[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 3331

Network Working Group                                   Ken Morneault
INTERNET-DRAFT                                          Cisco Systems
                                                            Ram Dantu
                                                              NetRake
                                                      Greg Sidebottom
                                                  gregside consulting
                                                           Tom George
                                                              Alcatel
                                                       Brian Bidulock
                                                              OpenSS7
                                                          Jacob Heitz
                                                               Lucent


Expires in June 2002                                         Feb 2002



        Signaling System 7 (SS7) Message Transfer Part (MTP) 2 -
                        User Adaptation Layer
                  <draft-ietf-sigtran-m2ua-14.txt>


Status of This Memo

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

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

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

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

To learn the current status of any Internet-Draft, please check the
'1id-abstracts.txt' listing contained in the Internet- Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or
ftp.isi.edu (US West Coast).




Abstract

This Internet Draft defines a protocol for backhauling of SS7 MTP2
User signalling messages over IP using the Stream Control
Transmission Protocol (SCTP).  This protocol would be used between a
Signalling Gateway (SG) and Media Gateway Controller (MGC).  It is
assumed that the SG receives SS7 signalling over a standard SS7
interface using the SS7 Message Transfer Part (MTP) to provide
transport.  The Signalling Gateway would act as a Signalling Link
Terminal.




Morneault, et al                                                [Page 1]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


                        TABLE OF CONTENTS

1.  Introduction..............................................3
  1.1  Scope..................................................3
  1.2  Terminology............................................3
  1.3  Signalling Transport Architecture......................5
  1.4  Services Provide by the M2UA Adaptation Layer..........7
  1.5  Function Provided by the M2UA Layer....................9
  1.6  Definition of the M2UA Boundaries.....................11
2.  Conventions..............................................13
3.  Protocol Elements........................................13
  3.1  Common Message Header.................................13
  3.2  M2UA Message Header...................................17
  3.3  M2UA Messages.........................................18
4.  Procedures...............................................48
  4.1  Procedures to Support the M2UA-User Layer.............49
  4.2  Receipt of Primitives from the Layer Management.......49
  4.3  AS and ASP State Maintenance..........................51
  4.4  Link Key Management Procedures........................62
5.  Examples of MTP2 User Adaptation (M2UA) Procedures.......63
  5.1  Establishment of associations between SG and MGC......63
       examples
  5.2  MTP Level 2 / MTP Level 3 Boundary Examples...........66
  5.3  Layer Management Communication Examples...............66
6.  Timers...................................................71
7.  Security Considerations..................................71
  7.1 Threats................................................71
  7.2 Protecting Confidentiality.............................72
8.  IANA Considerations......................................72
  8.1 SCTP Payload Protocol Identifier.......................72
  8.2 IUA Protocol Extensions................................72
9.  Acknowledgements.........................................74
10. References...............................................74
11. Author's Addresses.......................................75























Morneault, et al                                                [Page 2]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


1.  Introduction

This draft defines a protocol for the backhauling of SS7 [1] MTP2 User
[2] [3] [4] (i.e. MTP3) signalling messages over IP using the Stream Control
Transmission Protocol (SCTP) [8].  This protocol would be used between
a Signalling Gateway (SG) and Media Gateway Controller (MGC).

1.1 Scope

There is a need for Switched Circuit Network (SCN) signalling protocol
delivery from an Signalling Gateway (SG) to a Media Gateway
Controller (MGC) [9].  The delivery mechanism addresses the following
objectives:

*  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 SCTP active associations between the SG and
   MGC

The SG will terminate up to MTP Level 2 and the MGC will terminate
MTP Level 3 and above.  In other words, the SG will transport MTP
Level 3 messages over an IP network to a MGC.

1.2 Terminology

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
Signalling 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, ...).

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

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.

Backhaul - Refers to the transport of signalling 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 [9].

Fail-over - The capability to reroute signalling traffic as required
to an alternate Application Server Process within an Application Server
in the event of failure or unavailability of a currently used Application
Server Process.  Fail-back MAY apply upon the return to service of a
previously unavailable Application Server Process.

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

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





Morneault, et al                                                [Page 3]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


Interface Identifier - The Interface Identifier identifies the physical
interface at the SG for which the signalling messages are sent/received.
The format of the Interface Identifier parameter can be text or integer,
the values of which are assigned according to network operator policy.
The values used are of local significance only, coordinated between the
SG and ASP.

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.

Link Key - The link key is a locally unique (between ASP and SG)
value that identifies a registration request for a particular
Signalling Data Link and Signalling Terminal pair.

MTP - The Message Transfer Part of the SS7 protocol

MTP2 - MTP Level 2, the signalling datalink layer of SS7

MTP3 - MTP Level 3, the signalling network layer of SS7

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

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

Signalling Data Link - An SDL refers to a specific communications
facility that connects two Signalling Link Terminals.

Signalling Gateway (SG) - An SG is a signalling agent at the edge of
the IP network.  An SG appears to the SS7 as one or more Signalling
Link Terminals that are connected to one or more Signalling Data Links
in the SS7 network.  An SG contains a set of one or more unique
Signalling Gateway Processes, on which one or more is normally
actively processing traffic.  Where an SG contains more than one SGP,
the SG is a logical entity.

Signalling Gateway Process (SGP) - A process instance that uses M2UA to
communicate to and from a Signalling Link Terminal.  It serves as an
active, backup or load-sharing proces of a Signalling Gateway.

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

Stream - A stream refers to an SCTP stream; a unidirectional logical
channel established from one SCTP endpoint to another associated SCTP
endpoint, within which all user messages are delivered in-sequence
except for those submitted to the unordered delivery service.



Morneault, et al                                                [Page 4]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


1.3  M2UA Overview

The framework architecture that has been defined for SCN signalling
transport over IP [9] uses two components:  a signalling common
transport protocol and an adaptation module to support the services
expected by a particular SCN signalling protocol from its underlying
protocol layer.

Within this framework architecture, this document defines a SCN
adaptation module that is suitable for the transport of SS7 MTP2 User
messages.  The only SS7 MTP2 User is MTP3.  The M2UA uses the services
of the Stream Control Transmission Protocol [8] as the underlying
reliable signalling common transport protocol.

In a Signalling Gateway, it is expected that the SS7 MTP2-User signalling
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 signalling messages to and
from an SS7 Signalling End Point (SEP) or Signalling Transfer Point (STP).
The SG then provides a interworking of transport functions
with the IP transport, in order to transfer the MTP2-User signalling
messages to and from an Application Server Process where the peer MTP2-
User protocol layer exists.

1.3.1  Example - SG to MGC

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

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

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

    NIF  - Nodal Interworking Function
    SEP  - SS7 Signalling Endpoint
    IP   - Internet Protocol
    SCTP - Stream Control Transmission Protocol (Reference [8])

        Figure 1  M2UA in the SG to MGC Application

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


Morneault, et al                                                [Page 5]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


It is recommended that the M2UA use the services of the Stream
Control Transmission Protocol (SCTP) as the underlying reliable
common signalling transport protocol.  The use of SCTP provides
the following features:

  - explicit packet-oriented delivery (not stream-oriented)
  - sequenced delivery of user messages within multiple streams,
    with an option for order-of-arrival delivery of individual
    user messages,
  - optional multiplexing of user messages into SCTP datagrams,
  - network-level fault tolerance through support of multi-homing
    at either or both ends of an association,
  - resistance to flooding and masquerade attacks, and
  - data segmentation to conform to discovered path MTU size

There are scenarios without redundancy requirements and
scenarios in which redundancy is supported below the transport
layer.  In these cases, the SCTP functions above MAY NOT be a
requirement and TCP can be used as the underlying common
transport protocol.



Morneault, et al                                                [Page 6]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


1.3.2  ASP Fail-over Model and Terminology

The M2UA layer supports ASP fail-over functions in order to support a
high availability of call and transaction processing capability.  All
MTP2-User messages incoming to a SGP from the SS7 network are assigned
to the unique Application Server, based on the Interface Identifier of
the message.

The M2UA layer supports a n+k redundancy model (active-standby,
loadsharing, broadcast) where n is the minimum number of redundant
ASPs required to handle traffic and k ASPs are available to take over
for a failed or unavailable ASP.  Note that 1+1 active/standby
redundancy is a subset of this model.  A simplex 1+0 model is also
supported as a subset, with no ASP redundancy.

1.3.3  Client/Server Model

It is recommended that the SGP and ASP be able to support both client
and server operation.  The peer endpoints using M2UA SHOULD be
configured so that one always takes on the role of client and the
other the role of server for initiating SCTP associations.  The
default orientation would be for the SGP to take on the role of server
while the ASP is the client.  In this case, ASPs SHOULD initiate the
SCTP association to the SGP.

The SCTP and TCP Registered User Port Number Assignment for M2UA
is 2904.

1.4  Services Provided by the M2UA Adaptation Layer

The SS7 MTP3/MTP2(MTP2-User) interface is retained at the termination
point in the IP network, so that the M2UA protocol layer is required to
provide the equivalent set of services to its users as provided by the
MTP Level 2 to MTP Level 3.

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

M2UA supports a MTP Level 2 / MTP Level 3 interface boundary that enables
a seamless, or as seamless as possible, operation of the MTP2-User peers
in the SS7 and IP domains.  An example of the primitives that need to be
supported can be found in [10].

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

The M2UA layer needs to provide some messages that will facilitate
communication between Layer Management modules on the SG and MGC.






Morneault, et al                                                [Page 7]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


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 received
M2UA message (e.g., an interface identifier value is not known to the
SG).

1.4.3  Support for management of active associations between SG and MGC

The M2UA layer on the SG keeps the state of the configured ASPs.  A set
of primitives between M2UA layer and the Layer Management are defined
below to help the Layer Management manage the association(s) between
the SG and the MGC. The M2UA layer can be instructed by the Layer
Management to establish a SCTP association to a peer M2UA node.  This
procedure can be achieved using the M-SCTP ESTABLISH primitive.

M-SCTP_ESTABLISH

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

M-SCTP_RELEASE

The M-SCTP_RELEASE primitives are used to request, indicate, and
confirm the release of a 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 an AS/ASP
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.


Morneault, et al                                                [Page 8]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


M-ASP_STATUS

The ASP status is stored inside M2UA layer on both the SG and MGC
sides.  The M-ASP_STATUS primitive can be used by Layer Management to
request the status of the Application Server Process from the M2UA
layer.  This primitive can also be used to indicate the status of the
Application Server Process.

M-ASP_MODIFY

The M-ASP_MODIFY primitive can be used by Layer Management to modify
the status of the Application Server Process.  In other words, the
Layer Management on the ASP side uses this primitive to initiate
the ASPM procedures.

M-AS_STATUS

The M-AS_STATUS primitive can be used by Layer Management to request
the status of the Application Server.  This primitive can also be
used to indicate the status of the Application Server.

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 Signalling 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.

The SGP maps an Interface Identifier to an SCTP association/stream
only when an ASP sends an ASP Active message for a particular Interface
Identifier.  It must be noted, however, that this mapping is dynamic
and could change at any time due to a change of ASP state.  This mapping
could even temporarily be invalid, for example during failover of one
ASP to another.  Therefore, the SGP MUST maintain the states of AS/ASP
and reference them during the routing of an messages to an AS/ASP.

Note that only one SGP SHOULD provide Signalling Link Terminal
services to an SS7 link.  Therefore, within an SG, an Application
Server SHOULD be active for only one SGP at any given point in time.

An example of the logical view of relationship between SS7 link,
Interface Identifier, AS and ASP in an SGP is shown below:










Morneault, et al                                                [Page 9]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


            /-------------------------------------------------+
           /   /----------------------------------------------|--+
          /   /                                               v  |
         /   /    +----+             act+-----+   +-------+ -+--+|-+-
SS7 link1-------->|IID |-+          +-->| ASP |-->| Assoc |      v
           /      +----+ |  +----+  |   +-----+   +-------+ -+--+--+-
          /              +->| AS |--+                        Streams
         /        +----+ |  +----+   stb+-----+
SS7 link2-------->|IID |-+              | ASP |
                  +----+                +-----+

where IID = Interface Identifier

A SGP MAY support more than one AS.  An AS MAY support more than
one Interface Identifier.

1.5.2  Support for the management of SCTP associations between the
       SGPs and ASPs

The M2UA layer at the SG maintains the availability state of all
configured ASPs, in order to manage the SCTP associations and the
traffic between the SG and ASPs.  As well, the active/inactive state
of remote ASP(s) are also maintained.  The Active ASP(s) are the
one(s) currently receiving traffic from the SG.

The M2UA layer MAY be instructed by local management to establish an
SCTP association to a peer M2UA node.  This can be achieved using the
M-SCTP_ESTABLISH primitive to request, indicate and confirm the
establishment of an SCTP association with a peer M2UA node.

The M2UA layer MAY also need to inform local management of the status of
the underlying SCTP associations using the M-SCTP_STATUS request and
indication primitive. For example, the M2UA MAY inform local management
of the reason for the release of an SCTP association, determined either
locally within the M2UA layer or by a primitive from the SCTP.

Also the M2UA layer may need to inform the local management of the
change in status of an ASP or AS.  This may be achieved using the M-ASP
STATUS request or M-AS_STATUS request primitives.

1.5.3 Status of ASPs

The M2UA layer on the SG MUST maintain the state of the ASPs it is
supporting.  The state of an ASP changes because of reception of
peer-to-peer messages (ASPM messages as described in Section 3.3.2)
or reception of indications from the local SCTP association.  ASP
state transition procedures are described in Section 4.3.1.

At a SGP, an Application Server list MAY contain active and inactive
ASPs to support ASP fail-over procedures.  When, for example, both
a primary and a backup 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 SGP to reflect the active Application Server Process.

Also the M2UA layer MAY need to inform the local management of the
change in status of an ASP or AS.  This can be achieved using the M-ASP
STATUS or M-AS_STATUS primitives.


1.5.4  SCTP Specifics

1.5.4.1  SCTP Stream Management

SCTP allows a user specified number of streams to be opened during
initialization of the association.  It is the responsibility of the
M2UA layer to ensure proper management of these streams.  Because of
the unidirectional nature of streams, a M2UA layer is not aware of the
stream information from its peer M2UA layer.  Instead, the Interface
Identifier is in the M2UA message header.

The use of SCTP streams within M2UA is recommended in order to minimize
transmission and buffering delay, therefore improving the overall
performance and reliability of the signalling elements.  A separate
SCTP stream can be used for each SS7 link.  Or, an implementation may
choose to split the SS7 link across several streams based on SLS.
This method may be of particular interest for high speed SS7 links
(MTP3b) since high speed links have a 24-bit sequence number and the
stream sequence number is 16-bits.


Morneault, et al                                               [Page 10]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


SCTP Stream '0' SHOULD NOT be used for MTP2 User Adaptation (MAUP)
messages (see Section 3) since stream '0' SHOULD only be used for ASP
Management (ASPM) messages (see Section 4.3.3).

1.5.5  Seamless SS7 Network Management Interworking

The M2UA layer on the SGP SHOULD pass an indication of unavailability
of the M2UA-User (MTP3) to the local Layer Management, if the
currently active ASP moves from the ACTIVE state.  The actions taken by
M2UAon the SGP with regards to MTP Level 2 should be in accordance
with the appropriate MTP specifications.

1.5.6  Flow Control / Congestion

It is possible for the M2UA layer to be informed of IP network
congestion onset and abatement by means of an implementation dependent
function (i.e. an indication from the SCTP).  The handling of
this congestion indication by M2UA is implementation dependent.
However, the actions taken by the SG should be accordance with the
appropriate MTP specification and should enable SS7 functionality
(e.g. flow control) to be correctly maintained.

1.5.7  Audit of SS7 Link State

After a failover of one ASP to another ASP, it may be necessary for the
M2UA on the ASP to audit the current SS7 link state to ensure consistency.
The M2UA on the SGP would respond to the audit request with information
regarding the current state of the SS7 link (i.e. in-service,
out-of-service, congestion state, LPO/RPO state).

1.6  Definition of the M2UA Boundaries

1.6.1  Definition of the M2UA / MTP Level 3 boundary

DATA
ESTABLISH
RELEASE
STATE
DATA RETRIEVAL
DATA RETRIEVAL COMPLETE

1.6.2  Definition of the M2UA / MTP Level 2 boundary

DATA
ESTABLISH
RELEASE
STATE
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 [8] Section 9.


Morneault, et al                                               [Page 11]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


1.6.4  Definition of Layer Management / M2UA Boundary

   M-SCTP_ESTABLISH request
   Direction: LM -> M2UA
   Purpose: LM requests ASP to establish an SCTP association with an
            SGP.

   M-SCTP_ESTABLISH confirm
   Direction: M2UA -> LM
   Purpose: ASP confirms to LM that it has established an SCTP
            association with an SGP.

   M-SCTP_ESTABLISH indication
   Direction: M2UA -> LM
   Purpose: SGP informs LM that an ASP has established an SCTP
            association.

   M-SCTP_RELEASE request
   Direction: LM -> M2UA
   Purpose: LM requests ASP to release an SCTP association with SGP.

   M-SCTP_RELEASE confirm
   Direction: M2UA -> LM
   Purpose: ASP confirms to LM that it has released SCTP association
            with SGP.

   M-SCTP_RELEASE indication
   Direction: M2UA -> LM
   Purpose: SGP informs LM that ASP has released an SCTP association.

   M-SCTP_RESTART indication
   Direction: M2UA -> LM
   Purpose: M2UA informs LM that a SCTP Restart indication has
            been received.

   M-SCTP_STATUS request
   Direction: LM -> M2UA
   Purpose: LM requests M2UA to report status of SCTP association.

   M-SCTP_STATUS indication
   Direction: M2UA -> LM
   Purpose: M2UA reports status of SCTP association.

   M-ASP_STATUS request
   Direction: LM -> M2UA
   Purpose: LM requests SGP to report status of remote ASP.

   M-ASP_STATUS indication
   Direction: M2UA -> LM
   Purpose: SGP reports status of remote ASP.

   M-AS_STATUS request
   Direction: LM -> M2UA
   Purpose: LM requests SG to report status of AS.


Morneault, et al                                               [Page 12]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


   M-AS_STATUS indication
   Direction: M2UA -> LM
   Purpose: SG reports status of AS.

   M-NOTIFY indication
   Direction: M2UA -> LM
   Purpose: ASP reports that it has received a NOTIFY message
            from its peer.

   M-ERROR indication
   Direction: M2UA -> LM
   Purpose: ASP or SGP reports that it has received an ERROR
            message from its peer.

   M-ASP_UP request
   Direction: LM -> M2UA
   Purpose: LM requests ASP to start its operation and send an ASP UP
            message to the SGP.

   M-ASP_UP confirm
   Direction: M2UA -> LM
   Purpose: ASP reports that it has received an ASP UP Acknowledgement
            message from the SGP.

   M-ASP_DOWN request
   Direction: LM -> M2UA
   Purpose: LM requests ASP to stop its operation and send an ASP DOWN
            message to the SGP.

   M-ASP_DOWN confirm
   Direction: M2UA -> LM
   Purpose: ASP reports that is has received an ASP DOWN Acknowledgement
            message from the SGP.

   M-ASP_ACTIVE request
   Direction: LM -> M2UA
   Purpose: LM requests ASP to send an ASP ACTIVE message to the SGP.

   M-ASP_ACTIVE confirm
   Direction: M2UA -> LM
   Purpose: ASP reports that is has received an ASP ACTIVE Acknowledgement
            message from the SGP.

   M-ASP_INACTIVE request
   Direction: LM -> M2UA
   Purpose: LM requests ASP to send an ASP INACTIVE message to the SGP.

   M-ASP_INACTIVE confirm
   Direction: M2UA -> LM
   Purpose: ASP reports that is has received an ASP INACTIVE
            Acknowledgement message from the SGP.

   M-LINK_KEY_REG Request
   Direction:  LM -> M2UA
   Purpose: LM requests ASP to register Link Key with SG by sending REG
            REQ message.


Morneault, et al                                               [Page 12]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


   M-LINK_KEY_REG Confirm
   Direction:   M2UA -> LM
   Purpose: ASP reports to LM that it has successfully received a REG
            RSP message from SG.

   M-LINK_KEY_REG Indication
   Direction:  M2UA -> LM
   Purpose:  SG reports to LM that it has successfully processed an
             incoming REG REQ message from ASP.

   M-LINK_KEY_DEREG Request
   Direction:  LM -> M2UA
   Purpose:  LM requests ASP to de-register Link Key with SG by sending
             DEREG REQ message.

   M-LINK_KEY_DEREG Confirm
   Direction:  M2UA -> LM
   Purpose:  ASP reports to LM that it has successfully received a
             DEREG RSP message from SG.

   M-LINK_KEY_DEREG  Indication
   Direction:  M2UA -> LM
   Purpose:  SG reports to LM that it has successfully processed an
             incoming DEREG REQ message from ASP.

2.0 Conventions

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

3.0  Protocol Elements

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

3.1  Common Message Header

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


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

                  Figure 2  Common Message Header

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


Morneault, et al                                               [Page 13]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


3.1.1  Version

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

       Value    Version
       -----    -------
         1      Release 1.0

3.1.2  Spare

The Spare field is 8-bits.  It SHOULD be set to all '0's by the sender
and ignored by the receiver.

3.1.3  Message Class

The following List contains the valid Message Classes:

   Message Class: 8 bits (unsigned integer)

         0      Management (MGMT) Message [IUA/M2UA/M3UA/SUA]
         1      Transfer Messages [M3UA]
         2      SS7 Signalling Network Management (SSNM) Messages [M3UA/SUA]
         3      ASP State Maintenance (ASPSM) Messages [IUA/M2UA/M3UA/SUA]
         4      ASP Traffic Maintenance (ASPTM) Messages [IUA/M2UA/M3UA/SUA]
         5      Q.921/Q.931 Boundary Primitives Transport (QPTM)
                Messages [IUA]
         6      MTP2 User Adaptation (MAUP) Messages [M2UA]
         7      Connectionless Messages [SUA]
         8      Connection-Oriented Messages [SUA]
         9      Routing Key Management (RKM) Messages (M3UA)
        10      Interface Identifier Management (IIM) Messages (M2UA)
     11 to 127  Reserved by the IETF
    128 to 255  Reserved for IETF-Defined Message Class extensions

3.1.4  Message Type

The following List contains the Message Types for the valid Message
Classes:

     MTP2 User Adaptatation (MAUP) Messages

         0      Reserved
         1      Data
         2      Establish Request
         3      Establish Confirm
         4      Release Request
         5      Release Confirm
         6      Release Indication
         7      State Request
         8      State Confirm
         9      State Indication
        10      Data Retrieval Request
        11      Data Retrieval Confirm
        12      Data Retrieval Indication
        13      Data Retrieval Complete Indication
        14      Congestion Indication
        15      Data Acknowledge
     16 to 127  Reserved by the IETF
    128 to 255  Reserved for IETF-Defined MAUP extensions


Morneault, et al                                               [Page 14]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


     Application Server Process State Maintenance (ASPSM) messages

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

     Application Server Process Traffic Maintenance (ASPTM) messages

         0      Reserved
         1      ASP Active (ACTIVE)
         2      ASP Inactive (INACTIVE)
         3      ASP Active Ack (ACTIVE ACK)
         4      ASP Inactive Ack (INACTIVE ACK)
      5 to 127  Reserved by the IETF
    128 to 255  Reserved for IETF-Defined ASPTM extensions

     Management (MGMT) Messages

         0      Error (ERR)
         1      Notify (NTFY)
      2 to 127  Reserved by the IETF
    128 to 255  Reserved for IETF-Defined MGMT extensions

  Interface Identifier Management (IIM) Messages

         0        Reserved
         1        Registration Request (REG REQ)
         2        Registration Response (REG RSP)
         3        Deregistration Request (DEREG REQ)
         4        Deregistration Response (DEREG RSP)
      5 to 127    Reserved by the IETF
    128 to 255    Reserved for IETF-Defined IIM extensions

3.1.5  Message Length

The Message Length defines the length of the message in octets,
including the header.  The Message Length MUST include parameter
padding bytes, if any.  The Message Length MUST NOT be longer
than a MTP3 message [2] [3] [5] plus the length of the common and
M2UA message headers.

3.1.6  Variable-Length Parameter Format

M2UA messages consist of a Common Header followed by zero or more
variable-length parameters, as defined by the message type.  The
variable-length parameters contained in a message are defined in a
Tag-Length-Value format as shown below.



Morneault, et al                                               [Page 15]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


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

Mandatory parameters MUST be placed before optional parameters in a
message.

Parameter Tag: 16 bits (unsigned integer)

The Type field is a 16 bit identifier of the type of parameter.  It
takes a value of 0 to 65534.  The common parameters used by adaptation
layers are in the range of 0x00 to 0xff.   The M2UA specific parameters
have Tags in the range 0x300 to 0x3ff.

The common parameter tags (used by all User Adaptation layers) that
M2UA uses are defined below:

   Parameter Value     Parameter Name
   ---------------     --------------
         0 (0x00)       Reserved
         1 (0x01)       Interface Identifier (Integer)
         2 (0x02)       Unused
         3 (0x03)       Interface Identifier (Text)
         4 (0x04)       Info String
         5 (0x05)       Unused
         6 (0x06)       Unused
         7 (0x07)       Diagnostic Information
         8 (0x08)       Interface Identifier (Integer Range)
         9 (0x09)       Heartbeat Data
        10 (0x0a)       Unused
        11 (0x0b)       Traffic Mode Type
        12 (0x0c)       Error Code
        13 (0x0d)       Status Type/Information
        14 (0x0e)       Unused
        15 (0x0f)       Unused
        16 (0x10)       Unused
        17 (0x11)       ASP Identifier
        18 (0x12)       Unused
        19 (0x13)       Correlation Id
       18-255           Reserved

The M2UA specific parameter Tags defined are as follows:

   Parameter Value     Parameter Name
   ---------------     --------------
     768 (0x0300)      Protocol Data 1
     769 (0x0301)      Protocol Data 2 (TTC)
     770 (0x0302)      State Request
     771 (0x0303)      State Event
     772 (0x0304)      Congestion Status
     773 (0x0305)      Discard Status
     774 (0x0306)      Action
     775 (0x0307)      Sequence Number
     776 (0x0308)      Retrieval Result
     777 (0x0309)      Link Key
     778 (0x030a)      Local-LK-Identifier
     779 (0x030b)      Signalling Data Terminal (SDT) Identifier
     780 (0x030c)      Signailng Data Link (SDL) Identifier
     781 (0x030d)      Registration Result
     782 (0x030e)      Registration Status
     783 (0x030f)      De-Registration Result
     784 (0x0310)      De-Registration Status


Morneault, et al                                               [Page 16]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


Parameter Length: 16 bits (unsigned integer)

The Parameter Length field contains the size of the parameter in
bytes, including the Parameter Tag, Parameter Length, and Parameter
Value fields.  Thus, a parameter with a zero-length Parameter Value
field would have a Length field of 4.  The Parameter Length does not
include any padding bytes.

Parameter Value: variable-length.

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

The total length of a parameter (including Tag, Parameter Length and
Value fields) MUST be a multiple of 4 bytes.  If the length of the
parameter is not a multiple of 4 bytes, the sender pads the Parameter
at the end (i.e., after the Parameter Value field) with all zero
bytes.  The length of the padding is NOT included in the parameter
length field.  A sender MUST NOT pad with more than 3 bytes.  The
receiver MUST ignore the padding bytes.

3.2  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 messages.

This message header will contain the Interface Identifier.  The
Interface Identifier identifies the physical interface at the SG for
which the signalling messages are sent/received. The format of the
Interface Identifier parameter can be text or integer, the values of
which are assigned according to network operator policy.  The values
used are of local significance only, coordinated between the SG and
ASP.

The integer formatted Interface Identifier MUST be supported.  The
text formatted Interface Identifier MAY optionally be supported.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x1)           |           Length=8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier (integer)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Figure 3  M2UA Message Header (Integer-based Interface Identifier)


The Tag value for Integer-based Interface Identifier is 0x1.  The
length is always set to a value of 8.




Morneault, et al                                               [Page 17]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x3)           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                   Interface Identifier (text)                 |

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

     Figure 4  M2UA Message Header (Text-based Interface Identifier)

The Tag value for the Text-based [7] Interface Identifier is 0x3.  The
length is equal to the string length of the Interface Identifier
name plus four bytes for the Tag and Length fields.  The maximum
length of the text-based Interface Identifier is 255 octets.


3.3 M2UA Messages

The following section defines the messages and parameter contents.
The M2UA messages will use the common message header (Figure 2) and
the M2UA message header (Figure 3).

3.3.1 MTP2 User Adaptation Messages

3.3.1.1 Data

The Data message contains an SS7 MTP2-User Protocol Data Unit (PDU).
The Data message contains the following parameter:

    Protocol Data (mandatory)
    Correlation Id (optional)

The format for the Data Message parameters is as follows:


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x300)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                       Protocol Data                           /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x311)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Correlation Id                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The Protocol Data field contains the MTP2-User application message in
network byte order starting with the Signalling Information Octet (SIO).
The Correlation Id parameter uniquely identifies the MSU carried in the
Protocol Data within an AS.  This Correlation Id parameter is assigned
by the sending M2UA.  The purpose of the Correlation Id is to permit
the newly active ASP to synchronize its processing of the traffic in
each ordered stream with other ASPs in the broadcast group.


Morneault, et al                                               [Page 18]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


The format for a Data Message with TTC PDU parameters is as follows:


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x301)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                       Protocol Data                           /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag (0x13)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Correlation Id                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The Protocol Data field contains the MTP2-User application message in
network byte order starting with the Length Indicator (LI) octet.
The Japanese TTC variant uses the spare bits of the LI octet for
priority.  The length of the Protocol Data MUST NOT exceed the length
of a MTP2-User application message [2] [3].

3.3.1.2  Data Acknowledge Message

The Data Acknowledge message contains the Correlation Id of the Data
message which the sending M2UA is acknowledging as successfully
processed to the peer M2UA.

The Data Acknowledge message contains the following parameter:

     Correlation Id       Mandatory

The following format MUST be used for the Data Ack Message:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag (0x13)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Correlation Id                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The Correlation Id parameter of the Data message and the Data Ack
message provide a mechanism, for those SG implementations capable for
taking advantage of them, to obtain an acknowledgement that the MSU
has been transferred to the M2UA peer before acknowleding the MSU to
the SS7 peer, removing the risk of losing messages due to association
failure or SCTP congestion.

The Data Ack message MUST be sent if a Correlation Id parameter is
received from the peer.  Otherwise, the Data Ack message MUST NOT be
sent.


Morneault, et al                                               [Page 19]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


If the Data Acknowledge is not sent for Correlation Id(s) or is sent
with Invalid Correlation Id(s), the SS7 link will eventually fail
dueto lack of MTP Level 2 acknowledgements of the SS7 peer's MSUs.

3.3.1.3  Establish (Request, Confirmation)

The Establish Request message is used to establish the SS7 link or to
indicate that the channel has been established.  The MGC controls the
state of the SS7 link.  When the MGC desires the SS7 link to be
in-service, it will send the Establish Request message.  Note that
the SGP MAY already have the SS7 link established at its layer.
If so, upon receipt of an Establish Request, the SGP takes no action
except to send an Establish Confirm.

When the MGC sends an M2UA Establish Request message, the MGC MAY
start a timer.  This timer would be stopped upon receipt of an M2UA
Establish Confirm.  If the timer expires, the MGC would resend the
M2UA Establish Request message and restart the timer.  In other words,
the MGC MAY continue to request the establishment of the datalink
on periodic basis until the desired state is achieved or take some
other action (notify the Management Layer).

The mode (Normal or Emergency) for bringing the SS7 link in service is
defaulted to Normal.  The State Request (described in Section 3.3.1.5
below) can be used to change the mode to Emergency.

3.3.1.4  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.

3.3.1.5  State Request

The State Request message can be sent from a MGC to cause an action
on a particular SS7 link supported by the Signalling Gateway Process.
The SGP sends a State Confirm to the MGC if the action has been
successfully completed.  The State Confirm reflects that state value
received in the State Request message.

The State Request message contains the following parameter:

    State (mandatory)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x302)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             State                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




Morneault, et al                                               [Page 20]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


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

         Define           Value        Description
   STATUS_LPO_SET          0x0      Request local processor outage
   STATUS_LPO_CLEAR        0x1      Request local processor outage
                                    recovered
   STATUS_EMER_SET         0x2      Request emergency alignment
   STATUS_EMER_CLEAR       0x3      Request normal alignment (cancel
                                    emergency)
   STATUS_FLUSH_BUFFERS    0x4      Flush or clear receive, transmit
                                    and retransmit queues
   STATUS_CONTINUE         0x5      Continue or Resume
   STATUS_CLEAR_RTB        0x6      Clear the retransmit queue
   STATUS_AUDIT            0x7      Audit state of link
   STATUS_CONG_CLEAR       0x8      Congestion cleared
   STATUS_CONG_ACCEPT      0x9      Congestion accept
   STATUS_CONG_DISCARD     0xa      Congestion discard

3.3.1.6  State Confirm

The State Confirm message will be sent by the SGP in response to a State
Request from the MGC.  The State Confirm reflects that state value
received in the State Request message.

The State Confirm message contains the following parameter:

    State (mandatory)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x302)           |           Length = 8          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             State                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The valid values for State are shown in the following table.  The value
of the State field SHOULD reflect the value received in the State
Request message.

         Define           Value        Description
   STATUS_LPO_SET          0x0      Request local processor outage
   STATUS_LPO_CLEAR        0x1      Request local processor outage
                                    recovered
   STATUS_EMER_SET         0x2      Request emergency alignment
   STATUS_EMER_CLEAR       0x3      Request normal alignment (cancel
                                    emergency)
   STATUS_FLUSH_BUFFERS    0x4      Flush or clear receive, transmit
                                    and retransmit queues
   STATUS_CONTINUE         0x5      Continue or Resume
   STATUS_CLEAR_RTB        0x6      Clear the retransmit queue
   STATUS_AUDIT            0x7      Audit state of link
   STATUS_CONG_CLEAR       0x8      Congestion cleared
   STATUS_CONG_ACCEPT      0x9      Congestion accept
   STATUS_CONG_DISCARD     0xa      Congestion discard


Morneault, et al                                               [Page 21]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


3.3.1.7  State Indication

The MTP2 State Indication message can be sent from a SGP to an ASP to
indicate a condition on a SS7 link.

The State Indication message contains the following parameter:

    Event (mandatory)


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x303)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Event                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

       Define            Value          Description
   EVENT_RPO_ENTER        0x1      Remote entered processor outage
   EVENT_RPO_EXIT         0x2      Remote exited processor outage
   EVENT_LPO_ENTER        0x3      Link entered processor outage
   EVENT_LPO_EXIT         0x4      Link exited processor outage

3.3.1.8  Congestion Indication

The Congestion Indication message can be sent from a Signalling Gateway
Process to an ASP to indicate the congestion status and discard status
of a SS7 link.  When the MSU buffer fill increases above an Onset
threshold or decreases below an Abatement threshold or crosses a Discard
threshold in either direction, the SGP SHALL send a congestion indication
message when it supports SS7 MTP2 variants that support multiple congestion
levels.

The SGP SHALL send the message only when there is actually a change
in either the discard level or the congestion level to report,
meaning it is different from the previously sent message.  In addition,
the SGP SHALL use an implementation dependent algorithm to limit the
frequency of congestion indication messages.

An implementation may optionally send Congestion Indication messages on
a "high priority" stream in order to potentially reduce delay.

The Congestion Indication message contains the following parameters:

    Congestion Status (mandatory)
    Discard Status (optional)






Morneault, et al                                               [Page 22]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x304)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Congestion Status                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x305)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Discard Status                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The valid values for Congestion Status and Discard Status are shown in
the following table.

         Define        Value        Description
       LEVEL_NONE       0x0       No congestion
       LEVEL_1          0x1       Congestion Level 1
       LEVEL_2          0x2       Congestion Level 2
       LEVEL_3          0x3       Congestion Level 3

For SS7 networks that do not support multiple levels of congestion, only
the LEVEL_NONE and LEVEL_3 values will be used.  For SS7 networks that
support multiple levels of congestion, it is possible for all values to
be used.  Refer to [2], [3] and [12] for more details on the Congestion
and Discard Status of SS7 signalling links.

3.3.1.9  Retrieval Request

The MTP2 Retrieval Request message is used during the MTP Level 3
changeover procedure to request the BSN, to retrieve PDUs from the
transmit and retransmit queues or to flush PDUs from the retransmit
queue.  Examples of the use of Retrieval Request for SS7 Link
Changeover are provided in Section 5.3.6.

The Retrieval Request message contains the following parameters:

    Action (mandatory)
    Sequence Number (optional)


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x306)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Action                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x307)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Sequence Number                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




Morneault, et al                                               [Page 23]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


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

        Define         Value       Description
   ACTION_RTRV_BSN      0x1     Retrieve the backward sequence number
   ACTION_RTRV_MSGS     0x2     Retrieve the PDUs from the transmit
                                and retransmit queues

In the Retrieval Request message, the Sequence Number field SHOULD NOT
be present if the Action field is ACTION_RTRV_BSN.  The Sequence Number
field contains the Forward Sequence Number (FSN) of the far end if the
Action is ACTION_RTRV_MSGS.

3.3.1.10  Retrieval Confirm

The MTP2 Retrieval Confirm message is sent by the Signalling Gateway
in response to a Retrieval Request message.  Examples of the use of
Retrieval Confirm for SS7 Link Changeover are provided in Section
5.3.6.

The Retrieval Confirm message contains the following parameters:

    Action (mandatory)
    Result (mandatory)
    Sequence Number (optional)


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x306)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Action                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x308)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Result                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x307)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Sequence Number                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The valid values for Action are the same as in Retrieval Request.

The values for Result are shown below: in the following table.

        Define         Value       Description
   RESULT_SUCCESS       0x0     Action successful
   RESULT_FAILURE       0x1     Action failed

When the Signalling Gateway Process sends a Retrieval Confirm to a
Retrieval Request, it echos the Action field.  If the Action was
ACTION_RTRV_BSN and the SGP successfully retrieved the BSN, the SGP
will put the Backward Sequence Number (BSN) in the Sequence Number
field and will indicate a success in the Result field.  If the BSN
could not be retrieved, the Sequence Number field will not be included
and the Result field will indicate failure.


Morneault, et al                                               [Page 24]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


For a Retrieval Confirm with Action of ACTION_RTRV_MSGS, the value of
the Result field will indicate success or failure.  A failure means
that the buffers could not be retrieved.  The Sequence Number field is
not used with ACTION_RTRV_MSGS.

3.3.1.11  Retrieval Indication

The Retrieval Indication message is sent by the Signalling Gateway with
a PDU from the transmit or retransmit queue.  The Retrieval Indication
message does not contain the Action or seq_num fields, just a MTP3
Protocol Data Unit (PDU) from the transmit or retransmit queue.
Examples of the use of Retrieval Indication for SS7 Link Changeover are
provided in Section 5.3.6.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag (0x300)          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                       Protocol Data                           /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

For TTC Data messages, the following parameter will be used to indicate
a TTC PDU which starts at LI.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag (0x301)          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     TTC Protocol Data                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The M2UA implementation MAY consider the use of the bundling feature
of SCTP for Retrieval Indication messages.

3.3.1.12  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 retrieval is complete.  In addition, it MAY contain a PDU (which
MUST be the last PDU) from the transmit or retransmit queue.

3.3.2  Application Server Process Maintenance (ASPM) Messages

The ASPM messages will only use the common message header.

3.3.2.1  ASP Up (ASPUP)

The 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.

Morneault, et al                                               [Page 25]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


The ASPUP message contains the following parameters

    ASP Identifier (optional)
    Info String (optional)

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


The format for ASPUP Message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xe)           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        ASP Identifier*                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x4)           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The optional ASP Identifier parameter would contain a unique value
that is locally significant among the ASPs that support an AS.  The
SGP should save the ASP Identifier to be used, if necessary, with the
Notify message (see Section 3.3.3.2).

The optional INFO String parameter can carry any meaningful UTF-8 [6]
character string along with the message.  Length of the INFO String
parameter is from 0 to 255 octets.  No procedures are presently
identified for its use but the INFO String MAY be used for debugging
purposes.

3.3.2.2 ASP Up Ack

The ASP Up Ack message is used to acknowledge an ASP Up message
received from a remote M2UA peer.

The ASPUP Ack message contains the following parameters:

    INFO String (optional)





Morneault, et al                                               [Page 26]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


The format for ASPUP Ack Message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x4)           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional Info String parameter is the
same as for the ASP UP message (See Section 3.3.2.1).

3.3.2.3  ASP Down (ASPDN)

The ASP Down (ASPDN) message is used to indicate to a remote M2UA peer
that the adaptation layer is not ready to receive traffic or
maintenance messages.

The ASPDN message contains the following parameters

     INFO String (optional)

The format for the ASPDN message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x4)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional Info String parameter is the
same as for the ASP Up message (See Section 3.3.2.1).

3.3.2.4 ASP Down Ack

The ASP Down Ack message is used to acknowledge an ASP Down message
received from a remote M2UA peer.

The ASP Down Ack message contains the following parameters:

     INFO String (optional)


Morneault, et al                                               [Page 27]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


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

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x4)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional Info String parameter is the
same as for the ASP UP message (See Section 3.3.2.1).

3.3.2.5  Heartbeat (BEAT)

The Heartbeat message is optionally used to ensure that the M2UA
peers are still available to each other.

The BEAT message contains the following parameter:

     Heartbeat Data           Optional

The format for the BEAT message is as follows:


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


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

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

3.3.2.6  Heartbeat Ack (BEAT ACK)

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

The BEAT ACK message contains the following parameter:

     Heartbeat Data           Optional


Morneault, et al                                               [Page 28]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


The format for the BEAT ACK message is as follows:

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

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

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

3.3.2.7  ASP Active (ASPAC)

The ASPAC message is sent by an ASP to indicate to an SGP that it is
Active and ready to be used.

The ASPAC message contains the following parameters:

     Traffic Mode Type (optional)
     Interface Identifier (optional)
        - Combination of integer and integer ranges, OR
        - string (text formatted)
     INFO String (optional)

The format for the ASPAC message using integer formatted Interface
Identifiers is as follows:





















Morneault, et al                                               [Page 29]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xb)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Traffic Mode Type                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Tag (0x1=integer)         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Interface Identifiers*                    /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Tag (0x8=integer range)    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier Start1*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier Stop1*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier Start2*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier Stop2*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     .                                                            .
     .                                                            .
     .                                                            .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier StartN*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier StopN*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \              Additional Interface Identifiers                 /
   /                    of Tag Type 0x1 or 0x8                     \
   \                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x4)             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The format for the ASPAC message using text formatted (string)
Interface Identifiers is as follows:









Morneault, et al                                               [Page 30]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xb)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Traffic Mode Type                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Tag (0x3=string)        |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Interface Identifier*                     /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \              Additional Interface Identifiers                 /
   /                       of Tag Type 0x3                         \
   \                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x4)             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The Traffic Mode 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            Override
     0x2            Load-share
     0x3            Broadcast

Within a particular AS, only one Traffic Mode Type can be used.
The Override value indicates that the ASP is operating in Override
mode, where the ASP takes over all traffic in an Application Server
(i.e., primary/backup operation), over-riding any currently active
ASPs in the AS.   In Load-share mode, the ASP will share in the traffic
distribution with any other currently active ASPs.  In Broadcast mode,
all of the Active ASPs receive all message traffic in the Application
Server.

The optional Interface Identifiers parameter contains a list of
Interface Identifier integers (Type 0x1 or Type 0x8) or text strings
(Type 0x3)indexing the Application Server traffic that the sending
ASP is configured/registered to receive.  If integer formatted
Interface Identifiers are being used, the ASP can also send ranges of
Interface Identifiers (Type 0x8).  Interface Identifier types Integer
(0x1) and Integer Range (0x8) are allowed in the same message.  Text
formatted Interface Identifiers (0x3) cannot be used with either
Integer (0x1) or Integer Range (0x8) types.



Morneault, et al                                               [Page 31]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


If no Interface Identifiers are included, the message is for all
provisioned Interface Identifiers within the AS(s) in which the
ASP is provisioned.  If only a subset of Interface Identifiers for an
AS are included, the ASP is noted as Active for all the Interface
Identifiers provisioned for that AS.

Note:  If the optional Interface Identifier parameter is present, the
integer formatted Interface Identifier MUST be supported, while the
text formatted Interface Identifier MAY be supported.

An SGP that receives an ASPAC with an incorrect or unsupported Traffic
Mode Type for a particular Interface Identifier will respond with an
Error Message (Cause: Unsupported Traffic Handling Mode).

The format and description of the optional Info String parameter is the
same as for the ASP UP message (See Section 3.3.2.1).

3.3.2.8  ASP Active Ack

The ASP Active (ASPAC) Ack message is used to acknowledge an ASP Active
message received from a remote M2UA peer.

The ASPAC Ack message contains the following parameters:

     Traffic Mode Type (optional)
     Interface Identifier (optional)
        - Combination of integer and integer ranges, OR
        - string (text formatted)
     INFO String (optional)

The format for the ASPAC Ack message with Integer-formatted Interface
Identifiers is as follows:















Morneault, et al                                               [Page 32]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xb)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Traffic Mode Type                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Tag (0x1=integer)         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Interface Identifiers*                    /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Tag (0x8=integer range)    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier Start1*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier Stop1*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier Start2*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier Stop2*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                            .
    .                                                            .
    .                                                            .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier StartN*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier StopN*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \              Additional Interface Identifiers                 /
   /                    of Tag Type 0x1 or 0x8                     \
   \                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x4)             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+













Morneault, et al                                               [Page 33]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


The format for the ASP Active Ack message using text formatted (string)
Interface Identifiers is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xb)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Traffic Mode Type                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Tag (0x3=string)        |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Interface Identifier*                     /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \              Additional Interface Identifiers                 /
   /                       of Tag Type 0x3                         \
   \                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x4)             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The format and description of the optional Info String parameter is the
same as for the ASP Up message (See Section 3.3.2.1).

The format of the Traffic Mode Type and Interface Identifier parameters
is the same as for the ASP Active message (See Section 3.3.2.5).

3.3.2.9  ASP Inactive (ASPIA)

The ASP Inactive (ASPIA) message is sent by an ASP to indicate to an
SGP that it is no longer an active ASP to be used from within a list
of ASPs.  The SGP will respond with an ASPIA Ack message and either
discard incoming messages or buffer for a timed period and then
discard.

The ASPIA message contains the following parameters:

     Interface Identifiers (optional)
        - Combination of integer and integer ranges, OR
        - string (text formatted)
     INFO String (optional)

The format for the ASP Inactive message parameters using Integer
formatted Interface Identifiers is as follows:




Morneault, et al                                               [Page 34]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Tag (0x1=integer)         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Interface Identifiers*                    /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Tag (0x8=integer range)    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier Start1*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier Stop1*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier Start2*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier Stop2*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                            .
    .                                                            .
    .                                                            .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier StartN*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier StopN*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \              Additional Interface Identifiers                 /
   /                    of Tag Type 0x1 or 0x8                     \
   \                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x4)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The format for the ASP Inactive message using text formatted (string)
Interface Identifiers is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Tag (0x3=string)        |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Interface Identifier*                     /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \              Additional Interface Identifiers                 /
   /                      of Tag Type 0x3                          \
   \                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x4)             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Morneault, et al                                               [Page 35]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


The format and description of the optional Interface Identifiers and
Info String parameters is the same as for the ASP Active message (See
Section 3.3.2.3).

The optional Interface Identifiers parameter contains a list of
Interface Identifier integers indexing the Application Server traffic
that the sending ASP is configured/registered to receive, but does not
want to receive at this time.

3.3.2.10 ASP Inactive Ack

The ASP Inactive (ASPIA) Ack message is used to acknowledge an ASP
Inactive message received from a remote M2UA peer.

The ASPIA Ack message contains the following parameters:

     Interface Identifiers (optional)
        - Combination of integer and integer ranges, OR
        - string (text formatted)
     INFO String (optional)

The format for the ASPIA Ack message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Tag (0x1=integer)         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Interface Identifiers*                    /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Tag (0x8=integer range)    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier Start1*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier Stop1*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier Start2*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier Stop2*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                             .
    .                                                             .
    .                                                             .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier StartN*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier StopN*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \              Additional Interface Identifiers                 /
   /                    of Tag Type 0x1 or 0x8                     \
   \                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x4)             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Morneault, et al                                               [Page 36]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


The format for the ASP Inactive Ack message using text formatted
(string) Interface Identifiers is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Tag (0x3=string)        |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Interface Identifier*                     /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \              Additional Interface Identifiers                 /
   /                      of Tag Type 0x3                          \
   \                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x4)             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The format of the Interface Identifier parameter is the same as for
the ASP Inactive message (See Section 3.3.2.7).

The format and description of the optional Info String parameter is
the same as for the ASP Up message (See Section 3.3.2.1).

3.3.3  Layer Management (MGMT) Messages

3.3.3.1  Error (ERR)

The Error (ERR) message is used to notify a peer of an error event
associated with an incoming message.  For example, the message type
might be unexpected given the current state, or a parameter value might
be invalid.

The ERR message contains the following parameters:

     Error Code (mandatory)
     Interface Identifier (optional)
     Diagnostic Information (optional)

The format for the ERR message is as follows:







Morneault, et al                                               [Page 37]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xc)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Error Code                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Tag (0x1, 0x3, or 0x8)    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Interface Identifier(s)*                  /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0x7)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Diagnostic Information*                   /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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
     Unsupported Message Class              0x3
     Unsupported Message Type               0x4
     Unsupported Traffic Handling Mode      0x5
     Unexpected Message                     0x6
     Protocol Error                         0x7
     Unsupported Interface Identifier Type  0x8
     Invalid Stream Identifier              0x9
     Not Used in M2UA                       0xa
     Not Used in M2UA                       0xb
     Not Used in M2UA                       0xc
     Refused - Management Blocking          0xd
     ASP Identifier Required                0xe
     Invalid ASP Identifier                 0xf
     ASP Active for Interface Identifier(s) 0x10
     Invalid Parameter Value                0x11
     Parameter Field Error                  0x12
     Unexpected Parameter                   0x13
     Not Used in M2UA                       0x14
     Not Used in M2UA                       0x15
     Missing Parameter                      0x16


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

The "Invalid Interface Identifier" error would be sent by a SGP if
an ASP sends a message (i.e. an ASP Active message) with an invalid
(unconfigured) Interface Identifier value.  One of the optional
Interface Identifier parameters (Integer-based, text-based or integer
range) MUST be used with this error code to identify the invalid
Interface Identifier(s) received.

Morneault, et al                                               [Page 38]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


The "Unsupported Traffic Handling Mode" error would be sent by a SGP
if an ASP sends an ASP Active with an unsupported Traffic Handling
Mode.  An example would be a case in which the SGP did not support
load-sharing.  One of the optional Interface Identifier parameters
(Integer-based, text-based or integer range) MAY be used with this
error code to identify the Interface Identifier(s).

The "Unexpected Message" error would be sent by an ASP if it received
a MAUP message from an SGP while it was in the Inactive state.

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

The "Invalid Stream Identifier" error would be sent if a message
was received on an unexpected SCTP stream (i.e.  a MGMT message
was received on a stream other than "0").

The "Unsupported Interface Identifier Type" error would be sent by
a SGP if an ASP sends a Text formatted Interface Identifier and the
SGP only supports Integer formatted Interface Identifiers.  When
the ASP receives this error, it will need to resend its message with
an Integer formatted Interface Identifier.

The "Unsupported Message Class" error would be sent if a message with
an unexpected or unsupported Message Class is received.

The "Refused - Management Blocking" error is sent when an ASP Up or
ASP Active message is received and the request is refused for
management reasons (e.g., management lock-out").

The "ASP Identifier Required" is sent by a SGP in response
to an ASPUP message which does not contain an ASP Identifier
parameter when the SGP requires one.  The ASP SHOULD resend the
ASPUP message with an ASP Identifier.

The "Invalid ASP Identifier" is send by a SGP in response to an
ASPUP message with an invalid (i.e. non-unique) ASP Identifier.

The "ASP Currently Active for Interface Identifier(s)" error is
sent by a SGP when a Deregistration request is received from an ASP
that is active for Interface Identifier(s) specified in the
Deregistration request.  One of the optional Interface Identifier
parameters (Integer-based, text-based or integer range) MAY be used
with this error code to identify the Interface Identifier(s).

The "Invalid Parameter Value " error is sent if a message is received
with an invalid parameter value (e.g., a State Request with an
an undefined State).

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

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

The "Missing Parameter" error would be sent if a mandatory parameter
were not included in a message.

The optional Diagnostic information can be any information germane 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 SHOULD be the first 40 bytes of the offending
message.


Morneault, et al                                               [Page 39]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


3.3.3.2  Notify (NTFY)

The Notify message is used to provide an autonomous indication of M2UA
events to an M2UA peer.

The NTFY message contains the following parameters:

     Status Type (mandatory)
     Status Information (mandatory)
     ASP Identifier (optional)
     Interface Identifiers (optional)
     INFO String (optional)

The format for the Notify message with Integer-formatted Interface
Identifiers is as follows:


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xd)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Status Type            |      Status Information       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xe)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        ASP Identifier*                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Tag (0x1=integer)         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Interface Identifiers*                    /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Tag (0x8=integer range)    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier Start1*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier Stop1*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier Start2*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier Stop2*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                             .
    .                                                             .
    .                                                             .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Interface Identifier StartN*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Interface Identifier StopN*                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \              Additional Interface Identifiers                 /
   /                    of Tag Type 0x1 or 0x8                     \
   \                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x4)             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Morneault, et al                                               [Page 40]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


The format for the Notify message with Text-formatted Interface
Identifiers is as follows:


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xd)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Status Type            |      Status Information       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag (0xe)           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        ASP Identifier*                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Tag (0x3=string)        |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                     Interface Identifier*                     /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \              Additional Interface Identifiers                 /
   /                        of Tag Type 0x3                        \
   \                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x4)             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               \
   \                          INFO String*                         /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The Status Type parameter identifies the type of the Notify message.
The following are the valid Status Type values:

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

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

      Value          Description
       1      reserved
       2      Application Server Inactive (AS_Inactive)
       3      Application Server Active (AS_Active)
       4      Application Server Pending (AS_Pending)

These notifications are sent from an SGP to an ASP upon a change in
status of a particular Application Server.  The value reflects the
new state of the Application Server.  The Interface Identifiers of
the AS MAY be placed in the message if desired.


Morneault, et al                                               [Page 41]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


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

      Value          Description
         1       Insufficient ASP resources active in AS
         2       Alternate ASP Active
         3       ASP Failure

In the Insufficient ASP Resources case, the SGP is indicating to an
ASP-INACTIVE ASP(s) in the AS that another ASP is required in order to
handle the load of the AS (Load-sharing mode).  For the Alternate ASP
Active case, the formerly Active ASP is informed when an alternate
ASP transitions to the ASP Active state in Override mode.  The ASP
Identifier (if available) of the Alternate ASP MUST be placed in the
message.  For the ASP Failure case, the SGP is indicating to ASP(s)
in the AS that one of the ASPs has transitioned to ASP-DOWN.  The ASP
Identifier (if available) of the failed ASP MUST be placed in the
message.

For each of the Status Information values in Status Type Other, the
Interface Identifiers of the affected AS MAY be placed in the message
if desired.

The format and description of the optional Interface Identifiers and
Info String parameters is the same as for the ASP Active message
(See Section 3.3.2.3).

3.3.4  Interface Identifier Management (IIM) Messages

The Interface Identifier Management messages are optional.  They are
used to support automatic allocation of Signalling Terminals or
Signalling Data Links [2][3].

3.3.4.1  Registration Request (REG REQ)

The REG REQ message is sent by an ASP to indicate to a remote M2UA
peer that it wishes to register one or more given Link Keys with the
remote peer.  Typically, an ASP would send this message to an SGP,
and expect to receive a REG RSP in return with an associated
Interface Identifier value.

The REG REQ message contains the following parameter:

     Link Key          (mandatory)

The format for the REG REQ message is as follows








Morneault, et al                                               [Page 42]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0309          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                           Link Key 1                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0309          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                           Link Key n                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Link Key:   fixed length

   The Link Key parameter is mandatory.  The sender of this message
   expects the receiver of this message will create a Link Key entry
   and assign a unique Interface Identifier value to it, if the Link
   Key entry does not yet exist.

   The Link Key parameter may be present multiple times in the same
   message.  This is used to allow the registration of multiple Link
   Keys in a single message.

The format of the Link Key parameter is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Local-LK-Identifier                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Signalling Data Terminal Identifier           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Signalling Data Link Identifier             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Local-LK-Identifier: 32-bit integer

   The mandatory Local-LK-Identifier field is used to uniquely
   (between ASP and SGP) identify the registration request.  The
   Identifier value is assigned by the ASP, and is used to correlate
   the response in a REG RSP message with the original registration
   request.  The Identifier value MUST remain unique until the REG
   RSP is received.

   The format of the Local-LK-Identifier field is as follows:


Morneault, et al                                               [Page 43]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x030a          |         Length = 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Local-LK-Identifier value                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Signalling Data Terminal Identifier

   The Signalling Data Terminal Identifier parameter is mandatory.
   It identifies the Signalling Data Terminal associated with the
   SS7 link for which the ASP is registering.  The format is as
   follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x030b          |         Length = 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Reserved             |        SDT Identifier         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The SDT Identifier is a 32-bit unsigned value which may only be
   significant to 12 or 14 bits depending on the SS7 variant which
   is supported by the MTP Level 3 at the ASP.  Insignificant SDTI
   bits are coded 0.

Signalling Data Link Identifier

   The Signalling Data Link Identifier parameter is mandatory.  It
   identifies the Signalling Data Link Identifier associated with
   the SS7 link for which the ASP is registering.  The format is as
   follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x030c          |         Length = 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Reserved             |        SDL Identifier         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The SDL Identifier is a 32-bit unsigned value which may only be
   significant to 12 or 14 bits depending on the SS7 variant which
   is supported by the MTP Level 3 at the ASP.  Insignificant SDLI
   bits are coded 0.

3.3.4.2  Registration Response (REG RSP)

The REG RSP message is used as a response to the REG REQ message
from a remote M2UA peer.  It contains indications of success/failure
for registration requests and returns a unique Interface Identifier
value for successful registration requests, to be used in subsequent
M2UA Traffic Management protocol.


Morneault, et al                                               [Page 44]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


The REG RSP message contains the following parameter:

     Registration Results   (mandatory)

The format for the REG RSP message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x030d          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                    Registration Result 1                      /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x030d          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                    Registration Result n                      /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Registration Results:  fixed length

   The Registration Results parameter contains one or more results,
   each containing the registration status for a single Link Key in
   the REG REQ message.  The number of results in a single REG RSP
   message MAY match the number of Link Key parameters found in the
   corresponding REG REQ message.  The format of each result 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Local-LK-Identifier                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Registration Status                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Interface Identifier                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Local-LK-Identifier:  32-bit integer

   The Local-LK-Identifier contains the same value as found in the
   matching Link Key parameter found in the REG REQ message.  The
   format of the Local-LK-Identifier is shown in Section 3.3.4.1.



Morneault, et al                                               [Page 45]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


Registration Status:  32-bit integer

   The Registration Result Status field indicates the success or the
   reason for failure of a registration request.

   Its values may be one of the following:

      0         Successfully Registered
        1         Error - Unknown
        2         Error - Invalid SDLI
        3         Error - Invalid SDTI
        4         Error - Invalid Link Key
        5         Error - Permission Denied
        6         Error - Overlapping (Non-unique) Link Key
        7         Error - Link Key not Provisioned
        8         Error - Insufficient Resources

   The format of the Registration Status field is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x030e          |         Length = 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Registration Status                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Interface Identifier:  32-bit integer

   The Interface Identifier field contains the Interface Identifier
   for the associated Link Key if the registration is successful.
   It is set to "0" if the registration was not successful.  The
   format of integer-based and text-based Interface Identifier
   parameters are shown in Section 3.2.

3.3.4.3  De-Registration Request (DEREG REQ)

The DEREG REQ message is sent by an ASP to indicate to a remote M2UA
peer that it wishes to de-register a given Interface Identifier.
Typically, an ASP would send this message to an SGP, and expects to
receive a DEREG RSP in return reflecting the Interface Identifier
and containing a de-registration status.

The DEREG REQ message contains the following parameter:

     Interface Identifier  (mandatory)

The format for the DEREG REQ message is as follows:











Morneault, et al                                               [Page 46]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Tag = 0x1 or 0x3          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                    Interface Identifier 1                     /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Tag = 0x1 or 0x3          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                    Interface Identifier n                     /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Interface Identifier

   The Interface Identifier parameter contains a Interface Identifier
   indexing the Application Server traffic that the sending ASP is
   currently registered to receive from the SGP but now wishes to
   de-register.  The format of integer-based and text-based Interface
   Identifier parameters are shown in Section 3.2.


3.3.4.4  De-Registration Response (DEREG RSP)

The DEREG RSP message is used as a response to the DEREG REQ message
from a remote M2UA peer.

The DEREG RSP message contains the following parameter:

     De-Registration Results   (mandatory)

The format for the DEREG RSP message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x030f          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                  De-Registration Result 1                     /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x030f          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                  De-Registration Result n                     /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Morneault, et al                                               [Page 47]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


De-Registration Results:  fixed length

   The De-Registration Results parameter contains one or more results,
   each containing the de-registration status for a single Interface
   Identifier in the DEREG REQ message.  The number of results in a
   single DEREG RSP message MAY match the number of Interface Identifier
   parameters found in the corresponding DEREG REQ message.  The format
   of each result 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Interface Identifier                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     De-Registration Status                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Interface Identifier:  32-bit integer

   The Interface Identifier field contains the Interface Identifier
   value of the matching Link Key to de-register, as found in the
   DEREG REQ.  The format of integer-based and text-based Interface
   Identifier parameters are shown in Section 3.2.

De-Registration Status:  32-bit integer

   The De-Registration Result Status field indicates the success or
   the reason for failure of the de-registration.

   Its values may be one of the following:

      0         Successfully De-registered
        1         Error - Unknown
        2         Error - Invalid Interface Identifier
        3         Error - Permission Denied
        4         Error - Not Registered

   The format of the De-Registration Status field is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0310          |         Length = 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    De-Registration Status                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.0  Procedures

The M2UA layer needs to respond to various primitives it receives from
other layers as well as messages it receives from the peer-to-peer
messages.  This section describes various procedures involved in
response to these events.


Morneault, et al                                               [Page 48]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


4.1 Procedures to Support the M2UA-User Layer

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

4.1.1  MTP Level 2 / MTP Level 3 Boundary Procedures

On receiving a primitive from the local upper layer, the M2UA layer
will send the corresponding MAUP message (see Section 3) to its peer.
The M2UA layer MUST fill in various fields of the common and specific
headers correctly.  In addition the message SHOULD be sent on the SCTP
stream that corresponds to the SS7 link.

4.1.2  MAUP Message Procedures

On receiving MAUP 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.

4.2 Receipt of Primitives from the Layer Management

On receiving primitives from the local Layer Management, the M2UA layer
will take the requested action and provide an appropriate response
primitive to Layer Management.

An M-SCTP_ESTABLISH request primitive from Layer Management at an ASP
will initiate the establishment of an SCTP association.  The M2UA
layer will attempt to establish an SCTP association with the remote
M2UA peer by sending an SCTP-ASSOCIATE primitive to the local SCTP
layer.

When an SCTP association has been successfully established, the SCTP
will send an SCTP-COMMUNICATION_UP notification primitive to the local
M2UA layer.  At the SGP that initiated the request, the M2UA layer will
send an M-SCTP_ESTABLISH confirm primitive to Layer Management when
the association setup is complete.  At the peer M2UA layer, an
M-SCTP_ESTABLISH indication primitive is sent to Layer Management
upon successful completion of an incoming SCTP association setup.

An M-SCTP_RELEASE request primitive from Layer Management initates the
shutdown of an SCTP association.  The M2UA layer accomplishes a
graceful shutdown of the SCTP association by sending an SCTP-SHUTDOWN
primitive to the SCTP layer.

When the graceful shutdown of the SCTP association has been
accomplished, the SCTP layer returns an SCTP-SHUTDOWN_COMPLETE
notification primitive to the local M2UA layer.  At the M2UA Layer that
initiated the request, the M2UA layer will send an M-SCTP_RELEASE
confirm primitive to Layer Management when the association shutdown is
complete.   At the peer M2UA Layer, an M-SCTP_RELEASE indication
primitive is sent to Layer Management upon abort or successful
shutdown of an SCTP association.


Morneault, et al                                               [Page 49]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


An M-SCTP_STATUS request primitive supports a Layer Management query
of the local status of a particular SCTP association.  The M2UA layer
simply maps the M-SCTP_STATUS request primitive to an SCTP-STATUS
primitive to the SCTP layer.  When the SCTP responds, the M2UA layer
maps the association status information to an M-SCTP_STATUS confirm
primitive.  No peer protocol is invoked.

Similar LM-to-M2UA-to-SCTP and/or SCTP-to-M2UA-to-LM primitive mappings
can be described for the various other SCTP Upper Layer primitives in
RFC2960 [8]  such as INITIALIZE, SET PRIMARY, CHANGE HEARTBEAT,
REQUEST HEARTBEAT, GET SRTT REPORT, SET FAILURE THRESHOLD, SET PROTOCOL
PARAMETERS, DESTROY SCTP INSTANCE, SEND FAILURE, AND NETWORK STATUS
CHANGE.  Alternatively, these SCTP Upper Layer primitives (and Status
as well) can be considered for modeling purposes as a Layer Management
interaction directly with the SCTP Layer.

M-NOTIFY indication and M-ERROR indication primitives indicate to Layer
Management the notification or error information contained in a
received M2UA Notify or Error message respectively.  These indications
can also be generated based on local M2UA events.

An M-ASP_STATUS request primitive supports a Layer Management query of
the status of a particular local or remote ASP.  The M2UA layer
responds with the status in an M-ASP_STATUS confirm primitive.  No M2UA
peer protocol is invoked.

An M-AS_STATUS request supports a Layer Management query of the status
of a particular AS.  The M2UA responds with an M-AS_STATUS confirm
primitive.  No M2UA peer protocol is invoked.

M-ASP_UP request, M-ASP_DOWN request, M-ASP_ACTIVE request and M-ASP_
INACTIVE request primitives allow Layer Management at an ASP to
initiate state changes.  Upon successful completion, a corresponding
confirm primitive is provided by the M2UA layer to Layer Management.
If an invocation is unsuccessful, an Error indication primitive is
provided in the primitive.  These requests result in outgoing ASP Up,
ASP Down, ASP Active and ASP Inactive messages to the remote M2UA peer
at an SGP.

4.2.1  Receipt of M2UA Peer Management Messages

Upon successful state changes resulting from reception of ASP Up,
ASP Down, ASP Active and ASP Inactive messages from a peer M2UA, the
M2UA layer SHOULD invoke corresponding M-ASP_UP, M-ASP_DOWN, M-
ASP_ACTIVE and M-ASP_INACTIVE, M-AS_ACTIVE, M-AS_INACTIVE, and M-
AS_DOWN indication primitives to the local Layer Management.

M-NOTIFY indication and M-ERROR indication primitives indicate to Layer
Management the notification or error information contained in a
received M2UA Notify or Error message.  These indications can also be
generated based on local M2UA events.


Morneault, et al                                               [Page 50]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


All MGMT messages, except BEAT and BEAT Ack, SHOULD be sent with
sequenced delivery to ensure ordering.  All MGMT messages, with the
exception of ASPTM, BEAT and BEAT Ack messages, SHOULD be sent on SCTP
stream '0'.  All ASPTM messages SHOULD be sent on the stream which
normally carries the data traffic to which the message applies.  BEAT
and BEAT Ack messages MAY be sent using out-of-order delivery, and
MAY be sent on any stream.

4.3  AS and ASP State Maintenance

The M2UA layer on the SGP maintains the state of each remote ASP, in
each Application Server that the ASP is configured to receive traffic,
as input to the M2UA message distribution function.

4.3.1  ASP States

The state of each remote ASP, in each AS that it is configured to
operate, is maintained in the M2UA layer in the SGP.  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 (e.g., ASP Active message indicating "Override");
   * Reception of indications from the SCTP layer; or
   * Local Management intervention.

The ASP state transition diagram is shown in Figure 5.  The possible
states of an ASP are:

ASP-DOWN: The remote M2UA peer at the ASP is unavailable and/or the
related SCTP association is down.  Initially all ASPs will be in this
state.  An ASP in this state SHOULD NOT be sent any M2UA messages, with
the exception of Heartbeat, ASP Down Ack and Error messages.

ASP-INACTIVE: The remote M2UA peer at the ASP is available (and the
related SCTP association is up) but application traffic is stopped.
In this state the ASP MAY be sent any non-MAUP M2UA messages.

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







Morneault, et al                                               [Page 51]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


                 Figure 5: ASP State Transition Diagram

                                   +--------------+
                                   |  ASP-ACTIVE  |
            +----------------------|              |
            |      Other   +-------|              |
            |   ASP in AS  |       +--------------+
            |   Overrides  |           ^     |
            |              |    ASP    |     | ASP
            |              |    Active |     | Inactive
            |              |           |     v
            |              |       +--------------+
            |              |       |              |
            |              +------>| ASP-INACTIVE |
            |                      +--------------+
            |                          ^     |
  ASP Down/ |                     ASP  |     | ASP Down /
  SCTP CDI/ |                     Up   |     | SCTP CDI/
  SCTP RI   |                          |     v SCTP RI
            |                      +--------------+
            |                      |              |
            +--------------------->|   ASP-DOWN   |
                                   |              |
                                   +--------------+


SCTP CDI: The SCTP CDI denotes the local SCTP layer's Communication
Down Indication to the Upper Layer Protocol (M2UA) on an SGP. The local
SCTP layer will send this indication when it detects the loss of
connectivity to the ASP's peer SCTP layer.  SCTP CDI is understood as
either a SHUTDOWN_COMPLETE notification or COMMUNICATION_LOST
notification from the SCTP layer.

SCTP RI: The local SCTP layer's Restart indication to the upper layer
protocol (M2UA) on an SG.  The local SCTP will send this indication when
it detects a restart from the ASP's peer SCTP layer.

4.3.2  AS States

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

   * ASP state transitions
   * Recovery timer triggers

The possible states of an AS are:

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


Morneault, et al                                               [Page 52]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


AS-INACTIVE: The Application Server is available but no application
traffic is active (i.e., one or more related ASPs are in the ASP-
INACTIVE state, but none in the ASP-ACTIVE state).  The recovery timer
T(r) is not running or has expired.

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

AS-PENDING: An active ASP has transitioned to ASP-INACTIVE or ASP-DOWN
and it was the last remaining active ASP in the AS.  A recovery timer
T(r) SHOULD be started and all incoming signalling messages SHOULD be
queued by the SGP.  If an ASP becomes ASP-ACTIVE before T(r) expires,
the AS is moved to the AS-ACTIVE state and all the queued messages will
be sent to the ASP.

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

Figure 6 shows an example AS state machine for the case where the
AS/ASP data is pre-configured.  For other cases where the AS/ASP
configuration data is created dynamically, there would be differences
in the state machine, especially at creation of the AS.

For example, where the AS/ASP configuration data is not created until
Registration of the first ASP, the AS-INACTIVE state is entered
directly upon the first successful REG REQ from an ASP.  Another
example is where the AS/ASP configuration data is not created until the
first ASP successfully enters the ASP-ACTIVE state.  In this case the
AS-ACTIVE state is entered directly.



















Morneault, et al                                             [Page 53]

Internet Draft       SS7 MTP2 User Adaptation Layer           Feb 2002


                 Figure 6: AS State Transition Diagram

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

    Tr = Recovery Timer


4.3.3 M2UA Management Procedures for Primitives

Before the establishment of an SCTP association the ASP state at both
the SGP and ASP is assumed to be in the state ASP-DOWN.

Once the SCTP association is established (see Section 4.2.1) and
assuming that the local M2UA-User is ready, the local M2UA ASP
Maintenance (ASPM) function will initiate the relevant procedures,
using the ASP Up/ASP Down/ASP Active/ASP Inactive messages to convey
the ASP state to the SGP (see Section 4.3.4).

If the M2UA layer subsequently receives an SCTP-COMMUNICATION_DOWN
or SCTP-RESTART indication primitive 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 ASP-DOWN.

In the case of SCTP-COMMUNICATION_DOWN, the SCTP client MAY try to re-
establish the SCTP association.  This MAY be done by the M2UA layer
automatically, or Layer Management MAY re-establish using the
M-SCTP_ESTABLISH request primitive.


Morneault, et al                                               [Page 54]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


In the case of an SCTP-RESTART indication at an ASP, the ASP is now
considered by its M2UA peer to be in the ASP-DOWN state.  The ASP, if
it is to recover, must begin any recovery with the ASP-Up procedure.

4.3.4 ASPM Procedures for Peer-to-Peer Messages

4.3.4.1 ASP Up Procedures

After an ASP has successfully established an SCTP association to an
SGP, the SGP waits for the ASP to send an ASP Up message, indicating
that the ASP M2UA peer is available.  The ASP is always the initiator
of the ASP Up message.  This action MAY be initiated at the ASP by an
M-ASP_UP request primitive from Layer Management or MAY be initiated
automatically by an M2UA management function.

When an ASP Up message is received at an SGP and internally the remote
ASP is in the ASP-DOWN state and not considered locked-out for local
management reasons, the SGP marks the remote ASP in the state ASP-
INACTIVE and informs Layer Management with an M-ASP_Up indication
primitive.  If the SGP is aware, via current configuration data, which
Application Servers the ASP is configured to operate in, the SGP
updates the ASP state to ASP-INACTIVE in each AS that it is a member.

Alternatively, the SGP may move the ASP into a pool of Inactive ASPs
available for future configuration within Application Server(s),
determined in a subsequent Registration Request or ASP Active
procedure.  If the ASP Up message contains an ASP Identifier, the SGP
should save the ASP Identifier for that ASP.  The SGP MUST send an
ASP Up Ack message in response to a received ASP Up message even if
the ASP is already marked as ASP-INACTIVE at the SGP.

If for any local reason (e.g., management lock-out) the SGP cannot
respond with an ASP Up Ack message, the SGP responds to an ASP Up
message with an Error message with Reason "Refused - Management
Blocking".

At the ASP, the ASP Up Ack message received is not acknowledged. Layer
Management is informed with an M-ASP_UP confirm primitive.

When the ASP sends an ASP Up message it starts timer T(ack).  If the
ASP does not receive a response to an ASP Up message within T(ack), the
ASP MAY restart T(ack) and resend ASP Up messages until it receives an
ASP Up Ack message.  T(ack) is provisionable, with a default of 2
seconds.  Alternatively, retransmission of ASP Up messages MAY be put
under control of Layer Management.  In this method, expiry of T(ack)
results in an M-ASP_UP confirm primitive  carrying a negative
indication.

The ASP MUST wait for the ASP Up Ack message before sending any other
M2UA messages (e.g., ASP Active or REG REQ).  If the SGP receives any
other M2UA messages before an ASP Up message is received (other than
ASP Down - see Section 4.3.4.2), the SGP MAY discard them.


Morneault, et al                                               [Page 55]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


If an ASP Up message is received and internally the remote ASP is in
the ASP-ACTIVE state, an ASP Up Ack message is returned, as well as
an Error message ("Unexpected Message), and the remote ASP state is
changed to ASP-INACTIVE in all relevant Application Servers.

If an ASP Up message is received and internally the remote ASP is
already in the ASP-INACTIVE state, an ASP Up Ack message is returned
and no further action is taken.

4.3.4.1.1  M2UA Version Control

If an ASP Up message with an unsupported version is received, the
receiving end responds with an Error message, indicating the version
the receiving node supports and notifies Layer Management.

This is useful when protocol version upgrades are being performed in a
network.  A node upgraded to a newer version SHOULD support the older
versions used on other nodes it is communicating with.  Because ASPs
initiate the ASP Up procedure it is assumed that the Error message
would normally come from the SGP.

4.3.4.2 ASP Down Procedures

The ASP will send an ASP Down message to an SGP when the ASP wishes to
be removed from service in all Application Servers that it is a member
and no longer receive any MAUP or ASPTM messages.  This action MAY be
initiated at the ASP by an M-ASP_DOWN request primitive from Layer
Management or MAY be initiated automatically by an M2UA management
function.

Whether the ASP is permanently removed from any AS is a function of
configuration management.  In the case where the ASP previously used
the Registration procedures (see Section 4.4) to register within
Application Servers but has not deregistered from all of them prior to
sending the ASP Down message, the SGP MUST consider the ASP as
Deregistered in all Application Servers that it is still a member.

The SGP marks the ASP as ASP-DOWN, informs Layer Management with an
M-ASP_Down indication primitive, and returns an ASP Down Ack message
to the ASP.

The SGP MUST send an ASP Down Ack message in response to a received ASP
Down message from the ASP even if the ASP is already marked as ASP-DOWN
at the SGP.

At the ASP, the ASP Down Ack message received is not acknowledged.
Layer Management is informed with an M-ASP_DOWN confirm primitive.  If
the ASP receives an ASP Down Ack without having sent an ASP Down
message, the ASP SHOULD now consider itself as in the ASP-DOWN state.
If the ASP was previously in the ASP-ACTIVE or ASP_INACTIVE state, the
ASP SHOULD then initiate procedures to return itself to its previous
state.



Morneault, et al                                               [Page 56]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


When the ASP sends an ASP Down message it starts timer T(ack).  If the
ASP does not receive a response to an ASP Down message within T(ack),
the ASP MAY restart T(ack) and resend ASP Down messages until it
receives an ASP Down Ack message.  T(ack) is provisionable, with a
default of 2 seconds.  Alternatively, retransmission of ASP Down
messages MAY be put under control of Layer Management.  In this method,
expiry of T(ack) results in an M-ASP_DOWN confirm primitive carrying a
negative indication.

4.3.4.4 ASP Active Procedures

Anytime after the ASP has received an ASP Up Ack message from the SGP,
the ASP MAY send an ASP Active message to the SGP indicating that
the ASP is ready to start processing traffic.  This action MAY be
initiated at the ASP by an M-ASP_ACTIVE request primitive from Layer
Management or MAY be initiated automatically by a M2UA management
function.  In the case where an ASP wishes to process the traffic for
more than one Application Server across a common SCTP association, the
ASP Active message(s) SHOULD contain a list of one or more Interface
Identifiers to indicate for which Application Servers the ASP Active
message applies. It is not necessary for the ASP to include any
Interface Identifiers of interest in a single ASP Active message,
thus requesting to become active in all Interface Identifiers at the
same time.  Multiple ASP Active messages MAY be used to activate
within the Application Servers independently, or in sets.  In the
case where an ASP Active message does not contain a Interface
Identifier parameter, the receiver must know, via configuration data,
which Application Server(s) the ASP is a member.

For the Application Servers that the ASP can successfully activate,
the SGP responds with one or more ASP Active Ack messages, including
the associated Interface Identifier(s) and reflecting any Traffic Mode
Type value present in the related ASP Active message.  The Interface
Identifier parameter MUST be included in the ASP Active Ack message(s)
if the received ASP Active message contained any Interface Identifiers.
Depending on any Traffic Mode Type request in the ASP Active message
or local configuration data if there is no request, the SGP moves the
ASP to the correct ASP traffic state within the associated Application
Server(s).  Layer Management is informed with an M-ASP_Active
indication.  If the SGP receives any Data messages before an ASP Active
message is received, the SGP MAY discard them.  By sending an ASP
Active Ack message, the SGP is now ready to receive and send traffic
for the related Interface Identifier(s).  The ASP SHOULD NOT send MAUP
messages for the related Interface Identifier(s) before receiving an
ASP Active Ack message, or it will risk message loss.

Multiple ASP Active Ack messages MAY be used in response to an ASP
Active message containing multiple Interface Identifiers, allowing
the SGP to independently acknowledge the ASP Active message for
different (sets of) Interface Identifiers.  The SGP MUST send
an Error message ("Invalid Interface Identifier") for each Interface
Identifier value that cannot be successfully activated.


Morneault, et al                                               [Page 57]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


In the case where an "out-of-the-blue" ASP Active message is received
(i.e., the ASP has not registered with the SG or the SG has no static
configuration data for the ASP), the message MAY be silently discarded.

The SGP MUST send an ASP Active Ack message in response to a received
ASP Active message from the ASP, if the ASP is already marked in the
ASP-ACTIVE state at the SGP.

At the ASP, the ASP Active Ack message received is not acknowledged.
Layer Management is informed with an M-ASP_ACTIVE confirm primitive.
It is possible for the ASP to receive Data message(s) before the ASP
Active Ack message as the ASP Active Ack and Data messages from an SG
may be sent on different SCTP streams.  Message loss is possible as
the ASP does not consider itself in the ASP-ACTIVE state until
reception of the ASP Active Ack message.

When the ASP sends an ASP Active message it starts timer T(ack).  If
the ASP does not receive a response to an ASP Active message within
T(ack), the ASP MAY restart T(ack) and resend ASP Active message(s)
until it receives an ASP Active Ack message.  T(ack) is provisionable,
with a default of 2 seconds.  Alternatively, retransmission of ASP
Active messages MAY be put under control of Layer Management.  In
this method, expiry of T(ack) results in an M-ASP_ACTIVE confirm
primitive carrying a negative indication.

There are three modes of Application Server traffic handling in the SGP
M2UA layer:  Override, Loadshare and Broadcast.  When included, the
Traffic Mode Type parameter in the ASP Active message indicates the
traffic handling mode to be used in a particular Application Server.
If the SGP determines that the mode indicated in an ASP Active message
is unsupported or incompatible with the mode currently configured for
the AS, the SGP responds with an Error message ("Unsupported / Invalid
Traffic Handling Mode").  If the traffic handling mode of the
Application Server is not already known via configuration data, then
the traffic handling mode indicated in the first ASP Active message
causing the transition of the Application Server state to AS-ACTIVE MAY
be used to set the mode.

In the case of an 0verride mode AS, reception of an ASP Active message
at an SGP causes the (re)direction of all traffic for the AS to the ASP
that sent the ASP Active message.  Any previously active ASP in the AS
is now considered to be in state ASP-INACTIVE and SHOULD no longer
receive traffic from the SGP within the AS.  The SGP then MUST send a
Notify message ("Alternate ASP Active") to the previously active ASP
in the AS, and SHOULD stop traffic to/from that ASP.  The ASP receiving
this Notify MUST consider itself now in the ASP-INACTIVE state, if it
is not already aware of this via inter-ASP communication with the
Overriding ASP.

In the case of a Load-share mode AS, reception of an ASP Active
message at an SGP causes the direction of traffic to the ASP sending
the ASP Active message, in addition to all the other ASPs that are
currently active in the AS.  The algorithm at the SGP for load-sharing
traffic within an AS to all the active ASPs is implementation
dependent.  The algorithm could, for example be round-robin or based
on information in the Data message (e.g., such as the SLS in the
Routing Label).


Morneault, et al                                               [Page 58]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


An SGP, upon reception of an ASP Active message for the first ASP in
a Loadshare AS, MAY choose not to direct traffic to a newly active ASP
until it determines that there are sufficient resources to handle the
expected load (e.g., until there are "n" ASPs in state ASP-ACTIVE in
the AS).

All ASPs within a load-sharing mode AS must be able to process any
Data message received for the AS, to accommodate any potential
fail-over or rebalancing of the offered load.

In the case of a Broadcast mode AS, reception of an ASP Active message
at an SGP causes the direction of traffic to the ASP sending the ASP
Active message, in addition to all the other ASPs that are currently
active in the AS.  The algorithm at the SGP for broadcasting
traffic within an AS to all the active ASPs is a simple broadcast
algorithm, where every message is sent to each of the active ASPs.

An SGP, upon reception of an ASP Active message for the first
ASP in a Broadcast AS, MAY choose not to direct traffic to a newly
active ASP until it determines that there are sufficient resources to
handle the expected load (e.g., until there are "n" ASPs in state
ASP-ACTIVE in the AS).

Whenever an ASP in a Broadcast mode AS becomes ASP-ACTIVE, the SGP
MUST tag the first DATA message broadcast in each SCTP stream with a
unique Correlation Id parameter.  The purpose of this Correlation Id
is to permit the newly active ASP to synchronize its processing of
traffic in each ordered stream with the other ASPs in the broadcast
group.

4.3.4.5 ASP Inactive Procedures

When an ASP wishes to withdraw from receiving traffic within an AS, the
ASP sends an ASP Inactive message to the SGP.  This action MAY be
initiated at the ASP by an M-ASP_INACTIVE request primitive from
Layer Management or MAY be initiated automatically by an M2UA
management function.  In the case where an ASP is processing the
traffic for more than one Application Server across a common SCTP
association, the ASP Inactive message contains one or more Interface
Identifiers to indicate for which Application Servers the ASP Inactive
message applies.  In the case where an ASP Inactive message does not
contain a Interface Identifier parameter, the receiver must know, via
configuration data, which Application Servers the ASP is a member and
move the ASP to the ASP-INACTIVE state in all Application Servers.
In the case of an Override mode AS, where another ASP has already
taken over the traffic within the AS with an ASP Active ("Override")
message, the ASP that sends the ASP Inactive message is already
considered by the SGP to be in state ASP-INACTIVE.  An ASP Inactive
Ack message is sent to the ASP, after ensuring that all traffic is
stopped to the ASP.



Morneault, et al                                               [Page 59]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


In the case of a Load-share mode AS, the SGP moves the ASP to the ASP-
INACTIVE state and the AS traffic is re-allocated across the remaining
ASPs in the state ASP-ACTIVE, as per the load-sharing algorithm
currently used within the AS.  A Notify message ("Insufficient ASP
resources active in AS") MAY be sent to all inactive ASPs, if required.
An ASP Inactive Ack message is sent to the ASP after all traffic
is halted and Layer Management is informed with an M-ASP_INACTIVE
indication primitive.

In the case of a Broadcast mode AS, the SGP moves the ASP to the
ASP-INACTIVE state and the AS traffic is broadcast only to the
remaining ASPs in the state ASP-ACTIVE.  A Notify message
("Insufficient ASP resources active in AS") MAY be sent to all
inactive ASPs, if required.  An ASP Inactive Ack message is sent to
the ASP after all traffic is halted and Layer Management is informed
with an M-ASP_INACTIVE indication primitive.

Multiple ASP Inactive Ack messages MAY be used in response to an
ASP Inactive message containing multiple Interface Identifers,
allowing the SGP to independently acknowledge for different (sets
of) Interface Identifiers.  The SGP sends an Error message ("Invalid
Interface Identifier") message for each invalid or unconfigured
Interface Identifer value in a received ASP Inactive message.

The SGP MUST send an ASP Inactive Ack message in response to a received
ASP Inactive message from the ASP and the ASP is already marked as ASP-
INACTIVE at the SGP.

At the ASP, the ASP Inactive Ack message received is not acknowledged.
Layer Management is informed with an M-ASP_INACTIVE confirm primitive.
If the ASP receives an ASP Inactive Ack without having sent an ASP
Inactive message, the ASP SHOULD now consider itself as in the
ASP-INACTIVE state.  If the ASP was previously in the ASP-ACTIVE
state, the ASP SHOULD then initiate procedures to return itself to
its previous state.

When the ASP sends an ASP Inactive message it starts timer T(ack).
If the ASP does not receive a response to an ASP Inactive message
within T(ack), the ASP MAY restart T(ack) and resend ASP Inactive
messages  until it receives an ASP Inactive Ack message.  T(ack) is
provisionable, with a default of 2 seconds.  Alternatively,
retransmission of ASP Inactive messages MAY be put under control of
Layer Management.  In this method, expiry of T(ack) results in a M-
ASP_Inactive confirm primitive carrying a negative indication.

If no other ASPs in the Application Server are in the state ASP-ACTIVE,
the SGP MUST send a Notify message ("AS-Pending") to all of the ASPs
in the AS which are in the state ASP-INACTIVE.  The SGP SHOULD start
buffering the incoming messages for T(r)seconds, after which messages
MAY be discarded.  T(r) is configurable by the network operator.  If
the SGP receives an ASP Active message from an ASP in the AS before
expiry of T(r), the buffered traffic is directed to that ASP and the
timer is cancelled.  If T(r) expires, the AS is moved to the
AS-INACTIVE state.


Morneault, et al                                               [Page 60]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


4.3.4.6 Notify Procedures

A Notify message reflecting a change in the AS state MUST be sent to
all ASPs in the AS, except those in the ASP-DOWN state, with
appropriate Status Information and any ASP Identifier of the failed
ASP.  At the ASP, Layer Management is informed with an M-NOTIFY
indication primitive.  The Notify message MUST be sent whether the
AS state change was a result of an ASP failure or reception of an
ASP State Management (ASPSM) / ASP Traffic Management (ASPTM) message.
In the second case, the Notify message MUST be sent after any related
acknowledgement messages (e.g., ASP Up Ack, ASP Down Ack, ASP Active
Ack, or ASP Inactive Ack).

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

In the case where a Notify message does not contain a Interface
Identifier parameter, the receiver must know, via configuration data,
of which Application Servers the ASP is a member and take the
appropriate action in each AS.

4.3.4.7 Heartbeat Procedures

The optional Heartbeat procedures MAY be used when operating over
transport layers that do not have their own heartbeat mechanism for
detecting loss of the transport association (i.e., other than SCTP).

Either M2UA peer may optionally send Heartbeat messages periodically,
subject to a provisionable timer T(beat).  Upon receiving a Heartbeat
message, the M2UA peer MUST respond with a Heartbeat Ack message.

If no Heartbeat Ack message (or any other M2UA message) is received
from the M2UA peer within 2*T(beat), the remote M2UA peer is considered
unavailable.  Transmission of Heartbeat messages is stopped and the
signalling process SHOULD attempt to re-establish communication if it
is configured as the client for the disconnected M2UA peer.

The Heartbeat message may optionally contain an opaque Heartbeat Data
parameter that MUST be echoed back unchanged in the related Heartbeat
Ack message.  The sender, upon examining the contents of the returned
Heartbeat Ack message, MAY choose to consider the remote M2UA peer as
unavailable.  The contents/format of the Heartbeat Data parameter is
implementation-dependent and only of local interest to the original
sender.  The contents may be used, for example, to support a Heartbeat
sequence algorithm (to detect missing Heartbeats), and/or a timestamp
mechanism (to evaluate delays).

Note: Heartbeat related events are not shown in Figure 5 "ASP state
transition diagram".




Morneault, et al                                               [Page 61]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


4.4  Link Key Management Procedures

The Interface Identifier Management procedures are optional.  They can
be used to support automatic allocation of Signalling Terminals or
Signalling Data Links [2][3].

4.4.1 Registration

An ASP MAY dynamically register with an SGP as an ASP within an
Application Server for individual Interface Identifier(s) using
the REG REQ message.  A Link Key parameter in the REG REQ specifies
the parameters associated with the Link Key.

The SGP examines the contents of the received Link Key parameters (SDLI
and SDTI) and compares them with the currently provisioned Interface
Identifiers.  If the received Link Key matches an existing SGP Link Key
entry, and the ASP is not currently included in the list of ASPs for
the related Application Server, the SGP MAY authorize the ASP to be
added to the AS.  Or, if the Link Key does not currently exist and the
received Link Key data is valid and unique, an SGP supporting dynamic
configuration MAY authorize the creation of a new Interface Identifier
and related Application Server and add the ASP to the new AS.  In either
case, the SGP returns a Registration Response message to the ASP,
containing the same Local-LK-Identifier as provided in the initial
request, a Registration Result "Successfully Registered" and the
Interface Identifier.  A unique method of Interface Identifier valid
assignment at the SG/SGP is implementation dependent but MUST be
guaranteed to be unique for each Application server or Link Key
served by SGP.

If the SGP determines that the received Link Key data is invalid, or
contains invalid parameter values, the SGP returns a Registration
Response message to the ASP, containing a Registration Result "Error
- Invalid Link Key", "Error - Invalid SDTI", "Error - Invalid SDLI"
as appropriate.

If the SGP determins that the Link Key parameter overlaps with an
existing Link Key entry, the SGP returns a Registration Response
message to the ASP, with a Registration Status of "Error -
Overlapping (Non-Unique) Link Key".  An incoming signalling message
received at an SGP cannot match against more than one Link Key.

If the SGP does not authorize the registration request, the SGP
returns a REG RSP message to the ASP containing the Registration
Result "Error - Permission Denied".

If an SGP determines that a received Link Key does not currently
exist and the SGP does not support dynamic configuration, the SGP
returns a Registration Response message to the ASP, containing a
Registration Result "Error - Link Key not Provisioned".

If an SGP determines that a received Link Key does not currently
exist and the SGP supports dynamic reconfiguration but does not have
the capacity to add new Link Key and Application Server entries, the
SGP returns a Registration Response message to the ASP, containing a
Registration Result "Error - Insufficient Resources".


Morneault, et al                                               [Page 62]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


An ASP MAY register multiple Link Keys at once by including a number
of Link Key parameters in a single REG REQ message.  The SGP MAY
response to each registration request in a single REG RSP message,
indicating the success or failure result for each Link Key in a
separate Registration Result parameter.  Alternatively, the SGP MAY
respond with multiple REG RSP messages, each with one or more
Registration Result parameters.  The ASP uses the Local-LK-Identifier
parameter to correlate the requests with the responses.

4.4.2 Deregistration

An ASP MAY dynamically de-register with an SGP as an ASP within an
Application Server for individual Interface Identifier(s) using
the DEREG REQ message.  A Interface Identifier parameter in the
DEREG REQ specifies which Interface Identifier to de-register.

The SGP examines the contents of the received Interface Identifier
parameter and validates that the ASP is currently registered in the
Application Server(s) related to the included Interface
Identifier(s).  If validated, the ASP is de-registered as an ASP in
the related Application Server.

The deregistration procedure does not necessarily imply the deletion
of Link Key and Application Server configuration data at the SGP.
Other ASPs may continue to be associated with the Application
Server, in which case the Link Key data CANNOT be deleted.  If a
Deregistration results in no more ASPs in an Application Server, an
SGP MAY delete the Link Key data.

The SGP acknowledges the de-registration requires by returning a DEREG
RSP to the requesting ASP.  The result of the de-registration is
found in the Deregistration Result parameter, indicating success or
failure with cause.

An ASP MAY de-register multiple Interface Identifiers at once by
including a number of Interface Identifiers in a single DEREG REQ
message.  The SGP MUST response to each deregistration request in a
single DEREG RSP message, indicating the success or failure result
for each Interface Identifier in a separate Deregistration Result
parameter.

5.0  Examples of MTP2 User Adaptation (M2UA) Procedures

5.1  Establishment of associations between SGP and MGC examples

5.1.1 Single ASP in an Application Server (1+0 sparing)

This scenario shows the example M2UA message flows for the establishment
of traffic between an SGP and an ASP, where only one ASP is configured
within an AS (no backup).  It is assumed that the SCTP association is
already set-up.



Morneault, et al                                               [Page 63]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


             SGP                       ASP1
              |
              |<---------ASP Up----------|
              |--------ASP Up Ack------->|
              |                          |
              |<-------ASP Active--------|
              |------ASP Active Ack----->|
              |                          |
              |------NTFY(AS-ACTIVE)---->|

5.1.2 Single ASP in an Application Server (1+0 sparing) with Dynamic
      Registration

This scenario is the same as the one shown in Section 5.1.1 except
with a dynamic registration (automatic allocation) of Interface
Identifier(s).

             SGP                       ASP1
              |
              |<---------ASP Up----------|
              |--------ASP Up Ack------->|
              |                          |
              |<--------REG REQ----------|
              |------REG REQ RESP------->|
              |                          |
              |<-------ASP Active--------|
              |------ASP Active Ack----->|
              |                          |
              |------NTFY(AS-ACTIVE)---->|

5.1.3 Two ASPs in Application Server (1+1 sparing)

This scenario shows the example M2UA message flows for the establishment
of traffic between an SGP and two ASPs in the same Application Server,
where ASP1 is configured to be active and ASP2 to be standby in the event
of communication failure or the withdrawal from service of ASP1.  ASP2 MAY
act as a hot, warm, or cold standby depending on the extent to which ASP1
and ASP2 share call/transaction state or can communicate call state under
failure/withdrawal events.


       SGP                       ASP1                       ASP2
        |                         |                          |
        |<--------ASP Up----------|                          |
        |-------ASP Up Ack------->|                          |
        |                         |                          |
        |<-----------------------------ASP Up----------------|
        |----------------------------ASP Up Ack------------->|
        |                         |                          |
        |                         |                          |
        |<-------ASP Active-------|                          |
        |-----ASP Active Ack----->|                          |
        |                         |                          |
        |                         |                          |
        |-----NTFY(AS-ACTIVE)---->|                          |
        |                         |                          |
        |------------------NTFY(AS-ACTIVE)------------------>|


Morneault, et al                                               [Page 64]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


5.2 ASP Traffic Fail-over Examples

5.2.1 (1+1 Sparing, withdrawal of ASP, backup Override)

Following on from the example in Section 5.1.2, and ASP withdraws from
service:

       SGP                       ASP1                       ASP2
        |                         |                          |
        |<-----ASP Inactive-------|                          |
        |----ASP Inactive Ack---->|                          |
        |                         |                          |
        |------------------NTFY(AS-PENDING)----------------->|
        |                         |                          |
        |<------------------------------ ASP Active----------|
        |-----------------------------ASP Active Ack-------->|
        |                         |                          |
        |------------------NTFY(AS-ACTIVE)------------------>|
        |                         |                          |

In this case, the SGP notifies ASP2 that the AS has moved to the
AS-PENDING state.  ASP2 sends ASP Active to bring the AS back to
the AS-ACTIVE state.  If ASP2 did not send the ASP Active message
before T(r) expired, the SGP would send a NOTIFY (AS-DOWN).

Note: If the SGP detects loss of the M2UA peer (through a detection
of SCTP failure), the initial SGP-ASP1 ASP Inactive message exchange
would not occur.

       SGP                       ASP1                       ASP2
        |                         |                          |
  (detects SCTP failure)
        |------------------NTFY(AS-PENDING)----------------->|
        |                         |                          |
        |<------------------------------ ASP Active----------|
        |-----------------------------ASP Active Ack-------->|
        |                         |                          |
        |------------------NTFY(AS-ACTIVE)------------------>|
        |                         |                          |

5.2.2 (1+1 Sparing, backup Override)

Following on from the example in Section 5.1.2, and ASP2 wishes to
override ASP1 and take over the traffic:

       SGP                       ASP1                       ASP2
        |                         |                          |
        |<-------------------------------ASP Active----------|
        |-----------------------------ASP Active Ack-------->|
        |----NTFY(Alt ASP-Act)--->|                          |
        |                         |                          |


Morneault, et al                                               [Page 65]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


In this case, the SGP notifies ASP1 that an alternative ASP has
overridden it.

5.3  SGP to MGC, MTP Level 2 to MTP Level 3 Boundary Procedures

When the M2UA layer on the ASP has a MAUP message to send to the SGP, it
will do the following:

  - Determine the correct SGP

  - Find the SCTP association to the chosen SGP

  - Determine the correct stream in the SCTP association based on
    the SS7 link

  - Fill in the MAUP message, fill in M2UA Message Header, fill in
    Common Header

  - Send the MAUP message to the remote M2UA peer in the SGP, over the
    SCTP association

When the M2UA layer on the SGP has a MAUP message to send to the ASP, it
will do the following:

  - Determine the AS for the Interface Identifier

  - Determine the Active ASP (SCTP association) within the AS

  - Determine the correct stream in the SCTP association based on
    the SS7 link

  - Fill in the MAUP message, fill in M2UA Message Header, fill in
    Common Header

  - Send the MAUP message to the remote M2UA peer in the ASP, over the
    SCTP association

5.3.1  SS7 Link Alignment

The MGC can request that a SS7 link be brought into alignment using the
normal or emergency procedure [2][3].  An example of the message flow
to bring a SS7 link in-service using the normal alignment procedure is
shown below.


Morneault, et al                                               [Page 66]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


       MTP2            M2UA                  M2UA               MTP3
        SGP             SGP                   ASP                ASP

        <----Start Req---|<---Establish Req----|<----Start Req------

        ---In Serv Ind-->|----Establish Cfm--->|----In Serv Ind---->


An example of the message flow to bring a SS7 link in-service using the
emergency alignment procedure.

 MTP2            M2UA                               M2UA           MTP3
  SGP             SGP                                ASP            ASP

  <----Emer Req----|<--State Req (STATUS_EMER_SET)----|<----Emer Req---

  -----Emer Cfm--->|---State Cfm (STATUS_EMER_SET)--->|----Emer Cfm---->

  <---Start Req----|<-------Establish Req-------------|<---Start Req----

  ---In Serv Ind-->|--------Establish Cfm------------>|---In Serv Ind-->

5.3.2  SS7 Link Release

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

     MTP2               M2UA                  M2UA                MTP3
      SGP                SGP                   ASP                 ASP

       <-----Stop Req-----|<---Release Req------|<-----Stop Req------

       --Out of Serv Ind->|----Release Cfm----->|--Out of Serv Ind-->


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

       MTP2           M2UA                  M2UA              MTP3
        SGP            SGP                   ASP               ASP

         --Out of Serv->|----Release Ind----->|--Out of Serv-->


5.3.3  Set and Clear Local Processor Outage

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

  MTP2            M2UA                               M2UA           MTP3
   SGP             SGP                                ASP            ASP

   <----LPO Req----|<---State Req (STATUS_LPO_SET)----|<----LPO Req---

   -----LPO Cfm--->|----State Cfm (STATUS_LPO_SET)--->|----LPO Cfm---->


Morneault, et al                                               [Page 67]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


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

  MTP2            M2UA                               M2UA          MTP3
   SGP             SGP                                ASP           ASP

   <---LPO Req---|<---State Req (STATUS_LPO_CLEAR)----|<----LPO Req---

   ----LPO Cfm-->|----State Cfm (STATUS_LPO_CLEAR)--->|----LPO Cfm---->


5.3.4  Notification of Remote Processor Outage

The SGP can indicate Remote has entered or exited the Processor Outage
condition for a SS7 link.  It uses the State Indication message as shown
below.

 MTP2           M2UA                                M2UA           MTP3
  SGP            SGP                                 ASP            ASP

  ----RPO Ind---->|----State Ind (EVENT_RPO_ENTER)-->|-----RPO Ind---->

  -RPO Rcvr Ind-->|----State Ind (EVENT_RPO_EXIT)--->|--RPO Rcvr Ind-->


5.3.5  Notification of SS7 Link Congestion

The SGP can indicate that a SS7 link has become congested.  It uses the
Congestion Indication message as shown below.

 MTP2           M2UA                                M2UA           MTP3
  SGP            SGP                                 ASP            ASP

  ----Cong Ind---->|--------Cong Ind (STATUS)------->|----Cong Ind---->

  -Cong Cease Ind->|--------Cong Ind (STATUS)------->|-Cong Cease Ind->

5.3.6  SS7 Link Changeover

An example of the message flow for an error free changeover is shown
below.  In this example, there were three messages in the retransmission
queue that needed to be retrieved.


  MTP2          M2UA                            M2UA             MTP3
   SGP           SGP                             ASP              ASP

   <-Rtrv BSN Req-|<--Rtrv Req (ACTION_RTRV_BSN)--|<--Rtrv BSN Req---
                               (seq_num = 0)

   -Rtrv BSN Cfm->|---Rtrv Cfm (ACTION_RTRV_BSN)->|---Rtrv BSN Cfm-->
                               (seq_num = BSN)

   <-Rtrv Msg Req-|<-Rtrv Req (ACTION_RTRV_MSGS)--|<--Rtrv Msg Req---
                               (seq_num = FSN)

   -Rtrv Msg Cfm->|--Rtrv Cfm (ACTION_RTRV_MSGS)->|---Rtrv Msg Cfm-->
                               (seq_num = 0)

   -Rtrv Msg Ind->|---------Retrieval Ind ------->|---Rtrv Msg Ind-->
   -Rtrv Msg Ind->|---------Retrieval Ind ------->|---Rtrv Msg Ind-->
   -Rtrv Msg Ind->|---------Retrieval Ind ------->|---Rtrv Msg Ind-->

   -Rtrv Compl Ind->|----Retrieval Compl Ind ---->|-Rtrv Compl Ind-->


Note:  The number of Retrieval Indication is dependent on the number of
messages in the retransmit queue that have been requested.  Only one
Retrieval Complete Indication SHOULD be sent.


Morneault, et al                                               [Page 68]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


An example of a message flow with an error retrieving the BSN is shown
below.

  MTP2          M2UA                            M2UA             MTP3
   SGP           SGP                             ASP              ASP

   <-Rtrv BSN Req-|<--Rtrv Req (ACTION_RTRV_BSN)--|<--Rtrv BSN Req---

   -BSN Not Rtrv->|---Rtrv Cfm (ACTION_RTRV_BSN)->|---BSN Not Rtrv-->
                               (seq_num = -1)

An example of a message flow with an error retrieving the messages is
shown below.

   <-Rtrv BSN Req-|<--Rtrv Req (ACTION_RTRV_BSN)--|<--Rtrv BSN Req---

   -Rtrv BSN Cfm->|---Rtrv Cfm (ACTION_RTRV_BSN)->|---Rtrv BSN Cfm-->
                               (seq_num = BSN)

   <-Rtrv Msg Req-|<-Rtrv Req (ACTION_RTRV_MSGS)--|<--Rtrv Msg Req---
                               (seq_num = FSN)

   -Rtrv Msg Cfm->|--Rtrv Cfm (ACTION_RTRV_MSGS)->|---Rtrv Msg Cfm-->
                               (seq_num = -1)

An example of a message flow for a request to drop messages (clear
retransmission buffers) is shown below.


  MTP2          M2UA                            M2UA             MTP3
   SGP           SGP                             ASP              ASP

 -Clr RTB Req----|<-StateReq (STATUS_CLEAR_RTB)--|<--Clr RTB Req-----

 -Clr RTB Req--->|-StateCfm (STATUS_CLEAR_RTB)-->|---Clr RTB Req---->


5.3.7  Flush and Continue

The following message flow shows a request to flush buffers.

  MTP2            M2UA                              M2UA          MTP3
   SGP             SGP                               ASP           ASP

   <--Flush Req----|<-State Req (STATUS_FLUSH_BUFS)--|<---Flush Req--

   ---Flush Cfm--->|--State Cfm (STATUS_FLUSH_BUFS)->|---Flush Cfm-->

The following message flow shows a request to continue.

  MTP2            M2UA                              M2UA          MTP3
   SGP             SGP                               ASP           ASP

   <---Cont Req----|<--State Req (STATUS_CONTINUE)---|<---Cont Req---

   ----Cont Cfm--->|---State Cfm (STATUS_CONTINUE)-->|----Cont Cfm-->


Morneault, et al                                               [Page 69]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


5.3.8  Auditing of SS7 link state

It may be necessary for the ASP to audit the current state of a SS7 link.
The flows below show an example of the request and all the potential
responses.

Below is an example in which the SS7 link is out-of-service.

 MTP2           M2UA                              M2UA           MGMT
  SGP            SGP                               ASP            ASP

                 |<----State Req (STATUS_AUDIT)----|<----Audit-------

                                                                 MTP3
                                                                  ASP

                 |-----------Release Ind---------->|-Out of Serv Ind->

                                                                 MGMT
                                                                  ASP

                 |-----State Cfm (STATUS_AUDIT)--->|----Audit Cfm--->

Below is an example in which the SS7 link is in-service.

 MTP2           M2UA                              M2UA           MGMT
  SGP            SGP                               ASP            ASP

                 |<----State Req (STATUS_AUDIT)----|<----Audit-------

                                                                 MTP3
                                                                  ASP

                 |-----------Establish Cfm-------->|---In Serv Ind-->

                                                                 MGMT
                                                                  ASP

                 |-----State Cfm (STATUS_AUDIT)--->|----Audit Cfm--->

Below is an example in which the SS7 link is in-service, but congested.



Morneault, et al                                               [Page 70]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


 MTP2           M2UA                              M2UA           MGMT
  SGP            SGP                               ASP            ASP

                 |<----State Req (STATUS_AUDIT)----|<----Audit-------

                                                                 MTP3
                                                                  ASP

                 |-----------Establish Cfm-------->|---In Serv Ind-->

                 |----------Congestion Ind-------->|---Cong Ind----->

                                                                 MGMT
                                                                  ASP

                 |-----State Cfm (STATUS_AUDIT)--->|----Audit Cfm--->

Below is an example in which the SS7 link is in-service, but in Remote
Processor Outage.

 MTP2           M2UA                              M2UA           MGMT
  SGP            SGP                               ASP            ASP

                 |<----State Req (STATUS_AUDIT)----|<---Audit Req----

                                                                 MTP3
                                                                  ASP

                 |-----------Establish Ind-------->|---In Serv Ind-->

                 |---State Ind (EVENT_RPO_ENTER)-->|----RPO Enter--->

                                                                 MGMT
                                                                  ASP

                 |-----State Cfm (STATUS_AUDIT)--->|----Audit Cfm--->

6.0 Timer Values

The recommended default values for M2UA timers are:

     T(r)                                    2 seconds
     T(ack)                                  2 seconds
     T(beat)   Heartbeat Timer               30 seconds

7.0 Security Considerations

M2UA is designed to carry signalling messages for telephony services.
As such, M2UA MUST involve the security needs of several parties: the
end users of the services; the network providers and the applications
involved.  Additional requirements MAY come from local regulation.
While having some overlapping security needs, any security solution
SHOULD fulfill all of the different parties' needs.

7.1 Threats

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

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


Morneault, et al                                               [Page 71]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


M2UA runs on top of SCTP.  SCTP [8] provides certain transport related
security features, such as:

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

When M2UA is running in professionally managed corporate or service
provider network, it is reasonable to expect that this network includes
an appropriate security policy framework. The "Site Security Handbook"
[13] SHOULD be consulted for guidance.

When the network in which M2UA runs in involves more than one party, it
MAY NOT be reasonable to expect that all parties have implemented
security in a sufficient manner.  In such a case, it is recommended that
IPSEC is used to ensure confidentiality of user payload.  Consult [14]
for more information on configuring IPSEC services.

7.2 Protecting Confidentiality

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

8.0 IANA Considerations

8.1 SCTP Payload Protocol Identifier

A request will be made to IANA to assign an M2UA value for the Payload
Protocol Identifier in SCTP Payload Data chunk.  The following SCTP
Payload Protocol Identifier has been registered:

        M2UA    "2"

The SCTP Payload Protocol Identifier is included in each SCTP Data chunk,
to indicate which protocol the SCTP is carrying.  This Payload Protocol
Identifier is not directly used by SCTP but MAY be used by certain
network entities to identify the type of information being carried in a
Data chunk.

The User Adaptation peer MAY use the Payload Protocol Identifier as a
way of determining additional information about the data being presented
to it by SCTP.

8.2  M2UA Protocol Extensions

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

 -- through definition of additional message classes,
 -- through definition of additional message types, and
 -- through definition of additional message parameters.

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


Morneault, et al                                               [Page 72]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


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

8.2.1 IETF Defined Message Classes

The documentation for a new message class MUST include the following
information:

(a) A long and short name for the message class.
(b) A detailed description of the purpose of the message class.

8.2.2 IETF Defined Message Types

Documentation of the message type MUST contain the following
information:

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

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

8.2.3 IETF-defined TLV Parameter Extension

Documentation of the message parameter MUST contain the following
information:

(a) Name of the parameter type.
(b) Detailed description of the structure of the parameter field. This
    structure MUST conform to the general type-length-value format
    described in Section 3.1.5.
(c) Detailed definition of each component of the parameter value.
(d) Detailed description of the intended use of this parameter type,
    and an indication of whether and under what circumstances
    multiple instances of this parameter type may be found within the
    same message type.

9.0  Acknowledgements

The authors would like to thank John Loughney, Neil Olson, Michael
Tuexen, Nikhil Jain, Steve Lorusso, Dan Brendes, Joe Keller, Heinz
Prantner, Barry Nagelberg, Naoto Makinae, Joyce Archibald, Mark
Kobine, Nitin Tomar, Harsh Bhondwe and Karen King for their valuable
comments and suggestions.












Morneault, et al                                               [Page 73]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


10.0  References

10.1  Normative

[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 Signalling System Number 7', Volume 1, December 1995

[5] Telecommunication Technology Committee (TTC) Standard JT-Q704,
    Message Transfer Part Signaling Network Functions,
    April 28, 1992.

[6] UTF-8, a transformation format of ISO 10646, RFC 2279, January
    1998

[7] Coded Character Set--7-Bit American Standard Code for
    Information Interchange, ANSI X3.4-1986.

10.2  Informative

[8] Stream Control Transmission Protocol, RFC 2960, October 2000

[9] Architectural Framework for Signalling Transport, RFC 2719,
    October 1999

[10] ITU-T Recommendation Q.2140, 'B-ISDN ATM Adaptation Layer',
    February 1995

[11] ITU-T Recommendation Q.2210, 'Message transfer part level 3
     functions and messages using the services of ITU-T
     Recommendation Q.2140', August 1995

[12] ITU-T Recommendation Q.751.1, 'Network Element Management
     Information Model for the Message Transfer Part', October 1995

[13] Site Security Handbook, RFC 2196, September 1997

[14] Security Architecture for the Internet Protocol, RFC 2401



Morneault, et al                                               [Page 74]

Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


11.0  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

Ram Dantu, Ph.D.                                   Tel +1-214-291-1111
NetRake Corporation                           EMail rdantu@netrake.com
3000 Technology Drive
Plano, TX 75074
USA

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

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

Brian Bidulock                                     Tel +1-972-839-4489
OpenSS7 Project                            EMail: bidulock@openss7.org
c/o #424, 4701 Preston Park Blvd.
Plano, TX 75093
USA

Jacob Heitz                                        Tek +1-510-747-2917
Lucent Technologies                           Email: jheitz@lucent.com
1701 Harbor Bay Parkway
Alameda, CA, 94502
USA




















Morneault, et al                                               [Page 75]
Internet Draft         SS7 MTP2 User Adaptation Layer           Feb 2002


Appendix A:  Signalling Network Architecture

A Signalling Gateway will support the transport of MTP2-User signalling
traffic received from the SS7 network to one or more distributed ASPs
(e.g., MGCs).  Clearly, the 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
availability and transfer performance of the physical nodes involved in
any particular exchange of information.  However, the M2UA protocol is
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 signalling 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 ASP.

Depending of course on the reliability of the SGP and ASP functional
elements, this can typically be met by the spreading SS7 links in a
SS7 linkset [1] across SGPs or 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 MAY be distributed over at least two Hosts.

An example logical network architecture relevant to carrier-grade
operation in the IP network domain is shown in Figure 7 below:


       **************                              **************
       *  ********__*______________________________*__********  * Host1
  SG1  *  * SGP1 *__*________________       _______*__* ASP1 *  *
       *  ********  *                |     |       *  ********  *
       *      .     *                |     |       *            *
       *      .     *                |     |       **************
       **************                |     |
                                     |     |
       **************                |     |
       *  ********__*______________________|
  SG2  *  * SGP2 *__*________        |
       *  ********  *        |       |
       *      .     *        |       |
       *      .     *        |       |
       **************        |       |             **************
                             |       |_____________*__********  * Host2
                             |_____________________*__* ASP2 *  *
              .                                    *  ********  *
              .            SCTP Associations       *            *
              .                                    **************
                                                           .
                                                           .
                                                           .

                    Figure 7:  Logical Model Example


To avoid a single point of failure, it is recommended that a minimum
of two ASPs be configured in an AS list, resident in separate hosts
and, therefore, available over different SCTP associations.  For
example, in the network shown in Figure 7, all messages for the
Interface Identifiers could be sent to ASP1 in Host1 or ASP2 in
Host2.  The AS list at SGP1 might look like the following:

    Interface Identifiers - Application Server #1
        ASP1/Host1  - State = Active
        ASP2/Host2  - State = Inactive

In this 1+1 redundancy case, ASP1 in Host1 would be sent any incoming
message for the Interface Identifiers registered.  ASP2 in Host2 would
normally be brought to the active state upon failure of ASP1/Host1.
In this example, both ASPs are Inactive or Active, meaning that the
related SCTP association and far-end M2UA peer is ready.

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 call/-
transaction state or be able to pass the call/transaction state between
each other.  Also, in the 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 scope of this document.


Html markup produced by rfcmarkup 1.111, available from https://tools.ietf.org/tools/rfcmarkup/