Network Working Group                                   Ken Morneault
INTERNET-DRAFT                                          Cisco Systems
                                                        Mallesh Kalla
                                                            Telcordia
                                                      Greg Sidebottom
                                                      Nortel Networks
                                                            Ram Dantu
                                                             IPMobile
                                                           Tom George
                                                              Alcatel

Expires in six months                                   December 1999                                      March 2000

                  SS7 MTP2-User Adaptation Layer
                  <draft-ietf-sigtran-m2ua-02.txt>
                  <draft-ietf-sigtran-m2ua-03.txt>

Status of This Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups.  Note that other groups may also distribute
working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
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Abstract

This Internet Draft defines a protocol for backhauling of SS7 MTP2
User signaling messages over IP using the Simple Control Transmission
Protocol (SCTP).  One application of this  This protocol would be to use it used between a Signaling
Gateway (SG) and Media Gateway Controller (MGC).
In this case, the Signaling Gateway would be acting as a Signaling
Link Terminal.  Another application of this protocol would be to use
it between a SG and a SCP.  In either application, it  It is assumed that
the SG receives SS7 signaling over a standard SS7 interface using the
SS7 Message Transfer Part (MTP) to provide transport.  The Signaling
Gateway would act as a Signaling Link Terminal.

                        TABLE OF CONTENTS

1.  Introduction..............................................2
  1.1  Scope..................................................2
  1.2  Terminology............................................3
  1.3  Signaling Transport Architecture.......................3
  1.4  Services Provide by the M2UA Adaptation Layer..........4 Layer..........6
  1.5  Function Provided by the M2UA Layer....................6 Layer....................8
  1.6  Definition of the M2UA Boundaries......................7 Boundaries......................9
2.  Protocol Elements.........................................8 Elements.........................................9
  2.1  Common Message Header..................................8 Header.................................10
  2.2  M2UA Message Header....................................9 Header...................................11
  2.3  M2UA Messages.........................................10 Messages.........................................11
3.  Procedures...............................................17  Procedures...............................................20
  3.1  Procedures to Support Service in Section 1.4.1........17 1.4.1........20
  3.2  Procedures to Support Service in Section 1.4.2........17 1.4.2........21
  3.3  Procedures to Support Service in Section 1.4.3........17 1.4.3........21
4.  Examples of MTP2 User Adaptation (M2UA) Procedures.......22 Procedures.......26
  4.1  Establishment of associations between SG and MGC......22 MGC......26
       examples
  4.2  MTP Level 2 / MTP Level 3 Boundary Examples...........23 Examples...........28
  4.3  Layer Management Communication Examples................25 Examples...............29
5.  Security.................................................31  Security.................................................30
6.  Acknowledgements.........................................31  IANA Considerations......................................31
7.  References...............................................31  Acknowledgements.........................................31
8.  References...............................................32
9.  Author's Addresses.......................................32 Addresses.......................................33

1.  Introduction

1.1 Scope

There is a need for SCN signaling protocol delivery from an Signaling
Gateway (SG) to a Media Gateway Controller (MGC) or IP Signaling Point
(IPSP).  The delivery mechanism should meet the following criteria:

*  Support for MTP Level 2 / MTP Level 3 interface boundary
*  Support for communication between Layer Management modules on SG and
   MGC
*  Support for management of active associations between the SG and MGC

In other words, the Signaling Gateway will transport MTP Level 3
messages to a Media Gateway Controller (MGC) or IP Signaling Point
(IPSP).  In the case of delivery from an SG to an IPSP, both the SG and
IPSP function as traditional SS7 nodes using the IP network as a new
type of SS7 link.  This allows for full MTP Level 3 message handling
and network management capabilities.

1.2 Terminology

MTP2-User - A protocol that normally uses the services of MTP Level 2
(i.e. MTP3).

Interface - For the purposes of this document, an interface is a SS7
signaling link.

Association - An association refers to a SCTP association.  The
association will provide the transport for the delivery of protocol
data units for one or more interfaces.

Stream - A stream refers to a SCTP stream.

Backhaul - Refers to the transport of signaling from the point of
interface for the associated data stream (i.e., SG function in the MGU)
back to the point of call processing (i.e., the MGCU), if this is not
local [4].

Application Server (AS) - A logical entity serving a specific application
instance.  An example of an Application Server is a MGC handling the
MTP Level 3 and call processing for SS7 links terminated by the
Signaling Gateways.  Practically speaking, an AS is modeled at the SG
as an ordered list of one or more related Application Server Processes
(e.g., primary, secondary, tertiary, Ó). ...).

Application Server Process (ASP) - A process instance of an Application
Server.  Examples of Application Server Processes are primary or backup
MGC instances.

Application Server Process Path (ASP Path or just Path) - A Path to a
remote Application Server Process instance.  A Path maps 1:1 to an SCTP
association.

Fail-over - The capability to re-route signaling traffic as required
to a next-preferred an alternate Application Server Process Process, or group of ASPs, within
an Application Server in the event of failure or unavailability of the a
currently used Application Server Process (e.g., from primary MGC to back-up MGC).
Fail-over Process.  Fail-back may also apply upon
the return to service of a previously unavailable Application Server
Process.

Signaling Link Terminal (SLT) - Refers to the means of performing all
of the functions defined at MTP level 2 regardless of their
implementation [2].

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

Layer Management - Layer Management is a nodal function in an SG or
ASP that handles the inputs and outputs between the M2UA layer and a
local management entity.

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

Stream - A stream refers to an SCTP stream.

1.3 Signaling Transport Architecture

The framework architecture that has been defined [4] for SCN signaling
transport over IP [5] uses multiple components, including an IP transport
protocol, a signaling
common transport protocol (SCTP) and an adaptation module to support the functions
services expected by a particular SCN signaling protocol from its
underlying protocol layer.

In reference to the SIGTRAN

Within this framework architecture [4], architecture, this document defines a SCN
adaptation module that is suitable for the transport of SS7 MTP2 User. User
messages.  The only SS7 MTP2 User is MTP3.  The M2UA uses the services
of the Simple Common Transport protocol [6] as the underlying reliable
signaling common transport protocol.

In a Signaling Gateway, it is expected that the SS7 MTP2-User signaling
is transmitted and received from the PSTN over a standard SS7 network
interface, using the SS7 Message Transfer Part Level 1 and Level 2 [3,4]
to provide reliable transport of the MTP3-User signaling messages to and
from an SS7 Signaling End Point (SEP) or Signaling Transfer Point (STP).
The SG then provides a functional inter-working of transport functions
with the IP transport, in order to transfer the MTP2-User signaling
messages to and from an Application Server Process where the peer MTP2-
User protocol layer exists.

1.3.1  Case 1:  Example - SG to MGC

In a Signaling Gateway, it is expected that the SS7 signaling is
received over a standard SS7 network termination, using the SS7 Message
Transfer Part (MTP) to provide transport of SS7 signaling messages to
and from an SS7 Signaling End Point (SEP) or SS7 Signaling Transfer
Point (STP).  In other words, the SG acts as a Signaling Link Terminal
(SLT) [2].  The SG then provides interworking of transport functions
with IP Signaling Transport, in order to transport the MTP3 signaling
messages to the MGC where the peer MTP3 protocol layer exists, as shown
below:

    ******    SS7    ******      IP     *******
    *SEP *-----------* SG *-------------* MGC *
    ******           ******             *******

    +----+                              +----+
    |S7UP|                              |S7UP|
    +----+                              +----+
    |MTP +                              |MTP |
    |S7UP|
    | L3 |            (NIF)             |L3  |
    +----+         +----+----+          +----+
    |MTP |         |MTP |M2UA|          |M2UA|
    |L3
    |    |         |    +----+          +----+
    |L2  |         |L2  |SCTP|          |SCTP|
    |L1  |         |L1  +----+          +----+
    |    |         |    |UDP    |IP  |          |UDP          |IP  |
    +----+         +---------+          +----+

    NIF  - Nodal Interworking Function
    SEP  - SS7 Signaling Endpoint
    UDP
    IP   - User Datagram Internet Protocol
    SCTP - Simple Control Transmission Protocol
           (Refer to Reference [5])

            Figure 1: 1  M2UA in the SG to MGC Application

Note: STPs may be present in the SS7 path between the SEP and the SG.

1.3.2  Case 2:  SG to IPSP

The following figure shows Signaling Network Architecture

A Signaling Gateway will support the seamless interworking at transport of MTP2-User signaling
traffic received from the MTP3
layer.  MTP3 is adapted SS7 network to one or more distributed ASPs
(e.g., MGCs).  Clearly, the SCTP layer using MTP2 User Adaptation
Layer (M2UA).  In this example, the Signaling Gateway could be an STP.
All M2UA protocol description cannot in itself
meet any performance and reliability requirements for such transport.
A physical network architecture is required, with data on the primitives between MTP3
availability and MTP2 are supported by M2UA.  Any transfer performance of the physical nodes involved in
any particular exchange of information.  However, the diagram could have SCCP or other M2UA protocol must
be flexible enough allow its operation and management in a variety of
physical configurations that will enable Network Operators to meet
their performance and reliability requirements.

To meet the stringent SS7 user parts.

    ****** signaling reliability and performance
requirements for carrier grade networks, these Network Operators should
ensure that there is no single point of failure provisioned in the end-
to-end network architecture between an SS7  ****** node and an IP      ************
    *SEP *-------* ASP.  Depending
of course on the reliability of the SG *-------------*   IPSP and ASP functional elements, this
can typically be met by the spreading links in a linkset across SGs, the
provision of redundant QOS-bounded IP network paths for SCTP Associations
between SCTP End Points, and redundant Hosts.  The distribution of ASPs
within the available Hosts is also important.  For a particular
Application Server, the related ASPs should be distributed over at least
two Hosts.

An example physical network architecture relevant to carrier-grade
operation in the IP network domain is shown in Figure 2 below:

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

    +----+                           +---------+
    |TCAP|      *_________________________________________*  ********  * Host1
  *      *                                _________*  * ASP1 *  *
  *  SG1 *   SCTP Associations           |   TCAP         *  ********  *
  *      *_______________________        |
    +----+                           +---------+
    |SCCP|         *            *
  ********                       |   SCCP       |
    +----+    +---------+            +---------+
    |MTP         **************
                                 |       |   MTP
  ********                       |       |   MTP
  *      *_______________________________|
  *      *                       |
    |L3  |    |   L3    |            |    L3   |
    |L2  |    +----+----+            +----+----+
    |L1  |    |MTP |M2UA|            |M2UA|MTP |
    |    |    |L2  +----+            +----+L2  |
    |    |    |L1  |SCTP|            |SCTP|L1  |
    |    |    |    |----|            |----|
  *  SG2 *    SCTP Associations  |
  *      *____________           |
  *      *            |          |    |UDP
  ********            |            |UDP          |                 **************
                      |
    +----+    +----+----+            +----+----+

    SEP   - SS7 Signaling Endpoint
    IPSP  - IP Signaling Point
    UDP   - User Datagram Protocol
    SCTP  - Simple Control Transmission Protocol
            (Refer to Reference [5])          |_________________*  ********  * Host2
                      |____________________________*  * ASP1 *  *
                                                   *  ********  *
                                                   *            *
                                                   **************
                                                           .
                                                           .
                                                           .

                    Figure 2:  M2UA 2 - Physical Model Example

For carrier grade networks, Operators should ensure that under failure
or isolation of a particular ASP, stable calls or transactions are not
lost.  This implies that ASPs need, in some cases, to share the SG call/-
transaction state or be able to IPSP Application

In this case, pass the SCTP association acts as an SS7 link call/transaction state between
each other.  Also, in the SG
and case of ASPs performing call processing,
coordination may be required with the related Media Gateway to transfer
the MGC control for a particular trunk termination.  However, this
sharing or communication is outside the IPSP. scope of this document.

1.3.4  ASP Fail-over Model and Terminology

The association contains two streams, one M2UA supports ASP fail-over functions in each
direction.  The IPSP may or may not have order to support a termination high
availability of call and transaction processing capability.  All MTP2-
User messages incoming to an SG from the SS7
network.

1.3.3  UDP port

A request will be made to IANA network are assigned to assign a UDP port for M2UA.

1.4  Services Provided by
unique Application Server, based on the M2UA Adaptation Layer Interface Identifier of the
message.

The SS7 MTP3/MTP2(MTP2-User) interface Application Server is retained at the termination
point in the IP network, so that the M2UA protocol layer is required to
provide the equivalent set practical terms a list of services all ASPs currently
registered to its users as provided by process MTP2-User messages from certain Interface
Identifiers.  One or more ASPs in the
MTP Level 2 to MTP Level 3.

This includes list are normally active (i.e.,
handling traffic) while any others may be unavailable or inactive, to be
possibly used in the following services:

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

Also provision event of failure or unavailability of the active
ASP(s).

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

To avoid a single point of the MTP2-User peers failure, it is recommended that a minimum of
two ASPs be in the SS7 list, resident in separate hosts  and
IP domains.  This includes

Data

Provides therefore
available over different SCTP Associations.  For example, in the ability
network shown in Figure 1, all messages to transport MTP2 User information (in DPC x could be sent to ASP1
in Host1 or ASP1 in Host2.  The AS list at SG1 might look like this:

    Interface Identiers - Application Server #1
        ASP1/Host1  - State=Up, Active
        ASP1/Host2  - State=Up, Inactive

In this ˘1+1÷ redundancy case,
MTP Level 3 PDUs).

Link Establish

Provides the ability to request MTP Level 2 to bring SS7 links
in-service.

Link Release

Provides the ability to request MTP Level 2 to take SS7 links out-of-
service.  Also, provides mechanism ASP1 in Host1 would be sent any incoming
message for MTP2 to autonomously indicate
that SS7 link(s) have gone out-of-service.

Link State

Provides the ability to request state change or information on a
per link basis.  Some examples Interface Identifiers registered.  ASP1 in Host2 would
normally be brought to the forcing of Local Processor
Outage active state upon failure of, or flushing buffers.

Link Status

Provides a means for asychronous notification loss of link state changes to
be reported to
connectivity to, ASP1/Host1.  In this example, both ASPs are Up, meaning
that the upper layer (MTP Level 3).  An examples related SCTP association and far-end M2UA peer is ready.

The AS List at SG1 might also be set up in loadshare mode:

    Interface Identifiers - Application Server #1
        ASP1/Host1 - State = Up, Active
        ASP1/Host2 - State = Up, Active

In this case, both the ASPs would be sent a portion of the
reporting traffic.

In the process of remote processor
outage event.

Data Retrieval

Provides a mechanism to perform SS7 link changeover procedure fail-over or fail-back, it is recommended that in the
case of a SS7 link failure.

1.4.2  Support for communication between Layer Management modules
       on SG and MGC ASPs supporting call processing, stable calls do not fail.  It
is envisioned that the M2UA layer needs to provide some messages possible that
will facilitate calls in ˘transition÷ may fail, although measures of
communication between Layer Management modules on the SG
and MGC.

To facilitate reporting of errors that arise because of backhauling MTP
Level 3 scenario, the following primitive is defined:

M-ERROR

The M-ERROR message is ASPs involved can be used to indicate mitigate this.
For example, the two ASPs may share call state via shared memory, or may
use an error with a received
M2UA message (e.g., interface identifier value is not known ASP to the SG).

1.4.3  Support for management of active associations between SG and MGC ASP protocol to pass call state information.

1.3.5 Client/Server Model

The M2UA layer on the SG keeps takes on the state role of various ASPs it server while the ASP is associated
with.  A set of primitives between M2UA layer and the Layer Management
are defined below client.  ASPs
must initiate the SCTP association to help the SG.

The SCTP (and UDP/TCP) Registered User Port Number Assignment for M2UA
is 2904.

1.4  Services Provided by the M2UA Adaptation Layer Management manage

The SS7 MTP3/MTP2(MTP2-User) interface is retained at the association(s)
between termination
point in the SG and IP network, so that the MGC.

M-SCTP ESTABLISH

The M-SCTP ESTABLISH primitive M2UA protocol layer is used required to request, indicate and confirm
provide the establishment equivalent set of SCTP association services to a peer M2UA node.

The M2UA layer may also need its users as provided by the
MTP Level 2 to inform MTP Level 3.

This includes the status following services:

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

Also provision is made for protocol elements that enable a seamless, or
as seamless as possible, operation of the SCTP
association(s) to MTP2-User peers in the Layer Management. SS7 and
IP domains.  This can be achieved using includes

Data

Provides the following primitive.

M-SCTP STATUS

The M-SCTP STATUS primitive is used ability to transport MTP2 User information (in this case,
MTP Level 3 PDUs).

Link Establish

Provides the ability to request and MTP Level 2 to bring SS7 links
in-service.

Link Release

Provides the ability to request MTP Level 2 to take SS7 links out-of-
service.  Also, provides mechanism for MTP2 to autonomously indicate
that SS7 link(s) have gone out-of-service.

Link State

Provides the status
of underlying SCTP association(s).

The Layer Management may need ability to inform request state change or information on a
per link basis.  Some examples would be the M2UA layer forcing of Local Processor
Outage or flushing buffers.

Link Status

Provides a user status
(i.e., failure, active, etc.), so that messages can be exchanged between
M2UA layer peers means for asynchronous notification of link state changes to stop traffic
be reported to the local M2UA user.  This can upper layer (MTP Level 3).  An example would be
achieved using the following primitive.

M-ASP STATUS

The M-ASP STATUS primitive is used by the Layer Management to indicate
the status
reporting of the local M2UA user remote processor outage event.

Data Retrieval

Provides a mechanism to perform SS7 link changeover procedure in
the M2UA layer.

1.5  Functions Provided by the M2UA Layer

1.5.1  Mapping

The M2UA layer must maintain a map case of a Interface ID to a physical
interface SS7 link failure.

1.4.2  Support for communication between Layer Management modules
       on SG and MGC

It is envisioned that the Signaling Gateway.  A physical interface would be a
V.35 line, T1 line/timeslot, E1 line/timeslot, etc.   The M2UA layer
must also maintain a map of Interface ID needs to SCTP association provide some messages that
will facilitate communication between Layer Management modules on the SG
and MGC.

To facilitate reporting of errors that arise because of backhauling MTP
Level 3 scenario, the following primitive is defined:

M-ERROR

The M-ERROR message is used to indicate an error with a
stream within received
M2UA message (e.g., interface identifier value is not known to the association.

1.5.2  Status SG).

1.4.3  Support for management of ASPs active associations between SG and MGC

The M2UA layer on the Signaling Gateway must maintain SG keeps the state of one or
more Application Server Process(es) various ASPs it is associated
with.  The state of
an ASP changes because of reception of peer-to-peer messages or reception  A set of indications from the local SCTP association.  ASP state transition
procedures are described in Section Section 3.3.

1.5.3  Flow Control / Congestion

It is possible for the primitives between M2UA layer to be informed of IP network congestion
by means of an implementation-dependent function  (i.e. an indication
from the SCTP).  If and the M2UA layer Layer Management
are defined below to help the Layer Management manage the association(s)
between the SG and the MGC.

M-SCTP ESTABLISH

The M-SCTP ESTABLISH primitive is used to request, indicate and confirm
the establishment of SCTP association to a peer M2UA node.

The M2UA layer may also need to inform the status of the SCTP
association(s) to the Layer Management.  This can be achieved using
the following primitive.

M-SCTP STATUS

The M-SCTP STATUS primitive is used to request and indicate the status
of underlying SCTP association(s).

The Layer Management may need to inform the M2UA layer of a user status
(i.e., failure, active, etc.), so that messages can be exchanged between
M2UA layer peers to stop traffic to the local M2UA user.  This can be
achieved using the following primitive.

M-ASP STATUS

The M-ASP STATUS primitive is used by the Layer Management to indicate
the status of the local M2UA user to the M2UA layer.

1.5  Functions Provided by the M2UA Layer

1.5.1  Mapping

The M2UA layer must maintain a map of a Interface ID to a physical
interface on the Signaling Gateway.  A physical interface would be a
V.35 line, T1 line/timeslot, E1 line/timeslot, etc.   The M2UA layer
must also maintain a map of Interface Identifier to SCTP association
and to the related stream within the association.

1.5.2  Flow Control / Congestion

It is possible for the M2UA layer to be informed of IP network congestion
by means of an implementation-dependent function  (i.e. an indication
from the SCTP).  If the M2UA layer receives this indication, the action(s)
taken are implementation dependent.

1.5.4

1.5.3  SCTP Stream Management

SCTP allows user specified number of streams to be opened during the
initialization.  It is the responsibility of the M2UA layer to ensure
proper management of these streams.  SCTP streams provide a means for
avoiding head of line blocking.  For that reason, a stream will should be used
per SS7 signaling link terminated by the Signaling Gateway.  The SS7
signaling link can be identified by the optional Interface Identifier
in the M2UA specific message header (refer to Section 2.2).

1.5.5

1.5.4  Seamless SS7 Network Management Interworking

If the SG loses the SCTP association to the MGC, it should follow
MTP 2 processor outage procedures [2].

1.5.6

1.5.5  Management Inhibit/Uninhibit

Local Management at an ASP or SG may wish to stop traffic across an
SCTP association in order to temporarily remove the association from
service or to perform testing and maintenance activity.  The function
could optionally be used to manage control the start of traffic on to a newly-available newly-
available SCTP association.

1.5.6  Active Association Control

At an SG, an Application Server list may contain active and inactive
ASPs to support ASP loads-haring and fail-over procedures. When, for
example, both a primary and a back-up ASP are available, M2UA peer
protocol is required to control which ASP is currently active.  The
ordered list of ASPs within a logical Application Server is kept
updated in the SG to reflect the active Application Server Process(es).

1.6  Definition of the M2UA Boundaries

1.6.1  Definition of the M2UA / MTP Level 3 boundary

DATA
ESTABLISH
RELEASE
STATE
STATUS
RETRIEVAL
DATA RETRIEVAL
DATA RETRIEVAL COMPLETE

1.6.2  Definition of the M2UA / MTP Level 2 boundary

DATA
ESTABLISH
RELEASE
STATE
STATUS
RETRIEVAL
DATA RETRIEVAL
DATA RETRIEVAL COMPLETE

1.6.3  Definition of the Lower Layer Boundary between M2UA and SCTP

The upper layer and layer management primitives provided by SCTP are
provided in Reference [6] Section 9.

1.6.4  Definition of Layer Management / M2UA Boundary

M-ERROR
M-SCTP ESTABLISH
M-SCTP STATUS
M-ASP STATUS

2.0  Protocol Elements

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

2.1  Common Message Header

The protocol messages for MTP2 User MTP2-User Adaptation require a message header
structure which contains a version, message type type, message length, and
message length. contents.   This message header is common among all SCN signaling
protocol adaptation layers. layers:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8    15 16           31
   +---------------+---------------+ 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Vers    Version    |     Spare     |   Msg         Message Type          |
   +---------------+---------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Message Length                         |
   +-------------------------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 2 3  Common Message Header

All fields in an M2UA message MUST be transmitted in the network byte
order, unless otherwise stated.

2.1.1  Version

The version field (vers) contains the version of the M2UA adapation
layer.  The supported versions are:

      01

      0000 0001   Release 1.0 of M2UA adaptation protocol

2.1.2  Message Type

The valid message types are defined in Section 2.2.2 and the message
contents are described in Section 2.3.  Each message can contain
parameters.

The following list contains the message types for the defined messages.

     MTP2 User Adaptatation (MAUP) Messages

        Data Request                                       0601
        Data Indication                            0602
        Establish Request                          0603                          0602
        Establish Confirm                          0604                          0603
        Release Request                            0605                            0604
        Release Confirm                            0606                            0605
        Release Indication                         0607                         0606
        State Request                              0608                              0607
        State Confirm                              0609                              0608
        State Indication                           060a                           0609
        Data Retrieval Request                     060b                     060a
        Data Retrieval Confirm                     060c                     060b
        Data Retrieval Indication                  060d                  060c
        Data Retrieval Complete Indication         060e         060d

     Application Server Process Maintenance (ASPM) Messages

        ASP Up (ASPUP)                             0301
        ASP Down (ASPDN)                           0302
        ASP Active (ASPAC)                         0401
        ASP Inactive (ASPIA)                       0402
     Management (MGMT) Messages

        Error                                      0001                                      0000

2.1.3  Message Length

The Message length defines the length of the message in octets, not
including the header.

2.2  M2UA Message Header

In addition to the common message header, there will be a M2UA specific
message header.  The M2UA specific message header will immediately
follow the common message header, but will only be used with MAUP and
MGMT messages.

This message header will contain the Interface Identifier.  The
Interface Identifier identifies the physical interface at the SG for
which the signaling messages are sent/received.  Or, the Interface Identifier

can be left empty (a null string of length zero).  The format of the
Interface Identifier
follows the same endpoint naming scheme provided in MGCP [7].  For example,
if a Signaling Gateway terminates a E1 and the SS7 signaling link parameter is one
timeslot 16, the interface identifier could be an integer, the following:

       e1/16@sgw1.example.net

The use values of wildcards is not acceptable.

Ed's Note:  The Interface Identifier string should be padded which are
assigned according to 32-bit
boundaries. network operator policy.  The length field indicates the end values used are of
local significance only, coordinated between the string. SG and ASP.

    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            15 16           31
   +---------------+---------------+ 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x1)           |     Length           Length=4            |
   +-------------------------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Interface Identifier                     |

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

                Figure 3 4  M2UA Message Header

The Tag value for Interface Identifier is 0x1.  The length provides the
length is always
set to a value of the Interface Identifier string in bytes. 4.

2.3 M2UA Messages

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

2.3.1 MTP2 User Adaptation Messages

2.3.1.1 Data (Request, Indication)

The Data message contains an SS7 MTP2-User Protocol Data Unit (PDU).  The
Data message contains the protocol data.

The format for the Data Message parameters is as follows:

    0            15 16           31
   +-------------------------------+
                   ...                   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                       Protocol Data                           |
                   ...
   +---------------+---------------+

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

The Protocol Data field contains the MTP2-User application message. message in
network byte order.

2.3.1.2  Establish (Request, Confirmation)

The Establish Request message is used to establish the channel link or to
indicate that the channel has been established.  Note that the gateway
may already have the channel SS7 link established at its layer.  If so, upon
receipt of an Establish Request, the gateway takes no action except to
send an Establish Confirm.

    0            15 16           31
   +---------------+---------------+
   |             State             |
   +---------------+---------------+

The valid values mode (Normal of Emergency) for bringing the link in service is
defaulted to Normal.  The State are shown Request (described in Section 2.3.1.4
below) can be used to change the following table.

         Define            Value          Description
   ESTABLISH_NORMAL        0x0     Follow normal procedure for
                                    establishing a SS7 link
   ESTABLISH_EMERGENCY     0x1     Follow emergency procedure for
                                    establishing a SS7 link mode to Emergency.

2.3.1.3  Release (Request, Indication, Confirmation)

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

    0            15 16           31
   +---------------+---------------+                   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Reason                            |
   +---------------+---------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

      Define     Value           Description
   RELEASE_MGMT   0x0     Management layer generated release. release
   RELEASE_PHYS   0x1     Physical layer alarm generated release. release
   RELEASE_SIOS   0x2     Receipt of SIOS
   RELEASE_OTHER
   RELEASE_T6     0x3     Release due to expiration of Timer T6
   RELEASE_T7     0x4     Release due to expiration of Timer T7
   RELEASE_BSN    0x5     Release due to invalid BSN (2 of 3)
   RELEASE_FIB    0x6     Release due to invalid FIB (2 of 3)
   RELEASE_SUERM  0x7     Release due to failure reported by SUERM
   RELEASE_IAC    0x8     Release due to initial alignment failed
   RELEASE_OTHER  0x9     Other reason SS7 link out-of-service

(should we keep it simple, or provide list of reasons that would
enable debugging)

2.3.1.4  State (Request, Confirm)

The State Request message can be sent from a MGC to cause an action
on a particular SS7 link supported by the Signaling Gateway.  The
gateway sends a State Confirm to the MGC if the action has been success-
fully completed.  The State Confirm reflects that state value received
in the State Request message.

    0            15 16           31
   +---------------+---------------+                   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             State                             |
   +---------------+---------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

         Define           Value        Description
   STATUS_LOC_PROC_SET
   STATUS_LPO_SET          0x0      Request local processor outage.
   STATUS_LOC_PROC_CLEAR outage
   STATUS_LPO_CLEAR        0x1      Request local processor outage
                                    recovered.
                                    recovered
   STATUS_EMER_SET         0x2      Request emergency alignment
                                    procedure.
                                    procedure
   STATUS_EMER_CLEAR       0x3      Request normal alignment (cancel
                                    emergency) procedure. procedure
   STATUS_FLUSH_BUFFERS    0x4      Flush transmit and retransmit buffers.
                                    buffers
   STATUS_CONTINUE         0x5      Continue.      Continue

2.3.1.5  State Indication

The MTP2 State Indication message can be sent from a gateway to a call
agent an
ASP to indicate a condition on a channel. link.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0            15 16           31
   +---------------+---------------+ 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             State                             |
   +---------------+---------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

       Define            Value          Description
   EVENT_ENTER_LPO        0x0      Entered local processor outage. outage
   EVENT_EXIT_LPO         0x1      Exited local processor outage. outage
   EVENT_ENTER_CONG       0x2      Entered a congested state. state
   EVENT_EXIT_CONG        0x3      Exited a congested state. state
   EVENT_PHYS_UP          0x4      Physical interface up. up
   EVENT_PHYS_DOWN        0x5      Physical interface down. down
   EVENT_PROTOCOL_ERR     0x6      Protocol error occurred. occurred
   EVENT_REM_ENTER_CONG   0xc      Remote entered congestion. congestion
   EVENT_REM_EXIT_CONG    0xd      Remote exited congestion. congestion
   EVENT_REM_ENTER_PO     0xe      Remote entered processor outage. outage
   EVENT_REM_EXIT_PO      0xf      Remote exited processor outage. outage

2.3.1.6  Retrieval (Request, Confirm)

The MTP2 Retrieval Request message is used during the MTP Level 3
changeover procedure to request the BSN, to retrieve PDUs from the
retransmit queue or to flush PDUs from the retransmit queue.

    0            15 16           31
   +---------------+---------------+                   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Action                             |
   +---------------+---------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            fsn_bsn                            |
   +---------------+---------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

        Define         Value       Description
   ACTION_RTRV_BSN      0x1     Retrieve the backward sequence number. number
   ACTION_RTRV_MSGS     0x2     Retrieve the PDUs from the retransmit
                                queue.
                                queue
   ACTION_DROP_MSGS     0x3     Drop the PDUs in the retransmit queue. queue

In the Retrieval Request message, the fsn_bsn field contains the FSN of
the far end if the action is ACTION_RTRV_MSGS.

When the Signaling Gateway sends a Retrieval Confirm to this request,
it echos the action and puts the BSN in the fsn_bsn field if the action
was ACTION_RTRV_BSN.  If there is a failure in retrieving the BSN, the
fsn_bsn should contain a -1 (0xffffffff).

2.3.1.7  Retrieval Indication

The Retrieval Indication message is sent by the Signaling Gateway
with a PDU from the retransmit queue.  The Retrieval Indication
message does not contain the Action or fsn_bsn fields, just a PDU from
the retransmit queue.

    0            15 16           31
   +---------------+---------------+
   |                   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |

   .                     PDU from retransmit     .
   . queue               .                 |                               |
   +---------------+---------------+

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

2.3.1.8  Retrieval Complete Indication

The MTP2 Retrieval Complete Indication message is exactly the same as
the MTP2 Retrieval Indication message except that it also indicates that
it contains the last PDU from the retransmit queue.

2.3.2  Application Server Process Maintenance (ASPM) Messages

The ASPM messages will only use the common message header.

2.3.2.1  ASP UP (ASPUP)

The ASPUP ASP UP (ASPUP) message is used to indicate to a remote M2UA peer
that the Adaptation layer is ready to receive traffic or maintenance
messages.

The ASPUP message contains the following parameters:

     Adaptation Layer Identifer (optional)
     SCN
     Protocol Identifier (optional)

The Adaptation Layer Identifier is a string that identifies the
adaptation layer.  This string must be set to "M2UA" which means
the length will be 4.

The Protocol Identifier field contains the identity of the specific SCN
signaling protocol being transported.  The Protocol ID defines the
protocol type, variant, and version, and thereby specifies the components
and encoding of the PROTOCOL DATA field.  The Protocol Identifier also
defines what SCN protocol message components are included in the PROTOCOL
DATA.

(Ed. Note: Need encoding of mime-type value or OID or fixed
string/integer that will be administered outside of this document
(IANA). Also, perhaps bring in text from Christian's mime document - See
"draft-ietf-sigtran-mime-isup.txt" for an example of an application/ISUP
media type defined according to the rules defined in RFC 2048.?)
     INFO String (optional)

The format for the ASPUP message Message parameters is as follows:

    0            15 16           31
   +---------------+---------------+                   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 (0x2)           |             Length            |
   +---------------+---------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                 Adaptation Layer Identifier Identifier*                  |

   +---------------+---------------+
   |   Tag (0x3)   |    Length     |
   +---------------+---------------+

   |      Protocol Identifier      |

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

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x4)           |             Length            |
   +---------------+---------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                          INFO String String*                         |

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

Note:  Strings are padded to 32-bit boundaries.

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

The length field
indicates optional INFO String parameter can carry any meaningful 8-BIT ASCII
character string along with the end message.  Length of the string.

2.3.2.2  ASP Down (ASPDN)

The ASPDN message is used to indicate to a remote M2UA peer that the
layer INFO String
parameter is not ready from 0 to receive traffic or maintenance messages.

The ASPDN message contains 255 characters.  No procedures are presently
identified for its use but the following parameters: INFO String

The format may be used for the ASPDN message debugging
purposes.

The optional Adaptation Layer Identifier (ALI) is as follows:

    0            15 16           31
   +---------------+---------------+
   |   Tag (0x4)   |    Length     |
   +---------------+---------------+

   |          INFO String          |

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

#####
We discussed adding a reason code.  Reason could string that
identifies the adaptation layer.  This string must be failure or
management inhibit.
#####

2.3.2.3 set to "M2UA"
which results in a length of 4.  The ALI would normally only be used in
the initial ASP Active (ASPAC) Up message across a new SCTP association to ensure both
peers are assuming the same adaptation layer protocol.

Note: Strings are padded to 32-bit boundaries.  The ASPAC length field
indicates the end of the string.

2.3.2.2  ASP Down (ASPDN)

The ASP Down (ASPDN) message is sent by an ASP used to indicate to an SG a remote M2UA peer
that it is the active ASP adaptation layer is not ready to be used from within a list of primary and back-up ASPs
for a particular signaling mapping relationship. receive traffic or maintenance
messages.

The ASPAC ASPDN message contains the following parameters:

     Controlled/Forced flag (C/F flag)

     Reason
     INFO String (Optional)

The format for the ASPAC ASPDN message parameters is as follows:

    0            15 16           31
   +---------------+---------------+                   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            C/F flag                              Reason                           |
   +---------------+---------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x4)           |            Length             |
   +---------------+---------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                         INFO String String*                          |

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

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

The format and description of the optional Info String parameter is the
same as for the ASP Up message (See Section 2.3.2.1.)

The Reason parameter indicates the reason that the remote M2UA
adaptation layer is unavailable.  The valid values for C/F flag Reason are shown
in the following table.

        Define

     Value         Description
   FORCED               0x0     Force sending of all messages to ASP
   CONTROLLED
     0x1     Only send "new work" to ASP

2.3.2.4        Management Inhibit

2.3.2.3  ASP Inactive (ASPIA) Active (ASPAC)

The ASPIA ASPAC message is sent by an ASP to indicate to an SG that it is
no longer the the active ASP
Active and ready to be used from within a list of primary
and back-up ASP for a particular signaling mapping relationship.  The
SG will respond with an ASPIA message and either buffer or discard
incoming messages for a timed period and then discard. used.

The ASPIA ASPAC message contains the following parameters:

     Type
     Interface Identifier (Optional)
     INFO String (Optional)

The format for the ASPIA ASPAC message is as follows:

    0            15 16           31
   +---------------+---------------+                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Type                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xx)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                     Interface Identifiers*                    |

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x4)             |             Length            |
   +---------------+---------------+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                          INFO String String*                         |

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

2.3.3  Layer Management (MGMT) Messages

2.3.3.1  Error (ERR)

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

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

The ERR message contains Type parameter identifies the following parameters:

     Error Code

The format for traffic mode of operation of the ERR message is as follows:

    0     7 8    15 16           31
   +---------------+---------------+
   |           Error Code          |
   +---------------+---------------+ ASP
within an AS. The Error Code can be one of valid values for Type are shown in the following values:

     Invalid Version table.

    Value          Description
     0x1
     Invalid Interface Identifier            Over-ride
     0x2
     Invalid SCN Version            Load-share
     0x3
     Invalid Adaptation Layer Identifier    0x4
     Invalid Stream Identifier              0x5
     Invalid Message            New traffic

Within a particular Routing Context, only one Type                   0x6

3.0  Procedures can be used.  The M2UA layers needs to respond to various primitives it receives from
other layers as well as messages it receives from
Over-ride value indicates that the peer-to-peer
messages.  This section describes various procedures involved in
response to these events.

3.1  Procedures to Support Service ASP is operating in Section 1.4.1

These procedures achieve Over-ride mode,
where the M2UA layer's "Transport of MTP Level 2 /
MTP Level 3 boundary" service.

3.1.1  MTP Level 2 / MTP Level 3 Boundary Procedures

On receiving a primitives from ASP takes over all traffic in an Application Server (i.e.,
primary/back-up operation), over-riding any currently active ASPs in
the local layer, AS.  In loadshare mode, the M2UA layer ASP will
send the corresponding MAUP message (see Section 2) to its peer.  The
M2UA layer must fill share in various fields of the common and specific headers
correctly. traffic distribution
with any other currently active ASPs.  In addition New Traffic mode the message needs ASP wishes
to be sent take on traffic in the SCTP stream
that corresponds AS but does not expect to the SS7 link.

3.1.2  MAUP Message Procedures

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

3.2  Procedures
related to Support Service calls/transactions that are pending completion in Section 1.4.2

These procedures achieve the IUA layer's "Support another ASP.

An SG that receives an ASPAC with an incorrect type for Communication
between Layer Managements" service.

3.2.1  Layer Management Primitives Procedure

On receiving these primitives from the local layer, the M2UA layer a particular
Interface Identifier will
send the corresponding MGMT message (Error) to its peer. respond with an Error Message.

The M2UA layer
must fill in the various fields of the common and specific headers
correctly.

3.2.2 MGMT message procedures

Upon receipt optional Interface Identifiers parameter contains a list of MGMT messages the M2UA layer must invoke
Interface Identifier integers indexing the corresponding
Layer Management primitives (M-ERROR) to Application Server traffic
that the local layer management.

3.3 Procedures sending ASP is configured/registered to Support Service in Section 1.4.3

These procedures achieve the M2UA layer's "Support for management of
active associations receive.  There is
one-to-one relationship between SG an Interface Identifier and MGC" service.

3.3.1 State Maintenance

3.3.1.1  ASP States

The state of an AS Name.
If no Interface Identifiers are present, then the each ASP message is maintained in the M2UA layer on intended
for all Interface Identifiers supported by the SG.

The
state format and description of an ASP changes due to events. The events include:

   * Reception messages from peer M2UA layer
   * Reception of indications from layers below

The ASP state transition diagram the optional Info String parameter is shown in Figure 4. the
same as for the ASP Up message (See Section 2.3.2.1.)

2.3.2.4  ASP Inactive (ASPIA)

The possible states
of ASPIA message is sent by an ASP are:

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

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

ASP-ACTIVE: Application Server Process is available and application traffic to indicate to an SG that it is active.  At most one no
longer an active ASP per AS can to be in used from within a list of ASPs.  The SG will
respond with an ASPIA message and either discard incoming messages or
buffer for a timed period and then discard.

The ASPIA message contains the active state.

                 Figure 4: ASP State Transition Diagram

                               +-------------+
                     |-------->|             |
                     | following parameters:

     Type
     Interface Identifiers (Optional)
     INFO String (Optional)

The format for the ASPIA message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  ASP-ACTIVE                             Type                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xx)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                     Interface Identifiers*                    |

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x4)           |         +-------------+            Length             |             ^
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                          INFO String*                         |

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

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

    Value          Description
     0x1            Over-ride
     0x2            Load-share
     0x3            Graceful Withdrawal

The format and description of the optional Interface Identifiers and
Info String parameters is the same as for the ASP
                     | Active message (See
Section 2.3.2.3.)  If no Interface Identifiers are present, then the
message is intended for all Interface Identifiers supported by the SG.

2.3.3  Layer Management (MGMT) Messages

2.3.3.1  Error (ERR)

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

The ERR message contains the following parameters:

     Error Code
     Diagnostic Information (optional)

The format for the ERR message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Error Code                           | Inactive
                     |             |     v
                     |         +-------------+
                     |         |             |
         ASP Down /  |         |             |
          SCTP CDI   |         |  ASP-UP     |
                     |         |             |
                     |         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xx)           |         +-------------+            Length             |             ^
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                     Diagnostic Information*                   |        ASP

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

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

     Invalid Version                        0x1
     Invalid Interface Identifier           0x2
     Invalid Adaptation Layer Identifier    0x3
     Invalid Message Type                   0x4
     Invalid Traffic Handling Mode          0x5
     Invalid Stream Identifier              0x5

The optional Diagnostic information can be any information germain to
the error condition, to assist in identification of the error condition.
In the case of an Invalid Version Error Code the Diagnostic information
includes the supported Version parameter.  In the other cases, the
Diagnostic information may be the first 40 bytes of the offending message.

2.3.3.2  Notify (NTFY)

The Notify message used to provide autonomous notification of M2UA events.

The NTFY message contains the following parameters:

     Status Type
     Status Identification
     Interface Identifiers (Optional)
     INFO String (Optional)

The format for the NTFY message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Status Type            | ASP Down /    Status Identification      |        Up
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0xx)             | SCTP CDI             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |    v                      Interface Identifiers*                   |         +-------------+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x4)             |             Length            |
                     |-------->|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                          INFO String*                         |  ASP-DOWN   |
                               |             |
                               |             |
                               +-------------+

SCTP CDI: Local SCTP layer's Communication Down Indication to the Upper Layer
  Protocol (M2UA) on an SG. SCTP will send this indication when it
  detects the loss of connectivity to ASP's SCTP layer.

3.3.1.2  AS States

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

The state Status Type parameter identifies the type of the AS is maintained in Notify message.  Following are the ITUN layer valid Status Type values:

      Value          Description
       0x1   Application Server state change (AS_State_Change)
       0x2   Application Server Process state change (ASP_State_Change)
       0x3   Other

The Status Information parameter contains more detailed information for the notification, based on the SG.  The
state value of the Status Type.  If the Status Type is AS_State_Change the following Status Information values are used:

      Value          Description
       0x1	 Application Server Down (AS_Down)
       0x2	 Application Server Up (AS_Up)
       0x3	 Application Server Active (AS_Active)
       0x4	 Application Server Pending (AS_Pending)

These notifications are sent from an AS changes due SG to events. These events include:

   * an ASP state transitions
   * Recovery timer triggers upon a change in status of a particular Application Server.  The possible states value reflects the new state of an AS the Application Server.

If the Status type is ASP_State_Change, the Status Information values are:

AS-DOWN:

      Value          Description
       0x1	 Application Server is unavailable.  This state implies that all
  ASPs Process (ASP) Down
       0x2	 Application Server Process (ASP) Up
       0x3	 Application Server Process (ASP) Active
       0x4	 Application Server Process (ASP) Active_Old
       0x5   Application Server Process (ASP) Active_New

These notifications are sent from an SG to an ASP upon a change in status
of a particular Application Server process within the ASP-DOWN ASP list of a
particular Application Server.  The value reflects the new state for this AS.

AS-UP: One or more ASPs are in of the ASP-UP state.

AS-ACTIVE:
Application Server Process.

If the Status Type is available and application traffic is
  active. Other, then the following Status Information values
are defined:

      Value          Description
       0x1    Insufficient ASP resources active in AS

This notification is not based on the SG reporting the state implies that one change of an
ASP or AS.  For the value defined the SG is indicating to an ASP(s) in
the ASP-ACTIVE state.

AS-PENDING: Currently Active AS that another ASP became inactive or SCTP association with
  it is lost.  A Recovery timer will be started and required in coming SCN messages
  will be queuedby order to handle the load of the AS.

The format and description of the optional Interface Identifiers and Info
String parameters is the same as for the SG.  If an ASP becomes Active before message (See
Section 2.3.2.3.)

3.0  Procedures

The M2UA layers needs to respond to various primitives it receives from
other layers as well as messages it receives from the recovery
  timer (Tr) expires, peer-to-peer
messages.  This section describes various procedures involved in
response to these events.

3.1  Procedures to Support Service in Section 1.4.1

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

3.1.1  MTP Level 2 / MTP Level 3 Boundary Procedures

On receiving a primitive from the local upper layer, the M2UA layer will move
send the corresponding MAUP message (see Section 2) to AS-ACTIVE state its peer.  The
M2UA layer must fill in various fields of the common and all specific headers
correctly.  In addition the
  queued messages will message needs to be sent on the SCTP stream
that corresponds to the active ASP.  If SS7 link.

3.1.2  MAUP Message Procedures

On receiving MAUP messages from a peer M2UA layer, the recovery timer
  expires before M2UA layer on an ASP becomes active,
SG stops queuing messages and
  discards or MGC needs to invoke the corresponding layer primitives to the
local MTP Level 2 or MTP Level 3 layer.

3.2  Procedures to Support Service in Section 1.4.2

These procedures achieve the M2UA layer's "Support for Communication
between Layer Managements" service.

3.2.1  Layer Management Primitives Procedure

On receiving these primitives from the local layer, the M2UA layer will
send the corresponding MGMT message (Error) to its peer.  The M2UA layer
must fill in the various fields of the common and specific headers
correctly.

3.2.2 MGMT message procedures

Upon receipt of MGMT messages the M2UA layer must invoke the corresponding
Layer Management primitives (M-ERROR) to the local layer management.

3.3 Procedures to Support Service in Section 1.4.3

These procedures achieve the M2UA layer's "Support for management of
active associations between SG and MGC" service.

3.3.1 State Maintenance

The M2UA layer on the SG maintains the state of each AS, in each
Appliction Server that it is configured to receive traffic.

3.3.1.1  ASP States

The state of each ASP, in each AS that it is configured, is maintained
in the M2UA layer in the SG.  The state of a particular ASP in a
particular AS changes due to events.  The events include:

   * Reception of messages from the peer M2UA layer at the ASP
   * Reception of some messages from the peer M2UA layer at other ASPs
     in the AS
   * Reception of indications from the SCTP layer
   * Switch-over Time triggers

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

ASP-DOWN: The remote M2UA peer at the ASP is unavailable and/or the SCTP
association is down.  Initially all ASPs will be in this state.

ASP-UP: The remote M2UA peer at the ASP is available (and the SCTP
association is up) but application traffic is stopped.

ASP-ACTIVE: The remote M2UA peer at the ASP is available and application
traffic is active (for a particular Routing Context or set of Routing
Contexts).

ASP-ACT-OLD: The remote M2UA peer at the ASP is available and application
traffic is active (for a particular Routing Context or set of Routing
Contexts), but for draining of current call/transactions only (i.e., no
new calls/transactions)

ASP-ACT-NEW: The remote M2UA peer at the ASP is available and application
traffic is active (for a particular Routing Context or set of Routing
Contexts), but for new calls/transactions only (i.e., not for traffic
related to completing calls/transactions in another ASP).

                                  +-------------+
           +----------------------|             |
           |       Some other    /|  ASP-ACTIVE |<--------\
           |       ASP        /   +-------------+         |
           |       Takeover  /        ^     |             | Ts
           |               /   ASP    |     | ASP         |
           |              /    Active |     | Inactive    |
           |             v            |     v             |
           | +-------------+      +-------------+       +-------------+
           | |             |      |             |       |             |
           | | ASP-ACT-OLD |----->|  ASP-UP     |------>| ASP-ACT-NEW |
           | +-------------+ Ts / +-------------+ ASP   +-------------+
           |    |    ASP Inactive  ^    |        Takeover   |
           |<---|                  |    |                   |
           |                       |    |                   |
 ASP Down/ |                  ASP  |    | ASP Down /        | ASP
 SCTP CDI  |                  Up   |    | SCTP CDI          | Down/
           |                       |    v                   | SCTP
           |                   +-------------+              | CDI
           |                   |             |              |
           +------------------>|             |<-------------+
                               |  ASP-DOWN   |
                               +-------------+

SCTP CDI: The local SCTP layer's Communication Down Indication to the
Upper Layer Protocol (M2UA) on an SG. The local SCTP will send this
indication when it detects the loss of connectivity to the ASP's peer
SCTP layer.

Ts: Switch-over Time Triggers.  This timer is configurable by the
Operator on a per AS basis.

3.3.1.2  AS States

The state of the AS is maintained in the M2UA layer on the SG.  The
state of an AS changes due to events. These events include:

   * ASP state transitions
   * Recovery timer triggers

The possible states of an AS are:

AS-DOWN: The Application Server is unavailable.  This state implies that
  all queued messages. related ASPs are in the ASP-DOWN state for this AS.  Initially the
  AS will move to AS-UP if at least one
  ASP be in this state.

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

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

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

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

Ed's Note:  If AS moves from AS-PENDING state to AS-UP or AS-DOWN
states, the Layer Management on MG may take appropriate SCN
notification actions.

      +----------+  one ASP trans ACTIVE   +-------------+
      |          |------------------------>|             |
      |  AS-UP   |                         |  AS-ACTIVE  |
      |          |                         |             |
      |          |<                       -|             |
      +----------+ \                     / +-------------+
         ^   |      \ Tr Trigger        /       ^    |
         |   |       \ at least one    /        |    |
         |   |        \ ASP in UP     /         |    |
         |   |         \             /          |    |
         |   |          \           /           |    |
         |   |           \     /---/            |    |
 one ASP |   |            \   /         one ASP |    | ACTIVE ASP
 trans   |   | all ASP     \-/----\     trans   |    | trans to UP or
 to UP   |   | trans to     /      \    ACTIVE  |    | ACTIVE ASP
         |   | DOWN        /        \           |    | SCTP CDI CLN
         |   |            /          \          |    |
         |   |           /            \         |    |
         |   |          /all ASP       \        |    |
         |   v         / trans to       \       |    v
      +----------+    /  DOWN            \ +-------------+
      |          |<--/                    -|             |
      | AS-DOWN  |                         | AS-PENDING  |
      |          |                         |  (queueing) |
      |          |<------------------------|             |
      +----------+    Tr Trigger no ASP    +-------------+
                       in UP state or
                     prev ACTIVE ASP trans
                        to DOWN state

      Tr = Recovery Timer

                 Figure 5: AS State Transition Diagram

3.3.2 ASPM procedures for primitives

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

When

As the ASP is responsible for initiating the setup of an SCTP
association to an SG, the M2UA layer at an ASP receives an M-SCTP
ESTABLISH request primitive from the Layer Management, the M2UA layer
will try to establish an SCTP association with the remote M2UA peer. peer at
an SG.  Upon reception of an eventual SCTP-Communication Up confirm
primitive from the SCTP, the M2UA layer will invoke the primitive M-SCTP
ESTABLISH confirm to the Layer Management.

Alternatively, if the remote M2UA-peer establishes

At the SCTP association
first, SG, the M2UA layer will receive an SCTP Communication Up
indication primitive from the SCTP. The M2UA layer will then invoke the
primitive M-SCTP ESTABLISH indication to the Layer Management.

Once the SCTP association is established, The M2UA layer at an ASP will
then find out the state of its local M2UA-user from the Layer Management
using the primitive M-ASP STATUS.  Based on the status of the local
M2UA-User, the local ASP ITUN M2UA Application Server Process Maintenance
(ASPM) function will initiate the ASPM procedures, using the ASP-Up/-Down/-Active/
-Inactive ASP-Up/-
Down/-Active/-Inactive messages to convey the ASP-state to the SG - see
Section 3.3.3.

If the M2UA layer subsequently receives an SCTP-Communication Down
indication from the underlying SCTP layer, it will inform the Layer
Management by invoking the M-SCTP STATUS indication primitive.  The
state of the ASP will be moved to "Down" at both the SG and ASP.

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

3.3.3 ASPM procedures for peer-to-peer messages

3.3.3.1

All ASPM messages are sent on a sequenced stream to ensure ordering.
SCTP stream Š0Ă is used.

3.3.3.2 ASP-Up

After an ASP UP

The has successfully established an SCTP association to an SG,
the SG will mark waits for the path as up if ASP to send an explicit ASP-Up message, indicating that the
ASP UP (ASPUP) M2UA peer is available.  The ASP is always the initiator of the
ASP-Up exchange.

When an ASP-Up message is received at an SG and internally the path ASP is allowed to come up (i.e., not in a
locked local maintenance state). An ASP UP (ASPUP) message will be sent
to acknowledge
locked-out for local management reasons, the received ASPUP. SG marks the remote ASP as
ŠUpĂ.  The SG will respond to a ASPUP responds with a
ASPDN an Notify (ASP-Up) message if to the path is ASP in a locked maintenance state.
acknowledgement.  The SG will send sends a ASPUP Notify (ASP-Up) message in response to
a received ASPUP ASP-Up message from the MGC ASP even if that path was the ASP is already marked
as UP ˘Up÷ at the SG.

The paths are controlled by

If for any local reason the MGC. The SG will only send ASPUP in
response to cannot respond with an ASP-Up, the reception of SG
responds to a ASPUP ASP-Up with a ASP-Down message.

The MGC will send ASPUP

At the ASP, the Notify (ASP-Up) message received from the SG is not
acknowledged by the ASP.  If the ASP does not receive a response from
the SG, or an ASP-Down is received, the ASP may resend ASP-Up messages
every 2 (add text regarding this being
a configurable timer) seconds until the path comes up (i.e. until it receives a ASPUP Notify (ASP-Up) message from the SG for that path). SG.
The MGC ASP may decide to reduce the frequency (say to every 5 seconds) if the an acknowledge-
ment a
Notify (ASP-Up) is not received after a few tries.

The MGC should ASP must wait for the ASPUP Notify (ASP-Up) message from the SG before transmitting
sending any ASP maintenance traffic control messages (ASPIA (ASPAC or ASPAC) ASPIA) or M2UA Data
messages or it will risk message loss.  The ASPUP message received from  If the SG receives Data messages
before an ASP Up is not
acknowledged by received, the MGC. SG should discard.

3.3.3.2 ASP-Down

The ASP Down will send an ASP-Down to an SG when the ASP is to be removed from
the list of ASPs in all Application Servers that it is a member.

The SG will mark marks the ASP as down ˘Down÷ and send a ASPDN returns an Notify (ASP-Down) message
to the MGC ASP if one of the following events occur:

    - a ASP Down(ASPDN) an ASP-Down message is received from the MGC, ASP,
    - another ASPM message is received from the ASP is and the SG has
      locked by local maintenance. out the ASP for management reasons.

The SG will also send sends a ASPDN Notify (ASP-Down) message when the ASP is already down and in response to a ASPDN) message is received ASP-
Down message from the MGC.

The MGC will send ASPDN whenever it wants to take down a ASP.  Since ASP even if the
ASPDN messages to ASP is already marked as ˘Down÷ at
the SG or SG.

If the ASPDN responses ASP does not receive a response from the SG can be lost
(for example, during a MGC node failover), SG, the MGC can ASP may send ASPDN ASP-
Down messages every 2 seconds until the path comes down (i.e. until it receives a ASPDN ASP-Down message from
the SG for that path).

3.3.4 or the SCTP association goes down.  The ASP may decide to reduce
the frequency (say to every 5 seconds) if an ASP-Down is not received
after a few tries.

3.3.3.3  M2UA Version Control

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

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

The version field in  Because ASPs
initiate the ASP-Up procedure it is assumed that the Error message header associated with the will
indicate would
normally come from the version supported by SG.

3.3.3.4 ASP-Active

Anytime after the node.

3.3.5 ASP Inactive

When has received a ASPIA message is received, message transmission Notify (ASP-Up) acknowledgement from
the SG, the ASP sends an ASP-Active (ASPAC) to the SG indicating that the
ASP ceases.
The SG will either discard all incoming messages or is ready to start buffering the
incoming messages for N seconds after which messages will be discarded.

If processing traffic.  In the case where an ASP is down, all of
configured/registered to process the Paths that were supported by that ASP
are, by default, down.

3.3.6  ASP Active traffic for more than one Application
Server across an SCTP association, the ASPAC contains one or more
Interface Identifiers to indicate for which Application Servers the
ASPAC applies.

When a an ASP Active (ASPAC) message is received, the SG will start routing responds to the
ASP with a Notify message acknowledging that the ASPAC was received and
starts sending traffic for the associated Application Server(s) to that
ASP.  Reception

There are two modes of a Application Server traffic handling in the SG
M2UA - Over-ride, Load-balancing and New Traffic.  The Type parameter in
the ASPAC message overrides any previous messge indicates the mode used in a particular Application
Server.  If the SG determines that the mode indicates in an ASPAC
messages and results is
incompatible with the traffic handling mode currently used in the ASP associated with AS,
the ASPAC SG responds with an Error message to
become indicating ˘Invalid Traffic
Handling Mode÷.

In the newly active ASP.

4.0  Examples of MTP2 User Adaptation (M2UA) Procedures

4.1  Establishment case of associations between SG and MGC examples

An example an Over-ride mode AS, reception of the an ASPAC message flows for establishing active associations between
SG and MGC is shown below. at an
SG                  ASP1

                        <----------- ASP Up
                  ASP Up ---------->
                  (ACK)
                        <----------- ASP Active
              ASP Active ---------->
              (ACK)

An example of message flows for establishment of associations with two
ASPs and causes the message flows for take-over redirection of all traffic for the primary (ASP1) by AS to the
secondary (ASP2).

                 SG                    ASP1               ASP2

                        <----------- ASP Up
                  ASP Up ---------->
                  (ACK)
                        <------------------------------ ASP Up
                  ASP Up ------------------------------>
                  (ACK)
                        <----------- ASP Active
              ASP Active ---------->
              (ACK)
                              ...

                        <----------- ASP Inactive which sent
the ASPAC.  Any previously active ASP Inactive ---------->
            (ACK)

                         (this message in the AS is optional)
            ASP now considered Inactive ------------------------------>
                        <------------------------------ ASP Active
              ASP Active ------------------------------>
              (ACK)

An example of message flows for establishment of associations with two
ASPs
and will no longer receive traffic within the AS.  The SG responds to the
ASPAC with a Notify (ASP-Active) message flows for controlled take-over of to the primary (ASP1)
by ASP.  The SG sends a
Notify (ASP-Inactive) to any previously active ASP in the secondary (ASP2). AS.

In this case, the case of a Loadshare mode AS, reception of an ASPAC message at an
SG sends new work causes the direction of traffic to ASP2.

                 SG                    ASP1               ASP2

                        <----------- ASP Up
                  ASP Up ---------->
                  (ACK)
                        <------------------------------ ASP Up
                  ASP Up ------------------------------>
                  (ACK)
                        <----------- ASP Active
              ASP Active ---------->
              (ACK)
                              ...

                        <------------------------------ ASP Active
                                                        (New Work)
              ASP Active ------------------------------>
              (ACK)

                        <----------- ASP Inactive the ASP Inactive ---------->
            (ACK)

4.2  Case 1:  SG sending the ASPAC, in
addition to MGC, MTP Level 2 all the other ASPs that are currently active in the AS.
The algorithm at the SG for loadsharing traffic within an AS to MTP Level 3 Boundary Procedures

4.2.1  SS7 Link Alignment all the
active ASPs is application and network dependent.  The MGC can request that SG responds to
the ASPAC with a SS7 link be brought into alignment using Notify (ASP-Active) message to the
normal or emergency procedure.  An example of ASP.

In the case of a New Traffic mode AS, reception of an ASPAC message flow at
an SG causes the direction of traffic to bring
a SS7 link in-service using the normal alignment procedure ASP sending the ASPAC.
However, traffic related to completing calls/transactions in another ASP
is shown
below. not sent to the new ASP (i.e., new calls/transactions only). How an
SG                             MGC

                        <----------- Establish Request (ESTABLISH_NORMAL)
	Establish Response ---------->

An example accomplishes the differentiation of old and new transactions and any
loadsharing of traffic is application and implementation dependent.  The
SG responds to the ASPAC with a Notify (ASP-Active_New) message flow to bring a SS7 link in-service using the
emergency alignment procedure.

           SG                             MGC

                        <----------- Establish Request (ESTABLISH_EMER)
	Establish Response ---------->

4.2.2  SS7 Link Release

The MGC can request that ASP.
After a SS7 link be taken out-of-service.  It uses configurable time Ts, the Release Request message as shown below.

            SG                             MGC

                        <------------ Release Request (RELEASE_MGMT)
	Release Response  ------------>

The SG can autonomously indicate that a SS7 link has gone out-of-service
as shown below.

            SG                             MGC

	Release Indication ------------>
      (RELEASE_PHYS)

4.2.3  Set and Clear Local Processor Outage ASP is moved to be added

4.2.4  Notification of Processor Outage (local or remote) the ASP-Active state and
a Notify (ASP-Active) is sent to the ASP.  Most likely, the New Traffic
mode would not be added

4.2.5  Flush Buffers or Continue used in M2UA.

3.3.3.5 ASP Inactive

When an ASP wishes to be added

4.2.6  SS7 Link Changeover

An example of withdraw from receiving traffic the message flow for a changeover is shown below.

            SG                             MGC

                         <---------- Retrieval Request (MTP2_RTRV_BSN)
	Retrieval Confirm  ---------->
	(with BSN)
                         <---------- Retrieval Request (MTP2_RTRV_MSGS
                                                         with FSN)
	Retrieval Confirm  ---------->

	Retrieval Ind 	 ----------->
	Retrieval Ind 	 ----------->
	Rtrvl Complete Ind ---------->

Note:  The number of Retrieval Indication ASP sends an
ASP Inactive (ASPIA) to the SG.  In the case where an ASP is dependent on configured/-
registered to process the number of
messages in traffic for more than one Application Server
across an SCTP association, the retransmit queue that have been requested.  Only ASPIA contains one
Retrieval Complete Indication should be sent.

4.3  Case 2:  SG to IPSP, MTP Level 2 or more Routing
Contexts to MTP Level 3 Boundary Procedures

In general, messages passed between MTP3 and M2UA indicate for which Application Servers the ASPIA applies.

There are two modes of Application Server traffic handling in the same as
those passed between MTP3 and MTP2. SG
M2UA interprets messages when withdrawing an ASP from MTP3 service - Over-ride, Load-balancing
and sends Graceful Withdrawal.  The Type parameter in the appropriate message to SCTP. Likewise, messages from
SCTP are ASPIA messge
indicates the mode used to generate in a meaningful message to MTP3.

4.3.1  Link Initialization (Alignment)

The MTP3 layer can request particular Application Server. If the SG
determines that the mode indicates in an SS7 link ASPAC is incompatible with
the traffic handling mode currently used in the AS, the SG responds
with an Error message indicating ˘Invalid Traffic Handling Mode÷.

In the case of an Over-ride mode AS, where normally another ASP has
already taken over the traffic within the AS with an Over-ride ASPAC,
the ASP which sent the ASPIA is already considered by the SG to be brought into alignment
using
˘Inactive÷.  A Notify (ASP_Up) message is resent to the normal or emergency procedure.  An example ASP.

In the case of a Loadshare mode AS, the SG moves the ASP to the
˘Inactive÷ state and the AS traffic is re-allocated across the remaining
˘active÷ ASPs per the laoadsharing algorithm currently used within the
AS.  A Notify (ASP-Up) message
flow is sent to bring an SS7 link in-service the ASP after the traffic is shown below.

There are two alignment procedures normal alignment
halted to the ASP.

In the case of Graceful Withdrawal, the SG diverts all traffic related
to new calls/transactions to other "active" ASPs and emergency
alignment.  During normal alignment, communication therafter sends only
traffic related to incomplete transactons to the other end ASP. A Notify (ASP-
Act_Old) is
tested for a period of time sent to make sure that the communication link
satisfies ASP and the performance requirements of ASP is moved to the application.  The
examples "Active_Old" state.
When the outstanding calls/transactions are RTT drained, or after a
configurable time Ts, the SG moves the ASP to the "Up" state and packet loss.  Normal alignment is used when there
are other links available sends
a Notify (ASP-Up) message to the same destination. Emergency alignment
is ASP.  Most likely, Graceful Withdrawal
will not be used when there are with M2UA.

If no other links ASPs are ˘Active÷ in the Application Server, the SG either
discards all incoming messages (except messages related to an ˘Active_Old÷
ASP) for the same destination.  During
emergency, AS or starts buffering the link is not tested incoming messages for a long period of time. Instead, T(r)seconds
after which messages will be discarded.  T(r) is configurable by the
network operator.  If the SG receives an indication ASPAC from an ASP in the SCTP layer AS
before expiry of T(r), the buffered traffic is used directed to bring the link ASP and
the timer is cancelled.

4.0  Examples of MTP2 User Adaptation (M2UA) Procedures

4.1  Establishment of associations between SG and MGC examples

4.1.1 Single ASP in
service.

The procedure an Application Server (˘1+0÷ sparing)

This scenario shows the example M2UA message flows for beginning the establishment
of traffic between an Association SG and an ASP, where only one ASP is described in configured
within an AS (no backup).  It is assumed that the SCTP
standard [5].

    MTP3        M2UA        SCTP        SCTP        M2UA        MTP3
    ----        ----        ----        ----        ----        ----

     Power On
     ------------>

     Out of Service
     <------------

     Emergency OR
     Emergency Ceases
     ------------>

     Start
     ------------>

                 Associate
                 ------------>

                             (SCTP Association
                              procedure)

                 Communication Up        Communication Up
                 <------------           ------------>

     Indication                                      Indication
     (Link In Service)                               (Link In Service)
     <------------                                   ------------>

For association is
already set-up.

             SG                       ASP1
              |
              |<---------ASP Up----------|
              |------NTFY (ASP-Up)------>|
              |                          |
              |<-------ASP Active--------|
              |----NTFY (ASP_Active)---->|
              |                          |

4.1.2 Two ASPs in Application Server (˘1+1÷ sparing)

This scenario shows the Emergency Ceases case, proving begins at this time. See example M2UA message flows for the
section on Link Proving below.

4.3.2  Link Proving

One function establishment
of traffic between an SG and two ASPs in the adaptation layer same Application Server,
where ASP1 is configured to make sure that be ˘active÷ and ASP2 a ˘standby÷ in the link
meets event
of communication failure or the performance requirements withdrawal from service of ASP1.  ASP2 may
act as a hot, warm, or cold standby depending on the application.  This extent to which ASP1
and ASP2 share call/transaction state or can communicate call state under
failure/withdrawal events.  The example message flow is
usually done by proving the link.  For example, for proving the link,
we need same whether
the adaptation layer to issue ASP-Active messages are Over-ride or Load-share mode although typically
this example would use an heartbeat/RTT to its peer.
This is done before declaring link is Over-ride mode.

       SG                        ASP1                        ASP2
        |                         |                          |
        |<--------ASP Up----------|                          |
        |-------TFY (ASP-Up)----->|                          |
        |                         |                          |
        |<-----------------------------ASP Up----------------|
        |----------------------------NTFY (ASP-Up)---------->|
        |                         |                          |
        |                         |                          |
        |<-------ASP Active-------|                          |
        |----NTFY(ASP-Active)---->|                          |
        |                         |                          |

4.1.3 Two ASPs in service an Application Server (˘1+1÷ sparing, load-sharing case)

This scenario shows a similar case to its application.
For this purpose, the existing "status" command is used.  Note how the
link meets performance requirements is implementation dependent.
Also, the proving period can be configurable.

Proving is done by both ends of Section 4.1.2 but where the link. To simplify two
ASPs are brought to ˘active÷ and loadshare the diagram,
proving is shown on one end only. traffic load.  In the following diagram the Link has just completed the alignment
procedure.

The Status primitive this
case, one ASP is sent sufficient to determine if handle the Heartbeats were
delivered successfully within total traffic load.

       SG                       ASP1                       ASP2
        |                         |                          |
        |<---------ASP Up---------|                          |
        |-------NTFY(ASP-Up)----->|                          |
        |                         |                          |
        |<------------------------------ASP Up---------------|
        |-----------------------------NTFY(ASP Up)---------->|
        |                         |                          |
        |                         |                          |
        |<--ASP Active (Ldshr)----|                          |
        |----NTFY(ASP-Active)---->|                          |
        |                         |                          |
        |<----------------------------ASP Active (Ldshr)-----|
        |-----------------------------NTFY(ASP-Active)------>|
        |                         |                          |

4.1.4 Three ASPs in an Application Server (˘n+k÷ sparing, load-sharing case)

This scenario shows the desired time period.

    MTP3        M2UA        SCTP        SCTP example M2UA        MTP3
    ----        ----        ----        ----        ----        ----

                 Request Heartbeat
                 ------------>
                             (Heartbeat sent
                              and acknowledged)
                 Request Heartbeat
                 ------------>
                             (Heartbeat sent
                              and acknowledged)

                 Request Heartbeat
                 ------------>
                             (Heartbeat sent
                              and acknowledged)

                 Heartbeats are sent message flows for M seconds (Note A).

                 Status
                 ------------>

     Indication
     (Link In Service) (After checking that link is sane)
     <------------

Note A M is implementation-dependent.

4.3.3  Message Transmission the establishment
of traffic between an SG and Reception

Messages three ASPs in the same Application Server,
where two of the ASPs are transmitted using brought to ˘active÷ and share the Data Request primitive from MTP3 load. In
this case, a minimum of two ASPs are required to
M2UA. The diagram shows handle the case where total traffic
load (2+1 sparing).

   SG                  ASP1                 ASP2                 ASP3
    |                    |                   |                   |
    |<------ASP Up-------|                   |                   |
    |----NTFY(ASP-Up)--->|                   |                   |
    |                    |                   |                   |
    |<--------------------------ASP Up-------|                   |
    |------------------------NTFY(ASP-Up)--->|                   |
    |                    |                   |                   |
    |<---------------------------------------------ASP Up--------|
    |--------------------------------------------NTFY(ASP-Up)--->|
    |                    |                   |                   |
    |                    |                   |                   |
    |<-ASP Act. (Ldshr)--|                   |                   |
    |---NTFY(ASP-Act.)-->|                   |                   |
    |                    |                   |                   |
    |<--------------------ASP Act. (Ldshr)---|                   |
    |----------------------NTFY(ASP-Act.)--->|                   |
    |                    |                   |                   |

4.2 ASP Traffic Fail-over Examples

4.2.1 (1+1 Sparing, withdrawal of ASP, Back-up Over-ride)

Following on from the Link is In Service. The
message is passed example in Section 4.1.2, and ASP withdraws from MTP3 of
service:

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

Note: If the source to MTP3 SG detects loss of the destination.

    MTP3        M2UA        SCTP        SCTP        M2UA        MTP3
    ----        ----        ----        ----        ----        ----

     Request
     (Message for
      transmission)
     ------------>

                 Send
                 ------------>

                             (SCTP sends message)

                                         Receive
                                         ------------>

                                                     Indication
                                                     (Received message)
                                                     ------------>

4.3.4  Link Status Indication

The M2UA layer sends an indication that the Link is In Service peer (M2UA heartbeat loss or Out
detection of Service after receiving a Communication indication SCTP failure), the initial SG-ASP1 ASP Inactive message
exchange would not occur.

4.2.2 (1+1 Sparing, Back-up Over-ride)

Following on from the SCTP
layer. In either case, MTP3 responds example in its usual way.

    MTP3        M2UA        SCTP        SCTP        M2UA        MTP3
    ----        ----        ----        ----        ----        ----

                 Communication Up
                 <------------

                 (If Emergency Ceases,
                  Link proving is done
                  by M2UA now.)

     Indication
     (Link In Service)
     <------------

    MTP3        M2UA        SCTP        SCTP        M2UA        MTP3
    ----        ----        ----        ----        ----        ----

                 Communication Lost
                 <------------

     Indication
     (Link Out of Service)
     <------------

4.3.5  Congestion Notification Section 4.1.2, and ASP2 wishes to Upper layer

MTP3 layer expects notification over-
ride ASP1 and take over the traffic:

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

4.2.3 (n+k Sparing, Load-sharing case, withdrawal of ASP)

Following on from the link congestion.  For example,
this is accomplished by two messages 1) Link Congestion Onset 2) Link
Congestion Abated.  Congestion is assumed if M2UA layer notices
repeated failures to send requests example in Section 4.1.4, and ASP1 withdraws from
service:

   SG                  ASP1                 ASP2                 ASP3
    |                    |                   |                   |
    |<----ASP Inact.-----|                   |                   |
    |--NTFY(ASP-Inact.)->|                   |                   |
    |                    |                   |                   |
    |---------------------------------NTFY(Ins. ASPs)(Optional)->|
    |                    |                   |                   |
    |<-----------------------------------------ASP Act. (Ldshr)--|
    |-------------------------------------------ASP Act. (Ack)-->|
    |                    |                   |                   |

The Notify message to SCTP (this is implementation
dependent and it ASP3 is assumed that optional, as well as the SEND Failure has an error code
"life time expired").  Subsequently M2UA ASP-Active from
ASP3.  The optional Notify can start polling status of
SCTP.  If all only occur if the messages are successfully transmitted over a period SG maintains knowledge
of time (implementation dependent) then it is assumed that the
congestion is abated. minimum ASP resources required - for example if the SG knows that
˘n+k÷ = ˘2+1÷ for a loadshare AS and ˘n÷ currently equals ˘1÷.

Note: If the congestion condition should continue, SG detects loss of the link will be taken out ASP1 M2UA peer (M2UA heartbeat loss
or detection of service.  In this case, it is possible
to start SCTP failure), the link changeover procedure. first SG-ASP1 ASP Inactive message
exchange would not occur.

4.3  SG to MGC, MTP Level 2 to MTP Level 3 Boundary Procedures

4.3.1  SS7 Link Alignment

The US National version of MGC can request that a SS7 has congestion levels. For US National
SS7, link be brought into alignment using the Indication primitive for Congestion Onset should report
normal or emergency procedure.  An example of the
congestion level.

In message flow to bring
a SS7 link in-service using the normal alignment procedure is shown
below.

          SG                                    ASP
           |                                     |
           |<---------Establish Req--------------|
           |                                     |
           |----------Establish Cfm------------->|
           |                                     |

An example below, M2UA has sent a of the message flow to SCTP.

    MTP3        M2UA        SCTP        SCTP        M2UA        MTP3
    ----        ----        ----        ----        ----        ----

                 Send Failure
                 <------------
                 Send Failure
                 <------------

                 Send Failure
                 <------------
                 "N" consecutive fails -
                  implementation specific

     Indication
     (Congestion Onset)
     <------------

                 Status
                 ------------>
                 Status
                 ------------>

                 Status
                 ------------>
                 polled for certain time until
                 congestion ceases -
                 implementation specific

     Indication
     (Congestion Abatement)
     <------------

4.3.6 bring a SS7 link in-service using the
emergency alignment procedure.

          SG                                    ASP
           |                                     |
           |<----State Req (STATUS_EMER_SET)-----|
           |                                     |
           |-----State Cfm (STATUS_EMER_SET)---->|
           |                                     |
           |<---------Establish Req--------------|
           |                                     |
           |----------Establish Cfm------------->|
           |                                     |

4.3.2  SS7 Link Deactivation Release

The MGC can request that a SS7 link be taken out-of-service.  It uses
the Release Request message as shown below.

          SG                                    ASP
           |                                     |
           |<-----Release Req (RELEASE_MGMT)-----|
           |                                     |
           |------------Release Cfm------------->|
           |                                     |

The MTP3 SG can request autonomously indicate that a SS7-IP SS7 link be taken out-of-service. has gone out-of-service
as shown below.

          SG                                    ASP
           |                                     |
           |------Release Ind (RELEASE_PHYS)---->|
           |                                     |

4.3.3  Set and Clear Local Processor Outage

The MGC can set a Local Processor Outage condition.  It uses the Release
State Request message as shown below.

    MTP3        M2UA        SCTP        SCTP        M2UA        MTP3
    ----        ----        ----        ----        ----        ----

     Request
     (Deactivate Link)
     ------------>

                 Terminate
                 ------------>

                 Terminate Successful
                 <------------

                 Communication Lost
                 <------------

     Indication
     (Link Out of Service)
     <------------

4.3.7  Link Changeover

          SG                                    ASP
           |                                     |
           |<-----State Req (STATUS_LPO_SET)-----|
           |                                     |
           |------State Cfm (STATUS_LPO_SET)---->|
           |                                     |

The objective of the changeover is to ensure that signaling traffic
carried by the unavailable signaling link is diverted to MGC can clear a Local Processor Outage condition.  It uses the
alternative signaling link as quickly as possible while avoiding
State Request message loss, duplication, or mis-sequencing.  For this purpose, the
changeover procedure includes data retrieval, which is performed
before reopening the alternative signaling links to the diverted
traffic.  Data retrieval consists of identifying all those messages in
the retransmission buffer of the unavailable signaling link which have
not been received by the far end.  Retrieval includes transferring the
concerned messages to the transmission buffers of the alternative
links.  In order to support changeover, the SCTP SSN must be used in
place of the FSN/BSN as shown below.

          SG                                    ASP
           |                                     |
           |<----State Req (STATUS_LPO_CLEAR)----|
           |                                     |
           |-----State Cfm (STATUS_LPO_CLEAR)--->|
           |                                     |

4.3.4  Notification of SS7.

Stream Sequence Numbers used by SCTP (Signaling Control Transport
Protocol) are sixteen bits long.  MTP2's forward and backward sequence
numbers are only seven bits long.  Hence it is necessary to modify
MTP3 to accomodate the larger SSNs.  Reference [7] Processor Outage (local or remote)

The SG can be used as indicate a guide
for the MTP3 changes.

For data retrieval, MTP3 requests Backward Sequence Number (BSN) from
M2UA.  This is Local or Remote Processor Outage condition.  It
uses the sequence number State Indication message as shown below.

          SG                                    ASP
           |                                     |
           |-----State Ind (EVENT_ENTER_LPO)---->|
           |                                     |
           |-----State Ind (EVENT_EXIT_LPO)----->|
           |                                     |

          SG                                    ASP
           |                                     |
           |-----State Ind (EVENT_ENTER_RPO)---->|
           |                                     |
           |-----State Ind (EVENT_EXIT_RPO)----->|
           |                                     |

4.3.5  SS7 Link Changeover

An example of the last message received by the
local end.  During normal period, SCTP delivers ordered flow for a changeover is shown below.  In this
example, there were three messages to
the application.  However, during congestion or failure condition, in the
sequence numbers retransmission queue that
needed to be retrieved.

           SG                                    ASP
           |                                     |
           |----Retrieval Req (MTP2_RTRV_BSN)--->|
           |                                     |
           |------Retrieval Cfm (with BSN)------>|
           |                                     |
           |---Retrieval Req (MTP2_RTRV_MSGS)--->|
           |                      with FSN       |
           |                                     |
           |-----------Retrieval Cfm------------>|
           |                                     |
           |-----------Retrieval Ind------------>|
           |-----------Retrieval Ind------------>|
           |-------Retrieval Complete Ind------->|
           |                                     |

Note:  The number of Retrieval Indication is dependent on the acknowledged number of
messages can have gaps.  In
particular, in the SACK (selective acknowledgement message) message can retransmit queue that have several of these gaps.  Hence, it been requested.  Only one
Retrieval Complete Indication should be sent.

5.0 Security

5.1 Introduction

M2UA is important designed to scan through
these gaps and find the sequence number before first gap.  This is carry signaling messages for telephony services. As such,
M2UA must involve the
number from which security needs of several parties: the remote end has to transmit the messages.  So,
this is users
of the number considered as services; the Backward Sequence Number network providers and
communicated to the remote end.  In a similar way, the remote end also
detects the BSN and indicates to applications involved.
Additional requirements may come from local end. As soon as the MTP3 regulation.  While having some
overlapping security needs, any security solution should fulfill all of the
local end receives this BSN, MTP3 retrieves all
different parties' needs.

5.2 Threats

There is no quick fix, one-size-fits-all solution for security.  As a
transport protocol, M2UA has the unacknowledged
messages starting from BSN.  This following security objectives:

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

M2UA runs on top of SCTP.  SCTP [6] provides certain transport related
security features, such as:

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

When M2UA is accomplished through "Retrieve
FSN" message.  After all running in professionally managed corporate or service
provider network, it is reasonable to expect that this network includes
an appropriate security policy framework. The "Site Security Handbook" [9]
should be consulted for guidance.

When the messages are sent from network in which M2UA runs in involves more than one party, it
may not be reasonable to MTP3, expect that all parties have implemented security
in a
retrieval complete message sufficient manner.  In such a case, it is sent.

Note recommended that IPSEC is
used to ensure confidentiality of user payload.  Consult [10] for more
information on configuring IPSEC services.

5.3 Protecting Confidentiality

Particularly for mobile users, the sequence numbers requirement for confidentiality may
include the masking of IP addresses and messages requested by MTP3 are sent
from SCTP ports.  In this case application
level encryption is not sufficient; IPSEC ESP should be used instead.
Regardless of which level performs the encryption, the IPSEC ISAKMP
service should be used for key management.

6.0 IANA Considerations

A request will be made to IANA to assign an M2UA in value for the Communication Lost primitive.

    MTP3        M2UA Payload
Protocol Identifier in SCTP Payload Data chunk.  The following SCTP Payload
Protocol Identifier will be registered:

        M2UA        MTP3
    ----        ----        ----        ----        ----        ----

                 Communication Lost
                 <------------

     Indication
     (Link Out of Service)
     <------------

     Request
     (Retrieve BSN)
     ------------>

                 (M2UA locates
                  first gap in
                  received messages)

     Indication
     (Indicate BSN)
     <------------

     Request - COO (BSN) on another link
     ------------------------------------------------------------>

                                                      Request
                                                      (Retrieve BSN)
                                                     <------------

                                                     Indication
                                                     (Indicate BSN)
                                                     ------------>

                                               Request - COA (BSN)
     <------------------------------------------------------------

     Request
     (Retrieve FSN)
     ------------>

                 (M2UA locates
                  first gap    tbd

The SCTP Payload Protocol Identifier is included in
                  acknowledgements)

     Indication
     (FSB Not retrievable) (in case)
     <------------

     Indication
     (Retrieved Message)
     <------------

     Indication
     (Retrieved Message)
     <------------

     Indication
     (Retrieval Complete)
     <------------

     Send messages on another link.

4.4 Layer Management Communication Examples

An example of each SCTP Data chunk,
to indicate which protocol the message flows for communication between Layer Manage-
ment modules between SG and MGC SCTP is shown below. An active association
between MGC and SG carrying.  This Payload Protocol
Identifier is established (section 4.1) prior not directly used by SCTP but may be used by certain network
entities to identify the following
message flows.

                  SG                       MGC

                        <----------- Establish Request
                   Error ---------->
		   (Invalid Interface Id)

5.0  Security

SCN adaptation layers rely on SCTP type of information being carried in a Data chunk.

The User Adaptation peer may use the Payload Protocol Identifier as a way
of determining additional information about the data being presented to provide security.

6.0 it
by SCTP.

7.0  Acknowledgements

The authors would like to thank Ian Rytina Rytina, Hanns Juergen Schwarzbauer
and ZhangYi for his their valuable comments and suggestions.

7.0

8.0  References

[1] ITU-T Recommendation Q.700, 'Introduction To ITU-T Signalling
    System No. 7 (SS7)'

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

[3] ANSI T1.111 'Signalling System Number 7 - Message Transfer Part'

[4] Bellcore GR-246-CORE 'Bell Communications Research Specification
    of Signaling System Number 7', Volume 1, December 1995

[4]

[5] Framework Architecture for Signaling Transport, draft-ietf-sigtran-
    framework-arch-03.txt, June 1999

[5]

[6] Simple Control Transmission Protocol, draft-ietf-sigtran-sctp-00.txt,
    August 1999

[6] draft-ietf-sigtran-sctp-07.txt,
    March 2000

[7] Media Gateway Control Protocol (MGCP), draft-huitema-megaco-mgcp-
    v1-03.txt, August 1999

[7]

[8] ITU-T Recommendation Q.2210, 'Message transfer part level 3
    functions and messages using the services of ITU-T
    Recommendation Q.2140'

8.0

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

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

9.0  Author's Addresses

Ken Morneault                                     Tel: +1-703-484-3323
Cisco Systems Inc.                           EMail: kmorneau@cisco.com
13615 Dulles Technology Drive
Herndon, VA. 20171
USA

Malleswar Kalla                                   Tel: +1-973-829-5212
Telcordia Technologies             EMail: kalla@research.telcordia.com
MCC 1J211R
445 South Street
Morristown, NJ 07960
USA

Greg Sidebottom                                   Tel: +1-613-763-7305
Nortel Networks                     EMail: gregside@nortelnetworks.com
3685 Richmond Rd,
Nepean, Ontario
Canada  K2H5B7

Ram Dantu, Ph.D.                                  Tel: +1-972-477-8446
Alcatel USA                           EMail: ram.dantu@usa.alcatel.com
1000 Coit Road
Plano,                     Tel +1-972-234-6070 extension 211
IPmobile                                     EMail rdantu@ipmobile.com
1651 North Glenville, Suite 216
Richardson, TX 74075 75081
USA

Tom George                                        Tel: +1-972-519-3168
Alcatel USA                          EMail: tom.george@usa.alcatel.com
1000 Coit Road
Plano, TX 74075
USA

This Internet Draft expires June September 2000.