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draft-bidulock-sigtran-loadsel-04

Description: Request For Comments

You can download source copies of the file as follows:

draft-bidulock-sigtran-loadsel-04.txt in text format.
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draft-bidulock-sigtran-loadsel-04.pdf in pdf format.

Listed below is the contents of file draft-bidulock-sigtran-loadsel-04.txt.




Network Working Group                                     Brian Bidulock
INTERNET-DRAFT                                       OpenSS7 Corporation

                                                        October 16, 2005
Expires in April 2006

                        Load Selection (LOADSEL)
                                  for
                   Signalling User Adaptation Layers

                <draft-bidulock-sigtran-loadsel-04.txt>

Status of this Memo

    "By submitting this Internet-Draft, each author represents that any
  applicable patent or other IPR claims of which he or she is aware have
  been or will be disclosed, and any of which he or she becomes aware
  will be disclosed, in accordance with Section 6 of BCP 79."

    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 a "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.

Copyright

    Copyright (C) The Internet Society (2005).

Abstract

    This Internet-Draft describes Load Selection (LOADSEL) for
  Signalling User Adaptation Protocols [IUA-BIS..SUA, DUA..TUA], which
  permits an Application Server Processes (ASP) to indicate its
  placement within an Application Server and permits an Signalling
  Gateway (SG) to distribute traffic over ASPs in Application Servers
  under Application Server Process (ASP) control.

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Contents

    A complete table of contents, list of illustrations and tables, and
  a change history, are included at the end of this document.

1.  Introduction

1.1.  Scope

    This Internet-Draft provides parameters and associated procedures in
  extension to the parameters and procedures of the Signalling User
  Adaptation Layers (UAs) [IUA-BIS..SUA, DUA..TUA], for the purpose of
  permitting Application Server Process control over placement of ASPs
  within Application Servers (or Load Groups) [LOADGRP] as part of the
  normal procedures of these UA protocols.

    UA implementations supporting LOADSEL are intended to be compatible
  with UA implementations not supporting LOADSEL.

1.2.  Abbreviations

      AS      --Application Server.
      ASP     --Application Server Process.
      IANA    --Internet Assigned Numbers Authority
      I-D     --Internet-Draft
      IETF    --Internet Engineering Task Force
      IP      --Internet Protocol.
      IPSP    --IP Signalling Point.
      SCCP    --Signalling Connection Control Part.
      SCTP    --Stream Control Transmission Protocol.
      SG      --Signalling Gateway.
      SGP     --Signalling Gateway Process.
      SIGTRAN --IETF Signalling Transport WG
      SPP     --Signalling Peer Process.
      SS7     --Signalling System No. 7.
      SUA     --SS7 SCCP-User Adaptation Layer.
      TCAP    --Transaction Capabilities Application Part.
      TUA     --SS7 TCAP-User Adaptation Layer.
      UA      --User Adaptation Layer.
      WG      --Working Group

1.3.  Terminology

    LOADSEL supplements the terminology used in the UA documents [IUA-
  BIS..SUA, DUA..TUA] by adding the following terms:

  Load Selection - a partition of traffic within an Application Server
      described by the Load Selection parameter and identified by a Load
      Selector parameter.

  Load Selector (LS) - an identifier that uniquely identifies a
      partition of traffic flow within an Application Server.  This

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      identifier is only guaranteed unique within the scope of an
      Application Server and must be combined with a Routing Context (or
      Interface Identifier(s)) (explicitly or implicitly) to uniquely
      define a partition of traffic flow at a Signalling Gateway.

  Signalling User Adaptation Layer (UA) - one or more of the Stream
      Control Transmission Protocol (SCTP) [RFC 2960] ISDN Signalling
      User Adaptation Layers [IUA-BIS, DUA..GR303UA00] or SS7 Signalling
      User Adaptation Layers [M2UA..SUA, ISUA, TUA] supporting the
      concept of an Application Server.

1.4.  Overview

    UA procedures with regard to traffic distribution and ASP traffic
  management provide a mechanism to select the algorithm for
  coordinating state and distributing traffic over a number of
  Application Server Processes (ASPs) serving an Application Server
  (AS).  These existing procedures provide only simplified distribution
  approaches which are not amenable in the following situations:

   (1)   Connection- or Transaction-Oriented traffic flows which group
         the messages corresponding to a connection or a transaction.

   (2)   Large scale systems that need to adapt to dynamic traffic
         loading.

   (3)   Systems that need dynamic reconfiguration under ASP control for
         maintenance or fail-over purposes.

   (4)   Systems that require ASP control over load-sharing.

    LOADSEL for the Signalling User Adaptation Layers [IUA-BIS..SUA,
  DUA..TUA] permits close control over the placement and grouping of
  Application Server Processes serving an Application Server that
  provides for load selection placement within the Application Server: a
  capability not present in the existing scheme.

    Under existing UA traffic distribution, there is no mechanism which
  permits an Application Server Process (ASP) to indicate which of a
  number of ASPs it wishes to override in an Override AS.  There is also
  no mechanism which permits an ASP to indicate which traffic flows it
  wishes to process within a Load-share or Broadcast AS.

    LOADSEL provides the ability for the ASP itself to control its
  placement within an AS, be informed of the failure of ASPs serving
  other load selections within the AS, and chose to activate itself to
  receive additional load selections within the AS.  LOADSEL also
  permits grouping of ASPs within a load selection.

1.4.1.  Non-Load Selection Traffic Distribution

    Figure 1 illustrates the existing traffic distribution algorithm
  that is used across the Signalling User Adaptation Layers.

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                                             ____
                    Traffic                 /....\
                    Mode Type          ____|__....|
                                      |       |...|
          _______ /------------------>|  ASP  |...|
         |       |---\                |_______|...|
         |  SGP  |--\ \                ____|__....|
         |_______|-\ \ \              |       |...|
                  \ \ \ \------------>|  ASP  |...|
          _______  \ \ \              |_______|...|
         |       |  \ \ \              ____|__....| Application
         |  SGP  |   \ \ \            |       |...| Server
         |_______|    \ \ \---------->|  ASP  |...|
                       \ \            |_______|...|
                        \ \            ____|__....|
                         \ \          |       |...|
                          \ \-------->|  ASP  |...|
                           \          |_______|...|
                            \          ____|__....|
                             \        |       |...|
                              \------>|  ASP  |...|
                                      |_______|...|
                                           |......|
                                            \____/

           Figure 1.  Non-Load Selection Traffic Distribution

    When an SGP distributes a Signalling User Adaptation Layer message
  toward the Application Server based on the Routing (Link) Key, it
  selects an ASP that is active for the AS according to the Traffic Mode
  Type that is associated with the AS.  The Traffic Mode Type describes
  three general distribution algorithms: Override, Load-share and
  Broadcast.

    The detailed actions taken for these distribution algorithms are
  described in Section 4 of the Signalling User Adaptation Layer
  specifications [IUA-BIS..SUA, DUA..TUA]; however, they can be
  summarized as follows:

  Override:-  When distributing messages to an Override Application
      Server, the SGP selects the ASP which is active for the
      Application Server.  In an Override Application Server, at most
      one ASP can be active for the AS at any given point in time.  The
      active ASP for the AS is selected.

      A major limitation of the Override AS that is removed by LOADSEL
      is that only one ASP can be active within an Application Server.
      This does not work when the number of ASPs required to service an
      AS is greater than one.

  Load-share:-  When distributing messages to a Load-share Application
      Server, the SGP selects one of the ASPs that are active for the
      Application Server using an implementation dependent load-sharing

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      algorithm based on some unspecified aspect of the traffic or
      static configuration data.

      A major limitation of the Load-share AS is that each ASP in the
      Application Server must be capable of handling any (and all)
      traffic within the Load-share AS.  Under the current approach an
      SGP does not distinguish between ASPs in a Load-share AS and,
      aside from perhaps attempting to equally distribute traffic load
      over the available ASPs, it is not possible for the ASPs to
      control which traffic flows it receives.  This causes management
      difficulties when the number of ASPs required to service an AS is
      large, but the number of spare ASPs is small.  It also causes
      considerable difficulty when each ASP does not have access to the
      entire AS call or transaction state.

  Broadcast:-  When distributing messages to a Broadcast Application
      Server, the SGP sends a copy of the message to each of the ASPs
      that are active for the Application Server.  The ASPs themselves
      decide which, if any, of the ASPs will process the message.

      A major limitation of the Broadcast AS is that each ASP receives
      each message.  This does not scale well when the number of ASPs
      needed to service an AS is large.

    LOADSEL enhances the traffic distribution algorithms of the existing
  Signalling User Adaptation Layers by providing ASP control over its
  placement within an AS by load selection.

1.4.2.  Load Selection Traffic Distribution

    Figure 2 illustrates the LOADSEL traffic distribution algorithms
  that are used across the Signalling User Adaptation Layers as a result
  of the LOADSEL messages and procedures.

    LOADSEL introduces the concept of a Load Selector.  A Load Selector
  is an identifier that is used to identify a traffic flow within (or
  across) Application Server(s).  Signalling Gateway Processes (SGPs)
  distribute traffic first over the Load Selector and then distribute
  traffic within the Load Selector.  Each Load Selector describes (and
  is identified by) an identifier within the Application Server.  The
  Load Selector identifies the traffic flows that will be distributed to
  ASPs associated with the Load Selector within an Application Server.

    When an SGP distributes a Signalling User Adaptation Layer message
  toward an Application Server based on the Routing (Link) Key, it first
  derives a Load Selector according to a UA-specific, AS-specific and
  implementation-dependent load selection algorithm.  This load
  selection algorithm is configured at the SGP and may consist, for
  example, of the Signalling Link Selection (SLS) [Q.704], Circuit
  Identification Code (CIC) [Q.723, Q.763], Subsystem Number (SSN)
  [Q.713], Destination Local Reference (DLR) [Q.713], or Transaction Id
  (TID) [Q.773], value contained in the message for distribution.

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                 Traffic        Load         ____
                 Mode Type      Selection   /....\
                                       ____|__....|
                                LS1   |       |...|
          _______ /------------------>|  ASP  |...|
         |       |---\                |_______|...|
         |  SGP  |--\ \                ____|__....|
         |_______|-\ \ \        LS2   |       |...|
                    \ \ \------------>|  ASP  |...|
          _______    \ \              |_______|...|
         |       |    \ \              ____|__....| Application
         |  SGP  |     \ \      LS3   |       |...| Server
         |_______|      \ \---------->|  ASP  |...|
                         \            |_______|...|
                          \            ____|__....|
                           \          |       |...|
                            \-------->|  ASP  |...|
                            |         |_______|...|
                            |   LS4    ____|__....|
                            |         |       |...|
                            \-------->|  ASP  |...|
                                      |_______|...|
                                           |......|
                                            \____/

             Figure 2.  Load Selection Traffic Distribution

    Once the SGP has determined the Load Selector to which the message
  corresponds, an ASP that is active for the associated Load Selection
  within the AS is selected.  When multiple ASPs are active for the same
  Load Selection within an AS, the SGP uses the traffic handling mode
  based on the Traffic Mode Type associated with the Application Server
  (or Load Group[1]) to choose the ASP within the load selection.

    Under LOADSEL, the Traffic Mode Type continues to describe three
  general distribution algorithms: Override, Load-share and Broadcast.
  The change in the behaviour of the SGP when selecting an ASP for
  traffic distribution introduced by LOADSEL is that the SGP also takes
  into account the concept of a Load Selector.  The LOADSEL procedures
  are summarized as follows:

  Override:-  When distributing messages to an Override Application
      Server, the SGP first determines the Load Selector associated with
      the message.  The SGP then distributes the message to the ASP that
      is active for the traffic flow indicated by the Load Selector
      within the AS.  In an Override Application Server, at most one ASP
      can be active for the AS within a Load Selector at any given point
      in time.  The active ASP associated with the Load Selector for the
      AS is used.

  Load-share:-  When distributing messages to a Load-share Application
      Server, the SGP first determines the Load Selector associated with
      the message.  The SGP then selects one of the active ASPs

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      associated with the Load Selector within the AS using an
      implementation dependent load-sharing algorithm based on some
      unspecified aspect of the traffic or static configuration data.

  Broadcast:-  When distributing messages to a Broadcast Application
      Server, the SGP first determines the Load Selector associated with
      the message.  The SGP then selects all of the active ASPs
      associated with the Load Selector within the AS and sends a copy
      of the message to each ASP.  (The ASPs themselves decide which
      ASP(s) will process the message.)

    The result of this extension is that Application Server Processes
  have control over their placement within an Application Server and can
  control the traffic that they receive by registering and activating
  for specific Load Selectors within the AS.

Notes for Section 1

  [1]  Another draft: UA Load Grouping [LOADGRP], provides for
       selection of Load Distribution methods within a Load Selector.
       The draft [LOADGRP] refers to a group of ASPs within the same
       traffic load selection as a Load Group and associates a Load
       Distribution with the load group that can be: Override, Load-
       share or Broadcast.  LOADSEL is applicable both to the normal
       Traffic Mode Type of an AS, as well as to the Load Distribution
       within a Load Group.

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 [RFC 2119].

3.  Protocol Elements

    The following subsections describe the parameters which are added by
  this extension, their format and the messages in which they are used.

3.1.  Parameters

    LOADSEL adds one new parameter: the Load Selector parameter.

3.1.1.  Load Selector

    The Load Selector parameter is used in the REG RSP, ASPAC, ASPAC
  ACK, ASPIA, ASPIA ACK, and NTFY messages.  It is used to identify the
  placement of the ASP within an Application Server.  It identifies the
  Load Selection (partition of traffic flow) for which the ASP is
  registering, activating or deactivating, or when the SG is indicating
  or notifying of an ASP state change.

  The Load Selector parameter is formatted as follows: [1]

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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 = 0x0018        |              Length           |
   +-------------------------------+-------------------------------+
   \                                                               \
   /                        Load Selector  1                       /
   \                                                               \
   +---------------------------------------------------------------+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +---------------------------------+-----------------------------+
   \                                                               \
   /                        Load Selector  n                       /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The Load Selector parameter contains the following fields:

  Load Selector field: n x 32-bits (unsigned integer)

    The Load Selector forms and extension to the Routing (Link) Key and
    an attribute of the Application Server as indicated by the Routing
    Context (Interface Identifier(s)).

    The Load Selector field is an identifier, that MUST be unique within
    an Application Server and MAY be unique within an administrative
    domain, that identifies the placement or Load Selection of an ASP
    within an AS.  This identifier, in conjunction with any Application
    Server identifier (i.e, Routing Context or Interface Identifier(s)),
    identifies the traffic flow for which an ASP is registering,
    activating or deactivating, or for which an SG is providing
    notification of an ASP or AS state change.

    When the Load Selector parameter is included in the ASPAC, ASPAC
  ACK, ASPIA, ASPIA ACK or NTFY message, one Routing Context (Interface
  Identifier(s)) representing a single Application Server SHOULD be
  associated (specified or implied) with the message.

3.1.2.  Load Selection

    The Load Selection parameter is used in the REG REQ message.  It is
  used to register the placement of an ASP within an Application Server.

  The Load Selection parameter is formatted as follows: [2]

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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 = 0x0019         |             Length            |
    +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
    \                                                               \
    /                       Load Key Parameter(s)                   /
    \                                                               \
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The Load Key Parameter(s) can contain the following parameters:

      UA     Parameters
      ----------------------------------------------------
      M2UA   SLS Range                   Mandatory     *1
      ----------------------------------------------------
      M3UA   Service Indicators          Conditional   *2
             CIC Range                   Conditional
      ----------------------------------------------------
      SUA    Address Range               Conditional   *3
             DLR Label                   Conditional
             TID Label                   Conditional
      ----------------------------------------------------
      ISUA   CIC Range                   Mandatory
      ----------------------------------------------------
      TUA    Address Range               Conditional   *3
             Transaction Id Range        Conditional   *4
      ----------------------------------------------------

  Note 1: The SLS Range parameter has not yet been defined for M2UA
          [M2UA].

  Note 2: When the Service Indicators parameter is used in the Load
          Selection, it SHOULD be more restricted than (a subset of) any
          Service Indicators parameter present in the Routing Key
          parameter for routing purposes.

  Note 3: When the Address Range parameter is used in the Load
          Selection, it SHOULD be more restrictive than (a subset of)
          any Address Range parameter present in the Routing Key
          parameter for routing purposes.

  Note 4: When the Transaction Id Range parameter is used in the Load
          Selection, it SHOULD be more restrictive than (a subset of)
          any Transaction Id Range parameter present in the Routing Key
          parameter for routing purposes.

    The Load Selection parameter SHOULD contain at least one Load
  Selection Parameter.

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3.2.  Messages

    LOADSEL adds the Load Selector parameter as an OPTIONAL parameter to
  be used in conjunction with the common Traffic Mode Type in the
  following messages: [3]

      REG REQ     Registration Request message
      REG RSP     Registration Response message
      ASPAC       ASP Active message
      ASPAC ACK   ASP Active Ack message
      ASPIA       ASP Inactive message
      ASPIA ACK   ASP Inactive Ack message
      NTFY        Notify message

3.2.1.  Registration Request (REG REQ)

    LOADSEL supplements the Registration Request (REG REQ) message by
  permitting the following optional parameters to be included in the
  Routing Key [M3UA-BIS, SUA, ISUA, TUA] or Link Key [M2UA] parameter
  within the message:

      Extension Parameters
      -----------------------------------------
      Load Selection              Optional

    The Load Selector parameter is used in the Routing Key (Link Key) to
  further refine the traffic load selection to be received by the
  registering ASP.

  The format of the resulting Routing Key or Link Key parameter is as
  follows: [4]

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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 =                |           Length = 8          |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   |                    Local-RK(LK)-Identifier                    |
   +-------------------------------+-------------------------------+
   |          Tag = 0x0000         |           Length = 8          |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   |                       Traffic Mode Type                       |
   +-------------------------------+-------------------------------+
   |          Tag = 0x0019         |             Length            |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   \                                                               \
   /                        Load Selection                         /
   \                                                               \
   +---------------------------------------------------------------+
   \                                                               \
   /                         Key Parameter(s)                      /
   \                                                               \
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    When an ASP wishes to register within a Load Selection associated
  with an Application Server, it includes the Load Selection parameter
  in the Routing Key (Link Key) for that Application Server in the REG
  REQ message.

    The Load Selection parameter indicates the traffic load selection to
  be used within the Application Server as identifier by the Routing
  (Link) Key parameter.

    When the ASP includes the Load Selection parameter in the Routing
  (Link) Key it expects the SGP to respond with a Load Selector
  parameter in addition to the Routing Context to indicate the
  identifier for the Load Selection specified.  In this way, the Load
  Selection parameter is analogous to the Routing Key and the Load
  Selector parameter is analogous to the Routing Context.

    No other changes to the REG REQ message, Routing Key or Link Key
  parameters formats are provided by this extension.

3.2.2.  Registration Response (REG RSP)

    LOADSEL supplements the Registration Response (REG RSP) message by
  permitting the following optional parameters to be include in the
  Registration Result parameter within the message:

      Extension Parameters
      -----------------------------------------

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      Load Selector               Optional

    The Load Selector parameter is used in the Regsitration Result to
  provide an identifier for the registered Load Selection.

  The format of the resulting Registration Response parameter is as
  follows:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Tag =                |             Length            |
    +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
    |                    Local-RK(LK)-Identifier                    |
    +---------------------------------------------------------------+
    |                      Regsitration Status                      |
    +---------------------------------------------------------------+
    |             Routing Context (Interface Identifier)            |
    +---------------------------------------------------------------+
    |                         Load Selector                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    When the SGP replies to a REG REQ that contained a Load Selection
  parameter, and the registration is successful, it returns the Load
  Selector in the REG RSP associated with the Load Selection in the REG
  REQ.

    When the registration is unsuccessful (i.e. the Registration Status
  indicates an error), the Load Selector SHOULD NOT be included in the
  REG RSP message.

    LOADSEL extends the common Registration Status parameter in the REG
  RSP message by adding the following values to the Registration Status:

        Value[5]   Description
        -----------------------------------------------------
           12      Error - Unsupported Load Selection
           13      Error - Invalid Load Selection
           14      Error - Cannot Support Unique Loadsharing
           15      Error - Unsupported LS Parameter Field

    No other changes to the REG RSP message or Registration Response
  parameter formats are provided by this extension.

3.2.3.  ASP Active (ASPAC)

    LOADSEL supplements the ASP Active (ASPAC) message by permitting the
  following optional parameters to be included in the ASPAC message:

      Extension Parameters
      -----------------------------------------
      Load Selector               Optional

Internet Draft                 UA LOADSEL               October 16, 2005

  The format of the resulting ASPAC message is as follows: [3][6]

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x000b         |           Length = 8          |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   |                        Traffic Mode Type                      |
   +---------------------------------------------------------------+
   \                                                               \
   /                         Routing Context                       /
   \                               or                              \
   /                     Interface Identifier(s)                   /
   \                                                               \
   +-------------------------------+-------------------------------+
   |          Tag = 0x0018         |             Length            |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   \                                                               \
   /                          Load Selector                        /
   \                                                               \
   +-------------------------------+-------------------------------+
   |          Tag = 0x0004         |             Length            |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   \                                                               \
   /                            Info String                        /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The Load Selector parameter is used by the ASP in the ASPAC message
  to indicate the range of traffic for which the ASP is activating.  The
  Application Servers for which the Load Selectors apply is either
  indicated in the ASPAC message by providing the associated Routing
  Context (Interface Identifier(s)) or, if there is no Routing Context
  (Interface Identifier) parameter in the ASPAC message, the associated
  Application Servers are implied by SGP and ASP configuration data.
  (See Section 4.1.5 - "ASP Active Procedures".)

    No other changes to the ASPAC message format are provided by this
  extension.

3.2.4.  ASP Active Ack (ASPAC ACK)

    LOADSEL supplements the ASP Active Ack (ASPAC ACK) message by
  permitting the following optional parameters to be included in the
  ASPAC ACK message:

      Extension Parameters
      -----------------------------------------
      Load Selector               Optional

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  The format of the resulting ASPAC ACK message is as follows: [3][7]

    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                     |
   +---------------------------------------------------------------+
   \                                                               \
   /                         Routing Context                       /
   \                               or                              \
   /                     Interface Identifier(s)                   /
   \                                                               \
   +-------------------------------+-------------------------------+
   |          Tag = 0x0018         |            Length             |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   \                                                               \
   /                           Load Selector                       /
   \                                                               \
   +-------------------------------+-------------------------------+
   |          Tag = 0x0004         |            Length             |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   \                                                               \
   /                            Info String                        /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The Load Selector parameter is used by the SGP in the ASPAC ACK
  message to indicate the range of traffic for which the SGP has
  activated the ASP.  The Application Servers for which the Load
  Selectors apply is either indicated in the ASPAC ACK message by
  providing the associated Routing Context (Interface Identifier(s)) or,
  if there is no Routing Context (Interface Identifier) parameter in the
  ASPAC ACK message, the associated Application Servers are implied by
  SGP and ASP configuration data.  (See Section 4.1.5 - "ASP Active
  Procedures".)

    No other changes to the ASPAC ACK message format are provided by
  this extension.

3.2.5.  ASP Inactive (ASPIA)

    LOADSEL supplements the ASP Inactive (ASPIA) message by permitting
  the following parameters to be included in the ASPIA message:

      Extension Parameters
      -----------------------------------------
      Load Selector               Optional

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  The format of the resulting ASPIA message is as follows: [3][8]

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         Routing Context                       /
   \                               or                              \
   /                     Interface Identifier(s)                   /
   \                                                               \
   +-------------------------------+-------------------------------+
   |          Tag = 0x0018         |            Length             |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   \                                                               \
   /                           Load Selector                       /
   \                                                               \
   +-------------------------------+-------------------------------+
   |          Tag = 0x0004         |            Length             |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   \                                                               \
   /                            Info String                        /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The Load Selector parameter is used by the ASP in the ASPIA message
  to indicate the range of traffic for which the ASP is deactivating.
  The Application Servers for which the Load Selectors apply is either
  indicated in the ASPIA message by providing the associated Routing
  Context (Interface Identifiers) or, if there is no Routing Context
  (Interface Identifier) parameter in the ASPIA message, the associated
  Application Servers are implied by SGP and ASP configuration data.
  (See Section 4.1.6 - "ASP Inactive Procedures".)

    No other changes to the ASPIA message format are provided by this
  extension.

3.2.6.  ASP Inactive Ack (ASPIA ACK)

    LOADSEL supplements the ASP Inactive Ack (ASPIA ACK) message by
  permitting the following parameters to be included in the ASPIA ACK
  message:

      Extension Parameters
      -----------------------------------------
      Load Selector               Optional

  The format of the resulting ASPIA ACK message is as follows: [3][9]

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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         Routing Context                       /
   \                               or                              \
   /                     Interface Identifier(s)                   /
   \                                                               \
   +-------------------------------+-------------------------------+
   |          Tag = 0x0018         |            Length             |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   \                                                               \
   /                           Load Selector                       /
   \                                                               \
   +-------------------------------+-------------------------------+
   |          Tag = 0x0004         |            Length             |
   +- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
   \                                                               \
   /                            Info String                        /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The Load Selector parameter is used by the SGP in the ASPIA ACK
  message to indicate the range of traffic for which the SGP has
  deactivated the ASP.  The Application Servers for which the Load
  Selectors apply is either indicated in the ASPIA ACK message by
  providing the associated Routing Context (Interface Identifiers) or,
  if there is no Routing Context (Interface Identifier) parameter in the
  ASPIA ACK message, the associated Application Servers are implied by
  SGP and ASP configuration data.  (See Section 4.1.6 - "ASP Inactive
  Procedures".)

    No other changes to the ASPIA ACK message format are provided by
  this extension.

3.2.7.  Error (ERR)

    LOADSEL supplements the Error (ERR) message by adding the following
  values to the common mandatory Error Code parameter in the ERR
  message:

      29   Invalid Load Selector [10]

  These new error codes are interpreted as follows: [3]

  The "Invalid Load Selector" error would be sent in an ERR message if
      the SG determines that one or more Load Selectors in the Load
      Selector parameter provided by the ASP is invalid, is not
      configured, or cannot be supported.

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    No other changes to the ERR message or Error Code parameter format
  are provided by this extension.  See Section 4 for extension
  procedures associated with the ERR message.

3.2.8.  Notify (NTFY)

    LOADSEL supplements the Notify (NTFY) message by permitting the
  following parameters to be included in the NTFY message:

      Extension Parameters
      -----------------------------------------
      Load Selector               Optional

  The format of the resulting NTFY message is as follows: [3][11]

    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 Information      |
   +---------------------------------+-----------------------------+
   |          Tag = 0x0012           |         Length = 8          |
   +- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
   |                          ASP Identifier                       |
   +---------------------------------------------------------------+
   \                                                               \
   /                         Routing Context                       /
   \                               or                              \
   /                     Interface Identifier(s)                   /
   \                                                               \
   +---------------------------------+-----------------------------+
   |          Tag = 0x0018           |          Length             |
   +- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
   \                                                               \
   /                           Load Selector                       /
   \                                                               \
   +---------------------------------+-----------------------------+
   |          Tag = 0x0004           |          Length             |
   +- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
   \                                                               \
   /                            Info String                        /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The Load Selector parameter is used by the SGP in the NTFY message
  to indicate the traffic load positions which led to or have
  contributed to the change in state of an associated Application Server
  when sending a NTFY message that indicates and Application Server
  state change.  The Application Servers for which the Load Selectors
  apply is either indicated in the NTFY message by providing the

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  associated Routing Context (Interface Identifiers) or, if there is no
  Routing Context (Interface Identifier) parameter in the NTFY message,
  the associated Application Servers are implied by SGP and ASP
  configuration data.  (See Section 4.1.7 - "Notification Procedures".)

    No other changes to the NTFY message format are provided by this
  extension.

Notes for Section 3

  [1]  EDITOR'S NOTE:-  The parameter tag values shown as 0x0018) will
       be assigned by IANA within the common parameter range of the
       SIGTRAN UAs and may change its value in further versions of
       this document.

  [2]  EDITOR'S NOTE:-  The parameter tag values shown as 0x0019) will
       be assigned by IANA within the common parameter range of the
       SIGTRAN UAs and may change its value in further versions of
       this document.

  [3]  For a detailed description of these messages, see Section 3 of
       the SIGTRAN UA specifications cited under "References" [IUA-
       BIS..SUA, DUA..TUA].

  [4]  EDITOR'S NOTE:-  The parameter tag values shown as 0x0019) will
       be assigned by IANA within the common parameter range of the
       SIGTRAN UAs and may change its value in further versions of
       this document.

  [5]  EDITOR'S NOTE:-  The Registration Status values shown as 12,
       13, 14 and 15 will be assigned by IANA as a value of the UA-
       specific Registration Status parameter for each SIGTRAN UA and
       may change its value in further versions of this document.

  [6]  EDITOR'S NOTE:-  The parameter tag values shown as 0x0018) will
       be assigned by IANA within the common parameter range of the
       SIGTRAN UAs and may change its value in further versions of
       this document.

  [7]  EDITOR'S NOTE:-  The parameter tag values shown as 0x0018) will
       be assigned by IANA within the common parameter range of the
       SIGTRAN UAs and may change its value in further versions of
       this document.

  [8]  EDITOR'S NOTE:-  The parameter tag values shown as 0x0018) will
       be assigned by IANA within the common parameter range of the
       SIGTRAN UAs and may change its value in further versions of
       this document.

  [9]  EDITOR'S NOTE:-  The parameter tag values shown as 0x0018) will
       be assigned by IANA within the common parameter range of the
       SIGTRAN UAs and may change its value in further versions of
       this document.

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  [10] EDITOR'S NOTE:-  The Error Code value shown as 29) will be
       assigned by IANA as a value of the common Error Code parameter
       for SIGTRAN UAs and may change its value in further versions of
       this document.

  [11] EDITOR'S NOTE:-  The parameter tag values shown as 0x0018) will
       be assigned by IANA within the common parameter range of the
       SIGTRAN UAs and may change its value in further versions of
       this document.

4.  Procedures

    LOADSEL provides for an additional level of control over the traffic
  distribution patterns within an Application Server.  LOADSEL provides
  the Load Selector parameter which may be optionally included in the
  ASPAC, ASPAC ACK, ASPIA, ASPIA ACK and NTFY messages.  In addition, it
  provides procedures for use of the Load Selector parameter in
  association with these messages.

4.1.  AS and ASP State Maintenance

    In addition to the SGP maintaining the state of each remote ASP in
  each Application Server that the ASP is configured to receive traffic,
  under LOADSEL, SGP MAY also maintain the state of each remote ASP in
  each Load Selection within an Application server that the ASP is
  configured to receive traffic.  Aside from the procedures described in
  Section 4.1.7 "Notification Procedures", no management procedures are
  provided by LOADSEL for maintaining the state of a Load Selection
  within an Application Server.  The Load Selection state is maintained
  separate from the ASP and AS states.

4.1.1.  ASP State

    LOADSEL uses the existing UA [IUA-BIS..SUA, DUA..TUA] definitions
  and procedures with regard to ASP State.

4.1.2.  AS State

    The state of the Application Server is maintained in the Signalling
  User Adaptation Layer on the SGPs.  The state of the Application
  Server changes due to ASP state transitions.  The possible states of
  an Application Server using LOADSEL are:

  AS-DOWN:        The Application Server is unavailable.  This state
                  implies that all related ASPs are in the ASP-DOWN
                  state for this AS.  Initially, the AS will be in this
                  state.  An Application Server is in the AS-DOWN state
                  when it is removed from a configuration.

  AS-INACTIVE:    The Application Server is available but no application
                  traffic is active (i.e, one or more related ASPs are
                  in the ASP-INACTIVE state, but there is no ASP in the
                  ASP-ACTIVE state).  The recovery timer T(r) is not
                  running or has expired.

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

  AS-PENDING:     An active ASP has transition to ASP-INACTIVE or ASP-
                  DOWN and it was the last remaining active ASP for a
                  Load Selection in the AS.  A recovery timer T(r)
                  SHOULD be started and all incoming signalling messages
                  SHOULD be queue by the SGP for each of the Load
                  Selections for which there is no ASP in the ASP-ACTIVE
                  state.  If an ASP becomes ASP-ACTIVE for each Load
                  Selection in the AS before T(r) expires, the AS is
                  moved to the AS-ACTIVE state and all the queued
                  messages for the Load Selection will be sent to the
                  newly active ASPs on each Load Selection.

4.1.3.  ASP Up Procedures

    When an SGP receives an ASP Up messages from an ASP and the ASP is
  configured at the SGP in one or more Load Selections associated with
  one or more Application Servers, if the ASP is not already in the ASP-
  INACTIVE state for the associated Application Servers, the SGP moves
  the ASP into the ASP-INACTIVE state for the configured Load Selections
  within the associated Application Servers.  In any event, the SGP
  responds with an ASPUP ACK message.

    If the ASP transition to the ASP-INACTIVE state within these Load
  Selections results in a state change in the associated Application
  Servers, the SGP moves the Application Server to the AS-INACTIVE
  state.  If the ASP transition to the ASP-INACTIVE state for the given
  Load Selection within an associated Application Server results in a
  change in state of the AS (or the Load Selections associated with the
  AS), the SGP also follows the "Notification Procedures" (described in
  Section 4.1.7) for the Application Server.

    Otherwise, the "ASP Up Procedures" described by the UAs [1] apply
  also to LOADSEL.

4.1.4.  ASP Down Procedures

    When an SGP receives an ASP Down messages from an ASP and the ASP is
  configured at the SGP in one or more Load Selections associated with
  one or more Application Servers, if the ASP is not already in the ASP-
  DOWN state for the associated Application Servers, the SGP moves the
  ASP to the ASP-DOWN state for the configured Load Selections within
  the associated Application Servers.  In any event, the SGP responds
  with an ASP Down Ack.

    If the ASP transition to the ASP-DOWN state within these Load
  Selections results in a state change in the associated Application
  Servers, the SGP moves the Application Server to the AS-DOWN state.

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    Otherwise, the "ASP Down Procedures" described by the UAs [1] apply
  also to LOADSEL.

4.1.5.  ASP Active Procedures

    When an ASP wishes to activate for a set of Load Selections
  associated with an Application Server, it includes the Load Selector
  parameter in the ASPAC message.

    When an SGP receives and ASPAC message requesting activation for a
  set of Load Selections within an AS or the SG otherwise activates the
  ASP for a set of Load Selections within an AS, the SG sends an ASPAC
  ACK message including the Load Selector parameter indicating the Load
  Selections for which the ASP has been activated.  If the SGP is
  responding to an ASP that included the Load Selector parameter in the
  ASPAC message, the SG MUST include the Load Selector parameter in the
  response ASPAC ACK message.

    If the Load Selector included in an ASPAC message contains invalid
  information or indicate an unsupported Load Selection, or a Load
  Selector parameter required by the SGP is missing, the SGP replies to
  the ASPAC message with an ERR("Invalid Load Selector") message and
  takes no further action with regard to AS or ASP state.

    The Application Servers associated with the Load Selector is
  indicated in the ASPAC (ACK) message by Routing Context (Interface
  Identifiers) or, when the Routing Context (Interface Identifier)
  parameter is missing from the ASPAC (ACK) message, is implied by ASP
  and SGP configuration data.  When the Load Selector parameter is
  included in the ASPAC (ACK) message, the Routing Context (Interface
  Identifier) parameter or implicit configuration data SHOULD be
  associated with a single Application Server.

    If the ASP transition to the ASP-ACTIVE state for the given Load
  Selections within an associated Application Server results in a change
  in state of the AS (or the Load Selections associated with the AS),
  the SGP follows the "Notification Procedures" (described in Section
  4.1.7) for the Application Server.

    Otherwise, the "ASP Active Procedures" described by the UAs [1]
  apply also to LOADSEL.

4.1.6.  ASP Inactive Procedures

    When an ASP wishes to deactivate for a set of Load Selections
  associated with an Application Server, it includes the Load Selector
  parameter in the ASPIA message.

    When an SGP receives an ASPIA message requesting deactivation for a
  set of Load Selections within an AS or the SG otherwise deactivates
  the ASP for a set of Load Selections within an AS, the SG sends an
  ASPIA ACK message including the Load Selector parameter for which the
  ASP has been deactivated.  If the SGP is responding to an ASP that
  included the Load Selector parameter in the ASPIA message, the SG MUST

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  include the Load Selector parameter in the response ASPIA ACK message.

    If the SGP receives an ASPIA message from an ASP that is active for
  a set of Load Selections associated with the Application Server for
  which the ASP is requesting deactivation, and the Load Selector
  parameter is not present in the ASPIA message, the SGP will interpret
  this as a request to deactivate the ASP for all the Load Selections
  associated with the Application Server for which the ASP is active.

    If the Load Selector included in an ASPAC message contains invalid
  information or indicates an unsupported Load Selector, the SGP replies
  to the ASPAC message with an ERR("Invalid Load Selector") message and
  takes no further action with regard to AS or ASP state.

    The Application Servers associated with the Load Selector is
  indicated in the ASPIA (ACK) message by Routing Context (Interface
  Identifiers) or, when the Routing Context (Interface Identifier)
  parameter is missing from the ASPIA (ACK) message, is implied by ASP
  and SGP configuration data.  When the Load Selector parameter is
  included in the ASPIA (ACK) message, the Routing Context (Interface
  Identifier) parameter or implicit configuration data SHOULD be
  associated with a single Application Server.

    If the ASP transition to the ASP-INACTIVE state for the given Load
  Selections within an associated Application Server results in a change
  in state of the AS (or the Load Selections associated with the AS),
  the SGP follows the "Notification Procedures" (described in Section
  4.1.7) for the Application Server.

    Otherwise, the "ASP Inactive Procedures" described by the UAs [1]
  apply also to LOADSEL.

4.1.7.  Notify Procedures

4.1.7.1.  AS State Change

    When an ASP makes a state transition and is configured for a set of
  Load Selections in one or more Application Servers, the ASP state
  transition may result in a change to the state of the associated
  Application Servers, or Load Selections within those AS, at the SGP.
  When a recovery timer T(r) expires, the associated Application Server
  will transition from the AS-PENDING state to the AS-INACTIVE state.

    Whenever an AS changes state, or the condition of the AS Load
  Selections perpetuating the current AS state changes, the SGP MUST
  notify all ASPs not in the ASP-DOWN state configured for the
  Application Server by sending a Notify (NTFY) message to each
  indicating the state of the Application Server in the Status
  Information field of the Status parameter in the NTFY message.

    When an Application Server is configured for LOADSEL, the SGP MUST
  also include a list of Load Selections in the Load Selector parameter
  for which the Application Server is configured that caused the AS
  state change or is perpetuating the AS state.

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    The SGP includes the Routing Context (Interface Identifiers) that
  identifies the Application Server for which the NTFY message is being
  sent.  If, however, the ASP is not configured for more than one
  Application Server, the Routing Context (Interface Identifier) MAY be
  excluded from the NTFY message as it is implied by configuration data.

    Otherwise, the "Notification Procedures" described by the UAs [1]
  apply also to LOADSEL.

    Examples are given in Section 5.

4.1.7.2.  ASP Override

    Whenever an ASP becomes active for a Load Selection in an Override
  Application Server, the Load Selector MUST be placed in a NTFY message
  with a Status Information indicating "Alternate ASP active in AS",
  along with the Routing Context (Interface Identifiers) for the
  associated AS and any ASP Identifier associated with the ASP for which
  the notification is being given.

    Otherwise, the "Notification Procedures" described by the UAs [1]
  apply also to LOADSEL.

4.1.8.  Registration Procedures

    LOADSEL provides the ability for the ASP to obtain a Load Selector
  value for a given range of traffic (Load Selection) using dynamic
  registration.

    When the ASP wishes to register a Load Selector as part of the
  normal registration procedure, it includes the Load Selection
  parameter in the REG REQ message to the SGP.  The Load Selection
  parameter describes the range of traffic load for which the ASP wishes
  to obtain a Load Selector value.

    When an SGP receives a REG REQ message with a Load Selection
  parameter, it will determine whether the Load Selection parameter
  describes a  non-overlapping load selection and then, if the
  registration of the associated Routing Key is successful, it assigns a
  Load Selector to the traffic range and returns the value in the Load
  Selector parameter in the REG RSP message.

    In addition to the normal registration procedures of the UAs, the
  following additional error conditions can occur:

  "Error - Unsupported Load Selection"

     This error MUST be sent in an Registration Response (REG RSP)
     message whenever the SG determines that the Load Selection provided
     in a REG REQ message has not been configured and the SG does not
     support dynamic allocation of Load Selectors for the specified Key,
     and MUST be sent in an Registration Response (REG RSP) message
     whenever the SG determines that the Load Selection provided in a
     REG REQ message is not supported by the SG.

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  "Error - Invalid Load Selection."

     If the SGP determines that the received Load Selection data is
     invalid, or contains invalid parameter values, the SGP returns a
     Registration Response (REG RSP) message to the ASP containing a
     Registration Result "Error - Invalid Load Selection".

  "Error - Cannot Support Unique Loadsharing."

     If the SGP determines that a unique Load Selection cannot be
     created, the SGP returns a Registration Response (REG RSP) message
     to the ASP, with a Registration Status of "Error - Cannot Support
     Unique Loadsharing." An incoming signalling message received at an
     SGP should not match against more than one Load Selection.

  "Error - Unsupported LS Parameter Field."

     If the SGP determines that one or more of the Load Selection
     parameters are not supported for the purpose of creating new Load
     Selection entries, the SGP returns a Registration Response (REG
     RSP) message to the ASP, containing a Registration Result "Error -
     Unsupported LS Parameter Field".  This result MAY be used if, for
     example, the SGP does not support the CIC Range parameter.

    Otherwise, the "Registration Procedures" described by the UAs [1]
  apply also to LOADSEL.

4.2.  Interworking Procedures

    LOADSEL supports the ASP Extension procedures described in ASPEXT
  [ASPEXT] and defines the following ASP Extension value:

      1   LOADSEL Extension

    The following procedures may be used where the ASPEXT procedures are
  not used:

    Whenever an ASP receives an ASPIA ACK not containing a Load Selector
  parameter in response to an ASPAC containing the parameter, the ASP
  will assume that the the SGP or IPSP does not support LOADSEL and MUST
  fall back to the non-Load Selection UA procedures.

    Whenever an ASP receives an ERR message or an unsuccessful REG RSP
  message indicating a problem with the Load Selection parameter in the
  REG REQ message, the ASP will assume that the SGP or IPSP does not
  support LOADSEL and MUST fall back to the non-Load Selection UA
  procedures.

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Notes for Section 4

  [1]  For a detailed description of these procedures, see Section 4
       of the SIGTRAN UA specifications cited under "References" [IUA-
       BIS..SUA, DUA..TUA].

  [2]  EXAMPLE:- An ASP (e.g, ASP-1) moving to state ASP-INACTIVE
       within a Load Selector (e.g, LS-1) results in the state of the
       AS moving to AS-PENDING.  The SGP sends NTFY("Application
       Server Pending") with "LS-1" in the Load Selector parameter in
       the NTFY message.  If immediately after (and before T(r)
       expires) another ASP (e.g, ASP-2) moves to state ASP-INACTIVE
       within another Load Selector (e.g, LS-2) resulting the state of
       the AS being "held" in the AS-PENDING state, the SGP sends
       NTFY("Application Server Pending") again, but this time
       includes both "LS-1" and "LS-2" in the Load Selector parameter
       in the NTFY message.

       EXAMPLE:- When all ASPs are inactive for a Load Selection
       within an Override AS, the AS will transition to the AS-PENDING
       state.  The SGP will send a NTFY("Application Server Pending")
       message to all ASPs configured for the Application Server that
       are not in the ASP-DOWN state.  This message should include in
       the Load Selector parameter the Load Selections in which there
       is no ASP in the ASP-ACTIVE state for the AS.

5.  Examples

    Figure 3 illustrates the example configuration that is used for all
  the examples in this section.  The example configuration consist of:

   + Two SGs (SG1 and SG2) acting as STPs in the SS7 network and
     consisting (for example) of a single SGP.  Each SG is connected to
     each of the ASPs in the example configuration.
   + Four ASPs (ASP1, ASP2, ASP3 and ASP4).  Each ASP is connected to
     both of the SGs in the example configuration.
   + Two Load Selections (LS1 and LS2) are associated with the
     Application Server.  The traffic that corresponds to each Load
     Selections is different in each example.

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                           SCTP
                           Associations  ________      _________
                _________   ............|        |    /         \
               |         |..:    .......|  ASP1  |   |    AS1    |
               |         |.....  :      |________|   |           |
       ________|   SG1   |....:  :                   | ......... |
              /|         |...::  :       ________    | :       : |
       \     / |_________|  :::..:......|        |   | :  LS1  : |
        \   /       |       ::   :......|  ASP2  |   | :.......: |
         \ /        |       ::   ::     |________|   |           |
          X         |       ::   ::                  |           |
         / \        |       ::   ::      ________    |           |
        /   \   ____|____   ::...::.....|        |   |           |
       /     \ |         |..:....::.....|  ASP3  |   | ......... |
       _______\|         |..:.....::    |________|   | :       : |
               |   SG2   |..:......:                 | :  LS2  : |
               |         |..:.....       ________    | :.......: |
               |_________|  :....:......|        |   |           |
                                 :......|  ASP4  |   |           |
                                        |________|    \_________/

                    Figure 3.  Example Configuration

5.1.1.  Initialization

  SG1   SG2                           ASP1  ASP2  ASP3  ASP4      AS1
   :     :                             :     :     :     :         :
   :<----:-Establish Association------>:     :     :     :         :
   :<----:-ASPUP-----------------------:     :     :     :         :
   :-----:-ASPUP ACK------------------>:     :     :     :         :
   :     :                             :     :     :     :         :
   :<----:-Establish Association-------:---->:     :     :         :
   :<----:-ASPUP-----------------------:-----:     :     :         :
   :-----:-ASPUP ACK-------------------:---->:     :     :         :
   :     :                             :     :     :     :         :
   :<----:-Establish Association-------:-----:---->:     :         :
   :<----:-ASPUP-----------------------:-----:-----:     :         :
   :-----:-ASPUP ACK-------------------:-----:---->:     :         :
   :     :                             :     :     :     :         :
   :<----:-Establish Association-------:-----:-----:---->:         :
   :<----:-ASPUP-----------------------:-----:-----:-----:         :
   :-----:-ASPUP ACK-------------------:-----:-----:---->:         :
   :     :                             :     :     :     :         :
   :     : (Same message exchange for SG2)   :     :     :         :
   :     :                             :     :     :     :         :

                   Figure 4.  Example - Initialization

    Figure 4 illustrates the common initialization procedure use for all
  of the examples.  Each ASP establishes an SCTP Association with SG1

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  and sends an ASPUP message to which it receives and ASP Up response.
  The ASPs are not statically configured to serve specific AS or LS
  within the AS, so no Notify messages are received.  The same sequence
  of messages are also exchanged with SG2.

5.2.  M3UA with Override AS and Load Selection based on CIC

    This example is for an M3UA [M3UA-BIS] configuration with the
  Application Server (AS1) configured with a Traffic Mode Type of
  Override.  The Application Server (AS1) has associated with it a
  Routing Key (RK1) that consists of a Destination Point Code that
  corresponds to the AS1 (MGC1) point code (PC1), an Originating Point
  Code that corresponds to a remote MGC2 point code (PC2), and the SI
  value for ISUP (SI=5).  The Load Selections (LS1 and LS2) correspond
  to two sets of CIC values which correspond to two different trunk
  groups between MGC1 and MGC2 (TG1 and TG2).

5.2.1.  Activation

  SG1   SG2                           ASP1  ASP2  ASP3  ASP4      AS1
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS1/RC1)--------------:     :     :     :         :
   :-----:-ASPAC ACK(LS1/RC1)--------->:     :     :     :         :
   :-----:-NTFY(AS_Act)(LS1/RC1)------>:     :     :     :  (LS1)  :
   :     :                             :     :     :     :         :
   :<----:-DATA----------------------->:<----:-----:-----:-------->:
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS2/RC1)--------------:-----:     :     :         :
   :-----:-ASPAC ACK(LS2/RC1)----------:---->:     :     :         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)-->:     :     :     :         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:---->:     :     :  (LS2)  :
   :     :                             :     :     :     :         :
   :<----:-DATA------------------------:---->:<----:-----:-------->:
   :     :                             :     :     :     :         :
   :<----:-ASPIA(LS1/RC1)--------------:-----:-----:     :         :
   :-----:-ASPIA ACK(LS1/RC1)----------:-----:---->:     :         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:---->:     :         :
   :     :                             :     :     :     :         :
   :<----:-ASPIA(LS1,LS2/RC1)----------:-----:-----:-----:         :
   :-----:-ASPIA ACK(LS1,LS2/RC1)------:-----:-----:---->:         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:-----:---->:         :
   :     :                             :     :     :     :         :
   :     : (Same message exchange for SG2)   :     :     :         :
   :     :                             :     :     :     :         :

                   Figure 5.  M3UA Example - Activation

    Figure 5 illustrates activation of the ASPs for Load Selections
  within the Override Application Server.  The sequence of events is as
  follows:

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   (1)   ASP1 sends an ASPAC message to SG1 identifying Load Selection
         LS1 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.  Data is transferred
         between the SG and ASP1 for Load Selection LS1 within AS1.

   (2)   ASP2 sends an ASPAC message to SG1 identifying Load Selection
         LS2 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.  ASP1 also receives
         notification that AS1/RC1 is active for LS2.  Data is
         transferred between the SG and ASP2 for Load Selection LS2
         within AS1.

   (3)   ASP3 sends an ASPIA message to SG1 identifying Load Selection
         LS1 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.

   (4)   ASP4 sends an ASPIA message to SG1 identifying Load Selection
         LS1 and LS2 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.

   (5)   The same exchange is repeated for SG2.

5.2.2.  Failure of ASP1

  SG1   SG2                           ASP1  ASP2  ASP3  ASP4      AS1
   :     :                             :     :     :     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA----------------------->:<----:-----:-----:-------->:
   :     :                             :     :     :     :         :
   :<----:-COMM LOST----------XXXX-----:     :     :     :         :
   :-----:-NTFY(ASP Fail)(ASP1)--------:---->:     :     :         :
   :-----:-NTFY(ASP Fail)(ASP1)--------:-----:---->:     :         :
   :-----:-NTFY(ASP Fail)(ASP1)--------:-----:-----:---->:         :
   :-----:-NTFY(AS_Pending)(LS1/RC1)---:---->:     :     :         :
   :-----:-NTFY(AS_Pending)(LS1/RC1)---:-----:---->:     :         :
   :-----:-NTFY(AS_Pending)(LS1/RC1)---:-----:-----:---->:         :
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS1/RC1)--------------:-----:-----:-----:         :
   :-----:-ASPAC ACK(LS1/RC1)----------:-----:-----:---->:         :
   :-----:-NTFY(AS_Active)(LS1,LS2/RC1):---->:     :     :         :
   :-----:-NTFY(AS_Active)(LS1,LS2/RC1):-----:---->:     :         :
   :-----:-NTFY(AS_Active)(LS1,LS2/RC1):-----:-----:---->:         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA------------------------:-----:-----:---->:<------->:
   :     :                             :     :     :     :         :

                Figure 6.  M3UA Example - Failure of ASP1

    Figure 6 illustrates the failure of ASP1.  The sequence of events is
  as follows:

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   (1)   Data for LS1 within AS1 is exchanged between SG1 and ASP1.
         Data for LS2 within AS1 is exchanged between SG1 and ASP2.

   (2)   Communication is lost between SG1 and ASP1.  ASP2, ASP3, and
         ASP4 are notified of the failure of ASP1 and the change of
         state of AS1 to AS-PENDING for LS1.  Data for LS2 in AS1 is
         unaffected.

   (3)   ASP4 (spare) responds to the AS-PENDING notification and
         activates for LS1 in AS1/RC1.  ASP2, ASP3 and ASP4 receive an
         AS-ACTIVE notification.  Data for LS1 in AS1 is now exchanged
         with ASP4.

5.2.3.  Sparing

  SG1   SG2                           ASP1  ASP2  ASP3  ASP4      AS1
   :     :                             :     :     :     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA----------------------->:<----:-----:-----:-------->:
   :<----:-DATA----------------------->:<----:-----:-----:-------->:
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS1/RC1)--------------:-----:-----:-----:         :
   :-----:-ASPAC ACK(LS1/RC1)----------:-----:-----:---->:         :
   :-----:-NTFY(Alt ASP)(ASP4)-------->:     :     :     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA------------------------:-----:-----:---->:<------->:
   :<----:-DATA------------------------:-----:-----:---->:<------->:
   :     :                             :     :     :     :         :

                    Figure 7.  M3UA Example - Sparing

    Figure 7 illustrates a sparing situation where one ASP takes over
  traffic from another so that the original ASP can be taken out of
  service.  The sequence of events is as follows:

   (1)   Data for LS1 in AS1 is exchange between SG1 and ASP1.

   (2)   ASP4 (spare) activates for LS1 in AS1 and receives and
         acknowledgement.  ASP4 has overridden ASP1 and a notification
         is sent to ASP1 that indicates that ASP4 in now the "Alternate
         ASP Active for AS".

   (3)   Data for LS1 in AS1 is now being exchanged between SG1 and
         ASP4.

   (4)   ASP1 can now be taken down and out of service.

5.3.  SUA with Load-share AS and Load Selection based on GT

    This example is for an SUA [SUA] configuration with the Application
  Server (AS1) configured with a Traffic Mode Type of Load-share.  The

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  Application Server (AS1) has associated with it (RK1) that consists of
  Destination Point Code and Subsystem Number that corresponds to the
  AS1 (HLR1) point code (PC1).  The Load Selections (LS1 and LS2)
  correspond to two sets of Global Titles which correspond to Mobile and
  GSTN numbering.

5.3.1.  Activation

  SG1   SG2                           ASP1  ASP2  ASP3  ASP4      AS1
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS1/RC1)--------------:     :     :     :         :
   :-----:-ASPAC ACK(LS1/RC1)--------->:     :     :     :         :
   :-----:-NTFY(AS_Act)(LS1/RC1)------>:     :     :     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA----------------------->:<----:-----:-----:-------->:
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS2/RC1)--------------:-----:     :     :         :
   :-----:-ASPAC ACK(LS2/RC1)----------:---->:     :     :         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)-->:     :     :     :         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:---->:     :     :         :
   :     :                             :     :     :     :  (LS2)  :
   :<----:-DATA------------------------:---->:<----:-----:-------->:
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS1/RC1)--------------:-----:-----:     :         :
   :-----:-ASPAC ACK(LS1/RC1)----------:-----:---->:     :         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:---->:     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA----------------------->:<----:-----:-----:-------->:
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :     :                             :     :     :     :         :
   :<----:-ASPIA(LS1,LS2/RC1)----------:-----:-----:-----:         :
   :-----:-ASPIA ACK(LS1,LS2/RC1)------:-----:-----:---->:         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:-----:---->:         :
   :     :                             :     :     :     :         :
   :     : (Same message exchange for SG2)   :     :     :         :
   :     :                             :     :     :     :         :

                   Figure 8.  SUA Example - Activation

    Figure 8 illustrates activation of the ASPs for Load Selections
  within the Load-share Application Server.  The sequence of events is
  as follows:

   (1)   ASP1 sends an ASPAC message to SG1 identifying Load Selection
         LS1 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.  Data is transferred
         between the SG and ASP1 for Load Selection LS1 within AS1.

   (2)   ASP2 sends an ASPAC message to SG1 identifying Load Selection
         LS2 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.  ASP1 also receives

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         notification that AS1/RC1 is active for LS2.  Data is
         transferred between the SG and ASP2 for Load Selection LS2
         within AS1.

   (3)   ASP3 sends an ASPAC message to SG1 identifying Load Selection
         LS1 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.  Data is load-shared
         between the SG and ASP1 and ASP3 for Load Selection LS1 within
         AS1.

   (4)   ASP4 sends an ASPAC message to SG1 identifying Load Selection
         LS1 and LS2 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.

   (5)   The same exchange is repeated for SG2.

5.3.2.  Failure of ASP1 and ASP2

  SG1   SG2                           ASP1  ASP2  ASP3  ASP4      AS1
   :     :                             :     :     :     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA----------------------->:<----:-----:-----:-------->:
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :     :                             :     :     :     :  (LS2)  :
   :<----:-DATA------------------------:---->:<----:-----:-------->:
   :     :                             :     :     :     :         :
   :<----:-COMM LOST----------XXXX-----:     :     :     :         :
   :-----:-NTFY(ASP Fail)(ASP1)--------:---->:     :     :         :
   :-----:-NTFY(ASP Fail)(ASP1)--------:-----:---->:     :         :
   :-----:-NTFY(ASP Fail)(ASP1)--------:-----:-----:---->:         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :     :                             :     :     :     :         :
   :<----:-COMM LOST----------XXXX-----:-----:     :     :         :
   :-----:-NTFY(ASP Fail)(ASP2)--------:-----:---->:     :         :
   :-----:-NTFY(ASP Fail)(ASP2)--------:-----:-----:---->:         :
   :-----:-NTFY(AS_Pending)(LS2/RC1)---:-----:---->:     :         :
   :-----:-NTFY(AS_Pending)(LS2/RC1)---:-----:-----:---->:         :
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS2/RC1)--------------:-----:-----:-----:         :
   :-----:-ASPAC ACK(LS2/RC1)----------:-----:-----:---->:         :
   :-----:-NTFY(AS_Active)(LS2/RC1)----:-----:---->:     :         :
   :-----:-NTFY(AS_Active)(LS2/RC1)----:-----:-----:---->:         :
   :     :                             :     :     :     :  (LS2)  :
   :<----:-DATA------------------------:-----:-----:---->:<------->:
   :     :                             :     :     :     :         :

            Figure 9.  SUA Example - Failure of ASP1 and ASP2

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    Figure 9 illustrates the failure of ASP1 followed by the failure of
  ASP2.  The sequence of events is as follows:

   (1)   Data for LS1 within AS1 is load-shared between ASP1 and ASP3.
         Data for LS2 within AS1 is exchanged with ASP2.

   (2)   Communication is lost between SG1 and ASP1.  ASP2, ASP3, and
         ASP4 are notified of the failure of ASP1.  Data for LS1 in AS1
         is directed toward ASP3 only.  Data for LS2 in AS1 is
         unaffected.

   (3)   Communication is lost between SG1 and ASP2.  ASP3 and ASP4 are
         notified of the failure of ASP1 as well of the AS1 state change
         to AS-PENDING.  Data for LS2 is queued at the SG.

   (4)   ASP4 (spare) responds to the AS-PENDING notification and
         activates for LS2 in AS1/RC1.  ASP3 and ASP4 receive an AS-
         ACTIVE notification.  Data for LS2 in AS1 is now exchanged with
         ASP4.

5.3.3.  Sparing

  SG1   SG2                           ASP1  ASP2  ASP3  ASP4      AS1
   :     :                             :     :     :     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA----------------------->:<----:-----:-----:-------->:
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS1/RC1)--------------:-----:-----:-----:         :
   :-----:-ASPAC ACK(LS1/RC1)----------:-----:-----:---->:         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA----------------------->:<----:-----:-----:-------->:
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :<----:-DATA------------------------:-----:-----:---->:<------->:
   :     :                             :     :     :     :         :
   :<----:-ASPIA(LS1/RC1)--------------:     :     :     :         :
   :-----:-ASPIA ACK(LS1/RC1)--------->:     :     :     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :<----:-DATA------------------------:-----:-----:---->:<------->:
   :     :                             :     :     :     :         :

                    Figure 10.  SUA Example - Sparing

    Figure 10 illustrates a sparing situation where one ASP takes over
  traffic from another so that the original ASP can be taken out of
  service.  The sequence of events is as follows:

   (1)   Data for LS1 in AS1 is load-shared between SG1 and ASP1 and
         ASP3.

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   (2)   ASP4 (spare) activates for LS1 in AS1 and receives and
         acknowledgement.  Data for LS1 in AS1 is now being load-shared
         between SG1 and ASP1, ASP3 and ASP4.

   (3)   ASP1 deactivates for LS1 in AS1 and receives and
         acknowledgement but no notification.

   (4)   Data or LS1 in AS1 is now load-shared between SG1 and ASP3 and
         ASP4.

   (5)   ASP1 can now be taken down and out of service.

5.4.  TUA with Broadcast AS and Load Selection based on DID

    This example is for an TUA [TUA] configuration with the Application
  Server (AS1) configured with a Traffic Mode Type of Broadcast.  The
  Application Server (AS1) has associated with it (RK1) that consists of
  Destination Point Code and Subsystem Number that corresponds to the
  AS1 (HLR1) point code (PC1).  The Load Selections (LS1 and LS2)
  correspond to two sets of Dialogue Ids which correspond to even and
  odd Dialogue Ids.

5.4.1.  Activation

  SG1   SG2                           ASP1  ASP2  ASP3  ASP4      AS1
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS1/RC1)--------------:     :     :     :         :
   :-----:-ASPAC ACK(LS1/RC1)--------->:     :     :     :         :
   :-----:-NTFY(AS_Act)(LS1/RC1)------>:     :     :     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA-(CorrId)-------------->:<----:-----:-----:-------->:
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS2/RC1)--------------:-----:     :     :         :
   :-----:-ASPAC ACK(LS2/RC1)----------:---->:     :     :         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)-->:     :     :     :         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:---->:     :     :         :
   :     :                             :     :     :     :  (LS2)  :
   :<----:-DATA-(CorrId)---------------:---->:<----:-----:-------->:
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS1/RC1)--------------:-----:-----:     :         :
   :-----:-ASPAC ACK(LS1/RC1)----------:-----:---->:     :         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:---->:     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA-(CorrId)---------------:-----:---->:<----:-------->:
   :     :                             :     :     :     :         :
   :<----:-ASPIA(LS1,LS2/RC1)----------:-----:-----:-----:         :
   :-----:-ASPIA ACK(LS1,LS2/RC1)------:-----:-----:---->:         :
   :-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:-----:---->:         :
   :     :                             :     :     :     :         :
   :     : (Same message exchange for SG2)   :     :     :         :
   :     :                             :     :     :     :         :

                   Figure 11.  TUA Example - Activation

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    Figure 11 illustrates activation of the ASPs for Load Selections
  within the Broadcast Application Server.  The sequence of events is as
  follows:

   (1)   ASP1 sends an ASPAC message to SG1 identifying Load Selection
         LS1 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.  Data is transferred
         between the SG and ASP1 for Load Selection LS1 within AS1.  The
         initial Data Messages for LS1 within AS1 are tagged with a
         Correlation Id.

   (2)   ASP2 sends an ASPAC message to SG1 identifying Load Selection
         LS2 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.  ASP1 also receives
         notification that AS1/RC1 is active for LS2.  Data is
         transferred between the SG and ASP2 for Load Selection LS2
         within AS1.  The initial Data Messages for LS2 within AS1 are
         tagged with a Correlation Id.

   (3)   ASP3 sends an ASPAC message to SG1 identifying Load Selection
         LS1 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.  Data is broadcast the SG
         and ASP1 and ASP3 for Load Selection LS1 within AS1.  The
         initial Data Messages for LS1 within AS1 are tagged with a
         Correlation Id.

   (4)   ASP4 sends an ASPIA message to SG1 identifying Load Selection
         LS1 and LS2 within Application Server AS1/RC1 and receives an
         acknowledgement and a notification.

   (5)   The same exchange is repeated for SG2.

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5.4.2.  Failure of ASP1 and ASP2

  SG1   SG2                           ASP1  ASP2  ASP3  ASP4      AS1
   :     :                             :     :     :     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA----------------------->:<----:---->:<----:-------->:
   :<----:-DATA----------------------->:<----:---->:<----:-------->:
   :     :                             :     :     :     :  (LS2)  :
   :<----:-DATA------------------------:---->:<----:-----:-------->:
   :     :                             :     :     :     :         :
   :<----:-COMM LOST----------XXXX-----:     :     :     :         :
   :-----:-NTFY(ASP Fail)(ASP1)--------:---->:     :     :         :
   :-----:-NTFY(ASP Fail)(ASP1)--------:-----:---->:     :         :
   :-----:-NTFY(ASP Fail)(ASP1)--------:-----:-----:---->:         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :     :                             :     :     :     :         :
   :<----:-COMM LOST----------XXXX-----:-----:     :     :         :
   :-----:-NTFY(ASP Fail)(ASP2)--------:-----:---->:     :         :
   :-----:-NTFY(ASP Fail)(ASP2)--------:-----:-----:---->:         :
   :-----:-NTFY(AS_Pending)(LS2/RC1)---:-----:---->:     :         :
   :-----:-NTFY(AS_Pending)(LS2/RC1)---:-----:-----:---->:         :
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS2/RC1)--------------:-----:-----:-----:         :
   :-----:-ASPAC ACK(LS2/RC1)----------:-----:-----:---->:         :
   :-----:-NTFY(AS_Active)(LS2/RC1)----:-----:---->:     :         :
   :-----:-NTFY(AS_Active)(LS2/RC1)----:-----:-----:---->:         :
   :     :                             :     :     :     :  (LS2)  :
   :<----:-DATA-(CorrId)---------------:-----:-----:---->:<------->:
   :     :                             :     :     :     :         :

                Figure 12.  TUA Example - Failure of ASP1

    Figure 12 illustrates the failure of ASP1 followed by the failure of
  ASP2.  The sequence of events is as follows:

   (1)   Data for LS1 within AS1 is broadcast to ASP1 and ASP3.  Data
         for LS2 within AS1 is exchanged with ASP2.

   (2)   Communication is lost between SG1 and ASP1.  ASP2, ASP3, and
         ASP4 are notified of the failure of ASP1.  Data for LS1 in AS1
         is directed toward ASP3 only.  Data for LS2 in AS1 is
         unaffected.

   (3)   Communication is lost between SG1 and ASP2.  ASP3 and ASP4 are
         notified of the failure of ASP1 as well of the AS1 state change
         to AS-PENDING.  Data for LS2 is queued at the SG.

   (4)   ASP4 (spare) responds to the AS-PENDING notification and
         activates for LS2 in AS1/RC1.  ASP3 and ASP4 receive an AS-

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         ACTIVE notification.  Data for LS2 in AS1 is now exchanged with
         ASP4.  Initial DATA messages for LS2 in AS1 are tagged with a
         Correlation Id.

5.4.3.  Sparing

  SG1   SG2                           ASP1  ASP2  ASP3  ASP4      AS1
   :     :                             :     :     :     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA----------------------->:<----:-----:-----:-------->:
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :     :                             :     :     :     :         :
   :<----:-ASPAC(LS1/RC1)--------------:-----:-----:-----:         :
   :-----:-ASPAC ACK(LS1/RC1)----------:-----:-----:---->:         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA----------------------->:<----:-----:-----:-------->:
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :<----:-DATA-(CorrId)---------------:-----:-----:---->:<------->:
   :     :                             :     :     :     :         :
   :<----:-ASPIA(LS1/RC1)--------------:     :     :     :         :
   :-----:-ASPIA ACK(LS1/RC1)--------->:     :     :     :         :
   :     :                             :     :     :     :  (LS1)  :
   :<----:-DATA------------------------:-----:---->:<----:-------->:
   :<----:-DATA------------------------:-----:-----:---->:<------->:
   :     :                             :     :     :     :         :

                    Figure 13.  TUA Example - Sparing

    Figure 13 illustrates a sparing situation where one ASP takes over
  traffic from another so that the original ASP can be taken out of
  service.  The sequence of events is as follows:

   (1)   Data for LS1 in AS1 is broadcast from SG1 to ASP1 and ASP3.

   (2)   ASP4 (spare) activates for LS1 in AS1 and receives and
         acknowledgement.  Data for LS1 in AS1 is now being broadcast
         from SG1 to ASP1, ASP3 and ASP4.  Initial data for LS1 in AS1
         is tagged with a Correlation Id.

   (3)   ASP1 deactivates for LS1 in AS1 and receives and
         acknowledgement but no notification.

   (4)   Data or LS1 in AS1 is now broadcast from SG1 to ASP3 and ASP4.

   (5)   ASP1 can now be taken down and out of service.

6.  Security

    LOADSEL does not introduce any new security risks or considerations
  that are not already inherent in the UA [IUA-BIS..SUA, DUA..TUA]
  Please see SIGTRAN Security document [SIGSEC] for security

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  considerations and recommendations that are applicable to each UA.

7.  IANA Considerations

    LOADSEL adds the following parameter tag value (described in Section
  3) to the Common Parameter numbering range of the SIGTRAN UAs [IUA-
  BIS..SUA, DUA..TUA]:

      Tag Value[1]   Parameter Name
      ------------------------------
         0x0018      Load Selector
         0x0019      Load Selection

    LOADSEL adds the following value to the Error Code parameter
  (described in Section 3 and 4) for the SIGTRAN UAs [IUA-BIS..SUA,
  DUA..TUA].

      29   Invalid Load Selector [2]

    LOADSEL adds the following values to the Registration Status field
  of the Registration Result parameter for the UAs [M2UA..SUA, ISUA,
  TUA].

      12   Error - Unsupported Load Selection [3]
      13   Error - Invalid Load Selection
      14   Error - Cannot Support Unique Loadsharing
      15   Error - Unsupported LS Parameter Field

Notes for Section 7

  [1]  EDITOR'S NOTE:-  The Load Selector and Load Selection tag
       values shown throughout this document as 0x0018) and 0x0019)
       will be assigned by IANA within the common parameter range of
       the SIGTRAN UAs and may change its value in further versions of
       this document.

  [2]  EDITOR'S NOTE:-  The Error Code value shown throughout this
       document as 29) will be assigned by IANA as a value of the
       common Error Code parameter for SIGTRAN UAs and may change its
       value in further versions of this document.

  [3]  EDITOR'S NOTE:-  The Registration Status values shown as 12,
       13, 14 and 15 will be assigned by IANA as a value of each UA-
       specific Registration Status parameter for each SIGTRAN UA and
       may change its value in further versions of this document.

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0.  Revision History

    This section provides historical information on the changes made to
  this draft.  This section will be removed from the document when the
  document is finalized.

0.4.  Changes from Version 0.3 to Version 0.4

   + updated to IETF boilerplate for first and last page.
   + updated references, version numbers and dates.

0.3.  Changes from Version 0.2 to Version 0.3

   + updated references, version numbers and dates.

0.2.  Changes from Version 0.1 to Version 0.2

   + added list of abbreviations.
   + moved history section here.
   + updated version numbers and dates.
   + updated references.
   + split reference section.
   + updated security section.
   + moved notes to end of document.

0.1.  Changes from Version 0.0 to Version 0.1

   + added this section,
   + updated release version and dates,
   + updated references,
   + updated postscript diagrams,
   + minor formatting changes,
   + updated author's address.

0.0.  Version 0.0

    The initial version of this document.

0.0.0.  Change Log

    $Log: draft-bidulock-sigtran-loadsel-04.me,v $
    Revision 0.9.2.3  2005/10/17 11:53:46  brian
    - updated drafts for republication

    Revision 0.9.2.2  2005/05/14 08:33:20  brian
    - copyright header correction

    Revision 0.9.2.1  2004/03/16 05:10:43  brian
    - Added drafts and figures.

    Revision 0.8.2.2  2003/08/01 12:23:15  brian
    Added abbreviations, updated format.

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R.  References

R.1.  Normative References

  [RFC 2119]  Bradner, S., "Key words for use in RFCs to Indicate
       Requirement Levels," RFC 2119 - BCP 14, The Internet Society
       (March 1997).

  [IUA-BIS]  Morneault, K., Rengasami, S., Kalla, M. and Sidebottom, G.,
       "ISDN Q.921-User Adaptation Layer," draft-ietf-sigtran-
       rfc3057bis-00.txt, The Internet Society (May 2003).  Work In
       Progress.

  [M2UA]  Morneault, K., Dantu, R., Sidebottom, G., Bidulock, B. and
       Heitz, J., "Signaling System 7 (SS7) Message Transfer Part 2
       (MTP2) - User Adaptation Layer," RFC 3331, Internet Engineering
       Task Force - Signalling Transport Working Group (September,
       2002).

  [M3UA-BIS]  Pastor, J., Morneault, K., "Signaling System 7 (SS7)
       Message Transfer Part 3 (MTP3)-User Adaptation Layer (M3UA),"
       <draft-ietf-sigtran-rfc3332bis-05.txt>, Internet Engineering Task
       Force - Signalling Transport Working Group (October 2005).  Work
       In Progress

  [SUA]  Loughney, J., Sidebottom, G., Coene, L., Verwimp, G., Keller,
       J. and Bidulock, B., "Signalling Connection Control Part User
       Adaptation Layer (SUA)," RFC 3868, Internet Engineering Task
       Force - Signalling Transport Working Group (October, 2004).

  [RFC 2960]  Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
       Schwarzbauer, H. J., Taylor, T., Rytina, I., Kalla, H., Zhang, L.
       and Paxson, V., "Stream Control Transmission Protocol (SCTP),"
       RFC 2960, The Internet Society (February 2000).

  [SIGSEC]  Loughney, J., Tuexen, M. and Pastor-Balbas, J., "Security
       Considerations for Signaling Transport (SIGTRAN) Protocols," RFC
       3788, Internet Engineering Task Force - Signalling Transport
       Working Group (June 2004).

R.2.  Informative References

  [DUA]  Mukundan, R., Mangalpally, N., Morneault, K. and Vydyam, A.,
       "Digital Private Network Signaling System (DPNSS)/Digital Access
       Signaling System 2 (DASS 2) Extensions to the IUA Protocol," RFC
       4129, Internet Engineering Task Force - Signalling Transport
       Working Group (August 2005).

  [V5UA]  Weilandt, E., Khanchandani, N. and Rao, S., "V5.2-User
       Adaption Layer (V5UA)," RFC 3807, Internet Engineering Task Force
       - Signalling Transport Working Group (June 2004).

  [GR303UA00]  Mukundan, R., Morneault, K., "GR-303 extensions to the

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       IUA Protocol," draft-ietf-sigtran-gr303ua-00.txt, Internet
       Engineering Task Force - Signalling Transport Working Group
       (December 2002).  Work In Progress

  [ISUA]  Bidulock, B., "SS7 ISUP-User Adaptation Layer (ISUA)," <draft-
       bidulock-sigtran-isua-03.txt>, Internet Engineering Task Force -
       Signalling Transport Working Group (October 16, 2005).  Work In
       Progress.

  [TUA]  Bidulock, B., "SS7 TCAP-User Adaptation Layer (TUA)," <draft-
       bidulock-sigtran-tua-04.txt>, Internet Engineering Task Force -
       Signalling Transport Working Group (October 16, 2005).  Work In
       Progress.

  [LOADGRP]  Bidulock, B., "Load Grouping Extension for Signalling User
       Adaptation Layers (LOADGRP)," <draft-bidulock-sigtran-
       loadgrp-04.txt>, Internet Engineering Task Force - Signalling
       Transport Working Group (October 16, 2005).  Work In Progress.

  [Q.704]  ITU, "Message Transfer Part - Signalling Network Functions
       and Messages," ITU-T Recommendation Q.704, ITU-T
       Telecommunication Standardization Sector of ITU, Geneva (March
       1993).  (Previously "CCITT Recommendation")

  [Q.723]  ITU, "Signalling System No. 7 - Telephone User Part - Formats
       and codes," ITU-T Recommendation Q.723, ITU-T Telecommunication
       Standardization Sector of ITU, Geneva (November 1988).
       (Previously "CCITT Recommendation")

  [Q.763]  ITU, "Signalling System No. 7 - Formats and Codes of the ISDN
       User Part," ITU-T Recommendation Q.763, ITU-T Telecommunication
       Standardization Sector of ITU, Geneva (March 1993).  (Previously
       "CCITT Recommendation")

  [Q.713]  ITU, "Signalling Connection Control Part Formats and Codes,"
       ITU-T Recommendation Q.713, ITU-T Telecommunication
       Standardization Sector of ITU, Geneva (March 1993).  (Previously
       "CCITT Recommendation")

  [Q.773]  ITU, "Signalling System No. 7 - Transaction Capabilities
       Formats and Encoding," ITU-T Recommendation Q.773, ITU-T
       Telecommunication Standardization Sector of ITU, Geneva (March
       1993).  (Previously "CCITT Recommendation")

  [ASPEXT]  Bidulock, B., "Application Server Process (ASP) Extension
       Framework," <draft-bidulock-sigtran-aspext-04.txt>, Internet
       Engineering Task Force - Signalling Transport Working Group
       (October 16, 2005).  Work In Progress.

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Acknowledgements

    The authors would like to thank Tolga Asveren, Ken Morneault, Barry
  Nagelberg, Benjamin J. Wilson, Jacques Rajchgod, Greg Sidebottom and
  Gery Verwimp for their valuable comments and suggestions.

Author's Addresses

  Brian Bidulock
  OpenSS7 Corporation
  1469 Jeffreys Crescent
  Edmonton, AB  T6L 6T1
  Canada

  Phone: +1-780-490-1141
  Email: bidulock@openss7.org
  URL: http//www.openss7.org/

  This draft expires April 2006.

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                        List of Illustrations

  Figure 1. Non-Load Selection Traffic Distribution ...............    4
  Figure 2. Load Selection Traffic Distribution ...................    6
  Figure 3. Example Configuration .................................   26
  Figure 4. Example - Initialization ..............................   26
  Figure 5. M3UA Example - Activation .............................   27
  Figure 6. M3UA Example - Failure of ASP1 ........................   28
  Figure 7. M3UA Example - Sparing ................................   29
  Figure 8. SUA Example - Activation ..............................   30
  Figure 9. SUA Example - Failure of ASP1 and ASP2 ................   31
  Figure 10. SUA Example - Sparing ................................   32
  Figure 11. TUA Example - Activation .............................   34
  Figure 12. TUA Example - Failure of ASP1 ........................   35
  Figure 13. TUA Example - Sparing ................................   36

                          Table of Contents

  Status of this Memo .............................................    1
  Copyright .......................................................    1
  Abstract ........................................................    1
  Contents ........................................................    2
  1 Introduction ..................................................    2
  1.1 Scope .......................................................    2
  1.2 Abbreviations ...............................................    2
  1.3 Terminology .................................................    2
  1.4 Overview ....................................................    3
  1.4.1 Non-Load Selection Traffic Distribution ...................    3
  1.4.2 Load Selection Traffic Distribution .......................    5
  Notes for Section 1 .............................................    7
  2 Conventions ...................................................    7
  3 Protocol Elements .............................................    7
  3.1 Parameters ..................................................    7
  3.1.1 Load Selector .............................................    7
  3.1.2 Load Selection ............................................    8
  3.2 Messages ....................................................   10
  3.2.1 Registration Request (REG REQ) ............................   10
  3.2.2 Registration Response (REG RSP) ...........................   11
  3.2.3 ASP Active (ASPAC) ........................................   12
  3.2.4 ASP Active Ack (ASPAC ACK) ................................   13
  3.2.5 ASP Inactive (ASPIA) ......................................   14
  3.2.6 ASP Inactive Ack (ASPIA ACK) ..............................   15
  3.2.7 Error (ERR) ...............................................   16
  3.2.8 Notify (NTFY) .............................................   17
  Notes for Section 3 .............................................   18
  4 Procedures ....................................................   19
  4.1 AS and ASP State Maintenance ................................   19
  4.1.1 ASP State .................................................   19
  4.1.2 AS State ..................................................   19
  4.1.3 ASP Up Procedures .........................................   20
  4.1.4 ASP Down Procedures .......................................   20
  4.1.5 ASP Active Procedures .....................................   21
  4.1.6 ASP Inactive Procedures ...................................   21

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  4.1.7 Notify Procedures .........................................   22
  4.1.8 Registration Procedures ...................................   23
  4.2 Interworking Procedures .....................................   24
  Notes for Section 4 .............................................   25
  5 Examples ......................................................   25
  5.1.1 Initialization ............................................   26
  5.2 M3UA with Override AS and Load Selection based on CIC .......   27
  5.2.1 Activation ................................................   27
  5.2.2 Failure of ASP1 ...........................................   28
  5.2.3 Sparing ...................................................   29
  5.3 SUA with Load-share AS and Load Selection based on GT .......   29
  5.3.1 Activation ................................................   30
  5.3.2 Failure of ASP1 and ASP2 ..................................   31
  5.3.3 Sparing ...................................................   32
  5.4 TUA with Broadcast AS and Load Selection based on DID .......   33
  5.4.1 Activation ................................................   33
  5.4.2 Failure of ASP1 and ASP2 ..................................   35
  5.4.3 Sparing ...................................................   36
  6 Security ......................................................   36
  7 IANA Considerations ...........................................   37
  Notes for Section 7 .............................................   37
  0 Revision History ..............................................   38
  0.4 Changes from Version 0.3 to Version 0.4 .....................   38
  0.3 Changes from Version 0.2 to Version 0.3 .....................   38
  0.2 Changes from Version 0.1 to Version 0.2 .....................   38
  0.1 Changes from Version 0.0 to Version 0.1 .....................   38
  0.0 Version 0.0 .................................................   38
  0.0.0 Change Log ................................................   38
  R References ....................................................   39
  R.1 Normative References ........................................   39
  R.2 Informative References ......................................   39
  Acknowledgements ................................................   41
  Author's Addresses ..............................................   41
  List of Illustrations ...........................................   42
  Table of Contents ...............................................   42

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Intellectual Property

  The IETF takes no position regarding the validity or scope of any
  Intellectual Property Rights or other rights that might be claimed to
  pertain to the implementation or use of the technology described in
  this document or the extent to which any license under such rights
  might or might not be available; nor does it represent that it has
  made any independent effort to identify such rights.  Information on
  the procedures with respect to rights in RFC documents can be found in
  BCP 78 and BCP 79.

  Copies of IPR disclosures made to the IETF Secretariat and any
  assurances of licenses to be made available, or the result of an
  attempt made to obtain general license or permission for the use of
  such proprietary rights by implementers or users of this specification
  can be obtained from the IETF on-line IPR repository at
  http://www.ietf.org/ipr.

  The IETF invites any interested party to bring to its attention any
  copyrights, patents or patent applications, or other proprietary
  rights that may cover technology that may be required to implement
  this standard.  Please address to the IETF at ietf-ipr@ietf.org.

Disclaimer of Validity

  This document and the information contained herein is provided on an
  "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
  OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
  ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
  INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
  INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
  WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Full Copyright Statement

  Copyright (C) The Internet Society (2005).  This document is subject
  to the rights, licenses and restrictions contained in BCP 78, and
  except as set forth therein, the authors retain all their rights.

Acknowledgement

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

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