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Network Working Group                          Greg Sidebottom (Editor)
INTERNET-DRAFT                                             Guy Mousseau
                                                        Nortel Networks
                                                             Lyndon Ong
                                                   Point Reyes Networks
                                                             Ian Rytina
                                                               Ericsson
                                             Hanns-Juergen Schwarzbauer
                                                      Klaus Gradischnig
                                                                Siemens
                                                          Ken Morneault
                                                                  Cisco
                                                          Mallesh Kalla
                                                              Telcordia
                                                         Normand Glaude
                                               Performance Technologies


Expires in six months                                         Feb 2001



                SS7 MTP3-User Adaptation Layer (M3UA)
                  <draft-ietf-sigtran-m3ua-06.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
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or to cite them other than as 'work in progress.'

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To learn the current status of any Internet-Draft, please check the
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ftp.isi.edu (US West Coast).



Abstract

This Internet Draft defines a protocol for supporting the transport of
any SS7 MTP3-User signalling (e.g., ISUP and SCCP messages) over IP
using the services of the Stream Control Transmission Protocol.  Also,
provision is made for protocol elements that enable a seamless
operation of the MTP3-User peers in the SS7 and IP domains. This


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protocol would be used between a Signalling Gateway (SG) and a Media
Gateway Controller (MGC) or IP-resident Database.  It is assumed that
the SG receives SS7 signalling over a standard SS7 interface using the
SS7 Message Transfer Part (MTP) to provide transport.

















































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                        TABLE OF CONTENTS

1. Introduction.......................................................4
    1.1 Scope.........................................................4
    1.2 Terminology...................................................4
    1.3 M3UA Overview.................................................6
    1.4 Functional Areas.............................................12
    1.5 Sample Configurations........................................23
    1.6 Definition of M3UA Boundaries................................26
2. Conventions.......................................................29
3. M3UA Protocol Elements............................................29
    3.1 Common Message Header........................................29
    3.2 Variable-Length Parameter....................................32
    3.3 Transfer Messages............................................33
    3.4 SS7 Signalling Network management (SSNM) Messages............36
    3.5 Application Server Process Maintenance (ASPM) Messages.......44
    3.6 Management Messages..........................................60
4. Procedures........................................................63
    4.1 Procedures to Support the Services of the M3UA Layer.........63
    4.2 Receipt of M3UA Peer Management Messages.....................65
    4.3 Procedures to support the M3UA Management services...........66
    4.4 Procedures to Support the M3UA Services......................78
5. Examples of M3UA Procedures.......................................81
    5.1 Establishment of Association and Traffic
        Between SGs and ASPs.........................................81
    5.2 ASP traffic Fail-over Examples...............................86
    5.3 M3UA/MTP3-User Boundary Examples.............................87
6. Security..........................................................91
    6.1 Introduction.................................................91
    6.2 Threats......................................................91
    6.3 Protecting Confidentiality...................................91
7. IANA Considerations...............................................92
    7.1 SCTP Payload Protocol Identifier.............................92
    7.2 M3UA Protocol Extensions.....................................92
8. Acknowledgements..................................................93
9. References........................................................93
10. Author's Addresses...............................................95















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1.  Introduction

1.1 Scope

There is a need for Switched Circuit Network (SCN) signalling protocol
delivery from an SS7 Signalling Gateway (SG) to a Media Gateway
Controller (MGC) or IP-resident Database as described in the Framework
Architecture for Signalling Transport [1].  The delivery mechanism
SHOULD meet the following criteria:

*  Support for the transfer of all SS7 MTP3-User Part messages (e.g.,
   ISUP, SCCP, TUP, etc.)
*  Support for the seamless operation of MTP3-User protocol peers
*  Support for the management of SCTP transport associations and
   traffic between an SG and one or more MGCs or IP-resident Databases
*  Support for MGC or IP-resident Database process fail-over and load-
   sharing
*  Support for the asynchronous reporting of status changes to
   management

In simplistic transport terms, the SG will terminate SS7 MTP2 and MTP3
protocol layers and deliver ISUP, SCCP and/or any other MTP3-User
protocol messages, as well as certain MTP network management events,
over SCTP transport associations to MTP3-User peers in MGCs or IP-
resident Databases.


1.2 Terminology

Application Server (AS) - A logical entity serving a specific Routing
Key. An example of an Application Server is a virtual switch element
handling all call processing for a unique range of PSTN trunks,
identified by an SS7 DPC/OPC/CIC_range.  Another example is a virtual
database element, handling all HLR transactions for a particular SS7
DPC/OPC/SCCP_SSN combination.  The AS contains a set of one or more
unique Application Server Processes, of which one or more is normally
actively processing traffic.

Application Server Process (ASP) - A process instance of an Application
Server. An Application Server Process serves as an active or standby
process of an Application Server (e.g., part of a distributed virtual
switch or database). Examples of ASPs are processes (or process
instances) of MGCs, IP SCPs or IP HLRs.  An ASP contains an SCTP end-
point and may be configured to process signalling traffic within more
than one Application Server.

Association - An association refers to an SCTP association.  The
association provides the transport for the delivery of MTP3-User
protocol data units and M3UA adaptation layer peer messages.



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IP Server Process (IPSP) - A process instance of an IP-based
application.  An IPSP is essentially the same as an ASP, except that it
uses M3UA in a point-to-point fashion.  Conceptually, an IPSP does not
use the services of a Signalling Gateway.

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

Signalling Process - A process instance that uses M3UA to communicate
with other signalling process.  An ASP, a signalling gateway process
and an IPSP are all signalling processes.

Routing Key: A Routing Key describes a set of SS7 parameters and
parameter values that uniquely define the range of signalling traffic
to be handled by a particular Application Server. Parameters within the
Routing Key cannot extend across more than a single SS7 Destination
Point Code.

Routing Context - A value that uniquely identifies a Routing Key.
Routing Context values are either configured using a configuration
management interface, or by using the routing key management procedures
defined in this document.

Fail-over - The capability to re-route signalling traffic as required
to an alternate Application Server Process, or group of ASPs, within an
Application Server in the event of failure or unavailability of a
currently used Application Server Process.  Fail-over also applies upon
the return to service of a previously unavailable Application Server
Process.

Signalling Point Management Cluster (SPMC) - The complete set of
Application Servers represented to the SS7 network under one specific
SS7 Point Code of one specific Network Appearance.  SPMCs are used to
sum the availability / congestion / User_Part status of an SS7
destination point code that is distributed in the IP domain, for the
purpose of supporting MTP3 management procedures at an SG.  In some
cases, the SG itself may also be a member of the SPMC.  In this case,
the SG availability / congestion / User_Part status must also be taken
into account when considering any supporting MTP3 management actions.

MTP - The Message Transfer Part of the SS7 protocol.

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

MTP3-User - Any protocol normally using the services of the SS7 MTP3
(e.g., ISUP, SCCP, TUP, etc.).

Network Appearance - The Network Appearance identifies an SS7 network
context for the purposes of logically separating the signalling traffic


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between the SG and the Application Server Processes over a common SCTP
Association.  An example is where an SG is logically partitioned to
appear as an element in four separate national SS7 networks.  A Network
Appearance implicitly defines the SS7 Point Code(s), Network Indicator
and MTP3 protocol type/variant/version used within a specific SS7
network partition.  A physical SS7 route-set or link-set at an SG can
appear in only one network appearance. The Network Appearance is not
globally significant and requires coordination only between the SG and
the ASP. Therefore, in the case where an ASP is connected to more than
one SG, the same SS7 network context may be identified by different
Network Appearances depending over which SG a message is being
transmitted/received.

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

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

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

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


1.3 M3UA Overview

1.3.1 Protocol Architecture.

The framework architecture that has been defined for SCN signalling
transport over IP [1] uses multiple components, including a common
signalling transport protocol and an adaptation module to support the
services expected by a particular SCN signalling protocol from its
underlying protocol layer.

Within the framework architecture, this document defines an MTP3-User
adaptation module suitable for supporting the transfer of messages of
any protocol layer that is identified to the MTP Level 3 layer, in SS7
terms, as a user part.  The list of these protocol layers include, but
is not limited to, ISDN User Part (ISUP) [2,3,4], Signalling Connection
Control Part (SCCP) [5,6,7] and Telephone User Part (TUP) [8].  TCAP
[9,10,11] or RANAP [12] messages are transferred transparently by the
M3UA as SCCP payload, as they are SCCP-User protocols.

It is recommended that the M3UA use the services of the Stream Control
Transmission Protocol (SCTP) [13] as the underlying reliable common
signalling transport protocol. This is to take advantage of various
SCTP features such as:



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   - 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.

Under certain scenarios, such as back-to-back connections without
redundancy requirements, the SCTP functions above MAY NOT be a
requirement and TCP can be used as the underlying common transport
protocol.

1.3.2 Services Provided by the M3UA Layer

The M3UA Layer at an ASP or IPSP provides the equivalent set of
primitives at its upper layer to the MTP3-Users as provided by the MTP
Level 3 to its local MTP3-Users at an SS7 SEP.  In this way, the ISUP
and/or SCCP layer at an ASP or IPSP is unaware that the expected MTP3
services are offered remotely from an MTP3 Layer at an SG, and not by a
local MTP3 layer.  The MTP3 layer at an SG may also be unaware that its
local users are actually remote user parts over M3UA.  In effect, the
M3UA extends access to the MTP3 layer services to a remote IP-based
application.  The M3UA does not itself provide the MTP3 services.
However, in the case where an ASP is connected to more than one SG, the
M3UA Layer at an ASP must maintain the status of configured SS7
destinations and route messages according to the availability /
congestion status of the routes to these destinations via each SG.

The M3UA Layer may also be used for point-to-point signalling between
two IP Server Processes (IPSPs).  In this case, the M3UA provides the
same set of primitives and services at its upper layer as the MTP3.
However, in this case the expected MTP3 services are not offered
remotely from an SG.  The MTP3 services are provided but the procedures
to support these services are a subset of the MTP3 procedures due to
the simplified point-to-point nature of the IPSP to IPSP relationship.

1.3.2.1 Support for the transport of MTP3-User Messages

The M3UA provides the transport of MTP-TRANSFER primitives across an
established SCTP association between an SG and an ASP or between IPSPs.

The MTP-TRANSFER primitive information is encoded as in MTP3-User
messages.  In this way, the SCCP and ISUP messages received from the
SS7 network by the SG are not re-encoded into a different format for
transport between the M3UA peers.  The MTP3 Service Information Octet
(SIO) and Routing Label (OPC, DPC, and SLS) are included, encoded as
expected by the MTP3 and MTP3-User protocol layer.


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At an ASP, in the case where a destination is reachable via multiple
SGs, the M3UA must also choose via which SG the message is to be routed
or support load balancing across the SGs, ensuring that no mis-
sequencing occurs.

The M3UA does not impose a 272-octet signaling information field (SIF)
length limit as specified by the SS7 MTP Level 2 protocol [14] [15]
[16].  Larger information blocks can be accommodated directly by
M3UA/SCTP, without the need for an upper layer segmentation/re-assembly
procedure as specified in recent SCCP or ISUP versions.  However, in
the context of an SG, the maximum 272-octet block size must be followed
when inter-working to a SS7 network that does not support the transfer
of larger information blocks to the final destination.  This avoids
potential ISUP or SCCP fragmentation requirements at the SG.  However,
if the SS7 network is provisioned to support the Broadband MTP [20] to
the final SS7 destination, the information block size limit may be
increased past 272 octets.

1.3.2.2 Native Management Functions

The M3UA provides management of the underlying SCTP transport protocol
to ensure that SG-ASP and IPSP-IPSP transport is available to the
degree called for by the MTP3-User signalling applications.

The M3UA provides the capability to indicate errors associated with
received M3UA messages and to notify, as appropriate, local management
and/or the peer M3UA.

1.3.2.3 Inter-working with MTP3 Network Management Functions

At the SG, the M3UA must also provide inter-working with MTP3
management functions to support seamless operation of the user SCN
signalling applications in the SS7 and IP domains.  This includes:

  - Providing an indication to MTP3-Users at an ASP that a remote
    destination in the SS7 network is not reachable.

  - Providing an indication to MTP3-Users at an ASP that a remote
    destination in the SS7 network is now reachable.

  - Providing an indication to MTP3-Users at an ASP that messages to a
    remote MTP3-User peer in the SS7 network are experiencing SS7
    congestion.

  - Providing an indication to MTP3-Users at an ASP that the routes to
    a remote MTP3-User peer in the SS7 network are restricted.

  - Providing an indication to MTP3-Users at an ASP that a remote MTP3-
    User peer is unavailable.



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The M3UA layer at an ASP may initiate an audit of the availability, the
restricted or the congested state of remote SS7 destinations.  This
information is requested from the M3UA at the SG.

The M3UA layer at an ASP may also indicate to the SG that the M3UA
itself or the ASP or the ASP's Host is congested.

1.3.2.4 Support for the management of SCTP associations between the SG
and ASPs.

The M3UA layer at the SG maintains the availability state of all
configured remote ASPs, in order to manage the SCTP Associations and
the traffic between the M3UA peers.  As well, the active/inactive and
congestion state of remote ASPs is maintained.

The M3UA layer MAY be instructed by local management to establish an
SCTP association to a peer M3UA 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 M3UA node.  In order
to avoid redundant SCTP associations between two M3UA peers, one side
(client) must be designated to establish the SCTP association, or M3UA
configuration knowledge maintained to detect redundant associations
(e.g., via knowledge of the expected local and remote SCTP endpoint
addresses).

The M3UA 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 M3UA MAY inform local management
of the reason for the release of an SCTP association, determined either
locally within the M3UA layer or by a primitive from the SCTP.

Also the M3UA 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.

1.3.2.5 Support for the management of connections to multiple SGs

As shown in Figure 1 an ASP may be connected to multiple SGs. In such a
case a particular SS7 destination may be reachable via more than SG,
i.e., via more than one route. As MTP3 users only maintain status on a
destination and not on a route basis, M3UA must maintain the status
(availability, restriction, and/or congestion of route to destination)
of the individual routes, derive the overall availability or congestion
status of the destination from the status of the individual routes, and
inform the MTP3 users of this derived status whenever it changes.

1.3.3 Signalling Network Architecture

A Signalling Gateway is used to support the transport of MTP3-User
signalling traffic received from the SS7 network to multiple


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distributed ASPs (e.g., MGCs and IP Databases).  Clearly, the M3UA
protocol is not designed to meet the performance and reliability
requirements for such transport by itself.  However, the conjunction of
distributed architecture and redundant networks does allow for a
sufficiently reliable transport of signalling traffic over IP.  The
M3UA protocol is flexible enough to allow its operation and management
in a variety of physical configurations, enabling Network Operators to
meet their performance and reliability requirements.

To meet the stringent SS7 signalling reliability and performance
requirements for carrier grade networks, Network Operators SHOULD
ensure that no single point of failure is present in the end-to-end
network architecture between an SS7 node and an IP-based application.
This can typically be achieved through the use of redundant SGs,
redundant hosts, and the provision of redundant QOS-bounded IP network
paths for SCTP Associations between SCTP End Points. Obviously, the
reliability of the SG, the MGC and other IP-based functional elements
also needs to be taken into account.  The distribution of ASPs within
the available Hosts must also be considered.  As an example, for a
particular Application Server, the related ASPs should be distributed
over at least two Hosts.

One example of a physical network architecture relevant to SS7 carrier-
grade operation in the IP network domain is shown in Figure 1 below:




























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          SG                                     MGC

  Host#1 **************                          ************** Host#1
     =   *  ********__*__________________________*__********  *   =
    SG1  *  * SGP1 *__*_____      _______________*__* ASP1 *  *  MGC1
         *  ********  *     \    /               *  ********  *
         *  ********__*______\__/________________*__********  *
         *  * SGP2 *__*_______\/______      _____*__* ASP2 *  *
         *  ********  *       /\      |    |     *  ********  *
         *      :     *      /  \     |    |     *      :     *
         *  ********  *     /    \    |    |     *  ********  *
         *  * SGPn *  *     |    |    |    |     *  * ASPn *  *
         *  ********  *     |    |    |    |     *  ********  *
         **************     |    |    |    |     **************
                            |    |    \    /
  Host#2 **************     |    |     \  /      ************** Host#2
     =   *  ********__*_____|    |______\/_______*__********  *   =
    SG2  *  * SGP1 *__*_________________/\_______*__* ASP1 *  *  MGC2
         *  ********  *                /  \      *  ********  *
         *  ********__*_______________/    \_____*__********  *
         *  * SGP2 *__*__________________________*__* ASP2 *  *
         *  ********  *                          *  ********  *
         *      :     *     SCTP Associations    *      :     *
         *  ********  *                          *  ********  *
         *  * SGPn *  *                          *  * ASPn *  *
         *  ********  *                          *  ********  *
         **************                          **************

                      Figure 1 - Physical Model


In this model, each host has many application processes.  In the case
of the MGC, an ASP may provide service to one or more application
server, and is identified as an SCTP end point.  In the case of the SG,
a pair of signalling gateway processes may represent, as an example, a
single network appearance, serving a signalling point management
cluster.

This example model can also be applied to IPSP-IPSP signalling.  In
this case, each IPSP would have its services distributed across 2 hosts
or more, and may have multiple server processes on each host.

In the example above, each signalling process (SGP, ASP or IPSP) is the
end point to more than one SCTP association, leading to many other
signalling processes.  To support this, a signalling process must be
able to support distribution of M3UA messages to many simultaneous
active associations.  This message distribution function is based on
the status of provisioned routing keys, the availability of signalling
points in the SS7 network, and the redundancy model (active-standby,
load-sharing, n+k) of the remote signalling processes.



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For carrier grade networks, the failure or isolation of a particular
signalling process SHOULD NOT cause stable calls or transactions to be
lost.  This implies that signalling processes need, in some cases, to
share the call/transaction state or be able to pass the call state
information between each other.  In the case of ASPs performing call
processing, coordination may also be required with the related Media
Gateway to transfer the MGC control for a particular trunk termination.
However, this sharing or communication of call/transaction state
information is outside the scope of this document.

This model serves as an example.  M3UA imposes no restrictions as to
the exact layout of the network elements, the message distribution
algorithms and the distribution of the signalling processes.  Instead,
it provides a framework and a set of messages that allow for a flexible
and scalable signalling network architecture, aiming to provide
reliability and performance.


1.4 Functional Areas

1.4.1 Signalling Point Code Representation

Within an SS7 network, a Signalling Gateway is charged with
representing a set of nodes in the IP domain into the SS7 network for
routing purposes.  The SG itself, as a physical node in the SS7
network, must be addressable with an SS7 Point Code for MTP3 Management
purposes. The SG Point Code is also used for addressing any local MTP3-
Users at the SG such as an SG-resident SCCP function.

An SG may be logically partitioned to operate in multiple SS7 network
Appearances.  In such a case, the SG must be addressable with a Point
Code in each network appearance, and represents a set of nodes in the
IP domain into each SS7 network.  Alias Point Codes [15] may also be
used within an SG network appearance.

The M3UA places no restrictions on the SS7 Point Code representation of
an AS.  Application Servers can be represented under the same Point
Code of the SG, their own individual Point Codes or grouped with other
Application Servers for Point Code preservation purposes.  A single
Point Code may be used to represent the SG and all the Application
Servers together, if desired.

Where Application Servers are grouped under a Point Code address, an
SPMC will include more than one AS. If full advantage of SS7 management
procedures is to be taken (as is advisable in carrier grade networks)
care must be taken that, if one AS of an SPMC becomes unavailable, all
Application Servers of the SPMC become unavailable from the SG.
Otherwise, usage of SS7 transfer prohibited procedures by the SG
becomes problematic as either traffic to the unavailable AS cannot be
stopped/diverted or traffic to a still available AS will be
unnecessarily stopped/diverted. (Depending on the network configuration


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it may even be necessary to assign an individual SS7 point code to each
AS.)

Observing this principle is of particular importance if alternative
routing possibilities exist on the SS7 level (e.g. via mated SGs) or
application level (e.g. via another MGC/MG).

If an ASP or group of ASPs is available to the SS7 network via more
than one SG, each with its own Point Code, the ASP(s) should be
represented by a Point Code that is separate from any SG Point Code.
This allows these SGs to be viewed from the SS7 network as "STPs", each
having an ongoing  "route" to the same ASP(s).  Under failure
conditions where the ASP(s) become(s) unavailable from one of the SGs,
this approach enables MTP3 route management messaging between the SG
and SS7 network, allowing simple SS7 re-routing through an alternate SG
without changing the Destination Point Code Address of SS7 traffic to
the ASP(s).

Where an AS can be reached via more than one SG it is equally important
that the corresponding Routing Keys in the involved SGs are identical.
(Note: It is possible for the Routing Key configuration data to be
temporarily out-of-synch during configuration updates).


                           +--------+
                           |        |
              +------------+  SG 1  +--------------+
  +-------+   |  SS7 links | "STP"  |  IP network  |     ----
  |  SEP  +---+            +--------+              +---/      \
  |   or  |                                           |  ASPs  |
  |  STP  +---+            +--------+              +---\      /
  +-------+   |            |        |              |     ----
              +------------+  SG 2  +--------------+
                           | "STP"  |
                           +--------+

Note: there is no SG-to-SG communication shown, so each SG can be
reached only via the direct linkset from the SS7 network.

The following example shows a signalling gateway partitioned into two
network appearances.

                               SG
  +-------+              +---------------+
  |  SEP  +--------------| SS7 Ntwk |M3UA|              ----
  +-------+   SS7 links  |   "A"    |    |            /      \
                         |__________|    +-----------+  ASPs  |
                         |          |    |            \      /
  +-------+              | SS7 Ntwk |    |              ----
  |  SEP  +--------------+   "B"    |    |
  +-------+              +---------------+


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1.4.2 Routing Contexts and Routing Keys

1.4.2.1 Overview

The distribution of SS7 messages between the SG and the Application
Servers is determined by the Routing Keys and their associated Routing
Contexts. A Routing Key is essentially a set of SS7 parameters used to
filter SS7 messages, whereas the Routing Context parameter is a 4-byte
value (integer) that is associated to that Routing Key in a 1:1
relationship. The Routing Context therefore can be viewed as an index
into a sending node's Message Distribution Table containing the Routing
Key entries.

Possible SS7 address/routing information that comprise a Routing Key
entry includes, for example, the OPC, DPC, SIO found in the MTP3
routing label, or other MTP3-User specific fields such as the ISUP CIC,
SCCP subsystem number, or TCAP transaction ID.  Some example Routing
Keys are: the DPC alone, the DPC/OPC combination, the DPC/OPC/CIC
combination, or the DPC/SSN combination.  The particular information
used to define an M3UA Routing Key is application and network
dependent, and none of the above examples are mandated.

An Application Server Process may be configured to process signalling
traffic related to more than one Application Server, over a single SCTP
Association.  In ASP Active and Inactive management messages, the
signalling traffic to be started or stopped is discriminated by the
Routing Context parameter.  At an ASP, the Routing Context parameter
uniquely identifies the range of signalling traffic associated with
each Application Server that the ASP is
configured to receive.

1.4.2.2 Routing Key Limitiations

>From an SS7 network perspective, a Routing Key is limited to within a
single SS7 Destination Point Code. This is important, as the SG must be
able to present this point code to the SS7 network, without
compromising the integrity of the Signaling Point Management Cluster.

Some SS7 networks may require the SG to generate UPU messages in
failure conditions. In this case, the AS and SG may optionally limit a
Routing Key to a single Service Indicator (ISUP, TUP, SCCP, etc.).  The
SG generation of a UPU message into the SS7 network is implementation
dependent, therefore no specific procedures are outlined in this
document.

Routing Keys MUST be unique in the sense that a received SS7 signalling
message cannot be matched to more than one Routing Key. It is not
necessary for the parameter range values within a particular Routing
Key to be contiguous.  For example, an AS could be configured to



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support call processing for multiple ranges of PSTN trunks that are not
represented by contiguous CIC values.

1.4.2.3 Managing Routing Contexts and Routing Keys

There are two ways to ways to provision a Routing Key at an SG. A
Routing Key may be configured using an implementation dependent
management interface, statically or dynamically in full accordance to
the M3UA specifications. A Routing Key may also be configured using the
M3UA dynamic registration/deregistration procedures defined in this
document.  An M3UA element must implement at least one method of
Routing Key provisioning.

When using a management interface to configure Routing Keys, the
message distribution function within the SG is not limited to the set
of parameters defined in this document.  Other implementation dependent
distribution algorithms may be used.

1.4.2.4 Message Distribution the SG

In order to direct messages received from the SS7 MTP3 network to the
appropriate IP destination, the SG must perform a message distribution
function using information from the received MTP3-User message.

To support this message distribution, the SG must maintain the
equivalent of a network address translation table, mapping incoming SS7
message information to an Application Server for a particular
application and range of traffic.  This is accomplished by comparing
elements of the incoming SS7 message to provisioned Routing Keys in the
SG.  These Routing Keys in turn make reference to an Application Server
that is enabled by one or more ASPs.  These ASPs provide dynamic status
information on their availability, traffic handling capability and
congestion to the SG using various management messages defined in the
M3UA protocol.

The list of ASPs in an AS is assumed to be dynamic, taking into account
the availability, traffic handling capability and congestion status of
the individual ASPs in the list, as well as configuration changes and
possible fail-over mechanisms.

Normally, one or more ASPs are active in the AS (i.e., currently
processing traffic) but in certain failure and transition cases it is
possible that there may be active ASP available.  Both load-sharing and
backup scenarios are supported.

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

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1.4.2.5 Message Distribution at the ASP

In order to direct messages to the SS7 network, the ASP must also
perform a message distribution function in order to choose the proper
SG or SGP for a given message.  This is accomplished by observing the
Destination Point Code (and possibly other elements of the outgoing
message such as the SLS value), together with the SS7 destination
availability/restricted/congestion status via the SG(s) and the
availability of the SG and SGPs themselves.

A remote Signalling Gateway may be composed of one or more SGPs that
are capable of routing SS7 traffic.  As is the case with ASPs, a
dynamic list of SGPs in an SG can be maintained, taking into account
the availability status of the individual SGPs, configuration changes
and fail-over mechanisms. There is, however, no M3UA messaging to
manage the status of an SGP. Whenever an SCTP association to an SGP
exists, it is assumed to be available.  Also, every SGP of one SG
communicating with one ASP regarding one AS provides identical SS7
connectivity to this ASP.

1.4.3 SS7 and M3UA Interworking

In the case of SS7 and M3UA inter-working, the M3UA adaptation layer is
designed to provide an extension of the MTP3 defined user primitives.

1.4.3.1 Signalling Gateway SS7 Layers

The SG is responsible for terminating MTP Level 3 of the SS7 protocol,
and offering an IP-based extension to its users.

>From an SS7 perspective, it is expected that the Signalling Gateway
(SG) transmits and receives SS7 Message Signalling Units (MSUs) to and
from the PSTN over a standard SS7 network interface, using the SS7
Message Transfer Part (MTP) [14,15,16] to provide reliable transport of
the messages.

As a standard SS7 network interface, the use of MTP Level 2 signalling
links is not the only possibility.  ATM-based High Speed Links can also
be used with the services of the Signalling ATM Adaptation Layer (SAAL)
[17,18].  It is possible for IP-based links to be present, using the
services of the MTP2-User Adaptation Layer (M2UA) [19].  These SS7
datalinks may be terminated at a Signalling Transfer Point (STP) or at
a Signalling End Point (SEP).  Using the services of MTP3, the SG may
be capable of communicating with remote SS7 SEPs in a quasi-associated
fashion, where STPs may be present in the SS7 path between the SEP and
the SG.

Where ATM-based High Speed Links are used in the SS7 network, it is
possible for the SG to use the services of the MTP-3b [20] for reliable



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transport to and from an SS7 SEP or STP. The maximum SIF length
supported by the MTP-3b is 4095 octets compared to the 272-octet
maximum of the MTP3.  However, for MTP3-Users to take advantage of the
larger SDU between MTP3-User peers, network architects should ensure
that MTP3-b is used end-to-end between the SG and the SS7-resident
peer.

1.4.3.2 SS7 and M3UA Inter-Working at the SG

The SG provides a functional inter-working of transport functions
between the SS7 network and the IP network by also supporting the M3UA
adaptation layer.  It allows the transfer of MTP3-User signalling
messages to and from an IP-based Application Server Process where the
peer MTP3-User protocol layer exists.

The Signalling Gateway must maintain knowledge of SS7 node and
Signalling Point Management Cluster (SPMC) status in their respective
domains in order to perform a seamless inter-working of the IP-based
signalling and the SS7 domains.  For example, SG knowledge of the
availability and/or congestion status of the SPMC and SS7 nodes must be
maintained and disseminated in the respective networks, in order to
ensure that end-to-end operation is transparent to the communicating
SCN protocol peers at the SS7 node and ASP.

When the SG determines that the transport of SS7 messages to an SPMC
(or possibly to parts of an SPMC) is encountering congestion, the SG
should inform the MTP3 route management function (by an implementation-
dependent mechanism).  This information is used by the MTP3 to mark the
"route" to the affected destination as congested and to trigger MTP
Transfer Controlled (TFC) messages to any SS7 SEPs generating traffic
to the congested DPC, as per current MTP3 procedures.

When the SG determines that the transport of SS7 messages to all ASPs
in a particular SPMC is interrupted, then it should similarly inform
the MTP3 route management function.  This information is used by the
MTP3 to mark the "route" to the affected destination as unavailable,
and in the case of the SG acting as a signalling transfer point (i.e.,
the Point Code of the SG is different from that of the SPMC), to send
MTP Transfer Prohibited (TFP) messages to the relevant adjacent SS7
nodes, according to the local SS7 network procedures.

When the SG determines that the transport of SS7 messages to an ASP in
a particular SPMC can be resumed, the SG should similarly inform the
MTP3 route management function.  This information is used by the MTP3
to mark the route to the affected destination as available, and in the
case of a signalling transfer point, to send MTP Transfer Allowed (TFA)
messages to the relevant adjacent SS7 nodes, according to the local SS7
network procedures.




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For SS7 user part management, it is required that the MTP3-User
protocols at ASPs receive indications of SS7 signalling point
availability, SS7 network congestion, and remote User Part
unavailability as would be expected in an SS7 SEP node.  To accomplish
this, the MTP-PAUSE, MTP-RESUME and MTP-STATUS indication primitives
received at the MTP3 upper layer interface at the SG need to be
propagated to the remote MTP3-User lower layer interface at the ASP.
(These indication primitives are, of course, also made available to any
existing local MTP3-Users at the SG, if present.)

It is important to clarify that MTP3 management messages such as TFPs
or TFAs received from the SS7 network are not "encapsulated" and sent
blindly to the ASPs.  Rather, the existing MTP3 management procedures
are followed within the MTP3 function of the SG to re-calculate the
MTP3 route set status and to initiate any required signalling-route-
set-test procedures into the SS7 network.  Only when an SS7 destination
status changes are MTP-PAUSE or MTP-RESUME primitives invoked.  These
primitives can also be invoked due to local SS7 link set conditions as
per existing MTP3 procedures.

In the case where the MTP in the SG undergoes an MTP restart, event
communication to the concerned ASPs should be handled as follows:

When the SG discovers SS7 network isolation, the SG sends an indication
to all concerned available ASPs (i.e., ASPs in the "active" or
"inactive" state), using a DUNA message.  For the purposes of MTP
Restart, all SPMCs with point codes different from that of the SG with
at least one ASP that is active or that has sent an ASPAC message to
the SG during the first part of the restart procedure should be
considered as available.  If the M3UA at the SG receives any ASPAC
messages during the restart procedure, it delays the ASPAC-ACK messages
until the end of the restart procedure.  During the second part of the
restart procedure the M3UA at the SG informs all concerned ASPs in the
"active" or "inactive" state of any unavailable SS7 destinations.  At
the end of the restart procedure the M3UA sends an ASPAC-ACK message to
all ASPs in the "active" state.

1.4.3.3 Application Server

A cluster of application servers is responsible for providing the
overall support for one or more SS7 upper layers.  From an SS7
standpoint, a Signalling Point Management Cluster (SPMC) provides
complete support for the upper layer service for a given point code.
As an example, an SPMC providing MGC capabilities must provide complete
support for ISUP (and any other MTP3 user located at the point code of
the SPMC) for a given point code, according to the local SS7 network
specifications.

This measure is necessary to allow the SG to accurately represent the
signalling point on the local SS7 network.


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In the case where an ASP is connected to more than one SG, the M3UA
must maintain the status of configured SS7 destinations and route
messages according to availability/congestion/restricted status of the
routes to these destinations.

When an ASP enters the "Inactive" state towards an SG the M3UA must
mark all SS7 destinations configured to be reachable via this SG as
available.

When the M3UA at an ASP receives a DUNA message indicating SS7 network
isolation at an SG, it will stop any affected traffic via this SG and
clear any unavailability state of SS7 destinations via this SG. When
the M3UA subsequently receives any DUNA messages from an SG it will
mark the effected SS7 destinations as unavailable via that SG.  When
the M3UA receives an ASPAC-ACK message it can resume traffic to
available SS7 destinations via this SG, provided the ASP is in the
active state towards this SG.

1.4.3.3 IPSP Considerations

Since IPSPs use M3UA in a point-to-point fashion, there is no concept
of routing of messages beyond the remote end.  Therefore, SS7 and M3UA
inter-working is not necessary for this model.

1.4.4 Redundancy Models

The network address translation and mapping function of the M3UA layer
supports signalling process fail-over functions in order to support a
high availability of call and transaction processing capability.

1.4.4.1 Application Server Redundancy

All MTP3-User messages (e.g., ISUP, SCCP) incoming to an SG from the
SS7 network are assigned to a unique Application Server, based on the
information in the message and the provisioned Routing Keys.

The Application Server is, in practical terms, a list of all ASPs
configured to process a range of MTP3-User traffic defined by one
Routing Key.  One or more ASPs in the list are normally active (i.e.,
handling traffic) while any others may be unavailable or inactive, to
be possibly used in the event of failure or unavailability of the
active ASP(s).

The fail-over model supports an "n+k" redundancy model, where "n" ASPs
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.  A
"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.




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At the SG, an Application Server list contains active and inactive ASPs
to support ASP load-sharing and fail-over procedures.  The list of ASPs
within a logical Application Server is kept updated in the SG to
reflect the active Application Server Process(es).

To avoid a single point of failure, it is recommended that a minimum of
two ASPs be in the list, resident in separate hosts and therefore
available over different SCTP Associations.  For example, in the
network shown in Figure 1, all messages to DPC x could be sent to ASP1
in Host1 or ASP1 in Host2.  The AS list at SG1 might look like the
following:

    Routing Key {DPC=x) - "Application Server #1"
        ASP1/Host1  - State=Up, Active
        ASP1/Host2  - State=Up, Inactive

In this "1+1" redundancy case, ASP1 in Host1 would be sent any incoming
message with DPC=x.  ASP1 in Host2 would normally be brought to the
active state upon failure of, or loss of connectivity to, ASP1/Host1.
In this example, both ASPs are Up, meaning that the related SCTP
association and far-end M3UA peer is ready.

The AS List at SG1 might also be set up in load-share mode:

    Routing Key {DPC=x) - "Application Server #1"
        ASP1/Host1 - State = Up, Active
        ASP1/Host2 - State = Up, Active

In this case, both the ASPs would be sent a portion of the traffic.
For example the two ASPs could together form a database, where incoming
queries may be sent to any active ASP.

Care must be exercised by a Network Operator in the selection of the
routing information to be used as the Routing Key for a particular AS.
For example, where Application Servers are defined using ranges of ISUP
CIC values, the Operator is implicitly splitting up control of the
related circuit groups.  Some CIC value range assignments may interfere
with ISUP circuit group management procedures.

In the process of fail-over, it is recommended that in the case of ASPs
supporting call processing, stable calls do not fail.  It is possible
that calls in "transition" MAY fail, although measures of communication
between the ASPs involved can be used to mitigate this.  For example,
the two ASPs MAY share call state via shared memory, or MAY use an ASP
to ASP protocol to pass call state information.  Any ASP-to-ASP
protocol is outside the scope of this document.






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1.4.4.2 Signalling Gateway Redundancy

Signalling Gateways MAY also be distributed over multiple hosts.  Much
like the AS model, SGs may be comprised of one or more SG Processes
(SGPs), distributed over one or more hosts, using an active/standby or
a load-sharing model.  An SGP is viewed as a remote SCTP end-point from
an ASP perspective.  There is, however, no M3UA protocol to manage the
status of an SGP. Whenever an SCTP association to an SGP exists, the
SGP is assumed to be available.  Also, every SGP within an SG
communicating with an ASP provides identical SS7 connectivity to this
ASP. Should an SGP lose all or partial SS7 connectivity and other SGPs
exist, the SGP must terminate the SCTP associations to the concerned
ASPs.

It is therefore possible for an ASP to route signalling messages
destined to the SS7 network using more than one SGP.  In this model, a
Signalling Gateway is deployed as a cluster of hosts acting as a single
SG.  A primary/back-up redundancy model is possible, where the
unavailability of the SCTP association to a primary SGP could be used
to reroute affected traffic to an alternate SGP.  A load-sharing model
is possible, where the signalling messages are load-shared between
multiple SGPs.

It may also be possible for an ASP to use more than one SG to access a
specific SS7 end point, in a model that resembles an SS7 STP mated
pair.  Typically, SS7 STPs are deployed in mated pairs, with traffic
load-shared between them.  Other models are also possible, subject to
the limitations of the local SS7 network provisioning guidelines.

>From the perspective of the M3UA at an ASP, a particular SG is capable
of transferring traffic to an SS7 destination if an SCTP association
with at least one SGP of the SG is established, the SGP has returned an
ASPAC Ack message acknowledging to the ASP M3UA that the ASP is
actively handling traffic for that destination, and the SG has not
indicated that the destination is inaccessible.  When an ASP is
configured to use multiple SGs for transferring traffic to the SS7
network, the ASP must maintain knowledge of the current capability of
the SGs to handle traffic to destinations of interest.  This
information is crucial to the overall reliability of the service, for
both active/standby and load-sharing model, in the event of failures,
recovery and maintenance activities.  The ASP M3UA may also use this
information for congestion avoidance purposes.  The distribution of the
MTP3-user messages over the SGs should be done in such a way to
minimize message mis-sequencing, as required by the SS7 User Parts.

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

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1.4.6 Congestion Management

The M3UA Layer is informed of local and IP network congestion by means
of an implementation-dependent function (e.g., an implementation-
dependent indication from the SCTP of IP network congestion).

At an ASP or IPSP, the M3UA indicates congestion to local MTP3-Users by
means of an MTP-Status primitive, as per current MTP3 procedures, to
invoke appropriate upper layer responses.

When an SG determines that the transport of SS7 messages to a
Signalling Point Management Cluster (SPMC) is encountering congestion,
the SG should trigger SS7 MTP3 Transfer Controlled management messages
to originating SS7 nodes, as per current MTP3 procedures. The
triggering of SS7 MTP3 Management messages from an SG is an
implementation-dependent function.

The M3UA at an ASP or IPSP should indicate local congestion to an M3UA
peer with an SCON message.  When an SG M3UA receives an SCON message
from an ASP, and the SG determines that an SPMC is now encountering
congestion, it should trigger SS7 MTP3 Transfer Controlled management
messages to concerned SS7 destinations according to current MTP
procedures.

1.4.7 SCTP Stream Mapping.

The M3UA at both the SG and ASP also supports the assignment of
signalling traffic into streams within an SCTP association.  Traffic
that requires sequencing must be assigned to the same stream.  To
accomplish this, MTP3-User traffic may be assigned to individual
streams based on, for example, the SLS value in the MTP3 Routing Label
or the ISUP CIC assignment, subject of course to the maximum number of
streams supported by the underlying SCTP association.

The use of SCTP streams within M3UA is recommended in order to minimize
transmission and buffering delays, therefore improving the overall
performance and reliability of the signalling elements.  The
distribution of the MTP3 user messages over the various streams should
be done in such a way to minimize message mis-sequencing, as required
by the SS7 User Parts.

1.4.8 Client/Server Model

The SG takes on the role of server while the ASP is the client. ASPs
MUST initiate the SCTP association to the SG.

In the case of IPSP to IPSP communication, the peer endpoints using
M3UA SHOULD be configured so that one always takes on the role of
client and the other the role of server for initiating SCTP
associations and M3UA messaging.


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The SCTP (and UDP/TCP) Registered User Port Number Assignment for M3UA
is 2905.


1.5 Sample Configurations

1.5.1 Example 1: ISUP message transport

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

  +------+                                  +------+
  | ISUP |               (NIF)              | ISUP |
  +------+         +------+-+------+        +------+
  | MTP3 |         | MTP3 | | M3UA |        | M3UA |
  +------|         +------+ +------+        +------+
  | MTP2 |         | MTP2 | | SCTP |        | SCTP |
  +------+         +------+ +------+        +------+
  |  L1  |         |  L1  | |  IP  |        |  IP  |
  +------+         +------+ +------+        +------+
      |_______________|         |______________|

    SEP - SS7 Signalling End Point
    SCTP - Stream Control Transmission Protocol
    NIF - Nodal Inter-working Function

In this example, the SG provides an implementation-dependent nodal
inter-working function (NIF) that allows the MGC to exchange SS7
signalling messages with the SS7-based SEP.  The NIF within the SG
serves as the interface within the SG between the MTP3 and M3UA.  This
nodal inter-working function has no visible peer protocol with either
the MGC or SEP.  It also provides network status information to one or
both sides of the network.

For internal SG modeling purposes, at the NIF level, SS7 signalling
messages that are destined to the MGC are received as MTP-TRANSFER
indication primitives from the MTP Level 3 upper layer interface and
are sent to the local M3UA-resident message distribution function for
ongoing routing to the final IP destination.  MTP-TRANSFER primitives
received from the local M3UA network address translation and mapping
function are sent to the MTP Level 3 upper layer interface as MTP-
TRANSFER request primitives for on-going MTP Level 3 routing to an SS7
SEP.  For the purposes of providing SS7 network status information the
NIF also delivers MTP-PAUSE, MTP-RESUME and MTP-STATUS indication
primitives received from the MTP Level 3 upper layer interface to the
local M3UA-resident management function. In addition, as an
implementation and network option, restricted destinations are
communicated from MTP network management to the local M3UA-resident
management function.


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1.5.2  Example 2: SCCP Transport between IPSPs

        ********    IP    ********
        * IPSP *          * IPSP *
        ********          ********

        +------+          +------+
        |SCCP- |          |SCCP- |
        | User |          | User |
        +------+          +------+
        | SCCP |          | SCCP |
        +------+          +------+
        | M3UA |          | M3UA |
        +------+          +------+
        | SCTP |          | SCTP |
        +------+          +------+
        |  IP  |          |  IP  |
        +------+          +------+
            |________________|

This example shows an architecture where no Signalling Gateway is used.
In this example, SCCP messages are exchanged directly between two IP-
resident IPSPs with resident SCCP-User protocol instances, such as
RANAP or TCAP.  SS7 network inter-working is not required, therefore
there is no MTP3 network management status information for the SCCP and
SCCP-User protocols to consider.  Any MTP-PAUSE, -RESUME or -STATUS
indications from the M3UA to the SCCP should consider the status of the
SCTP Association and underlying IP network and any congestion
information received from the remote site.























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1.5.3 Example 3: SG resident SCCP layer, with remote ASP

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

  +------+         +---------------+        +------+
  | SCCP-|         |     SCCP      |        | SCCP-|
  | User |         +---------------+        | User |
  +------+           |   _____   |          +------+
  | SCCP |           |  |     |  |          | SCCP |
  +------+         +------+-+------+        +------+
  | MTP3 |         | MTP3 | | M3UA |        | M3UA |
  +------|         +------+ +------+        +------+
  | MTP2 |         | MTP2 | | SCTP |        | SCTP |
  +------+         +------+ +------+        +------+
  |  L1  |         |  L1  | |  IP  |        |  IP  |
  +------+         +------+ +------+        +------+
      |_______________|         |______________|

    STP - SS7 Signalling Transfer Point

In this example, the SG contains an instance of the SS7 SCCP protocol
layer that may, for example, perform the SCCP Global Title Translation
(GTT) function for messages logically addressed to the SG SCCP.  If the
result of a GTT for an SCCP message yields an SS7 DPC or DPC/SSN
address an SCCP peer located in the IP domain, the resulting MTP-
TRANSFER request primitive is sent to the local M3UA-resident network
address translation and mapping function for ongoing routing to the
final IP destination.

Similarly, the SCCP instance in an SG can perform the SCCP GTT service
for messages logically addressed to it from SCCP peers in the IP
domain.  In this case, MTP-TRANSFER messages are sent from the local
M3UA-resident network address translation and mapping function to the
SCCP for GTT.  If the result of the GTT yields the address of an SCCP
peer in the SS7 network then the resulting MTP-TRANSFER request is
given to the MTP3 for delivery to an SS7-resident node.

It is possible that the above SCCP GTT at the SG could yield the
address of an SCCP peer in the IP domain and the resulting MTP-TRANSFER
primitive would be sent back to the M3UA for delivery to an IP
destination.

For internal SG modeling purposes, this may be accomplished with the
use of an implementation-dependent nodal inter-working function within
the SG that effectively sits below the SCCP and routes MTP-TRANSFER
messages to/from both the MTP3 and the M3UA, based on the SS7 DPC or
DPC/SSN

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address information.  This nodal inter-working function has no visible
peer protocol with either the ASP or SEP.

Note that the services and interface provided by the M3UA are the same
as in Example 1 and the functions taking place in the SCCP entity are
transparent to M3UA.  The SCCP protocol functions are not reproduced in
the M3UA protocol.


1.6 Definition of M3UA Boundaries

1.6.1 Definition of the boundary between M3UA and an MTP3-User.

>From ITU Q.701 [14]:

   MTP-TRANSFER request
   MTP-TRANSFER indication
   MTP-PAUSE indication
   MTP-RESUME indication
   MTP-STATUS indication

1.6.2 Definition of the boundary between M3UA and SCTP

An example of the upper layer primitives provided by the SCTP are
provided in Reference [13] Section 10.

1.6.3 Definition of the Boundary between M3UA and Layer Management

   M-SCTP ESTABLISH request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to establish an SCTP association with an
            SG.

   M-STCP ESTABLISH confirm
   Direction: M3UA -> LM
   Purpose: ASP confirms to LM that it has established an SCTP
            association with an SG.

   M-SCTP ESTABLISH indication
   Direction: M3UA -> LM
   Purpose: M3UA informs LM that a remote ASP has established an SCTP
            association.

   M-SCTP RELEASE request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to release an SCTP association with SG.






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   M-SCTP RELEASE confirm
   Direction: M3UA -> LM
   Purpose: ASP confirms to LM that it has released SCTP association
            with SG.

   M-SCTP RELEASE indication
   Direction: M3UA -> LM
   Purpose: M3UA informs LM that a remote ASP has released an SCTP
            Association or the SCTP association has failed.

   M-SCTP STATUS request
   Direction: LM -> M3UA
   Purpose: LM requests M3UA to report the status of an SCTP
            association.

   M-SCTP STATUS confirm
   Direction: M3UA -> LM
   Purpose: M3UA reports the status of an SCTP association.

   M-ASP STATUS request
   Direction: LM -> M3UA
   Purpose: LM requests M3UA to report the status of a local or remote
            ASP.

   M-ASP STATUS confirm
   Direction: M3UA -> LM
   Purpose: M3UA reports status of local or remote ASP.

   M-AS STATUS request
   Direction: LM -> M3UA
   Purpose: LM requests M3UA to report the status of an AS.

   M-AS STATUS confirm
   Direction: M3UA -> LM
   Purpose: M3UA reports the status of an AS.

   M-NOTIFY indication
   Direction: M3UA -> LM
   Purpose: M3UA reports that it has received a NOTIFY message
            from its peer.

   M-ERROR indication
   Direction: M3UA -> LM
   Purpose: M3UA reports that it has received an ERROR message from
            its peer or that a local operation has been unsuccessful.

   M-ASP UP request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to start its operation and send an ASP-UP
            Message to its peer.


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   M-ASP UP confirm
   Direction: M3UA -> LM
   Purpose: ASP reports that is has received an ASP UP Acknowledgement
            message from the SG.

   M-ASP UP indication
   Direction: M3UA -> LM
   Purpose: M3UA reports it has successfully processed an incoming ASP-
            UP request from its peer.

   M-ASP DOWN request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to stop its operation and send an ASP-DOWN
            Message to its peer.

   M-ASP DOWN confirm
   Direction: M3UA -> LM
   Purpose: ASP reports that is has received an ASP DOWN
            Acknowledgement message from the SG.

   M-ASP DOWN indication
   Direction: M3UA -> LM
   Purpose: M3UA reports it has successfully processed an incoming ASP-
            DOWN request from its peer.

   M-ASP-ACTIVE request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to send an ASP-ACTIVE message to its peer.

   M-ASP ACTIVE confirm
   Direction: M3UA -> LM
   Purpose: ASP reports that is has received an ASP ACTIVE
            Acknowledgement message from the SG.

   M-ASP ACTIVE indication
   Direction: M3UA -> LM
   Purpose: LM reports it has successfully processed an incoming ASP-
            ACTIVE request from its peer.

   M-ASP-INACTIVE request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to send an ASP- Inactive message to the SG.

   M-ASP INACTIVE confirm
   Direction: LM -> M3UA
   Purpose: ASP reports that is has received an ASP INACTIVE
            Acknowledgement message from the SG.





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   M-ASP INACTIVE indication
   Direction: M3UA -> LM
   Purpose: LM reports it has successfully processed an incoming ASP-
            INACTIVE request from its peer.

   M-AS ACTIVE indication
   Direction: M3UA -> LM
   Purpose: LM reports that an AS has moved to the ACTIVE state.

   M-AS INACTIVE indication
   Direction: M3UA -> LM
   Purpose: LM reports that an AS has moved to the INACTIVE state.

   M-AS DOWN indication
   Direction: M3UA -> LM
   Purpose: LM reports that an AS has moved to the DOWN state.


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 M3UA Protocol Elements

The general M3UA message format includes a Common Message Header
followed by zero or more parameters as defined by the Message Type.
For forward compatibility, all Message Types may have attached
parameters even if none are specified in this version.

3.1 Common Message Header

The protocol messages for MTP3-User Adaptation require a message header
which contains the adaptation layer version, the message type, and
message length.


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




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All fields in an M3UA message MUST be transmitted in the network byte
order, unless otherwise stated.

3.1.1 M3UA Protocol Version: 8 bits (unsigned integer)

   The version field contains the version of the M3UA adaptation layer.

   The supported versions are the following:

         1      Release 1.0

3.1.2  Message Classes and Types

The following list contains the valid Message Classes:

Message Class: 8 bits (unsigned integer)

   The following list contains the valid Message Type Classes:

     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 to 127 Reserved by the IETF
  28 to 255 Reserved for IETF-Defined Message Class extensions

Message Type: 8 bits (unsigned integer)

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

     Management (MGMT) Message

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

     Transfer Messages

         0        Reserved
         1        Payload Data (DATA)
      2 to 127    Reserved by the IETF
    128 to 255    Reserved for IETF-Defined Transfer extensions

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     SS7 Signalling Network Management (SSNM) Messages

         0        Reserved
         1        Destination Unavailable (DUNA)
         2        Destination Available (DAVA)
         3        Destination State Audit (DAUD)
         4        SS7 Network Congestion State (SCON)
         5        Destination User Part Unavailable (DUPU)
         6        Destination Restricted (DRST)
      7 to 127    Reserved by the IETF
    128 to 255    Reserved for IETF-Defined SSNM extensions

  ASP 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        Heatbeat Ack (BEAT ACK)
      7 to 127    Reserved by the IETF
    128 to 255    Reserved for IETF-Defined ASPSM extensions

  ASP 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

  Routing Key Management (RKM) 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 ASPTM extensions

3.1.3  Reserved: 8 bits

   The Reserved field SHOULD be set to all '0's and ignored by the
   receiver.




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3.1.4  Message Length: 32-bits (unsigned integer)

   The Message Length defines the length of the message in octets,
   including the Common Header.  For messages with a final parameter
   containing padding, the parameter padding MUST be included in the
   Message Length.

   Note: A receiver SHOULD accept the message whether or not the final
   parameter padding is included in the message length.


3.2 Variable-Length Parameter Format

M3UA messages consist of a Common Header followed by zero or more
variable length parameters, as defined by the message type.  All the
parameters contained in a message are defined in a Tag-Length-Value
format as shown below.

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

Where more than one parameter is included in a message, the parameters
may be in any order, except where explicitly mandated.  A receiver
SHOULD accept the parameters in any order.

Parameter Tag: 16 bits (unsigned integer)

   The Tag field is a 16-bit identifier of the type of parameter. It
   takes a value of 0 to 65534.  The parameter Tags defined are as
   follows:

         0        Reserved
         1        Network Appearance
         2        Protocol Data 1
         3        Protocol Data 2
         4        Info String
         5        Affected Destinations
         6        Routing Context
         7        Diagnostic Information
         8        Heartbeat Data
         9        User/Cause
        10        Reason
        11        Traffic Mode Type


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        12        Error Code
        13        Status Type/ID
        14        Congestion Indications
        15        Concerned Destination
        16        Routing Key
        17        Registration Result
        18        De-registration Result
        19        Local_Routing Key Identifier
        20        Destination Point Code
        21        Service Indicators
        22        Subsystem Numbers
        23        Originating Point Code List
        24        Circuit Range
        25        Registration Results
        26        De-Registration Results
     27 to 65534  Reserved by the IETF

   The value of 65535 is reserved for IETF-defined extensions.  Values
   other than those defined in specific parameter description are
   reserved for use by the IETF.

Parameter Length: 16 bits (unsigned integer)

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

Parameter Value: variable-length.

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

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


3.3 Transfer Messages

The following section describes the Transfer messages and parameter
contents.






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3.3.1 Payload Data Message (DATA)

The DATA message contains the SS7 MTP3-User protocol data, which is an
MTP-TRANSFER primitive, including the complete MTP3 Routing Label. The
Data message contains the following variable length parameters:

     Network Appearance       Optional
     Protocol Data 1 or 2     Mandatory

The following format MUST be used for the Data 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 = 1            |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Network Appearance*                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 3            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                        Protocol Data                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Network Appearance: 32-bits (unsigned integer)

   The optional Network Appearance parameter identifies the SS7 network
   context for the message, for the purposes of logically separating
   the signalling traffic between the SG and the Application Server
   Process over a common SCTP Association.  An example is where an SG
   is logically partitioned to appear as an element in four different
   national SS7 networks.

   In a Data message, the Network Appearance implicitly defines the SS7
   Point Code format used, the SS7 Network Indicator value, and the
   MTP3 and possibly the MTP3-User protocol type/variant/version used
   within the SS7 network partition.  Where an SG operates in the
   context of a single SS7 network, or individual SCTP associations are
   dedicated to each SS7 network context, the Network Appearance
   parameter is not required.

   The Network Appearance parameter value is of local significance
   only, coordinated between the SG and ASP. Therefore, in the case
   where an ASP is connected to more than one SG, the same SS7 network
   context may be identified by different Network Appearances depending
   over which SG a message is being transmitted/received.




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

Protocol Data 1 or 2: variable length

   One of two possible Protocol Data parameters are included in a DATA
   message: Protocol Data 1 or Protocol Data 2.

   The Protocol Data 1 parameter contains the original SS7 MTP3
   message, including the Service Information Octet and Routing Label.

   The Protocol Data 1 parameter contains the following fields:

       Service Information Octet. Includes:
            Service Indicator,
            Network Indicator,
            and Spare/Priority codes

       Routing Label. Includes:
            Destination Point Code,
            Originating Point Code,
            And Signalling Link Selection Code (SLS)

       User Protocol Data.  Includes:
            MTP3-User protocol elements (e.g., ISUP, SCCP, or TUP
               parameters)

   The Protocol Data 2 parameter contains all the information in
   Protocol Data 1 as described above, plus the MTP2 Length Indicator
   octet.  The MTP2 Length Indicator (LI) octet appears before the SIO
   and Routing Label information.  The MTP2 Length Indicator octet is
   required for some national MTP variants that use the spare bits in
   the LI to carry additional information of interest to the MTP3 and
   MTP3-User (e.g., the Japan TTC standard use of LI spare bits to
   indicate message priority)

   The Payload Data format is as defined in the relevant MTP standards
   for the SS7 protocol being transported.  The format is either
   implicitly known or identified by the Network Appearance parameter.
   Note: In the SS7 Recommendations, the format of the messages and
   fields within the messages are based on bit transmission order.  In
   these recommendations the Least Significant Bit (LSB) of each field
   is positioned to the right.  For this document the received SS7
   fields are populated octet by octet as received into the 4-octet
   word as shown in the examples below.

   For the ANSI protocol example, the Protocol Data field format is
   shown below:



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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      SIO      |  DPC Member  |  DPC Cluster  |  DPC Network   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  OPC Member  |  OPC Cluster  |  OPC Network   |      SLS      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                        Protocol Data                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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


   Within each octet the Least Significant Bit (LSB) per the SS7
   Recommendations is to the right (e.g., bit 7 of SIO is the LSB).

   For the ITU international protocol example, the Protocol Data field
   is shown below.


     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      SIO      | DPC     | DPC |OPC| DPC | DPC |   OPC       |@|
    |               | Region *| SP *|SP*|Zone*| reg.|  Region    *| |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  SLS  | OPC |$|      Protocol                                 |
    |      *| SP *| |        Data                                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    * marks LSB of each field;  @ = OPC SP MSB;  $ = OPC region MSB



3.4 SS7 Signalling Network Management (SSNM) Messages

3.4.1 Destination Unavailable (DUNA)

The DUNA message is sent from the SG to all concerned ASPs to indicate
that the SG has determined that one or more SS7 destinations are
unreachable.  It is also sent in response to a message from the ASP to
an unreachable SS7 destination.  As an implementation option the SG may
suppress the sending of subsequent "response" DUNAs regarding a certain
unreachable SS7 destination for a certain period in order to give the
remote side time to react. The MTP3-User at the ASP is expected to stop
traffic to the affected destination through the SG initiating the DUNA
as per the defined MTP3-User procedures.



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The DUNA message contains the following parameters:

     Network Appearance      Optional
     Affected Destinations   Mandatory
     Info String             Optional

The format for DUNA Message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 1            |           Length =8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Network Appearance*                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 5            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Mask      |                 Affected DPC 1                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask      |                 Affected DPC n                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Tag = 4           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String*                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Network Appearance: 32-bit unsigned integer

   See Section 3.3.1

Affected Destinations: n x 32-bits

   The Affected Destinations parameter contains up to sixteen Affected
   Destination Point Code fields, each a three-octet parameter to allow
   for 14-, 16- and 24-bit binary formatted SS7 Point Codes.  Affected
   Point Codes that are less than 24-bits, are padded on the left to
   the 24-bit boundary.  The encoding is shown below for ANSI and ITU
   Point Code examples.







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ANSI 24-bit Point Code:

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

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

   ITU 14-bit Point Code:

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

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

   It is optional to send an Affected Destinations parameter with more
   than one Affected DPC but it is mandatory to receive and process it.
   All the Affected DPCs included must be within the same Network
   Appearance.  Including multiple Affected DPCs may be useful when
   reception of an MTP3 management message or a linkset event
   simultaneously affects the availability status of a list of
   destinations at an SG.

Mask: 8-bits (unsigned integer)

   The Mask field associated with each Affected DPC in the Affected
   Destinations parameter, used to identify a contiguous range of
   Affected Destination Point Codes, independent of the point code
   format.  Identifying a contiguous range of Affected DPCs may be
   useful when reception of an MTP3 management message or a linkset
   event simultaneously affects the availability status of a series of
   destinations at an SG.  For example, if all DPCs in an ANSI cluster
   are determined to be unavailable due to local linkset
   unavailability, the DUNA could identify potentially 256 Affected
   DPCs in a single Affected DPC field.

   The Mask parameter represents a bit mask that can be applied to the
   related Affected DPC field.  The bit mask identifies how many bits
   of the Affected DPC field are significant and which are effectively
   "wildcarded".  For example, a mask of "8" indicates that the least
   significant eight bits of the DPC is "wildcarded".  For an ANSI 24-
   bit Affected DPC, this is equivalent to signalling that all DPCs in
   an ANSI Cluster are unavailable.  A mask of "3" indicates that the
   least significant three bits of the DPC is "wildcarded".  For a 14-
   bit ITU Affected DPC, this is equivalent to signaling that an ITU


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   Region is unavailable. A mask value equal to the number of bits in
   the DPC indicates that the entire network appearance is affected û
   this is used to indicate network isolation to the ASP.

Info String: variable length

   The optional INFO String parameter can carry any 8-bit ASCII
   character string along with the message.  Length of the INFO
   String parameter is from 0 to 255 characters.  No procedures are
   presently identified for its use but the INFO String MAY be used by
   Operators to identify in text form the location reflected by the
   Affected DPC for debugging purposes.

3.4.2 Destination Available (DAVA)

The DAVA message is sent from the SG to all concerned ASPs to indicate
that the SG has determined that one or more SS7 destinations are now
reachable (and not restricted), or in response to a DAUD message if
appropriate. The ASP MTP3-User protocol is allowed to resume traffic to
the affected destination through the SG initiating the DUNA.

The DAVA message contains the following parameters:

     Network Appearance       Optional
     Affected Destinations    Mandatory
     Info String              Optional

The format and description of the Network Appearance, Affected
Destinations and Info String parameters is the same as for the DUNA
message (See Section 3.4.1.)

3.4.3 Destination State Audit (DAUD)

The DAUD message can be sent from the ASP to the SG to audit the
availability/congestion state of SS7 routes to one or more affected
destinations.

The DAUD message contains the following parameters:

     Network Appearance      Optional
     Affected Destinations   Mandatory
     Info String             Optional

The format and description of DAUD Message parameters is the same as
for the DUNA message (See Section 3.4.1.)

3.4.4 SS7 Network Congestion (SCON)

The SCON message can be sent from the SG to all concerned ASPs to
indicate congestion in the SS7 network to one or more destinations, or


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to an ASP in response to a DATA or DAUD message as appropriate.  For
some MTP protocol variants (e.g., ANSI MTP) the SCON may be sent when
the SS7 congestion level changes.  The SCON message MAY also be sent
from the M3UA of an ASP to an M3UA peer indicating that the M3UA or the
ASP is congested.

The SCON message contains the following parameters:

     Network Appearance       Optional
     Affected Destinations    Mandatory
     Concerned Destination    Optional     Congestion Indications
Optional
     Info String              Optional

The format for SCON 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 = 1            |           Length =8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Network Appearance*                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 5            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Mask     |                 Affected DPC 1                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Mask     |                 Affected DPC n                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 15           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    reserved   |                 Concerned DPC                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 14           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Reserved                    |  Cong. Level* |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 4            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         INFO String*                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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The format and description of the Network Appearance, Affected
Destinations, and Info String parameters is the same as for the DUNA
message (See Section 3.4.1.)

The Affected Destinations parameter can be used to indicate congestion
of multiple destinations or ranges of destinations.  However, an SCON
MUST not be delayed in order to "collect" individual congested
destinations into a single SCON as any delay might affect the timing of
congestion indications to the M3UA Users.  One use for including a
range of Congested DPCs is when the SG supports an ANSI cluster route
set to the SS7 network that becomes congested due to outgoing link set
congestion.

Concerned Destination: 32-bits

   The optional Concerned Destination parameter is only used if the
   SCON is sent from an ASP to the SG. It contains the point code of
   the originator of the message that triggered the SCON. The Concerned
   Destination parameter contains one Concerned Destination Point Code
   field, a three-octet parameter to allow for 14-, 16- and 24-bit
   binary formatted SS7 Point Codes.  A Concerned Point Code that is
   less than 24-bits, is padded on the left to the 24-bit boundary. The
   SG sends a Transfer Controlled Message to the Concerned Point Code
   using the single Affected DPC contained in the SCON to populate the
   (affected) Destination field of the TFC message. Normally the
   Affected DPC will be equal to the point code of the ASP.

Congested Indications: 32-bits

   The optional Congestion Indications parameter contains a Congestion
   Level field.  This optional parameter is used to communicate
   congestion levels in national MTP networks with multiple congestion
   thresholds, such as in ANSI MTP3.  For MTP congestion methods
   without multiple congestion levels (e.g., the ITU international
   method) the parameter is not included.

Congestion Level field: 8-bits (unsigned integer)

   The Congestion Level field, associated with all of the Affected
   DPC(s) in the Affected Destinations parameter, contains one of the
   Following values:

         0     No Congestion or Undefined
         1     Congestion Level 1
         2     Congestion Level 2
         3     Congestion Level 3

   The congestion levels are defined in the congestion method in the
   appropriate national MTP recommendations [14,15].



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3.4.5 Destination User Part Unavailable (DUPU)

The DUPU message is used by an SG to inform an ASP that a remote peer
MTP3-User Part (e.g., ISUP or SCCP) at an SS7 node is unavailable.

The DUPU message contains the following parameters:

     Network Appearance       Optional
     Affected Destinations    Mandatory
     User/Cause               Mandatory
     Info String              Optional

The format for DUPU Message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 1            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Network Appearance*                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 5            |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Mask = 0    |                  Affected DPC                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 9            |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Cause             |            User               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 4            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String*                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


User/Cause: 32-bits

   The Unavailability Cause and MTP3-User Identity fields, associated
   with the Affected DPC in the Affected Destinations parameter, are
   encoded as follows:

Unavailability Cause field: 16-bits (unsigned integer)

   The Unavailability Cause parameter provides the reason for the
   unavailability of the MTP3-User.  The valid values for the
   Unavailability Cause parameter are shown in the following table.
   The values agree with those provided in the SS7 MTP3 User Part
   Unavailable message.  Depending on the MTP3 protocol used in the


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   network appearance, additional values may be used - the
   specification of the relevant MTP3 protocol variant/version
   recommendation is definitive.

         0         Unknown
         1         Unequipped Remote User
         2         Inaccessible Remote User

MTP3-User Identity field: 16-bits (unsigned integer)

   The MTP3-User Identity describes the specific MTP3-User that is
   unavailable (e.g., ISUP, SCCP, ...).  Some of the valid values for
   the MTP3-User Identity are shown below.  The values agree with those
   provided in the SS7 MTP3 User Part Unavailable message and Service
   Indicator.  Depending on the MTP3 protocol variant/version used in
   the network appearance, additional values may be used.  The relevant
   MTP3 protocol variant/version recommendation is definitive.

       0 to 2       Reserved
          3         SCCP
          4         TUP
          5         ISUP
       6 to 8       Reserved
          9         Broadband ISUP
         10        Satellite ISUP

The format and description of the Affected Destinations parameter is
the same as for the DUNA message (See Section 3.4.1.) except that the
Mask field is not used and only a single Affected DPC is included.
Ranges and lists of Affected DPCs cannot be signaled in a DUPU, but
this is consistent with UPU operation in the SS7 network. The Affected
Destinations parameter in an MTP3 User Part Unavailable message (UPU)
received by an SG from the SS7 network contains only one destination.

The format and description of the Network Appearance and Info String
parameters is the same as for the DUNA message (See Section 3.4.1.).


3.4.6 Destination Restricted (DRST)

The DRST message is optionally sent from the SG to all concerned ASPs
to indicate that the SG has determined that one or more SS7
destinations are now restricted, or in response to a DAUD message if
appropriate. The M3UA at the ASP is expected to send traffic to the
affected destination via an alternate SG of equal priority, but only if
such an alternate route exists and is available. If the affected
destination is currently considered unavailable by the ASP, traffic to
the affected destination through the SG initiating the DRST should be
resumed.



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This message is optional for the SG to send and optional for the ASP to
process. It is for use in the "STP" case described in Section 1.4.2.

The DRST message contains the following parameters:

     Network Appearance       Optional
     Affected Destinations    Mandatory
     Info String              Optional

The format and description of the Network Appearance, Affected
Destinations and Info String parameters is the same as for the DUNA
message (See Section 3.4.1.)


3.5 Application Server Process Maintenance (ASPM) Messages

3.5.1 ASP Up (ASPUP)

The ASP UP (ASPUP) message is used to indicate to a remote M3UA peer
that the Adaptation layer is ready to receive SSNM or ASPM management
messages for all Routing Keys that the ASP is configured to serve.

The ASPUP message contains the following parameters:

     INFO String                   Optional

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 = 4            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String*                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.4.1.)


3.5.2 ASP Up Ack

The ASP UP Ack message is used to acknowledge an ASP-Up message
received from a  remote M3UA peer.





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The ASPUP Ack message contains the following parameters:

     INFO String (optional)

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 =4             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String*                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.4.1.)


3.5.3 ASP Down (ASPDN)

The ASP Down (ASPDN) message is used to indicate to a remote M3UA peer
that the adaptation layer is NOT ready to receive traffic or
maintenance messages.

The ASPDN message contains the following parameters:

     Reason         Mandatory
     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 = 10            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Reason                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag =4             |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         INFO String*                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.4.1.)

Reason: 32-bit (unsigned integer)

   The Reason parameter indicates the reason that the remote M3UA
   adaptation layer is unavailable.  The valid values for Reason are
   shown in the following table.

         0       Unspecified
         1       User Unavailable
         2       Management Blocking

3.5.4 ASP Down Ack

The ASP Down Ack message is used to acknowledge an ASP-Down message
received from a remote M3UA peer, or to reply to an ASPM message from
an ASP which is locked out for management reasons.

The ASP Down Ack message contains the following parameters:

     Reason          Mandatory
     INFO String     Optional

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 = 10            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Reason                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 4            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         INFO String*                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.4.1.)

The format of the Reason parameter is the same as for the ASP-Down
message. (See Section 3.4.3)

3.5.5 Registration Request (REG REQ)

The REG REQ message is sent by an ASP to indicate to a remote M3UA peer
that it wishes to register one or more given Routing Key with the


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remote peer.  Typically, an ASP would send this message to an SGP, and
expects to receive a REG RSP in return with an associated Routing
Context value.

The REG REQ message contains the following parameters:

     Routing Key           Mandatory

The format for the REG REQ 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 = 16           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         Routing Key 1                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 16           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         Routing Key n                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Routing Key: variable length

   The Routing Key parameter is mandatory. The sender of this message
   expects that the receiver of this message will create a Routing
   Key entry and assign a unique Routing Context value to it, if the
   Routing Key entry does not already exist.

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











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The format of the Routing 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-RK-Identifier                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Destination Point Code                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Network Appearance (optional)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       SI (optional)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         SSN (optional)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Origination Point Code List (optional)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Circuit Range List (optional)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Local-RK-Identifier: 32-bit integer

   The mandatory Local-RK-Identifier field is used to uniquely identify
   the registration request. The Identifier value is assigned by the
   ASP, and is used to correlate the response in an 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-RK-Identifier 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 = 19            |         Length = 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Local-RK-Identifier value                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Destination Point Code:

   The Destination Point Code parameter is mandatory, and identifies
   the Destination Point Code of incoming SS7 traffic for which the ASP
   is registering.  The format is the same as described for the
   Affected Destination parameter in the DUNA Message (See Section
   3.4.1). Its format is:







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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 20            |         Length = 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |            Destination Point Code             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Network Appearance:

   The optional Network Appearance parameter field identifies the SS7
   Network context for the Routing Key, and has the same format as in
   the Data message (See Section 3.3.1). Its format is:

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

Service Indicators (SI): n X 8-bit integers

   The SI field contains one or more Service Indicators from the values
   as described in the MTP3-User Identity field of the DUPU Message.
   The absence of the SI parameter in the Routing Key indicates the use
   of any SI values, excluding of course MTP management.  Where an SI
   parameter does not contain a multiple of four SIs, the parameter is
   padded out to 32-byte alignment.  An SI value of zero is not valid
   in M3UA.  The SI format is:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 21            |         Length = var.         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      SI #1    |     SI #2     |    SI #3      |    SI #4      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      SI #n    |             0 Padding, if necessary           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Subsystem Numbers (SSN): n X 8-bit integers

   The optional SSN field contains one or more SCCP subsystem numbers,
   and is used in conjunction with an SI values of 3 (i.e., SCCP) only.
   Where an SSN parameter does not contain a multiple of four SSNs, the
   parameter is padded out to 32-byte alignment. The subsystem number


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   values associated are defined by the local network operator, and
   typically follow ITU-T Recommendation Q.713.  An SSN value of zero
   is not valid in M3UA.  The format of this 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 = 22            |         Length = var.         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SSN #1    |    SSN #2     |   SSN #3      |   SSN #4      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SSN #n    |             0 Padding, if necessary           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

OPC List:

   The Originating Point Code List parameter contains one or more SS7
   OPC entries, and its format is the same as the Destination Point
   Code parameter.

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 23            |         Length = var.         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #1            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #2            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #n            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Circuit Range:

   An ISUP controlled circuit is uniquely identified by the SS7 OPC,
   DPC and CIC value.  For the purposes of identifying Circuit Ranges
   in an M3UA Routing Key, the optional Circuit Range parameter
   includes one or more circuit ranges, each identified by an OPC and
   Upper/Lower CIC value.  The DPC is implicit as it is mandatory and
   already included in the DPC parameter of the Routing Key.  The
   Origination Point Code is encoded the same as the Destination Point
   Code parameter, while the CIC values are 16-bit integers.

   The Circuit Range format is as follows:






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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 24            |         Length = var.         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #1            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Lower CIC Value #1      |      Upper CIC Value #1       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #2            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Lower CIC Value #2      |      Upper CIC Value #2       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask = 0   |          Origination Point Code #n            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Lower CIC Value #n      |      Upper CIC Value #n       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.5.6 Registration Response (REG RSP)

The REG RSP message is used as a response to the REG REQ message from a
remote M3UA peer.  It contains indications of success/failure for
registration requests and returns a unique Routing Context value for
successful registration requests, to be used in subsequent M3UA Traffic
Management protocol.

The REG RSP message contains the following parameters:

     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 = 25           |         Length = var.         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Registration Result 1                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Registration Result n                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








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Registration Results:

   The Registration Results parameter contains one or more results,
   each containing the registration status for a single Routing Key in
   an REG REQ message.  The number of results in a single REG RSP
   message MAY match the number of Routing 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-RK-Identifier value                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Registration Status                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Routing Context                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Local-RK-Identifier: 32-bit integer

   The Local-RK-Identifier contains the same value as found in the
   matching Routing Key parameter found in the REG Req message.

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:

        0           Successfully Registered
        1           Error - Unknown
        2           Error - Invalid DPC
        3           Error - Invalid Network Appearance
        4           Error - Invalid Routing Key
        5           Error - Permission Denied
        6           Error - Overlapping (Non-unique) Routing Key
        7           Error - Routing Key not Provisioned
        8           Error - Insufficient Resources

Routing Context: 32-bit integer

   The Routing Context field contains the Routing Context value for the
   associated Routing Key if the registration was successful. It is set
   to "0" if the registration was not successful.






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3.5.7 De-Registration Request (DEREG REQ)

The DEREG REQ message is sent by an ASP to indicate to a remote M3UA
peer that it wishes to de-register a given Routing Key. Typically, an
ASP would send this message to an SGP, and expects to receive a DEREG
RSP in return with the associated Routing Context value.

The DEREG REQ message contains the following parameters:

     Routing Context       Mandatory

The format for the DEREG REQ 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 = 6            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Routing Context: n X 32-bit integers

   The Routing Context parameter contains (a list of) integers indexing
   the Application Server traffic that the sending ASP is currently
   registered to receive from the SG but now wishes to deregister.


3.5.8 De-Registration Response (DEREG RSP)

The DEREG RSP message is used as a response to the DEREG REQ message
from a remote M3UA peer.

The DEREG RSP message contains the following parameters:

     De-registration Results    Mandatory

The format for the DEREG RSP message is as follows:












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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 18           |           Length = var        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  De-Registration Result 1                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  De-Registration Result n                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

De-Registration Results:

   The De-Registration Results parameter contains one or more results,
   each containing the de-registration status for a single Routing
   Context in a DEREG REQ message.  The number of results in a single
   DEREG RSP message MAY match the number of Routing Contexts 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Routing Context                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    De-Registration Status                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Routing Context: 32-bit integer

   The Routing Context field contains the Routing Context value of the
   matching Routing Key to deregister, as found in the DEREG Req.

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:
        0           Successfully De-registered
        1           Error - Unknown
        2           Error - Invalid Routing Context
        3           Error - Permission Denied
        4           Error - Not Registered






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3.5.5 ASP Active (ASPAC)

The ASPAC message is sent by an ASP to indicate to a remote M3UA peer
that it is Active and ready to process signalling traffic for a
particular Application Server.  The ASPAC affects only the ASP state
for the routing keys identified by the Routing Contexts, if present.

The ASPAC message contains the following parameters:

     Traffic Mode Type     Mandatory
     Routing Context       Optional
     INFO String           Optional

The format for the ASPAC 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 = 11            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Traffic Mode Type                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 6            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context*                        /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 4              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String*                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Traffic Mode Type: 32-bit (unsigned integer)

   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.

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






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   Within a particular Routing Context, only one Traffic Mode Type
   can be used.  The Over-ride value indicates that the ASP is
   operating in Over-ride mode, and the ASP takes over all
   traffic in an Application Server (i.e., primary/back-up 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.  The Standby versions of the Over-ride and
   Load-share Types indicate that the ASP is declaring itself ready to
   accept traffic but leaves it up to the sender as to when the traffic
   is started.  Over-ride (Standby) indicates that the traffic sender
   continues to use the currently active ASP until it can no longer
   send/receive traffic (i.e., the currently active ASP transitions to
   Down or Inactive).  At this point the sender MUST move the standby
   ASP to Active and commence traffic.  Load-share (Standby) is similar
   - the sender continues to load-share to the current ASPs until it is
   determined that there is insufficient resources in
   the Load-share group.  When there are insufficient ASPs, the sender
   MUST move the ASP to Active.

Routing Context: n X 32-bit integers

   The optional Routing Context parameter contains (a list of) integers
   indexing the Application Server traffic that the sending ASP is
   configured/registered to receive.

   There is one-to-one relationship between an index entry and an SG
   Routing Key or AS Name.  Because an AS can only appear in one
   Network Appearance, the Network Appearance parameter is not required
   in the ASPAC message.

   An Application Server Process may be configured to process traffic
   for more than one logical Application Server.  From the perspective
   of an ASP, a Routing Context defines a range of signalling traffic
   that the ASP is currently configured to receive from the SG.  For
   example, an ASP could be configured to support call processing for
   multiple ranges of PSTN trunks and therefore receive related
   signalling traffic, identified by separate SS7 DPC/OPC/CIC_ranges.

The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.4.1.)


3.5.6 ASP Active Ack

The ASPAC Ack message is used to acknowledge an ASP-Active message
received from a remote M3UA peer.  In the case where an ASPAC (Over-
ride (standby)) or ASPAC (load-share (standby) is received, a second
ASPACK Ack is sent when the ASP is moved to the "Active" state from
"Active (Standby)".



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The ASPAC Ack message contains the following parameters:

     Traffic Mode Type     Mandatory
     Routing Context       Optional
     INFO String           Optional

The format for the ASPAC 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 = 11            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Traffic Mode Type                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 6            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context*                        /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 4            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String*                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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

The format of the Traffic Mode Type and Routing Context parameters is
the same as for the ASP-Active message. (See Section 3.4.5).


3.5.7  ASP Inactive (ASPIA)

The ASPIA message is sent by an ASP to indicate to a remote M3UA peer
that it is no longer an active ASP to be used from within a list of
ASPs.  The ASPIA affects only the ASP state in the Routing Keys
identified by the Routing Contexts, if present.

The ASPIA message contains the following parameters:

     Routing Context         Optional
     INFO String             Optional





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The format for the ASPIA message parameters is as follows:

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


The format and description of the optional Routing Context and Info
String parameters is the same as for the ASPAC message (See Section
3.5.5.)

3.5.8 ASP Inactive Ack

The ASPIA Ack message is used to acknowledge an ASP-Inactive message
received from a remote M3UA peer.

The ASPIA Ack message contains the following parameters:

     Routing Context       Optional
     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 = 6            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context*                        /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 4            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String*                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.4.1.)

The format of the Routing Context parameter is the same as for the ASP-
Inactive message. (See Section 3.5.7).


3.5.9 Heartbeat (BEAT)

The Heartbeat message is optionally used to ensure that the M3UA peers
are still available to each other.  It is recommended for use when the
M3UA runs over a transport layer other than the SCTP, which has its own
heartbeat.

The BEAT message contains the following parameters:

     Heatbeat 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 = 8            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Heartbeat Data *                        /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Heartbeat Data parameter contents are defined by the sending node.
The Heartbeat Data could include, for example, a Heartbeat Sequence
Number and/or Timestamp.  The receiver of a Heartbeat message does not
process this field as it is only of significance to the sender.  The
receiver MUST respond with a BEAT-Ack message.


3.5.10 Heartbeat Ack (Beat-Ack)

The Heartbeat Ack message is sent in response to a received Heartbeat
message.  It includes all the parameters of the received Heartbeat
message, without any change.










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3.6  Management Messages

3.6.1  Error (ERR)

The Error 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
     Diagnostic Information     Optional

The format for the ERR message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 12           |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Error Code                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 7            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                     Diagnostic Information*                   /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Error Code: 32-bits (unsigned integer)

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

     1      Invalid Version
     2      Invalid Network Appearance
     3      Unsupported Message Class
     4      Unsupported Message Type
     5      Unsupported/Invalid Traffic Handling Mode
     6      Unexpected Message
     7      Protocol Error
     8      Invalid Routing Context
     9      Invalid Stream Identifier
    10      Invalid Parameter Value


The "Invalid Version" error is sent if a message was received with an
invalid or unsupported version.  The Error message contains the


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supported version in the Common header.  The Error message could
optionally provide the supported version in the Diagnostic Information
area.

The "Invalid Network Appearance" error is sent by a SG if an ASP sends
a message with an invalid (unconfigured) Network Appearance value.

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

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

The "Unsupported/Invalid Traffic Handling Mode" error is sent by a SG
if an ASP sends an ASP Active with an unsupported Traffic Handling Mode
or a Traffic Handling mode that is inconsistent with the presently
configured mode for the Application Server.  An example would be a case
in which the SG did not support load-sharing.

The "Unexpected Message" error MAY be sent if a defined and recognized
message is received that is not expected in the current state( in some
cases the ASP may optionally silently discard the message and not send
an Error).  For example, silent discard is used by an ASP if it
received a Transfer message from an SG while it was in the Inactive
state.

The "Protocol Error" error is sent for any protocol anomaly(i.e.,
reception of a parameter that is syntactically correct but unexpected
in the current situation.

The "Invalid Routing Context" error is sent by an SG if an Asp sends a
message with an invalid (unconfigured) Routing Context value.

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

The " Invalid Parameter Value " error is sent if a message was received
with an invalid parameter value (e.g., a DUPU message was received with
a Mask value other than "0").

Diagnostic Information: variable length

   When included, 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
   Network Appearance, Traffic Handling Mode, Routing Context or
   Parameter Value, the Diagnostic information includes the received
   parameter.  In the other cases, the Diagnostic information may be
   the first 40 bytes of the offending message.


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Error messages are not generated in response to other Error messages.


3.6.2 Notify (NTFY)

The Notify message used to provide an autonomous indication of M3UA
events to an M3UA peer.

The NTFY message contains the following parameters:

     Status Type/ID              Mandatory
     Routing Context            Optional
     INFO String                Optional

The format for the NTFY message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 13             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Status Type            |    Status Identification      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 6              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context*                        /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 4              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String*                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Status Type: 16-bits (unsigned integer)

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

         1     Application Server State Change (AS-StateChange)
         2     Other

Status Information: 16-bits (unsigned integer)

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



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   If the Status Type is AS_State_Change the following Status
   Information values are used:

         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 SG to an ASP upon a change in
   status of a particular Application Server. The value reflects the
   new state of the Application Server.

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

         1    Insufficient ASP resources active in AS
         2    Alternate ASP Active

These notifications are not based on the SG reporting the state change
of an ASP or AS.  In the Insufficent ASP Resources case, the SG is
indicating to an "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, an ASP is informed when an alternate
ASP transitions to the ASP-Active state in Over-ride mode.

The format and description of the optional Routing Context and Info
String parameters is the same as for the ASPAC message (See Section
3.4.6.)


4.0 Procedures

The M3UA layer needs to respond to various local primitives it receives
from other layers as well as the messages that it receives from the
peer M3UA layer.  This section describes the M3UA procedures in
response to these events.

4.1 Procedures to support the services of the M3UA layer

4.1.1 Receipt of primitives from the M3UA-User

On receiving an MTP-Transfer request primitive from an upper layer, or
the nodal inter-working function at an SG, the M3UA layer sends a
corresponding DATA message (see Section 3) to its M3UA peer.  The M3UA
peer receiving the Data message sends an MTP-Transfer indication
primitive to the upper layer.

The M3UA message distribution function (see Section 1.4.2.1) determines
the Application Server (AS) based on comparing the information in the
MTP-Transfer request primitive with a provisioned Routing Key.


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>From the list of ASPs within the AS table, an Active ASP is selected
and a DATA message is constructed and issued on the corresponding SCTP
Association.  If more than one ASP is active (i.e., traffic is to be
load-shared across all the active ASPs), one of the active ASPs from
the list is selected.  The selection algorithm is implementation
dependent but could, for example, be round-robin or based on, for
example, the SLS or ISUP CIC.  The appropriate selection algorithm must
be chosen carefully as it is dependent on application assumptions and
understanding of the degree of state coordination between the active
ASPs in the AS.

In addition, the message needs to be sent on the appropriate SCTP
stream, again taking care to meet the message sequencing needs of the
signalling application.

When there is no Routing Key match, or only a partial match, for an
incoming SS7 message, a default treatment must be specified.  Possible
solutions are to provide a default Application Server at the SG that
directs all unallocated traffic to a (set of) default ASP(s), or to
drop the message and provide a notification to management in an M-Error
indication primitive.  The treatment of unallocated traffic is
implementation dependent.

4.1.2 Receipt of primitives from the Layer Management

On receiving primitives from the local Layer Management, the M3UA layer
will take the requested action and provide an appropriate  response
primitive to Layer Management.

An M-SCTP ESTABLISH request from Layer Management at an ASP or IPSP
will initiate the establishment of an SCTP association.  The M3UA layer
will attempt to establish an SCTP association with the remote M3UA peer
at 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 to the local M3UA
layer.  At the SG or IPSP that initiated the request, the M3UA will
send an M-SCTP ESTABLISH confirm to Layer Management when the
association set-up is complete.  At the peer M3UA layer, an M-SCTP
ESTABLISH indication is sent to Layer Management upon successful
completion of an incoming SCTP association set-up.

An M-SCTP RELEASE request from Layer Management initates the tear-down
of an SCTP association.  M3UA accomplishes a graceful shutdown of the
SCTP association by sending a SHUTDOWN primitive to the SCTP layer.

When the graceful shutdown of the SCTP association has been
accomplished, the SCTP layer returns a SHUTDOWN COMPLETE notification



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to the local M3UA Layer.  At the M3UA Layer that initiated the request,
the M3UA will send an M-SCTP RELEASE confirm to Layer Management when
the association teardown is complete.   At the peer M3UA Layer, an M-
SCTP RELEASE indication is sent to Layer Management upon successful
tear-down of an SCTP association.

An M-SCTP STATUS request supports a Layer Management query of the local
status of a particular SCTP association.  The M3UA simply maps the M-
SCTP STATUS request to a STATUS primitive to the SCTP.  When the SCTP
responds, the M3UA maps the association status information to an M-SCTP
STATUS confirm.  No peer protocol is invoked.

Similar LM-to-M3UA-to-SCTP and/or SCTP-to-M3UA-LM mappings can be
described for the various other SCTP Upper layer primitives in RFC2960
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 M3UA Notify or Error message respectively.  These indications
can also be generated based on local M3UA events.

An M-ASP STATUS request supports a Layer Management query of the status
of a particular local or remote ASP.  The M3UA responds with the status
in an M-ASP STATUS confirm.  No M3UA peer protocol is invoked.

An M-AS STATUS request supports a Layer Management query of the status
of a particular AS.  The M3UA responds with an M-AS STATUS confirm.  No
M3UA 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 is provided by the M3UA to Layer Management.  If an invocation
is unsuccessful, an Error indication is provided.

These requests result in outgoing M3UA ASP-UP, ASP-DOWN, ASP-ACTIVE and
ASP-INACTIVE messages to the remote M3UA peer at an SG or IPSP.


4.2 Receipt of M3UA Peer Management messages

Upon successful state changes resulting from reception of M3UA ASP-UP,
ASP-DOWN, ASP-ACTIVE and ASP-INACTIVE messages from a peer M3UA, the




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M3UA layer MUST 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
indications to the local Layer Management.

M-NOTIFY indication and M-ERROR indication indicate to Layer Management
the notification or error information contained in a received M3UA
Notify or Error message.  These indications can also be generated based
on local M3UA events.


4.3 Procedures to support the M3UA Management services

These procedures support the M3UA management of SCTP Associations
between SGs and ASPs.

4.3.1 AS and ASP State Maintenance

The M3UA layer on the SG maintains the state of each remote ASP, in
each Application Server that the ASP is configured to receive traffic,
as input to the M3UA message distribution function.  Similarly, where
IPSPs use M3UA in a point-to-point fashion, the M3UA layer in an IPSP
maintains the state of remote IPSPs. For the purposes of the following
procedures, only the SG/ASP case is described but the SG side of the
procedures also apply to an IPSP sending traffic to an AS consisting of
a set of remote IPSPs.


4.3.1.1 ASP States

The state of each remote ASP, in each AS that it is configured to
operate, is maintained in the M3UA layer in the SG. The state of a
particular ASP in a particular AS changes due to events. The events
include:

   * Reception of messages from the peer M3UA layer at the ASP;
   * Reception of some messages from the peer M3UA layer at other ASPs
     in the AS (e.g., ASPAC Take-over);
   * Reception of indications from the SCTP layer; or
   * Local Management intervention.

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

ASP-DOWN: The remote M3UA 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 M3UA messages.

ASP-INACTIVE: The remote M3UA peer at the ASP is available (and the
related SCTP association is up) but application traffic is stopped.  In
this state the ASP can be sent any non-Data M3UA messages.


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ASP-ACTIVE: The remote M3UA peer at the ASP is available and
application traffic is active (for a particular Routing Context or set
of Routing Contexts).

ASP-STANDBY: The remote M3UA peer at the ASP is available and ready to
receive application traffic at any time (for a particular Routing
Context or set of Routing Contexts).  In this state the ASP can be sent
any non-Data M3UA messages.


                 Figure 4: ASP State Transition Diagram

                                   +--------------+
                                   |  ASP-ACTIVE  |
            +----------------------|      or      |
            |    Alternate +-------| ASP-STANDBY* |
            |       ASP    |       +--------------+
            |     Takeover |           ^     |
            |              |    ASP    |     | ASP
            |              |    Active |     | Inact
            |              |           |     v
            |              |       +--------------+
            |              |       |              |
            |              +------>| ASP-INACTIVE |
            |                      +--------------+
            |                          ^     |
  ASP Down/ |                     ASP  |     | ASP Down /
  SCTP CDI  |                     Up   |     | SCTP CDI
            |                          |     v
            |                      +--------------+
            |                      |              |
            +--------------------->|   ASP-DOWN   |
                                   |              |
                                   +--------------+


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

SCTP CDI: The local SCTP layer's Communication Down Indication to the
Upper Layer Protocol (M3UA) on an SG. The local SCTP 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.

4.3.1.2  AS States

The state of the AS is maintained in the M3UA layer on the SG.

The state of an AS changes due to events. These events include:


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   * 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.

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 inactive and it was the
last remaining active ASP in the AS (and no STANDBY ASPs are available.
A recovery timer T(r) will be started and all incoming SCN messages
will be queued by the SG. If an ASP becomes active before T(r) expires,
the AS will move to AS-ACTIVE state and all the queued messages will be
sent to the active ASP.

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























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                 Figure 5: AS State Transition Diagram

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

    Tr = Recovery Timer


4.3.2 M3UA Management procedures for primitives

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

Once the SCTP association is established (See Section 4.1.2) and
assuming that the local M3UA-User is ready, the local ASP M3UA
Application Server Process Maintenance (ASPM) function will initiate
the ASPM procedures, using the ASP-Up/-Down/-Active/-Inactive messages
to convey the ASP-state to the SG - see Section 4.3.3.

If the M3UA layer subsequently receives an SCTP-Communication Down
indication from the underlying SCTP layer, it will inform the Layer
Management by invoking the M-SCTP STATUS indication primitive. The
state of the remote ASP will be moved to "Down".  At an ASP, the MTP3-
User at an ASP will be informed of the unavailability of any affected
SS7 destinations through the use of MTP-PAUSE primitives.  In the case


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of SS7 network isolation, the local MTP3-Users may be informed by
implementation-dependent means as there is currently no primitive
defined for conveying this information.

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

4.3.3 M3UA Management procedures for peer-to-peer messages

All M3UA MGMT and ASP Maintenance messages are sent on a sequenced
stream to ensure ordering.  SCTP stream '0' is used.

4.3.3.1 ASP-Up

After an ASP has successfully established an SCTP association to an SG,
the SG waits for the ASP to send an ASP-Up message, indicating that the
ASP M3UA peer is available.  The ASP is always the initiator of the
ASP-Up exchange.  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 M3UA management function.

When an ASP-Up message is received at an SG and internally the remote
ASP is in the "Down" state and not considered locked-out for local
management reasons, the SG marks the remote ASP as "Inactive" and
informs Layer Management with an M-ASP-Up indication primitive.  If the
SG knows, via current configuration data, which Application Servers the
ASP is configured to operate in, it can update the ASP status to
"Inactive" in each AS that it is a member.  Alternatively, the SG may
move the ASP into a pool of Inactive ASPs available for future
activation in Application Server(s) denoted in the subsequent ASP-
Active Routing Contexts.  The SG responds with an ASP-Up Ack message in
acknowledgement.  The SG sends an ASP-Up Ack message in response to a
received ASP-Up message even if the ASP is already marked as "Inactive"
at the SG.

If for any local reason (e.g., management lock-out) the SG cannot
respond with an ASP-Up Ack, the SG responds to an ASP-Up with an ASP-
Down Ack message with Reason "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 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 a M-ASP-Up confirmation carrying a negative indication.



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The ASP must wait for the ASP-Up Ack message before sending any other
M3UA messages (e.g., ASPAC, REG REQ).  If the SG receives any other
M3UA messages before an ASP Up is received, the SG should discard them.

If an ASP-Up is received and internally the remote ASP is in the
"Active" or "Standby" state, an Error ("Unexpected Message) is returned
and the remote ASP state is not changed.

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

4.3.3.2 ASP-Down

The ASP will send an ASP-Down to an SG when the ASP wishes to be
removed from service in all Application Servers that it is a member and
no longer receive any M3UA traffic or management 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 M3UA
management function.

Whether the ASP is permanently removed from any AS is a function of
configuration management.

The SG marks the ASP as "Down", informs Layer Management with an M-ASP-
Down indication primitive, and returns an ASP-Down Ack message to the
ASP if one of the following events occur:

    - an ASP-Down message is received from the ASP,
    - another ASPM message is received from the ASP and the SG has
      locked out the ASP for management reasons.

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

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

When the ASP sends an ASP-Down it starts timer T(ack).  If the ASP does
not receive a response to an ASP-Down 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 a M-ASP-Down confirmation carrying a negative indication.






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4.3.3.3 M3UA 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 SG.

4.3.3.4 ASP-Active

Anytime after the ASP has received an ASP-Up Ack from the SG or IPSP,
the ASP sends an ASP-Active (ASPAC) to the SG 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 an M3UA 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 ASPAC contains
a list of one or more Routing Contexts to indicate for which
Application Servers the ASPAC applies. It is not necessary for the ASP
to include all Routing Contexts of interest in the initial ASPAC
message, thus becoming active in all Routing Contexts at the same time.
Multiple ASPAC messages MAY be used to activate within the Application
Servers independently.  In the case where an ASP-Active message does
not contain a Routing Context parameter, the receiver must know, via
configuration data, which Application Server(s) the ASP is a member.

When an ASP Active (ASPAC) message is received, the SG or IPSP responds
with an ASPAC Ack message(with the same Type value contained in the
received APAC), acknowledging that the ASPAC was received and,
depending on the ASPAC Type value, moves the ASP to the "Active" or
"Standby" state within the associated Application Server(s). Layer
Management is informed with an ASP-Active indication primitive. If the
SG or IPSP receives any Data messages before an ASPAC is received, the
SG or IPSP should discard them.  By sending an ASPAC Ack, the SG or
IPSP is now ready to receive and send traffic for the related Routing
Contexts.  The ASP MUST not send Data messages before receiving an
ASPAC Ack.

Multiple ASPAC Ack messages MAY be used in response to an ASPAC
containing multiple Routing Contexts, allowing the SG or IPSP to
independently Ack for different (sets of) Routing Contexts.  The SG or
IPSP sends an Error ("Invalid Routing Context") message for each
invalid or un-configured Routing Context value in a received ASPAC
message.




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The SG MUST send an ASP-Active Ack message in response to a received
ASP-Active message from the ASP and the ASP is already marked as
"Active" at the SG.

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

When the ASP sends an ASP-Active it starts timer T(ack).  If the ASP
does not receive a response to an ASP-Active within T(ack), the ASP MAY
restart T(ack) and resend ASP-Active messages 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 a M-ASP-Active confirmation carrying a negative
indication.

There are four modes of Application Server traffic handling in the SG
M3UA - Over-ride, Over-ride (Standby), Loadshare and Load-share
(Standby).  The Traffic Mode Type parameter in the ASPAC message
indicates the traffic handling mode used in a particular Application
Server. If the SG determines that the mode indicated in an ASPAC is
unsupported or incompatible with the mode currently configured for the
AS, the SG responds with an Error message indicating "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 ASPAC message causing
the transition of the Application Server state to "Active" MAY be used
to set the mode.

In the case of an Over-ride mode AS, reception of an ASPAC message at
an SG causes the redirection of all traffic for the AS to the ASP that
sent the ASPAC.  Any previously active ASP in the AS is now considered
Inactive and will no longer receive traffic from the SG within the AS.
The SG or IPSP sends a Notify (Alternate ASP-Active) to the previously
active ASP in the AS, after stopping all traffic to that ASP.

In the case of Over-ride (Standby) mode the traffic is not started to
the ASP until the previously active ASP transitions to "Inactive or
"Down" state.  At this point the ASP that sent the Over-Ride (Standby)
ASPAC is moved to the Active state and the traffic is redirected.  A
second ASP-Active Ack message with a new Traffic Mode Type ("Over-
ride", previously "Over-ride(Standby)") is sent to the ASP. A Notify
(Alternate ASP-Active) message is not sent in this case.

In the case of a Load-share mode AS, reception of an ASPAC message at
an SG or IPSP causes the direction of traffic to the ASP sending the
ASPAC, in addition to all the other ASPs that are currently active in
the AS.  The algorithm at the SG for load-sharing traffic within an AS




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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, SCCP SSN, ISUP CIC value).

An SG or IPSP, upon reception of an ASPAC 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 sufficient ASPs "Active" in the
AS).

In the case of Load-share (Standby) mode, the traffic is not started to
the ASP until the SG or IPSP determines that there are insufficient
resources available in the AS.  This is likely when one of the active
load-sharing ASPs transitions to the "Inactive" or "Down" state.  At
this point the ASP that sent the Load-share (Standby) ASPAC is moved to
the Active state and traffic is started.  A second ASP-Active Ack
message with a new Traffic Mode Type ("Load-share" - previously
"Loadshare(Standby)") is sent to the ASP. A Notify ("Insufficient ASP
resources active in AS ") message is not sent in this case.

All ASPs within a load-sharing mode AS must be able to handle any
traffic within the AS, in order to accommodate any potential fail-over
or rebalancing of the offered load.

4.3.3.5 ASP Inactive

When an ASP wishes to withdraw from receiving traffic within an AS, the
ASP sends an ASP Inactive (ASPIA) to the SG or IPSP.  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 M3UA
management function.   In the case where an ASP is processing the
traffic for more than one Application Server across a common SCTP
association, the ASPIA contains one or more Routing Contexts to
indicate for which Application Servers the ASPIA applies.  In the case
where an ASP-Inactive message does not contain a Routing Context
parameter, the receiver must know, via configuration data, which
Application Servers the ASP is a member and move the ASP to the
"Inactive" state in each AS.

In the case of an Over-ride mode AS, where another ASP has already
taken over the traffic within the AS with an Over-ride ASPAC, the ASP
that sends the ASPIA is already considered by the SG to be "Inactive".
An ASPIA Ack message is sent to the ASP, after ensuring that all
traffic is stopped to the ASP.

In the case of a Load-share mode AS, the SG moves the ASP to the
"Inactive" state and the AS traffic is re-allocated across the
remaining "active" ASPs per the load-sharing algorithm currently used
within the AS.  A NTFY(Insufficient ASP resources active in AS) may be
sent to all inactive ASPs, if required.  However, if a Loadshare


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(Standby) ASP is available, it may be now immediately included in the
loadshare group and a Notify message is not sent.  An ASPIA Ack message
is sent to the ASP after all traffic is halted and Layer Management is
informed with an ASP-INACTIVE indication primitive.

Multiple ASPIA Ack messages MAY be used in response to an ASPIA
containing multiple Routing Contexts, allowing the SG or IPSP to
independently Ack for different (sets of) Routing Contexts.  The SG or
IPSP sends an Error ("Invalid Routing Context") message for each
invalid or un-configured Routing Context value in a received ASPIA
message.

The SG 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
"Inactive" at the SG.

At the ASP, the ASP-INACTIVE Ack message received is not acknowledged.
Layer Management is informed with an M-ASP INACTIVE confirm primitive.
When the ASP sends an ASP-Inactive it starts timer T(ack).  If the ASP
does not receive a response to an ASP-Inactive 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 confirmation carrying a negative
indication.

If no other ASPs are "Active" or "Standby" in the Application Server,
the SG sends a NTFY(AS-Pending) to all inactive ASPs of the AS and
either discards all incoming messages for the AS or starts buffering
the incoming messages for T(r)seconds, after which messages will be
discarded.  T(r) is configurable by the network operator.  If the SG
receives an ASPAC from an ASP in the AS before expiry of T(r), the
buffered traffic is directed to the ASP and the timer is cancelled.  If
T(r) expires, the AS is moved to the "Inactive" state.

4.3.3.6 Notify

A Notify message reflecting a change in the AS state is sent to all
ASPs in the AS, except those in the "Down" state, with appropriate
Status Identification.  At the ASP, Layer Management is informed with
an M-NOTIFY indication primitive.

In the case where a Notify (AS-Pending) message is sent by an SG that
now has no ASPs active to service the traffic, or a NTFY(Insufficient
ASP resources active in AS) is sent in the Loadshare mode, the Notify
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.



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4.3.3.7 Heartbeat

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 the
SCTP).

After receiving an ASP-Up Ack message from an M3UA peer in response to
an ASP-Up message, an ASP may optionally send Beat messages
periodically, subject to a provisionable timer T(beat).  Upon receiving
a BEAT message, the M3UA peer MUST respond with a BEAT ACK message.  If
no BEAT ACK message (or any other M3UA message), is received by the ASP
within the timer 2*T(beat), the ASP will consider the remote M3UA peer
as "Down".

At the ASP, if no BEAT ACK message (or any other M3UA message) is
received from the M3UA peer within 2*T(beat), the remote M3UA peer is
considered unavailable.  Transmission of BEAT messages is stopped and
ASP-Up procedures are used to re-establish communication with the SG
M3UA peer.

The BEAT message may optionally contain an opaque Heartbeat Data
parameter that MUST be echoed back unchanged in the related Beat Ack
message.  The ASP upon examining the contents of the returned BEAT Ack
message MAY choose to consider the remote ASP 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 4 "ASP state
transition diagram".

4.3.4 Routing Key Management procedures

4.3.4.1 Registration

An ASP MAY dynamically register with an SG as an ASP within an
Application Server using the REG REQ message. A Routing Key parameter
in the REG REQ specifies the parameters associated with the Routing
Key.

The SG examines the contents of the received Routing Key parameter and
compares it with the currently provisioned Routing Keys.  If the
received Routing Key matches an existing SG Routing Key entry, and the
ASP is not currently included in the list of ASPs for the related
Application Server, the ASP MAY authorize the ASP to be added to the
AS.  Or, if the Routing Key does not currently exist and the received
Routing Key data is valid and unique, an SG supporting dynamic


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configuration MAY authorize the creation of a new Routing Key and
related Application Server and add the ASP to the new AS.  In either
case, the SG returns a Registration Response message to the ASP,
containing the same Local-RK-Identifier as provided in the initial
request, and a Registration Result "Successfully Registered".  A unique
Routing Context value assigned to the SG Routing Key is included. The
method of Routing Context value assignment at the SG/SGP is
implementation dependent but must be guaranteed to be unique across all
SGPs in an SG.

If the SG determines that the received Routing Key data is invalid, or
contains invalid parameter values, the SG returns a Registration
Response message to the ASP, containing a Registration Result "Error -
Invalid Routing Key", "Error - Invalid DPC, "Error - Invalid Network
Appearance" as appropriate.

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

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

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

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

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

Upon successful registration of an ASP in an AS, the SG can now send
related SSNM messaging, if this did not previously start upon the ASP
transitioning to "Inactive".



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4.3.4.2 Deregistration

An ASP MAY dynamically deregister with an SG as an ASP within an
Application Server using the DEREG REQ message. A Routing Context
parameter in the DEREG REQ specifies which Routing Key to de-register.

The SG examines the contents of the received Routing Context parameter
and validates that the ASP is currently registered in the Application
Server(s) related to the included Routing Context(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
Routing Key and Application Server configuration data at the SG. Other
ASPs may continue to be associated with the Application Server, in
which case the Routing Key data CANNOT be deleted.  If a Deregistration
results in no more ASPs in an Application Server, an SG MAY delete the
Routing Key data.

The SG acknowledges the de-registration request 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 deregister multiple Routing Contexts at once by including a
number of Routing Contexts in a single DEREG REQ message.  The SG MUST
respond to each deregistration request in a single DEREG RSP message,
indicating the success or failure result for each Routing Context in a
separate Deregistration Result parameter.


4.4 Procedures to support the M3UA services

4.4.1 At an SG

On receiving an MTP-PAUSE, MTP-RESUME, or MTP-STATUS indication
primitive from the nodal inter-working function at an SG, the SG M3UA
layer will send a corresponding SSNM DUNA, DAVA, SCON, or DUPU message
(see Section 2) to the M3UA peers at concerned ASPs.  The M3UA layer
must fill in various fields of the SSNM messages consistently with the
information received in the primitives.

The SG M3UA determines the set of concerned ASPs to be informed based
on the SS7 network partition for which the primitive indication is
relevant. In this way, all ASPs configured to send/receive traffic
within a particular network appearance are informed.  If the SG
operates within a single SS7 network appearance, then all ASPs are
informed.




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Optionally, the SG M3UA may filter further based on the Affected Point
Code in the MTP-PAUSE, MTP-Resume, or MTP-Status indication primitives.
In this way ASPs can be informed only of affected destinations to which
they actually communicate.  The SG M3UA may also suppress DUPU messages
to ASPs that do not implement an MTP3-User protocol peer for the
affected MTP3-User.

DUNA, DAVA, SCON messages must be sent on a sequenced stream as these
primitives should arrive in order.  Stream 0 is used.  Sequencing is
not required for the DUPU or DAUD message, which may optionally be sent
un-sequenced.  The same applies for the SCON message if the
international congestion method (see Q.704) is used.

4.4.2 At an ASP

4.4.2.1 Single SG configurations

At an ASP, upon receiving an SSNM message from the remote M3UA Peer,
the M3UA layer invokes the appropriate primitive indications to the
resident M3UA-Users.  Local management is informed.

In the case where a local event has caused the unavailability or
congestion status of SS7 destinations, the M3UA at the ASP should pass
up appropriate indications n the primitives to the M3UA User, as though
equivalent SSNM messages were received.  For example, the loss of an
SCTP association to an SG may cause the unavailability of a set of SS7
destinations.  MTP-Pause indications to the M3UA User is appropriate.
To accomplish this, the M3UA layer at an ASP maintains the status of
routes via the SG, much like an MTP3 layer maintains route-set status.

4.4.2.2 Multiple SG configurations

At an ASP, upon receiving an SSNM message from the remote M3UA Peer,
the M3UA layer updates the status of the affected route(s) via the
originating SG and determines, whether or not the overall availability
or congestion status of the effected destination(s) has changed. In
this case the M3UA layer invokes the appropriate primitive indications
to the resident M3UA-Users.  Local management is informed.

4.4.3 ASP Auditing

An ASP may optionally initiate an audit procedure in order to enquire
of an SG the availability and, if the congestion method with multiple
congestion levels and message priorities is used, congestion status of
an SS7 destination or set of destinations.  A Destination Audit (DAUD)
message is sent from the ASP to the SG requesting the current
availability and congestion status of one or more SS7 Destination Point
Codes.




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The DAUD may be sent un-sequenced. The DAUD may be sent by the ASP in
the following cases:

   - Periodic.  A Timer originally set upon reception of DUNA or SCON
     message has expired without a subsequent DAVA, DUNA or SCON
     updating the availability/congestion status of the affected

     Destination Point Codes.  The Timer is reset upon issuing a DAUD.
     In this case the DAUD is sent to the SG that originally sent the
     SSNM message.

   - the ASP is newly "Inactive" or "Active" or has been isolated from
     an SG for an extended period.  The ASP can request the
     availability/congestion status of one or more SS7 destinations to
     which it expects to communicate.

In the first case, the DAUD procedure must not be invoked for the case
of  received SCON containing a congestion level value of "no
congestion" or undefined" (i.e., congestion Level = "0").  This is
because the value indicates either congestion abatement or that the ITU
MTP3 international congestion method is being used.  In the
international congestion method, the MTP3 at the SG MTP3 does not
maintain the congestion status of any destinations and therefore the SG
cannot provide any congestion information in response to the DAUD.  For
the same reason, in the second case a DAUD cannot reveal any congested
destination(s).

The SG MUST respond to a DAUD with the MTP3 status of the routeset
associated with each Destination Point Code(s) in the DAUD.  The status
of each SS7 destination requested is indicated in a DUNA (if
unavailable), DAVA (if available/uncongested) or an SCON (if
available/congested).  Optionally, any DUNA or DAVA message in response
to a DAUD may contain a list of up to sixteen Affected Point Codes.
Note that from the point of view of an ASP sending an DAUD, the
subsequent reception of an SCON implies that the Affected Destination
is available.  The reception of a DAVA implies that the routeset to the
Affected Destination is not congested.  Obviously with the reception of
an DUNA, the routeset to the Affected Destination can not also be
congested.













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5.0 Examples of M3UA Procedures

5.1 Establishment of Association and Traffic between SGs and ASPs

5.1.1a Single ASP in an Application Server ("1+0" sparing), No
Registration

This scenario shows the example M3UA message flows for the
establishment of traffic between an SG 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. The sending of DUNA/SCON messages by the
SG is not shown but would be similar to 5.1.2.

             SG                              ASP1
              |                                |
              |<-------------ASP Up------------|
              |-----------ASP-Up Ack---------->|
              |                                |
              |<------- ASP Active(RCn)--------|  RC: Routing Context
              |-----ASP Active Ack (RCn)------>|      (optional)
              |                                |

Note: If ASPAC contains an optional Routing Context parameter, The
ASPAC only applies for the specified RC value. For an unknown RC value,
the SG responds with an Error message.


5.1.1b Single ASP in Application Server ("1+0" sparing), With Dynamic
Registration

This scenario is the same as for 5.1.1a but with the optional exchange
of registration information.  In this case the Registration is accepted
by the SG.



















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             SG                              ASP1
              |                                |
              |<------------ASP Up-------------|
              |----------ASP-Up Ack----------->|
              |                                |
              |<----REGISTER REQ(LRCn,RKn)-----|  LRC: Local Routing
              |                                |       Context
              |----REGISTER RESP(LRCn,RCn)---->|   RK: Routing Key
              |                                |   RC: Routing Context
              |                                |
              |<------- ASP Active(RCn)--------|
              |-----ASP Active Ack (RCn)------>|
              |                                |

Note: In the case of an unsuccessful registration attempt (e.g.,
Invalid RKn), the Register Response will contain an unsuccessful
indication and the ASP will not subsequently send an ASPAC.


5.1.1c Single ASP in multiple Application Servers (each with "1+0"
sparing), With Dynamic Registration (Case 1 û Multiple Registration
Requests)

             SG                              ASP1
              |                                |
              |<------------ASP Up-------------|
              |----------ASP-Up Ack----------->|
              |                                |
              |<----REGISTER REQ(LRC1,RK1)-----|  LRC: Local Routing
              |                                |       Context
              |----REGISTER RESP(LRC1,RC1)---->|   RK: Routing Key
              |                                |   RC: Routing Context
              |                                |
              |<------- ASP Active(RC1)--------|
              |-----ASP Active Ack (RC1)------>|
              |                                |
              :                                :
              :                                :
              |                                |
              |<----REGISTER REQ(LRCn,RKn)-----|
              |                                |
              |----REGISTER RESP(LRCn,RCn)---->|
              |                                |
              |                                |
              |<------- ASP Active(RCn)--------|
              |-----ASP Active Ack (RCn)------>|
              |                                |





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Note: In the case of an unsuccessful registration attempt (e.g.,
Invalid RKn), the Register Response will contain an unsuccessful
indication and the ASP will not subsequently send an ASPAC. Each LRC/RK
pair registration is considered independently.

It is not necessary to follow a Registration Request/Response with an
ASP Active before sending the next Registration Request. The ASP Active
can happen any time after the related successful Registration.


5.1.1.d Single ASP in multiple Application Servers (each with "1+0"
sparing), With Dynamic Registration (Case 2 û Single Registration
Request)


             SG                              ASP1
              |                                |
              |<------------ASP Up-------------|
              |----------ASP-Up Ack----------->|
              |                                |
              |<---REGISTER REQ({LRC1,RK1},----|
              |                   ...,         |
              |                 {LRCn,RKn}),----|
              |                                |
              |---REGISTER RESP({LRC1,RC1},--->|
              |                  ...,          |
              |                 (LRCn,RCn})    |
              |                                |
              |<------- ASP Active(RC1)--------|
              |-----ASP Active Ack (RC1)------>|
              |                                |
              :                                :
              :                                :
              |                                |
              |<------- ASP Active(RCn)--------|
              |-----ASP Active Ack (RCn)------>|
              |                                |

Note: In the case of an unsuccessful registration attempt (e.g.,
Invalid RKn), the Register Response will contain an unsuccessful
indication and the ASP will not subsequently send an ASPAC. Each LRC/RK
pair registration is considered independently.

The ASP Active can happen any time after the related successful
Registration, and may have more than one RC.







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5.1.2 Two ASPs in Application Server ("1+1" sparing)

This scenario shows the example M3UA message flows for the
establishment of traffic between an SG and two ASPs in the same
Application Server, where ASP1 is configured to be "active" and ASP2 a
"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.
The example message flow is the same whether the ASP-Active messages
are Over-ride or Load-share mode although typically this example would
use an Over-ride mode. In the case of MTP Restart, the SG starts
sending any relevant DUNA and SCON messages to the ASPs as soon as they
enter the ASP-INACTIVE state. The ASP-Active Ack message is only sent
after all relevant DUNA/SCON messages have been transmitted to the
concerned ASP.


       SG                        ASP1                        ASP2
        |                         |                          |
        |<--------ASP Up----------|                          |
        |-------ASP-Up Ack------->|                          |
        |                         |                          |
        |<-----------------------------ASP Up----------------|
        |-----------------------------ASP-Up Ack------------>|
        |                         |                          |
        |                         |                          |
        |<-------ASP Active-------|                          |
        |------ASP-Active Ack---->|                          |
        |                         |                          |


5.1.3 Two ASPs in an Application Server ("1+1" sparing, load-sharing
case)

This scenario shows a similar case to Section 4.1.2 but where the two
ASPs are brought to "active" and load-share the traffic load.  In this
case, one ASP is sufficient to handle the total traffic load. The
sending of DUNA/SCON messages by the SG is not shown but would be
similar to 5.1.2.












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


5.1.4 Three ASPs in an Application Server ("n+k" sparing, load-sharing
case)

This scenario shows the example M3UA message flows for the
establishment of traffic between an SG and three ASPs in the same
Application Server, where two of the ASPs are brought to "active" and
share the load. In this case, a minimum of two ASPs are required to
handle the total traffic load (2+1 sparing). The sending of DUNA/SCON
messages by the SG is not shown but would be similar to 5.1.2.


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






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5.2 ASP Traffic Fail-over Examples

5.2.1 (1+1 Sparing, withdrawal of ASP, Back-up Over-ride)

Following on from the example in Section 5.1.2, and ASP1 withdraws from
service:

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

Note: If the SG detects loss of the M3UA peer (M3UA heartbeat loss or
detection of SCTP failure), the initial SG-ASP1 ASP Inactive message
exchange would not occur.


5.2.2 (1+1 Sparing, Back-up Over-ride)

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

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


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

Following on from the example in Section 5.1.4, and ASP1 withdraws from
service:

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


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For the Notify to occur the SG maintains knowledge of the minimum ASP
resources required - for example if the SG knows that "n+k" = "2+1" for
a load-share AS and "n" currently equals "1".

Note: If the SG detects loss of the ASP1 M3UA peer (M3UA heartbeat loss
or detection of SCTP failure), the first SG-ASP1 ASP Inactive message
exchange would not occur.


5.3  M3UA/MTP3-User Boundary Examples

5.3.1 At an ASP

This section describes the primitive mapping from the MTP3 User to M3UA
at an ASP.

5.3.1.1 Support for MTP-Transfer on the ASP

5.3.1.1.1 Support for MTP-Transfer Request
When the MTP3-User on the ASP has data to send into the SS7 network, it
will use the MTP-Transfer Request primitive.  The M3UA on the ASP will
do the following when it receives an MTP-Transfer Request primitive
from the M3UA user:

  - Determine the correct SG

  - Determine the correct association to the chosen SG

  - Determine the correct stream in the association (e.g., based on
    SLS)

  - Determine whether to complete the optional fields of the Data
    message

  - Map the MTP-Transfer Request primitive into the Protocol Data
    field of an m3ua Data message

  - Send the Data message to the remote M3UA peer in the SG, over the
    SCTP association

        SG                       ASP
        |                         |
        |<-----Data Message-------|<--MTP-Transfer req.
        |                         |


5.3.1.1.2 Support for MTP Transfer Indication

When the M3UA on the ASP has received Data messages from the remote
M3UA peer in the SG it will do the following:


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  - Evaluate the optional fields of the Data message if present

  - Map the Payload of a Data message into the MTP-Transfer Indication
    primitive

  - Pass the MTP-Transfer Indication primitive to the user part. In
    case of multiple user parts, the optional fields of the Data
    message are used to determine the concerned user part.

        SG                       ASP
        |                         |
        |------Data Message------>|-->MTP-Transfer ind.
        |                         |

5.3.1.1.3 Support for ASP Querying of SS7 Destination States

There are situations such as temporary loss of connectivity to the SG
that may cause the M3UA on the ASP to audit SS7 destination
availability states.  Note: there is no primitive for the MTP3-User to
request this audit from the M3UA as this is initiated by an internal
M3UA management function.

The M3UA on the ASP normally sends Destination State Audit (DAUD)
messages for each of the destinations that the ASP supports.

       SG                        ASP
        |                         |
        |<-----DAUD Message ------|
        |<-----DAUD Message ------|
        |<-----DAUD Message ------|
        |                         |
        |                         |

5.3.2 At an SG

This section describes the MTP3 upper layer primitive mapping to the
M3UA at the SG.

5.3.2.1 Support for MTP-Transfer Request at the SG

When the M3UA on the SG has received Data messages from its peer
destined to the SS7 network it will do the following:

  - Evaluate the optional fields of the Data message if present to
    determine the network appearance

  - Map the Protocol data of the Data message into an MTP-Transfer
    Request primitive

  - Pass the MTP-Transfer Request primitive to the MTP3 of the
    concerned network appearance.

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                            SG                        ASP
                             |                         |
        <---MTP-Transfer req.|<------Data Message------|
                             |                         |


5.3.2.2 Support for MTP-Transfer Indication at the SG

When the MTP3 on the SG has data to pass its user parts, it will use
the MTP-Transfer Indication primitive.  The M3UA on the SG will do the
following when it receives an MTP-Transfer Indication:

  - Determine the correct ASP

  - Determine the correct association to the chosen ASP

  - Determine the correct stream in the association (e.g., based on
    SLS)

  - Determine whether to complete the optional fields of the Data
    message

  - Map the MTP-Transfer Indication primitive into the Protocol Data
    field of an M3UA Data message

  - Send the Data message to the remote M3UA peer in the ASP, over the
    SCTP association

                           SG                        ASP
                            |                         |
       --MTP-Transfer ind.->|------Data Message------>|
                            |                         |


5.3.2.3 Support for MTP-PAUSE, MTP-RESUME, MTP-STATUS

The MTP-PAUSE, MTP-RESUME and MTP-STATUS indication primitives from the
MTP3 upper layer interface at the SG need to be made available to the
remote MTP3 User Part lower layer interface at the concerned ASP(s).

5.3.2.3.1 Destination Unavailable

The MTP3 on the SG will generate an MTP-PAUSE primitive when it
determines locally that an SS7 destination is unreachable.  The M3UA
will map this primitive to a Destination Unavailable (DUNA) message.
The SG M3UA determines the set of concerned ASPs to be informed based
on internal SS7 network information associated with the MTP-PAUSE
primitive indication.




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                   SG                       ASP
                    |                         |
 --MTP-PAUSE ind.-->|------DUNA Message ----->|--MTP-PAUSE ind.-->
                    |                         |


5.3.2.3.2 Destination Available

The MTP3 on the SG will generate an MTP-RESUME primitive when it
determines locally that an SS7 destination that was previously
unreachable is now reachable.  The M3UA will map this primitive to a
Destination Available (DAVA) message.  The SG M3UA determines the set
of concerned ASPs to be informed based on internal SS7 network
information associated with the MTP-RESUME primitive indication.

                   SG                       ASP
                    |                         |
--MTP-RESUME ind.-->|------DAVA Message ----->|--MTP-RESUME ind.-->
                    |                         |


5.3.2.3.3 SS7 Network Congestion

The MTP3 on the SG will generate an MTP-STATUS primitive when it
determines locally that the route to an SS7 destination is congested.
The M3UA will map this primitive to a SS7 Network Congestion State
(SCON) message.  It will determine which ASP(s) to send the DUPU to
based on the intended Application Server.

                     SG                       ASP
                       |                         |
   --MTP-STATUS ind.-->|------SCON Message ----->|--MTP-STATUS ind.-->
                       |                         |

5.3.2.3.4 Destination User Part Unavailable

The MTP3 on the SG will generate an MTP-STATUS primitive when it
receives an UPU message from the SS7 network.  The M3UA will map this
primitive to a Destination User Part Unavailable (DUPU) message.  It
will determine which ASP(s) to send the DUPU based on the intended
Application Server.

                      SG                       ASP
                       |                         |
   --MTP-STATUS ind.-->|------DUPU Message ----->|--MTP-STATUS ind.-->
                       |                         |






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6.0 Security

6.1 Introduction

M3UA is designed to carry signalling messages for telephony services.
As such, M3UA 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.

6.2 Threats

There is no quick fix, one-size-fits-all solution for security.  As a
transport protocol, M3UA has the following security objectives:

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

M3UA runs on top of SCTP.  SCTP [6] provides certain transport related
security features, such as some protection against:

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

When M3UA 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"
[21] should be consulted for guidance.

When the network in which M3UA 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
[22] for more information on configuring IPSEC services.

6.3 Protecting Confidentiality

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






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7.0 IANA Considerations

7.1 SCTP Payload Protocol Identifier

A request will be made to IANA to assign an M3UA value for the Payload
Protocol Identifier in SCTP Payload Data chunk.  The following SCTP
Payload Protocol Identifier will be registered:

        M3UA    "3"

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.

7.2 M3UA 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].

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

7.2.1 IETF Defined Message Classes

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

7.2.2 IETF Defined Message Types

The documentation for a new message type MUST include 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 for each
    field within the message.


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(d) A detailed procedural description of the use of the new message
    type within the operation of the protocol.
(e) A detailed description of error conditions when receiving this
    message type.

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

7.2.3 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.


8.0 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, Selvam Rengasami, Shyamal
Prasad, Joyce Archibald, Ray Singh, Antonio Roque Alvarez and many
others for their valuable comments and suggestions.


9.0  References

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

[2] ITU-T Recommendations Q.761 to Q.767, 'Signalling System No.7 (SS7)
    - ISDN User Part (ISUP)'

[3] ANSI T1.113 - 'Signaling System Number 7 - ISDN User Part

[4] ETSI ETS 300 356-1 "Integrated Services Digital Network (ISDN);
    Signalling System No.7; ISDN User Part (ISUP) version 2 for the
    international interface; Part 1: Basic services"

[5] ITU-T Recommendations Q.711-715, 'Signalling System No. 7 (SS7) -
    Signalling Connection Control Part (SCCP)'



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

[7] ETSI ETS 300 009-1, "Integrated Services Digital Network (ISDN);
    Signalling System No.7; Signalling Connection Control Part (SCCP)
    (connectionless and connection-oriented class 2) to support
    international interconnection; Part 1: Protocol specification"

[8] ITU-T Recommendations Q.720, 'Telephone User Part'

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

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

[11] ETSI ETS 300 287-1, "Integrated Services Digital Network (ISDN);
     Signalling System No.7; Transaction Capabilities (TC) version 2;
     Part 1: Protocol specification"

[12] 3G TS 25.410 V3.1.0 (2000-01) Technical Specification - 3rd
     Generation partnership Project; Technical Specification Group
     Radio Access Network; UTRAN Iu Interface: General Aspects and
     Principles (3G TS 25.410 Version 3.1.0 Release 1999)

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

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

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

[16] ETSI ETS 300 008-1, "Integrated Services Digital Network (ISDN);
     Signalling System No.7; Message Transfer Part (MTP) to support
     international interconnection; Part 1: Protocol specification"

[17] ITU-T Recommendation Q.2140 'B-ISDN ATM Adaptation Layer - Service
     Specific Coordination Function for signalling at the Network Node
     Interface (SSCF at NNI)

[18] ITU-T Recommendation Q.2110 'B-ISDN ATM Adaptation Layer - Service
     Specific Connection Oriented Protocol (SSCOP)

[19] MTP2-User Adaptation Layer <draft-ietf-sigtran-m2ua-05.txt>, Nov.
     2000, Work in Progress

[20] ITU-T Recommendation Q.2210 'B-ISDN MTP'




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

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


10.0  Author's Addresses

Greg Sidebottom
Nortel Networks
3685 Richmond Rd,
Nepean, Ontario, Canada  K2H 5B7
gregside@nortelnetworks.com

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

Lyndon Ong
Point Reyes Networks
1991 Concourse Dr.
San Jose, CA, USA  95131
long@pointreyesnet.com

Ian Rytina
Ericsson Australia
37/360 Elizabeth Street
Melbourne, Victoria 3000, Australia
ian.rytina@ericsson.com

Hanns Juergen Schwarzbauer
SIEMENS AG
Hofmannstr. 51
81359 Munich, Germany
HannsJuergen.Schwarzbauer@icn.siemens.de

Klaus D. Gradischnig
SIEMENS AG
Hofmannstr. 51
81359 Munich, Germany
klaus.gradischnig@icn.siemens.de

Ken Morneault
Cisco Systems Inc.
13615 Dulles Technology Drive
Herndon, VA, USA  20171
EMail: kmorneau@cisco.com




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Malleswar Kalla
Telcordia Technologies
MCC 1J211R
445 South Street
Morristown, NJ, USA  07960
Email: kalla@research.telcordia.com

Normand Glaude
Performance Technologies
150 Metcalf Sreet, Suite 1300
Ottawa, Ontario, Canada  K2P 1P1
EMail: nglaude@microlegend.com




















This draft expires August 2001.



















Sidebottom et al                                             [Page 96]


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