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draft-ietf-sigtran-sua-05

Description: Request For Comments

You can download source copies of the file as follows:

draft-ietf-sigtran-sua-05.txt in text format.

Listed below is the contents of file draft-ietf-sigtran-sua-05.txt.




INTERNET-DRAFT                                             J. Loughney
Internet Engineering Task Force                                  Nokia
                                           G. Sidebottom, Guy Mousseau
Issued:  1 February 2001                               Nortel Networks
Expires: 1 August 2001                                      S. Lorusso
                                                   Unisphere Solutions
                                                  L. Coene, G. Verwimp
                                                               Siemens
                                                             J. Keller
                                                               Tekelec
                                                            F. Escobar
                                                              Ericsson
                                                  W. Sully, S. Furniss
                                                               Marconi

                  SS7 SCCP-User Adaptation Layer (SUA)
                    <draft-ietf-sigtran-sua-05.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 1 August 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    February 1, 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 .............................11
 1.5 Internal Functions Provided in the SUA Layer ...................13
 1.6 Definition of SUA Boundaries ...................................15
2 Conventions........................................................16
3 Protocol Elements..................................................16
 3.1 Common Message Header ..........................................16
 3.2 SUA Connectionless Messages ....................................19
 3.3 Connection Oriented Messages ...................................21
 3.4 SS7 Signaling Network Management Messages ......................29
 3.5 Application Server Process Maintenance Messages ................34
 3.6 ASP Traffic Maintenance Messages ...............................36
 3.7 Management Messages ............................................39
 3.8 Common Parameters ..............................................40
 3.9 SUA-Specific parameters ........................................49
4 Procedures.........................................................62
 4.1 SCCP _ SUA Interworking at the SG ..............................62
 4.2 Primitives received from the local SUA-user ....................63
 4.3 Layer Management Procedures ....................................64
 4.4 SUA Management Procedures ......................................65
5 Examples of SUA Procedures.........................................71
 5.1 SG Architecture ................................................71
 5.2 IP-IP Architecture .............................................74
6 Message Routing Scenarios..........................................76
 6.1 Basic case with single SG acting as end- or relay-point ........76
 6.2 Replicated SG acting as end-point ..............................77
 6.3 Replicated SG acting as relay-point ............................78
7 Security...........................................................79
 7.1 Introduction ...................................................79
 7.2 Threats ........................................................79
 7.3 Protecting Confidentiality .....................................79
8 IANA Considerations................................................80
 8.1 SCTP Payload Protocol ID .......................................80
 8.2 Port Number ....................................................80
 8.3 Protocol Extensions ............................................80
9 Timer Values.......................................................81
10 Acknowledgements..................................................81
10 Authors' Addresses................................................81
11 References........................................................83
Appendix A: Message mapping between SCCP and SUA.....................84
Copyright Statement..................................................85

Loughney, et al.                                            [Page 2]
Internet Draft       SS7 SCCP-User Adaptation Layer    February 1, 2000

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. Depending 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 Signaling Gateway Processes, which are 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 a virtual IP
   database element handling all request for a SCCP-user.  The AS

Loughney, et al.                                            [Page 3]
Internet Draft       SS7 SCCP-User Adaptation Layer    February 1, 2000

   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.

   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
   SS7 network ID and SCCP SSN for 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. In the case of SUA, the
   Routing Key should be limited to a combination of SS7 network ID and
   SCCP SSN to identify an AS, in order to more easily support SCCP
   management procedures.

   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.

   Network Appearance - The Network Appearance identifies an SS7
   network context (network ID) for the purposes of logically
   separating the signaling traffic between the SG and the Application
   Server Processes over a common SCTP Association.  This partitioning
   is necessary where an SG is logically partitioned to appear as an
   end-node elements in multiple separate national SS7 networks, in
   which case there is a separate network appearance for each SS7

Loughney, et al.                                            [Page 4]
Internet Draft       SS7 SCCP-User Adaptation Layer    February 1, 2000

   network. It is also necessary when an SG is configured as an STP and
   hosts multiple point codes within the same network, in which case
   each point code is a separate network appearance.

   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.

   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. The first section considers the SS7-IP
   interworking architectures for connectionless and connection-
   oriented transport.  For this case, it is assumed that the ASP
   initiates the establishment of the SCTP association with SG.

1.3.1 Protocol Architecture for Connectionless 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.  For messages destined for an ASP, there
   are two scenarios.

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

Loughney, et al.                                            [Page 5]
Internet Draft       SS7 SCCP-User Adaptation Layer    February 1, 2000

        * 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

1.3.1.1 SG as endpoint

   In this case, the connectionless SCCP messages are routed on PC and
   SSN.  The subsystem identified by SSN and SS7 network appearance is
   regarded as local to the SG.  This means from SS7 point of view, the
   SCCP-user is located at the SG.

   By means of configuration, the SG knows the local SCCP-user is
   actually representing an AS, serviced by a set of ASPs working in
   n+k redundancy mode.  An ASP is selected and a CLDT message is sent
   on the appropriate SCTP association/stream.

   Actually, the primitive interface between SCCP and SCCP-user is
   transported here over SUA.  An example for a INAP/TCAP message
   exchange between SEP and ASP is given below.

   Address information in CLDT message (TC_Query) from SG to ASP :

     -  Association ID : SG-ASP,
     -  Stream ID : based on SLS (and possibly OPC, SS7 network ID),
     -  Network appearance : based on SS7 network ID,
     -  Source address : valid combination of SSN, PC and GT, as
        needed for back-routing,
     -  Destination address : at least SSN, to select the SCCP-user
        at the ASP.

   The Network Appearance is needed if the SG operates in more than one
   SS7 network, since PC and SSN only have meaning within a specific
   SS7 network.  In the response, the ASP should pass a unique,
   unambiguous source address.

Loughney, et al.                                            [Page 6]
Internet Draft       SS7 SCCP-User Adaptation Layer    February 1, 2000

   Address information in CLDT message (TC_Response) from ASP to SG :

     - Association ID : ASP-SG,
     - Stream ID : implementation dependent, but in-sequence-
       delivery must be taken care of,
     - Network appearance : as received in previous message,
     - Source address : unique ASP address that when used as
       SCCP called party address in the SEP, MUST yield the
       same ASP again; the SSN could be sufficient,
     - Destination address : copied from source address in received
       CLDT message.

   Further messages from the SEP belonging to the same TCAP transaction
   will now reach the same ASP.

1.3.1.2 SG as relay-point

   A Global Title translation must be executed at the SG, before the
   destination of the message can be determined.  The actual location
   of the SCCP-user is irrelevant to the SS7 network.  GT Translation
   yields an "SCCP entity set", which now may contain one or more AS.
   Selection of the AS is thus based on the SCCP called party address
   (and possibly other SS7 parameters depending on the implementation).
   Basically this means splitting the SS7 traffic over different AS's
   based on GT information.  After this, the same as in 1.3.1.1
   applies.

1.3.2 Protocol Architecture for Connection-Oriented Transport

   In this architecture, the SCCP and SUA layers interface in the SG to
   associate the two connection sections needed for the connection-
   oriented data transfer between SEP and ASP.  Both connection
   sections are setup when routing the Connect Request messages from
   SEP via SG to ASP.  The routing of the Connect Request message is
   done in the same wavy as described in 1.3.1.

   Further messages for this connection are routed on DPC in the SS7
   connection section (MTP routing label), and on IP address in the IP
   connection section (SCTP header).  No other routing information is
   present in the SCCP or SUA messages themselves. Resources are kept
   within the SG to forward messages from one section to another and to
   populate the MTP routing label or SCTP header, based on the
   destination local reference of these messages (Connect Confirm, Data
   Transfer, ...)

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

Loughney, et al.                                            [Page 7]
Internet Draft       SS7 SCCP-User Adaptation Layer    February 1, 2000

        * STP  *         *             *        *      *
        ********         ***************        ********

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

   The above architecture may simplify, in some cases, to carrying SS7
   application protocols 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  |
          +------+        +------+
             |                |
             +----------------+

Loughney, et al.                                            [Page 8]
Internet Draft       SS7 SCCP-User Adaptation Layer    February 1, 2000

       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.

Loughney, et al.                                            [Page 9]
Internet Draft       SS7 SCCP-User Adaptation Layer    February 1, 2000

   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.

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       *
  * | ******** | *                                      *  ********  *
  * | * SGP1 +---------------------------------------------+ ASP1 *  *
  * | ******** | *                                      *  ********  *
  * | ******** | *                                      *  ********  *
  * | * SGP2 +--------------------------+       +----------+ ASP2 *  *
  * | ******** | *                      |       |       *  ********  *
  * +----------+ *                      |       |       *      .     *
  * +----------+ *                      |       |       *      .     *
  * | AS2      | *                      |       |       *      .     *
  * | ******** | *                      |       |       *  ********  *
  * | * SGP1 +----------------------------------+       *  * ASPN *  *
  * | ******** | *   SCTP Associations  |               *  ********  *
  * | ******** | *                      |               **************
  * | * SGP2 +----------------          |
  * | ******** | *           |          |               **************
  * +----------+ *           |          |               *  AS4       *
  ****************           |          |               *  ********  *
                             |          +------------------+ ASP1 *  *
                             |                          *  ********  *
                             |                          *      .     *
                             |                          *      .     *
                             |                          *            *
                             |                          *  ********  *
                             +-----------------------------+ ASPn *  *
                                                        *  ********  *

Loughney, et al.                                            [Page 10]
Internet Draft       SS7 SCCP-User Adaptation Layer    February 1, 2000

                                                        **************

                Figure 2: Signaling Gateway Architecture

   The pair of SGs can either operate as replicated endpoints or as
   replicated relay points from the SS7 network point of view.

   Replicated endpoints : only for the first message in a transaction
   or connection one of the SGs is chosen, depending on the traffic
   mode (primary/backup or loadsharing) and overload conditions.  Once
   selected, the same SG is used for the subsequent messages.

   Replicated relay points : in normal circumstances, the path from SEP
   to ASP will always go via the same SG when in-sequence-delivery is
   requested.  However, linkset failures may cause MTP to re-route to
   the other SG.

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

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.

Loughney, et al.                                            [Page 11]
Internet Draft       SS7 SCCP-User Adaptation Layer    February 1, 2000

   * 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

   The SUA layer needs to support the following SCCP network management
   primitives (a reference to ITU and ANSI sections where these
   primitives and corresponding parameters are described, is also
   given):

   Generic   |Specific   |
   Name      |Name       |ANSI/ITU Reference
   ----------+-----------+---------------------------------------------
   N-Coord   |Request    |ITU-Q.711   Chap 6.3.2.3.1 (Tab 13/Q.711)
             |Indication |ANSI-T1.112 Chap 2.3.2.3.1 (Tab 8D/T1.112.1)
             |Response   |
             |Confirm    |
   ----------+-----------+---------------------------------------------
   N-State   |Request    |ITU-Q.711   Chap 6.3.2.3.2 (Tab 14/Q.711)
             |Indication |ANSI-T1.112 Chap 2.3.2.3.2 (Tab 8E/T1.112.1)
   ----------+-----------+---------------------------------------------
   N-Pcstate |Indication |ITU-Q.711   Chap 6.3.2.3.3 (Tab 15/Q.711)
             |           |ANSI-T1.112 Chap 2.3.2.3.4 (Tab 8G/T1.112.1)

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.

Loughney, et al.                                            [Page 12]
Internet Draft       SS7 SCCP-User Adaptation Layer    February 1, 2000

     *    Provide the initiation of an audit of remote SS7
          endpoints at the SG.

1.4.6 Relay function

   An SCTP association exists between two SUA endpoints. For network
   scalability purposes, the SUA may be enhanced with a relay
   functionality to determine the next hop SCTP association towards the
   destination SUA endpoint.

   The determination of the next hop may be based on Global Title
   information (e.g. E.164 number), in analogy with SCCP GTT in SS7
   networks, modelled in [ITU-T Q.714]. It may also be based on
   Hostname information.

   The relay function is invoked when :

   - routing is on Global Title,
   - routing is on Hostname.

   Translation/resolution of the above address information must yield
   either of the following :

   - Route on SSN : SCTP association ID towards the destination node +
     SSN + Network Appearance (optional)
   - Route on GT : SCTP association ID towards next relay node + (new)
     GT + SSN (optional) + Network Appearance (optional)
   - Routing on Hostname : SCTP association ID towards next relay node
     + (new) Hostname + SSN (optional) + Network Appearance (optional)
   - A local SUA-user (combined relay/end node)

   To prevent endless hopping, the hop counter is used. The originating
   end node (be it an SS7 or an IP node) sets the value of the hop
   counter to the maximum value (15). Each time the relay function is
   invoked within an intermediate (relay) node, the hop counter must be
   decremented. When the value reaches zero, and the translation result
   is still _Route on GT_ or _Route on Hostname_, the return or refusal
   procedures are invoked with reason _Hop counter violation_.

1.5 Internal Functions Provided in the SUA Layer

1.5.1 Address Translation and Mapping at the SG

   The SG MUST provide address translation and mapping functions to
   direct messages received from the SS7 network to the appropriate IP
   destination.

   In order to support message distribution, the SG maintains an
   address translation table, which maps the incoming SS7 messages to
   the appropriate AS.  The relevant fields of the incoming SS7 message
   is compared to the existing Routing Keys.  The Routing Keys

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   reference an Application Server, which will have one or more ASPs
   processing traffic for the AS.  The availability and status of the
   ASPs is handled by SUA ASP management messages.

   Possible SS7 address/routing information that comprise
   a Routing Key entry includes, for example, OPC, DPC, SIO found in
   the MTP3 routing label, or other specific fields such as the
   SCCP subsystem number, or TCAP transaction ID. Some possibilities
   include:

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

   An Application Server maintains a list of ASPs that are available to
   process the traffic.  The list is dynamic, based upon the
   availability of the individual ASPs in the list.  SUA ASP management
   messages are used to convey the status of these ASPs and their
   availability in failover situations.

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

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

1.5.2 Address Translation and Mapping at the ASP

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

   A remote Signaling Gateway may be composed of one or more SGPs that
   are capable of routing SS7 traffic.  As is the case with ASPs, a
   dynamic list of SGPs in an SG can be maintained, taking into account
   the availability status of the individual SGPs, configuration
   changes and fail-over mechanisms. There is, however, no SUA
   messaging to manage the status of an SGP. Whenever an SCTP
   association to an SGP exists, it is assumed to be available.  Also,
   every SGP of one SG communicating with one ASP regarding one AS
   provides identical SS7 connectivity to this ASP.

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1.5.3 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 (a reference to ITU and ANSI sections where these primitives
   and corresponding parameters are described, is also given):

   Generic     |Specific  |
   Name        |Name      |ANSI/ITU Reference
   ------------+----------+-------------------------------------------
   N-Connect   |Request   |ITU-Q.711   Chap 6.1.1.2.2 (Tab 2/Q.711)
               |Indication|ANSI-T1.112 Chap 2.1.1.2.2 (Tab 2/T1.112.1)
               |Response  |
               |Confirm   |
   ------------+----------+-------------------------------------------
   N-Data      |Request   |ITU-Q.711   Chap 6.1.1.2.3 (Tab 3/Q.711)
               |Indication|ANSI-T1.112 Chap 2.1.1.2.3 (Tab 3/T1.112.1)
   ------------+----------+-------------------------------------------
   N-Expedited |Request   |ITU-Q.711   Chap 6.1.1.2.3 (Tab 4/Q.711)
   Data        |Indication|ANSI-T1.112 Chap 2.1.1.2.3 (Tab 4/T1.112.1)
   ------------+----------+-------------------------------------------
   N-Reset     |Request   |ITU-Q.711   Chap 6.1.1.2.3 (Tab 5/Q.711)
               |Indication|ANSI-T1.112 Chap 2.1.1.2.3 (Tab 5/T1.112.1)
               |Response  |
               |Confirm   |
   ------------+----------+-------------------------------------------
   N-Disconnect|Request   |ITU-Q.711   Chap 6.1.1.2.4 (Tab 6/Q.711)
               |Indication|ANSI-T1.112 Chap 2.1.1.2.4 (Tab 6/T1.112.1)
   ------------+----------+-------------------------------------------
   N-Inform    |Request   |ITU-Q.711   Chap 6.1.1.3.1 (Tab 7/Q.711)
               |Indication|ANSI-T1.112 Chap 2.1.1.2.5 (Tab 6A/T1.112.1)
   ------------+----------+-------------------------------------------
   N-Unit Data |Request   |ITU-Q.711   Chap 6.2.2.3.1 (Tab 10/Q.711)
               |Indication|ANSI-T1.112 Chap 2.2.2.3.1 (Tab 8A/T1.112.1)
   ------------+----------+-------------------------------------------
   N-Notice    |Indication|ITU-Q.711   Chap 6.2.2.3.2 (Tab 11/Q.711)
               |          |ANSI-T1.112 Chap 2.2.2.3.2 (Tab 8B/T1.112.1)

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1.6.2 Definition of the lower boundary

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

2 Conventions

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

3 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.

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

3.1 Common Message Header

   The protocol messages for 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.

3.1.1 SUA Protocol Version

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

         01   SUA version 1.0

3.1.2 Message Classes

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   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
     8         Connection-Oriented Messages
     9 - 127   Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

3.1.3 Message Types

   SUA Management Messages

     0         Error (ERR)
     1         Notify (NTFY)
     2 - 127   Reserved by the IETF
     128- 255  Reserved for IETF-Defined Message Class Extensions

   SS7 Signaling Network Management (SSNM) Messages

     0         Reserved
     1         Destination Unavailable (DUNA)
     2         Destination Available (DAVA)
     3         Destination State Audit (DAUD)
     4         SS7 Network Congestion (SCON)
     5         Destination User Part Unavailable (DUPU)
     6         SCCP Management (SCMG)
     7 - 127   Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

   Application Server Process Maintenance (ASPM) Messages

     0         Reserved
     1         ASP Up (UP)
     2         ASP Down (DOWN)
     3         Heartbeat (BEAT)
     4         ASP Up Ack (UP ACK)
     5         ASP Down Ack (Down ACK)
     6         Heartbeat Ack (BEAT ACK)
     7 - 127   Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

   ASP Traffic Maintenance (ASPTM) Messages

     0         Reserved
     1         ASP Active (ACTIVE)

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     2         ASP Inactive (INACTIVE)
     3         ASP Active Ack (ACTIVE ACK)
     4         ASP Inactive Ack (INACTIVE ACK)
     5 - 127   Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

   Connectionless Messages

     0         Reserved
     1         Connectionless Data Transfer (CLDT)
     2         Connectionless Data Response (CLDR)
     3 - 127   Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

   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        Connection Oriented Error (COERR)
     11        Inactivity Test (COIT)
     12 - 127  Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

3.1.4 Message Length

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

3.1.5 Tag-Length-Value Format

   SUA messages consist of a Common Header followed by zero or more
   parameters, as defined by the message type.  The Tag-Length-Value
   (TLV)  parameters contained in a message are defined in a Tag-
   Length-Value format as shown below.

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

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

   Parameter Tag: 16 bits (unsigned integer)

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

   Parameter Length: 16 bits (unsigned integer)

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

   Parameter Value: variable-length.

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

      The total length of a parameter (including Tag, Parameter Length
      and Value fields) MUST be a multiple of 4 bytes. If the length of
      the parameter is not a multiple of 4 bytes, the sender pads the
      Parameter at the end (i.e., after the Parameter Value field) with
      all zero bytes. The length of the padding is NOT included in the
      parameter length field. A sender should NEVER pad with more than
      3 bytes. The receiver MUST ignore the padding bytes.

   Implementation note : the use of TLV in principle allows the
   parameters to be placed in a random order in the message. However,
   some guidelines should be considered for easy processing in the
   following order :

   - parameters needed to correctly process other message parameters,
     preferably should precede these parameters (such as Network
     Appearance), mandatory parameters preferably should precede any
     optional parameters,
   - the data parameter will normally be the final one in the message.

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

3.2.1 Connectionless Data Transfer (CLDT)

   This message transfers data between one SUA to another.

       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 = 0x0001          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Network Appearance                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0101          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0102          |      Parameter Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                        Source Address                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |      Parameter Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Network Appearance            Optional
     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).

3.2.2 Connectionless Data Response (CLDR)

   This message is used as a response message by the peer to report
   errors in the received CLDT message, when the return on error option
   is set.

       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                     |

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0101          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           SCCP Cause                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0102          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                        Source Address                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Network Appearance            Optional
     Flags                         Mandatory
     SCCP Cause                    Mandatory
     Source Address                Mandatory
     Destination Address           Mandatory
     Data                          Optional

   Implementation note:

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

3.3 Connection Oriented Messages

3.3.1 Connection Oriented Data Transfer (CODT)

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

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      |                        Sequence number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Sequence number               Mandatory *1
     Destination Reference Number  Mandatory
     Data                          Mandatory

   NOTE *1:    Mandatory when CODT message maps a DT2 message.
               Otherwise, the parameter is not be present.

   Implementation note:

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

3.3.2 Connection Oriented Data Acknowledge (CODA)

   This message is used to acknowledge receipt of data by the peer.
   This message is used only with protocol class 3.

       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                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |              Length           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0108          |              Length           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Receive Sequence Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x010A          |           Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Credit                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters

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     Network Appearance            Optional
     Destination Reference Number  Mandatory
     Receive Sequence number       Mandatory *1
     Credit                        Mandatory *1

   NOTE *1:    Mandatory when representing Data Acknowledgement (AK).

   Implementation note:

   This message covers the following SCCP messages: Data
   Acknowledgement (AK), Expedited Data Acknowledgement (EA).

3.3.3 Connection Request (CORE)

   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 = 0x0001          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Network Appearance                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0101          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Source Reference Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0102          |           Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                        Source Address                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x010A          |           Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Credit                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |           Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

3.3.4 Connection Acknowledge (COAK)

   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 = 0x0101          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Source Reference Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x010A          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Credit                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Flags                         Mandatory
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory
     Credit                        Optional *2
     Destination Address           Optional *1
     Data                          Optional

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   NOTE *1:    Destination Address parameter will be present in case
               that the received CORE message conveys the Source
               Address parameter.
   Note *2:    Used for protocol class 3.

   Implementation note:

   This message covers the following SCCP message: Connection Confirm
   (CC).

3.3.5 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 = 0x0001          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Network Appearance                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           SCCP Cause                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0001          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
        Destination Reference Number    Mandatory
        SCCP 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.

Loughney, et al.                                            [Page 25]
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3.3.6 Release Request (RELRE)

   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 = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Source Reference Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          SCCP Cause                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0101          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   Implementation Note:

   This message covers the following SCCP message: Connection Refused
   (RLSD).

3.3.7 Release Complete (RELCO)

   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

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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 = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Source Reference Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory

   Implementation Note:

   This message covers the following SCCP message: Release Complete
   (RLC).

3.3.8 Reset Request (RESRE)

   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 = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Source Reference Number                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           SCCP Cause                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   Implementation note:

   This message covers the following SCCP message: reset request (RSR).

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3.3.9 Reset Confirm (RESCO)

   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 = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Source Reference Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory

   Implementation note:

   This message covers the following SCCP message: Reset Confirmation
   (RSC).

3.3.10 Connection Oriented Error (COERR)

   The COERR message is sent to indicate a protocol data unit 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 = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          SCCP Cause                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Destination Reference Number  Mandatory
     SCCP Cause                    Mandatory

   Implementation Note:

   This message covers the following SCCP message: Protocol Data Unit
   Error (ERR)

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3.3.11 Connection Oriented Inactivity Test (COIT)

   This message is used for auditing the signaling connection state and
   the consistency of connection data at both ends of the signaling
   connection.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Source Reference Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0107          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x010A          |           Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Credit                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Flags                         Mandatory
     Source Reference Number       Mandatory
     Destination Reference number  Mandatory
     Sequence number               Mandatory *1
     Credit                        Mandatory *1

   NOTE *1:    Information in these parameter fields reflect those
               values sent in the last data form 2 or data
               acknowledgement message. They are ignored if the
               protocol class indicates class 2.

   Implementation note:

   This message covers the following SCCP message: Inactivity Test
   (IT).

3.4 SS7 Signaling Network Management Messages

3.4.1 Destination Unavailable (DUNA)

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   In the scope of SUA, this message is covered by the PC state
   indication passed between SCCP and local SCCP-user. The DUNA message
   is sent from the SG to all concerned ASPs (servicing SCCP-users
   considered local to the SG, see chapter 1.3.1.1), when an SS7
   destination has become 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 = 0x0001          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Network Appearance                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0005          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Affected Point Code                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Network Appearance            Optional
     Affected Point Code           Mandatory
     Info String                   Optional

3.4.2 Destination Available (DAVA)

   In the scope of SUA, this message is covered by the PC state
   indication passed between SCCP and local SCCP-user. The DAVA message
   is sent from the SG to all concerned ASPs (servicing SCCP-users
   considered local to the SG, see chapter 1.3.1.1) to indicate 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 DAVA.

       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                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0005          |             Length            |

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Affected Point Code                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Network Appearance            Optional
     Affected Point Code           Mandatory
     Info String                   Optional

3.4.3 Destination State Audit (DAUD)

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

   Parameters
     Network Appearance            Optional
     Affected Point Code           Mandatory
     Info String                   Optional

3.4.4 SS7 Network Congestion (SCON)

   The SCON message can be sent from the SG to all concerned ASPs to
   indicate that the congestion level in the SS7 network to a specified
   destination has changed.

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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 = 0x0001          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Network Appearance                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0010          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Congestion Level                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x000E          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      \                          Affected PC                          \
      /                                                               /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Network Appearance            Optional
     Congestion Level              Mandatory
     Affected PC                   Mandatory
     Info String                   Optional

3.4.5 Destination User Part Unavailable (DUPU)

   The DUPU message is used in local broadcast procedures (SUA for SCCP
   - SCCP user interface). In remote broadcast procedures, use SCMG
   message formatID SSP (peer SUA message)

   The format for DUPU Message parameters is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0001          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Network Appearance                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0005          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Affected Point Code                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0009          |             Length            |

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

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

3.4.6 SCCP Management Message (SCMG)

   The SCMG message is sent 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 = 0x0001          |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Network Appearance                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x010B       |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     SCMG Format Identifier                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x010C       |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         SMI/Subsystem                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x0005       |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     /                          Affected PC                          /
     \                                                               \
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x000E       |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Congestion Level                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x0004       |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     /                          INFO String                          \
     \                                                               /
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters

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     Network Appearance            Optional
     SCMG Format Identifier        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 not
               present.

3.5 Application Server Process Maintenance Messages

3.5.1 ASP Up (UP)

   The ASP UP (UP) message is used to indicate to a remote SUA peer
   that the Adaptation layer is up and running.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        ASP Capabilities                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0004       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     ASP Capabilities              Optional
     Info String                   Optional

3.5.2 ASP Up Ack (UP ACK)

   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 = 0x0109       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        ASP Capabilities                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0004       |             Length            |

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     ASP Capabilities              Optional
     Info String                   Optional

3.5.3 ASP Down (DN)

   The ASP Down (DN) message is used to indicate to a remote SUA peer
   that the adaptation layer is not running.

       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 = 0x000A       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Reason                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0004       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Reason              Mandatory
     Info String         Optional

3.5.4 ASP Down Ack (DOWN ACK)

   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 = 0x000A       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Reason                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0004       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Reason                        Mandatory

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     Info String                   Optional

3.5.5 Heartbeat (BEAT)

   The Heartbeat message is optionally used to ensure that the SUA
   peers are still available to each other.

   The format for the BEAT message is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0008       |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Heartbeat Data                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Heartbeat Data           Optional

3.5.6 Heartbeat Ack (BEAT ACK)

   The Heartbeat ACK message is sent in response to a BEAT message. A
   peer MUST send a BEAT ACK in response to a BEAT message. It includes
   all the parameters of the received Heartbeat message, without any
   change.

   The format for the BEAT ACK message is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0008       |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Heartbeat Data                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Heartbeat Data           Optional

3.6 ASP Traffic Maintenance Messages

3.6.1 ASP Active (ACTIVE)

   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 ACTIVE message is as follows:

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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x000B         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Traffic Mode Type                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0004         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Traffic Mode Type        Mandatory
     Routing Context          Optional
     Info String              Optional

3.6.2 ASP Active Ack (ACTIVE ACK)

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

   The format for the ACTIVE Ack message is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x000B         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Traffic Mode Type                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0004         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
        Traffic Mode Type     Mandatory

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        Routing Context       Optional
        Info String           Optional

   The format of the Traffic Mode Type and Routing Context parameters
   is the same as for the ASP-Active message.

   The format and description of the optional Info String parameter is
   the same as for the ASP-Active message.

3.6.3  ASP Inactive (INACTIVE)

   The INACTIVE 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0004         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          INFO String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context          Optional
     INFO String              Optional

3.6.4 ASP Inactive Ack (INACTIVE ACK)

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

   The format for the INACTIVE Ack message is as follows:

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

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          INFO String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context     Optional
     INFO String         Optional

   The format of the Traffic Mode Type and Routing Context parameters
   is the same as for the ASP-Active message.

   The format and description of the optional Info String parameter is
   the same as for the ASP-Active message.

3.7 Management Messages

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

3.7.1 Error (ERR)

   The ERR message is sent between two SUA peers to indicate an error
   situation.  The Data parameter is optional, 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x000C         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Error Code                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0007         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                        Diagnostic Info                        /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Error Code                    Mandatory
     Diagnostic Info               Optional

3.7.2 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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      |          Tag = 0x000D         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Status Type/ID                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0006         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0004         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The NTFY message contains the following parameters:

   Parameters
     Status Type/ID                Mandatory
     Routing Context               Optional
     Info String                   Optional

3.8 Common Parameters

   These TLV parameters are common across the different adaptation
   layers.

   Parameter Name                     Parameter ID
   ==============                     ============
   Network Appearance                   0x0001
   Not used in SUA                      0x0002
   Data                                 0x0003
   Info String                          0x0004
   Affected Point Code                  0x0005
   Routing Context                      0x0006
   Diagnostic Info                      0x0007
   Heartbeat Data                       0x0008
   Cause/User                           0x0009
   Reason                               0x000A
   Traffic Mode Type                    0x000B
   Not used                             0x000C
   Status Type                          0x000D
   Congestion Level                     0x000E

3.8.1 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 Process
   over a common SCTP Association.  An example is where an SG is

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   logically partitioned to appear as an element in several different
   national SS7 networks.

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

   The Network Appearance implicitly defines the SS7 Point Code format
   used, the SS7 Network Indicator value and SCCP protocol
   type/variant/version used within the SS7 network partition.  Where
   an SG operates in the context of a single SS7 network, or individual
   SCTP associations are dedicated to each SS7 network context, the
   Network Appearance parameter is not required.

   The Network Appearance parameter value is of local significance
   only, coordinated between the SG and ASP.

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

     3.8.2 Not used

     Parameter ID 0x02 is not used in SUA.

3.8.3 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                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Data parameter field contains the SS7 SCCP-User application
   message, for example an INAP/TCAP message.

3.8.4 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.

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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 = 0x0004         |            length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          info string                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.8.5 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|

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   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 can be used to identify a contiguous range of
   Affected Destination Point Codes, independent of the point code
   format.  Identifying a contiguous range of Affected 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.

   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 "wild-carded".  For example, a mask of "8" indicates
   that the last eight bits of the PC is "wild-carded".  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 "wild-carded".  For a 14-bit ITU
   Affected PC, this is equivalent to signaling that an ITU Region is
   unavailable.

3.8.6 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             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Routing Context parameter contains (a list of) 4-byte unsigned
   integers indexing the Application Server traffic that the sending
   ASP is configured/registered to receive.  There is one-to-one
   relationship between an index entry and a SG Routing Key or AS Name.
   Since an AS can only appear in one Network Appearance, the Network
   Appearance parameter is not required in the ASP Active message.

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

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3.8.7 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0007          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Diagnostic Information*                   /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.8.8 Heartbeat Data

   The Heartbeat Data field contents are defined by the sending node.
   It may include a Heartbeat Sequence Number and/or Timestamp, other
   implementation specific details.

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

       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 = 0x0008          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Heartbeat Data                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The data field can be used to store information in the heartbeat
   message useful to the sending node (e.g. the data field can contain
   a time stamp, a sequence number, etc.).

3.8.9 Cause/User

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0009          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Cause              |             User              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-