Network Working Group                                   Greg Sidebottom
INTERNET-DRAFT                                             Guy Mousseau
                                                        Nortel Networks
                                                             Lyndon Ong
                                                                  Ciena
                                                             Ian Rytina
                                                               Ericsson
                                             Hanns Juergen Schwarzbauer
                                                                Siemens
                                                      Klaus Gradischnig
                                                                NeuStar
                                                          Ken Morneault
                                                                  Cisco
                                                          Mallesh Kalla
                                                              Telcordia
                                                         Normand Glaude
                                               Performance Technologies
                                                         Brian Bidulock
                                                                OpenSS7

Expires in six months                                         Jul 2001

                SS7 MTP3-User Adaptation Layer (M3UA)
                  <draft-ietf-sigtran-m3ua-07.txt>
                  <draft-ietf-sigtran-m3ua-08.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
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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
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.

                        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........................................21
    1.6 Definition of M3UA Boundaries................................24
2. Conventions.......................................................28
3. M3UA Protocol Elements............................................28
    3.1 Common Message Header........................................28
    3.2 Variable-Length Parameter....................................31
    3.3 Transfer Messages............................................32
    3.4 SS7 Signalling Network management (SSNM) Messages............35
    3.5 ASP State Maintenance (ASPM) Messages........................43
    3.6 Routing Key Management (RKM) Messages........................46
    3.7 ASP Traffic Maintenance (ASPTM) Messages.....................55
    3.8 Management(MGMT) Messages....................................60
4. Procedures........................................................64
    4.1 Procedures to Support the M3UA-User and Layer Management
        Layers.......................................................64
    4.2 Procedures to Support the Management of SCTP Associations
        with M3UA Peers..............................................67
    4.3 Procedures to support the Unavailability or Congestion
        Status of SS7 Destinations...................................81
    4.4 MTP3 Restart.................................................83
5. Examples of M3UA Procedures.......................................84
    5.1 Establishment of Association and Traffic
        Between SGs and ASPs.........................................84
    5.2 ASP traffic Fail-over Examples...............................89
    5.3 Normal Withdrawal of an ASP from an Application Server
        and Tear-down of an Association..............................90
    5.4.M3UA/MTP3-User Boundary Examples.............................91
6. Security..........................................................95
    6.1 Introduction.................................................95
    6.2 Threats......................................................95
    6.3 Protecting Confidentiality...................................95
7. IANA Considerations...............................................96
    7.1 SCTP Payload Protocol Identifier.............................96
    7.2 M3UA Protocol Extensions.....................................96
8. Acknowledgements..................................................97
9. References........................................................97
10.  Bibliography....................................................99
11.  Author's Addresses..............................................99

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 SIO/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.  An AS is contained within a
single Network Appearance.  Note that there is a 1:1
relationship between an AS and a Routing Key.

Application Server Process (ASP) - A process instance of an Application
Server. An Application Server Process serves as an active or back-up
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.

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, back-up or back-up, load-sharing or broadcast
process of a Signalling Gateway.

Signalling Gateway - An SG is a signaling agent that receives/sends SCN
native signaling at the edge of the IP network [1].  An SG appears to
the SS7 network as an SS7 Signalling Point.  An SG contains a set of one
or more unique Signalling Gateway Processes, of which one or more is
normally actively processing traffic.  Where an SG contains more than
one SGP, the SG is a logical entity and the contained SGPs must might
typically be coordinated into a single management view to the SS7
network and to the supported Application Servers.

Signalling Process - A process instance that uses M3UA to communicate
with other signalling process. processes.  An ASP, an SGP 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 Signalling Point Code.
Management Cluster.

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. a single MTP
entity (Signalling Point).  SPMCs are used to
sum aggregate the availability/congestion/User_Part
availability, congestion, and user part status of an SS7
destination point code MTP entity
(Signalling Point) that is distributed in the IP domain, for the purpose
of supporting MTP3 management procedures at an SG. towards the SS7 network.  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 should 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 uniquely identifies an SS7
entity (Point Code) into an SS7 network, as presented by the SG.  It is
used for the purposes of logically separating the signalling traffic
between the SG and the Application Server Processes over a common SCTP
association.  This partitioning is necessary where an SG is logically
partitioned to appear as end node elements in multiple separate SS7
networks, in which case there is a separate network appearance for each
point code in the SS7 networks.  It is also necessary when an SG is
configured as an STP hosting multiple point codes, or when configured
as multiple end nodes within the same network, in which case each point
code is a separate network appearance.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 separate SS7 network
partition. network.

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 (SGP, ASP or IPSP) 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. an MTP User.
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 protocol as SCCP
payload, as they are SCCP-User protocols.

It is recommended that 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:

   - 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 SGP, and not by
a local MTP3 layer.  The MTP3 layer at an SGP 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 layer does not itself provide the MTP3 services.
However, in the case where an ASP is connected to more than one SGP,
the M3UA layer at an ASP must should maintain the status of configured SS7
destinations and route messages according to the availability and
congestion status of the routes to these destinations via each SGP.

The M3UA layer may also be used for point-to-point signalling between
two IP Server Processes (IPSPs).  In this case, the M3UA layer 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 SGP.  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 layer provides the transport of MTP-TRANSFER primitives across
an established SCTP association between an SGP 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 User Part messages received from the
SS7 network by the SGP 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.

At an ASP, in the case where a destination is reachable via multiple
SGPs, the M3UA layer must also choose via which SGP the message is to
be routed or support load balancing across the SGPs, ensuring that no
missequencing occurs.

The M3UA layer does not impose a 272-octet signalling 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 SGPs.
However, if the SS7 network is provisioned to support the Broadband MTP
[20] to the final SS7 destination, the information block size limit may MAY
be increased past 272 octets.

1.3.2.2 Native Management Functions

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

The M3UA layer 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 SGP, the M3UA layer 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
    destination in the SS7 network are experiencing SS7 congestion.

  - Providing an indication to the M3UA layer at an ASP that the routes
    to a remote destination in the SS7 network are restricted.

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

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

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

1.3.2.4 Support for the Management of SCTP Associations between the SGP
and ASPs.

The M3UA layer at the SGP 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 primitives 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) SHOULD be designated to establish the SCTP association, or
M3UA configuration knowledge information maintained to detect redundant
associations (e.g., via knowledge of the expected local and remote SCTP
endpoint addresses).

Local management MAY request from the M3UA layer the status of the
underlying SCTP associations using the M-SCTP_STATUS request and

confirm primitives.  Also, the M3UA MAY autonomously 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 inform the local management of the change in
status of an ASP or AS.  This may MAY be achieved using the M-ASP_request M-ASP_STATUS
request or M-AS_STATUS request primitives.

1.3.2.5 Support for the Management of Connections to Multiple SGPs

As shown in Figure 1 an ASP may be connected to multiple SGPs. In such
a case a particular SS7 destination may be reachable via more than one
SGP, i.e., via more than one route. As MTP3 users only maintain status
on a destination and not on a route basis, the M3UA layer 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
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 SGPs or
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
and SGPs within the available Hosts SHOULD MAY 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:

          SG                                     MGC

  Host#1 **************                          ************** Host#3
     =   *  ********__*__________________________*__********  *   =
         *  * SGP1 *__*_____      _______________*__* ASP1 *  *  MGC1
         *  ********  *     \    /               *  ********  *
         *  ********__*______\__/________________*__********  *
         *  * SGP2 *__*_______\/______      _____*__* ASP2 *  *
         *  ********  *       /\      |    |     *  ********  *
         *      :     *      /  \     |    |     *      :     *
         *  ********  *     /    \    |    |     *  ********  *
         *  * SGPn *  *     |    |    |    |     *  * ASPn *  *
         *  ********  *     |    |    |    |     *  ********  *
         **************     |    |    |    |     **************
                            |    |    \    /
  Host#2 **************     |    |     \  /      ************** Host#4
     =   *  ********__*_____|    |______\/_______*__********  *   =
         *  * SGP1 *__*_________________/\_______*__* ASP1 *  *  MGC2
         *  ********  *                /  \      *  ********  *
         *  ********__*_______________/    \_____*__********  *
         *  * SGP2 *__*__________________________*__* ASP2 *  *
         *  ********  *                          *  ********  *
         *      :     *     SCTP Associations    *      :     *
         *  ********  *                          *  ********  *
         *  * SGPn *  *                          *  * ASPn *  *
         *  ********  *                          *  ********  *
         **************                          **************

                      Figure 1 - Physical Model

In this model, each host has MAY have many application processes.  In the
case of the MGC, an ASP may provide service to one or more Application
Servers, and is identified as an SCTP end point.  A pair of signalling
gateway processes may Signalling
Gateway Processes MAY represent, as an example, a single Signalling
Gateway, serving a signalling point management cluster.

This example model can also be applied to IPSP-IPSP signalling.  In
this case, each IPSP would MAY 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 more than one
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, Routing Keys, the availability status of the signalling
routes to signalling points in the SS7 network, network , and the redundancy
model (active-standby, load-sharing, broadcast, n+k) of the remote
signalling processes.

For carrier grade networks, the failure or isolation of a particular
signalling process SHOULD NOT 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

For example, within an SS7 network, a Signalling Gateway might be
charged with representing a set of nodes in the IP domain into the SS7
network for routing purposes.  The SG itself, as a signalling point in
the SS7 network, might also be addressable with an SS7 Point Code for
MTP3 Management purposes. The SG Point Code might also be 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 could 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.

Where an SG contains more than one SGP, the MTP3 routeset, SPMC and
remote AS/ASP states of each SGP SHOULD be coordinated across all the
SGPs.  Re-routing of traffic between the SGPs SHOULD also be supported

The M3UA places no restrictions on the SS7 Point Code representation of
an AS. supported.

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.

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 will typically be
represented by a Point Code that is separate from any SG Point Code.
This allows allows, for example, 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 SGP it is equally
important that the corresponding
Routing Keys in the involved SGPs are should be identical.  (Note: It is
possible for the SGP 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:.  SG-to SG -SG communication is recommended for carrier grade
networks, using an MTP3 linkset or an equivalent, to allow re-routing
between the SGs in the event of route failures.  Where SGPs are used,
inter-SGP communication is recommended.  Inter-SGP protocol is outside
of the scope of this document.

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"    |    |
  +-------+              +---------------+

1.4.2 Routing Contexts and Routing Keys

1.4.2.1 Overview

The distribution of SS7 messages between the SGP 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 MTP3-User specific fields such (such as the ISUP CIC, SCCP
subsystem number, 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 ASP 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 Limitations

Routing Keys SHOULD be unique in the sense that each received SS7
signalling message SHOULD have a full or partial match to a single
routing result to an Application Server. 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 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 provision a Routing Key at an SGP. A
Routing Key may be configured statically using an implementation
dependent management interface, or dynamically using the M3UA Routing
Key registration procedure. 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 SGP 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 at the SGP

In order to

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

To support this message distribution, the SGP must might, for example,
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 could be accomplished
by comparing elements of the incoming SS7 message to currently defined
Routing Keys in the SGP.  These Routing Keys could in turn make reference map directly
to an Application Server that is enabled by one or more ASPs.  These
ASPs provide dynamic status information on regarding their availability,
traffic handling capability and congestion to the SGP 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 the AS but in certain failure and transition cases it is
possible that there may be no active ASP available.  Both load-sharing  Broadcast, load-
sharing and backup scenarios are supported.

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

1.4.2.5 Message Distribution at the ASP

In order to direct messages to the SS7 network, the

The ASP must also
perform choose an SGP to direct a message distribution function in order to choose the proper
SGP for a given message. SS7 network.  This
is accomplished by observing the Destination Point Code (and possibly
other elements of the outgoing message such as the SLS value).Where value).

Implementation Note: Where more than one route (or SGP) is
possible for routing to the SS7 network, the ASP SHOULD could, for example,
maintain a dynamic table of available SGP routes for the SS7
destinations, taking into account the SS7 destination
availability/restricted/congestion status received from the SGP(s), the
availability status of the individual SGPs and configuration changes and
fail-over mechanisms. There is, however, no M3UA messaging to manage the
status of an SGP (e.g., SGP-Up/Down/Active/Inactive messaging).
Whenever an SCTP

association to an SGP exists, the SGP is assumed to be ready for the
purposes of responding to M3UA ASPSM messages. messages (Refer to Section 3).

Every SGP of one SG 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
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].

Note: It is also possible for IP-based interfaces to be present, using
the services of the MTP2-User Adaptation Layer (M2UA) [23] [26] or M2PA []. [27].

These may could be terminated at a Signalling Transfer Point (STP) or
Signalling End Point (SEP).  Using the services of MTP3, the SG may could 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.

1.4.3.2 SS7 and M3UA Inter-Working at the SG

The SGP 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 relevant 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.  Where more than one SGP

constitutes an SG, the knowledge of the SGPs must be coordinated into
an overall SG view.

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 also made available to any existing
local MTP3-Users at the SG, if present.)

MTP3 management messages (such as TFPs or TFAs received from the SS7
network) MUST NOT be encapsulated as Data message Payload Data and sent
either from SG to ASP or from ASP to SG.  The SG MUST terminate these
messages and generate M3UA messages as appropriate.

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 could 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. code.

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

1.4.3.4 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 which match a provisioned
Routing Key at an SG from the
SS7 network SGP are assigned mapped to a unique an Application Server, based on the
information in the message and the provisioned Routing Keys. Server.

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

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/back-up redundancy is a subset of this model. A simplex
"1+0" model is also supported as a subset, with no ASP redundancy.

At the SGP, an Application Server list contains active and inactive
ASPs to support ASP broadcast, load-sharing and fail-over procedures.
The list of ASPs within a logical Application Server is kept updated in
the SGP 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 Host3 or ASP1 in Host4.  The AS list at SGP1 in
Host 1 might look like the following:

    Routing Key {DPC=x) - "Application Server #1"
        ASP1/Host3  - State = Active
        ASP1/Host3
        ASP1/Host4  - State = Inactive

In this "1+1" redundancy case, ASP1 in Host3 would be sent any incoming
message with DPC=x.  ASP1 in Host4 would normally be brought to the
"active" state upon failure of, or loss of connectivity to, ASP1/Host1.

The AS List at SGP1 in Host1 might also be set up in load-share mode:

    Routing Key {DPC=x) - "Application Server #1"
        ASP1/Host3 - State = Active
        ASP1/Host4 - State = 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 might need to 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 to support this function is outside the scope of this
document.

1.4.4.2 Signalling Gateway Redundancy

Signalling Gateways MAY also be distributed over multiple hosts.  Much
like the AS model, SGs may comprise one or more SG Processes (SGPs),
distributed over one or more hosts, using an active/back-up or a load-
sharing model.  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 SHOULD 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.  A broadcast model is also possible, where signalling
messages are sent to each active SGP in the SG. The distribution of the
MTP3-user messages over the SGPs should be done in such a way to
minimize message mis-sequencing, as required by the SS7 User Parts.

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 layer 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 acknowledgement to the ASP to indicate that the ASP is
actively handling traffic for that destination, and the SGP has not
indicated that the destination is inaccessible.  When an ASP is
configured to use multiple SGPs for transferring traffic to the SS7
network, the ASP must maintain knowledge of the current capability of
the SGPs to handle traffic to destinations of interest.  This
information is crucial to the overall reliability of the service, for

both active/back-up and

active/back-up, load-sharing model, and broadcast models, 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 SGPs 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.

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 layer 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 MAY trigger SS7 MTP3 Transfer Controlled management messages
to originating SS7 nodes, per the congestion procedures of the relevant
MTP3 standard. The triggering of SS7 MTP3 Management messages from an
SG is an implementation-dependent function.

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

1.4.7 SCTP Stream Mapping.

The M3UA layer at both the SGP and ASP also supports the assignment of
signalling traffic into streams within an SCTP association.  Traffic
that requires sequencing must SHOULD 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

It is recommended that the SGP and ASP be able to support both client
and server
operation. 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. The default orientation would be for the SGP to take on
the role
of server while the ASP is the client. In this case, ASPs SHOULD
initiate the
SCTP association to the SGP

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.

The SCTP Registered User Port Number Assignment for M3UA is 2905.

1.5 Sample Configurations

1.5.1 Example 1: ISUP Message Transport

  ********   SS7   *****************   IP   ********
  * SEP  *---------*      SGP      *--------* 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 SGP 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 SGP
serves as the interface within the SGP 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 SGP 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,
translated to MTP-TRANSFER request primitives, and sent to the local
M3UA-resident message distribution function for ongoing routing to the
final IP destination.  Messages received from the local M3UA network
address translation and mapping function as MTP-TRANSFER indication
primitives 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.

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, MTP-RESUME or MTP-
STATUS indications from the M3UA layer to the SCCP layer should
consider the status of the SCTP Association and underlying IP network
and any congestion information received from the remote site.

1.5.3 Example 3: SGP Resident SCCP Layer, with Remote ASP

  ********   SS7   *****************   IP   ********
  * SEP  *---------*               *--------*      *
  *  or  *         *      SGP      *        * 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 SGP 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 of 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 SGP can perform the SCCP GTT service
for messages logically addressed to it from SCCP peers in the IP
domain.  In this case, MTP-TRANSFER indication primitives 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 primitive is given to the MTP3 for delivery to an SS7-
resident node.

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

For internal SGP modeling purposes, this may be accomplished with the
use of an implementation-dependent nodal inter-working function within
the SGP that effectively sits below the SCCP and routes MTP-TRANSFER

request/indication messages to/from both the MTP3 and the M3UA layer,
based on the SS7 DPC or DPC/SSN 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 layer are the
same as in Example 1 and the functions taking place in the SCCP entity
are transparent to the M3UA layer.  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 its
            peer.

   M-STCP_ESTABLISH confirm
   Direction: M3UA -> LM
   Purpose: ASP confirms to LM that it has established an SCTP
            association with its peer.

   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 its
            peer.

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

   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 RESTART indication
   Direction: M3UA -> LM
   Purpose: M3UA informs LM that an SCTP restart indication has been
            received.

   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 responds with the status of an SCTP association.

   M-SCTP STATUS indication
   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.
   M-ASP_UP confirm
   Direction: M3UA -> LM
   Purpose: ASP reports that is has received an ASP UP Ack message from
            its peer.

   M-ASP_UP indication
   Direction: M3UA -> LM
   Purpose: M3UA reports it has successfully processed an incoming ASP
            Up message 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
            Ack message from its peer.

   M-ASP_DOWN indication
   Direction: M3UA -> LM
   Purpose: M3UA reports it has successfully processed an incoming ASP
            Down message from its peer, or the SCTP association has
            been lost/reset.

   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
            Ack message from its peer.

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

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

   M-ASP_INACTIVE confirm
   Direction: LM -> M3UA
   Purpose: ASP reports that is has received an ASP Inactive
            Ack message from its peer.

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

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

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

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

If dynamic registration of RK is supported by the M3UA layer, the layer
MAY support the following additional primitives:

   M-RK_REG request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to register RK(s) with its peer by sending
            REG REQ message

   M-RK_REG confirm
   Direction: M3UA -> LM
   Purpose: ASP reports that it has received REG RSP message with
            registration status as successful from its peer.

   M-RK_REG indication
   Direction: M3UA -> LM
   Purpose: M3UA informs LM that it has successfully processed an
            incoming REG REQ message.

   M-RK_DEREG request
   Direction: LM -> M3UA
   Purpose: LM requests ASP to de-register RK(s) with its peer by
            sending DEREG REQ message.

   M-RK_DEREG confirm
   Direction: M3UA -> LM
   Purpose: ASP reports that it has received DEREG REQ message with de-
            registration status as successful from its peer.

   M-RK_DEREG indication
   Direction: M3UA -> LM
   Purpose: M3UA informs LM that it has successfully processed an
            incoming DEREG REQ from its peer.

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. 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                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                                                               /

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
     1     Transfer Messages
     2     SS7 Signalling Network Management (SSNM) Messages
     3     ASP State Maintenance (ASPSM) Messages
     4     ASP Traffic Maintenance (ASPTM) Messages
     5     Reserved for Other Sigtran Adaptation Layers
     6      Reserved for Other Sigtran Adaptation Layers
     7     Reserved for Other Sigtran Adaptation Layers
     8     Reserved for Other Sigtran Adaptation Layers
     9     Routing Key Management (RKM) Messages
  10 to 127 Reserved by the IETF
 128 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) Messages (See Section 3.6)

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

     Transfer Messages (See Section 3.3)

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

     SS7 Signalling Network Management (SSNM) Messages (See Section
3.4)

         0        Reserved
         1        Destination Unavailable (DUNA)
         2        Destination Available (DAVA)
         3        Destination State Audit (DAUD)
         4        SS7 Network Congestion (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 (See Section 3.5)

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

  ASP Traffic Maintenance (ASPTM) Messages (See Section 3.5)

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

  Routing Key Management (RKM) Messages (See Section 3.7)

         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 RKM extensions

3.1.3  Reserved: 8 bits

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

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.  Common parameters used by adaptation
   layers are in the range of 0x00 to 0xff. 0x3f.   M3UA-specific parameters
   have Tags in the range 0x80 0x0200 to 0xbf. 0x02ff.  The parameter Tags defined
   are as follows:

         0x00

         0x0000        Reserved
         0x80
         0x0200        Network Appearance
         0x81
         0x0201        Protocol Data 1
         0x82
         0x0202        Protocol Data 2
         0x04
         0x0004        INFO String
         0x83
         0x0203        Affected Destinations
         0x06
         0x0006        Routing Context
         0x07
         0x0007        Diagnostic Information
         0x09
         0x0009        Heartbeat Data
         0x84
         0x0204        User/Cause
         0x0a
         0x000a        Reason
         0x0b
         0x000b        Traffic Mode Type
         0x0c
         0x000c        Error Code
         0x0d
         0x000d        Status
         0x85
         0x000e        ASP Identifier
         0x0205        Congestion Indications
         0x86
         0x0206        Concerned Destination
         0x87
         0x0207        Routing Key
         0x88
         0x0208        Registration Result
         0x89
         0x0209        De-registration Result
         0x8a
         0x020a        Local_Routing Key Identifier
         0x8b
         0x020b        Destination Point Code
         0x8c
         0x020c        Service Indicators
         0x8d
         0x02        Subsystem Numbers
         0x8e
         0x020e      Originating Point Code List
         0x8f
         0x020f      Circuit Range
         0x90        Registration Results
         0x91        De-Registration Results
      0x92

     0x0210 to ffff...Reserved 0xffff...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 NOT 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.

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 = 0x80 0x0200           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Network Appearance                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Tag = 0x81 0x0201 or 0x82 0x0202     |             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 SGP and the ASP 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 specific SS7 network partition. network.  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.  In other cases the parameter MUST be
   included.

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

   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

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

Protocol Data 1 or 2: variable length

   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.  The received SS7 fields are populated
   octet by octet as received into the 4-octet word as shown in the two
   examples below.

   For the ANSI protocol example, the Protocol Data 1 field format 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 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 (with the 3/8/3 Point
   Code format), the Protocol Data 1 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                                 |
    |      *|Zone*| |        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 all SGPs in an SG to all concerned ASPs
to indicate that the SG has determined that one or more SS7
destinations are unreachable.  It is also sent by an SGP 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" DUNA messages 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 SGPs initiating the DUNA message as
per the defined MTP3-User procedures.

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 = 0x80 0x0200          |           Length =8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Network Appearance                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x83 0x0203          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Mask      |                 Affected DPC 1                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Mask      |                 Affected DPC n                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x04 0x0004         |             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.

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
   Region is unavailable. A mask value equal to the number of bits in
   the DPC indicates that the entire network appearance is affected  -
   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 SGP 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 informed and may now resume
traffic to the affected destination.  The ASP M3UA layer routes the
MTP3_user traffic through the SGP(s) initiating the DAVA message.

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 MAY be sent from the ASP to the SGP 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 SGP to all concerned ASPs to
indicate congestion in the SS7 network to one or more destinations, or

to an ASP in response to a DATA or DAUD message as appropriate.  For
some MTP protocol variants (e.g., ANSI MTP) the SCON message may be
sent when the SS7 congestion level changes.  The SCON message MAY also
be sent from the M3UA layer of an ASP to an M3UA peer indicating that
the M3UA layer 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 = 0x80 0x0200          |           Length =8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Network Appearance                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x83 0x0203          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Mask     |                 Affected DPC 1                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Mask     |                 Affected DPC n                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x86 0x0206          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    reserved   |                 Concerned DPC                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x85 0x0205          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Reserved                    |  Cong. Level  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 0x04 0x0004       |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         INFO String                           /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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
message MUST not be delayed in order to "collect" individual congested
destinations into a single SCON message 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 message is sent from an ASP to the SGP. It contains the point
   code of the originator of the message that triggered the SCON
   message. 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. Any resulting Transfer Controlled (TFC) message
   from the SG is sent to the Concerned Point Code  using the single
   Affected DPC contained in the SCON message to populate the
  (affected) Destination field of the TFC message

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].

3.4.5 Destination User Part Unavailable (DUPU)

The DUPU message is used by an SGP 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 = 0x80 0x0200          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Network Appearance                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x83 0x0203          |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Mask = 0    |                  Affected DPC                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x84 0x0204          |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Cause             |            User               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x04 0x0004          |             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
   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 align 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
         11        Reserved
         12        AAL type 2 Signalling
         13        Bearer Independent Call Control (BICC)
         14        Gateway Control Protocol
         15        Reserved

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 signalled in a DUPU
message, 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 SGP 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 SGP to all concerned ASPs
to indicate that the SG has determined that one or more SS7
destinations are now restricted from the point of view of the SGP, or
in response to a DAUD message if appropriate. The M3UA layer at the ASP
is expected to send traffic to the affected destination via an
alternate SGP of equal priority, but only if such an alternate route
exists and is available. If the affected destination is currently
considered unavailable by the ASP, The MTP3-User should be informed
that traffic to the affected destination can be resumed.  In this case,
the M3UA layer should route the traffic through the SGP initiating the
DRST message.

This message is optional for the SGP to send and it is optional for the
ASP to act on any information received in the message. It is for use in
the "STP" case described in Section 1.4.1.

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 ASP State Maintenance (ASPSM) Messages

3.5.1 ASP Up

The ASP Up message is used to indicate to a remote M3UA peer that the
adaptation layer is ready to receive any SSNM or ASPSM/ASPTM messages
for all Routing Keys that the ASP is configured to serve.

The ASP Up message contains the following parameters:

     ASP Identifier                Optional
     INFO String                   Optional

The format for ASP Up 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 = 0x04 0x000e          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         ASP Identifier                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0004            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format and description of the optional INFO String ASP Identifier parameter contains a unique value that is
locally significant among the
same as ASPs that support an AS. The SGP should
save the ASP Identifier to be used, if necessary, with the Notify
message (see Section 3.8.2).

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 Acknowledgement (ASP Up Ack)

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

The ASP Up Ack message contains the following parameters:

     INFO String (optional)

The format for ASP Up 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 =0x04 =0x0004             |             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 INFO String in
an ASP Up Ack message is independent from the INFO String in the ASP Up
message (i.e., it does not have to echo back the INFO String received).

3.5.3 ASP Down

The ASP Down message is used to indicate to a remote M3UA peer that the
adaptation layer is NOT ready to receive DATA, SSNM SSNM, RKM or ASPTM
messages.

The ASP Down message contains the following parameters:

     Reason         Mandatory

     INFO String    Optional

The format for the ASP Down 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 = 0x0a            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Reason                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag =0x04 =0x0004           |            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).

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 Acknowledgement (ASP Down Ack)

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

The ASP Down Ack message contains the following parameters:

     Reason          Mandatory
     INFO String     Optional

The format for the ASP Down 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 = 0x0a            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Reason                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x04 0x0004          |            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 INFO String in an ASP Down Ack message is independent from the INFO
String in the ASP Down message (i.e., it does not have to echo back the
INFO String received).

The format of the Reason parameter is the same as for the ASP-Down
message. (See Section 3.5.3).

3.5.5 Heartbeat (BEAT)

The BEAT 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 = 0x09 0x0009            |            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 BEAT message does not
process this field as it is only of significance to the sender.  The
receiver MUST respond with a BEAT Ack message.

3.5.6 Heartbeat Acknowledgement (BEAT Ack)

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

3.6 Routing Key Management (RKM) Messages

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

The REG REQ message contains the following parameters:

     Routing Key           Mandatory

One or more Routing Key parameters MAY be included.  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 = 0x87 0x0207         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                         Routing Key 1                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x87 0x0207         |            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.

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                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Traffic Mode Type                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     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 message 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          ag         Tag = 0x8a 0x020a          |         Length = 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Local-RK-Identifier value                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Traffic Mode Type: 32-bit (unsigned integer)

   The Traffic Mode Type parameter is mandatory and identifies the
   traffic mode of operation of the ASP(s) within an Application
   Server.  The valid values for Traffic Mode Type are shown in the
   following table:

      1     Over-ride
      2     Load-share
      3     Broadcast

If the receiver of the REG REQ creates a new Routing Key entry, then
the Traffic Mode Type sets the traffic mode for the new Application
Server.  If the receiver of the REG REQ determines that a matching
Routing Key already exists, the Traffic Mode Type MUST match the
existing traffic mode for the AS.

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:

    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 = 0x8b 0x020b          |         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).  The absence of the Network
   Appearance parameter in the Routing Key indicates the use
   of any Network Appearance value, 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 = 0x80 0x0200          |         Length = 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Network Appearance                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   The optional 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 value, 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 = 0x8c 0x020c          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      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.
   The absence of the SSN parameter in the Routing Key indicates the
   use of any SSN value, in the case of SCCP traffic.  Where an SSN
   parameter does not contain a multiple of four SSNs, the parameter is
   padded out to 32-byte alignment. The subsystem number values
   associated are defined by the local network operator, and typically
   follow ITU-T Recommendation Q.713 [5].  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 = 0x8d 0x020d            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     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.  The absence of the OPC List parameter in the
   Routing Key indicates the use of any OPC value,
    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 = 0x8e 0x020e          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    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
   absence of the Circuit Range parameter in the Routing Key indicates
   the use of any Circuit Range values, in the case of ISUP/TUP
   traffic.  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:

    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 = 0x8f 0x020f        |              Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    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       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.6 2 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 Result   Mandatory

One or more Registration Result parameters MAY be included.  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 = 0x90 0x0208         |              Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Registration Result 1                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0208        |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Registration Result n                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Registration Results:

   The Registration Results Result 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 be anywhere from one to the
   total number of number of Routing Key parameters found in the
   corresponding REG REQ message. Where multiple REG RSP messages are
   used in reply to REG REQ message, a specific result SHOULD be in
   only one REG RSP 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 (See
   Section 3.5.5.1).

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 - Cannot Support Unique Routing
        7           Error - Routing Key not Currently Provisioned
        8           Error - Insufficient Resources
        9           Error - Unsupported RK parameter Field
       10           Error  - Unsupported/Invalid Traffic Handling Mode

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.

3.6.3 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 message 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 = 0x06 0x0006            |            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 SGP but now wishes to deregister.

3.6.4 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 Result    Mandatory

One or more De-registration Result parameters MAY be included.  The
format for the DEREG RSP message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x89 0x0209         |               Length          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  De-Registration Result 1                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0209        |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  De-Registration Result n                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

De-Registration Results:

   The De-Registration Results Result 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 be anywhere from
   one to the total number of number of Routing Contexts Context values found in
   the corresponding REG REQ message. Where multiple DEREG RSP messages
   are used in reply to DEREG REQ message, a specific result SHOULD be
   in only one DEREG RSP 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
   message.

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
        5           Error  - ASP Currently Active for Routing Context

3.7 ASP Traffic Maintenance (ASPTM) Messages

3.7.1 ASP Active

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

The ASP Active message contains the following parameters:

     Traffic Mode Type     Mandatory
     Routing Context       Optional
     INFO String           Optional

The format for the ASP Active 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 = 0x0b 0x000b            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Traffic Mode Type                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x06 0x0006            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x04 0x0004            |             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 Traffic Mode
   Type are shown in the following table:

         1         Over-ride
         2         Load-share
         3         Broadcast
         5         Over-ride (Standby)
         4
         6         Load-share (Standby)
         7         Broadcst (Standby)

   Within a particular Routing Context, Over-ride Over-ride,Load-share and Load-share,
   Broadcast, either active or standby, MUST NOT be mixed.  The Over-ride 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
   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  In Broadcast
   mode, the ASP will receive the same messages as any other currently
   active ASP.  The Standby versions of the Over-
   ride and Over-ride, Load-share and
   Broadcast 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
   state ASP-DOWN or ASP-ACTIVE). ASP-INACTIVE).  At this point the sender MUST move
   the standby ASP to the ASP-ACTIVE state and commence traffic.  Load-share  Load-
   share (Standby) is and Broadcast (Standby) are similar - the sender
   continues to load-share or broadcast to the current ASPs until it is
   determined
   that there is insufficient resources in the Load-share or Broadcast
   group.  When there are insufficient ASPs, the sender MUST move the
   ASP to state ASP-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 SGP
   Routing Key or AS Name.  Because an AS can only appear in one
   Network Appearance, the Network Appearance parameter is not required
   in the ASP Active 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 SGP.  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).

3.7.2 ASP Active Acknowledgement (ASP Active Ack)

The ASP Active Ack message is used to acknowledge an ASP Active message
received from a remote M3UA peer.  In the case where an ASP Active
(Over-ride (standby)), ASP Active (Load-share (standby)) or ASP Active (Load-share
(Broadcast (standby)) message is
received, a second ASP Active Ack message is sent when the ASP is moved
from the ASP-STANDBY to the ASP-ACTIVE state.

The ASP Active Ack message contains the following parameters:

     Traffic Mode Type     Mandatory
     Routing Context       Optional
     INFO String           Optional

The format for the ASP Active Ack message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0b 0x000b        |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Traffic Mode Type                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 0x06 0x0006       |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x04 0x0004        |             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 INFO String in an ASP Active Ack message is independent from the
INFO String in the ASP Active message (i.e., it does not have to echo
back the INFO String received).

The format of the Traffic Mode Type and Routing Context parameters is
the same as for the ASP Active message. (See Section 3.5.5).

3.7.3  ASP Inactive

The ASP Inactive 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 ASP Inactive message affects only the ASP state in the
Routing Keys identified by the Routing Contexts, if present.

The ASP Inactive message contains the following parameters:

     Routing Context         Optional
     INFO String             Optional

The format for the ASP Inactive 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 = 0x06 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x04 0x0004          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

3.7.4 ASP Inactive Acknowledgement (ASP Inactive Ack)

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

The ASP Inactive Ack message contains the following parameters:

     Routing Context       Optional
     INFO String           Optional

The format for the ASP Inactive 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 = 0x06 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context* Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x04 0x0004          |             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 INFO String in an ASP Inactive Ack message is independent from the
INFO String in the ASP Inactive message (i.e., it does not have to echo
back the INFO String received).

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

3.8  Management (MGMT) Messages

3.8.1  Error

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 Error message contains the following parameters:

     Error Code                 Mandatory
     Diagnostic Information     Optional

The format for the Error 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 = 0x0c 0x000c         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Error Code                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x07 0x0007         |            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
    11      Refused - Management Blocking
    12      Unknown Routing Context
    13      Missing, Duplicated or Invalid ASP Identifier

The "Invalid Version" error is sent if a message was received with an
invalid or unsupported version.  The Error message contains the
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 SGP 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 SGP
if an ASP sends an ASP Active message with an unsupported Traffic Mode
Type  or a Traffic Mode Type that is inconsistent with the presently
configured mode for the Application Server.  An example would be a case
in which the SGP 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 message).  For example, silent discard is used by an ASP if it
received a DATA message from an SGP while it was in the ASP-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 if a message is received
from a peer with an invalid (unconfigured) Routing Context value.

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

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

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

The "Unknown Routing Context" Error is sent if a message is received
from a peer without a Routing Context parameter and it is not known by
configuration data which Application Servers are referenced.

The "Refused - Missing, Duplicated or Invalid ASP Identifier" error is
sent when an ASP-Up message is received and the request is refused
because an ASP ID is required, or the value is invalid/duplicated.

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 parameter MUST be added
   and include the offending parameter.  In the other cases, the
   Diagnostic information MAY be the first 40 bytes of the offending
   message.

Error messages MUST NOT be generated in response to other Error
messages.

3.8.2 Notify

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

The Notify message contains the following parameters:

     Status                     Mandatory
     ASP Identifier             Optional
     Routing Context            Optional
     INFO String                Optional

The format for the Notify 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 = 0x0d 0x000d           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Status Type            |    Status Information      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x06 0x000e           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        ASP Identifier                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag = 0x0006           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x04 0x0004          |             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-State_Change)
         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.

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

   If the Status Type is 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 SGP reporting the state change
of an ASP or AS.  In the Insufficent ASP Resources case, the SGP is
indicating to an ASP_INACTIVE ASP in the AS that another ASP is
required in order to handle the load of the AS (Load-sharing or Broadcast 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 ASP Identifier, Routing
Context and Info String parameters is the same as for the ASP Active
message (See Section 3.5.5.)

4. 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 M3UA-User and Layer Management Layers

4.1.1 Receipt of Primitives from the M3UA-User

On receiving an MTP-TRANSFER request primitive from an upper layer at
an ASP/IPSP, or the nodal inter-working function at an SGP, 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.

>From the list of ASPs within the AS table, an ASP in the ASP-ACTIVE
state is selected and a DATA message is constructed and issued on the
corresponding SCTP association.  If more than one ASP is in the ASP-
ACTIVE state (i.e., traffic is to be load-shared across more than one
ASP), one of the ASPs in the ASP_ACTIVE state is selected from the
list.  If the ASPs are in Broadcast Mode, all active ASPs will be
selected and the message sent to each of the active ASPs.  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 ASP_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 SGP that
directs all unallocated traffic to a (set of) default ASP(s), or to
drop the message and provide a notification to Layer 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 primitive 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 by sending an SCTP-ASSOCIATE primitive to the local
SCTP layer.

When an SCTP association has been successfully established, the SCTP
will send an SCTP-COMMUNICATION_UP notification primitive to the local
M3UA layer.  At the SGP or IPSP that initiated the request, the M3UA
layer will send an M-SCTP_ESTABLISH confirm primitive to Layer
Management when the association set-up is complete.  At the peer M3UA
layer, an M-SCTP_ESTABLISH indication primitive is sent to Layer
Management upon successful completion of an incoming SCTP association
set-up.

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

When the graceful shutdown of the SCTP association has been
accomplished, the SCTP layer returns an SCTP-SHUTDOWN_COMPLETE
notification primitive to the local M3UA layer.  At the M3UA Layer that
initiated the request, the M3UA layer will send an M-SCTP_RELEASE
confirm primitive to Layer Management when the association teardown is
complete.   At the peer M3UA Layer, an M-SCTP_RELEASE indication
primitive is sent to Layer Management upon successful tear-down of an
SCTP association.

An M-SCTP_STATUS request primitive supports a Layer Management query of
the local status of a particular SCTP association.  The M3UA layer
simply maps the M-SCTP_STATUS request primitive to an SCTP-STATUS

primitive to the SCTP layer.  When the SCTP responds, the M3UA layer
maps the association status information to an M-SCTP_STATUS confirm
primitive.  No peer protocol is invoked.

Similar LM-to-M3UA-to-SCTP and/or SCTP-to-M3UA-to-LM primitive mappings
can be described for the various other SCTP Upper Layer primitives in
RFC2960 [13]  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 primitive supports a Layer Management query of
the status of a particular local or remote ASP.  The M3UA layer
responds with the status in an M-ASP_STATUS confirm primitive.  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
primitive.  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 primitive is provided by the M3UA layer to Layer Management.
If an invocation is unsuccessful, an Error indication primitive is
provided in the primitive.

These requests result in outgoing ASP Up, ASP Down, ASP Active and
ASP Inactive messages to the remote M3UA peer at an SGP or IPSP.

4.1.3 Receipt of M3UA Peer Management Messages

Upon successful state changes resulting from reception of ASP Up,
ASP Down, ASP Active and ASP Inactive messages from a peer M3UA, the
M3UA layer SHOULD invoke corresponding M-ASP_UP, M-ASP_DOWN, M-
ASP_ACTIVE and M-ASP_INACTIVE, M-AS_ACTIVE, M-AS_INACTIVE, and M-
AS_DOWN indication primitives to the local Layer Management.

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

4.2 Procedures to Support the Management of SCTP Associations with M3UA
Peers

These procedures support the M3UA management of SCTP Associations
between SGPs and ASPs or between IPSPs.

4.2.1 AS and ASP State Maintenance

The M3UA layer on the SGP maintains the state of each remote ASP, in
each Application Server that the ASP is configured to receive traffic,
as input to the 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 SGP/ASP case is described but the SGP side of the
procedures also apply to an IPSP sending traffic to an AS consisting of
a set of remote IPSPs.

4.2.1.1 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 SGP. 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., ASP Active message indicating "Over-ride");
   * 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 MAY be sent any non-DATA M3UA messages.

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 MAY be sent
any non-Data M3UA messages.

                 Figure 4: ASP State Transition Diagram

                                   +--------------+
                                   |  ASP-ACTIVE  |
            +----------------------|      or      |
            |      Other   +-------| ASP-STANDBY* |
            |   ASP in AS  |       +--------------+
            |   Overrides  |           ^     |
            |              |    ASP    |     | ASP
            |              |    Active |     | Inactive
            |              |           |     v
            |              |       +--------------+
            |              |       |              |
            |              +------>| ASP-INACTIVE |
            |                      +--------------+
            |                          ^     |
  ASP Down/ |                     ASP  |     | ASP Down /
  SCTP CDI CDI/ |                     Up   |     | SCTP CDI CDI/
  SCTP RI   |                          |     v SCTP RI
            |                      +--------------+
            |                      |              |
            +--------------------->|   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 SCTP CDI denotes the local SCTP layer's Communication
Down Indication to the Upper Layer Protocol (M3UA) on an SGP. The local
SCTP layer will send this indication when it detects the loss of
connectivity to the ASP's peer SCTP layer.  SCTP CDI is understood as
either a SHUTDOWN_COMPLETE notification or COMMUNICATION_LOST
notification from the SCTP layer.

SCTP RI: The local SCTP layer's Restart indication to the upper layer
protocol (M3UA) on an SG.  The local SCTP will send this indication when
it detects a restart from the ASP's peer SCTP layer.

4.2.1.2  AS States

The state of the AS is maintained in the M3UA layer on the SGP.  The
state of an AS changes due to events. These events include:

   * ASP state transitions
   * Recovery timer triggers

The possible states of an AS are:

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

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 or ASP-STANDBY states).  The
recovery timer
T(r) is not running or has expired.

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

AS-PENDING: An active ASP has transitioned to ASP-INACTIVE or ASP-DOWN
and it was the last remaining active ASP in the AS (and no ASPs in the
ASP-STANDBY state are available.  A recovery timer T(r) SHOULD be
started and all incoming signalling messages SHOULD be queued by the
SGP. If an ASP becomes ASP-ACTIVE before T(r) expires, the AS is moved
to the AS-ACTIVE state and all the queued messages will be
sent to the ASP.

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

Figure 5 shows an example AS state machine for the case where the
AS/ASP data is pre-configured.  For other cases where the AS/ASP
configuration data is created dynamically, there would be differences
in the state machine, especially at creation of the AS.

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

                 Figure 5: AS State Transition Diagram

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

    Tr = Recovery Timer

4.2.2 M3UA Management Procedures for Primitives

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

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

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

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.

In the case of SCTP-COMMUNICATION_DOWN, the SCTP client MAY try to re-
establish the SCTP Association.  This MAY be done by the M3UA layer
automatically, or Layer Management MAY re-establish using the M-
SCTP_ESTABLISH request primitive.

In the case of an SCTP-RESTART indication at an ASP, the ASP is now
considered by its M3UA peer to be in the ASP-DOWN state.  The ASP, if
it is to recover, must begin any recovery with the ASP-Up procedure.

4.2.3 M3UA Management Procedures for Peer-to-Peer Messages

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

4.2.3.1 ASP Up Procedures

After an ASP has successfully established an SCTP association to an
SGP, the SGP waits for the ASP to send an ASP Up message, indicating
that the ASP M3UA peer is available.  The ASP is always the initiator
of the ASP Up message.  This action MAY be initiated at the ASP by an
M-ASP_UP request primitive from Layer Management or MAY be initiated
automatically by an M3UA management function.

When an ASP Up message is received at an SGP and internally the remote
ASP is in the ASP-DOWN state and not considered locked-out for local
management reasons, the SGP marks the remote ASP in the state ASP-
INACTIVE and informs Layer Management with an M-ASP_Up indication
primitive.  If the SGP is aware, via current configuration data, which
Application Servers the ASP is configured to operate in, the SGP
updates the ASP state to ASP-INACTIVE in each AS that it is a member.
Alternatively, the SGP may move the ASP into a pool of Inactive ASPs
available for future configuration within Application Server(s),
determined in a subsequent Registration Request or ASP Active
procedure.  If the ASP Up message contains an ASP Identifier, the SGP
should save the ASP Identifier for that ASP.
The SGP responds with an ASP Up Ack message in
acknowledgement.  The SGP sends an ASP Up Ack message in response to a
received ASP Up message even if the ASP is already marked as ASP-
INACTIVE at the SGP.

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

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

enters the ASP-Inactive state from the ASP_Down state towards an SGP
the M3UA MUST mark all SS7 destinations configured to be reachable via
this SGP as available.

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

The ASP must wait for the ASP Up Ack message before sending any other
M3UA messages (e.g., ASP Active or REG REQ).  If the SGP receives any
other M3UA messages before an ASP Up message is received, the SGP
SHOULD discard them.

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

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

4.2.3.1.1 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 SGP.

4.2.3.1.2 IPSP Considerations

In the case of peer-to-peer IPSPs, either of the IPSPs (IPSP_A) may
start operations by sending an ASP Up message to the remote peer
(IPSP_B).  When the ASP Up message is received at IPSP_B and internally
the remote IPSP_A is in the ASP-DOWN state and not considered locked-
out for local management reasons, IPSP_B marks the remote IPSP_A in the
state ASP-INACTIVE and informs Layer Management with an M-ASP_Up
indication primitive.  IPSP_B returns an ASP-Up Ack message to IPSP_A.
IPSP_A moves IPSP_B to the ASP-INACTIVE state upon reception of an ASP
Up Ack message, if is not already in the ASP_INACTIVE state, and
informs Layer Management with an M-ASP_UP confirmation primitive.

If for any local reason (e.g., management lock-out) the IPSP_B cannot
respond with an ASP Up Ack message, it responds to an ASP Up message
with an Error message with Reason "Refused - Management Blocking" and
leaves IPSP_A in the ASP-DOWN state.

4.2.3.2 ASP-Down Procedures

The ASP will send an ASP Down message to an SGP when the ASP wishes to
be
removed from service in all Application Servers that it is a member and
no longer receive any DATA, SSNM or ASPTM messages.  This action MAY be
initiated at the ASP by an M-ASP_DOWN request primitive from Layer
Management or MAY be initiated automatically by an M3UA management
function.

Whether the ASP is permanently removed from any AS is a function of
configuration management.  In the case where the ASP previously used
the Registration procedures (see Section 3.5.5) to register within
Application Servers but has not deregistered from all of them prior to
sending the ASP Down message, the SGP SHOULD consider the ASP as
Deregistered in all Application Servers that it is still a member.

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

The SGP 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 ASP-DOWN
at the SGP.  The SGP sends an ASP Down Ack message even if the reason
in the received ASP Down message is considered invalid.

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

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

4.2.3.4 ASP-Active Procedures

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

For the Application Servers that the ASP can be successfully activated,
he
the SGP or IPSP responds with one or more ASP Active Ack messages,
including the associated Routing Context and Traffic Mode Type values.
The Routing Context parameter MUST be included in the Asp Active Ack
message if the received ASP Active message contained any Routing
Contexts.  Depending on the ASP Active Message Traffic Mode Type
request, the SGP moves the ASP to the correct ASP traffic state within
the associated Application Server(s). Layer Management is informed with
an M-ASP_Active indication. If the SGP or IPSP receives any Data
messages before an ASP Active message is received, the SGP or IPSP MAY
discard them.  By sending an ASP Active Ack message, the SGP or IPSP is
now ready to receive and send traffic for the related Routing
Context(s).  The ASP SHOULD NOT send Data messages for the related
Routing Context(s) before receiving an ASP Active Ack message, or it
will risk message loss.

Multiple ASP Active Ack messages MAY be used in response to an ASP
Active message containing multiple Routing Contexts, allowing the SGP
or IPSP to independently acknowledge the ASP Active message for
different (sets of) Routing Contexts.  The SGP or IPSP sends an Error
message ("Invalid Routing Context") for each Routing Context value that
the ASP cannot be successfully activated .

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

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

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

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

There are four six modes of Application Server traffic handling in the SGP
M3UA layer - Over-ride, Over-ride (Standby), Load-share, Load-share
(Standby), Broadcast and Load-share
(Standby). Broadcast Standby.  The Traffic Mode Type
parameter in the ASP Active message indicates the traffic handling mode
used in a particular Application Server. If the SGP determines that the
mode indicated in an ASP Active message is unsupported or incompatible
with the mode currently configured for the AS, the SGP responds with an
Error message ("Unsupported / Invalid Traffic Handling Mode").  If the
Traffic Handling mode of the Application Server is not already known via
configuration data, then the Traffic Handling mode indicated in the
first ASP Active message causing the transition of the Application
Server state to AS-ACTIVE MAY be used to set the mode.

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

In the case of Over-ride (Standby) mode the traffic is not started to
the ASP until the currently active ASP transitions to the ASP-INACTIVE
or ASP-DOWN state.  At this point the ASP that sent the ASP Active
message ("Over-Ride (Standby)") is moved to the ASP-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 message ("Alternate ASP-Active") is not sent
in this case.

If there is no currently active ASP, an ASP Active Ack message ("Over-
ride") is returned right away and the traffic is directed to the ASP.

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

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

In the case of a Load-share (Standby) mode AS, the traffic is not
started to the ASP until the SGP 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 either the ASP-INACTIVE or
ASP-DOWN state.  At this point the ASP that sent the ASP Active message
("Load-share (Standby)") is moved to the ASP_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 message ("Insufficient ASP resources active in AS ") is
not sent in this case.

If there is no currently active ASP, an ASP Active Ack message
("Loadshare") is returned right away and the traffic is directed to the
ASP.

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

4.2.3.5 ASP Inactive Procedures

When an ASP wishes to withdraw from receiving traffic within an AS,

In the
ASP sends case of a Broadcast mode AS, reception of an ASP Inactive Active message to the
at an SGP or IPSP.  This action MAY
be initiated at IPSP cuases the direction of traffic to the ASP by an M-ASP_INACTIVE request primitive from
Layer Management or MAY be initiated automatically by an M3UA
management function.   In sending the case where an
ASP is processing Active message, in addition to all the other ASPs that are
currently active in the AS. The algorithm at the SGP for broadcasting
traffic within an AS to all the active ASPs is a simple braoadcast
algorithm, where every message is sent to each of the active ASPs.

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

In the case of Broadcast (Standby) mode AS, the traffic is not started
to the ASP until the SGP or IPSP determines that there are sufficient
resuorces available in the AS. This is likely when one of the active
broadcast ASPs transitions to either the ASP-INACTIVE or ASP-DOWN
state. At this point the ASP that sent the ASP Active message
("Broadcast (Standby)") is moved to the ASP_ACTIVE state and traffic
is started. A second ASP Active Ack message with a new Traffic Mode
Type ("Broadcast" - previously "Broadcast (Standby)") is sent to the
ASP. A Notify message ("Insufficient ASP resources active in AS") is
not sent in this case.

If there is no currently active ASP, an ASP Active Ack message
("Broadcast") is returned right away and the traffic is directed to
the ASP.

4.2.3.5 ASP Inactive Procedures

When an ASP wishes to withdraw from receiving traffic within an AS, the
ASP sends an ASP Inactive message to the SGP 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 ASP Inactive message contains one or more Routing
Contexts to indicate for which Application Servers the ASP Inactive
message 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 ASP-INACTIVE state in each all Application Servers.
In the case of an Over-ride mode AS, where another ASP has already
taken over the traffic within the AS with an ASP Active ("Over-ride")
message, the ASP that sends the ASP Inactive message is already
considered by the SGP to be in state ASP-INACTIVE. .An ASP Inactive Ack
message is sent to the ASP, after ensuring that all traffic is stopped
to the ASP.

In the case of a Load-share Load-share mode AS, the SGP moves the ASP to the ASP-
INACTIVE state and the AS traffic is re-allocated across the remaining
ASPs in the state ASP-ACTIVE, as per the load-sharing algorithm
currently used within the AS.  A Notify message("Insufficient ASP
resources active in AS") MAY be sent to all inactive ASPs, if required.
However, if a Loadshare ("Standby") ASP is available, it may be now
immediately included in the loadshare group and a Notify message is not
sent.  An ASP Inactive Ack message is sent to the ASP after all traffic
is halted and Layer Management is informed with an M-ASP_INACTIVE
indication primitive.

In the case of a Broadcast mode AS, the SGP moves the ASP to the ASP-
INACTIVE
ASP-INACTIVE state and the AS traffic is re-allocated across broadcast only to the
remaining ASPs in the state ASP-ACTIVE, as per the load-sharing algorithm
currently used within the AS. ASP-ACTIVE. A Notify message("Insufficient message
("Insufficient ASP resources active in AS") MAY be sent to all
inactive ASPs, if required. However, if a Loadshare Broadcast ("Standby") ASP
is available, it may be now immediately included in the loadshare broadcast
group and a Notify message is not sent. An ASP Inactive Ack message
is sent to the ASP after all traffic is halted and Layer Management is
informed with an M-ASP_INACTIVE indication primitive.

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

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

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

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

4.2.3.6 Notify Procedures

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

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

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

4.2.3.7 Heartbeat Procedures

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

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

At the ASP, if

If no Heartbeat 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 Heartbeat messages is stopped and the ASP
signalling process SHOULD attempt to re-establish communication with if it is
configured as the SGP client for the disconnectd M3UA peer.

The Heartbeat message may optionally contain an opaque Heartbeat Data
parameter that MUST be echoed back unchanged in the related Heartbeat
Ack message.  The ASP, sender, upon examining the contents of the returned
Heartbeat Ack message, MAY choose to consider the remote M3UA peer as
unavailable.  The contents/format of the Heartbeat Data parameter is
implementation-dependent and only of local interest to the original
sender.  The contents may be used, for example, to support a Heartbeat
sequence algorithm (to detect missing Heartbeats), and/or a timestamp
mechanism (to evaluate delays).

Note: Heartbeat related events are not shown in Figure 4 "ASP state
transition diagram".

4.2.4 Routing Key Management Procedures

4.2.4.1 Registration

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

The SGP 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 SGP Routing Key entry, and the
ASP is not currently included in the list of ASPs for the related
Application Server, the SGP MAY authorize the ASP to be added to the
AS.  Or, if the Routing Key does not currently exist and the received
Routing Key data is valid and unique, an SGP supporting dynamic
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 SGP 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 SGP Routing Key is included. The
method of Routing Context value assignment at the SG/SGP SGP is
implementation dependent but must be guaranteed to be unique across all
SGPs in an SG. for each
Application Server or Routing Key supported by the SGP.

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

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

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

- Permission Denied".

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

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

If an SGP determines that one or more of the Routing Key parameters are
not supported for the purpose of creating new Routing Key entries, the
SGP returns a Registration Response message to the ASP, containing a
Registration Result "Error  - Unsupported RK parameter field".  This
result MAY be used if, for example, the SGP does not support RK Circuit
Range Lists in a Routing Key because the SGP does not support ISUP
traffic, or does not provide CIC range granularity.

A Registration Response "Error  - Unsupported Traffic Handling Mode" is
returned if the Routing Key in the REG REQ contains an Traffic Handling
Mode that is inconsistent with the presently configured mode for the
matching Application Server.

An ASP MAY register multiple Routing Keys at once by including a number
of Routing Key parameters in a single REG REQ message.  The SGP 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 SGP 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 SGP can now send
related SS7 Signalling Network Management messaging, if this did not
previously start upon the ASP transitioning to state ASP-INACTIVE

4.2.4.2 Deregistration

An ASP MAY dynamically deregister with an SGP as an ASP within an
Application Server using the DEREG REQ message.  A Routing Context
parameter in the DEREG REQ message specifies which Routing Keys to de-
register.  An ASP SHOULD move to the ASP-INACTIVE state for an
Application Server before attempting to deregister the Routing Key
(i.e., deregister after receiving an ASP Inactive Ack).  Also, an ASP
SHOULD deregister from all Application Servers that it is a member
before attempting to move to the ASP-Down state.

The SGP 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 SGP. Other
ASPs may continue to be associated with the Application Server, in
which case the Routing Key data MUST NOT be deleted.  If a
Deregistration results in no more ASPs in an Application Server, an SGP
MAY delete the Routing Key data.

The SGP acknowledges the deregistration request by returning a DEREG
RSP message to the requesting ASP.  The result of the deregistration 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 SGP MAY
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.

4.3 Procedures to Support the Availability or Congestion Status of SS7
Destination

4.3.1 At an SGP

On receiving an MTP-PAUSE, MTP-RESUME or MTP-STATUS indication
primitive from the nodal inter-working function at an SGP, the SGP M3UA
layer will send a corresponding SS7 Signalling Network Management
(SSNM) DUNA, DAVA, SCON, or DUPU message (see Section 3.4) 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 SGP M3UA layer determines the set of concerned ASPs to be informed
based on the specific 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 SGP
operates within a single SS7 network appearance, then all ASPs are
informed.

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 SGP M3UA layer MAY also suppress DUPU
messages to ASPs that do not implement an MTP3-User protocol peer for
the affected MTP3-User.

DUNA, DAVA, SCON, and DRST messages MUST be sent sequentially and
processed at the receiver in the order sent.  SCTP stream "0" is used to
provide the sequencing.  . The only exception to this is if the
international congestion method (see Q.704) is used.  If so, the
Unordered bit in the SCTP DATA chunk MAY be used for the SCON message.

Sequencing is not required for the DUPU or DAUD messages, which MAY
be sent un-sequenced.  Again, SCTP stream 0 is used, with optional use
of the Unordered bit in the SCTP DATA chunk.

4.3.2 At an ASP

4.3.2.1 Single SGP Configurations

At an ASP, upon receiving an SS7 Signalling Network Management (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 layer at the ASP MUST SHOULD
pass up appropriate indications in the primitives to the M3UA User, as
though equivalent SSNM messages were received.  For example, the loss
of an SCTP association to an SGP may cause the unavailability of a set
of SS7 destinations.  MTP-PAUSE indication primitives to the M3UA User
are appropriate.

Implementation Note: To accomplish this, the M3UA layer at an ASP
maintains the status of routes via the SG(P), much like an MTP3 layer
maintains route-set status.

4.3.2.2 Multiple SGP Configurations

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

An M3UA layer at the ASP MAY choose to maintain knowledge of which SGPs
are included in Signalling Gateways for the purpose of interpreting
SSNM messaging from one SGP so as to apply to all the SGPs in the SG.

4.3.3 ASP Auditing

An ASP may optionally initiate an audit procedure in order to enquire
of an SGP the availability and, if the national 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 SGP requesting the
current availability and congestion status of one or more SS7
Destination Point Codes.

The DAUD message 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 a DUNA, SCON
                or DRST message has expired without a subsequent DAVA,
                DUNA, SCON or DRST message 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
                SGP that originally sent the SSNM message.

   - Isolation. The ASP is newly ASP-INACTIVE or ASP-ACTIVE or has been
                isolated from an SGP for an extended period.  The ASP
                MAY request the availability/congestion status of one
                or more SS7 destinations to which it expects to
                communicate.

In the first of the cases above, the auditing  procedure must not be
invoked for the case of a received SCON message 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 layer at the SGP does not
maintain the congestion status of any destinations and therefore the
SGP cannot provide any congestion information in response to the DAUD.
For the same reason, in the second of the cases above a DAUD message
cannot reveal any congested destination(s).

The SGP MUST respond to a DAUD message with the MTP3
availability/congested status of the routeset associated with each
Destination Point Code(s) in the DAUD message.  The status of each SS7
destination requested is indicated in a DUNA message (if unavailable),
a DAVA message (if available), or a DRST (if restricted and the SGP
supports this feature).  If the SS7 destination is available and
congested, the SGP responds with an SCON message in addition to the
DAVA message.  If the SS7 destination is restricted and congested, the
SGP responds with an SCON message in addition to the DRST.  If the SGP
has no information on the availability/congestion status of the SS7
destination, the SGP responds with a DUNA message, as it has no routing
information to allow it to route traffic to this destination

Any DUNA or DAVA message in response to a DAUD message MAY contain a
list of up to sixteen Affected Point Codes.

4.4 MTP3 Restart

In the case where the MTP3 in the SG undergoes an MTP restart, event
communication SHOULD be handled as follows:

When the SG discovers SS7 network isolation, the SGPs send an
indication to all concerned available ASPs (i.e., ASPs in the ASP-ACTIVE, ASP-
STANDBY
ACTIVE, ASP-STANDBY or ASP-INACTIVE state) using a DUNA message.  For
the purpose of MTP restart, all Signalling Point Management Clusters
with point codes

different from that of the SG with at least one ASP in the ASP-ACTIVE
state or that has sent an ASP ACTIVE message to the SG during the first
part of the restart procedure should be considered as available.  If the
M3UA layer at the SGP receives any ASP ACTIVE messages during the
restart procedure, it delays the ASP ACTIVE ACK messages until the end
of the restart procedure.  During the second part of the restart
procedure the SGP M3UA layers at the SGPs inform all concerned ASPs in
the ASP-ACTIVE, ASP-STANDBY or ASP-INACTIVE states of any unavailable
unavailable/restricted SS7 destinations using the DUNA DUNA/DRST message.  At
the end of the restart procedure the SGP M3UA layers send an ASP ACTIVE
ACK message to all ASPs in the ASP-ACTIVE state.

When the M3UA layer at an ASP receives a DUNA message indicating SS7
network isolation at an SG, it will stop any affected traffic via this
route. When the M3UA subsequently receives any DUNA messages from an SGP
it will mark the affected SS7 destinations as unavailable via that SG.
When the M3UA receives an ASP ACTIVE ACK message it can resume traffic
to available SS7 destinations via this SGP, provided the ASP is in the
ASP-ACTIVE state towards this SGP.  The ASP MAY choose to audit the
availability of any unavailable destinations

5. Examples of M3UA Procedures

5.1 Establishment of Association and Traffic between SGPs and ASPs

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

5.1.1.1 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 SGP and an ASP, where only one ASP
is configured within an AS (no backup).  It is assumed that the SCTP
association is already set-up. The sending of any DUNA/SCON messages by
the SGP is not shown but is similar to the case described in Section
5.1.2.

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

Note: If the ASP Active message contains an optional Routing Context
parameter, The ASP Active message only applies for the specified RC
value(s). For an unknown RC value, the SGP responds with an Error
message.

5.1.1.2 Single ASP in Application Server ("1+0" sparing), Dynamic
Registration

This scenario is the same as for 5.1.1.1 but with the optional exchange
of registration information.  In this case the Registration is accepted
by the SGP.

             SGP                              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 message will contain an
unsuccessful indication and the ASP will not subsequently send an ASP
Active message.

5.1.1.3 Single ASP in Multiple Application Servers (each with "1+0"
sparing), Dynamic Registration (Case 1  - Multiple Registration
Requests)

             SGP                              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)------>|
              |                                |

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

It is not necessary to follow a Registration Request/Response message
pair with an ASP Active message before sending the next Registration
Request. The ASP Active message can be sent at any time after the
related successful registration.

5.1.1.4 Single ASP in Multiple Application Servers (each with "1+0"
sparing), Dynamic Registration (Case 2  - Single Registration Request)

             SGP                              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 message will contain an
unsuccessful indication and the ASP will not subsequently send an ASP
Active message. Each LRC/RK pair registration is considered
independently.

The ASP Active message can be sent at any time after the related
successful registration, and may have more than one RC.

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 SGP and two ASPs in the same
Application Server, where ASP1 is configured to be in the ASP-ACTIVE
state and ASP2 is to be a "back-up" in the event of communication
failure or the withdrawal from service of ASP1.  ASP2 may act as a hot,
warm, or cold back-up 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 indicate "Over-ride" or "Over-ride", "Load-share" or
"Broadcast" mode, although typically this example would use an Over-ride
mode. The
SGP MAY start sending any relevant DUNA, DRST and SCON messages to ASPs
as soon as they enter the ASP-INACTIVE state. In the case of MTP
Restart, the ASP-Active Ack message is only sent after all relevant
DUNA/DRST/SCON messages have been transmitted to the concerned ASP.

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

Note: It is also possible for ASP2 to send an ASP-Active ("Over-ride-
Standby") message after ASP1 goes ASP-ACTIVE  A similar sparing
arrangement is created, except that the SGP may re-direct traffic to
ASP2 more quickly in certain fail-over cases.

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

This scenario shows a similar case to Section 5.1.2 but where the two
ASPs are brought to the state ASP-ACTIVE and subsequently load-share
the traffic.  In this case, one ASP is sufficient to handle the total
traffic load. The sending of DUNA, DRST and SCON messages by the SGP is
not shown but is similar to the case described in Section 5.1.2.

       SGP                       ASP1                       ASP2
        |                         |                          |
        |<---------ASP Up---------|                          |
        |--------ASP Up Ack------>|                          |
        |                         |                          |
        |<------------------------------ASP Up---------------|
        |-----------------------------ASP Up Ack------------>|
        |                         |                          |
        |                         |                          |
        |<--ASP Active (Ldshr)----|                          |
        |-----ASP-Active Ack----->|                          |
        |                         |                          |
        |----------------------------NOTIFY (AS-ACTIVE------>|
        |                         |                          |
        |<----------------------------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 SGP and three ASPs in the same
Application Server, where two of the ASPs are brought to the state ASP-
ACTIVE and subsequently 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, DRST and SCON messages by the SGP is not shown but is
similar to the case described in Section 5.1.2.

   SGP                  ASP1                 ASP2                 ASP3
    |                    |                   |                   |
    |<------ASP Up-------|                   |                   |
    |-----ASP Up Ack---->|                   |                   |
    |                    |                   |                   |
    |<--------------------------ASP Up-------|                   |
    |-------------------------ASP Up Ack---->|                   |
    |                    |                   |                   |
    |<---------------------------------------------ASP Up--------|
    |---------------------------------------------ASP Up Ack---->|
    |                    |                   |                   |
    |                    |                   |                   |
    |<--ASP Act (Ldshr)--|                   |                   |
    |----ASP Act Ack---->|                   |                   |
    |                    |                   |                   |
    -----------Notify (AS-ACTIVE)----------->|                   |
    |-----------------------Notify (AS-ACTIVE)------------------>|
    |                    |                   |                   |
    |<--------------------ASP Act. (Ldshr)---|                   |
    |-----------------------ASP Act Ack----->|                   |
    |                    |                   |                   |

Note: It is also possible for ASP3 to send an ASP Active message
("Loadshare-Standby") after ASP1 and ASP2 go to the ASP-ACTIVE state  A
similar sparing arrangement is created, except that the SGP may
redirect traffic to ASP3 more quickly in certain fail-over cases.

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:

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

Note: If the SGP M3UA layer detects the loss of the M3UA peer (M3UA
heartbeat loss or detection of SCTP failure), the initial ASP Inactive
message exchange (i.e., SGP to ASP1) 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:

       SGP                       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:

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

For the Notify message to be sent, the SG maintains knowledge of the
minimum ASP resources required (e.g., if the SG knows that "n+k" =
"2+1" for a load-share AS and "n" currently equals "1").

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

5.3 Normal Withdrawal of an ASP from an Application Server and Tear-
down of an Association

An ASP which is now confirmed in the state ASP-INACTIVE (i.e., the ASP
has received an ASP Inactive Ack message) may now proceed to the ASP-
DOWN state, if it is to be removed from service.  Following on from
Section 5.2.1 or 5.2.3, where ASP1 has moved to the "Inactive" state:

       SGP                              ASP1
        |                               |
        |<-----ASP Inactive (RCn)-------|    RC: Routing Context
        |----ASP Inactive Ack (RCn)---->|
        |                               |
        |<-----DEREGISTER REQ(RCn)------|    See Notes
        |                               |
        |---DEREGISTER RESP(LRCn,RCn)-->|
        |                               |
        :                               :
        |                               |
        |<-----------ASP Down-----------|
        |---------ASP Down Ack--------->|
        |                               |

Note: The Deregistration procedure MUST be used if the ASP previously
used the Registration procedures for configuration within the
Application Server.  ASP Inactive and Deregister messages exchanges may
contain multiple Routing Contexts.

The ASP SHOULD be in the ASP-INACTIVE state and de-registered SHOULD have deregistered
in all its Routing Contexts before attempting to move to the ASP-DOWN
state.

5.4  M3UA/MTP3-User Boundary Examples

5.4.1 At an ASP

This section describes the primitive mapping between the MTP3 User and
the M3UA layer at an ASP.

5.4.1.1 Support for MTP-TRANSFER Primitives at the ASP

5.4.1.1.1 Support for MTP-TRANSFER Request Primitive

When the MTP3-User on the ASP has data to send into the SS7 network, it
uses the MTP-TRANSFER request primitive.  The M3UA layer at the ASP
will do the following when it receives an MTP-TRANSFER request
primitive from the M3UA user:

  - Determine the correct SGP;

  - Determine the correct association to the chosen SGP;

  - 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 a DATA message;

  - Send the DATA message to the remote M3UA peer at the SGP, over the
    SCTP association.

        SGP                       ASP
        |                         |
        |<-----DATA Message-------|<--MTP-TRANSFER req.
        |                         |

5.4.1.1.2 Support for the MTPTRANSFER MTP-TRANSFER Indication Primitive

When the M3UA layer on the ASP receives a DATA message from the remote
M3UA peer at the SGP, it will do the following:

  - Evaluate the optional fields of the DATA message, if present;
  - Map the Protocol Data field 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.

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

5.4.1.1.3 Support for ASP Querying of SS7 Destination States

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

       SGP                        ASP
        |                         |
        |<----------DAUD----------|
        |<----------DAUD----------|
        |<----------DAUD----------|
        |                         |
        |                         |

5.4.2 At an SGP

This section describes the primitive mapping between the MTP3-User and
the M3UA layer at an SGP.

5.4.2.1 Support for MTP-TRANSFER Request Primitive at the SGP

When the M3UA layer at the SGP 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 field of the DATA message into an MTP-
    TRANSFER request primitive;

  - Pass the MTP-TRANSFER request primitive to the MTP3 of the
    concerned Network Appearance.

                            SGP                        ASP
                             |                         |
        <---MTP-TRANSFER req.|<---------DATA ----------|
                             |                         |

5.4.2.2 Support for MTP-TRANSFER Indication Primitive at the SGP

When the MTP3 layer at the SGP has data to pass its user parts, it will
use the MTP-TRANSFER indication primitive.  The M3UA layer at the SGP
will do the following when it receives an MTP-TRANSFER indication
primitive:

  - Determine the correct ASP; ASP using the distribution function;

  - Select an ASP in the ASP-ACTIVE state

  - Determine the correct association to the chosen ASP;

  - Determine the correct stream in the SCTP 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 a DATA message;

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

                           SGP                        ASP
                            |                         |
       --MTP-TRANSFER ind.->|----------DATA --------->|
                            |                         |

5.4.2.3 Support for MTP-PAUSE, MTP-RESUME, MTP-STATUS Indication
Primitives

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

5.4.2.3.1 Destination Unavailable

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

                   SGP                       ASP
                    |                         |
 --MTP-PAUSE ind.-->|---------DUNA----------->|--MTP-PAUSE ind.-->
                    |                         |

5.4.2.3.2 Destination Available

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

                   SGP                       ASP
                    |                         |
--MTP-RESUME ind.-->|-----------DAVA--------->|--MTP-RESUME ind.-->
                    |                         |

5.4.2.3.3 SS7 Network Congestion

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

                     SGP                       ASP
                       |                         |
   --MTP-STATUS ind.-->|-----------SCON--------->|--MTP-STATUS ind.-->
                       |                         |

5.4.2.3.4 Destination User Part Unavailable

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

                      SGP                       ASP
                       |                         |
   --MTP-STATUS ind.-->|----------DUPU---------->|--MTP-STATUS ind.-->
                       |                         |

6. 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 fulfil 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 is recommended to be transported on SCTP.  SCTP [13] 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 [23] SHOULD
be used instead.  Regardless of which level performs the encryption,
the IPSEC ISAKMP [24] service SHOULD be used for key management.

7. IANA Considerations

7.1 SCTP Payload Protocol Identifier

IANA has assigned an M3UA value for the Payload Protocol Identifier in
the SCTP DATA chunk.  The following SCTP Payload Protocol Identifier is
registered:

        M3UA    "3"

The SCTP Payload Protocol Identifier value "3" SHOULD be included in
each SCTP DATA chunk, to indicate that the SCTP is carrying the M3UA
protocol. The value "0" (unspecified) is also allowed but any other
values MUST not be used.  This Payload Protocol Identifier is not
directly used by SCTP but MAY be used by certain network entities to
identify the type of information being carried in a DATA chunk.

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

7.2 M3UA Port Number

IANA has registered SCTP (and UDP/TCP) Port Number 2905 for M3UA.

7.3 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
Guidelines for Writing an IANA Considerations Section in RFCs (25]

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

7.3.1 IETF Defined Message Classes

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

7.3.2 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;
(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 ("Unsupported
Message Type").

7.3.3 IETF Defined 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 3.2;
(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. Acknowledgements

The authors would like to thank Antonio Roque Alvarez, Joyce Archibald,
Tolga Asveren, Brian Bidulock, Maria-Cruz Bartolome-Rodrigo, Dan Brendes, Nikhil Jain,
Joe Keller, Kurt Kite, Ming Lin, Steve Lorusso, John Loughney, Naoto
Makinae, Howard May, Barry Nagelberg, Neil Olson, Heinz Prantner,
Shyamal Prasad, Mukesh Punhani, Selvam Rengasami, Ray Singh, Michael
Tuexen, Nitin Tomar, Gery Verwimp, Kazuo Watanabe, Ben Wilson and many
others for their valuable comments and suggestions.

9.  References

[1] RFC 2719, "Framework Architecture for Signaling Transport", L. Ong
et al, October 1999

[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 to Q.715, "Signalling System No. 7
    (SS7) - Signalling Connection Control Part (SCCP)"

[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 Recommendation Q.720, "Telephone User Part"

[9] ITU-T Recommendations Q.771 to Q.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 V4.0.0 (2001-04) "Technical Specification - 3rd
     Generation partnership Project; Technical Specification Group
     Radio Access Network; UTRAN Iu Interface: General Aspects and
     Principles"

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

[14] ITU-T Recommendations Q.701 to 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] RFC 2119, "Key words for use in RFCs to Indicate Requirement
     Levels", S. Bradner, March 1997.

[20] ITU-T Recommendation Q.2210 "Message Transfer Part Level 3
     functions and messages using the services of ITU Recommendation
     Q.2140"

[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.

[23] RFC 2406, "IP Encapsulating Security Payload (ESP)", S.Kent and
     R. Atkinson, November 1998.

[24] RFC 2408, "Internet Security Association and Key Management
     Protocol", D. Maughan, M. Schertler, M. Schneider and J. Turner,
     November 1998.

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

10. Bibliography

[26] <draft-ietf-sigtran-m2ua-07.txt>, <draft-ietf-sigtran-m2ua-09.txt>, "MTP2-User Adaptation Layer",
     K. Morneault et al, February July 2001 (Work in Progress)

[27]<draft-ietf-sigtran-m2pa-02.txt>, "SS7 MTP2-User Peer-to-Peer
     Adaptation Layer", Tom George et al (Work in Progress)

11. Author's Addresses

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

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

Lyndon Ong
Ciena
10480 Ridgeview Court
Cupertino, CA 95014
lyong@ciena.com

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

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

Klaus D. Gradischnig
NeuStar, Inc
1120 Vermont Ave. N.W.Suite 400
Washington D.C 20005
klaus.gradischnig@neustar.com

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

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

Brian Bidulock
OpenSS7 Corporation
c/o #424, 4701 Preston Park Blvd.
Plano, TX, USA  75093
EMail: bidulock@openss7.org

This draft expires December 2001.