages will use the common message header (Figure 2) and
 the M2UA message header (Figure 3 and Figure 4).

3.3.1 MTP2 User Adaptation Messages

3.3.1.1 Data

 The Data message contains an SS7 MTP2-User Protocol Data Unit (PDU).
 The Data message contains the following parameter:
    Protocol Data (mandatory)
    Correlation Id (optional)
 The format for the Data 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 (0x300)           |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                       Protocol Data                           /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x13)            |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Correlation Id                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The Protocol Data field contains the MTP2-User application message in
 network byte order starting with the Signalling Information Octet
 (SIO).  The Correlation Id parameter uniquely identifies the MSU
 carried in the Protocol Data within an AS.  This Correlation Id
 parameter is assigned by the sending M2UA.  The purpose of the
 Correlation Id is to permit the newly active ASP to synchronize its
 processing of the traffic in each ordered stream with other ASPs in
 the broadcast group.

Morneault, et. al. Standards Track [Page 23] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The format for a Data Message with TTC PDU 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 (0x301)           |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                    TTC Protocol Data                          /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Tag (0x13)           |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Correlation Id                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The Protocol Data field contains the MTP2-User application message in
 network byte order starting with the Length Indicator (LI) octet.
 The Japanese TTC variant uses the spare bits of the LI octet for
 priority.
 The length of the Protocol Data and TTC Protocol Data MUST NOT exceed
 the length of a MTP2-User application message [2,3,5].

3.3.1.2 Data Acknowledge Message

 The Data Acknowledge message contains the Correlation Id of the Data
 message that the sending M2UA is acknowledging as successfully
 processed to the peer M2UA.
 The Data Acknowledge message contains the following parameter:
    Correlation Id       Mandatory
 The following format MUST be used for the Data Ack 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 (0x13)           |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Correlation Id                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The Correlation Id parameter of the Data message and the Data Ack
 message provide a mechanism, for those SG implementations capable of
 taking advantage of them, to obtain an acknowledgment that the MSU
 has been transferred to the M2UA peer before acknowledging the MSU to

Morneault, et. al. Standards Track [Page 24] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 the SS7 peer, removing the risk of losing messages due to association
 failure or SCTP congestion.
 The Data Ack message MUST be sent if a Correlation Id parameter is
 received from the peer.  Otherwise, the Data Ack message MUST NOT be
 sent.
 If the Data Acknowledge is not sent for Correlation Id(s) or is sent
 with Invalid Correlation Id(s), the SS7 link will eventually fail due
 to lack of MTP Level 2 acknowledgments of the SS7 peer's MSUs.

3.3.1.3 Establish (Request, Confirmation)

 The Establish Request message is used to establish the SS7 link or to
 indicate that the channel has been established.  The MGC controls the
 state of the SS7 link.  When the MGC desires the SS7 link to be in-
 service, it will send the Establish Request message.  Note that the
 SGP MAY already have the SS7 link established at its layer.  If so,
 upon receipt of an Establish Request, the SGP takes no action except
 to send an Establish Confirm.
 When the MGC sends an M2UA Establish Request message, the MGC MAY
 start a timer.  This timer would be stopped upon receipt of an M2UA
 Establish Confirm.  If the timer expires, the MGC would resend the
 M2UA Establish Request message and restart the timer.  In other
 words, the MGC MAY continue to request the establishment of the data
 link on a periodic basis until the desired state is achieved or some
 other action is taken (notify the Management Layer).
 The mode (Normal or Emergency) for bringing the SS7 link in service
 is defaulted to Normal.  The State Request (described in Section
 3.3.1.5 below) can be used to change the mode to Emergency.

3.3.1.4 Release (Request, Indication, Confirmation)

 This Release Request message is used to release the channel.  The
 Release Confirm and Indication messages are used to indicate that the
 channel has been released.

3.3.1.5 State Request

 The State Request message can be sent from a MGC to cause an action
 on a particular SS7 link supported by the Signalling Gateway Process.
 The SGP sends a State Confirm to the MGC if the action has been
 successfully completed.  The State Confirm reflects that state value
 received in the State Request message.

Morneault, et. al. Standards Track [Page 25] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The State Request message contains the following parameter:
  State (mandatory)
  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 (0x302)           |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             State                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The valid values for State are shown in the following table.
          Define           Value        Description
    STATUS_LPO_SET          0x0      Request local processor outage
    STATUS_LPO_CLEAR        0x1      Request local processor outage
                                     recovered
    STATUS_EMER_SET         0x2      Request emergency alignment
    STATUS_EMER_CLEAR       0x3      Request normal alignment (cancel
                                     emergency)
    STATUS_FLUSH_BUFFERS    0x4      Flush or clear receive, transmit
                                     and retransmit queues
    STATUS_CONTINUE         0x5      Continue or Resume
    STATUS_CLEAR_RTB        0x6      Clear the retransmit queue
    STATUS_AUDIT            0x7      Audit state of link
    STATUS_CONG_CLEAR       0x8      Congestion cleared
    STATUS_CONG_ACCEPT      0x9      Congestion accept
    STATUS_CONG_DISCARD     0xa      Congestion discard

3.3.1.6 State Confirm

 The State Confirm message will be sent by the SGP in response to a
 State Request from the MGC.  The State Confirm reflects that state
 value received in the State Request message.
 The State Confirm message contains the following parameter:
  State (mandatory)
  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 (0x302)           |           Length = 8          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             State                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Morneault, et. al. Standards Track [Page 26] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The valid values for State are shown in the following table.  The
 value of the State field SHOULD reflect the value received in the
 State Request message.
          Define           Value        Description
    STATUS_LPO_SET          0x0      Request local processor outage
    STATUS_LPO_CLEAR        0x1      Request local processor outage
                                     recovered
    STATUS_EMER_SET         0x2      Request emergency alignment
    STATUS_EMER_CLEAR       0x3      Request normal alignment (cancel
                                     emergency)
    STATUS_FLUSH_BUFFERS    0x4      Flush or clear receive, transmit
                                     and retransmit queues
    STATUS_CONTINUE         0x5      Continue or Resume
    STATUS_CLEAR_RTB        0x6      Clear the retransmit queue
    STATUS_AUDIT            0x7      Audit state of link
    STATUS_CONG_CLEAR       0x8      Congestion cleared
    STATUS_CONG_ACCEPT      0x9      Congestion accept
    STATUS_CONG_DISCARD     0xa      Congestion discard

3.3.1.7 State Indication

 The MTP2 State Indication message can be sent from a SGP to an ASP to
 indicate a condition on a SS7 link.
 The State Indication message contains the following parameter:
  Event (mandatory)
  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 (0x303)           |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             Event                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The valid values for Event are shown in the following table.
        Define            Value          Description
    EVENT_RPO_ENTER        0x1      Remote entered processor outage
    EVENT_RPO_EXIT         0x2      Remote exited processor outage
    EVENT_LPO_ENTER        0x3      Link entered processor outage
    EVENT_LPO_EXIT         0x4      Link exited processor outage

Morneault, et. al. Standards Track [Page 27] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

3.3.1.8 Congestion Indication

 The Congestion Indication message can be sent from a Signalling
 Gateway Process to an ASP to indicate the congestion status and
 discard status of a SS7 link.  When the MSU buffer fill increases
 above an Onset threshold or decreases below an Abatement threshold or
 crosses a Discard threshold in either direction, the SGP SHALL send a
 congestion indication message when it supports SS7 MTP2 variants that
 support multiple congestion levels.
 The SGP SHALL send the message only when there is actually a change
 in either the discard level or the congestion level to report,
 meaning it is different from the previously sent message.  In
 addition, the SGP SHALL use an implementation dependent algorithm to
 limit the frequency of congestion indication messages.
 An implementation may optionally send Congestion Indication messages
 on a "high priority" stream in order to potentially reduce delay.
 The Congestion Indication message contains the following parameters:
  Congestion Status (mandatory)
  Discard Status (optional)
  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 (0x304)           |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Congestion Status                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x305)           |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Discard Status                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The valid values for Congestion Status and Discard Status are shown
 in the following table.
          Define        Value        Description
        LEVEL_NONE       0x0       No congestion
        LEVEL_1          0x1       Congestion Level 1
        LEVEL_2          0x2       Congestion Level 2
        LEVEL_3          0x3       Congestion Level 3

Morneault, et. al. Standards Track [Page 28] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 For SS7 networks that do not support multiple levels of congestion,
 only the LEVEL_NONE and LEVEL_3 values will be used.  For SS7
 networks that support multiple levels of congestion, it is possible
 for all values to be used.  Refer to [2], [3] and [12] for more
 details on the Congestion and Discard Status of SS7 signalling links.

3.3.1.9 Retrieval Request

 The MTP2 Retrieval Request message is used during the MTP Level 3
 changeover procedure to request the BSN, to retrieve PDUs from the
 transmit and retransmit queues or to flush PDUs from the retransmit
 queue.  Examples of the use of Retrieval Request for SS7 Link
 Changeover are provided in Section 5.3.6.
 The Retrieval Request message contains the following parameters:
  Action (mandatory)
  Sequence Number (optional)
  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 (0x306)           |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                            Action                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x307)           |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Sequence Number                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The valid values for Action are shown in the following table.
         Define         Value       Description
    ACTION_RTRV_BSN      0x1     Retrieve the backward sequence number
    ACTION_RTRV_MSGS     0x2     Retrieve the PDUs from the transmit
                                 and retransmit queues
 In the Retrieval Request message, the Sequence Number field SHOULD
 NOT be present if the Action field is ACTION_RTRV_BSN.  The Sequence
 Number field contains the Forward Sequence Number (FSN) of the far
 end if the Action is ACTION_RTRV_MSGS.

Morneault, et. al. Standards Track [Page 29] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

3.3.1.10 Retrieval Confirm

 The MTP2 Retrieval Confirm message is sent by the Signalling Gateway
 in response to a Retrieval Request message.  Examples of the use of
 the Retrieval Confirm for SS7 Link Changeover are provided in Section
 5.3.6.
 The Retrieval Confirm message contains the following parameters:
  Action (mandatory)
  Result (mandatory)
  Sequence Number (optional)
  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 (0x306)           |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                            Action                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x308)           |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                            Result                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x307)           |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Sequence Number                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The valid values for Action are the same as in Retrieval Request.
 The values for Result are shown below:
         Define         Value       Description
    RESULT_SUCCESS       0x0     Action successful
    RESULT_FAILURE       0x1     Action failed
 When the Signalling Gateway Process sends a Retrieval Confirm to a
 Retrieval Request, it echos the Action field.  If the Action was
 ACTION_RTRV_BSN and the SGP successfully retrieved the BSN, the SGP
 will put the Backward Sequence Number (BSN) in the Sequence Number
 field and will indicate a success in the Result field.  If the BSN
 could not be retrieved, the Sequence Number field will not be
 included and the Result field will indicate failure.

Morneault, et. al. Standards Track [Page 30] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 For a Retrieval Confirm with Action of ACTION_RTRV_MSGS, the value of
 the Result field will indicate success or failure.  A failure means
 that the buffers could not be retrieved.  The Sequence Number field
 is not used with ACTION_RTRV_MSGS.

3.3.1.11 Retrieval Indication

 The Retrieval Indication message is sent by the Signalling Gateway
 with a PDU from the transmit or retransmit queue.  The Retrieval
 Indication message does not contain the Action or Sequence Number
 fields, just a MTP3 Protocol Data Unit (PDU) from the transmit or
 retransmit queue.  Examples of the use of the Retrieval Indication
 for SS7 Link Changeover are provided in Section 5.3.6.
  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 (0x300)          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                       Protocol Data                           /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 For TTC Data messages, the following parameter will be used to
 indicate a TTC PDU which starts at LI.
  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 (0x301)          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     TTC Protocol Data                         /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The M2UA implementation MAY consider the use of the bundling feature
 of SCTP for Retrieval Indication messages.

3.3.1.12 Retrieval Complete Indication

 The MTP2 Retrieval Complete Indication message is exactly the same as
 the MTP2 Retrieval Indication message except that it also indicates
 that retrieval is complete.  In addition, it MAY contain a PDU (which
 MUST be the last PDU) from the transmit or retransmit queue.

Morneault, et. al. Standards Track [Page 31] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

3.3.2 Application Server Process Maintenance (ASPM) Messages

 The ASPM messages will only use the common message header.

3.3.2.1 ASP Up (ASPUP)

 The ASP Up (ASPUP) message is used to indicate to a remote M2UA peer
 that the Adaptation layer is ready to receive traffic or maintenance
 messages.
 The ASPUP message contains the following parameters
    ASP Identifier (optional)
    Info String (optional)
 Note: The ASP Identifier MUST be used where the SGP cannot
       identify the ASP by pre-configured address/port number
       information (e.g., where an ASP is resident on a Host using
       dynamic address/port number assignment).
 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 (0x11)          |             Length = 8        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        ASP Identifier*                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Tag (0x4)           |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                          INFO String*                         /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The optional ASP Identifier parameter would contain a unique value
 that is locally significant among the ASPs that support an AS.  The
 SGP should save the ASP Identifier to be used, if necessary, with the
 Notify message (see Section 3.3.3.2).
 The optional INFO String parameter can carry any meaningful UTF-8 [6]
 character string along with the message.  Length of the INFO String
 parameter is from 0 to 255 octets.  No procedures are presently
 identified for its use but the INFO String MAY be used for debugging
 purposes.

Morneault, et. al. Standards Track [Page 32] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

3.3.2.2 ASP Up Ack

 The ASP Up Ack message is used to acknowledge an ASP Up message
 received from a remote M2UA peer.
 The ASPUP Ack message contains the following parameters:
    INFO String (optional)
 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 (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 3.3.2.1).

3.3.2.3 ASP Down (ASPDN)

 The ASP Down (ASPDN) message is used to indicate to a remote M2UA
 peer that the adaptation layer is not ready to receive traffic or
 maintenance messages.
 The ASPDN message contains the following parameters
     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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           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 3.3.2.1).

Morneault, et. al. Standards Track [Page 33] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

3.3.2.4 ASP Down Ack

 The ASP Down Ack message is used to acknowledge an ASP Down message
 received from a remote M2UA peer.
 The ASP Down Ack message contains the following parameters:
     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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           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 3.3.2.1).

3.3.2.5 Heartbeat (BEAT)

 The Heartbeat message is optionally used to ensure that the M2UA
 peers are still available to each other.
 The BEAT message contains the following parameter:
     Heartbeat Data           Optional
 The format for the BEAT message is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            Tag = 0x0009       |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                       Heartbeat Data                          /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The sending node defines the Heartbeat Data field contents.  It may
 include a Heartbeat Sequence Number and/or time stamp, or other
 implementation specific details.

Morneault, et. al. Standards Track [Page 34] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The receiver of a Heartbeat message does not process this field as it
 is only of significance to the sender.  The receiver echoes the
 content of the Heartbeat Data in a BEAT ACK message.

3.3.2.6 Heartbeat Ack (BEAT ACK)

 The Heartbeat ACK message is sent in response to a BEAT message.  A
 peer MUST send a BEAT ACK in response to a BEAT message.  It includes
 all the parameters of the received Heartbeat message, without any
 change.
 The BEAT ACK message contains the following parameter:
     Heartbeat Data           Optional
 The format for the BEAT ACK message is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            Tag = 0x0009       |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                       Heartbeat Data                          /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The sending node defines the Heartbeat Data field contents.  It may
 include a Heartbeat Sequence Number and/or time stamp, or other
 implementation specific details.
 The receiver of a Heartbeat message does not process this field as it
 is only of significance to the sender.  The receiver echoes the
 content of the Heartbeat Data in a BEAT ACK message.

3.3.2.7 ASP Active (ASPAC)

 The ASPAC message is sent by an ASP to indicate to an SGP that it is
 Active and ready to be used.
 The ASPAC message contains the following parameters:
    Traffic Mode Type (optional)
    Interface Identifier (optional)
       - Combination of integer and integer ranges, OR
       - string (text formatted)
    INFO String (optional)

Morneault, et. al. Standards Track [Page 35] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The format for the ASPAC message using integer formatted Interface
 Identifiers 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 (0xb)           |            Length = 8         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Traffic Mode Type                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Tag (0x1=integer)         |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     Interface Identifiers*                    /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    Tag (0x8=integer range)    |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier Start1*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier Stop1*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier Start2*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier Stop2*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                            .
   .                                                            .
   .                                                            .
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier StartN*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier StopN*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \              Additional Interface Identifiers                 /
 /                    of Tag Type 0x1 or 0x8                     \
 \                                                               /
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x4)             |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                          INFO String*                         /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Morneault, et. al. Standards Track [Page 36] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The format for the ASPAC message using text formatted (string)
 Interface Identifiers 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 (0xb)           |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Traffic Mode Type                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Tag (0x3=string)        |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     Interface Identifier*                     /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \              Additional Interface Identifiers                 /
 /                       of Tag Type 0x3                         \
 \                                                               /
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x4)             |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                          INFO String*                         /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The Traffic Mode 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            Override
     0x2            Load-share
     0x3            Broadcast
 Within a particular AS, only one Traffic Mode Type can be used.  The
 Override value indicates that the ASP is operating in Override mode,
 where the ASP takes over all traffic in an Application Server (i.e.,
 primary/backup operation), over-riding any currently active ASPs in
 the AS.  In Load-share mode, the ASP will share in the traffic
 distribution with any other currently active ASPs.  In Broadcast
 mode, all of the Active ASPs receive all message traffic in the
 Application Server.

Morneault, et. al. Standards Track [Page 37] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The optional Interface Identifiers parameter contains a list of
 Interface Identifier integers (Type 0x1 or Type 0x8) or text strings
 (Type 0x3)indexing the Application Server traffic that the sending
 ASP is configured/registered to receive.  If integer formatted
 Interface Identifiers are being used, the ASP can also send ranges of
 Interface Identifiers (Type 0x8).  Interface Identifier types Integer
 (0x1) and Integer Range (0x8) are allowed in the same message.  Text
 formatted Interface Identifiers (0x3) cannot be used with either
 Integer (0x1) or Integer Range (0x8) types.
 If no Interface Identifiers are included, the message is for all
 provisioned Interface Identifiers within the AS(s) in which the ASP
 is provisioned.  If only a subset of Interface Identifiers for an AS
 are included, the ASP is noted as Active for all the Interface
 Identifiers provisioned for that AS.
 Note: If the optional Interface Identifier parameter is present, the
       integer formatted Interface Identifier MUST be supported, while
       the text formatted Interface Identifier MAY be supported.
 An SGP that receives an ASPAC with an incorrect or unsupported
 Traffic Mode Type for a particular Interface Identifier will respond
 with an Error Message (Cause: Unsupported Traffic Handling Mode).
 The format and description of the optional Info String parameter is
 the same as for the ASP UP message (See Section 3.3.2.1).

3.3.2.8 ASP Active Ack

 The ASP Active (ASPAC) Ack message is used to acknowledge an ASP
 Active message received from a remote M2UA peer.
 The ASPAC Ack message contains the following parameters:
    Traffic Mode Type (optional)
    Interface Identifier (optional)
       - Combination of integer and integer ranges, OR
       - string (text formatted)
    INFO String (optional)

Morneault, et. al. Standards Track [Page 38] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The format for the ASPAC Ack message with Integer-formatted Interface
 Identifiers 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 (0xb)           |            Length = 8         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Traffic Mode Type                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Tag (0x1=integer)         |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     Interface Identifiers*                    /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    Tag (0x8=integer range)    |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier Start1*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier Stop1*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier Start2*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier Stop2*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  .                                                            .
  .                                                            .
  .                                                            .
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier StartN*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier StopN*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \              Additional Interface Identifiers                 /
 /                    of Tag Type 0x1 or 0x8                     \
 \                                                               /
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x4)             |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                          INFO String*                         /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Morneault, et. al. Standards Track [Page 39] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The format for the ASP Active Ack message using text formatted
 (string) Interface Identifiers 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 (0xb)           |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Traffic Mode Type                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Tag (0x3=string)        |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     Interface Identifier*                     /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \              Additional Interface Identifiers                 /
 /                       of Tag Type 0x3                         \
 \                                                               /
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         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 3.3.2.1).
 The format of the optional Interface Identifier parameter is the same
 as for the ASP Active message (See Section 3.3.2.7).
 The format and description of the optional Info String parameter is
 the same as for the ASP Up message (See Section 3.3.2.1).

3.3.2.9 ASP Inactive (ASPIA)

 The ASP Inactive (ASPIA) message is sent by an ASP to indicate to an
 SGP that it is no longer an active ASP to be used from within a list
 of ASPs.  The SGP will respond with an ASPIA Ack message and either
 discard incoming messages or buffer for a timed period and then
 discard.

Morneault, et. al. Standards Track [Page 40] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The ASPIA message contains the following parameters:
    Interface Identifiers (optional)
       - Combination of integer and integer ranges, OR
       - string (text formatted)
    INFO String (optional)
 The format for the ASP Inactive message parameters using Integer
 formatted Interface Identifiers 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 (0x1=integer)         |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     Interface Identifiers*                    /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    Tag (0x8=integer range)    |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier Start1*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier Stop1*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier Start2*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier Stop2*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  .                                                            .
  .                                                            .
  .                                                            .
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier StartN*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier StopN*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \              Additional Interface Identifiers                 /
 /                    of Tag Type 0x1 or 0x8                     \
 \                                                               /
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Tag (0x4)           |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                          INFO String*                         /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Morneault, et. al. Standards Track [Page 41] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The format for the ASP Inactive message using text formatted (string)
 Interface Identifiers 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 (0x3=string)        |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     Interface Identifier*                     /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \              Additional Interface Identifiers                 /
 /                      of Tag Type 0x3                          \
 \                                                               /
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x4)             |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                          INFO String*                         /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The format of the optional Interface Identifier parameter is the same
 as for the ASP Active message (See Section 3.3.2.7).
 The format and description of the optional Info String parameter is
 the same as for the ASP Up message (See Section 3.3.2.1).
 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, but does
 not want to receive at this time.

3.3.2.10 ASP Inactive Ack

 The ASP Inactive (ASPIA) Ack message is used to acknowledge an ASP
 Inactive message received from a remote M2UA peer.
 The ASPIA Ack message contains the following parameters:
    Interface Identifiers (optional)
       - Combination of integer and integer ranges, OR
       - string (text formatted)
    INFO String (optional)

Morneault, et. al. Standards Track [Page 42] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Tag (0x1=integer)         |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     Interface Identifiers*                    /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    Tag (0x8=integer range)    |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier Start1*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier Stop1*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier Start2*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier Stop2*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  .                                                             .
  .                                                             .
  .                                                             .
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier StartN*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier StopN*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \              Additional Interface Identifiers                 /
 /                    of Tag Type 0x1 or 0x8                     \
 \                                                               /
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x4)             |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                          INFO String*                         /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Morneault, et. al. Standards Track [Page 43] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The format for the ASP Inactive Ack message using text formatted
 (string) Interface Identifiers 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 (0x3=string)        |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     Interface Identifier*                     /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \              Additional Interface Identifiers                 /
 /                      of Tag Type 0x3                          \
 \                                                               /
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x4)             |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                          INFO String*                         /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The format of the optional Interface Identifier parameter is the same
 as for the ASP Active message (See Section 3.3.2.7).
 The format and description of the optional Info String parameter is
 the same as for the ASP Up message (See Section 3.3.2.1).

3.3.3 Layer Management (MGMT) Messages

3.3.3.1 Error (ERR)

 The Error (ERR) 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.
 An Error message MUST not be generated in response to other Error
 messages.
 The ERR message contains the following parameters:
    Error Code (mandatory)
    Interface Identifier (optional)
    Diagnostic Information (optional)

Morneault, et. al. Standards Track [Page 44] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Tag (0xc)           |            Length = 8         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          Error Code                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Tag (0x1, 0x3, or 0x8)    |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     Interface Identifier(s)*                  /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Tag (0x7)           |            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
    Unsupported Message Class              0x3
    Unsupported Message Type               0x4
    Unsupported Traffic Handling Mode      0x5
    Unexpected Message                     0x6
    Protocol Error                         0x7
    Unsupported Interface Identifier Type  0x8
    Invalid Stream Identifier              0x9
    Not Used in M2UA                       0xa
    Not Used in M2UA                       0xb
    Not Used in M2UA                       0xc
    Refused - Management Blocking          0xd
    ASP Identifier Required                0xe
    Invalid ASP Identifier                 0xf
    ASP Active for Interface Identifier(s) 0x10
    Invalid Parameter Value                0x11
    Parameter Field Error                  0x12
    Unexpected Parameter                   0x13
    Not Used in M2UA                       0x14
    Not Used in M2UA                       0x15
    Missing Parameter                      0x16

Morneault, et. al. Standards Track [Page 45] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The "Invalid Version" error would be sent if a message was received
 with an invalid or unsupported version.  The Error message would
 contain the supported version in the Common header.  The Error
 message could optionally provide the supported version in the
 Diagnostic Information area.
 The "Invalid Interface Identifier" error would be sent by a SGP if an
 ASP sends a message (i.e. an ASP Active message) with an invalid (not
 configured) Interface Identifier value.  One of the optional
 Interface Identifier parameters (Integer-based, text-based or integer
 range) MUST be used with this error code to identify the invalid
 Interface Identifier(s) received.
 The "Unsupported Traffic Handling Mode" error would be sent by a SGP
 if an ASP sends an ASP Active with an unsupported Traffic Handling
 Mode.  An example would be a case in which the SGP did not support
 load-sharing.  One of the optional Interface Identifier parameters
 (Integer-based, text-based or integer range) MAY be used with this
 error code to identify the Interface Identifier(s).
 The "Unexpected Message" error would be sent by an ASP if it received
 a MAUP message from an SGP while it was in the Inactive state.
 The "Protocol Error" error would be sent for any protocol anomaly
 (i.e. a bogus message).
 The "Invalid Stream Identifier" error would be sent if a message was
 received on an unexpected SCTP stream (i.e. a MGMT message was
 received on a stream other than "0").
 The "Unsupported Interface Identifier Type" error would be sent by a
 SGP if an ASP sends a Text formatted Interface Identifier and the SGP
 only supports Integer formatted Interface Identifiers.  When the ASP
 receives this error, it will need to resend its message with an
 Integer formatted Interface Identifier.
 The "Unsupported Message Class" error would be sent if a message with
 an unexpected or unsupported Message Class is received.
 The "Refused - Management Blocking" error is sent when an ASP Up or
 ASP Active message is received and the request is refused for
 management reasons (e.g., management lock-out").
 The "ASP Identifier Required" is sent by a SGP in response to an
 ASPUP message which does not contain an ASP Identifier parameter when
 the SGP requires one.  The ASP SHOULD resend the ASPUP message with
 an ASP Identifier.

Morneault, et. al. Standards Track [Page 46] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The "Invalid ASP Identifier" is sent by a SGP in response to an ASPUP
 message with an invalid (i.e. non-unique) ASP Identifier.
 The "ASP Currently Active for Interface Identifier(s)" error is sent
 by a SGP when a Deregistration request is received from an ASP that
 is active for Interface Identifier(s) specified in the Deregistration
 request.  One of the optional Interface Identifier parameters
 (Integer-based, text-based or integer range) MAY be used with this
 error code to identify the Interface Identifier(s).
 The "Invalid Parameter Value " error is sent if a message is received
 with an invalid parameter value (e.g., a State Request with an an
 undefined State).
 The "Parameter Field Error" would be sent if a message with a
 parameter has a wrong length field.
 The "Unexpected Parameter" error would be sent if a message contains
 an invalid parameter.
 The "Missing Parameter" error would be sent if a mandatory parameter
 was not included in a message.
 The optional Diagnostic information can be any information germane to
 the error condition, to assist in the 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 SHOULD be the first 40
 bytes of the offending message.

3.3.3.2 Notify (NTFY)

 The Notify message is used to provide an autonomous indication of
 M2UA events to an M2UA peer.
 The NTFY message contains the following parameters:
    Status Type (mandatory)
    Status Information (mandatory)
    ASP Identifier (optional)
    Interface Identifiers (optional)
    INFO String (optional)
 The format for the Notify message with Integer-formatted Interface
 Identifiers is as follows:

Morneault, et. al. Standards Track [Page 47] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

  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 (0xd)           |            Length = 8         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Status Type            |      Status Information       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Tag (0x11)          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        ASP Identifier*                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Tag (0x1=integer)         |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     Interface Identifiers*                    /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    Tag (0x8=integer range)    |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier Start1*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier Stop1*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier Start2*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier Stop2*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  .                                                             .
  .                                                             .
  .                                                             .
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Interface Identifier StartN*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Interface Identifier StopN*                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \              Additional Interface Identifiers                 /
 /                    of Tag Type 0x1 or 0x8                     \
 \                                                               /
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x4)             |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                          INFO String*                         /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Morneault, et. al. Standards Track [Page 48] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The format for the Notify message with Text-formatted Interface
 Identifiers 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 (0xd)           |            Length = 8         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Status Type            |      Status Information       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Tag (0x11)          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        ASP Identifier*                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Tag (0x3=string)        |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                     Interface Identifier*                     /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \              Additional Interface Identifiers                 /
 /                        of Tag Type 0x3                        \
 \                                                               /
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag (0x4)             |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /                                                               \
 \                          INFO String*                         /
 /                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The Status Type parameter identifies the type of the Notify message.
 The following are the valid Status Type values:
    Value          Description
     0x1   Application Server state change (AS_State_Change)
     0x2   Other

Morneault, et. al. Standards Track [Page 49] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 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
     1      reserved
     2      Application Server Inactive (AS_Inactive)
     3      Application Server Active (AS_Active)
     4      Application Server Pending (AS_Pending)
 These notifications are sent from an SGP to an ASP upon a change in
 status of a particular Application Server.  The value reflects the
 new state of the Application Server.  The Interface Identifiers of
 the AS MAY be placed in the message if desired.
 If the Status Type is Other, then the following Status Information
 values are defined:
    Value          Description
       1       Insufficient ASP resources active in AS
       2       Alternate ASP Active
       3       ASP Failure
 In the Insufficient ASP Resources case, the SGP is indicating to an
 ASP-INACTIVE ASP(s) in the AS that another ASP is required in order
 to handle the load of the AS (Load-sharing mode).  For the Alternate
 ASP Active case, the formerly Active ASP is informed when an
 alternate ASP transitions to the ASP Active state in Override mode.
 The ASP Identifier (if available) of the Alternate ASP MUST be placed
 in the message.  For the ASP Failure case, the SGP is indicating to
 ASP(s) in the AS that one of the ASPs has transitioned to ASP-DOWN.
 The ASP Identifier (if available) of the failed ASP MUST be placed in
 the message.
 For each of the Status Information values in Status Type Other, the
 Interface Identifiers of the affected AS MAY be placed in the message
 if desired.
 The format of the optional Interface Identifier parameter is the same
 as for the ASP Active message (See Section 3.3.2.7).
 The format and description of the optional Info String parameter is
 the same as for the ASP Up message (See Section 3.3.2.1).

Morneault, et. al. Standards Track [Page 50] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

3.3.4 Interface Identifier Management (IIM) Messages

 The Interface Identifier Management messages are optional.  They are
 used to support the automatic allocation of Signalling Terminals or
 Signalling Data Links [2][3].

3.3.4.1 Registration Request (REG REQ)

 The REG REQ message is sent by an ASP to indicate to a remote M2UA
 peer that it wishes to register one or more given Link Keys with the
 remote peer.  Typically, an ASP would send this message to an SGP,
 and expect to receive a REG RSP in return with an associated
 Interface Identifier value.
 The REG REQ message contains the following parameter:
    Link Key          (mandatory)
 The format for the REG REQ message is as follows
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag = 0x0309          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                           Link Key 1                          /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                              ...                              /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag = 0x0309          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                           Link Key n                          /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Link Key:   fixed length
    The Link Key parameter is mandatory.  The sender of this message
    expects that the receiver of this message will create a Link Key
    entry and assign a unique Interface Identifier value to it, if the
    Link Key entry does not yet exist.

Morneault, et. al. Standards Track [Page 51] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

    The Link Key parameter may be present multiple times in the same
    message.  This is used to allow the registration of multiple Link
    Keys in a single message.
 The format of the Link Key parameter is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Local-LK-Identifier                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Signalling Data Terminal Identifier           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                   Signalling Data Link Identifier             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Local-LK-Identifier: 32-bit integer
    The mandatory Local-LK-Identifier field is used to uniquely
    (between ASP and SGP) identify the registration request.  The
    Identifier value is assigned by the ASP, and is used to correlate
    the response in a REG RSP message with the original registration
    request.  The Identifier value MUST remain unique until the REG
    RSP is received.
    The format of the Local-LK-Identifier field is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag = 0x030a          |         Length = 8            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    Local-LK-Identifier value                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Morneault, et. al. Standards Track [Page 52] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 Signalling Data Terminal Identifier
    The Signalling Data Terminal Identifier parameter is mandatory.
    It identifies the Signalling Data Terminal associated with the SS7
    link for which the ASP is registering.  The format is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag = 0x030b          |         Length = 8            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Reserved             |        SDT Identifier         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    The SDT Identifier is a 32-bit unsigned value which may only be
    significant to 12 or 14 bits depending on the SS7 variant which is
    supported by the MTP Level 3 at the ASP.  Insignificant SDT
    Identifier bits are coded 0.
 Signalling Data Link Identifier
    The Signalling Data Link Identifier parameter is mandatory.  It
    identifies the Signalling Data Link Identifier associated with the
    SS7 link for which the ASP is registering.  The format is as
    follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag = 0x030c          |         Length = 8            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Reserved             |        SDL Identifier         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    The SDL Identifier is a 32-bit unsigned value which may only be
    significant to 12 or 14 bits depending on the SS7 variant which
    is supported by the MTP Level 3 at the ASP.  Insignificant SDLI
    bits are coded 0.

3.3.4.2 Registration Response (REG RSP)

 The REG RSP message is used as a response to the REG REQ message
 from a remote M2UA peer.  It contains indications of success/failure
 for registration requests and returns a unique Interface Identifier
 value for successful registration requests, to be used in subsequent
 M2UA Traffic Management protocol.

Morneault, et. al. Standards Track [Page 53] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The REG RSP message contains the following parameter:
    Registration Results   (mandatory)
 The format for the REG RSP message is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag = 0x030d          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                    Registration Result 1                      /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                              ...                              /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag = 0x030d          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                    Registration Result n                      /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Registration Results:  fixed length
    The Registration Results parameter contains one or more results,
    each containing the registration status for a single Link Key in
    the REG REQ message.  The number of results in a single REG RSP
    message MAY match the number of Link Key parameters found in the
    corresponding REG REQ message.  The format of each result is as
    follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Local-LK-Identifier                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Registration Status                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Interface Identifier                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Morneault, et. al. Standards Track [Page 54] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 Local-LK-Identifier:  32-bit integer
    The Local-LK-Identifier contains the same value as found in the
    matching Link Key parameter found in the REG REQ message.  The
    format of the Local-LK-Identifier is shown in Section 3.3.4.1.
 Registration Status:  32-bit integer
    The Registration Result Status field indicates the success or the
    reason for failure of a registration request.
    Its values may be one of the following:
          0         Successfully Registered
          1         Error - Unknown
          2         Error - Invalid SDLI
          3         Error - Invalid SDTI
          4         Error - Invalid Link Key
          5         Error - Permission Denied
          6         Error - Overlapping (Non-unique) Link Key
          7         Error - Link Key not Provisioned
          8         Error - Insufficient Resources
    The format of the Registration Status field is as follows:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Tag = 0x030e          |         Length = 8            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Registration Status                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Interface Identifier:  32-bit integer
    The Interface Identifier field contains the Interface Identifier
    for the associated Link Key if the registration is successful.  It
    is set to "0" if the registration was not successful.  The format
    of integer-based and text-based Interface Identifier parameters
    are shown in Section 3.2.

3.3.4.3 De-Registration Request (DEREG REQ)

 The DEREG REQ message is sent by an ASP to indicate to a remote M2UA
 peer that it wishes to de-register a given Interface Identifier.
 Typically, an ASP would send this message to an SGP, and expects to
 receive a DEREG RSP in return reflecting the Interface Identifier and
 containing a de-registration status.

Morneault, et. al. Standards Track [Page 55] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The DEREG REQ message contains the following parameter:
    Interface Identifier  (mandatory)
 The format for the DEREG REQ message is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Tag = 0x1 or 0x3          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                    Interface Identifier 1                     /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                              ...                              /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Tag = 0x1 or 0x3          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                    Interface Identifier n                     /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Interface Identifier
    The Interface Identifier parameter contains a Interface Identifier
    indexing the Application Server traffic that the sending ASP is
    currently registered to receive from the SGP but now wishes to
    de-register.  The format of integer-based and text-based Interface
    Identifier parameters are shown in Section 3.2.

3.3.4.4 De-Registration Response (DEREG RSP)

 The DEREG RSP message is used as a response to the DEREG REQ message
 from a remote M2UA peer.
 The DEREG RSP message contains the following parameter:
    De-Registration Results   (mandatory)

Morneault, et. al. Standards Track [Page 56] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The format for the DEREG RSP message is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag = 0x030f          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                  De-Registration Result 1                     /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                              ...                              /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Tag = 0x030f          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 \                                                               \
 /                  De-Registration Result n                     /
 \                                                               \
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 De-Registration Results:  fixed length
    The De-Registration Results parameter contains one or more
    results, each containing the de-registration status for a single
    Interface Identifier in the DEREG REQ message.  The number of
    results in a single DEREG RSP message MAY match the number of
    Interface Identifier parameters found in the corresponding DEREG
    REQ message.  The format of each result is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Interface Identifier                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     De-Registration Status                    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Interface Identifier:  32-bit integer
    The Interface Identifier field contains the Interface Identifier
    value of the matching Link Key to de-register, as found in the
    DEREG REQ.  The format of integer-based and text-based Interface
    Identifier parameters are shown in Section 3.2.

Morneault, et. al. Standards Track [Page 57] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 De-Registration Status:  32-bit integer
    The De-Registration Result Status field indicates the success or
    the reason for failure of the de-registration.
    Its values may be one of the following:
          0         Successfully De-registered
          1         Error - Unknown
          2         Error - Invalid Interface Identifier
          3         Error - Permission Denied
          4         Error - Not Registered
    The format of the De-Registration Status field is as follows:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Tag = 0x0310          |         Length = 8            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    De-Registration Status                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.0 Procedures

 The M2UA layer 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.

4.1 Procedures to Support the M2UA-User Layer

 These procedures achieve the M2UA layer "Transport of MTP Level 2 /
 MTP Level 3 boundary" service.

4.1.1 MTP Level 2 / MTP Level 3 Boundary Procedures

 On receiving a primitive from the local upper layer, the M2UA layer
 will send the corresponding MAUP message (see Section 3) to its peer.
 The M2UA layer MUST fill in various fields of the common and specific
 headers correctly.  In addition the message SHOULD be sent on the
 SCTP stream that corresponds to the SS7 link.

4.1.2 MAUP Message Procedures

 On receiving MAUP messages from a peer M2UA layer, the M2UA layer on
 an SG or MGC needs to invoke the corresponding layer primitives to
 the local MTP Level 2 or MTP Level 3 layer.

Morneault, et. al. Standards Track [Page 58] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

4.2 Receipt of Primitives from the Layer Management

 On receiving primitives from the local Layer Management, the M2UA
 layer will take the requested action and provide an appropriate
 response primitive to Layer Management.
 An M-SCTP_ESTABLISH request primitive from Layer Management at an ASP
 will initiate the establishment of an SCTP association.  The M2UA
 layer will attempt to establish an SCTP association with the remote
 M2UA peer by sending an SCTP-ASSOCIATE primitive to the local SCTP
 layer.
 When an SCTP association has been successfully established, the SCTP
 will send an SCTP-COMMUNICATION_UP notification primitive to the
 local M2UA layer.  At the SGP that initiated the request, the M2UA
 layer will send an M-SCTP_ESTABLISH confirm primitive to Layer
 Management when the association setup is complete.  At the peer M2UA
 layer, an M-SCTP_ESTABLISH indication primitive is sent to Layer
 Management upon successful completion of an incoming SCTP association
 setup.
 An M-SCTP_RELEASE request primitive from Layer Management initiates
 the shutdown of an SCTP association.  The M2UA layer accomplishes a
 graceful shutdown of the SCTP association by sending an SCTP-SHUTDOWN
 primitive to the SCTP layer.
 When the graceful shutdown of the SCTP association has been
 accomplished, the SCTP layer returns an SCTP-SHUTDOWN_COMPLETE
 notification primitive to the local M2UA layer.  At the M2UA Layer
 that initiated the request, the M2UA layer will send an M-
 SCTP_RELEASE confirm primitive to Layer Management when the
 association shutdown is complete.  At the peer M2UA Layer, an M-
 SCTP_RELEASE indication primitive is sent to Layer Management upon
 abort or successful shutdown of an SCTP association.
 An M-SCTP_STATUS request primitive supports a Layer Management query
 of the local status of a particular SCTP association.  The M2UA layer
 simply maps the M-SCTP_STATUS request primitive to an SCTP-STATUS
 primitive to the SCTP layer.  When the SCTP responds, the M2UA layer
 maps the association status information to an M-SCTP_STATUS confirm
 primitive.  No peer protocol is invoked.
 Similar LM-to-M2UA-to-SCTP and/or SCTP-to-M2UA-to-LM primitive
 mappings can be described for the various other SCTP Upper Layer
 primitives in RFC 2960 [8] such as INITIALIZE, SET PRIMARY, CHANGE
 HEARTBEAT, REQUEST HEARTBEAT, GET SRTT REPORT, SET FAILURE THRESHOLD,
 SET PROTOCOL PARAMETERS, DESTROY SCTP INSTANCE, SEND FAILURE, AND
 NETWORK STATUS CHANGE.  Alternatively, these SCTP Upper Layer

Morneault, et. al. Standards Track [Page 59] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 primitives (and Status as well) can be considered for modeling
 purposes as a Layer Management interaction directly with the SCTP
 Layer.
 M-NOTIFY indication and M-ERROR indication primitives indicate to
 Layer Management the notification or error information contained in a
 received M2UA Notify or Error message respectively.  These
 indications can also be generated based on local M2UA events.
 An M-ASP_STATUS request primitive supports a Layer Management query
 of the status of a particular local or remote ASP.  The M2UA layer
 responds with the status in an M-ASP_STATUS confirm primitive.  No
 M2UA peer protocol is invoked.
 An M-AS_STATUS request supports a Layer Management query of the
 status of a particular AS.  The M2UA responds with an M-AS_STATUS
 confirm primitive.  No M2UA peer protocol is invoked.
 M-ASP_UP request, M-ASP_DOWN request, M-ASP_ACTIVE request and M-
 ASP_INACTIVE request primitives allow Layer Management at an ASP to
 initiate state changes.  Upon successful completion, a corresponding
 confirm primitive is provided by the M2UA layer to Layer Management.
 If an invocation is unsuccessful, an Error indication primitive is
 provided in the primitive.  These requests result in outgoing ASP Up,
 ASP Down, ASP Active and ASP Inactive messages to the remote M2UA
 peer at an SGP.

4.2.1 Receipt of M2UA Peer Management Messages

 Upon successful state changes resulting from reception of ASP Up, ASP
 Down, ASP Active and ASP Inactive messages from a peer M2UA, the M2UA
 layer SHOULD invoke corresponding M-ASP_UP, M-ASP_DOWN, M-ASP_ACTIVE
 and M-ASP_INACTIVE, M-AS_ACTIVE, M-AS_INACTIVE, and M-AS_DOWN
 indication primitives to the local Layer Management.
 M-NOTIFY indication and M-ERROR indication primitives indicate to
 Layer Management the notification or error information contained in a
 received M2UA Notify or Error message.  These indications can also be
 generated based on local M2UA events.
 All MGMT messages, except BEAT and BEAT Ack, SHOULD be sent with
 sequenced delivery to ensure ordering.  All MGMT messages, with the
 exception of ASPTM, BEAT and BEAT Ack messages, SHOULD be sent on
 SCTP stream '0'.  All ASPTM messages SHOULD be sent on the stream
 which normally carries the data traffic to which the message applies.
 BEAT and BEAT Ack messages MAY be sent using out-of-order delivery,
 and MAY be sent on any stream.

Morneault, et. al. Standards Track [Page 60] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

4.3 AS and ASP State Maintenance

 The M2UA layer on the SGP maintains the state of each remote ASP, in
 each Application Server that the ASP is configured to receive
 traffic, as input to the M2UA message distribution function.

4.3.1 ASP States

 The state of each remote ASP, in each AS that it is configured to
 operate, is maintained in the M2UA layer in the SGP.  The state of a
 particular ASP in a particular AS changes due to events.  The events
 include:
  • Reception of messages from the peer M2UA layer at the ASP;
  • Reception of some messages from the peer M2UA layer at other ASPs

in the AS (e.g., ASP Active message indicating "Override");

  • Reception of indications from the SCTP layer; or
  • Local Management intervention.
 The ASP state transition diagram is shown in Figure 5.  The possible
 states of an ASP are:
 ASP-DOWN: The remote M2UA peer at the ASP is unavailable and/or the
 related SCTP association is down.  Initially all ASPs will be in this
 state.  An ASP in this state SHOULD NOT be sent any M2UA messages,
 with the exception of Heartbeat, ASP Down Ack and Error messages.
 ASP-INACTIVE: The remote M2UA peer at the ASP is available (and the
 related SCTP association is up) but application traffic is stopped.
 In this state the ASP MAY be sent any non-MAUP M2UA messages.
 ASP-ACTIVE: The remote M2UA peer at the ASP is available and
 application traffic is active (for a particular Interface Identifier
 or set of Interface Identifiers).

Morneault, et. al. Standards Track [Page 61] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

                  Figure 5: ASP State Transition Diagram
                                    +--------------+
                                    |  ASP-ACTIVE  |
             +----------------------|              |
             |      Other   +-------|              |
             |   ASP in AS  |       +--------------+
             |   Overrides  |           ^     |
             |              |    ASP    |     | ASP
             |              |    Active |     | Inactive
             |              |           |     v
             |              |       +--------------+
             |              |       |              |
             |              +------>| ASP-INACTIVE |
             |                      +--------------+
             |                          ^     |
   ASP Down/ |                     ASP  |     | ASP Down /
   SCTP CDI/ |                     Up   |     | SCTP CDI/
   SCTP RI   |                          |     v SCTP RI
             |                      +--------------+
             |                      |              |
             +--------------------->|   ASP-DOWN   |
                                    |              |
                                    +--------------+
 SCTP CDI: The SCTP CDI denotes the local SCTP layer's Communication
 Down Indication to the Upper Layer Protocol (M2UA) on an SGP.  The
 local SCTP layer will send this indication when it detects the loss
 of connectivity to the ASP's peer SCTP layer.  SCTP CDI is understood
 as either a SHUTDOWN_COMPLETE notification or COMMUNICATION_LOST
 notification from the SCTP layer.
 SCTP RI: The local SCTP layer's Restart indication to the upper layer
 protocol (M2UA) on an SG.  The local SCTP will send this indication
 when it detects a restart from the ASP's peer SCTP layer.

4.3.2 AS States

 The state of the AS is maintained in the M2UA layer on the SGP.  The
 state of an AS changes due to events.  These events include:
  • ASP state transitions
  • Recovery timer triggers

Morneault, et. al. Standards Track [Page 62] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The possible states of an AS are:
 AS-DOWN: The Application Server is unavailable.  This state implies
 that all related ASPs are in the ASP-DOWN state for this AS.
 Initially the AS will be in this state.  An Application Server MUST
 be in the AS-DOWN state before it can be removed from a
 configuration.
 AS-INACTIVE: The Application Server is available but no application
 traffic is active (i.e., one or more related ASPs are in the ASP-
 INACTIVE state, but none in the ASP-ACTIVE state).  The recovery
 timer T(r) is not running or has expired.
 AS-ACTIVE: The Application Server is available and application
 traffic is active.  This state implies that at least one ASP is in
 the ASP-ACTIVE state.
 AS-PENDING: An active ASP has transitioned to ASP-INACTIVE or ASP-
 DOWN and it was the last remaining active ASP in the AS.  A recovery
 timer T(r) SHOULD be started and all incoming signalling messages
 SHOULD be queued by the SGP.  If an ASP becomes ASP-ACTIVE before
 T(r) expires, the AS is moved to the AS-ACTIVE state and all the
 queued messages will be sent to the ASP.
 If T(r) expires before an ASP becomes ASP-ACTIVE, the SGP stops
 queuing messages and discards all previously queued messages.  The AS
 will move to the AS-INACTIVE state if at least one ASP is in the
 ASP-INACTIVE state, otherwise it will move to the AS-DOWN state.
 Figure 6 shows an example AS state machine for the case where the
 AS/ASP data is pre-configured.  For other cases where the AS/ASP
 configuration data is created dynamically, there would be differences
 in the state machine, especially at the creation of the AS.
 For example, where the AS/ASP configuration data is not created until
 Registration of the first ASP, the AS-INACTIVE state is entered
 directly upon the first successful REG REQ from an ASP.  Another
 example is where the AS/ASP configuration data is not created until
 the first ASP successfully enters the ASP-ACTIVE state.  In this case
 the AS-ACTIVE state is entered directly.

Morneault, et. al. Standards Track [Page 63] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

                  Figure 6: AS State Transition Diagram
      +----------+   one ASP trans to ACTIVE   +-------------+
      |    AS-   |---------------------------->|     AS-     |
      | INACTIVE |                             |   ACTIVE    |
      |          |<---                         |             |
      +----------+    \                        +-------------+
         ^   |         \ Tr Expiry,                ^    |
         |   |          \ at least one             |    |
         |   |           \ ASP in ASP-INACTIVE     |    |
         |   |            \                        |    |
         |   |             \                       |    |
         |   |              \                      |    |
 one ASP |   | all ASP       \            one ASP  |    | Last ACTIVE
 trans   |   | trans to       \           trans to |    | ASP trans to
 to      |   | ASP-DOWN        -------\   ASP-     |    | ASP-INACTIVE
 ASP-    |   |                         \  ACTIVE   |    | or ASP-DOWN
 INACTIVE|   |                          \          |    | (start Tr)
         |   |                           \         |    |
         |   |                            \        |    |
         |   v                             \       |    v
      +----------+                          \  +-------------+
      |          |                           --|             |
      | AS-DOWN  |                             | AS-PENDING  |
      |          |                             |  (queuing)  |
      |          |<----------------------------|             |
      +----------+    Tr Expiry and no ASP     +-------------+
                      in ASP-INACTIVE state
    Tr = Recovery Timer

4.3.3 M2UA Management Procedures for Primitives

 Before the establishment of an SCTP association the ASP state at both
 the SGP and ASP is assumed to be in the state ASP-DOWN.
 Once the SCTP association is established (see Section 4.2.1) and
 assuming that the local M2UA-User is ready, the local M2UA ASP
 Maintenance (ASPM) function will initiate the relevant procedures,
 using the ASP Up/ASP Down/ASP Active/ASP Inactive messages to convey
 the ASP state to the SGP (see Section 4.3.4).
 If the M2UA layer subsequently receives an SCTP-COMMUNICATION_DOWN or
 SCTP-RESTART indication primitive from the underlying SCTP layer, it
 will inform the Layer Management by invoking the M-SCTP_STATUS
 indication primitive.  The state of the ASP will be moved to ASP-
 DOWN.

Morneault, et. al. Standards Track [Page 64] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 In the case of SCTP-COMMUNICATION_DOWN, the SCTP client MAY try to
 re-establish the SCTP association.  This MAY be done by the M2UA
 layer automatically, or Layer Management MAY re-establish using the
 M-SCTP_ESTABLISH request primitive.
 In the case of an SCTP-RESTART indication at an ASP, the ASP is now
 considered by its M2UA peer to be in the ASP-DOWN state.  The ASP, if
 it is to recover, must begin any recovery with the ASP-Up procedure.

4.3.4 ASPM Procedures for Peer-to-Peer Messages

4.3.4.1 ASP Up Procedures

 After an ASP has successfully established an SCTP association to an
 SGP, the SGP waits for the ASP to send an ASP Up message, indicating
 that the ASP M2UA peer is available.  The ASP is always the initiator
 of the ASP Up message.  This action MAY be initiated at the ASP by an
 M-ASP_UP request primitive from Layer Management or MAY be initiated
 automatically by an M2UA management function.
 When an ASP Up message is received at an SGP and internally the
 remote ASP is in the ASP-DOWN state and not considered locked-out for
 local management reasons, the SGP marks the remote ASP in the state
 ASP-INACTIVE and informs Layer Management with an M-ASP_Up indication
 primitive.  If the SGP is aware, via current configuration data,
 which Application Servers the ASP is configured to operate in, the
 SGP updates the ASP state to ASP-INACTIVE in each AS that it is a
 member.
 Alternatively, the SGP may move the ASP into a pool of Inactive ASPs
 available for future configuration within Application Server(s),
 determined in a subsequent Registration Request or ASP Active
 procedure.  If the ASP Up message contains an ASP Identifier, the SGP
 should save the ASP Identifier for that ASP.  The SGP MUST send an
 ASP Up Ack message in response to a received ASP Up message even if
 the ASP is already marked as ASP-INACTIVE at the SGP.
 If for any local reason (e.g., management lock-out) the SGP cannot
 respond with an ASP Up Ack message, the SGP responds to an ASP Up
 message with an Error message with Reason "Refused - Management
 Blocking".
 At the ASP, the ASP Up Ack message received is not acknowledged.
 Layer Management is informed with an M-ASP_UP confirm primitive.
 When the ASP sends an ASP Up message it starts timer T(ack).  If the
 ASP does not receive a response to an ASP Up message within T(ack),
 the ASP MAY restart T(ack) and resend ASP Up messages until it

Morneault, et. al. Standards Track [Page 65] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 receives an ASP Up Ack message.  T(ack) is provisionable, with a
 default of 2 seconds.  Alternatively, retransmission of ASP Up
 messages MAY be put under control of Layer Management.  In this
 method, expiry of T(ack) results in an M-ASP_UP confirm primitive
 carrying a negative indication.
 The ASP MUST wait for the ASP Up Ack message before sending any other
 M2UA messages (e.g., ASP Active or REG REQ).  If the SGP receives any
 other M2UA messages before an ASP Up message is received (other than
 ASP Down - see Section 4.3.4.2), the SGP MAY discard them.
 If an ASP Up message is received and internally the remote ASP is in
 the ASP-ACTIVE state, an ASP Up Ack message is returned, as well as
 an Error message ("Unexpected Message), and the remote ASP state is
 changed to ASP-INACTIVE in all relevant Application Servers.
 If an ASP Up message is received and internally the remote ASP is
 already in the ASP-INACTIVE state, an ASP Up Ack message is returned
 and no further action is taken.

4.3.4.1.1 M2UA Version Control

 If an ASP Up message with an unsupported version is received, the
 receiving end responds with an Error message, indicating the version
 the receiving node supports and notifies Layer Management.
 This is useful when protocol version upgrades are being performed in
 a network.  A node upgraded to a newer version SHOULD support the
 older versions used on other nodes it is communicating with.  Because
 ASPs initiate the ASP Up procedure it is assumed that the Error
 message would normally come from the SGP.

4.3.4.2 ASP Down Procedures

 The ASP will send an ASP Down message to an SGP when the ASP wishes
 to be removed from service in all Application Servers that it is a
 member and no longer receive any MAUP or ASPTM messages.  This action
 MAY be initiated at the ASP by an M-ASP_DOWN request primitive from
 Layer Management or MAY be initiated automatically by an M2UA
 management function.
 Whether the ASP is permanently removed from any AS is a function of
 configuration management.  In the case where the ASP previously used
 the Registration procedures (see Section 4.4) to register within
 Application Servers but has not unregistered from all of them prior
 to sending the ASP Down message, the SGP MUST consider the ASP as
 unregistered in all Application Servers that it is still a member.

Morneault, et. al. Standards Track [Page 66] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The SGP marks the ASP as ASP-DOWN, informs Layer Management with an
 M-ASP_Down indication primitive, and returns an ASP Down Ack message
 to the ASP.
 The SGP MUST send an ASP Down Ack message in response to a received
 ASP Down message from the ASP even if the ASP is already marked as
 ASP-DOWN at the SGP.
 At the ASP, the ASP Down Ack message received is not acknowledged.
 Layer Management is informed with an M-ASP_DOWN confirm primitive.
 If the ASP receives an ASP Down Ack without having sent an ASP Down
 message, the ASP SHOULD now consider itself as in the ASP-DOWN state.
 If the ASP was previously in the ASP-ACTIVE or ASP_INACTIVE state,
 the ASP SHOULD then initiate procedures to return itself to its
 previous state.
 When the ASP sends an ASP Down message it starts timer T(ack).  If
 the ASP does not receive a response to an ASP Down message within
 T(ack), the ASP MAY restart T(ack) and resend ASP Down messages until
 it receives an ASP Down Ack message.  T(ack) is provisionable, with a
 default of 2 seconds.  Alternatively, retransmission of ASP Down
 messages MAY be put under control of Layer Management.  In this
 method, expiry of T(ack) results in an M-ASP_DOWN confirm primitive
 carrying a negative indication.

4.3.4.3 ASP Active Procedures

 Anytime after the ASP has received an ASP Up Ack message from the
 SGP, the ASP MAY send an ASP Active message to the SGP indicating
 that the ASP is ready to start processing traffic.  This action MAY
 be initiated at the ASP by an M-ASP_ACTIVE request primitive from
 Layer Management or MAY be initiated automatically by a M2UA
 management function.  In the case where an ASP wishes to process the
 traffic for more than one Application Server across a common SCTP
 association, the ASP Active message(s) SHOULD contain a list of one
 or more Interface Identifiers to indicate for which Application
 Servers the ASP Active message applies.  It is not necessary for the
 ASP to include any Interface Identifiers of interest in a single ASP
 Active message, thus requesting to become active in all Interface
 Identifiers at the same time.  Multiple ASP Active messages MAY be
 used to activate within the Application Servers independently, or in
 sets.  In the case where an ASP Active message does not contain a
 Interface Identifier parameter, the receiver must know, via
 configuration data, of which Application Server(s) the ASP is a
 member.
 For the Application Servers that the ASP can successfully activate,
 the SGP responds with one or more ASP Active Ack messages, including

Morneault, et. al. Standards Track [Page 67] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 the associated Interface Identifier(s) and reflecting any Traffic
 Mode Type value present in the related ASP Active message.  The
 Interface Identifier parameter MUST be included in the ASP Active Ack
 message(s) if the received ASP Active message contained any Interface
 Identifiers.  Depending on any Traffic Mode Type request in the ASP
 Active message or local configuration data if there is no request,
 the SGP moves the ASP to the correct ASP traffic state within the
 associated Application Server(s).  Layer Management is informed with
 an M-ASP_Active indication.  If the SGP receives any Data messages
 before an ASP Active message is received, the SGP MAY discard them.
 By sending an ASP Active Ack message, the SGP is now ready to receive
 and send traffic for the related Interface Identifier(s).  The ASP
 SHOULD NOT send MAUP messages for the related Interface Identifier(s)
 before receiving an ASP Active Ack message, or it will risk message
 loss.
 Multiple ASP Active Ack messages MAY be used in response to an ASP
 Active message containing multiple Interface Identifiers, allowing
 the SGP to independently acknowledge the ASP Active message for
 different (sets of) Interface Identifiers.  The SGP MUST send an
 Error message ("Invalid Interface Identifier") for each Interface
 Identifier value that cannot be successfully activated.
 In the case where an "out-of-the-blue" ASP Active message is received
 (i.e., the ASP has not registered with the SG or the SG has no static
 configuration data for the ASP), the message MAY be silently
 discarded.
 The SGP MUST send an ASP Active Ack message in response to a received
 ASP Active message from the ASP, if the ASP is already marked in the
 ASP-ACTIVE state at the SGP.
 At the ASP, the ASP Active Ack message received is not acknowledged.
 Layer Management is informed with an M-ASP_ACTIVE confirm primitive.
 It is possible for the ASP to receive Data message(s) before the ASP
 Active Ack message as the ASP Active Ack and Data messages from an SG
 may be sent on different SCTP streams.  Message loss is possible as
 the ASP does not consider itself in the ASP-ACTIVE state until
 reception of the ASP Active Ack message.
 When the ASP sends an ASP Active message it starts timer T(ack).  If
 the ASP does not receive a response to an ASP Active message within
 T(ack), the ASP MAY restart T(ack) and resend ASP Active message(s)
 until it receives an ASP Active Ack message.  T(ack) is
 provisionable, with a default of 2 seconds.  Alternatively,
 retransmission of ASP Active messages MAY be put under the control of
 Layer Management.  In this method, expiry of T(ack) results in an M-
 ASP_ACTIVE confirm primitive carrying a negative indication.

Morneault, et. al. Standards Track [Page 68] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 There are three modes of Application Server traffic handling in the
 SGP M2UA layer: Override, Load share and Broadcast.  When included,
 the Traffic Mode Type parameter in the ASP Active message indicates
 the traffic handling mode to be used in a particular Application
 Server.  If the SGP determines that the mode indicated in an ASP
 Active message is unsupported or incompatible with the mode currently
 configured for the AS, the SGP responds with an Error message
 ("Unsupported / Invalid Traffic Handling Mode").  If the traffic
 handling mode of the Application Server is not already known via
 configuration data, the traffic handling mode indicated in the first
 ASP Active message causing the transition of the Application Server
 state to AS-ACTIVE MAY be used to set the mode.
 In the case of an Override mode AS, reception of an ASP Active
 message at an SGP causes the (re)direction of all traffic for the AS
 to the ASP that sent the ASP Active message.  Any previously active
 ASP in the AS is now considered to be in the state ASP-INACTIVE and
 SHOULD no longer receive traffic from the SGP within the AS.  The SGP
 then MUST send a Notify message ("Alternate ASP Active") to the
 previously active ASP in the AS, and SHOULD stop traffic to/from that
 ASP.  The ASP receiving this Notify MUST consider itself now in the
 ASP-INACTIVE state, if it is not already aware of this via inter-ASP
 communication with the Overriding ASP.
 In the case of a Load-share mode AS, reception of an ASP Active
 message at an SGP causes the direction of traffic to the ASP sending
 the ASP Active message, in addition to all the other ASPs that are
 currently active in the AS.  The algorithm at the SGP for load-
 sharing traffic within an AS to all the active ASPs is implementation
 dependent.  The algorithm could, for example be round-robin or based
 on information in the Data message (e.g., such as the SLS in the
 Routing Label).
 An SGP, upon reception of an ASP Active message for the first ASP in
 a Load share AS, MAY choose not to direct traffic to a newly active
 ASP until it determines that there are sufficient resources to handle
 the expected load (e.g., until there are "n" ASPs in state ASP-ACTIVE
 in the AS).
 All ASPs within a load-sharing mode AS must be able to process any
 Data message received for the AS, to accommodate any potential fail-
 over or balancing of the offered load.
 In the case of a Broadcast mode AS, reception of an ASP Active
 message at an SGP causes the direction of traffic to the ASP sending
 the ASP Active message, in addition to all the other ASPs that are
 currently active in the AS.  The algorithm at the SGP for

Morneault, et. al. Standards Track [Page 69] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 broadcasting traffic within an AS to all the active ASPs is a simple
 broadcast algorithm, where every message is sent to each of the
 active ASPs.
 An SGP, upon reception of an ASP Active message for the first ASP in
 a Broadcast AS, MAY choose not to direct traffic to a newly active
 ASP until it determines that there are sufficient resources to handle
 the expected load (e.g., until there are "n" ASPs in state ASP-ACTIVE
 in the AS).
 Whenever an ASP in a Broadcast mode AS becomes ASP-ACTIVE, the SGP
 MUST tag the first DATA message broadcast in each SCTP stream with a
 unique Correlation Id parameter.  The purpose of this Correlation Id
 is to permit the newly active ASP to synchronize its processing of
 traffic in each ordered stream with the other ASPs in the broadcast
 group.

4.3.4.4 ASP Inactive Procedures

 When an ASP wishes to withdraw from receiving traffic within an AS,
 the ASP sends an ASP Inactive message to the SGP.  This action MAY be
 initiated at the ASP by an M-ASP_INACTIVE request primitive from
 Layer Management or MAY be initiated automatically by an M2UA
 management function.  In the case where an ASP is processing the
 traffic for more than one Application Server across a common SCTP
 association, the ASP Inactive message contains one or more Interface
 Identifiers to indicate for which Application Servers the ASP
 Inactive message applies.  In the case where an ASP Inactive message
 does not contain a Interface Identifier parameter, the receiver must
 know, via configuration data, of which Application Servers the ASP is
 a member and move the ASP to the ASP-INACTIVE state in all
 Application Servers.  In the case of an Override mode AS, where
 another ASP has already taken over the traffic within the AS with an
 ASP Active ("Override") message, the ASP that sends the ASP Inactive
 message is already considered by the SGP to be in the state ASP-
 INACTIVE.  An ASP Inactive 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 SGP moves the ASP to the
 ASP-INACTIVE state and the AS traffic is re-allocated across the
 remaining ASPs in the state ASP-ACTIVE, as per the load-sharing
 algorithm currently used within the AS.  A Notify message
 ("Insufficient ASP resources active in AS") MAY be sent to all
 inactive ASPs, if required.  An ASP Inactive Ack message is sent to
 the ASP after all traffic is halted and Layer Management is informed
 with an M-ASP_INACTIVE indication primitive.

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 In the case of a Broadcast mode AS, the SGP moves the ASP to the
 ASP-INACTIVE state and the AS traffic is broadcast only to the
 remaining ASPs in the state ASP-ACTIVE.  A Notify message
 ("Insufficient ASP resources active in AS") MAY be sent to all
 inactive ASPs, if required.  An ASP Inactive Ack message is sent to
 the ASP after all traffic is halted and Layer Management is informed
 with an M-ASP_INACTIVE indication primitive.
 Multiple ASP Inactive Ack messages MAY be used in response to an ASP
 Inactive message containing multiple Interface Identifiers, allowing
 the SGP to independently acknowledge for different (sets of)
 Interface Identifiers.  The SGP sends an Error message ("Invalid
 Interface Identifier") for each invalid or not configured Interface
 Identifier value in a received ASP Inactive message.
 The SGP MUST send an ASP Inactive Ack message in response to a
 received ASP Inactive message from the ASP and the ASP is already
 marked as ASP-INACTIVE at the SGP.
 At the ASP, the ASP Inactive Ack message received is not
 acknowledged.  Layer Management is informed with an M-ASP_INACTIVE
 confirm primitive.  If the ASP receives an ASP Inactive Ack without
 having sent an ASP Inactive message, the ASP SHOULD now consider
 itself as in the ASP-INACTIVE state.  If the ASP was previously in
 the ASP-ACTIVE state, the ASP SHOULD then initiate procedures to
 return itself to its previous state.
 When the ASP sends an ASP Inactive message it starts timer
  T(ack).  If the ASP does not receive a response to an ASP Inactive
 message within T(ack), the ASP MAY restart T(ack) and resend ASP
 Inactive messages until it receives an ASP Inactive Ack message.
 T(ack) is provisionable, with a default of 2 seconds.  Alternatively,
 retransmission of ASP Inactive messages MAY be put under the control
 of Layer Management.  In this method, expiry of T(ack) results in a
 M-ASP_Inactive confirm primitive carrying a negative indication.
 If no other ASPs in the Application Server are in the state ASP-
 ACTIVE, the SGP MUST send a Notify message ("AS-Pending") to all of
 the ASPs in the AS which are in the state ASP-INACTIVE.  The SGP
 SHOULD start buffering the incoming messages for T(r)seconds, after
 which messages MAY be discarded.  T(r) is configurable by the network
 operator.  If the SGP receives an ASP Active message from an ASP in
 the AS before expiry of T(r), the buffered traffic is directed to
 that ASP and the timer is canceled.  If T(r) expires, the AS is moved
 to the AS-INACTIVE state.

Morneault, et. al. Standards Track [Page 71] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

4.3.4.5 Notify Procedures

 A Notify message reflecting a change in the AS state MUST be sent to
 all ASPs in the AS, except those in the ASP-DOWN state, with
 appropriate Status Information and any ASP Identifier of the failed
 ASP.  At the ASP, Layer Management is informed with an M-NOTIFY
 indication primitive.  The Notify message MUST be sent whether the AS
 state change was a result of an ASP failure or reception of an ASP
 State Management (ASPSM) / ASP Traffic Management (ASPTM) message.
 In the second case, the Notify message MUST be sent after any related
 acknowledgment messages (e.g., ASP Up Ack, ASP Down Ack, ASP Active
 Ack, or ASP Inactive Ack).
 In the case where a Notify ("AS-PENDING") message is sent by an SGP
 that now has no ASPs active to service the traffic, or where a Notify
 ("Insufficient ASP resources active in AS") message MUST be sent in
 the Load share or Broadcast mode, the Notify message does not
 explicitly compel the ASP(s) receiving the message to become active.
 The ASPs remain in control of what (and when) traffic action is
 taken.
 In the case where a Notify message does not contain a Interface
 Identifier parameter, the receiver must know, via configuration data,
 of which Application Servers the ASP is a member and take the
 appropriate action in each AS.

4.3.4.6 Heartbeat Procedures

 The optional Heartbeat procedures MAY be used when operating over
 transport layers that do not have their own heartbeat mechanism for
 detecting loss of the transport association (i.e., other than SCTP).
 Either M2UA peer may optionally send Heartbeat messages periodically,
 subject to a provisionable timer T(beat).  Upon receiving a Heartbeat
 message, the M2UA peer MUST respond with a Heartbeat Ack message.
 If no Heartbeat Ack message (or any other M2UA message) is received
 from the M2UA peer within 2*T(beat), the remote M2UA peer is
 considered unavailable.  Transmission of Heartbeat messages is
 stopped and the signalling process SHOULD attempt to re-establish
 communication if it is configured as the client for the disconnected
 M2UA peer.
 The Heartbeat message may optionally contain an opaque Heartbeat Data
 parameter that MUST be echoed back unchanged in the related Heartbeat
 Ack message.  The sender, upon examining the contents of the returned
 Heartbeat Ack message, MAY choose to consider the remote M2UA peer as
 unavailable.  The contents/format of the Heartbeat Data parameter is

Morneault, et. al. Standards Track [Page 72] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 implementation-dependent and only of local interest to the original
 sender.  The contents may be used, for example, to support a
 Heartbeat sequence algorithm (to detect missing Heartbeats), and/or a
 time stamp mechanism (to evaluate delays).
 Note: Heartbeat related events are not shown in Figure 5 "ASP state
       transition diagram".

4.4 Link Key Management Procedures

 The Interface Identifier Management procedures are optional.  They
 can be used to support automatic allocation of Signalling Terminals
 or Signalling Data Links [2][3].

4.4.1 Registration

 An ASP MAY dynamically register with an SGP as an ASP within an
 Application Server for individual Interface Identifier(s) using the
 REG REQ message.  A Link Key parameter in the REG REQ specifies the
 parameters associated with the Link Key.
 The SGP examines the contents of the received Link Key parameters
 (SDLI and SDTI) and compares them with the currently provisioned
 Interface Identifiers.  If the received Link Key matches an existing
 SGP Link Key entry, and the ASP is not currently included in the list
 of ASPs for the related Application Server, the SGP MAY authorize the
 ASP to be added to the AS.  Or, if the Link Key does not currently
 exist and the received Link Key data is valid and unique, an SGP
 supporting dynamic configuration MAY authorize the creation of a new
 Interface Identifier and related Application Server and add the ASP
 to the new AS.  In either case, the SGP returns a Registration
 Response message to the ASP, containing the same Local-LK-Identifier
 as provided in the initial request, a Registration Result
 "Successfully Registered" and the Interface Identifier.  A unique
 method of Interface Identifier valid assignment at the SG/SGP is
 implementation dependent but MUST be guaranteed to be unique for each
 Application server or Link Key served by SGP.
 If the SGP determines that the received Link Key data is invalid, or
 contains invalid parameter values, the SGP returns a Registration
 Response message to the ASP, containing a Registration Result "Error
 - Invalid Link Key", "Error - Invalid SDTI", "Error - Invalid SDLI"
 as appropriate.

Morneault, et. al. Standards Track [Page 73] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 If the SGP determines that the Link Key parameter overlaps with an
 existing Link Key entry, the SGP returns a Registration Response
 message to the ASP, with a Registration Status of "Error -
 Overlapping (Non-Unique) Link Key".  An incoming signalling message
 received at an SGP cannot match against more than one Link Key.
 If the SGP does not authorize the registration request, the SGP
 returns a REG RSP message to the ASP containing the Registration
 Result "Error - Permission Denied".
 If an SGP determines that a received Link Key does not currently
 exist and the SGP does not support dynamic configuration, the SGP
 returns a Registration Response message to the ASP, containing a
 Registration Result "Error - Link Key not Provisioned".
 If an SGP determines that a received Link Key does not currently
 exist and the SGP supports dynamic reconfiguration but does not have
 the capacity to add new Link Key and Application Server entries, the
 SGP returns a Registration Response message to the ASP, containing a
 Registration Result "Error - Insufficient Resources".
 An ASP MAY register multiple Link Keys at once by including a number
 of Link Key parameters in a single REG REQ message.  The SGP MAY
 respond to each registration request in a single REG RSP message,
 indicating the success or failure result for each Link Key in a
 separate Registration Result parameter.  Alternatively, the SGP MAY
 respond with multiple REG RSP messages, each with one or more
 Registration Result parameters.  The ASP uses the Local-LK-Identifier
 parameter to correlate the requests with the responses.

4.4.2 Deregistration

 An ASP MAY dynamically de-register with an SGP as an ASP within an
 Application Server for individual Interface Identifier(s) using the
 DEREG REQ message.  A Interface Identifier parameter in the DEREG REQ
 specifies which Interface Identifier to de-register.
 The SGP examines the contents of the received Interface Identifier
 parameter and validates that the ASP is currently registered in the
 Application Server(s) related to the included Interface
 Identifier(s).  If validated, the ASP is de-registered as an ASP in
 the related Application Server.
 The deregistration procedure does not necessarily imply the deletion
 of Link Key and Application Server configuration data at the SGP.
 Other ASPs may continue to be associated with the Application Server,

Morneault, et. al. Standards Track [Page 74] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 in which case the Link Key data CANNOT be deleted.  If a
 Deregistration results in no more ASPs in an Application Server, an
 SGP MAY delete the Link Key data.
 The SGP acknowledges the de-registration required by returning a
 DEREG RSP to the requesting ASP.  The result of the de-registration
 is found in the Deregistration Result parameter, indicating success
 or failure with cause.
 An ASP MAY de-register multiple Interface Identifiers at once by
 including a number of Interface Identifiers in a single DEREG REQ
 message.  The SGP MUST respond to each deregistration request in a
 single DEREG RSP message, indicating the success or failure result
 for each Interface Identifier in a separate Deregistration Result
 parameter.

5.0 Examples of MTP2 User Adaptation (M2UA) Procedures

5.1 Establishment of associations between SGP and MGC examples

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

 This scenario shows the example M2UA message flows for the
 establishment of traffic between an SGP 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.
              SGP                       ASP1
               |
               |<---------ASP Up----------|
               |--------ASP Up Ack------->|
               |                          |
               |<-------ASP Active--------|
               |------ASP Active Ack----->|
               |                          |
               |------NTFY(AS-ACTIVE)---->|

Morneault, et. al. Standards Track [Page 75] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

5.1.2 Single ASP in an Application Server (1+0 sparing) with Dynamic

    Registration
 This scenario is the same as the one shown in Section 5.1.1 except
 with a dynamic registration (automatic allocation) of an Interface
 Identifier(s).
              SGP                       ASP1
               |
               |<---------ASP Up----------|
               |--------ASP Up Ack------->|
               |                          |
               |<--------REG REQ----------|
               |------REG REQ RESP------->|
               |                          |
               |<-------ASP Active--------|
               |------ASP Active Ack----->|
               |                          |
               |------NTFY(AS-ACTIVE)---->|

5.1.3 Two ASPs in Application Server (1+1 sparing)

 This scenario shows the example M2UA message flows for the
 establishment of traffic between an SGP and two ASPs in the same
 Application Server, where ASP1 is configured to be active and ASP2 to
 be 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.
        SGP                       ASP1                       ASP2
         |                         |                          |
         |<--------ASP Up----------|                          |
         |-------ASP Up Ack------->|                          |
         |                         |                          |
         |<-----------------------------ASP Up----------------|
         |----------------------------ASP Up Ack------------->|
         |                         |                          |
         |                         |                          |
         |<-------ASP Active-------|                          |
         |-----ASP Active Ack----->|                          |
         |                         |                          |
         |                         |                          |
         |-----NTFY(AS-ACTIVE)---->|                          |
         |                         |                          |
         |------------------NTFY(AS-ACTIVE)------------------>|

Morneault, et. al. Standards Track [Page 76] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

5.2 ASP Traffic Fail-over Examples

5.2.1 (1+1 Sparing, withdrawal of ASP, backup Override)

 Following on from the example in Section 5.1.2, and ASP withdraws
 from service:
       SGP                       ASP1                       ASP2
         |                         |                          |
         |<-----ASP Inactive-------|                          |
         |----ASP Inactive Ack---->|                          |
         |                         |                          |
         |----NTFY(AS-PENDING)---->|                          |
         |------------------NTFY(AS-PENDING)----------------->|
         |                         |                          |
         |<------------------------------ ASP Active----------|
         |-----------------------------ASP Active Ack-------->|
         |                         |                          |
         |-----NTFY(AS-ACTIVE)---->|                          |
         |------------------NTFY(AS-ACTIVE)------------------>|
         |                         |                          |
 In this case, the SGP notifies ASP2 that the AS has moved to the AS-
 PENDING state.  ASP2 sends ASP Active to bring the AS back to the
 AS-ACTIVE state.  If ASP2 did not send the ASP Active message before
 T(r) expired, the SGP would send a NOTIFY (AS-DOWN).
 Note: If the SGP detects loss of the M2UA peer (through a detection
       of SCTP failure), the initial SGP-ASP1 ASP Inactive message
       exchange would not occur.
        SGP                       ASP1                       ASP2
         |                         |                          |
   (detects SCTP failure)
         |------------------NTFY(AS-PENDING)----------------->|
         |                         |                          |
         |<------------------------------ ASP Active----------|
         |-----------------------------ASP Active Ack-------->|
         |                         |                          |
         |------------------NTFY(AS-ACTIVE)------------------>|
         |                         |                          |

Morneault, et. al. Standards Track [Page 77] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

5.2.2 (1+1 Sparing, backup Override)

 Following on from the example in Section 5.1.2, and ASP2 wishes to
 override ASP1 and take over the traffic:
        SGP                       ASP1                       ASP2
         |                         |                          |
         |<-------------------------------ASP Active----------|
         |-----------------------------ASP Active Ack-------->|
         |----NTFY(Alt ASP-Act)--->|                          |
         |                         |                          |
 In this case, the SGP notifies ASP1 that an alternative ASP has
 overridden it.

5.3 SGP to MGC, MTP Level 2 to MTP Level 3 Boundary Procedures

 When the M2UA layer on the ASP has a MAUP message to send to the SGP,
 it will do the following:
  1. Determine the correct SGP
  1. Find the SCTP association to the chosen SGP
  1. Determine the correct stream in the SCTP association based on

the SS7 link

  1. Fill in the MAUP message, fill in M2UA Message Header, fill in

Common Header

  1. Send the MAUP message to the remote M2UA peer in the SGP, over

the SCTP association

 When the M2UA layer on the SGP has a MAUP message to send to the ASP,
 it will do the following:
  1. Determine the AS for the Interface Identifier
  1. Determine the Active ASP (SCTP association) within the AS
  1. Determine the correct stream in the SCTP association based on

the SS7 link

  1. Fill in the MAUP message, fill in M2UA Message Header, fill in

Common Header

  1. Send the MAUP message to the remote M2UA peer in the ASP, over

the SCTP association

Morneault, et. al. Standards Track [Page 78] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

5.3.1 SS7 Link Alignment

 The MGC can request that a SS7 link be brought into alignment using
 the normal or emergency procedure [2][3].  An example of the message
 flow to bring a SS7 link in-service using the normal alignment
 procedure is shown below.
     MTP2            M2UA                  M2UA               MTP3
      SGP             SGP                   ASP                ASP
      <----Start Req---|<---Establish Req----|<----Start Req------
  1. –In Serv Ind–>|—-Establish Cfm—>|—-In Serv Ind—→
 An example of the message flow to bring a SS7 link in-service using
 the emergency alignment procedure.

MTP2 M2UA M2UA MTP3

SGP             SGP                                ASP            ASP
<----Emer Req----|<--State Req (STATUS_EMER_SET)----|<----Emer Req---
  1. —-Emer Cfm—>|—State Cfm (STATUS_EMER_SET)—>|—-Emer Cfm—→
<---Start Req----|<-------Establish Req-------------|<---Start Req----
  1. –In Serv Ind–>|——–Establish Cfm————>|—In Serv Ind–>

5.3.2 SS7 Link Release

 The MGC can request that a SS7 link be taken out-of-service.  It uses
 the Release Request message as shown below.
   MTP2               M2UA                  M2UA                MTP3
    SGP                SGP                   ASP                 ASP
     <-----Stop Req-----|<---Release Req------|<-----Stop Req------
  1. -Out of Serv Ind→|—-Release Cfm—–>|–Out of Serv Ind–>

Morneault, et. al. Standards Track [Page 79] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The SGP can autonomously indicate that a SS7 link has gone out-of-
 service as shown below.
     MTP2           M2UA                  M2UA              MTP3
      SGP            SGP                   ASP               ASP
  1. -Out of Serv→|—-Release Ind—–>|–Out of Serv–>

5.3.3 Set and Clear Local Processor Outage

 The MGC can set a Local Processor Outage condition.  It uses the
 State Request message as shown below.
MTP2            M2UA                               M2UA           MTP3
 SGP             SGP                                ASP            ASP
 <----LPO Req----|<---State Req (STATUS_LPO_SET)----|<----LPO Req---
  1. —-LPO Cfm—>|—-State Cfm (STATUS_LPO_SET)—>|—-LPO Cfm—→
 The MGC can clear a Local Processor Outage condition.  It uses the
 State Request message as shown below.
MTP2            M2UA                               M2UA          MTP3
 SGP             SGP                                ASP           ASP
 <---LPO Req---|<---State Req (STATUS_LPO_CLEAR)----|<----LPO Req---
  1. —LPO Cfm–>|—-State Cfm (STATUS_LPO_CLEAR)—>|—-LPO Cfm—→

5.3.4 Notification of Remote Processor Outage

 The SGP can indicate that Remote has entered or exited the Processor
 Outage condition for a SS7 link.  It uses the State Indication
 message as shown below.

MTP2 M2UA M2UA MTP3

SGP            SGP                                 ASP            ASP
  1. —RPO Ind—→|—-State Ind (EVENT_RPO_ENTER)–>|—–RPO Ind—→
  1. RPO Rcvr Ind–>|—-State Ind (EVENT_RPO_EXIT)—>|–RPO Rcvr Ind–>

Morneault, et. al. Standards Track [Page 80] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

5.3.5 Notification of SS7 Link Congestion

 The SGP can indicate that a SS7 link has become congested.  It uses
 the Congestion Indication message as shown below.

MTP2 M2UA M2UA MTP3

SGP            SGP                                 ASP            ASP
  1. —Cong Ind—→|——–Cong Ind (STATUS)——→|—-Cong Ind—→
  1. Cong Cease Ind→|——–Cong Ind (STATUS)——→|-Cong Cease Ind→

5.3.6 SS7 Link Changeover

 An example of the message flow for an error free changeover is shown
 below.  In this example, there were three messages in the
 retransmission queue that needed to be retrieved.
MTP2          M2UA                            M2UA             MTP3
 SGP           SGP                             ASP              ASP
 <-Rtrv BSN Req-|<--Rtrv Req (ACTION_RTRV_BSN)--|<--Rtrv BSN Req---
                             (seq_num = 0)
  1. Rtrv BSN Cfm→|—Rtrv Cfm (ACTION_RTRV_BSN)→|—Rtrv BSN Cfm–>

(seq_num = BSN)

 <-Rtrv Msg Req-|<-Rtrv Req (ACTION_RTRV_MSGS)--|<--Rtrv Msg Req---
                             (seq_num = FSN)
  1. Rtrv Msg Cfm→|–Rtrv Cfm (ACTION_RTRV_MSGS)→|—Rtrv Msg Cfm–>

(seq_num = 0)

  1. Rtrv Msg Ind→|———Retrieval Ind ——→|—Rtrv Msg Ind–>
  2. Rtrv Msg Ind→|———Retrieval Ind ——→|—Rtrv Msg Ind–>
  3. Rtrv Msg Ind→|———Retrieval Ind ——→|—Rtrv Msg Ind–>
  1. Rtrv Compl Ind→|—-Retrieval Compl Ind —→|-Rtrv Compl Ind–>
    Note: The number of Retrieval Indication is dependent on the
       number of messages in the retransmit queue that have been
       requested.  Only one Retrieval Complete Indication SHOULD be
       sent.

Morneault, et. al. Standards Track [Page 81] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 An example of a message flow with an error retrieving the BSN is
 shown below.
MTP2          M2UA                            M2UA             MTP3
 SGP           SGP                             ASP              ASP
 <-Rtrv BSN Req-|<--Rtrv Req (ACTION_RTRV_BSN)--|<--Rtrv BSN Req---
  1. BSN Not Rtrv→|—Rtrv Cfm (ACTION_RTRV_BSN)→|—BSN Not Rtrv–>

(seq_num = -1)

 An example of a message flow with an error retrieving the messages is
 shown below.
 <-Rtrv BSN Req-|<--Rtrv Req (ACTION_RTRV_BSN)--|<--Rtrv BSN Req---
  1. Rtrv BSN Cfm→|—Rtrv Cfm (ACTION_RTRV_BSN)→|—Rtrv BSN Cfm–>

(seq_num = BSN)

 <-Rtrv Msg Req-|<-Rtrv Req (ACTION_RTRV_MSGS)--|<--Rtrv Msg Req---
                             (seq_num = FSN)
  1. Rtrv Msg Cfm→|–Rtrv Cfm (ACTION_RTRV_MSGS)→|—Rtrv Msg Cfm–>

(seq_num = -1)

 An example of a message flow for a request to drop messages (clear
 retransmission buffers) is shown below.
MTP2          M2UA                            M2UA             MTP3
 SGP           SGP                             ASP              ASP

-Clr RTB Req—-|←StateReq (STATUS_CLEAR_RTB)–|←-Clr RTB Req—–

-Clr RTB Req—>|-StateCfm (STATUS_CLEAR_RTB)–>|—Clr RTB Req—→

5.3.7 Flush and Continue

 The following message flow shows a request to flush buffers.
MTP2            M2UA                              M2UA          MTP3
 SGP             SGP                               ASP           ASP
 <--Flush Req----|<-State Req (STATUS_FLUSH_BUFS)--|<---Flush Req--
  1. –Flush Cfm—>|–State Cfm (STATUS_FLUSH_BUFS)→|—Flush Cfm–>

Morneault, et. al. Standards Track [Page 82] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The following message flow shows a request to continue.
MTP2            M2UA                              M2UA          MTP3
 SGP             SGP                               ASP           ASP
 <---Cont Req----|<--State Req (STATUS_CONTINUE)---|<---Cont Req---
  1. —Cont Cfm—>|—State Cfm (STATUS_CONTINUE)–>|—-Cont Cfm–>

5.3.8 Auditing of SS7 link state

 It may be necessary for the ASP to audit the current state of a SS7
 link.  The flows below show an example of the request and all the
 potential responses.
 Below is an example in which the SS7 link is out-of-service.

MTP2 M2UA M2UA MGMT

SGP            SGP                               ASP            ASP
               |<----State Req (STATUS_AUDIT)----|<----Audit-------
                                                               MTP3
                                                                ASP
               |-----------Release Ind---------->|-Out of Serv Ind->
                                                               MGMT
                                                                ASP
               |-----State Cfm (STATUS_AUDIT)--->|----Audit Cfm--->
 Below is an example in which the SS7 link is in-service.

MTP2 M2UA M2UA MGMT

SGP            SGP                               ASP            ASP
               |<----State Req (STATUS_AUDIT)----|<----Audit-------
                                                               MTP3
                                                                ASP
               |-----------Establish Cfm-------->|---In Serv Ind-->
                                                               MGMT
                                                                ASP
               |-----State Cfm (STATUS_AUDIT)--->|----Audit Cfm--->

Morneault, et. al. Standards Track [Page 83] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 Below is an example in which the SS7 link is in-service, but
 congested.

MTP2 M2UA M2UA MGMT

SGP            SGP                               ASP            ASP
               |<----State Req (STATUS_AUDIT)----|<----Audit-------
                                                               MTP3
                                                                ASP
               |-----------Establish Cfm-------->|---In Serv Ind-->
               |----------Congestion Ind-------->|---Cong Ind----->
                                                               MGMT
                                                                ASP
               |-----State Cfm (STATUS_AUDIT)--->|----Audit Cfm--->
 Below is an example in which the SS7 link is in-service, but in
 Remote Processor Outage.

MTP2 M2UA M2UA MGMT

SGP            SGP                               ASP            ASP
               |<----State Req (STATUS_AUDIT)----|<---Audit Req----
                                                               MTP3
                                                                ASP
               |-----------Establish Ind-------->|---In Serv Ind-->
               |---State Ind (EVENT_RPO_ENTER)-->|----RPO Enter--->
                                                               MGMT
                                                                ASP
               |-----State Cfm (STATUS_AUDIT)--->|----Audit Cfm--->

Morneault, et. al. Standards Track [Page 84] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

6.0 Timer Values

 The recommended default values for M2UA timers are:
    T(r)                                    2 seconds
    T(ack)                                  2 seconds
    T(beat)   Heartbeat Timer               30 seconds

7.0 Security Considerations

 M2UA is designed to carry signalling messages for telephony services.
 As such, M2UA 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.

7.1 Threats

 There is no quick fix, one-size-fits-all solution for security.  As a
 transport protocol, M2UA has the following security objectives:
  • Availability of reliable and timely user data transport.
  • Integrity of user data transport.
  • Confidentiality of user data.
 M2UA runs on top of SCTP.  SCTP [8] provides certain transport
 related security features, such as:
  • Blind Denial of Service Attacks
  • Flooding
  • Masquerade
  • Improper Monopolization of Services
 When M2UA is running in a 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" [13] SHOULD be consulted for guidance.
 When the network in which M2UA 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 [14] for more information on configuring IPSEC services.

Morneault, et. al. Standards Track [Page 85] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

7.2 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.

8.0 IANA Considerations

8.1 SCTP Payload Protocol Identifier

 A request will be made to IANA to assign an M2UA value for the
 Payload Protocol Identifier in SCTP Payload Data chunk.  The
 following SCTP Payload Protocol Identifier has been registered:
       M2UA    "2"
 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.

8.2 M2UA Protocol Extensions

 This protocol may also be extended through IANA in three ways:
  1. - through definition of additional message classes,
  2. - through definition of additional message types, and
  3. - through definition of additional message parameters.
 The definition and use of new message classes, types and parameters
 is an integral part of SIGTRAN adaptation layers.  Thus, these
 extensions are assigned by IANA through an IETF Consensus action as
 defined in [RFC2434].
 The proposed extension must in no way adversely affect the general
 working of the protocol.

Morneault, et. al. Standards Track [Page 86] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

8.2.1 IETF Defined Message Classes

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

8.2.2 IETF Defined Message Types

 Documentation of the message type MUST contain the following
 information:
 (a) A long and short name for the new message type.
 (b) A detailed description of the structure of the message.
 (c) A detailed definition and description of intended use of each
     field within the message.
 (d) A detailed procedural description of the use of the new message
     type within the operation of the protocol.
 (e) A detailed description of error conditions when receiving this
     message type.
 When an implementation receives a message type which it does not
 support, it MUST respond with an Error (ERR) message with an Error
 Code of Unsupported Message Type.

8.2.3 IETF-defined TLV Parameter Extension

 Documentation of the message parameter MUST contain the following
 information:
 (a) Name of the parameter type.
 (b) Detailed description of the structure of the parameter field.
     This structure MUST conform to the general type-length-value
     format described in Section 3.1.5.
 (c) Detailed definition of each component of the parameter value.
 (d) Detailed description of the intended use of this parameter type,
     and an indication of whether and under what circumstances
     multiple instances of this parameter type may be found within the
     same message type.

9.0 Acknowledgments

 The authors would like to thank Tom George (Alcatel) for contribution
 of text and effort on the specification.

Morneault, et. al. Standards Track [Page 87] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 The authors would like to thank John Loughney, Neil Olson, Michael
 Tuexen, Nikhil Jain, Steve Lorusso, Dan Brendes, Joe Keller, Heinz
 Prantner, Barry Nagelberg, Naoto Makinae, Joyce Archibald, Mark
 Kobine, Nitin Tomar, Harsh Bhondwe and Karen King for their valuable
 comments and suggestions.

10.0 References

10.1 Normative

 [1]  ITU-T Recommendation Q.700, 'Introduction To ITU-T Signalling
      System No. 7 (SS7)'
 [2]  ITU-T Recommendation Q.701-Q.705, 'Signalling System No. 7 (SS7)
      - Message Transfer Part (MTP)'
 [3]  ANSI T1.111 'Signalling System Number 7 - Message Transfer Part'
 [4]  Bellcore GR-246-CORE 'Bell Communications Research Specification
      of Signalling System Number 7', Volume 1, December 1995
 [5]  Telecommunication Technology Committee (TTC) Standard JT-Q704,
      Message Transfer Part Signaling Network Functions, April 28,
      1992.
 [6]  Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
      2279, January 1998.
 [7]  Coded Character Set--7-Bit American Standard Code for
      Information Interchange, ANSI X3.4-1986.

10.2 Informative

 [8]  Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
      H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and V. Paxson,
      "Stream Control Transmission Protocol", RFC 2960, October 2000.
 [9]  Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H., Coene, L.,
      Lin, H., Juhasz, I., Holdrege, M. and C. Sharp, "Architectural
      Framework for Signalling Transport", RFC 2719, October 1999.
 [10] ITU-T Recommendation Q.2140, 'B-ISDN ATM Adaptation Layer',
      February 1995
 [11] ITU-T Recommendation Q.2210, 'Message transfer part level 3
      functions and messages using the services of ITU-T
      Recommendation Q.2140', August 1995

Morneault, et. al. Standards Track [Page 88] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 [12] ITU-T Recommendation Q.751.1, 'Network Element Management
      Information Model for the Message Transfer Part', October 1995
 [13] Fraser, B., "Site Security Handbook", FYI 8, RFC 2196, September
      1997.
 [14] Kent, S. and R. Atkinson, "Security Architecture for the
      Internet Protocol", RFC 2401, November 1998.

Morneault, et. al. Standards Track [Page 89] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

Appendix A: Signalling Network Architecture

 A Signalling Gateway will support the transport of MTP2-User
 signalling traffic received from the SS7 network to one or more
 distributed ASPs (e.g., MGCs).  Clearly, the M2UA 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 M2UA protocol is flexible enough to 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 SS7 signalling 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 SS7 node and an IP
 ASP.
 Depending of course on the reliability of the SGP and ASP functional
 elements, this can typically be met by spreading SS7 links in a SS7
 linkset [1] across SGPs or SGs, the provision of redundant QoS-
 bounded IP network paths for SCTP Associations between SCTP End
 Points, and redundant Hosts.  The distribution of ASPs within the
 available Hosts is also important.  For a particular Application
 Server, the related ASPs MAY be distributed over at least two Hosts.

Morneault, et. al. Standards Track [Page 90] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 An example of logical network architecture relevant to carrier-grade
 operation in the IP network domain is shown in Figure 7 below:
  • * * ** * Host1 SG1 * * SGP1 ** _** ASP1 * * * * | | * * * . * | | * * * . * | |
  • * | |

| |

  • * | |
  • *|

SG2 * * SGP2 ** | * * | | * . * | | * . * | | | | | |_* * Host2

                            |_____________________*__* ASP2 *  *
             .                                    *  ********  *
             .            SCTP Associations       *            *
             .                                    **************
                                                          .
                                                          .
                                                          .
                   Figure 7: Logical Model Example
 To avoid a single point of failure, it is recommended that a minimum
 of two ASPs be configured in an AS list, resident in separate hosts
 and, therefore, available over different SCTP associations.  For
 example, in the network shown in Figure 7, all messages for the
 Interface Identifiers could be sent to ASP1 in Host1 or ASP2 in
 Host2.  The AS list at SGP1 might look like the following:
       Interface Identifiers - Application Server #1
           ASP1/Host1  - State = Active
           ASP2/Host2  - State = Inactive
 In this 1+1 redundancy case, ASP1 in Host1 would be sent any incoming
 message for the Interface Identifiers registered.  ASP2 in Host2
 would normally be brought to the active state upon failure of
 ASP1/Host1.  In this example, both ASPs are Inactive or Active,
 meaning that the related SCTP association and far-end M2UA peer is
 ready.

Morneault, et. al. Standards Track [Page 91] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 For carrier grade networks, Operators should ensure that under
 failure or isolation of a particular ASP, stable calls or
 transactions are not lost.  This implies that ASPs need, in some
 cases, to share the call/-transaction state or be able to pass the
 call/transaction state between each other.  Also, in the case of ASPs
 performing call processing, coordination MAY 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.

11.0 Authors' Addresses

 Ken Morneault
 Cisco Systems Inc.
 13615 Dulles Technology Drive
 Herndon, VA. 20171
 USA
 Phone: +1-703-484-3323
 EMail: kmorneau@cisco.com
 Ram Dantu, Ph.D.
 NetRake Corporation
 3000 Technology Drive
 Plano, TX 75074
 USA
 Phone: +1-214-291-1111
 EMail: rdantu@netrake.com
 Greg Sidebottom
 Signatus Technologies
 Kanata, Ontario, Canada
 EMail: greg@signatustechnologies.com
 Brian Bidulock
 OpenSS7 Corporation
 1469 Jeffreys Crescent
 Edmonton, AB  T6L 6T1
 Canada
 Phone: +1-780-490-1141
 EMail: bidulock@openss7.org

Morneault, et. al. Standards Track [Page 92] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

 Jacob Heitz
 Lucent Technologies
 1701 Harbor Bay Parkway
 Alameda, CA, 94502
 USA
 Phone: +1-510-747-2917
 EMail: jheitz@lucent.com

Morneault, et. al. Standards Track [Page 93] RFC 3331 SS7 MTP2 User Adaptation Layer September 2002

Full Copyright Statement

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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
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Morneault, et. al. Standards Track [Page 94]

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