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

INTERNET-DRAFT                                    J. Loughney (Editor)
Internet Engineering Task Force                                  Nokia
                                           G. Sidebottom, Guy Mousseau
Issued:  20 July 2001                                  Nortel Networks
Expires: 20 January 2002                                    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-07.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 20 January 2002

Abstract

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


Internet Draft       SS7 SCCP-User Adaptation Layer      July 20, 2001



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.............................12
 1.5 Internal Functions Provided in the SUA Layer...................14
 1.6 Definition of SUA Boundaries...................................16
2 Conventions.......................................................17
3 Protocol Elements.................................................17
 3.1 Common Message Header..........................................17
 3.2 SUA Connectionless Messages....................................21
 3.3 Connection Oriented Messages...................................23
 3.4 Signaling Network Management Messages..........................32
 3.5 Application Server Process State Maintenance Messages..........37
 3.6 ASP Traffic Maintenance Messages...............................40
 3.7 SUA Management Messages........................................43
 3.8 Common Parameters..............................................44
 3.9 SUA-Specific parameters........................................53
4 Procedures........................................................64
 4.1 SCCP û SUA Interworking at the SG..............................65
 4.2 Primitives received from the local SUA-user....................67
 4.3 Layer Management Procedures....................................67
 4.4 SUA Management Procedures......................................68
5 Examples of SUA Procedures........................................76
 5.1 SG Architecture................................................76
 5.2 IP-IP Architecture.............................................78
6 Security..........................................................80
 6.1 Introduction...................................................80
 6.2 Threats........................................................80
 6.3 Protecting Confidentiality.....................................81
7 IANA Considerations...............................................81
 7.1 SCTP Payload Protocol ID.......................................81
 7.2 Port Number....................................................81
 7.3 Protocol Extensions............................................81
8 Timer Values......................................................83
9 Acknowledgements..................................................83
10 Authors' Addresses...............................................83
11 References.......................................................84
Copyright Statement.................................................87











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1. Introduction

1.1 Scope

   There is on-going integration of SCN networks and IP networks.
   Network service providers are designing all IP architectures that
   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 addresses the following criteria:

     *    Support for transfer of SCCP-User Part messages (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-
   oriented 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

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   database element handling all requests for a SCCP-user.  The AS
   contains a set of one or more unique Application Server Processes,
   of which one or more is normally actively processing traffic.

   Application Server Process (ASP) - An Application Server Process
   serves as an active or backup 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.

   IP Server Process (IPSP) - A process instance of an IP-based
   application.  An IPSP is essentially the same as an ASP, except that
   it uses SUA in a peer-to-peer fashion.  Conceptually, an IPSP does
   not use the services of a Signaling Gateway.

   Signaling Gateway Process (SGP) - A process instance of a Signaling
   Gateway.  It serves as an active, standby or load-sharing process of
   a Signaling Gateway.

   Signaling Process - A process instance that uses SUA to communicate
   with other signaling process.  An ASP, a SGP and an IPSP are all
   signaling processes.

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

   Routing Key - The Routing Key describes a set of SS7 parameters
   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
   SCCP SSN plus an identifier to uniquely mark the network that the
   SSN belongs to, 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.  Routing Keys can be
   provisioned, for example, by a MIB.

   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 the SGP and
   the ASP (or between two ASPs), identifying the relevant Application
   Server.  From the perspective of an SGP/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. The Routing Context also uniquely identifies an SS7 entity
   (point code) into a SS7 network, as presented by the SG.

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   Address Mapping Function (AMF) - The AMF is an implementation
   dependent function that is responsible for resolving the address
   presented in the incoming SCCP/SUA message to correct SCTP
   association for the desired endpoint. The AMF MAY use routing
   context / rouging key information as selection criteria for the
   appropriate SCTP association.

   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-over may apply upon
   the return to service of a previously unavailable Application Server
   Process.

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

   Layer Management - Layer Management is a nodal function that handles
   the inputs and outputs between the M3UA layer and a local management
   entity.

   Host - The computing platform that the SGP or 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 that 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.


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

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

          SUAP - SCCP/SUA User Protocol (TCAP, for example)
          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 Routing Context 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 represented by an AS, and 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.

   The selection criterion can be based on a round robin mechanism, or
   any other method that guarantees a balanced load sharing over the
   active ASPs. However, when TCAP messages are transported, load
   sharing is only possible for the first message in a TCAP dialogue
   (TC_Begin, TC_Query, TC_Unidirectional). All other TCAP messages in
   the same dialogue are sent to the same ASP that was selected for the
   first message, unless the ASPs are able to share state and maintain

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   in sequence delivery. To this end, the SGP needs to know the TID
   allocation policy of the ASPs in a single AS:

     -    State sharing
     -    Fixed range of TIDs per ASP in the AS

   This information may be preconfigured in the SG, or may be
   dynamically exchanged via the ASP_Active message.

   An example for a INAP/TCAP message exchange between SEP and ASP is
   given below.

   Address information in CLDT message (e.g. TC_Query) from SGP to ASP,
   with association ID = SG-ASP, Stream ID based on SLS and possibly
   other parameters, e.g. OPC or Network ID:

     -   Routing Context: based on SS7 Network ID and AS membership,
         so that the message can be transported to the correct ASP.
     -   Source address: valid combination of SSN, PC and GT, as
         needed for back routing to the SEP.
     -   Destination address: at least SSN, to select the SCCP/SUA-
         user at the ASP.

   Address information in CLDT message (e.g. TC_Response) from ASP to
   SG, with association ID = ASP-SG, stream ID selected by
   implementation dependent means with regards to in-sequence-delivery:

     -  Routing Context: as received in previous message.
     -  Source address: unique address provided so that when used as
        the SCCP called party address in the SEP, it MUST yield the
        same AS, the SSN might 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 is 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 ASÆs.
   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 ASÆs
   based on GT information.  After this, the same as in 1.3.1.1
   applies.



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1.3.2 Protocol Architecture for Connection-Oriented Transport

   In this architecture, the SCCP and SUA layers interface in the SGP
   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 SGP to ASP or the other way.  The routing of the Connect
   Request message is done in the same way 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, ...)

   This means that in the SG, two local references are allocated, one
   3-byte value used for the SS7 section and one 4 byte value for the
   IP section. Also a resource containing the connection data for both
   sections is allocated, and either of the two local references can be
   used to retrieve this data e.g. for an incoming DT1 or CODT, for
   example.

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

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

          SUAP - SCCP/SUA 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


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   scenario, full SG functionality is not needed.  This architecture is
   considered in the next section.

1.3.3 All IP Architecture

   This architecture can be used to carry a protocol that 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   ********
          *      *--------*      *
          * IPSP *        * IPSP *
          *      *        *      *
          ********        ********

          +------+        +------+
          | SUAP |        | SUAP |
          +------+        +------+
          | SUA  |        | SUA  |
          +------+        +------+
          | SCTP |        | SCTP |
          +------+        +------+
          |  IP  |        |  IP  |
          +------+        +------+
             |                |
             +----------------+

       SUAP - SCCP/SUA 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 Peer-to-Peer Network Architecture

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











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

                    Figure 1: Generalized Architecture

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

1.3.5 Signaling Gateway Network Architecture

   When interworking between SS7 and IP domains is needed, the SGP acts
   as the gateway node between the SS7 network and the IP network.  The
   SGP 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.

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   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.

   An ASP may be connected to multiple SGPs (see figure 2). In such a
   case, a particular SS7 destination may be reachable via more than
   SG, therefore, more than one route. Given that proper SLS selection,
   loadsharing, and SG selection based on point code availability is
   performed at the ASP, it will be necessary for the ASP to maintain
   the status of each distant SGPs to which it communicates on the
   basis of the SG through which it may route.

   Signaling Gateway
    SCTP Associations
   +----------+                                       **************
   | SG1      |                                       *  AS3       *
   | ******** |                                       *  ********  *
   | * SGP11+--------------------------------------------+ ASP1 *  *
   | ******** |                                 /     *  ********  *
   | ******** |                                 |     *  ********  *
   | * SGP12+--------------------------------------------+ ASP2 *  *
   | ******** |                   \           / |     *  ********  *
   +----------+                    \          | |     *      .     *
                                    \         | |     *      .     *
   +----------+                      \        | |     *      .     *
   | SG2      |                       \       | |     *      .     *
   | ******** |                        \      | |     *  ********  *
   | * SGP21+---------------------------------+-+     *  * ASPN *  *
   | ******** |                          \            *  ********  *
   | ******** |                           \           **************
   | * SGP22+---+--+                       \
   | ******** | |  |                        \         **************
   +----------+ |  |                         \        *  AS4       *
                |  |                          \       *  ********  *
                |  +-------------------------------------+ ASP1 *  *
                |                                     *  ********  *
                |                                     *      .     *
                |                                     *      .     *
                |                                     *            *
                |                                     *  ********  *
                +----------------------------------------+ ASPn *  *
                                                      *  ********  *
                                                      **************

                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.


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   Replicated endpoints: the coupling between the SGs and the ASPs when
   the SGs act as replicated endpoints is an implementation issue.

   Replicated relay points: in normal circumstances, the path from SEP
   to ASP will always go via the same SGP 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 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.

     *    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.

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1.4.3 Native Management Functions

   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

   SUA uses the existing ASP management messages for ASP status
   handling. The interworking with SCCP management consists on the
   sending of DUNA, DAVA, DAUD, DRST or SCON messages on receipt of
   SSP, SSA, SST or SSC to the appropriate ASPs. See also chapter
   1.4.5. The primitives below are considered to be sent between the
   SCCP and SUA management functions in the SG to trigger events in the
   IP and SS7 domain.

   Generic   |Specific   |
   Name      |Name       |ANSI/ITU Reference
   ----------+-----------+---------------------------------------------
   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 SGP 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 SS7
          endpoint/peer is unreachable.
     *    Provide an indication to the SCCP-user at an ASP that a SS7
          endpoint/peer is reachable.
     *    Provide congestion indication to SCCP-user at an ASP.
     *    Provide the initiation of an audit of SS7 endpoints at the
          SG.

1.4.6 Relay function

   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, modeled in [ITU-T Q.714]. It may also be based on Hostname
   information, IP address, or pointcode contained in the called party
   address.

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   This allows for greater scalability, reliability and flexibility in
   wide-scale deployments of SUA.  The usage of a relay function is a
   deployment decision.

1.5 Internal Functions Provided in the SUA Layer

   To perform its addressing and relaying capabilities, the SUA makes
   use of a Address Mapping Function (AMF). This function is considered
   part of SUA, but the way it is realized is left implementation /
   deployment dependent (local tables, DNS (ENUM), LDAP, etc.)

   The AMF is invoked when a message is received at the incoming
   interface. The AMF is responsible for resolving the address
   presented in the incoming SCCP/SUA message to SCTP associations to
   destinations within the IP network. The AMF will select the
   appropriate SCTP association based upon routing context / routing
   key information available. The destination might be the end SUA node
   or a SUA relay node. The Routing Keys 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, SCCP subsystem number, or Transaction ID. IP addresses and
   host names can also be used as Routing Key Information.

   It is expected that the routing keys be provisioned via a MIB or
   external process, such as a database.

1.5.1 Address Mapping at the SG

   Normally, one or more ASPs are active in the AS (i.e., currently
   processing traffic) but in certain failure and transition cases it
   is possible that there may not be an active ASP available. The SGP
   will buffer the message destined for this AS for a time t(r) or
   until an ASP becomes available. When no ASP becomes available before
   expiry of t(r), the SGP will flush the buffered messages and
   initiate the appropriate return or refusal procedures.

   If there is no match for an incoming 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 Mapping at the ASP



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   To direct messages to the SS7 network, the ASP MUST perform an
   address mapping to choose the proper SGP for a given message.  This
   is accomplished by observing the Destination Point Code and other
   elements of the outgoing message, SS7 network status, SGP
   availability, and Routing Context configuration tables.

   A Signaling Gateway may be composed of one or more SGPs. 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.

   An ASP SHOULD send responses only to that SGP that it received
   messages from; within the routing context which it is currently
   active and receiving traffic.  The routing context itself is
   effectively used by the ASP to select the SGP.

1.5.3 Address Mapping Function at a Relay Node

   The relay function is invoked when:

     -    Routing is on Global Title
     -    Routing is on Hostname
     -    Routing is on SSN+PC or SSN+IP Address and the address
          presented is not the one of the relay node

   Translation/resolution of the above address information yields one
   of the following:

     -    Route on SSN: SCTP association ID towards the destination
          node, SSN and optionally Routing Context and/or IP address.
     -    Route on GT: SCTP association ID towards next relay node,
          (new) GT and optionally SSN and/or Routing Context.
     -    Routing on Hostname: SCTP association ID towards next relay
          node, (new) Hostname and optionally SSN and/or Routing
          Context.
     -    A local SUA-user (combined relay/end node)

   To prevent looping, a 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 or less). Each time the relay function is
   invoked within an intermediate (relay) node, the hop counter MUST be
   decremented. When the value reaches zero, the return or refusal
   procedures are invoked with reason "Hop counter violation".

1.5.4 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.

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

   Stream selection based on protocol class:

     -    Protocol class 0: SUA SHOULD select an unordered stream.
     -    Protocol class 1: SUA MUST select an ordered stream, based on
          a sequence parameter given by the upper layer over the
          primitive interface.
     -    Protocol classes 2 and 3: SUA will select an ordered stream,
          based on its own source local reference.

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)

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               |          |ANSI-T1.112 Chap 2.2.2.3.2 (Tab 8B/T1.112.1)

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 class, 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                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Message 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:

     1   SUA version 1.0


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3.1.2 Message Classes

   Message Classes

     0         SUA Management (MGMT) Message
     1         Reserved
     2         Signaling Network Management (SNM) 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

   Signaling Network Management (SNM) Messages

     0         Reserved
     1         Destination Unavailable (DUNA)
     2         Destination Available (DAVA)
     3         Destination State Audit (DAUD)
     4         Network Congestion (SCON)
     5         Reserved
     6         Destination Restricted (DRST)
     7 - 127   Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

   Application Server Process State Maintenance (ASPSM) Messages

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

   ASP Traffic Maintenance (ASPTM) Messages


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     0         Reserved
     1         ASP Active (ACTIVE)
     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 and including all padding bytes.

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.








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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Parameter Tag        |       Parameter Length        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \                                                               \
     /                       Parameter Value                         /
     \                                                               \
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameter Tag: 16 bits (unsigned integer)

      Tag field is a 16-bit identifier of the type of parameter. It
      takes a value of 0 to 65535.

   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. However, composite parameters will contain all
     padding bytes, since all parameters contained within this
     composite parameter will be considered multiples of 4 bytes.

   Parameter Value: variable-length.

         The Parameter Value field contains the actual information to
         be trasnfered 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 Routing Context).
     -    Mandatory parameters preferably SHOULD precede any optional
          parameters.
     -    The data parameter will normally be the final one in the
          message.

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     -    The receiver SHOULD accept parameters in any order, except
          where explicitly mandated.

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

   Parameters
     Routing Context               Mandatory
     Flags                         Mandatory
     Source Address                Mandatory
     Destination Address           Mandatory
     Data                          Mandatory



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   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 = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0101          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           SCCP Cause                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0102          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                        Source Address                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Flags                         Mandatory
     SCCP Cause                    Mandatory
     Source Address                Mandatory
     Destination Address           Mandatory
     Data                          Optional



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   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 = 0x0006         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0107          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   NOTE *1:   This parameter is not present in case of Expedited Data
              (ED).

   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.



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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 = 0x0006         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |              Length           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0108          |              Length           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Receive Sequence Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x010A          |              Length           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Credit                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     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.















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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 = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         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                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Flags                         Mandatory
     Source Reference Number       Mandatory
     Destination Address           Mandatory
     Source Address                Optional
     Credit                        Mandatory, protocol class 3 only
     Data                          Optional

   Implementation note: This message covers the following SCCP message:
   Connection Request (CR).

3.3.4 Connection Acknowledge (COAK)



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   This message is used to acknowledge a connection request from 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 = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         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
     Routing Context               Mandatory
     Flags                         Mandatory
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory
     Credit                        Mandatory *2
     Destination Address           Optional *1
     Data                          Optional

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


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   NOTE *2:    Only applicable 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 = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           SCCP Cause                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0003          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             Data                              /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context                    Mandatory
     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.

   Implementation note: This message covers the following SCCP message:
   Connection REFused (CREF).


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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 = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         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
     Routing Context               Mandatory
     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 ReLeaSeD (RLSD).

3.3.7 Release Complete (RELCO)




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

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Source Reference Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     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)
   to the peer endpoint.


















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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 = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Source Reference Number                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           SCCP Cause                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   Implementation note: This message covers the following SCCP message:
   ReSet Request (RSR).

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 = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0104          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Source Reference Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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   Parameters
     Routing Context               Mandatory
     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 = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0105          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0106          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          SCCP Cause                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Destination Reference Number  Mandatory
     SCCP Cause                    Mandatory

   Implementation note: This message covers the following SCCP message:
   Protocol Data Unit ERRor (ERR).

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.










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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 = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         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
     Routing Context               Mandatory
     Flags                         Mandatory
     Source Reference Number       Mandatory
     Destination Reference number  Mandatory
     Sequence number               Mandatory *1
     Credit                        Mandatory *1

   NOTE *1:   Information in these parameter fields reflects 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 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- or N-state
   indication passed between SCCP and local SCCP-user. The DUNA message
   is sent from the SGP or relay node to all concerned ASPs (servicing
   SCCP-users considered local to the SGP or relay node, see chapter
   1.3.1.1), when a destination or SCCP-user has become unreachable.
   The SUA-User at the ASP is expected to stop traffic to the affected
   destination or SCCP-user through the SGP or relay node initiating
   the DUNA.

   The format for DUNA Message parameters is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Destination Address                     /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /

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

   Parameters
     Routing Context               Optional
     Destination Address           Mandatory *1
     Info String                   Optional

   Note 1:    The destination address refers to the node that has
              become unavailable.  When the SSN is included in the
              Destination Address parameter, the DUNA/DAVA/DRST/SCON
              message corresponds to the SCCP N-STATE primitive. When
              SSN is not included in the Destination Address parameter,
              the DUNA/DAVA/DRST/SCON message corresponds to the
              SCCP N-PCSTATE primitive.

3.4.2 Destination Available (DAVA)

   In the scope of SUA, this message is covered by the PC- and N-state
   indication passed between SCCP and local SCCP-user. The DAVA message
   is sent from the SGP or relay node to all concerned ASPs (servicing
   SCCP-users considered local to the SGP or relay node, see chapter
   1.3.1.1) to indicate that a destination (PC or SCCP-user) is now
   reachable. The ASP SUA-User protocol is expected to resume traffic

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   to the affected destination through the SGP or relay node 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 = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0103          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /

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

   Parameters
     Routing Context               Optional
     Destination Address           Mandatory *1
     Info String                   Optional

   Note 1:    The destination address refers to the node that has
              become unavailable.  When the SSN is included in the
              Destination Address parameter, the DUNA/DAVA/DRST/SCON
              message corresponds to the SCCP N-STATE primitive. When
              SSN is not included in the Destination Address parameter,
              the DUNA/DAVA/DRST/SCON message corresponds to the
              SCCP N-PCSTATE primitive.

3.4.3 Destination State Audit (DAUD)

   The DAUD message can be sent from the ASP to the SGP (or relay node)
   to query the availability state of the 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 SGP (or relay node).










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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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /

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

   Parameters
     Routing Context               Optional
     Destination Address           Mandatory *1
     Info String                   Optional

   Note 1:    The destination address refers to the node that has
              become unavailable.  When the SSN is included in the
              Destination Address parameter, the DUNA/DAVA/DRST/SCON
              message corresponds to the SCCP N-STATE primitive. When
              SSN is not included in the Destination Address parameter,
              the DUNA/DAVA/DRST/SCON message corresponds to the
              SCCP N-PCSTATE primitive.

3.4.4 Network Congestion (SCON)

   The SCON message can be sent from the SGP or relay node 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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                     Destination Address                       /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x000F          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Congestion Level                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Optional
     Congestion Level              Mandatory
     Destination Address           Mandatory *1
     Info String                   Optional

   Note 1:    The destination address refers to the node that has
              become unavailable.  When the SSN is included in the
              Destination Address parameter, the DUNA/DAVA/DRST/SCON
              message corresponds to the SCCP N-STATE primitive. When
              SSN is not included in the Destination Address parameter,
              the DUNA/DAVA/DRST/SCON message corresponds to the
              SCCP N-PCSTATE primitive.

3.4.5 Destination Restricted (DRST)

   The DRST message is optionally sent from the SGP to all concerned
   ASPs to indicate that the SGP has determined that one or more
   destinations are now restricted from the point of view of the SGP,
   or in response to a DAUD message if appropriate. The SUA layer at
   the ASP is expected to send traffic to the affected destination via
   an alternate SGP of equal priority, but only if such an alternate
   route exists and is available. If the affected destination is
   currently considered unavailable by the ASP, the MTP3-User should be
   informed that traffic to the affected destination can be resumed.
   In this case, the SUA layer should route the traffic through the SGP
   initiating the DRST message.

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   This message is optional for the SGP to send and it is optional for
   the ASP to act on any information received in the 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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0006         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Destination Address                     /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0004          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Optional
     Destination Address           Mandatory *1
     Info String                   Optional

   Note 1:    The destination address refers to the node that has
              become unavailable.  When the SSN is included in the
              Destination Address parameter, the DUNA/DAVA/DRST/SCON
              message corresponds to the SCCP N-STATE primitive. When
              SSN is not included in the Destination Address parameter,
              the DUNA/DAVA/DRST/SCON message corresponds to the
              SCCP N-PCSTATE primitive.

3.5 Application Server Process State 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.










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       0                     1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x000E       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        ASP Identifier                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0109       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        ASP Capabilities                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0004       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /

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

   Parameters
     ASP Identifier                Optional *1
     ASP Capabilities              Optional
     Info String                   Optional

   Note 1:  ASP Identifier MUST be used where the IPSP/SGP cannot
            identify the ASP by pre-configured address/port number
            information (e.g., where an ASP is resident on a Host using
            dynamic address/port number assignment).

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 = 0x000E       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        ASP Identifier                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0109       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        ASP Capabilities                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x0004       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /

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

   Parameters

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     ASP Identifier                Optional *1
     ASP Capabilities              Optional
     Info String                   Optional

   Note 1:  ASP Identifier MUST be used where the IPSP/SGP cannot
            identify the ASP by pre-configured address/port number
            information (e.g., where an ASP is resident on a Host using
            dynamic address/port number assignment).

3.5.3 ASP Down (DOWN)

   The ASP Down (DOWN) 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 = 0x0004       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /

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

   Parameters
     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 = 0x0004       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /

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

   Parameters
     Info String                   Optional

   Note: ASP DOWN ACK will always be sent to acknowledge an ASP DOWN.

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:

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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 = 0x0009       |            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 = 0x0009       |            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 value of the Traffic Mode Type and Routing Context parameters is
   the same as for the ASP-Active message.

   The value 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:











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

   Parameters
     Routing Context     Optional
     INFO String         Optional

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

3.7 SUA 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



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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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x000D         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Status                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Tag = 0x000E       |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        ASP Identifier                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0006         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Routing Context                         /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0004         |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /

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

   The NTFY message contains the following parameters:

   Parameters
     Status                        Mandatory
     ASP Identifier                Optional *1
     Routing Context               Optional
     Info String                   Optional

   Note 1:  ASP Identifier MUST be used where the IPSP/SGP cannot
            identify the ASP by pre-configured address/port number
            information (e.g., where an ASP is resident on a Host using
            dynamic address/port number assignment).

3.8 Common Parameters

   These TLV parameters are common across the different adaptation
   layers.

   Parameter Name                     Parameter ID
   ==============                     ============
   Reserved                             0x0000
   Not used in SUA                      0x0001
   Not used in SUA                      0x0002
   Data                                 0x0003

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   Info String                          0x0004
   Affected Point Code                  0x0005
   Routing Context                      0x0006
   Diagnostic Info                      0x0007
   Not used in SUA                      0x0008
   Heartbeat Data                       0x0009
   Reason                               0x000A
   Traffic Mode Type                    0x000B
   Error Code                           0x000C
   Status                               0x000D
   ASP Identifier                       0x000E
   Congestion Level                     0x000F

3.8.1 Not Used

   Use of Parameter ID 0x0001 in SUA messages is not supported.

3.8.2 Not used

   Use of Parameter ID 0x0002 in SUA messages is not supported.

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 service providers may use the INFO String
   for debugging purposes.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0004         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                          Info String                          /

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

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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
   14-, 16- and 24-bit binary formatted SS7 Point Codes.  Affected
   Point codes that are less than 24-bits, are padded on the left to
   the 24-bit boundary.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0005         |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Mask       |                 Affected PC 1                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                             . . .                             /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   ANSI 24-bit Point Code:

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

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

   ITU 14-bit Point Code:

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

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

   It is optional to send an Affected Point 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 Routing Context.
   Including multiple Affected PCs may be useful when reception of a
   management message or a linkset event simultaneously affects the
   availability status of a list of destinations at an SG.

   Mask: 8-bits


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   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 are 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.

   For use in SUA, the mask parameter MUST always be coded zero and
   there MUST be only a single point code present.

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 a one-to-one
   relationship between an index entry and a Routing Key or AS Name.

   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.

   Additionally, the Routing Context parameter identifies the SS7
   network context for the message, for the purposes of logically
   separating the signaling traffic between the SGP and the Application
   Server Process over a common SCTP Association, when needed.  An
   example is where an SGP is logically partitioned to appear as an
   element in several different national SS7 networks.  It implicitly
   defines the SS7 Point Code format used, the SS7 Network Indicator
   value and SCCP protocol type/variant/version used within a separate
   SS7 network. It also defines the network context for the PC and SSN

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   values. Where an SGP operates in the context of a single SS7
   network, or individual SCTP associations are dedicated to each SS7
   network context, this functionality is not needed.

   Where the optional Routing Context parameter is present, it SHOULD
   be the first parameter in the message as it defines the format
   and/or interpretation of the parameters containing a PC or SSN
   value.

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 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 Not Used

   Parameter ID 0x0008 is not used in SUA.

3.8.9 Heartbeat Data

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

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

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0009          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Heartbeat Data                          /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   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.).

3.8.10 Reason

   The Reason parameter indicates the reason why the remote SUA
   adaptation layer is unavailable.

       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 = 8         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Reason                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Reason: 32-bit (unsigned integer)

   The valid values for Reason are shown in the following table.

          0         Unspecified
          1         User Unavailable
          2         Management Blocking
          3         ASP Fault

3.8.11 Traffic Mode Type

   The Traffic Mode Type parameter identifies the traffic mode of
   operation of the ASP within an AS.

       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 = 8        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Traffic Mode Type                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The valid values for Type are shown in the following table.

               1         Over-ride
               2         Load-share
               3         Over-ride (Standby)
               4         Loadshare (Standby)

   Within a Routing Context, Over-ride and Loadshare Types cannot be
   mixed.  The Over-ride value indicates that the ASP is operating in
   Over-ride mode, and the ASP wishes to take over all traffic for an
   Application Server (i.e., primary/back-up operation), over-riding
   any currently active ASP in the AS.  In Load-share mode, the ASP

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   wishes to share in the traffic distribution with any other currently
   active ASPs.  The Standby versions of the Over-ride and Loadshare
   Types indicate that the ASP is declaring itself ready to accept
   traffic but leaves it up to the sender as to when the traffic is
   started. Over-ride (Standby) indicates that the traffic sender
   continues to use the currently active ASP until it can no longer
   send/receive traffic (i.e., the currently active ASP transitions to
   Down or Inactive).  At this point the sender may immediately move
   the ASP to Active and commence traffic.  Loadshare (Standby) is
   similar - the sender continues to loadshare to the current ASPs
   until it is determined that there is insufficient resources in the
   Loadshare group.  When there are insufficient ASPs, the sender may
   immediately move the ASP to Active.

3.8.12 Error 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Tag =0x000C            |             Length = 8        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Error Code                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Error Code parameter indicates the reason for the Error Message.
   The Error parameter value can be one of the following values:

        Invalid Version                                0x01
        n/a                                            0x02
        Unexpected Message Class                       0x03
        Invalid Message Type                           0x04
        Unsupported Traffic Handling Mode              0x05
        Unexpected Message                             0x06
        Protocol Error                                 0x07
        Invalid Routing Context                        0x08
        Invalid Stream Identifier                      0x09
        Parameter Field Error                          0x0B
        Unexpected Parameter                           0x0C
        Duplicated Parameter                           0x0D
        Error - ASP Identifier Required                0x0E
        Error - Invalid ASP Identifier                 0x0F
        Refused - ASP Identifier Required              0x10

   The "Invalid Version" error would be sent if a message was received
   with an invalid or unsupported version.  The Error message would
   contain the supported version in the Common header.  The Error
   message could optionally provide the supported version in the
   Diagnostic Information area.

   The "Invalid Routing Context" error would be sent by a SG if an ASP
   sends a message with an invalid (unconfigured) Routing Context

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   value.  The Error message could optionally provide the invalid
   Routing Context in the Diagnostic Information area.

   The "Unexpected Message Class" error would be sent if a message with
   an unsupported Message Class were received.

   The "Unexpected Message Type" error would be sent if a message with
   an unsupported Message Type were received.

   The "Unsupported Traffic Handling Mode" error would be sent by a SGP
   if an ASP sends an ASP Active with an unsupported Traffic Handling
   Mode.  An example would be a case in which the SGP did not support
   load sharing.

   The "Unexpected Message" error would be sent by an ASP if it
   received a message that is unexpected in the ASP's current state.

   The "Protocol Error" error would be sent for any protocol anomaly
   (i.e. a bogus message).

   The "Invalid Routing Context" error would be sent by a SGP if the
   routing context cannot be supported, e.g. not unique.

   The "Invalid Stream Identifier" error would be sent if a message was
   received on an unexpected SCTP stream.

   The "Parameter Field Error" would be sent if a message with a
   parameter having a wrong length field.

   The "Unexpected Parameter" error would be sent if a message contains
   an invalid parameter.

   The "Duplicated Parameter" error would be sent if a message contains
   a parameter more than once.

   To be sent in response to an ASPUP message which does not contain an
   ASP Id parameter when the SGP requires one.  Then, instead of simply
   adding 8 bytes to ever ASPUP message as proposed, the ASP can go
   around again a second time with an ASP ID.

3.8.13 Status

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

       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 = 0x000D         |             Length = 8        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Status Type           |            Status ID          |

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

   The valid values for Status Type (16 bit unsigned integer) are:

          1     Application Server state change (AS_State_Change)
          2     Other

   The Status ID parameter contains more detailed information for the
   notification, based on the value of the Status Type.

   If the Status Type is AS_STATE_CHANGE, then the Status ID (16 bit
   unsigned integer) values are:

          1    reserved
          2    Application Server Inactive (AS-Inactive)
          3    Application Server Active (AS-Active)
          4    Application Server Pending (AS-Pending)


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

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

          1    Insufficient ASP resources active in AS
          2    Alternate ASP Active

   These notifications are not based on the SGP reporting the state
   change of an ASP or AS.  In the Insufficient ASP Resources case, the
   SGP is indicating to an "Inactive" ASP(s) in the AS that another ASP
   is required to handle the load of the AS (Load-sharing mode).  For
   the Alternate ASP Active case, an ASP is informed when an alternate
   ASP transitions to the ASP-Active state in Over-ride mode.

3.8.14 ASP Identifier















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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x000E          |             Length = 8        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        ASP Identifier                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ASP Identifier field: 32-bits (unsigned integer)

   The ASP Identifier field contains a unique value that is locally
   significant amoung the ASPs that support an AS.  The SGP should save
   the ASP Identifier to be used, if necessary, with the Notify message
   (see Section 3.7.2).

3.8.15 Congestion Level

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x000E          |             Length = 8        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Congestion Level                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Congestion Level field: 8-bits (unsigned integer)

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

3.9 SUA-Specific parameters

   These TLV parameters are specific to the SUA protocol.

   Parameter Name                     Parameter ID
   ==============                     ============
   Flags                                0x0101
   Source Address                       0x0102
   Destination Address                  0x0103
   Source Reference Number              0x0104
   Destination Reference Number         0x0105
   SCCP Cause                           0x0106
   Sequence Number                      0x0107
   Receive Sequence Number              0x0108
   ASP Capabilities                     0x0109
   Credit                               0x010A
   Reserved                             0x010B
   SMI / Subsystem                      0x010C



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   Destination/Source Address Sub-Parameters
   ===========================================
   Global Title                         0x8001
   Point Code                           0x8002
   Subsystem Number                     0x8003
   IPv4 Address                         0x8004
   Hostname                             0x8005
   IPv6 Addresses                       0x8006

3.9.1 Flags

   The Flags parameter is a conglomerate of following parameters,
   described in ITU-T Recommendation Q.713:

      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 = 8        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Seq. Control  |  Importance   |  Hop Counter  |  Protocol Cl. |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Sequence Control (1.1.2/Q.714)

         Bits 1-5 are coded with the value of the sequence control
         parameter associated with a group of messages and are chosen
         so as to ensure proper loadsharing of message groups over SLS
         values while ensuring that sequence control values within
         message groups have the sequence control value coded with the
         same value as the initial message of the message group.

         Bits 6-8 are spare bits and should be coded zero.

   Protocol class (3.6/Q.713)

          Bits 1-2 indicate the protocol class.

          Value     Description
            0       Class 0 (connectionless service)
            1       Class 1 (connectionless service)
            2       Class 2 (connection-oriented service)
            3       Class 3 (connection-oriented service)

          Bit 8 indicates the use of the return on error procedure.

          Value     Description
           0x0      No special options
           0x1      Return message on error

          Bits 3-7 are spare and should be coded zero.

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   Hop Counter (3.18/Q.713)

         The value of the hop counter is decremented with each global
         title translation, and should be in the range 15 to 1.

   Importance (3.19/Q.713)

         Bits 1-3 are coded to indicate the importance of the messages.
         The values are between 0 and 7, where the value of 0 indicates
         the least important and 7 indicates the most important.

         Bits 4-8 are spare bits and should be coded zero.

3.9.2 Source Address

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0102         |      Parameter Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Routing Indicator        |       Address Indicator       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                       Address parameter(s)                    /
      \                                                               \
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Source Address field may contain the SCCP Calling Party Address.
   See chapters 3.4 and 3.5 of ITU-T Recommendation Q.713.

   The following combinations of address parameters are valid :

     -    Global Title (e.g. E.164 number) + optional PC and/or SSN,
          SSN may be zero, when routing is done on Global Title
     -    SSN (non-zero) + optional PC and/or Global Title, when
          routing is done on PC + SSN. The PC is mandatory in the
          source address when sending from SGP to ASP, and in the
          destination address when sending from ASP to SGP to reach the
          SS7 SEP.
     -    Hostname + optional SSN, when routing is done by Hostname
     -    SSN (non-zero) and optional IP address (IPv4 or IPv6) when
          routing is done on IP address + SSN

3.9.2.1 Routing Indicator

   The following values are valid for the routing indicator :

     Reserved                      0
     Route on Global Title         1
     Route on SSN + PC             2

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     Route on Hostname             3
     Route on SSN + IP Address     4

   The routing indicator determines which address parameters need to be
   present in the address parameters field.

3.9.2.2 Address Indicator

   This parameter is needed for interworking with SS7 networks. The
   address indicator specifies what address parameters are actually
   received in the SCCP address from the SS7 network, or are to be
   populated in the SCCP address when the message is sent into the SS7
   network. The value of the routing indicator needs to be taken into
   account.

   The address indicator is coded as follows:

    Bit 1 is used to indicate inclusion of the SSN

    0         Do not include SSN when optional
     1         Include SSN

     Bit 2 is used to indicate inclusion of the PC

    0         Do not include PC, regardless of the routing indicator
              value
     1        Include PC

    Bit 3 is used to indicate inclusion of the Global Title

    0         Do not include GT when optional (routing indicator /= 1)
     1        Include GT

   Bits 4-8 are spare and should be coded zero.

3.9.2.3 Global Title

     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 = 0x8001          |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   No. Digits  | Trans. type   |    Num. Plan  | Nature of Add |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Global Title Digits                   |
     /                                                               /
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Number of Digits:

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   This is the number of digits contained in the Global Title.

   Translation type:

     0              Unknown
     1 - 63         International services
     64 - 127       Spare
     128 û 254      National network specific
     255            Reserved

   Numbering Plan:

     0         unknown
     1         ISDN/telephony numbering plan (Recommendations E.163 and
               E.164)
     2         generic numbering plan
     3         data numbering plan (Recommendation X.121)
     4         telex numbering plan (Recommendation F.69)
     5         maritime mobile numbering plan (Recommendations E.210,
               E.211)
     6         land mobile numbering plan (Recommendation E.212)
     7         ISDN/mobile numbering plan (Recommendation E.214)
     8 - 13    spare
     14        private network or network-specific numbering plan
     15 - 126  spare
     127       reserved.

   Nature of Address:

     0         unknown
     1         subscriber number
     2         reserved for national use
     3         national significant number
     4         international number
     5 - 255   Spare

   Global Title:

    Octets contain a number of address signals and possibly filler as
    shown:











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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |2 addr.|1 addr.|4 addr.|3 addr.|6 addr.|5 addr.|8 addr.|7 addr.|
     |  sig. | sig.  |  sig. | sig.  |  sig. | sig.  |  sig. | sig.  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        .............          |filler |N addr.|   filler      |
     |                               |if req | sig.  |               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All filler bits MUST be set to 0.

   Address signals to be coded as defined in ITU-T Q.713 Section
   3.4.2.3.1.

   The actual Global Title format to be used for interworking with the
   SS7 network is defined by the network ID, or is implicitly
   understood if the SGP only operates in one SS7 network partition.
   The formats are defined in chapter 3.4.2.3 of Q.713. The following
   conversions of the Translation Type, Numbering Plan and Nature of
   Address elements apply:

   1) SS7 network uses GTI = 0001

   Nature of Address is ignored. It is implicitly assumed that
   Translation Type = Unknown and Numbering Plan = E.164 (value 1).

   2) SS7 network uses GTI = 0010

   This is most commonly used in North American networks. The
   Translation Type implicitly determines Nature of Address and
   Numbering Plan. This data can be configured in the SG. The number of
   digits is always even and determined by the SCCP address length.

   3) SS7 network uses GTI = 0011

   Numbering Plan and Translation Type are taken over. It is implicitly
   assumed that the Nature of Address = Unknown.

   4) SS7 network uses GTI = 0100

   This format is used in international networks and most commonly in
   networks outside North America. All information to populate the
   source address is present in the SCCP Address.








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3.9.2.4 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Tag = 0x8002          |            Length = 8         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Point Code                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   See chapter 3.2.5 Affected Point Code for the layout of the Point
   Code field.

3.9.2.5 Subsystem Number

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Tag = 0x8003          |            Length = 8         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            spare       | SSN value     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The internationally standardized SSN values are described in chapter
   3.4.2.2 of Q.713.

3.9.2.6 IP Addresses

   The IP address formats can use different tags. It should be noted
   that if the source address is in a certain IP version, the
   destination address should also be in the same IP version.

     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 = 0x8004/0x8006      |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        IPv4 or IPv6 Address                   |
     /                                                               /
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Note: The tag value 0x8004 is for an IPv4 address and 0x8006 is for
   IPv6.







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3.9.2.7 Hostname

     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 = 0x8005          |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Host Name                          |
     /                                                               /
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   If the type of address is Host Name, then the labels in the host
   name have to be reversed to obtain an efficient Host Name encoding
   form for the Global title translation function.

   hostname: zzzz.yyy....edc.ab
   should be transformed to
   HTname : ab.edc....yyy.zzzz

   The labels of the Host Name are then encoded using the encoding
   rules of the labels described in [IDNS]. The end of the Host name is
   indicated by 0x00.

   Example:
   hostname = www.reindael.security.org
   First the name has to be reverse to have the gTLD on the left side.
   Global Title name: org.security.reindael.www

   Then the result of applying the rules of the iDNS is:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    x |       3       |       O       |       R       |       G       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +4 |       8       |       S       |       E       |       C       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +8 |       U       |       R       |       I       |       T       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +12|       Y       |       8       |       R       |       E       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +16|       I       |       N       |       D       |       A       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +20|       E       |       L       |       3       |       W       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +24|       W       |       W       |       00      |               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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3.9.3 Destination Address

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Tag = 0x0103         |      Parameter Length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Routing Indicator        |       Address Indicator       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     /                       address parameter(s)                    /
     \                                                               \
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of this parameter is identical to the Source Address
   parameter.

3.9.4 Source Reference Number

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0104         |             Length = 8        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Source Reference Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The source reference number is a 4 octet long integer. This is
   allocated by the source SUA instance.

3.9.5 Destination Reference Number

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0105         |             Length = 8        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Reference Number                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The destination reference number is a 4 octet long integer. This is
   allocated by the destination SUA instance.

3.9.6 SCCP Cause









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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 = 0x0106          |             Length = 8        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Spare               |   Cause Type  |  Cause Value  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This parameter bundles the SCCP parameters Release cause, Return
   cause, Reset cause, Error cause and Refusal cause.

   Cause Type can have the following values:

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

   Cause Value contains the specific cause value.  Below gives examples
   for ITU SCCP values.  ANSI references can be found in ANSI T1.112.3

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

3.9.7 Sequence Number

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0107         |             Length = 8        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Spare               |  Rec Seq Num|M| Sent Seq Num  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This parameter is used to indicate whether ômoreö data will follow
   in subsequent CODT messages, and/or to number each CODT message
   sequentially for the purpose of flow control. It contains the
   received as well as the sent sequence number, P(R) and P(S) in
   Q.713, chapters 3.7 and 3.9.

   As such it can also be used to acknowledge the receipt of data
   transfers from the peer in case of protocol class 3.

   Sent Sequence Number is one octet and is coded as follows:

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          Bits 2-8 are used to indicate the Send Sequence Number P(S).
          Bit 1 (LSB) of octet 1 is spare.

   Received Sequence Number is one octet, and is coded as follows:

          Bits 2-8 are used to indicate the Received Sequence Number
          P(R).
          Bit 1 (LSB) is used for the more data indication, as follows:

          0         no more data
          1         more data

3.9.8 Receive Sequence Number

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0108         |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    spare                      |  Rec Seq Num  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This parameter is used exclusively for protocol class 3 in the data
   acknowledgment message to indicate the lower edge of the receiving
   window. See Q.713, chapter 3.8.

   It is a 1 octet long integer coded as follows:

      Bits 8-2 are used to indicate the Receive Sequence Number P(R).

      Bit 1 is spare.

3.9.9 ASP Capabilities

   This parameter is used so that the ASP can report its capabilities
   regarding SUA for supporting different protocol classes and
   interworking scenarios.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x0109         |             Length = 8        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            spare              |0 0 0 0|a|b|c|d| Interworking  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Flags

     a - Protocol Class 3
     b - Protocol Class 2

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     c - Protocol Class 1
     d - Protocol Class 0

     It is mandatory to support at least Protocol Class 0.

   Interworking

     Values

     0x0 indicates no interworking with SS7 Networks.
     0x1 indicates IP Signaling Endpoint (ASP), interworking with SS7
         networks.
     0x2 indicates Signaling Gateway.
     0x3 indicates relay node support.

3.9.10 Credit

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Tag = 0x010A         |             Length = 8        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Credit                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The length of the credit field is is one octet.  See ITU-T Q.713
   Chapter 3.10. The parameter is used for protocol class 3
   exclusively.

3.9.11 SMI / Subsystem

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x010C       |             Length = 8        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             SMI               |     Spare     |      SSN      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Subsystem Number (SSN) is one octet.

   Subsystem Multiplicity Indicator (SMI) can have the following
   values:

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

4 Procedures


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

4.1 SCCP û SUA Interworking at the SG

   On the SG, the SCCP routing or interworking function determines that
   the message is sent to an AS via the SUA stack, based on information
   in the incoming message. The SUA Address Mapping Function identifies
   the appropriate Application Server (AS) and selects an active ASP
   from the list of ASPs servicing this AS. The appropriate ASP can be
   determined based on the routing information in the incoming message,
   local load sharing information, etc. The appropriate SUA message is
   then constructed and sent to the appropriate endpoint, via the
   correct SCTP association and stream.

   The SGP MUST take care of any segmentation / reassembly issues at
   the border of the SS7 and IP networks.  The IPSP may not have any
   knowledge about the requirements regarding the maximum supported
   message length of the SS7 network to which it is sending. However,
   since there is in principle no limit to the use of the more
   indicator in SS7 networks, there is still need for connection-
   oriented segmentation / reassembly procedures in the IPSP as well.

   If a SGP is operated in mated pair configuration, and it receives a
   non-first XUDT segment for which no reassembly process exists, it
   should pass on this segment to it's mate; if the segment was already
   received from the mated SGP or if no mated SGP is available, the
   return on error procedures is invoked.

4.1.1 Connection Oriented Procedures

   On receipt of a CR message from the SS7 network, a first connection
   section is established between the SGP and SS7 originating node. A
   second connection section is to be setup between the SGP and the
   appropriate ASP, determined by the SUA outgoing mapping function.

   Local resources and source local reference numbers are allocated to
   keep/retrieve the required address information and the connection
   state to format and route subsequent messages for the connection
   based on reference numbers only. The existing SCCP procedures MAY be
   deployed at the SGP to perform this coupling.

   The same applies for a CORE message received from the IP network,
   destined for an SS7 node. After allocating the necessary resources,
   the SUA incoming mapping function formats the appropriate SCCP
   message and passes it on to SCCP routing for further processing
   (sending into the SS7 network).



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   The SGP MUST take care of any segmentation / reassembly issues at
   the border of the SS7 and IP networks.  The IPSP may not have any
   knowledge about the requirements regarding the maximum supported
   message length of the SS7 network to which it is sending. However,
   since there is in principle no limit to the use of the more
   indicator in SS7 networks, there is still need for connection-
   oriented segmentation / reassembly procedures in the IPSP as well.

4.1.2 Connectionless Procedures

   The existing SCCP routing functions may be enhanced to support
   interworking with the SUA layer. The function of SUA can be limited
   to outgoing mapping (formatting of the CLDT or CLDR message) and
   selection of the correct SCTP association (ASP) and stream. For the
   direction ASP to SG, the SUA incoming mapping formats the
   appropriate SCCP message (UDT(S), XUDT(S) or LUDT(S)) and passes it
   on to SCCP routing for further processing.

4.1.3 SS7 Signaling Network Management Procedures

   When an SCCP Subsystem Management (SCMG) message is received from
   the SS7 network, the SGP needs to determine whether there are
   concerned Application Servers interested in subsystem status
   changes. The SUA management function is informed with the N-State
   indication primitive upon which it formats and transfers the
   applicable SNM message to the list of concerned ASPs using stream ID
   "0".

   When MTP-3 Management indications are received (MTP-PAUSE, MTP-
   RESUME, MTP-STATUS), SCCP Subsystem Management determines whether
   there are concerned local SCCP-users. When these local SCCP-users
   are in fact Application Servers, serviced by ASPs, SUA management is
   informed with the PC-State indication primitive upon which it
   formats and transfers the applicable SNM message (DUNA, DAVA, DRST
   or SCON) to the list of concerned ASPs using stream ID "0".

   If an ASP receives a DUNA, DRST or SCON from a SGP, the SUA layer at
   the ASP is expected to send traffic to the affected destination via
   an alternate SGP of equal priority, but only if such an alternate
   route exists and is available. The local ASP SHOULD maintain the
   status of the possible routes to the peer endpoint in the SS7
   network.  By maintaining the status of the possible routes, the ASP
   can determine if the remote peer is unavailable.

   When the DAUD message is received at the SGP from an ASP, the SGP
   checks the status of the specified SS7 destination and returns DAVA,
   DUNA, DRST or SCON depending on the result of the check. The SGP
   initiates SST (Subsystem Status Test) procedures by following the
   SCCP procedures described in Q.714; the receipt of a DAUD message
   does not trigger these.


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   SCCP Subsystem Management procedures may also be triggered in case
   of AS state changes, see chapter 4.4.1.2.

4.2 Primitives received from the local SUA-user

   These support the SUA transport of SCCP-User/SCCP boundary
   primitives. The same services as supported by SCCP (connectionless
   and connection-oriented) are to be provided by SUA. The SCCP-users
   at the SGP should be able to use the same primitive interface to
   SCCP/SUA without any changes. The SCCP-SUA interworking function
   takes care of selecting the appropriate stack.

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

   The address information passed by the SUA-user at an ASP MUST
   contain either:

     -    A valid SS7 address to reach a destination in the SS7 network
          via the appropriate SCTP association to a SG.
     -    A valid IP address/hostname to reach another ASP in the IP
          network via the appropriate SCTP association.

4.3 Layer Management Procedures

   On receiving primitives from the local Layer Management, the SUA
   layer will take the requested action and provide a response to Layer
   Management.

   An M-SCTP-ESTABLISH request from Layer Management will initiate the
   establishment of an SCTP association. An M-SCTP-ESTABLISH confirm
   will be sent to Layer Management when the initiated association set-
   up is complete. An M-SCTP-ESTABLISH indication is sent upon
   successful completion of an incoming SCTP association set-up from a
   peer SUA node.

   An M-SCTP-RELEASE request from Layer Management initiates the
   teardown of an SCTP association. An M-SCTP-RELEASE confirm is sent
   to Layer Management when the association teardown is complete. An M-
   SCTP-RELEASE indication is sent to Layer Management upon successful
   teardown of an SCTP association initiated by a peer SUA.

   An M-SCTP-STATUS request supports a Layer Management query of the
   local status of a particular SCTP association. The SUA responds with
   the association status in an M-SCTP-STATUS confirm. No peer SUA
   protocol is invoked.

   An M-ASP-STATUS request supports a Layer Management query of the
   status of a particular local or remote ASP. The SUA responds with an
   M-ASP-STATUS confirm. No peer SUA protocol is invoked.

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   An M-AS-STATUS request supports a Layer Management query of the
   status of a particular AS. The SUA responds with an M-AS-STATUS
   confirm. No peer SUA protocol is invoked.

   M-ASP-UP, -DOWN, -ACTIVE and ûINACTIVE request primitives allow
   Layer Management at an IPSP to force state changes. Upon successful
   completion, a corresponding confirm primitive is issued by SUA to
   the Layer Management. If the invocation is unsuccessful, an Error
   indication is provided.

   SUA Management informs layer Management about AS/ASP state changes
   with the corresponding indications. It is also informed of received
   NTFY or ERR messages, see chapter 4.4.3.

4.4 SUA Management Procedures

   This functionality comprises the handling of AS/ASP state and
   traffic management messages, SUA peer management messages, SCTP
   notifications and the interface with local Layer Management.
   These procedures support the SUA management of SCTP Associations and
   ASP paths between SGs and ASPs.

4.4.1 AS and ASP State and Traffic Management

   The SUA layer on each IPSP (e.g. SG) needs to maintain the state of
   each connected IPSP (e.g. ASP), as a way to manage the traffic to
   these IPSPs and the (logical) ASs they service.  In particular at a
   SG, the state of each connected ASP is needed as input to the SGs
   routing function.

4.4.1.1 ASP States

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

     -    ASP Management messages (ASP-Up, ASP-Down, ASP-Active, ASP-
          Inactive).
     -    SCTP Communication Down Notification (SCTP CDI).

   The state of the ASP within each AS is important in particular for
   the routing function at the SG, to direct traffic for a specific
   routing key (AS) to the appropriate ASP.

   At an ASP, if it is connected to a set of redundant SGs, this set
   can also be seen as an AS handling all traffic destined for the SS7
   network.

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

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

   ASP-UP: The Application Server Process is available but application
   traffic is not possible. The ASP can only handle management
   messages.

   ASP-ACTIVE: The Application Server Process is available and
   application traffic is possible. Whether traffic will be directed to
   this ASP depends on the Traffic Mode Type (over-ride, loadshare with
   or without Standby option).
                                   +-------------+
                                   | ASP-ACTIVE  |
            +----------------------|     or      |
            |               +------| ASP-STANDBY*|
            |         AS    |      +-------------+
            |      Override |          ^     |
            |               |   ASP    |     | ASP
            |               |   Active |     | Inactive
            |               |          |     v
            |               |      +-------------+
            |               +------|             |
            |                      | ASP-INACTIVE|
            |                      +-------------+
            |                          ^    |
   ASP Down |                     ASP  |    | ASP Down /
   SCTP CDI |                     Up   |    | SCTP CDI
            |                          |    v
            |                      +-------------+
            |                      |             |
            +--------------------->|  ASP-DOWN   |
                                   |             |
                                   +-------------+

   * Note: ASP-ACTIVE and ASP-STANDBY differ only in whether the ASP is
   currently receiving Data traffic within the AS.

                  Figure 4: ASP State Transition Diagram

   SCTP CDI: The local SCTP layer's SHUTDOWN COMPLETE notification or
   COMMUNICATION LOST notification. The shutdown of an SCTP association
   may have been requested by local Layer Management, see chapter 4.3.

   Local Layer Management

4.4.1.2 AS States

   The AS is configured in the IPSP as a logical entity to handle
   traffic for a specific (unique) routing key. The state of the AS is
   maintained in the SUA layer, and can change due to following events:

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     -    ASP state changes: when the first ASP within an AS goes UP or
          ACTIVE, or when the last ASP within an AS goes DOWN or
          INACTIVE
     -    Recovery Timer expiry

   The possible states of an AS are:

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

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

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

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

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





















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         +----------+ one ASP trans to ASP-ACTIVE +-------------+
         |          |---------------------------->|             |
         |  AS-UP   |                             |  AS-ACTIVE  |
         |          |<---                         |             |
         +----------+    \                        +-------------+
            ^   |         \ Tr Expiry,                ^    |
            |   |          \ at least one             |    |
            |   |           \ ASP in ASP-INACTIVE     |    |
            |   |            \                        |    |
            |   |             \                       |    |
            |   |              \                      |    |
    one ASP |   | all ASP       \            one ASP  |    | Last ACT.
    trans   |   | trans to       \           trans to |    | ASP trans
    to ASP- |   | ASP-DOWN        -------\  ASP-ACTIVE|    | to ASP-
    INACTIVE|   |                         \           |    | INACTIVE
            |   |                          \          |    | or ASP-
            |   |                           \         |    | DOWN
            |   |                            \        |    |
            |   v                             \       |    v
         +----------+                          \  +-------------+
         |          |                           --|             |
         | AS-DOWN  |                             | AS-PENDING  |
         |          |                             |  (queuing)  |
         |          |<----------------------------|             |
         +----------+       Tr Expiry no ASP      +-------------+
                            in ASP-INACTIVEstate


         Tr = Recovery Timer

                    Figure 5: AS State Transition Diagram

   The SGP maintains the availability of the ASs, and will need to
   issue the correct SCCP management message (where applicable) to the
   SS7 node(s).

   When an AS transitions to the UP or DOWN state, and it is the only
   (or last) one handling traffic for a certain SSN, an SSP message is
   broadcast to the concerned remote SCCP-users in the SS7 network.

   When an AS transitions to the ACTIVE state, and it is the first one
   handling traffic for a certain SSN, an SSA message is broadcast to
   the concerned remote SCCP-users in the SS7 network.

4.4.2 AS/ASP Management procedures

   Once an SCTP association is established between two IPSPs, one (or
   both) side(s) might issue an ASP-UP message.

4.4.2.1 ASP-Up


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   An ASP sends an ASP-UP to each communication partner.  When the ASP-
   UP message is received, the receiving IPSP can react in three
   different ways:

     -    Mark the remote ASP Inactive and reply with an ASP-UP Ack
          message in acknowledgement to every received ASP-UP, even if
          the ASP is already marked as Inactive.
     -    If for any local reason (e.g. management lock-out) the IPSP
          cannot respond with an ASP-UP Ack, it responds with an ASP-
          DOWN Ack message.
     -    If an unknown version is received with the ASP-UP message,
          the receiving end MUST respond with an Error message with
          Error Code ôInvalid Versionö. The version field in the common
          header will indicate to the sender which version(s) the
          receiving node supports. This is useful when protocol version
          upgrades are being performed. A node with the newer version
          should support the older versions as well to fallback upon in
          a subsequent ASP-UP message.

   If the ASP does not receive any of the above reactions, the ASP may
   resend ASP-Up messages until it receives a response. The ASP MUST
   wait for the ASP-UP Ack message before sending any other messages.
   If the remote peer receives any other SUA messages from an ASP,
   before an ASP-UP is received and acknowledged, the message should be
   discarded.

   If the ASP Up message contains an ASP Identifier, the SGP should
   save the ASP Identifier for that ASP, to be used in any Notify
   messages, which are sent indicating a change in the state of the
   ASP.

4.4.2.2 ASP-Down

   The IPSP will mark an ASP as down if one of the following events
   occur:

        - An ASP Down (DOWN) message is received from the ASP.
        - The ASP is locked by local Layer Management.

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

   The IPSP will send an ASP DOWN message whenever it wants to take
   down an ASP. Since it is possible for ASP DOWN and ASP DOWN Ack
   messages to be lost (for example, during a node failover), the IPSP
   can send ASP DOWN messages repeatedly until the path comes down
   (i.e. until it receives a ASP-DOWN message from the remote peer or
   the SCTP association goes down).



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4.4.2.3 ASP-Active

   When an ASP is ready to start processing traffic, it sends an ASP-
   ACTIVE message to the remote peer. When an ASP-ACTIVE message is
   received, the remote peer responds with an ASP-ACTIVE Ack. The ASP
   cannot send any other messages until after the ASP-ACTIVE Ack is
   received. If the ASP-ACTIVE Ack is not received within a certain
   time, the ASP may resend the ASP-ACTIVE message.

   The ASP-ACTIVE message optionally contains a list of one or more
   Routing Contexts, indicating which Application Servers the ASP is
   joining. If no Routing Contexts are present, then local
   configuration data is used to determine to which Application
   Server(s) the ASP belongs.

   The Traffic Mode Type parameter in the ASP-ACTIVE message indicates
   the traffic handling mode used in a particular Application Server,
   either Over-ride, Over-ride (Standby), Load-share or Load-share
   (Standby). If the remote peer determines that the mode indicated in
   an ASP-ACTIVE is incompatible with the mode currently used in the
   AS, the remote peer responds with an Error message indicating
   "Invalid Traffic Handling Mode".

   In the Over-ride mode, reception of an ASP-ACTIVE message at a
   remote peer causes the all traffic for the AS to be sent to the ASP
   that sent the ASP-ACTIVE. All previously active ASPs in the AS are
   now considered Inactive and will no longer receive traffic for that
   particular AS.  The remote peer sends a Notify (Alternate ASP-
   Active) to the previously active ASP in the AS, after stopping all
   traffic to that ASP. All existing connections/transactions with the
   previously active ASP should be terminated however.

   In the Over-ride (Standby) mode, the actions are the same with the
   exception that the traffic is not started to the ASP until the
   previously active ASP transitions to the "Inactive or "Down" state.
   At this point the ASP that sent the Over-Ride (Standby) ASP-ACTIVE
   message takes over the traffic. No Notify messages are needed.

   In the Load-share mode, reception of an ASP-ACTIVE message causes
   the redistribution of traffic to the ASP sending the ASP-ACTIVE, in
   addition to all the other ASPs that are currently active in the AS.
   The algorithm at the SGP for load-sharing traffic within an AS to
   all the active ASPs is implementation dependent. All ASPs marked for
   load sharing should be able to handle any traffic within the AS, to
   accommodate any potential fail-over or re-balancing of the offered
   load.

   In the Load-share (Standby) mode, the actions are the same as the
   Load-share mode, with the exception that the traffic is not started
   to the ASP until the remote peer determines that additional
   resources are needed to service the AS. When needed, the ASP that

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   sent the Loadshare (Standby) ASP-ACTIVE message is taken up in the
   loadsharing scheme and traffic is started. No Notify messages are
   needed to be sent.

   A node that receives an ASP-ACTIVE with an incorrect Traffic Mode
   Type for a particular Routing Context will respond with an Error
   Message with Error Cause ôInvalid Traffic Handling Modeö. A node
   that receives an unknown Routing Context value responds with an
   Error message with Error Cause ôInvalid Routing Contextö.

4.4.2.4 ASP-Inactive

   When an ASP wishes to withdraw from handling traffic, it sends an
   ASP-INACTIVE to the applicable remote peers, specifying the AS
   (Routing Context) from which it is withdrawing. If the ASP is
   withdrawing from more than one AS, then the ASP issues either
   multiple ASP-INACTIVE messages, if multiple SCTP associations exist
   to the remote ASPs; or a single ASP-INACTIVE message containing
   multiple Routing Contexts.

   The ASP could have been in one of two modes, Over-ride or Load-
   sharing.  In the Over-ride mode, the ASP that sent the ASP-INACTIVE
   is marked as Inactive. No further traffic is sent from and to the
   ASP marked Inactive.  The remote peer now should notify the
   remaining ASPs of situation.

   In the Load-sharing mode, the peer marks the ASP as Inactive and re-
   allocates the traffic to the remaining active ASPs. The load-sharing
   mechanism used is outside of the scope of SUA. If there are
   insufficient resources, a NTFY (Insufficient ASPs) may be sent to
   all inactive ASPs within the AS.  If a Loadshare (Standby) ASP is
   available, it may be now immediately included in the loadshare group
   and a Notify message MUST not be sent.  An ASP-INACTIVE Ack message
   is sent to the ASP after all traffic is halted.

   In the case when no other ASPs are active or standby in the
   Application Server, the remote peer should send a NTFY (AS-Pending)
   to all inactive ASPs of the AS. The remote peer then either discards
   all incoming messages for the AS or starts buffering the incoming
   messages for T(r) seconds, after which messages will be discarded.
   T(r) is configurable by the network operator.

   If the remote peer receives an ASP-ACTIVE from an ASP in the AS
   before expiry of T(r), the buffered traffic is directed to the ASP
   and the timer is cancelled.  If T(r) expires, the AS is moved to the
   "Down" state.

4.4.3 SUA peer management messages

4.4.3.1 Notify


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   A NTFY message reflecting a change in the AS state MUST be sent to
   all ASPs in the AS, except those in the ASP-DOWN state, with
   appropriate Status Type/ID and ASP Identifier of the failed ASP.
   The Notify message MUST be sent after any ASP State or Traffic
   Management acknowledgement messages (e.g., ASP Up Ack, ASP Down Ack,
   ASP Active Ack, or ASP Inactive Ack).

   In the case where a NTFY (AS-Pending) message is sent by an SGP that
   now has no active ASPs to service the traffic, or a NTFY
   (Insufficient ASPs) is sent in the Loadshare mode, the NTFY does not
   explicitly force the ASP(s) receiving the message to become active.
   The ASPs remain in control of what (and when) action is taken.

4.4.3.2 Error

   The ERR message is used to signal invalid protocol behavior.

4.4.4 Heartbeat procedure

   The optional Heartbeat message may be sent to query the status of
   the remote peer.  It is optional to send, but mandatory to
   acknowledge.  It MAY be used when operating over transport layers
   that do not have their own heartbeat mechanism for detecting loss of
   the transport association (i.e., other than SCTP).

   After an ASP or IPSP has received an ASP Up Ack from an SUA peer in
   response to an ASP Up message, either M3UA peer MAY optionally send
   Heartbeat messages periodically, subject to a provisionable timer
   T(beat).  Upon receiving a Heartbeat message, the SUA peer MUST
   respond with a Heartbeat ACK message.

   If no Heartbeat Ack message (or any other SUA message) is received
   from the peer within 2*T(beat), the remote peer is considered
   unavailable.  Transmission of Heartbeat messages is stopped and the
   signaling process SHOULD attempt to re-establish communication, if
   it is configured as the client for the disconnected M3UA peer.

   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.).  The data field MUST be
   echoed back unchanged in the related Heartbeat Ack message. The
   contents/format of the Heartbeat Data parameter is implementation-
   dependent and only of local interest to the original sender. The ASP
   sender, upon examining the contents of the returned Heartbeat Ack
   message, MAY choose to consider the remote M3UA peer as unavailable.

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




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5 Examples of SUA Procedures

   The following sequence charts overview the procedures of SUA.  These
   are meant as examples, they do not, in and of themselves, impose
   additional requirements upon an instance of SUA.

5.1 SG Architecture

   The sequences below outline logical steps for a variety of scenarios
   within a SG architecture.  Please note that these scenarios cover a
   Primary/Backup configuration.  Where there is a load-sharing
   configuration then the SGP can declare availability when 1 ASP
   issues ASPAC but can only declare unavailability when all ASPs have
   issued ASPIA.

5.1.1 Establishment of SUA connectivity

   The following is established before SUA/SCCP traffic can flow.

   Each node is configured (via MIB, for example) with the connections
   that need to be setup.


        ASP-a1            ASP-a2                SG                  SEP
       (Primary)           (Backup)
          |------Establish SCTP Association------|
                             |--Estab. SCTP Ass--|
                                                 |--Align SS7 link---|

               Each ASP declares to the SGP that it is running.

          +----------------ASP Up---------------->
          <--------------ASP Up Ack--------------+
                             +------ASP Up------->
                             <---ASP Up Ack------+

               The Primary ASP declares to the SGP that it is active.
               The SGP notifies all ASPs.

          +-------------ASP Active--------------->
          <----------ASP Active Ack--------------+
          <----------NTFY (ASP Active)-----------+
                             <-NTFY (ASP Active)-+

               The SGP declares the availability of the signaling
               user on ASP-a1 to the SEP.  The SGP has been
               configured (via a MIB) that the SEP is concerned
               about its signaling users.  The SGs SS7 address
               is presented in the SSA, i.e. the SGP represents the
               availability of ASP-a1 to the SEP.


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                                                 +--------SSA-------->

               The SEP declares its availability to the SGP since
               the SGP appears within its concerned list.  Similarly,
               the SGP informs the active ASP of the availability of
               the SEP as dictated by SGs concerned list.  N.B.
               The SGP maps the SS7 address of the SEP to an
               IP address that the SGP knows ASP-a1 will understand.

                                                 <--------SSA--------+
          <-----------------DAVA-----------------+

               Traffic can now flow.  A connectionless flow is shown
               for simplicity.  Nevertheless, the SGP is responsible
               for mapping IP to SS7 addresses and vice-versa.  Only
               the Routing Context for ASP-a1 persists from ASP-a1 to
               SEP.

          +-----------------CLDT----------------->
                                                 +--------UDT-------->

5.1.2 Failover scenarios

   The following sequences address failover of SEP and ASP

5.1.2.1 SEP Failover

   The SEP knows that the SGP is 'concerned' about its availability.
   Similarly, the SGP knows that ASP-a1 is concerned about the SEPs
   availability; therefore the incoming SSP is translated into DUNA.
   ASP-a1 uses a DAUD to instruct the SGP to invoke the SS7 Sub-system
   Test procedure.

        ASP-a1            ASP-a2                SG                  SEP
      (Primary)           (Backup)
                                                 <--------SSP--------+
          <-----------------DUNA-----------------+
          +-----------------DAUD----------------->
                                                 +--------SST-------->

5.1.2.2 Successful ASP Failover scenario

   The following is an example of a successful failover scenario, where
   there is a failover from ASP-a1 to ASP-a2, i.e. Primary to Backup.
   During the failover, the SGP buffers any incoming data messages from
   the SEP, forwarding them when the Backup becomes available.






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        ASP-a1            ASP-a2                SG                  SEP
      (Primary)           (Backup)
          +-------------ASP Inactive------------->
          <----------NTFY (ASP Inactive)---------+
                             <-NTFY (ASP Inact.)-+
                             +----ASP Active----->
                             <--ASP Active Ack---+
                             <-NTFY (ASP Active)-+
          <----------NTFY (ASP Active)-----------+

5.1.2.3 Unsuccessful ASP Failover scenario

        ASP-a1            ASP-a2                SG                  SEP
      (Primary)           (Backup)
          +-------------ASP Inactive------------->
          <----------NTFY (ASP Inactive)---------+
                             <-NTFY (ASP Inact.)-+

                After some time elapses (i.e. timeout).

                                                 +--------SSP-------->
                                                 <--------SST--------+

5.2 IP-IP Architecture

   The sequences below outline logical steps for a variety of scenarios
   within an IP-IP architecture.  Please note that these scenarios
   cover a Primary/Backup configuration.  Where there is a load-sharing
   configuration then the AS can declare availability when 1 ASP issues
   ASPAC but can only declare unavailability when all ASPs have issued
   ASPIA.

5.2.1 Establishment of SUA connectivity

   The following shows an example establishment of SUA connectivity.
   In this example, each IPSP consists of an Application Server and two
   ASPs.

   The following is established before SUA traffic can flow. A
   connectionless flow is shown for simplicity.

   Each node is configured (via MIB, for example) with the connections
   that need to be setup.








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   IP SEP A                                                  IP SEP B
   AS A                                                          AS B
   ASP-a1     ASP-a2                                 ASP-b2    ASP-b1
   (Primary) (Backup)                               (Backup) (Primary)

                       [Establish SCTP Connectivity]

   |------------- Establish SCTP Association -------------|
   |------------------ Establish SCTP Association ------------------|

              |------- Establish SCTP Association --------|
              |------------ Establish SCTP Association -------------|

                       [Establish SUA Connectivity]

   +----------------------ASP Up-------------------------->
   <--------------------ASP Up Ack------------------------+

   +---------------------------ASP Up------------------------------->
   <-------------------------ASP Up Ack-----------------------------+

              <----------------ASP Up---------------------+
              +----------------ASP Up Ack----------------->

              +------------------------ASP Up----------------------->
              <----------------------ASP Up Ack---------------------+

   +---------------------------ACTIVE------------------------------->
   <-------------------------ACTIVE Ack-----------------------------+

               [Traffic can now flow directly between ASPs]

   +-----------------------------CLDT------------------------------->


5.2.2 Failover scenarios

   The following sequences address failover of ASP

5.2.2.1 Successful ASP Failover scenario

   The following is an example of a successful failover scenario, where
   there is a failover from ASP-a1 to ASP-a2, i.e. Primary to Backup.
   Since data transfer passes directly between peer ASPs, ASP-b1 is
   notified of the failover of ASP-a1 and buffers outgoing data
   messages until ASP-a2 becomes available.





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   IP SEP A                                                  IP SEP B
   ASP-a1     ASP-a2                                 ASP-b2    ASP-b1
   (Primary) (Backup)                               (Backup) (Primary)

   +-----------------------------ASP Inact------------------------>
   <---------------------------ASP Inact Ack----------------------+

              <---------------NTFY (ASP-a1 Inactive)--------------+

              +---------------------ASP Act----------------------->
              <-------------------ASP Act Ack---------------------+

5.2.2.2 Unsuccessful ASP Failover scenario

   The sequence is the same as 4.2.2.1 except that, since the backup
   fails to come in then, the Notify messages declaring the
   availability of the backup are not sent.

6 Security

6.1 Introduction

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

6.2 Threats

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

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

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

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

   When SUA is running in professionally managed corporate or service
   provider network, it is reasonable to expect that this network


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   includes an appropriate security policy framework. The "Site
   Security Handbook" [2196] should be consulted for guidance.

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

6.3 Protecting Confidentiality

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

7 IANA Considerations

7.1 SCTP Payload Protocol ID

   IANA has assigned a SUA value for the Payload Protocol Identifier in
   the SCTP DATA chunk.  The following SCTP Payload Protocol Identifier
   is registered:

           SUA    "4"

   The SCTP Payload Protocol Identifier value "4" SHOULD be included in
   each SCTP DATA chunk, to indicate that the SCTP is carrying the SUA
   protocol. The value "0" (unspecified) is also allowed but any other
   values MUST not be used.  This Payload Protocol Identifier is not
   directly used by SCTP but MAY be used by certain network entities to
   identify the type of information being carried in a DATA chunk.

   The User Adaptation peer MAY use the Payload Protocol Identifier as
   a way of determining additional information about the data being
   presented to it by SCTP.A request will be made to IANA to assign CTP
   Payload Protocol IDs.

7.2 Port Number

   IANA has registered SCTP Port Number 14001 for SUA.  This port
   number is the port that the SGPs listen to when receiving SCTP
   datagrams.

7.3 Protocol Extensions

   This protocol may also be extended through IANA in three ways:

    - Through definition of additional message classes.

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    - Through definition of additional message types.
    - Through definition of additional message parameters.

   The definition and use of new message classes, types and parameters
   is an integral part of SIGTRAN adaptation layers.  Thus, these
   extensions are assigned by IANA through an IETF Consensus action as
   defined in [RFC2434].

   The proposed extension MUST in no way adversely affect the general
   working of the protocol.

7.3.1 IETF Defined Message Classes

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

7.3.2 IETF Defined Message Types

   Documentation of the message type MUST contain the following
   information:

   (a) A long and short name for the new message type;
   (b) A detailed description of the structure of the message.
   (c) A detailed definition and description of intended use of each
      field within the message.
   (d) A detailed procedural description of the use of the new message
      type within the operation of the protocol.
   (e) A detailed description of error conditions when receiving this
      message type.

   When an implementation receives a message type which it does not
   support, it MUST respond with an Error (ERR) message, with an Error
   Code = Unsupported Message Type.

7.3.4 IETF-defined TLV Parameter Extension

   Documentation of the message parameter MUST contain the following
   information:

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


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8 Timer Values

     Ta                                      2 seconds
     Tr                                      2 seconds
     T(ack)                                  2 seconds
     T(ias)    Inactivity Send timer         7 minutes
     T(iar)    Inactivity Receive timer      15 minutes
     T(beat)   Heartbeat Timer               30 seconds

9 Acknowledgements

   The authors would like to thank Brian Bidulock, Martin Booyens,
   Klaus Gradischnig, Miguel A. Garcia, Marja-Liisa Hamalainen, Sherry
   Karl, Markus Maanoja, Chirayu Patel, Michael Purcell, Michael
   Tuexen, Al Varney, Ben Wilson, Michael Wright and James Yu for their
   insightful comments and suggestions.

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

10 Authors' Addresses

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

   Greg Sidebottom
   Kanata, Ontario
   Canada
   EMail: gregside@home.com

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

   Stephen Lorusso
   Unisphere Networks
   10 Technology Park Drive
   Westford, MA  01886
   USA
   Phone: +1 (978) 589-0533
   EMail: SLorusso@UnisphereNetworks.com

   Lode Coene
   Siemens Atea
   Atealaan 34

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   B-2200 Herentals
   Belgium
   Phone: +32-14-252081
   EMail: lode.coene@siemens.atea.be

   Gery Verwimp
   Siemens Atea
   34 Atealaan
   PO 2200
   Herentals
   Belgium
   Phone: +32 14 25 3424
   EMail: gery.verwimp@siemens.atea.be

   Joe Keller
   Tekelec
   5200 Paramount Parkway
   Morrisville, NC 27560
   USA
   EMail: joe.keller@tekelec.com

   Florencio Escobar Gonzalez
   Ericsson Spain S.A.
   Retama 7, 2nd floor
   28045, Madrid
   Spain
   EMail: florencio.escobar@ericsson.com

   Steven Furniss
   Marconi
   New Century Park
   Coventry CV3 1HJ
   United Kingdom
   EMail: steven.furniss@marconi.com

   William Sully
   Marconi
   New Century Park
   Coventry CV3 1HJ
   United Kingdom
   EMail: william.sully@marconi.com

11 References

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

   [2396]         Berners-Lee, T., Fielding, R.T. and L. Masinter,
                  "Uniform Resource Identifiers (URI): Generic Syntax",
                  RFC 2396, August 1998.


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

   [2434]         RFC 2434 "Guidelines for Writing an IANA
                  Considerations Section in RFCs", T. Narten, H.
                  Alvestrand, October 1998.

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

   [ANSI-MTP]     ANSI T1.111 'Signaling System Number 7 - Message
                  Transfer Part'

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

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

   [ENUM]         RFC 2916 "E.164 number and DNS", P. Faltstrom,
                  September 2000.

   [IDNS]         Blanchet, M., Hoffman, P., "Internationalized domain
                  names using EDNS (IDNE)", <draft-ietf-idn-idne-
                  01.txt>, Work in progress, July 2000

   [ITU-MTP]      ITU-T Recommendations Q.701-Q.705, 'Signalling System
                  No. 7 (SS7) - Message Transfer Part (MTP)'

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

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

   [M3UA]         MTP3-User Adaptation Layer <draft-ietf-sigtran-m3ua-
                  06.txt>, March 2001, Work in Progress.

   [RANAP]        3G TS 25.413 V3.5.0 (2001-03) 'Technical
                  Specification 3rd Generation Partnership Project;
                  Technical Specification Group Radio Access Network;
                  UTRAN Iu Interface RANAP Signalling'

   [SCTP]         RFC 2960 "Stream Control Transport Protocol" R.
                  Stewart, et al, November 2000.

   [UTRAN IUR]    3G TS 25.422 V3.5.0 (2000-12) "Technical
                  Specification 3rd Generation Partnership Project;
                  Technical Specification Group Radio Access Network;


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                  UTRAN Iur Interface Signaling Transport (Release
                  1999)"


















































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Copyright Statement

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