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Versions: (draft-loughney-sigtran-sua) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 3868

INTERNET-DRAFT                                             J. Loughney
Internet Engineering Task Force                                  Nokia
                                           G. Sidebottom, Guy Mousseau
Issued:  4 October 2000                                Nortel Networks
Expires: 4 May 2001                                         S. Lorusso
                                                   Unisphere Solutions


                  SS7 SCCP-User Adaptation Layer (SUA)
                    <draft-ietf-sigtran-sua-02.txt>


Status of This Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute  working documents as Internet-
   Drafts.

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

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

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

   This draft expires on 4 May 2001

Abstract

   This Internet Draft defines a protocol for the transport of any SS7
   SCCP-User signaling (e.g., TCAP, RANAP, etc.) over IP using the
   Stream Control Transport Protocol.  The protocol should be modular
   and symmetric, to allow it to work in diverse architectures, such as
   a Signaling Gateway to IP Signaling Endpoint architecture as well as
   a peer-to-peer IP Signaling Endpoint architecture.  Protocol elements
   are added to allow seamless operation between peers in the SS7 and IP
   domains.

Internet Draft       SS7 SCCP-User Adaptation Layer      July 2, 2000



Abstract...............................................................1
1. Introduction........................................................3
 1.1 Scope ............................................................3
 1.2 Terminology ......................................................3
 1.3 Signaling Transport Architecture .................................5
 1.4 Services Provided by the SUA Layer ...............................9
 1.5 Internal Functions Provided in the SUA Layer ....................10
 1.6 Definition of SUA Boundaries ....................................11
2 Protocol Elements...................................................11
 2.1 Common Message Header ...........................................12
 2.2 SUA Connectionless Messages .....................................13
 2.3 Connection Oriented Messages ....................................15
 2.4 SS7 Signaling Network Management Messages .......................21
 2.5 Application Server Process Maintenance Messages .................24
 2.6 ASP Traffic Maintenance Messages ................................26
 2.7 Management Messages .............................................29
 2.8 Common Parameters ...............................................31
 2.9 SUA-Specific parameters .........................................35
3 Procedures..........................................................42
 3.1 Peer Message Procedures .........................................42
 3.2 Signaling Gateway Related Procedures ............................42
 3.3 Layer Management Procedures .....................................43
 3.4 SCTP Management Procedures ......................................43
4 Examples of SUA Procedures..........................................48
 4.1 Establishment of Association ....................................48
 4.2 ASP fail-over Procedures ........................................49
 4.3 SUA/SCCP-User Boundary Examples .................................49
5 Security............................................................49
 5.1 Introduction ....................................................49
 5.2 Threats .........................................................49
 5.3 Protecting Confidentiality ......................................50
6 IANA Considerations.................................................50
 6.1 SCTP Payload Protocol ID ........................................50
 6.2 Port Number .....................................................50
7 Timer Values........................................................50
8 Acknowledgements....................................................50
9 Authors' Addresses..................................................51
10 References.........................................................51
Appendix A: Message mapping between SCCP and SUA......................52
Appendix B: SCTP to SUA Message Mapping Examples......................53
Copyright Statement...................................................53


















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1. Introduction

1.1 Scope

   There is on-going integration of SCN networks and IP networks.
   Network service providers are designing all IP architectures which
   include support for SS7 and SS7-like signaling protocols. IP provides
   an effective way to transport user data and for operators to expand
   their networks and build new services. In these networks, there may
   be some need for interworking between the SS7 and IP domains.

   This document details the delivery of SCCP-user messages (MAP & CAP
   over TCAP, RANAP, etc.) and new third generation network protocol
   messages over IP between two signaling endpoints.  Consideration is
   given for the transport from an SS7 Signaling Gateway (SG) to an IP
   signaling node (such as an IP-resident Database) as described in the
   Framework Architecture for Signaling Transport [2719]. This protocol
   can also support transport of SCCP-user messages between two
   endpoints wholly contained within an IP network.

   The delivery mechanism SHOULD meet the following criteria:

   *  Support for transfer of SS7 SCCP-User Part messages (e.g., TCAP,
      RANAP, etc.)
   *  Support for SCCP connectionless service.
   *  Support for SCCP connection oriented service.
   *  Support for the seamless operation of SCCP-User protocol peers
   *  Support for the management of SCTP transport associations between
      a SG and one or more IP-based signaling nodes).
   *  Support for distributed IP-based signaling nodes.
   *  Support for the asynchronous reporting of status changes to
      management

   The protocol is modular in design, allowing different implementations
   to be made, based upon the environment that needs to be supported.
   Deepending upon the upper layer protocol supported, the SUA will need
   to support SCCP connectionless service, SCCP connect-orient service
   or both services.

1.2 Terminology

   Signaling Gateway (SG) - Network element that terminates SCN
   signaling and transports SCCP-User signaling over IP to an IP
   signaling endpoint.  A Signaling Gateway could be modeled as one or
   more Application Servers, which is located at the border of the SS7
   and IP networks.

   Application Server (AS) - A logical entity serving a specific Routing
   Key.  An example of an Application Server is an IP database handling
   all request for a unique set of SCCP-users.  The AS contains a set of
   one or more unique Application Server Processes, of which one or more
   is normally actively processing traffic.

   Application Server Process (ASP) - An Application Server Process
   serves as an active or standby process of an Application Server
   (e.g., part of a distributed signaling node or database element).
   Examples of ASPs are MGCs, IP SCPs, or IP-based HLRs.  An ASP
   contains an SCTP end-point and may be configured to process traffic
   within more than one Application Server.

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

   Routing Key - The Routing Key describes a set of SS7 parameter and
   /or parameter-ranges that uniquely defines the range of signaling
   traffic configured to be handled by a particular Application Server.
   An  example would be where a Routing Key consists of a particular PC
   and SSN to which all traffic would be directed to a particular
   Application Server.  Routing Keys are mutually exclusive in the sense
   that a received SS7 signaling message cannot be directed to more than
   one Routing Key.   A Routing Key cannot extend across more than a
   single SS7 PC, in order to more easily support SS7 Management
   procedures. It is not necessary for the parameter ranges within a
   particular Routing Key to be contiguous.

   Routing Context - An Application Server Process may be configured to
   process traffic within more than one Application Server.  In this
   case, the Routing Context parameter is exchanged between two ASPs,
   identifying the relevant Application Server.  From the perspective of
   an ASP, the Routing Context uniquely identifies the range of traffic
   associated with a particular Application Server, which the ASP is
   configured to receive. There is a 1:1 relationship between a Routing
   Context value and a Routing Key within an AS.  Therefore the Routing
   Context can be viewed as an index into an AS Table containing the AS
   Routing Keys.

   Fail-over - The capability to re-route signaling traffic as required
   to an alternate Application Server Process, or group of ASPs, within
   an Application Server in the event of failure or unavailability of a
   currently used Application Server Process.  Fail-back may apply upon
   the return to service of a previously unavailable Application Server
   Process.

   Signaling Point Management Cluster (SPMC) - A complete set of
   Application Servers represented to the SS7 network under the same SS7
   Point Code.  SPMCs are used to sum the availability / congestion /
   User_Part status of an SS7 destination point code that is distributed
   in the IP domain, for the purpose of supporting management procedures
   at an SG.

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

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

   Layer Management - Layer Management is a nodal function in an SG or
   ASP that handles the inputs and outputs between the SUA layer and a
   local management entity.

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   Host - The computing platform that the ASP process is running on.

   Stream - A stream refers to an SCTP stream; a uni-directional 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 un-ordered delivery service.

   Transport address - an address which serves as a source or
   destination for the unreliable packet transport service used by SCTP.
   In IP networks, a transport address is defined by the combination of
   an IP address and an SCTP port number.  Note, only one SCTP port may
   be defined for each endpoint, but each SCTP endpoint may have
   multiple IP addresses.

1.3 Signaling Transport Architecture

   The framework architecture that has been defined for SCN signaling
   transport over IP [2719] uses multiple components, including an IP
   transport protocol, a signaling common transport protocol and an
   adaptation module to support the services expected by a particular
   SCN signaling protocol from its underlying protocol layer.

   In general terms, the SUA architecture can be modeled as a peer-to-
   peer architecture.

1.3.1 Protocol Architecture for TCAP Transport

   In this architecture, the SCCP and SUA layers interface in the SG.
   There needs to be interworking between the SCCP and SUA layers to
   provide for the seamless transfer of the user messages as well as the
   management messages.  The SUA handles the SS7 address to IP address
   mapping.

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

     +------+                                +------+
     | TCAP |                                | TCAP |
     +------+         +------+------+        +------+
     | SCCP |         | SCCP | SUA  |        | SUA  |
     +------+         +------+------+        +------+
     | MTP3 |         | MTP3 |      |        |      |
     +------|         +------+ SCTP |        | SCTP |
     | MTP2 |         | MTP2 |      |        |      |
     +------+         +------+------+        +------+
     |  L1  |         |  L1  |  IP  |        |  IP  |
     +------+         +------+------+        +------+
         |               |         |            |
         +---------------+         +------------+

       TCAP - Transaction Capability Application Protocol
       STP  - SS7 Signaling Transfer Point




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1.3.2 Protocol Architecture for RANAP Transport

   In this architecture, the SS7 application protocol is invoked at the
   SG.  For messages destined for an ASP, the SUA handles address
   translation, for example by way of Global Title Translation or via
   mapping table, resolving the destination specified by SS7 Application
   to a SCTP association / IP address.

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

     +------+         +-------------+        +------+
     | S7AP |         |    S7AP     |        | S7AP |
     +------+         +------+------+        +------+
     | SCCP |         | SCCP | SUA  |        | SUA  |
     +------+         +------+------+        +------+
     | MTP3 |         | MTP3 |      |        |      |
     +------|         +------+ SCTP |        | SCTP |
     | MTP2 |         | MTP2 |      |        |      |
     +------+         +------+------+        +------+
     |  L1  |         |  L1  |  IP  |        |  IP  |
     +------+         +------+------+        +------+
         |               |         |            |
         +---------------+         +------------+

       S7AP - SS7 Application Protocol (e.g. - RANAP/RNSAP)
       STP  - SS7 Signaling Transfer Point

   This architecture may simplify, in some cases, to carrying an SS7
   application protocol between two IP based endpoints.  In this
   scenario, full SG functionality may not be needed.  This architecture
   is considered in the next section.

1.3.3 All IP Architecture

   This architecture can be used to carry a protocol which uses the
   transport services of SCCP, but is contained with an IP network.
   This allows extra flexibility in developing networks, especially when
   interaction between legacy signaling is not needed.  The architecture
   removes the need for signaling gateway functionality.

          ********   IP   ********
          *      *--------*      *
          *  AS  *        *  AS  *
          *      *        *      *
          ********        ********

          +------+        +------+
          |  AP  |        |  AP  |
          +------+        +------+
          | SUA  |        | SUA  |
          +------+        +------+
          | SCTP |        | SCTP |
          +------+        +------+
          |  IP  |        |  IP  |
          +------+        +------+

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             |                |
             +----------------+

       AP - Application Protocol (e.g. - RANAP/RNSAP)

   In the case where a collision occurs during initiation, there exist
   two possible solutions: 1) if there are sufficient resources, both
   initiations could be accepted; 2) both ASPs should back-off and after
   some amount of time, later re-establish an initiation.

1.3.4 Generalized Point-to-Point Network Architecture

   Figure 1 shows an example network architecture which can support
   robust operation and failover support.  There needs to be some
   management resources at the AS to manage traffic.


         ***********
         *   AS1   *
         * +-----+ * SCTP Associations
         * |ASP1 +-------------------+
         * +-----+ *                 |                   ***********
         *         *                 |                   *   AS3   *
         * +-----+ *                 |                   * +-----+ *
         * |ASP2 +-----------------------------------------+ASP1 | *
         * +-----+ *                 |                   * +-----+ *
         *         *                 |                   *         *
         * +-----+ *                 |                   * +-----+ *
         * |ASP3 | *            +--------------------------+ASP2 | *
         * +-----+ *            |    |                   * +-----+ *
         ***********            |    |                   ***********
                                |    |
         ***********            |    |                   ***********
         *   AS2   *            |    |                   *   AS4   *
         * +-----+ *            |    |                   * +-----+ *
         * |ASP1 +--------------+    +---------------------+ASP1 | *
         * +-----+ *                                     * +-----+ *
         *         *                                     *         *
         * +-----+ *                                     * +-----+ *
         * |ASP2 +-----------------------------------------+ASP1 | *
         * +-----+ *                                     * +-----+ *
         *         *                                     ***********
         * +-----+ *
         * |ASP3 | *
         * +-----+ *
         *         *
         ***********

                    Figure 1: Generalized Architecture

   In this example, the Application Servers are shown residing within
   one logical box, with ASPs located inside.  In fact, an AS could be
   distributed among several hosts.  In such a scenario, the host should
   share state as protection in the case of a failure.  Additionally, in
   a distributed system, one ASP could be registered to more than one
   AS.  This draft should not restrict such systems - though such a case
   in not specified.



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1.3.5 Generalized Signaling Gateway Network Architecture

   When interworking between SS7 and IP domains is needed, the SG acts
   as the gateway node between the SS7 network and the IP network.  The
   SG will transport SCCP-user signaling traffic from the SS7 network to
   the IP-based signaling nodes (for example  IP-resident Databases).
   The Signaling Gateway can be considered as a group of Application
   Servers with additional functionality to interface towards an SS7
   network.

   The SUA protocol should be flexible enough to allow different
   configurations and transport technology to allow the network
   operators to meet their operation, management and performance
   requirements.

   Figure 2 shows a possible realization of this architecture, with
   Signaling Gateway functionality.

  Signaling Gateway
  ****************
  * +----------+ *                                      **************
  * | AS1      | *                                      *  AS3       *
  * | ******** | *                                      *  ********  *
  * | * ASP1 +---------------------------------------------+ ASP1 *  *
  * | ******** | *                                      *  ********  *
  * | ******** | *                                      *  ********  *
  * | * ASP2 +--------------------------+       +----------+ ASP2 *  *
  * | ******** | *                      |       |       *  ********  *
  * +----------+ *                      |       |       *      .     *
  * +----------+ *                      |       |       *      .     *
  * | AS2      | *                      |       |       *      .     *
  * | ******** | *                      |       |       *  ********  *
  * | * ASP1 +----------------------------------+       *  * ASPN *  *
  * | ******** | *   SCTP Associations  |               *  ********  *
  * | ******** | *                      |               **************
  * | * ASP2 +----------------          |
  * | ******** | *           |          |               **************
  * +----------+ *           |          |               *  AS4       *
  ****************           |          |               *  ********  *
                             |          +------------------+ ASP1 *  *
                             |                          *  ********  *
                             |                          *      .     *
                             |                          *      .     *
                             |                          *            *
                             |                          *  ********  *
                             +-----------------------------+ ASPn *  *
                                                        *  ********  *
                                                        **************

                Figure 2: Signaling Gateway Architecture

1.3.6 ASP Fail-over Model and Terminology

   The SUA protocol supports ASP fail-over functions in order to support
   a high availability of transaction processing capability.

   An Application Server can be considered as a list of all ASPs
   configured/registered to handle SCCP-user messages within a certain
   range of routing information, known as a Routing Key.  One or more

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   ASPs in the list may normally be active to handle traffic, while
   others may  while any others are inactive but available in the event
   of failure or unavailability of the active ASP(s).

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

   To avoid a single point of failure, it is recommended that a minimum
   of two ASPs be resident in the list, resident in separate physical
   hosts and therefore available over different SCTP Associations.

1.4 Services Provided by the SUA Layer

1.4.1 Support for the transport of SCCP-User Messages

   The SUA needs to support the transfer of SCCP-user messages. The SUA
   layer at the SG needs to seamlessly transport the user messages.

1.4.2 SCCP Protocol Class Support

   Depending upon the SCCP-users supported, the SUA shall support the 4
   possible SCCP protocol classes transparently.  The SCCP protocol
   classes are defined as follows:

   * Protocol class 0 provides unordered transfer of SCCP-user
     messages in a connectionless manner.

   * Protocol class 1 allows the SCCP-user to select the in-sequence
     delivery of SCCP-user messages in a connectionless manner.

   * Protocol class 2 allows the bi-directional transfer of SCCP-user
     messages by setting up a temporary or permanent signaling
     connection.

   * Protocol class 3 allows the features of protocol class 2 with
     the inclusion of flow control.  Detection of message loss or
     mis-sequencing is included.

   Protocol classes 0 and 1 make up the SCCP connectionless service.
   Protocol classes 2 and 3 make up the SCCP connection-oriented
   service.

1.4.3 Native Management Functions

   The SUA layer may provide management of the underlying SCTP layer to
   ensure that transport is available according to the degree specified
   by the SCCP-user application.

   The SUA layer provides the capability to indicate errors associated
   with the SUA-protocol messages and to provide notification to local
   management and the remote peer as is necessary.

1.4.4 Interworking with SCCP Network Management Functions



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   The SUA layer needs to support the following SCCP network management
   functions:

     Coord Request
     Coord Indication
     Coord Response
     Coord Confirm
     State Request
     State Indication
     Pcstate Indication

1.4.5 Support for the management between the SG and ASP.

   The SUA layer should provide interworking with SCCP management
   functions at the SG for seamless inter-operation between the SCN
   network and the IP network.  It should:

     *    Provide an indication to the SCCP-user at an ASP
          that a remote SS7 endpoint/peer is unreachable.
     *    Provide an indication to the SCCP-user at an ASP
          that a remote SS7 endpoint/peer is reachable.
     *    Provide congestion indication to SCCP-user at an ASP.
     *    Provide the initiation of an audit of remote SS7
          endpoints at the SG.

1.5 Internal Functions Provided in the SUA Layer

1.5.1 Address Translation and Mapping at the SG

   SCCP users may present the following options to address their peer
   endpoints:

     Global Title
     PC + SSN
     Host Name
     IP Address(es)

   Global Titles are an interesting option for addressing.  Currently,
   the ITU does not support translation of Global Titles to IP
   addresses.  However, IP addresses are global in scope.  There exist
   many proprietary schemes for managing SS7 Address Translation to IP
   addresses, and is considered outside of the scope of this document to
   specify how this is done.

   Some discussion of address translation should be made to insure
   interoperability between implementations of the SUA.  For further
   instruction in the use of Global Titles the rules detailed in Annex B
   of ITU Q.713 [ITU SCCP] or [ANSI SCCP] should be consulted.

   That being said, currently, there is some work within the IETF
   studying translation of E.164 numbers to Host Names [ENUMS], [E.164-
   DNS].

   In many cases, the network operator may have some control over the
   SCCP-user protocols being transported by SUA.  If possible, the Upper
   Layer can present a Host Name or IP Address, which then can be
   directly passed to SCTP.



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   An example of address translation at the SG would be that the CDPA is
   extracted from the SCCP Header, processed by the SUA routing function
   which yields a SA.  The SA is fed back into extended SUA routing
   analysis which yields the ASP to route the message to.  This is why
   the Source Address and Destination address-routing should be
   performed based on the CDPA.

1.5.2 SCTP Stream Mapping

   The SUA supports SCTP streams. The SG/AS needs to maintain a list of
   SCTP and SUA-users for mapping purposes.  SCCP-users requiring
   sequenced message transfer need to be sent over a stream supporting
   sequenced delivery.

   SUA MUST use stream 0 for SUA management messages. It is recommended
   that sequenced delivery be in order to preserve the order of
   management message delivery.

1.6 Definition of SUA Boundaries

1.6.1 Definition of the upper boundary

   The following primitives are supported between the SUA and an SCCP-
   user.

     Unit Data Request
     Unit Data Indication
     Notice Indication

     Connect Request
     Connect Indication
     Connect Responding
     Connect Confirm

     Data Request
     Data Indication

     Expedited Data Request
     Expedited Data Indication

     Disconnect Request
     Disconnect Indication

     Reset Request
     Reset Indication
     Reset Response
     Reset Confirm

1.6.2 Definition of the lower boundary

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

2 Protocol Elements

   The general message format includes a Common Message Header together
   with a list of zero or more parameters as defined by the Message
   Type.


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   For forward compatibility, all Message Types may have attached
   parameters even if none are specified in this version.

2.1 Common Message Header

   The protocol messages for the SCCP-User Adaptation Protocol requires
   a message structure which contains a version, message type, message
   length and message contents.   This message header is common among
   all signaling protocol adaptation layers:

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


   Note that the 'data' portion of SUA messages SHALL contain SCCP-User
   data, not the encapsulated SCCP message.

   Optional parameters can only occur at most once in an SUA message.

2.1.1 SUA Protocol Version

   The version field (ver) contains the version of the SUA adaptation
   layer.  The supported versions are:

         01   SUA version 1.0

2.1.2 Message Classes

   Message Classes

     0         Management (MGMT) Message
     1         Reserved
     2         SS7 Signaling Network Management (SSNM) Messages
     3         ASP State Maintenance (ASPSM) Messages
     4         ASP Traffic Maintenance (ASPTM) Messages
     5         Reserved
     6         Reserved
     7         Connectionless Messages
     9         Connection-Oriented Messages
     8 - 255   Reserved

2.1.3 Message Types

   SUA Management Messages

     0         Error (ERR)
     1         Audit (AUD)
     2         Notify (NTFY)
     3 - 255   Reserved

   SS7 Signaling Network Management (SSNM) Messages

     0         Reserved

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     1         Destination Unavailable (DUNA)
     2         Destination Available (DAVA)
     3         Destination State Audit (DAUD)
     4         Destination User Part Unavailable (DUPU)
     5         SCCP Management (SCMG)
     6 - 255   Reserved for SSNM Messages

   Application Server Process Maintenance (ASPM) Messages

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

   ASP Traffic Maintenance (ASPTM) Messages

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

   Connectionless Messages

     0         Reserved
     1         Connectionless Data Transfer (CLDT)
     2         Connectionless Data Response (CLDR)
     3 - 255   Reserved

   Connection-Oriented Messages

     0         Reserved
     1         Connection Request (CORE)
     2         Connection Acknowledge (COAK)
     3         Connection Refused (COREF)
     4         Release Request (RELRE)
     5         Release Complete (RELCO)
     6         Reset Confirm (RESCO)
     7         Reset Request (RESRE)
     8         Connection Oriented Data Transfer (CODT)
     9         Connection Oriented Data Acknowledge (CODA)
     10 - 255  reserved

2.1.4 Message Length

   The Message Length defines the length of the message in octets,
   including the header.


2.2 SUA Connectionless Messages

   The following section describes the SUA Connectionless transfer
   messages and parameter contents.  The general message format includes
   a Common Message Header together with a list of zero or more


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   parameters as defined by the Message Type.  All Message Types can
   have attached parameters.

2.2.1 Connectionless Data Transfer

   This message transfers data between one SUA to another.

       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 = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0102          |      Parameter Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                        Source Address                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |      Parameter Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     destination address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Parameters
     Flags                         Mandatory
     Source Address                Mandatory
     Destination Address           Mandatory
     Data                          Mandatory

   Implementation note:

   This message covers the following SCCP messages: unitdata (UDT),
   extended unitdata (XUDT), long unitdata (LUDT).

2.2.2 Connectionless Data Response

   This message is used as a response message by the peer and/or report
   errors.

       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 = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       SCCP Error Cause                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0102          |             Length            |

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                        Source Address                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     destination address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Fixed Lengths Parameters
     Flags                         Mandatory
     Return Cause                  Mandatory
     Source Address                Mandatory
     Destination Address           Mandatory
     Data                          Optional

   Implementation note:

   This message covers the following SCCP messages: long unitdata
   service (LUDTS), unitdata service (UDTS), extended unitdata service
   (XUDTS).

2.3 Connection Oriented Messages

2.3.1 Connection Oriented Data Transfer

   This message transfers data between one SUA to another for connection
   oriented service.

       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 = 0x0107          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 destination reference number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0101          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Destination Reference Number  Mandatory
     Data                          Mandatory

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     Flags                         Mandatory *1
     Sequence number               Mandatory *2


   NOTE *1:    Mandatory for representing DT1 message.
   NOTE *2:    Mandatory for protocol class 3;
               Optional for protocol class 2.

   Implementation note:

   This message covers the following SCCP messages: data form 1 (DT1),
   data form 2 (DT2), expedited data (ED).

2.3.2 Connection Oriented Data Acknowledge

   This message is used to acknowledge receipt of data by the peer.

       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 = 0x0107          |              Length           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 destination reference number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0101          |              Length           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Destination Reference Number  Mandatory
     Sequence number               Mandatory *1

   NOTE *1:    Mandatory for protocol class 3;
               Optional for protocol class 2.

   Implementation note:

   This message covers the following SCCP messages: data acknowledgement
   (AK), expedited data acknowledgement (EA).

2.3.3 Connect Request

   This message is used for establishing a signaling connection between
   two peer endpoints.  This is used for connection oriented service.

        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 = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Source Reference Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0102          |           Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                        Source Address                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x010C          |           Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Credit                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |           Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Flags                         Mandatory
     Source Reference Number       Mandatory
     Destination Address           Mandatory
     Source Address                Optional
     Credit                        Optional
     Data                          Optional

2.3.4 Connection Acknowledge

   This message is used to acknowledge a connection request between two
   peer endpoints.

       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 = 0x0107          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Source Reference Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x010C          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Credit                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory
     Flags                         Optional
     Credit                        Optional
     Destination Address           Optional *1
     Credit                        Optional
     Data                          Optional

   NOTE *1:    Destination Address parameter will be present in case
               that the received CORE message conveys the Source Address
               parameter.

   Implementation note:

   This message covers the following SCCP message: connection confirm
   (CC).

2.3.5 Connection Refused (COREF)

   This message is used to refuse a connection request between two peer
   endpoints.

       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 = 0x0107          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        SCCP Error Cause                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0101          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
        Destination Reference Number    Mandatory
        SCCP Error Cause                Mandatory
        Destination Address             Optional *1
        Data                            Optional

   Note *1:    Destination Address parameter will be present in case
               that the received CORE message conveys the Source Address
               parameter.




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2.3.5 Release Request

   This message is used to request a signaling connection between two
   peer endpoints be released.  All associated resources can then be
   released.

       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 = 0x0107          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 destination reference number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   source reference number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Return Cause                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory
     Return Cause                  Mandatory
     Flags                         Optional
     Data                          Optional

   Implementation Note:

   This message covers the following SCCP message: connection refused
   (CREF).

2.3.6 Release Complete

   This message is used to acknowledge the release of a signaling
   connection between two peer endpoints.  All associated resources
   should be released.

       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 = 0x0107          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 destination reference number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   source reference number                     |

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory

2.3.7 Reset Request

   This message is used to indicate that the sending SCCP/SUA wants to
   initiate a reset procedure (re-initialization of sequence numbers)
   the peer endpoint.

       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 = 0x0107          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 destination reference number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   source reference number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0109          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        SCCP Error Cause                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory
     SCCP Error Cause              Mandatory

2.3.8 Reset Confirm

   This message is used to confirm the Reset Request.

       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 = 0x0107          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 destination reference number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   source reference number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory

2.3.9 Connection Oriented Error (COERR)

   The COERR message is sent when an invalid value is found in an
   incoming message.

       0                   1                   2                   3

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       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 = 0x0107          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 destination reference number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0109          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           SCCP Error                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Destination Reference Number  Mandatory
     SCCP Error                    Mandatory

   Implementation Note: This message covers the following SCCP message:
   Protocol data unit error (ERR)

2.4 SS7 Signaling Network Management Messages

2.4.1 Destination Unavailable

   The DUNA message is sent from the SG to all concerned ASPs to
   indicate that the SG has determined that an SS7 destination is
   unreachable.  The SUA-User at the ASP is expected to stop traffic to
   the affected destination through the SG initiating the DUNA.

   The format for DUNA Message parameters is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0006          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Affected Point Code                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0001          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Network Appearance                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Affected Point Code           Mandatory
     Network Appearance            Optional
     Info String                   Optional

2.4.2 Destination Available

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


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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0005          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Affected Point Code                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0005          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Network Appearance                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Affected Point Code           Mandatory
     Network Appearance            Optional
     Info String                   Optional

2.4.3 Destination State Audit

   The DAUD message can be sent from the ASP to the SG to query the
   availability state of the SS7 routes to an affected destination.  A
   DAUD may be sent periodically after the ASP has received a DUNA,
   until a DAVA is received. The DAUD can also be sent when an ASP
   recovers from isolation from the SG.

       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 = 0x0005          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Affected Point Code                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0001          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Network Appearance                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Affected Point Code           Mandatory
     Network Appearance            Optional
     Info String                   Optional

2.4.4 Destination User Part Unavailable

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

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   The format for DUPU Message parameters is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             cause                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0005          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Affected Point Code                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0001          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Network Appearance                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Cause                         Mandatory
     Affected Point Code           Mandatory Note *1
     Network Appearance            Optional
     Info String                   Optional

   The Cause Code parameter indicates the reason that the remote SUA
   adaptation layer is unavailable.  The valid values for Cause are as
   follows:

   Value      Description
     0         Unknown
     1         Unequipped Remote User
     2         Inaccessible Remote User

   Note *1:    Affected Point Code can only contain a single affected
   point code.

2.4.5 SCCP Management Message

   The SCMG message is sent from the between SUA Peers to indicate
   status of subsystems. Only one SCMG message type can be sent per
   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 = 0x010D       |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      SCMG  Message Type                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x010E       |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             SMI               |        Subsystem              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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     |            Tag = 0x0005       |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     /                          Affected PC                          /
     \                                                               \
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x0108       |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       congestion level                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x0004       |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     /                          INFO String                          \
     \                                                               /
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     SCMG Message Type             Mandatory
     Subsystem/SMI                 Mandatory
     Affected Point Code           Mandatory *1
     Congestion Level              Mandatory *2
     Info String                   Optional

   Note *1:    In the SCMG message, the Affected Point Code Parameter
               MUST contain, at most, a single Affected Point Code.

   Note *2:    When the SCMG Message Type is SSC, then the Congestion
               Level parameter is Mandatory, otherwise it is optional.

2.5 Application Server Process Maintenance Messages

2.5.1 ASP Up (ASPUP)

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

       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 = 0x010A       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        ASP Capabilities                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0002       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ALI                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0004       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     ASP Capabilities              Mandatory
     Adaptation Layer Identifier   Optional
     Info String                   Optional



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2.5.2 ASP Up Ack (UPACK)

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

       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 = 0x010A       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        ASP Capabilities                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0002       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ALI                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0004       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     ASP Capabilities              Mandatory
     Adaptation Layer Identifier   Optional
     Info String                   Optional

2.5.3 ASP Down (ASPDN)

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

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Cause Code                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0004       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Cause Code                         Mandatory
     Info String                   Optional

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

        Value      Description
        0x1        Processor Outage
        0x2        Management Inhibit

   Implementation note:



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   This message covers the following SCCP message: subsystem-prohibited
   (SSP).

2.5.4 ASP Down Ack (DNACK)

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

       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 = 0x0002       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ALI                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0004       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Adaptation Layer Identifier   Optional
     Info String                   Optional

2.5.5 Heartbeat (BEAT)

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

   The BEAT message contains no parameters.

2.6 ASP Traffic Maintenance Messages

2.6.1 ASP Active (ASPAC)

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

   The format for the ASPAC message is as follows:

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

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   The ASPAC message contains the following parameters:

        Type               Mandatory
        Routing Context    Optional
        INFO String        Optional

   Type: 32-bit (unsigned integer)

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

            1         Over-ride
            2         Load-share

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

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

2.6.2 ASP Active Ack

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

   The format for the ASPAC Ack message is as follows:

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

   The ASPAC Ack message contains the following parameters:

        Type               Mandatory
        Routing Context    Optional
        INFO String        Optional

   Type: 32-bit (unsigned integer)



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

            1         Over-ride
            2         Load-share

   The type field in the ASPAC Ack message should contain the type as
   the ASPAC message to which the message is acknowledging.

2.6.3  ASP Inactive (ASPIA)

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

   The format for the ASPIA message parameters is as follows:

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

   The ASPIA message contains the following parameters:

        Type                 Mandatory
        Routing Context      Optional
        INFO String          Optional

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

       Value          Description
        0x1            Over-ride
        0x2            Load-share

   Within a particular Routing Context, only one Type can be used.  The
   Override value indicates that the ASP is operating in Over-ride mode,
   and will no longer handle traffic within an Application Server (i.e.,
   it is now a backup in a primary/back-up arrangement).  The Load-share
   value indicates that the ASP is operating in Load-share mode and will
   no longer share in the traffic distribution with any other currently
   active ASPs.

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

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2.6.4 ASP Inactive Ack

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

   The format for the ASPIA Ack message is as follows:

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

   Parameters

     Type               Mandatory
     Routing Context    Optional
     INFO String        Optional

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

            1         Over-ride
            2         Load-share

   The type field in the Ack message should contain the type as the
   ASPIA message to which the message is acknowledging.

2.7 Management Messages

   These messages are used for managing SUA and the representations of
   the SCCP subsystems in the SUA layer.

2.7.1 Error (ERR)

   The ERR message is sent between two SUA peers to indicate an error
   situation.  The Data parameter is option, possibly used for error
   logging and/or debugging.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Cause                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0003         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             data                              /

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      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Cause                         Mandatory
     Data                          Optional

   The Cause parameter can be one of the following values:

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

2.7.2 Audit

   This message is used to audit the current state of the peer endpoint.

       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 = 0x0005          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Affected Point Code                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0001          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Network Appearance                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Affected Point Code           Mandatory
     Network Appearance            Optional
     Info String                   Optional

2.7.3 Notify (NTFY)

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

       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 = 0x010B         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Status                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0006         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /

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      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0004         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The NTFY message contains the following parameters:

   Parameters
     Status Type                   Mandatory
     Routing Context                    Optional
     Info String                   Optional

2.8 Common Parameters

   These TLV parameters are common across the different adaptation
   layers.

   Parameter Name                     Parameter ID
   ==============                     ============
   Network Appearance                   0x0001
   Application Layer Identifier         0x0002
   Data                                 0x0003
   Info String                               0x0004
   Affected Point Code                  0x0005
   Routing Context                      0x0006
   Diagnostic Info                      0x0007

2.8.1 Network Appearance

   The Network Appearance parameter identifies the SS7 network context
   for the message, for the purposes of logically separating the
   signaling traffic between the SG and the Application Server Processes
   over common SCTP Associations.  An example is where an SG is
   logically partitioned to appear as an element in four different
   national SS7 networks.  A Network Appearance implicitly defines the
   SS7 Destination Point Code used, the SS7 Network Indicator value and
   SCCP/SCCP-User protocol type/variant/version used within the SS7
   network partition.  Where an SG operates in the context of a single
   SS7 network, or individual SCTP associations are dedicated to each
   SS7 network appearance, the Network Appearance parameter is not
   required.

       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 = 0x0001         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        network appearance                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

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   Where an SG operates in the context of a single SS7 network, or
   individual SCTP associations are dedicated to each SS7 network
   context, the Network Appearance parameter is not required and the
   format of the Affected PC(s) is understood implicitly.

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

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

2.8.2 Adaptation Layer Identifier

       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 = 0x0002         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ALI                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The optional Adaptation Layer Identifier (ALI) is a string that
   identifies the adaptation layer.  This string MUST be set to "SUA"
   which results in a length of 3.  The ALI would normally only be used
   in the initial ASP Up message across a new SCTP association to ensure
   both peers are assuming the same adaptation layer protocol.

2.8.3 Data

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0003         |            length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.8.4 Info String

   The INFO String parameter can carry any meaningful 8-BIT ASCII
   character string along with the message.  Length of the INFO String
   parameter is from 0 to 255 characters.  No procedures are presently
   identified for its use but the INFO String may be used by Operators
   for debugging purposes.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0004         |            length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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2.8.5 Affected Point Code

   The Affected Point Code parameter contains one or more Affected
   Destination Point Codes, each a three-octet parameter to allow for 4-
   , 16- and 24-bit binary formatted SS7 Point Codes.  Affected Point
   codes that are less than 24-bits, are padded on the left to the 24-
   bit boundary.
       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 = 0x0005         |            length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Mask       |                 Affected PC 1                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             . . .                             /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The encoding is shown below for ANSI and ITU Point Code examples.

   ANSI 24-bit Point Code:

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

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

   ITU 14-bit Point Code:

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

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

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

   Mask: 8-bits

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



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

2.8.6 Routing Context

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

   The Type parameter identifies the message as an Over-ride or Load-
   share Active message.  The valid values for Type are shown in the
   following table.

        Value          Description
        0x1            Over-ride
        0x2            Load-share

   Within a particular Routing Context, only one Type can be used.

   The optional Routing Context parameter contains (a list of) integers
   indexing the Application Server traffic that the sending ASP is
   configured to receive.  There is one-to-one relationship between an
   index entry and an AS Name.  Because an AS can only appear in one
   Network Appearance, the Network Appearance parameter is not required
   in the ASPAC message

   An Application Server Process may be configured to process traffic
   for more than one logical Application Server.  From the perspective
   of an ASP, a Routing Context defines a range of signaling traffic
   that the ASP is currently configured to receive from the SG.

2.8.7 Diagnostic Information

   The Diagnostic Information can be used to convey any information
   relevant to an error condition, to assist in the identification of
   the error condition.  In the case of an Invalid Network Appearance,
   Adaptation Layer Identifier or Traffic Handling Mode, the Diagnostic
   information includes the received parameter.  In the other cases, the
   Diagnostic information may be the first 40 bytes of the offending
   message.



       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

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0007          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Diagnostic Information*                   /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.9 SUA-Specific parameters

   These TLV parameters are specific to the SUA protocol.

   Parameter Name                     Parameter ID
   ==============                     ============
   Sequence Number                      0x0101
   Source Address                       0x0102
   Destination Address                  0x0103
   Return Cause                         0x0104
   Flags                                0x0105
   Source Reference Number              0x0106
   Destination Reference Number         0x0107
   Congestion Level                     0x0108
   SCCP Error                           0x0009
   ASP Capabilities                     0x000A
   Status                               0x000B
   Credit                               0x000C
   SCMG Message Type                    0x000D
   SMI / Subsystem                      0x000E

2.9.1 Sequence Number

       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 = 0x0101         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This parameter is mapped from the SCCP Sequencing/segmenting
   parameter.  It is used exclusively for protocol class 3. It is used
   to number each DT message sequentially for the purpose of flow
   control.

2.9.2 Source Address (=CLG)

       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 = 0x0102         |      Parameter Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Type of Address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                        Source Address                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type of Address field is used to aid in the identification of the
   type of address.  If this field is set to 0, then the address field
   needs to be analyzed.

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   Type of Address

     Unknown/Undeterminable        0x00000000
     SS7 SCCP CLG                  0x00000001
     Host Name                     0x00000002
     IPv4 Address                  0x00000003
     IPv6 Address                  0x00000004

   The combinations of SS7 addressing schemes (ITU, ANSI, etc).
   supported is implementation dependant.

   The Source Address field can contain the SCCP Calling Party Address.
   It is possible to simply encapsulate the information, as presented by
   the upper layer.

2.9.3 Destination Address (=CLD)

       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 = 0x0103         |      Parameter Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Type of Address                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       destination address                     /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type of Address field is used to aid in the identification of the
   type of address.  If this field is set to 0, then the address field
   needs to be analyzed.

   Type of Address

     Unknown/Undeterminable        0x00000000
     SS7 SCCP CLD                  0x00000001
     Host Name                     0x00000002
     IPv4 Address                  0x00000003
     IPv6 Address                  0x00000004

   Note: the combinations of SS7 addressing schemes(ITU, ANSI, etc).
   supported is implementation dependant.

   The Destination Address field can contain the SCCP Called Party
   Address.  It is possible to simply encapsulate the information, as
   presented by the upper layer.

2.9.4 Return Cause

   The Return Cause corresponds to the return cause of the SCCP 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 = 0x0104         |             length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Cause Code                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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   The Length is a one octet unsigned integer.

   Possible values for the Return Cause are:

   0x01        no translation for an address of such nature
   0x02        no translation for this specific address
   0x03        subsystem congestion
   0x04        subsystem failure
   0x05        unequipped user
   0x06        MTP failure
   0x07        network congestion
   0x08        unqualified
   0x09        error in message transport (Note)
   0x0A        error in local processing (Note)
   0x0B        destination cannot perform reassembly (Note)
   0x0C        SCCP failure
   0x0D        hop counter violation
   0x0E        segmentation not supported
   0x0F        segmentation failure

   NOTE: Only applicable to XUDT(S) message.

2.9.5  Flags

       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 = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Hop Counter          |  segmenting   |D| B |A|   C   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   A      Error Return option
          Value      Description
          0x0        No error message
          0x1        Return message on error

   B      Protocol class
          Value      Description
          0x0        Class 0 (connectionless service)
          0x1        Class 1 (connectionless service)
          0x2        Class 2 (connection-oriented service)
          0x3        Class 3 (connection-oriented service

   C      Importance
          Value      Description
          0x0        Least important
               :
          0x7        Highest importance

   D      Segmentation
          Value      Description
          0x0        No segmentation
          0x1        Segmentation


   Segmenting field corresponds to the SCCP Segmenting parameter.


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       0 1 2 3 4 5 6 7 8
      +-+-+-+-+-+-+-+-+-+
      |    segmenting   |
      +-+-+-+-+-+-+-+-+-+

   Bit 8 is coded as the following:

   _ 0:   in all segments but the first;
   _ 1:   first segment.


   Bit 7 is used to keep in the message in sequence delivery option
   required by the SCCP user and is coded as follows:

   _ 0:   Class 0 selected;
   _ 1:   Class 1 selected.

   Bits 6 and 5 are spare bits.

   Bits 4-1 of octet 1 are used to indicate the number of remaining
   segments. The values 0000 to 1111 are possible; the value 0000
   indicates the last segment.


   Hop Counter
          Value          Description
          0x0
          :
          0x15           Maximum number of GTT

          0x16 - 0x255   Spare


2.9.6 Source Reference Number

       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 = 0x0106         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   source reference number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The source reference number is a 3 octet long integer, which is
   generated by the local source to identify a connection.

   Valid values are from 0x0 to 0xFFFFFE, while 0xFFFFFF is reserved for
   future use.

2.9.7 Destination Reference Number

       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 = 0x0107         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 destination reference number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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   The Destination Reference Number is a 3 octet long integer, which is
   generated by the destination node to identify a connection.

   Valid values are from 0x0 to 0xFFFFFE, while 0xFFFFFF is reserved for
   future use.

2.9.8 Congestion Level

       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 = 0x0108         |             length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       congestion level                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The length is one octet.

   The valid values for the Congestion Level parameter range from 0 to
   7, where 0 indicates least congested and 7 indicates most congested.

2.9.9 SCCP Error

       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 = 0x0109          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           spare               |   Cause Type  |  Cause Value  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Cause Type can have the following values:

        Return Cause               0x1
        Refusal Cause         0x2
        Release Cause         0x3
        Reset Cause           0x4
        Error Cause           0x5

   Cause Value contains the specific error value.  Below gives examples
   for ITU SCCP values.

   Cause value in        Correspondence with Reference
   SUA message           SCCP parameter
   ------------------    -----------------   ---------
   CLDA                  Return Cause        ITU-T Q.713 Chapter 3.12
   COREF                 Refusal Cause       ITU-T Q.713 Chapter 3.15
   RELRE                 Release Cause       ITU-T Q.713 Chapter 3.11
   RESRE                 Reset Cause         ITU-T Q.713 Chapter 3.13
   ERR                   Error Cause         ITU-T Q.713 Chapter 3.14

2.9.10 ASP Capabilities

   This parameter is used so that the ASP can report it's capabilities
   for supporting different protocol classes and interworking scenarios.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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      |          Tag = 0x010A         |             length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          SCCP Variant         |0 0 0 0|a|b|c|d| interworking  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The length is two octets.

   SCCP Variant field can contain the following values:

     Unidentified/unknown                    0x0
     ITU-I SCCP                              0x1
     ITU-N SCCP                              0x2
     ANSI SCCP                          0x3
     Japanese SCCP                      0x4
     Chinese SCCP                       0x5
     Other                              0x6

   Flags

     a - Protocol Class 3
     b - Protocol Class 2
     c - Protocol Class 1
     d - Protocol Class 0

     0 indicates no support for the Protocol Class.

   Interworking

   Values

     0x0 indicates no interworking with SS7 Networks.
     0x1 indicates IP Signaling Endpoint.
     0x2 indicates Signaling Gateway.

2.9.11 Status

   The Status Type parameter identifies the type of the status that is
   being notified.

       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 = 0x010B         |             length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Status Type           |         Status ID             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The valid values are shown in the following table.

          1     Application Server state change (AS_State_Change)
          2     Other

   The Status Id parameter identifies the status that is being notified.
   The valid values are shown in the following table.

   If the Status Type is AS_STATE_CHANGE

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

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

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

            1    Insufficient ASP resources active in AS

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

2.9.12 Credit

       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 = 0x010C         |             length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Credit                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The length is one octet.

2.9.13 SCMG Message Type

      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 = 0x010D       |           Length              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      SCMG  Message Type                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The SCMG Message Type field may have the following values:

     0         Reserved
     1         SSA
     2         SSP
     3         SST
     4         SOR
     5         SOG
     6         SSC
     7 - 252   Reserved
     253       SNR
     254       SBR
     255       SRT

2.9.14 SMI / Subsystem





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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x000E       |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             SMI               |     Spare     |      SSN      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Subsystem Number (SSN) is one octet.

   Subsystem multiplicity indicator (SMI) can have the following values:

     0x00      Reserved
     0x01      Replicated
     0x02      Solitary
     0x03      Unknown

3 Procedures

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

3.1 Peer Message Procedures

   On receiving a message, the SUA layer performs address translation
   and mapping (if needed), to determine the appropriate Application
   Server Process (ASP).  The appropriate ASP can be determined based on
   the routing information in the incoming message, local load sharing
   information, etc. The appropriate SUA message is then constructed and
   sent to the appropriate endpoint, via the correct SCTP association.

3.1.1 Connection Oriented Timers

   The SUA layer needs to start a timer after sending a CR, RLSD or RSR
   message.

   Add more text.

3.2 Signaling Gateway Related Procedures

   These support the SUA transport of SCCP-User/SCCP boundary
   primitives.

   On receiving a SCCP message at the SG, the SUA layer performs address
   translation and mapping, to determine the appropriate Application
   Server Process (ASP).  The appropriate ASP can be determined based on
   the information in the incoming message, local load sharing
   information, etc. The appropriate SUA message is then constructed and
   sent to the appropriate endpoint, via the correct SCTP association.

   The SUA needs to setup and maintain the appropriate SCTP association
   to the selected endpoint.   SUA also manages the usage SCTP streams.

3.2.1 MTP 3 - SUA interaction

   The Signaling Gateway will need to manage the availability of the
   ASPs within the IP network; while reporting the status of endpoints

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   in the SS7 network.  Therefore, there will be interworking between
   the MTP 3 layer and SUA.  MTP 3 indication messages (MTP Pause, MTP
   resume, MPT Status) need to be indicated to the peer SUA layer.

   MTP_PAUSE, MTP_STATUS (UPU) and SSP should be mapped on DUNA
   messages. It is possible that several ASPs must be informed via DUNA,
   depending on the ASs affected.

   MTP_RESUME and SSA should be mapped on DAVA messages to the affected
   ASPs.

   MTP_STATUS (Congestion) and SSC should be mapped on SCON messages to
   the affected ASPs.

   SST should be mapped on DAUD message to the affected ASPs.

3.3 Layer Management Procedures

   The SUA layer needs to send and receive layer management messages.

3.4 SCTP Management Procedures

   These procedures support the SUA management of SCTP Associations and
   ASP Paths between SGs and ASPs.

3.4.1 State Management

   The SUA layer on at each AS needs to maintain the state of each ASP
   under its control, as a way to manage the state and connections of
   the local ASPs.  At a SG, the state of each ASP is needed as input to
   the SGs address translation and mapping function.

3.4.1.1  ASP States

   The state of each ASP is maintained in the SUA layer at the
   controlling AS. The state of an ASP changes due to events. The events
   include:

      * Reception of messages from that ASP's SUA layer
      * Reception of messages from a different ASP's SUA layer
      * Reception of indications from the SCTP layer
      * Switch over timer triggers

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

   ASP-DOWN: The Application Server Process is unavailable.  Initially
   all ASPs will be in this state.

   ASP-UP: The Application Server Process is available but application
   traffic is stopped.

   ASP-ACTIVE: The Application Server Process is available and
   application traffic is active.


                  Figure 4: ASP State Transition Diagram



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

                  Figure 4: ASP State Transition Diagram

   SCTP Down: The local SCTP layer's SHUTDOWN COMPLETE notification or
   COMMUNICATION LOST notification.

3.4.1.2  AS States

   The state of the AS is maintained in the SUA layer.

   The state of an AS changes due to events. These events include:

      * ASP state transitions
      * Recovery timer triggers

   The possible states of an AS are:

   AS-DOWN: The Application Server is unavailable.  This state implies
   that all related ASPs are in the ASP-DOWN state for this AS.
   Initially the AS will be in this state.

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

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

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



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
























































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


         Tr = Recovery Timer

                    Figure 5: AS State Transition Diagram


3.4.2 ASPM procedures for primitives

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

   When the SUA layer receives an M-SCTP ESTABLISH request primitive
   from the Layer Management, the SUA layer will try to establish an
   SCTP association with the remote SUA peer.  Upon reception of an
   eventual SCTP-Communication Up confirm primitive from the SCTP, the
   SUA layer will invoke the primitive M-SCTP ESTABLISH confirm to the
   Layer Management.

   Alternatively, if the remote SUA-peer establishes the SCTP
   association first, the SUA layer will receive an SCTP Communication
   Up indication primitive from the SCTP. The SUA layer will then invoke
   the primitive M-SCTP ESTABLISH indication to the Layer Management.

   Once the SCTP association is established, The SUA layer at an ASP
   will then find out the state of its local SUA-user from the Layer
   Management using the primitive M-ASP STATUS.  Based on the status of
   the local SUA-User, the local ASP SUA Application Server Process
   Maintenance (ASPM) function will initiate the ASPM procedures, using
   the ASP-Up/-Down/-Active/-Inactive messages to convey the ASP-state
   to the SG - see Section 3.3.3.



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

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

3.4.3 ASPM procedures for peer-to-peer messages

3.4.3.1 ASP-Up

   The AS will mark the path as up if an explicit ASP UP (ASPUP) message
   is received and internally the path is allowed to come up (i.e., not
   in a locked local maintenance state). An ASP UP (ASPUP) message will
   be sent to acknowledge the received ASPUP. The SG will respond to a
   ASPUP with a ASPDN message if the path is in a locked maintenance
   state.

   The receiving ASP will send a ASPUP message in response to a received
   ASPUP message from the ASP even if that path was already marked as
   UP. The paths are controlled by the ASP.

   The ASP will send ASPUP messages every t(a) seconds until the path
   comes up (i.e. until it receives a ASPUP message from the remote peer
   for that path).  The ASP may decide to reduce the frequency (say to
   every 5 seconds) if the an acknowledgement is not received after a
   few tries.

   The ASP should wait for the ASPUP message from the remote peer before
   transmitting ASP maintenance messages (ASPIA or ASPAC) or SUA
   messages or it will risk message loss.

   3.4.3.2 ASP Down

   The AS will mark the ASP as down and send a ASPDN message to the ASP
   if one of the following events occur:

        - an ASP Down(ASPDN) message is received from the ASP,
        - the ASP is locked by local maintenance.

   The AS will also send a ASPDN message when the ASP is already down
   and a ASPDN) message is received from the ASP.

   The ASP will send ASPDN whenever it wants to take down a ASP.  Since
   it is possible for ASPDN messages and responses can be lost (for
   example, during a node failover), the ASP can send ASPDN messages
   every t(a) seconds until the path comes down (i.e. until it receives
   a ASPDN message from the remote peer for that path).


3.4.3.3 ASP Version Control

   If a ASP Up message with an unknown version is received, the
   receiving end will respond with an Error message.  This will indicate
   to the sender which version the receiving node supports.




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   This is useful when protocol version upgrades are being performed.  A
   node with the newer version should support the older versions used on
   other nodes it is communicating with.

   The version field in the Error message header associated will
   indicate the version supported by the node.

3.4.3.4 ASP Active

   When an ASP Active (ASPAC) message is received, the ASP will start
   traffic routing to that ASP.  Reception of a ASPAC message overrides
   any previous ASPAC messages and results in the ASP associated with
   the ASPAC message to become the newly active ASP.


3.4.3.5 ASP Inactive

   When a ASPIA message is received, message transmission to that ASP
   ceases.  The ASP will either discard all incoming messages or start
   buffering the incoming messages for T(r)seconds after which messages
   will be discarded.

   If the ASP is down, all of the Paths that were supported by that ASP
   are, by default, down.

4 Examples of SUA Procedures

4.1 Establishment of Association

4.1.1 SG Architecture

        SG               ASP1                ASP2
                         (Primary)           (Backup)
         |                  |                   |
         <----ASP Up--------+                   |
         +----ASP Up Ack --->                   |
         |                  |                   |
         <-----------------------ASP Up---------+
         +-----------------------ASP Up (Ack)--->
         |                  |                   |
         <----ASP Active----+                   |
         +-ASP Active Ack--->                   |
         |                  |                   |

4.1.2 IP to IP Architecture

      ASP1 (AS1)         ASP1 (AS2)         ASP2 (AS2)
                         (Primary)           (Backup)
         |                  |                   |
         <----ASP Up--------+                   |
         +----ASP Up Ack --->                   |
         |                  |                   |
         <-----------------------ASP Up---------+
         +-----------------------ASP Up Ack ---->
         |                  |                   |
         <----ASP Active----+                   |
         +-ASP Active Ack--->                   |
         |                  |                   |


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4.2 ASP fail-over Procedures

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


4.3 SUA/SCCP-User Boundary Examples

4.3.1 Data Transfer

   This is an example of data transfer, assuming associations are
   already established.  Note that the SCTP sack is shown purely for
   illustrative reasons.

        SEP           SG          SG         ASP         ASP
       SCCP          SUA         SCTP       SCTP         SUA
         |            |           |           |           |
         +----UDT----->           |           |           |
         |            +---Send---->           |           |
         |            |.. . . . . . . CLDT . . . . . . . .>
         |            |           +---data---->           |
         |            |           |           +-data arr-->
         |            |           |           <-rec data--|
         |            |           <---sack----+           |
         |            <-data arr--+           |           |
         |            +-rec data-->           |           |
         |            < . . . . . . . CLDA . . . . . . . ..
         |            |           |           |           |


5 Security

5.1 Introduction

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

5.2 Threats

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

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

   SUA runs on top of SCTP.  SCTP provides certain transport related
   security features, such as:

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

   When SUA is running in professionally managed corporate or service
   provider network, it is reasonable to expect that this network
   includes an appropriate security policy framework. The "Site Security
   Handbook" [2196] should be consulted for guidance.

   When the network in which SUA runs in involves more than one party,
   it may not be reasonable to expect that all parties have implemented
   security in a sufficient manner. End-to-end security should be the
   goal, therefore, it is recommended that IPSEC is used to ensure
   confidentiality of user payload.  Consult [2409] for more information
   on configuring IPSEC services.

5.3 Protecting Confidentiality

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

6 IANA Considerations

6.1 SCTP Payload Protocol ID

   A request will be made to IANA to assign SCTP Payload Protocol IDs.
   A Payload ID for the SUA will be registered.

   The Payload ID is included in each SCTP data chunk, to indicate which
   protocol SCTP is carrying. This Payload ID is not directly used by
   SCTP but may be used by certain network entities to identify the type
   of information being carried in this DATA chunk.

   It is assumed that the Payload ID for SUA will be 3.

6.2 Port Number

   SUA will use port number 14001, which is currently registered to
   "ITU-T SCCP".  This Port Number is the port which the SG listen to
   when receiving SCTP datagrams.

7 Timer Values

     Ta        2 seconds
     Tr        2 seconds

8 Acknowledgements

   The authors would like to thank Lode Coene, Joe Keller, Florencio
   Escobar-Gonzalez, Marja-Liisa Hamalainen and Markus Maanoja for their
   insightful comments and suggestions.

   Funding for the RFC editor function is currently provided by the
   Internet Society.

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9 Authors' Addresses

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

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

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

   Stephen Lorusso
   Unisphere Solutions
   One Executive Drive
   Chelmsford, MA 01824
   USA
   email: SLorusso@UnisphereSolutions.com

10 References

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

   [ITU SCCP]     ITU-T Recommendations Q.711-714, 'Signaling System No.
                  7 (SS7) - Signaling Connection Control Part (SCCP)'

   [ANSI SCCP]    ANSI T1.112 'Signaling System Number 7 - Signaling
                  Connection Control Part'

   [ITU TCAP]     ITU-T Recommendation Q.771-775 'Signaling System No. 7
                  SS7) - Transaction Capabilities (TCAP)

   [ANSI TCAP]    ANSI T1.114 'Signaling System Number 7 - Transaction
                  Capabilities Application Part'

   [RANAP]        3G TS 25.413 V3.0.0 (2000-01) 'Technical Specification
                  3rd Generation Partnership Project; Technical
                  Specification Group Radio Access Network; UTRAN Iu
                  Interface RANAP Signalling'

   [SCTP]         Stream Control Transport Protocol <draft-ietf-sigtran-
                  sctp-13.txt>, July 2000, Work in Progress.

   [M3UA]         MTP3-User Adaptation Layer <draft-ietf-sigtran-m3ua-
                  03.txt>, July 2000, Work in Progress.

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


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   [UTRAN IUR]    3G TS 25.420 V3.0.0 (2000-01) "Technical Specification
                  3rd Generation Partnership Project; Technical
                  Specification Group Radio Access Network; UTRAN Iur
                  Interface General Aspects and Principles"

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

   [ENUM]         "ENUM Requirements" <draft-ietf-enum-rqmts-01.txt>,
                  December 1999, Work in Progress.

   [E.164-DNS]    "E.164 number and DNS", <draft-ietf-enum-e164-dns-
                  03.txt>, July 2000, Work in Progress.


Appendix A: Message mapping between SCCP and SUA.

   This is for illustrative purposes only.

   SUA         SCCP      SCCP                     Classes          Mgt.
   SUA
   Name   Name      Full Name                0    1    2    3 Msg. Usage
   =====================================================================
   Connectionless Messages
   CLDT   UDT       Unitdata                 X    X    -    -    -    -
   CLDT   XUDT      Extended unitdata        X    X    -    -    -    -

   CLDT   LUDT      Long unitdata            X    X    -    -    -    -
   CLDA   UDTS      Unitdata service         X    X    -    -    -    -
   CLDA   XUDTS     Extended unitdata serv.  X    X    -    -    -    -
   CLDA   LUDTS     Long unitdata service    X    X    -    -    -    -

   Connection-Oriented Messages
   CODT   DT1       Data form 1              -    -    X    -    -    -
   CODT   DT2       Data form 2              -    -    -    X    -    -
   CODT   ED        Expedited data           -    -    -    X    -    -
   CODA   AK        Data acknowledgement     -    -    -    X    -    -
   CODA   EA        Expedited data ack.      -    -    -    X    -    -
   CORE   CR        Connection request       -    -    X    X    -    -
   COAK   CC        Connection confirm       -    -    X    X    -    -
   COAK   CREF      Connection refused       -    -    X    X    -    -
   RELRE  RLSD      Released                 -    -    X    X    -    -
   RELCO  RLC       Release complete         -    -    X    X    -    -
   RESRE  RSR       Reset request            -    -    -    X    -    -
   RESCO  RSC       Reset confirm            -    -    -    X    -    -

   General Protocol Messages
   ERR    ERR       Protocol data unit error -    -    X    X    -    X
   AUD    IT        Inactivity test          -    -    X    X    -    X

   SS7 MGT Messages
   DUNA   n/a       n/a                      -    -    -    -    -    X
   DAVA   n/a       n/a                      -    -    -    -    -    X
   DAUD   n/a       n/a                      -    -    -    -    -    X
   SCMG   SSC       SCCP/subsystem-congested -    -    -    -    X    -
   SCMG   SSA       subsystem-allowed        -    -    -    -    X    -
   SCMG   SSP       subsystem-prohibited     -    -    -    -    X    -
   SCMG   SST       subsystem-status-test    -    -    -    -    X    -
   SCMG   SOR       subsystem-oos-req        -    -    -    -    X    -

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   SCMG   SOG       subsystem-oos-grant      -    -    -    -    X    -

   SUA MGT Messages
   ASPUP  n/a       n/a                      -    -    -    -    -    X
   ASPDN  n/a       n/a                      -    -    -    -    -    X
   ASPAC  n/a       n/a                      -    -    -    -    -    X
   ASPIA  n/a       n/a                      -    -    -    -    -    X
   NTFY   n/a       n/a                      -    -    -    -    -    X

   -      = Message not applicable for this protocol class.
   X      = Message applicable for this protocol class.
   n/a    = not applicable

Appendix B: SCTP to SUA Message Mapping Examples

   CLDT

   - Pointer to Optional part shall be coded as 0 (as long as there
     is no optional parameter).

   - A and B flags are mapped from 'Protocol Class' parameter
     received in XUDT/LUDT/UDT (or from Data Request primitive).

   - C flag is mapped from 'Importance parameter' received in XUDT/LUDT
     (or from Data Request primitive), or if not present a default
     value for the message type shall be used.


Copyright Statement

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