| draft-ietf-sigtran-m3ua-06 Description: Request For Comments
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Network Working Group Greg Sidebottom (Editor)
INTERNET-DRAFT Guy Mousseau
Nortel Networks
Lyndon Ong
Point Reyes Networks
Ian Rytina
Ericsson
Hanns-Juergen Schwarzbauer
Klaus Gradischnig
Siemens
Ken Morneault
Cisco
Mallesh Kalla
Telcordia
Normand Glaude
Performance Technologies
Expires in six months Feb 2001
SS7 MTP3-User Adaptation Layer (M3UA)
<draft-ietf-sigtran-m3ua-06.txt>
Status of This Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026. Internet-Drafts are working
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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
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protocol would be used between a Signalling Gateway (SG) and a Media
Gateway Controller (MGC) or IP-resident Database. It is assumed that
the SG receives SS7 signalling over a standard SS7 interface using the
SS7 Message Transfer Part (MTP) to provide transport.
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TABLE OF CONTENTS
1. Introduction.......................................................4
1.1 Scope.........................................................4
1.2 Terminology...................................................4
1.3 M3UA Overview.................................................6
1.4 Functional Areas.............................................12
1.5 Sample Configurations........................................23
1.6 Definition of M3UA Boundaries................................26
2. Conventions.......................................................29
3. M3UA Protocol Elements............................................29
3.1 Common Message Header........................................29
3.2 Variable-Length Parameter....................................32
3.3 Transfer Messages............................................33
3.4 SS7 Signalling Network management (SSNM) Messages............36
3.5 Application Server Process Maintenance (ASPM) Messages.......44
3.6 Management Messages..........................................60
4. Procedures........................................................63
4.1 Procedures to Support the Services of the M3UA Layer.........63
4.2 Receipt of M3UA Peer Management Messages.....................65
4.3 Procedures to support the M3UA Management services...........66
4.4 Procedures to Support the M3UA Services......................78
5. Examples of M3UA Procedures.......................................81
5.1 Establishment of Association and Traffic
Between SGs and ASPs.........................................81
5.2 ASP traffic Fail-over Examples...............................86
5.3 M3UA/MTP3-User Boundary Examples.............................87
6. Security..........................................................91
6.1 Introduction.................................................91
6.2 Threats......................................................91
6.3 Protecting Confidentiality...................................91
7. IANA Considerations...............................................92
7.1 SCTP Payload Protocol Identifier.............................92
7.2 M3UA Protocol Extensions.....................................92
8. Acknowledgements..................................................93
9. References........................................................93
10. Author's Addresses...............................................95
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1. Introduction
1.1 Scope
There is a need for Switched Circuit Network (SCN) signalling protocol
delivery from an SS7 Signalling Gateway (SG) to a Media Gateway
Controller (MGC) or IP-resident Database as described in the Framework
Architecture for Signalling Transport [1]. The delivery mechanism
SHOULD meet the following criteria:
* Support for the transfer of all SS7 MTP3-User Part messages (e.g.,
ISUP, SCCP, TUP, etc.)
* Support for the seamless operation of MTP3-User protocol peers
* Support for the management of SCTP transport associations and
traffic between an SG and one or more MGCs or IP-resident Databases
* Support for MGC or IP-resident Database process fail-over and load-
sharing
* Support for the asynchronous reporting of status changes to
management
In simplistic transport terms, the SG will terminate SS7 MTP2 and MTP3
protocol layers and deliver ISUP, SCCP and/or any other MTP3-User
protocol messages, as well as certain MTP network management events,
over SCTP transport associations to MTP3-User peers in MGCs or IP-
resident Databases.
1.2 Terminology
Application Server (AS) - A logical entity serving a specific Routing
Key. An example of an Application Server is a virtual switch element
handling all call processing for a unique range of PSTN trunks,
identified by an SS7 DPC/OPC/CIC_range. Another example is a virtual
database element, handling all HLR transactions for a particular SS7
DPC/OPC/SCCP_SSN combination. The AS contains a set of one or more
unique Application Server Processes, of which one or more is normally
actively processing traffic.
Application Server Process (ASP) - A process instance of an Application
Server. An Application Server Process serves as an active or standby
process of an Application Server (e.g., part of a distributed virtual
switch or database). Examples of ASPs are processes (or process
instances) of MGCs, IP SCPs or IP HLRs. An ASP contains an SCTP end-
point and may be configured to process signalling traffic within more
than one Application Server.
Association - An association refers to an SCTP association. The
association provides the transport for the delivery of MTP3-User
protocol data units and M3UA adaptation layer peer messages.
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IP Server Process (IPSP) - A process instance of an IP-based
application. An IPSP is essentially the same as an ASP, except that it
uses M3UA in a point-to-point fashion. Conceptually, an IPSP does not
use the services of a Signalling Gateway.
Signalling Gateway Process (SGP) - A process instance of a Signalling
Gateway. It serves as an active, standby or load-sharing process of a
Signalling Gateway.
Signalling Process - A process instance that uses M3UA to communicate
with other signalling process. An ASP, a signalling gateway process
and an IPSP are all signalling processes.
Routing Key: A Routing Key describes a set of SS7 parameters and
parameter values that uniquely define the range of signalling traffic
to be handled by a particular Application Server. Parameters within the
Routing Key cannot extend across more than a single SS7 Destination
Point Code.
Routing Context - A value that uniquely identifies a Routing Key.
Routing Context values are either configured using a configuration
management interface, or by using the routing key management procedures
defined in this document.
Fail-over - The capability to re-route signalling traffic as required
to an alternate Application Server Process, or group of ASPs, within an
Application Server in the event of failure or unavailability of a
currently used Application Server Process. Fail-over also applies upon
the return to service of a previously unavailable Application Server
Process.
Signalling Point Management Cluster (SPMC) - The complete set of
Application Servers represented to the SS7 network under one specific
SS7 Point Code of one specific Network Appearance. SPMCs are used to
sum the availability / congestion / User_Part status of an SS7
destination point code that is distributed in the IP domain, for the
purpose of supporting MTP3 management procedures at an SG. In some
cases, the SG itself may also be a member of the SPMC. In this case,
the SG availability / congestion / User_Part status must also be taken
into account when considering any supporting MTP3 management actions.
MTP - The Message Transfer Part of the SS7 protocol.
MTP3 - MTP Level 3, the signalling network layer of SS7
MTP3-User - Any protocol normally using the services of the SS7 MTP3
(e.g., ISUP, SCCP, TUP, etc.).
Network Appearance - The Network Appearance identifies an SS7 network
context for the purposes of logically separating the signalling traffic
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between the SG and the Application Server Processes over a common SCTP
Association. An example is where an SG is logically partitioned to
appear as an element in four separate national SS7 networks. A Network
Appearance implicitly defines the SS7 Point Code(s), Network Indicator
and MTP3 protocol type/variant/version used within a specific SS7
network partition. A physical SS7 route-set or link-set at an SG can
appear in only one network appearance. The Network Appearance is not
globally significant and requires coordination only between the SG and
the ASP. Therefore, in the case where an ASP is connected to more than
one SG, the same SS7 network context may be identified by different
Network Appearances depending over which SG a message is being
transmitted/received.
Network Byte Order: Most significant byte first, a.k.a Big Endian.
Layer Management - Layer Management is a nodal function that handles
the inputs and outputs between the M3UA layer and a local management
entity.
Host - The computing platform that the ASP process is running on.
Stream - A stream refers to an SCTP stream; a uni-directional logical
channel established from one SCTP endpoint to another associated SCTP
endpoint, within which all user messages are delivered in-sequence
except for those submitted to the un-ordered delivery service.
1.3 M3UA Overview
1.3.1 Protocol Architecture.
The framework architecture that has been defined for SCN signalling
transport over IP [1] uses multiple components, including a common
signalling transport protocol and an adaptation module to support the
services expected by a particular SCN signalling protocol from its
underlying protocol layer.
Within the framework architecture, this document defines an MTP3-User
adaptation module suitable for supporting the transfer of messages of
any protocol layer that is identified to the MTP Level 3 layer, in SS7
terms, as a user part. The list of these protocol layers include, but
is not limited to, ISDN User Part (ISUP) [2,3,4], Signalling Connection
Control Part (SCCP) [5,6,7] and Telephone User Part (TUP) [8]. TCAP
[9,10,11] or RANAP [12] messages are transferred transparently by the
M3UA as SCCP payload, as they are SCCP-User protocols.
It is recommended that the M3UA use the services of the Stream Control
Transmission Protocol (SCTP) [13] as the underlying reliable common
signalling transport protocol. This is to take advantage of various
SCTP features such as:
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- Explicit packet-oriented delivery (not stream-oriented);
- Sequenced delivery of user messages within multiple streams,
with an option for order-of-arrival delivery of individual
user messages,
- Optional multiplexing of user messages into SCTP datagrams;
- Network-level fault tolerance through support of multi-homing
at either or both ends of an association;
- Resistance to flooding and masquerade attacks; and
- Data segmentation to conform to discovered path MTU size.
Under certain scenarios, such as back-to-back connections without
redundancy requirements, the SCTP functions above MAY NOT be a
requirement and TCP can be used as the underlying common transport
protocol.
1.3.2 Services Provided by the M3UA Layer
The M3UA Layer at an ASP or IPSP provides the equivalent set of
primitives at its upper layer to the MTP3-Users as provided by the MTP
Level 3 to its local MTP3-Users at an SS7 SEP. In this way, the ISUP
and/or SCCP layer at an ASP or IPSP is unaware that the expected MTP3
services are offered remotely from an MTP3 Layer at an SG, and not by a
local MTP3 layer. The MTP3 layer at an SG may also be unaware that its
local users are actually remote user parts over M3UA. In effect, the
M3UA extends access to the MTP3 layer services to a remote IP-based
application. The M3UA does not itself provide the MTP3 services.
However, in the case where an ASP is connected to more than one SG, the
M3UA Layer at an ASP must maintain the status of configured SS7
destinations and route messages according to the availability /
congestion status of the routes to these destinations via each SG.
The M3UA Layer may also be used for point-to-point signalling between
two IP Server Processes (IPSPs). In this case, the M3UA provides the
same set of primitives and services at its upper layer as the MTP3.
However, in this case the expected MTP3 services are not offered
remotely from an SG. The MTP3 services are provided but the procedures
to support these services are a subset of the MTP3 procedures due to
the simplified point-to-point nature of the IPSP to IPSP relationship.
1.3.2.1 Support for the transport of MTP3-User Messages
The M3UA provides the transport of MTP-TRANSFER primitives across an
established SCTP association between an SG and an ASP or between IPSPs.
The MTP-TRANSFER primitive information is encoded as in MTP3-User
messages. In this way, the SCCP and ISUP messages received from the
SS7 network by the SG are not re-encoded into a different format for
transport between the M3UA peers. The MTP3 Service Information Octet
(SIO) and Routing Label (OPC, DPC, and SLS) are included, encoded as
expected by the MTP3 and MTP3-User protocol layer.
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At an ASP, in the case where a destination is reachable via multiple
SGs, the M3UA must also choose via which SG the message is to be routed
or support load balancing across the SGs, ensuring that no mis-
sequencing occurs.
The M3UA does not impose a 272-octet signaling information field (SIF)
length limit as specified by the SS7 MTP Level 2 protocol [14] [15]
[16]. Larger information blocks can be accommodated directly by
M3UA/SCTP, without the need for an upper layer segmentation/re-assembly
procedure as specified in recent SCCP or ISUP versions. However, in
the context of an SG, the maximum 272-octet block size must be followed
when inter-working to a SS7 network that does not support the transfer
of larger information blocks to the final destination. This avoids
potential ISUP or SCCP fragmentation requirements at the SG. However,
if the SS7 network is provisioned to support the Broadband MTP [20] to
the final SS7 destination, the information block size limit may be
increased past 272 octets.
1.3.2.2 Native Management Functions
The M3UA provides management of the underlying SCTP transport protocol
to ensure that SG-ASP and IPSP-IPSP transport is available to the
degree called for by the MTP3-User signalling applications.
The M3UA provides the capability to indicate errors associated with
received M3UA messages and to notify, as appropriate, local management
and/or the peer M3UA.
1.3.2.3 Inter-working with MTP3 Network Management Functions
At the SG, the M3UA must also provide inter-working with MTP3
management functions to support seamless operation of the user SCN
signalling applications in the SS7 and IP domains. This includes:
- Providing an indication to MTP3-Users at an ASP that a remote
destination in the SS7 network is not reachable.
- Providing an indication to MTP3-Users at an ASP that a remote
destination in the SS7 network is now reachable.
- Providing an indication to MTP3-Users at an ASP that messages to a
remote MTP3-User peer in the SS7 network are experiencing SS7
congestion.
- Providing an indication to MTP3-Users at an ASP that the routes to
a remote MTP3-User peer in the SS7 network are restricted.
- Providing an indication to MTP3-Users at an ASP that a remote MTP3-
User peer is unavailable.
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The M3UA layer at an ASP may initiate an audit of the availability, the
restricted or the congested state of remote SS7 destinations. This
information is requested from the M3UA at the SG.
The M3UA layer at an ASP may also indicate to the SG that the M3UA
itself or the ASP or the ASP's Host is congested.
1.3.2.4 Support for the management of SCTP associations between the SG
and ASPs.
The M3UA layer at the SG maintains the availability state of all
configured remote ASPs, in order to manage the SCTP Associations and
the traffic between the M3UA peers. As well, the active/inactive and
congestion state of remote ASPs is maintained.
The M3UA layer MAY be instructed by local management to establish an
SCTP association to a peer M3UA node. This can be achieved using the
M-SCTP ESTABLISH primitive to request, indicate and confirm the
establishment of an SCTP association with a peer M3UA node. In order
to avoid redundant SCTP associations between two M3UA peers, one side
(client) must be designated to establish the SCTP association, or M3UA
configuration knowledge maintained to detect redundant associations
(e.g., via knowledge of the expected local and remote SCTP endpoint
addresses).
The M3UA layer MAY also need to inform local management of the status
of the underlying SCTP associations using the M-SCTP STATUS request and
indication primitive. For example, the M3UA MAY inform local management
of the reason for the release of an SCTP association, determined either
locally within the M3UA layer or by a primitive from the SCTP.
Also the M3UA layer may need to inform the local management of the
change in status of an ASP or AS. This may be achieved using the M-ASP
STATUS request or M-AS STATUS request primitives.
1.3.2.5 Support for the management of connections to multiple SGs
As shown in Figure 1 an ASP may be connected to multiple SGs. In such a
case a particular SS7 destination may be reachable via more than SG,
i.e., via more than one route. As MTP3 users only maintain status on a
destination and not on a route basis, M3UA must maintain the status
(availability, restriction, and/or congestion of route to destination)
of the individual routes, derive the overall availability or congestion
status of the destination from the status of the individual routes, and
inform the MTP3 users of this derived status whenever it changes.
1.3.3 Signalling Network Architecture
A Signalling Gateway is used to support the transport of MTP3-User
signalling traffic received from the SS7 network to multiple
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distributed ASPs (e.g., MGCs and IP Databases). Clearly, the M3UA
protocol is not designed to meet the performance and reliability
requirements for such transport by itself. However, the conjunction of
distributed architecture and redundant networks does allow for a
sufficiently reliable transport of signalling traffic over IP. The
M3UA protocol is flexible enough to allow its operation and management
in a variety of physical configurations, enabling Network Operators to
meet their performance and reliability requirements.
To meet the stringent SS7 signalling reliability and performance
requirements for carrier grade networks, Network Operators SHOULD
ensure that no single point of failure is present in the end-to-end
network architecture between an SS7 node and an IP-based application.
This can typically be achieved through the use of redundant SGs,
redundant hosts, and the provision of redundant QOS-bounded IP network
paths for SCTP Associations between SCTP End Points. Obviously, the
reliability of the SG, the MGC and other IP-based functional elements
also needs to be taken into account. The distribution of ASPs within
the available Hosts must also be considered. As an example, for a
particular Application Server, the related ASPs should be distributed
over at least two Hosts.
One example of a physical network architecture relevant to SS7 carrier-
grade operation in the IP network domain is shown in Figure 1 below:
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SG MGC
Host#1 ************** ************** Host#1
= * ********__*__________________________*__******** * =
SG1 * * SGP1 *__*_____ _______________*__* ASP1 * * MGC1
* ******** * \ / * ******** *
* ********__*______\__/________________*__******** *
* * SGP2 *__*_______\/______ _____*__* ASP2 * *
* ******** * /\ | | * ******** *
* : * / \ | | * : *
* ******** * / \ | | * ******** *
* * SGPn * * | | | | * * ASPn * *
* ******** * | | | | * ******** *
************** | | | | **************
| | \ /
Host#2 ************** | | \ / ************** Host#2
= * ********__*_____| |______\/_______*__******** * =
SG2 * * SGP1 *__*_________________/\_______*__* ASP1 * * MGC2
* ******** * / \ * ******** *
* ********__*_______________/ \_____*__******** *
* * SGP2 *__*__________________________*__* ASP2 * *
* ******** * * ******** *
* : * SCTP Associations * : *
* ******** * * ******** *
* * SGPn * * * * ASPn * *
* ******** * * ******** *
************** **************
Figure 1 - Physical Model
In this model, each host has many application processes. In the case
of the MGC, an ASP may provide service to one or more application
server, and is identified as an SCTP end point. In the case of the SG,
a pair of signalling gateway processes may represent, as an example, a
single network appearance, serving a signalling point management
cluster.
This example model can also be applied to IPSP-IPSP signalling. In
this case, each IPSP would have its services distributed across 2 hosts
or more, and may have multiple server processes on each host.
In the example above, each signalling process (SGP, ASP or IPSP) is the
end point to more than one SCTP association, leading to many other
signalling processes. To support this, a signalling process must be
able to support distribution of M3UA messages to many simultaneous
active associations. This message distribution function is based on
the status of provisioned routing keys, the availability of signalling
points in the SS7 network, and the redundancy model (active-standby,
load-sharing, n+k) of the remote signalling processes.
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For carrier grade networks, the failure or isolation of a particular
signalling process SHOULD NOT cause stable calls or transactions to be
lost. This implies that signalling processes need, in some cases, to
share the call/transaction state or be able to pass the call state
information between each other. In the case of ASPs performing call
processing, coordination may also be required with the related Media
Gateway to transfer the MGC control for a particular trunk termination.
However, this sharing or communication of call/transaction state
information is outside the scope of this document.
This model serves as an example. M3UA imposes no restrictions as to
the exact layout of the network elements, the message distribution
algorithms and the distribution of the signalling processes. Instead,
it provides a framework and a set of messages that allow for a flexible
and scalable signalling network architecture, aiming to provide
reliability and performance.
1.4 Functional Areas
1.4.1 Signalling Point Code Representation
Within an SS7 network, a Signalling Gateway is charged with
representing a set of nodes in the IP domain into the SS7 network for
routing purposes. The SG itself, as a physical node in the SS7
network, must be addressable with an SS7 Point Code for MTP3 Management
purposes. The SG Point Code is also used for addressing any local MTP3-
Users at the SG such as an SG-resident SCCP function.
An SG may be logically partitioned to operate in multiple SS7 network
Appearances. In such a case, the SG must be addressable with a Point
Code in each network appearance, and represents a set of nodes in the
IP domain into each SS7 network. Alias Point Codes [15] may also be
used within an SG network appearance.
The M3UA places no restrictions on the SS7 Point Code representation of
an AS. Application Servers can be represented under the same Point
Code of the SG, their own individual Point Codes or grouped with other
Application Servers for Point Code preservation purposes. A single
Point Code may be used to represent the SG and all the Application
Servers together, if desired.
Where Application Servers are grouped under a Point Code address, an
SPMC will include more than one AS. If full advantage of SS7 management
procedures is to be taken (as is advisable in carrier grade networks)
care must be taken that, if one AS of an SPMC becomes unavailable, all
Application Servers of the SPMC become unavailable from the SG.
Otherwise, usage of SS7 transfer prohibited procedures by the SG
becomes problematic as either traffic to the unavailable AS cannot be
stopped/diverted or traffic to a still available AS will be
unnecessarily stopped/diverted. (Depending on the network configuration
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it may even be necessary to assign an individual SS7 point code to each
AS.)
Observing this principle is of particular importance if alternative
routing possibilities exist on the SS7 level (e.g. via mated SGs) or
application level (e.g. via another MGC/MG).
If an ASP or group of ASPs is available to the SS7 network via more
than one SG, each with its own Point Code, the ASP(s) should be
represented by a Point Code that is separate from any SG Point Code.
This allows these SGs to be viewed from the SS7 network as "STPs", each
having an ongoing "route" to the same ASP(s). Under failure
conditions where the ASP(s) become(s) unavailable from one of the SGs,
this approach enables MTP3 route management messaging between the SG
and SS7 network, allowing simple SS7 re-routing through an alternate SG
without changing the Destination Point Code Address of SS7 traffic to
the ASP(s).
Where an AS can be reached via more than one SG it is equally important
that the corresponding Routing Keys in the involved SGs are identical.
(Note: It is possible for the Routing Key configuration data to be
temporarily out-of-synch during configuration updates).
+--------+
| |
+------------+ SG 1 +--------------+
+-------+ | SS7 links | "STP" | IP network | ----
| SEP +---+ +--------+ +---/ \
| or | | ASPs |
| STP +---+ +--------+ +---\ /
+-------+ | | | | ----
+------------+ SG 2 +--------------+
| "STP" |
+--------+
Note: there is no SG-to-SG communication shown, so each SG can be
reached only via the direct linkset from the SS7 network.
The following example shows a signalling gateway partitioned into two
network appearances.
SG
+-------+ +---------------+
| SEP +--------------| SS7 Ntwk |M3UA| ----
+-------+ SS7 links | "A" | | / \
|__________| +-----------+ ASPs |
| | | \ /
+-------+ | SS7 Ntwk | | ----
| SEP +--------------+ "B" | |
+-------+ +---------------+
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1.4.2 Routing Contexts and Routing Keys
1.4.2.1 Overview
The distribution of SS7 messages between the SG and the Application
Servers is determined by the Routing Keys and their associated Routing
Contexts. A Routing Key is essentially a set of SS7 parameters used to
filter SS7 messages, whereas the Routing Context parameter is a 4-byte
value (integer) that is associated to that Routing Key in a 1:1
relationship. The Routing Context therefore can be viewed as an index
into a sending node's Message Distribution Table containing the Routing
Key entries.
Possible SS7 address/routing information that comprise a Routing Key
entry includes, for example, the OPC, DPC, SIO found in the MTP3
routing label, or other MTP3-User specific fields such as the ISUP CIC,
SCCP subsystem number, or TCAP transaction ID. Some example Routing
Keys are: the DPC alone, the DPC/OPC combination, the DPC/OPC/CIC
combination, or the DPC/SSN combination. The particular information
used to define an M3UA Routing Key is application and network
dependent, and none of the above examples are mandated.
An Application Server Process may be configured to process signalling
traffic related to more than one Application Server, over a single SCTP
Association. In ASP Active and Inactive management messages, the
signalling traffic to be started or stopped is discriminated by the
Routing Context parameter. At an ASP, the Routing Context parameter
uniquely identifies the range of signalling traffic associated with
each Application Server that the ASP is
configured to receive.
1.4.2.2 Routing Key Limitiations
>From an SS7 network perspective, a Routing Key is limited to within a
single SS7 Destination Point Code. This is important, as the SG must be
able to present this point code to the SS7 network, without
compromising the integrity of the Signaling Point Management Cluster.
Some SS7 networks may require the SG to generate UPU messages in
failure conditions. In this case, the AS and SG may optionally limit a
Routing Key to a single Service Indicator (ISUP, TUP, SCCP, etc.). The
SG generation of a UPU message into the SS7 network is implementation
dependent, therefore no specific procedures are outlined in this
document.
Routing Keys MUST be unique in the sense that a received SS7 signalling
message cannot be matched to more than one Routing Key. It is not
necessary for the parameter range values within a particular Routing
Key to be contiguous. For example, an AS could be configured to
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support call processing for multiple ranges of PSTN trunks that are not
represented by contiguous CIC values.
1.4.2.3 Managing Routing Contexts and Routing Keys
There are two ways to ways to provision a Routing Key at an SG. A
Routing Key may be configured using an implementation dependent
management interface, statically or dynamically in full accordance to
the M3UA specifications. A Routing Key may also be configured using the
M3UA dynamic registration/deregistration procedures defined in this
document. An M3UA element must implement at least one method of
Routing Key provisioning.
When using a management interface to configure Routing Keys, the
message distribution function within the SG is not limited to the set
of parameters defined in this document. Other implementation dependent
distribution algorithms may be used.
1.4.2.4 Message Distribution the SG
In order to direct messages received from the SS7 MTP3 network to the
appropriate IP destination, the SG must perform a message distribution
function using information from the received MTP3-User message.
To support this message distribution, the SG must maintain the
equivalent of a network address translation table, mapping incoming SS7
message information to an Application Server for a particular
application and range of traffic. This is accomplished by comparing
elements of the incoming SS7 message to provisioned Routing Keys in the
SG. These Routing Keys in turn make reference to an Application Server
that is enabled by one or more ASPs. These ASPs provide dynamic status
information on their availability, traffic handling capability and
congestion to the SG using various management messages defined in the
M3UA protocol.
The list of ASPs in an AS is assumed to be dynamic, taking into account
the availability, traffic handling capability and congestion status of
the individual ASPs in the list, as well as configuration changes and
possible fail-over mechanisms.
Normally, one or more ASPs are active in the AS (i.e., currently
processing traffic) but in certain failure and transition cases it is
possible that there may be active ASP available. Both load-sharing and
backup scenarios are supported.
When there is no Routing Key match, or only a partial match, for an
incoming SS7 message, a default treatment MUST be specified. Possible
solutions are to provide a default Application Server at the SG that
directs all unallocated traffic to a (set of) default ASP(s), or to
drop the message and provide a notification to management. The
treatment of unallocated traffic is implementation dependent.
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1.4.2.5 Message Distribution at the ASP
In order to direct messages to the SS7 network, the ASP must also
perform a message distribution function in order to choose the proper
SG or SGP for a given message. This is accomplished by observing the
Destination Point Code (and possibly other elements of the outgoing
message such as the SLS value), together with the SS7 destination
availability/restricted/congestion status via the SG(s) and the
availability of the SG and SGPs themselves.
A remote Signalling Gateway may be composed of one or more SGPs that
are capable of routing SS7 traffic. As is the case with ASPs, a
dynamic list of SGPs in an SG can be maintained, taking into account
the availability status of the individual SGPs, configuration changes
and fail-over mechanisms. There is, however, no M3UA messaging to
manage the status of an SGP. Whenever an SCTP association to an SGP
exists, it is assumed to be available. Also, every SGP of one SG
communicating with one ASP regarding one AS provides identical SS7
connectivity to this ASP.
1.4.3 SS7 and M3UA Interworking
In the case of SS7 and M3UA inter-working, the M3UA adaptation layer is
designed to provide an extension of the MTP3 defined user primitives.
1.4.3.1 Signalling Gateway SS7 Layers
The SG is responsible for terminating MTP Level 3 of the SS7 protocol,
and offering an IP-based extension to its users.
>From an SS7 perspective, it is expected that the Signalling Gateway
(SG) transmits and receives SS7 Message Signalling Units (MSUs) to and
from the PSTN over a standard SS7 network interface, using the SS7
Message Transfer Part (MTP) [14,15,16] to provide reliable transport of
the messages.
As a standard SS7 network interface, the use of MTP Level 2 signalling
links is not the only possibility. ATM-based High Speed Links can also
be used with the services of the Signalling ATM Adaptation Layer (SAAL)
[17,18]. It is possible for IP-based links to be present, using the
services of the MTP2-User Adaptation Layer (M2UA) [19]. These SS7
datalinks may be terminated at a Signalling Transfer Point (STP) or at
a Signalling End Point (SEP). Using the services of MTP3, the SG may
be capable of communicating with remote SS7 SEPs in a quasi-associated
fashion, where STPs may be present in the SS7 path between the SEP and
the SG.
Where ATM-based High Speed Links are used in the SS7 network, it is
possible for the SG to use the services of the MTP-3b [20] for reliable
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transport to and from an SS7 SEP or STP. The maximum SIF length
supported by the MTP-3b is 4095 octets compared to the 272-octet
maximum of the MTP3. However, for MTP3-Users to take advantage of the
larger SDU between MTP3-User peers, network architects should ensure
that MTP3-b is used end-to-end between the SG and the SS7-resident
peer.
1.4.3.2 SS7 and M3UA Inter-Working at the SG
The SG provides a functional inter-working of transport functions
between the SS7 network and the IP network by also supporting the M3UA
adaptation layer. It allows the transfer of MTP3-User signalling
messages to and from an IP-based Application Server Process where the
peer MTP3-User protocol layer exists.
The Signalling Gateway must maintain knowledge of SS7 node and
Signalling Point Management Cluster (SPMC) status in their respective
domains in order to perform a seamless inter-working of the IP-based
signalling and the SS7 domains. For example, SG knowledge of the
availability and/or congestion status of the SPMC and SS7 nodes must be
maintained and disseminated in the respective networks, in order to
ensure that end-to-end operation is transparent to the communicating
SCN protocol peers at the SS7 node and ASP.
When the SG determines that the transport of SS7 messages to an SPMC
(or possibly to parts of an SPMC) is encountering congestion, the SG
should inform the MTP3 route management function (by an implementation-
dependent mechanism). This information is used by the MTP3 to mark the
"route" to the affected destination as congested and to trigger MTP
Transfer Controlled (TFC) messages to any SS7 SEPs generating traffic
to the congested DPC, as per current MTP3 procedures.
When the SG determines that the transport of SS7 messages to all ASPs
in a particular SPMC is interrupted, then it should similarly inform
the MTP3 route management function. This information is used by the
MTP3 to mark the "route" to the affected destination as unavailable,
and in the case of the SG acting as a signalling transfer point (i.e.,
the Point Code of the SG is different from that of the SPMC), to send
MTP Transfer Prohibited (TFP) messages to the relevant adjacent SS7
nodes, according to the local SS7 network procedures.
When the SG determines that the transport of SS7 messages to an ASP in
a particular SPMC can be resumed, the SG should similarly inform the
MTP3 route management function. This information is used by the MTP3
to mark the route to the affected destination as available, and in the
case of a signalling transfer point, to send MTP Transfer Allowed (TFA)
messages to the relevant adjacent SS7 nodes, according to the local SS7
network procedures.
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For SS7 user part management, it is required that the MTP3-User
protocols at ASPs receive indications of SS7 signalling point
availability, SS7 network congestion, and remote User Part
unavailability as would be expected in an SS7 SEP node. To accomplish
this, the MTP-PAUSE, MTP-RESUME and MTP-STATUS indication primitives
received at the MTP3 upper layer interface at the SG need to be
propagated to the remote MTP3-User lower layer interface at the ASP.
(These indication primitives are, of course, also made available to any
existing local MTP3-Users at the SG, if present.)
It is important to clarify that MTP3 management messages such as TFPs
or TFAs received from the SS7 network are not "encapsulated" and sent
blindly to the ASPs. Rather, the existing MTP3 management procedures
are followed within the MTP3 function of the SG to re-calculate the
MTP3 route set status and to initiate any required signalling-route-
set-test procedures into the SS7 network. Only when an SS7 destination
status changes are MTP-PAUSE or MTP-RESUME primitives invoked. These
primitives can also be invoked due to local SS7 link set conditions as
per existing MTP3 procedures.
In the case where the MTP in the SG undergoes an MTP restart, event
communication to the concerned ASPs should be handled as follows:
When the SG discovers SS7 network isolation, the SG sends an indication
to all concerned available ASPs (i.e., ASPs in the "active" or
"inactive" state), using a DUNA message. For the purposes of MTP
Restart, all SPMCs with point codes different from that of the SG with
at least one ASP that is active or that has sent an ASPAC message to
the SG during the first part of the restart procedure should be
considered as available. If the M3UA at the SG receives any ASPAC
messages during the restart procedure, it delays the ASPAC-ACK messages
until the end of the restart procedure. During the second part of the
restart procedure the M3UA at the SG informs all concerned ASPs in the
"active" or "inactive" state of any unavailable SS7 destinations. At
the end of the restart procedure the M3UA sends an ASPAC-ACK message to
all ASPs in the "active" state.
1.4.3.3 Application Server
A cluster of application servers is responsible for providing the
overall support for one or more SS7 upper layers. From an SS7
standpoint, a Signalling Point Management Cluster (SPMC) provides
complete support for the upper layer service for a given point code.
As an example, an SPMC providing MGC capabilities must provide complete
support for ISUP (and any other MTP3 user located at the point code of
the SPMC) for a given point code, according to the local SS7 network
specifications.
This measure is necessary to allow the SG to accurately represent the
signalling point on the local SS7 network.
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In the case where an ASP is connected to more than one SG, the M3UA
must maintain the status of configured SS7 destinations and route
messages according to availability/congestion/restricted status of the
routes to these destinations.
When an ASP enters the "Inactive" state towards an SG the M3UA must
mark all SS7 destinations configured to be reachable via this SG as
available.
When the M3UA at an ASP receives a DUNA message indicating SS7 network
isolation at an SG, it will stop any affected traffic via this SG and
clear any unavailability state of SS7 destinations via this SG. When
the M3UA subsequently receives any DUNA messages from an SG it will
mark the effected SS7 destinations as unavailable via that SG. When
the M3UA receives an ASPAC-ACK message it can resume traffic to
available SS7 destinations via this SG, provided the ASP is in the
active state towards this SG.
1.4.3.3 IPSP Considerations
Since IPSPs use M3UA in a point-to-point fashion, there is no concept
of routing of messages beyond the remote end. Therefore, SS7 and M3UA
inter-working is not necessary for this model.
1.4.4 Redundancy Models
The network address translation and mapping function of the M3UA layer
supports signalling process fail-over functions in order to support a
high availability of call and transaction processing capability.
1.4.4.1 Application Server Redundancy
All MTP3-User messages (e.g., ISUP, SCCP) incoming to an SG from the
SS7 network are assigned to a unique Application Server, based on the
information in the message and the provisioned Routing Keys.
The Application Server is, in practical terms, a list of all ASPs
configured to process a range of MTP3-User traffic defined by one
Routing Key. One or more ASPs in the list are normally active (i.e.,
handling traffic) while any others may be unavailable or inactive, to
be possibly used in the event of failure or unavailability of the
active ASP(s).
The fail-over model supports an "n+k" redundancy model, where "n" ASPs
is the minimum number of redundant ASPs required to handle traffic and
"k" ASPs are available to take over for a failed or unavailable ASP. A
"1+1" active/standby redundancy is a subset of this model. A simplex
"1+0" model is also supported as a subset, with no ASP redundancy.
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At the SG, an Application Server list contains active and inactive ASPs
to support ASP load-sharing and fail-over procedures. The list of ASPs
within a logical Application Server is kept updated in the SG to
reflect the active Application Server Process(es).
To avoid a single point of failure, it is recommended that a minimum of
two ASPs be in the list, resident in separate hosts and therefore
available over different SCTP Associations. For example, in the
network shown in Figure 1, all messages to DPC x could be sent to ASP1
in Host1 or ASP1 in Host2. The AS list at SG1 might look like the
following:
Routing Key {DPC=x) - "Application Server #1"
ASP1/Host1 - State=Up, Active
ASP1/Host2 - State=Up, Inactive
In this "1+1" redundancy case, ASP1 in Host1 would be sent any incoming
message with DPC=x. ASP1 in Host2 would normally be brought to the
active state upon failure of, or loss of connectivity to, ASP1/Host1.
In this example, both ASPs are Up, meaning that the related SCTP
association and far-end M3UA peer is ready.
The AS List at SG1 might also be set up in load-share mode:
Routing Key {DPC=x) - "Application Server #1"
ASP1/Host1 - State = Up, Active
ASP1/Host2 - State = Up, Active
In this case, both the ASPs would be sent a portion of the traffic.
For example the two ASPs could together form a database, where incoming
queries may be sent to any active ASP.
Care must be exercised by a Network Operator in the selection of the
routing information to be used as the Routing Key for a particular AS.
For example, where Application Servers are defined using ranges of ISUP
CIC values, the Operator is implicitly splitting up control of the
related circuit groups. Some CIC value range assignments may interfere
with ISUP circuit group management procedures.
In the process of fail-over, it is recommended that in the case of ASPs
supporting call processing, stable calls do not fail. It is possible
that calls in "transition" MAY fail, although measures of communication
between the ASPs involved can be used to mitigate this. For example,
the two ASPs MAY share call state via shared memory, or MAY use an ASP
to ASP protocol to pass call state information. Any ASP-to-ASP
protocol is outside the scope of this document.
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1.4.4.2 Signalling Gateway Redundancy
Signalling Gateways MAY also be distributed over multiple hosts. Much
like the AS model, SGs may be comprised of one or more SG Processes
(SGPs), distributed over one or more hosts, using an active/standby or
a load-sharing model. An SGP is viewed as a remote SCTP end-point from
an ASP perspective. There is, however, no M3UA protocol to manage the
status of an SGP. Whenever an SCTP association to an SGP exists, the
SGP is assumed to be available. Also, every SGP within an SG
communicating with an ASP provides identical SS7 connectivity to this
ASP. Should an SGP lose all or partial SS7 connectivity and other SGPs
exist, the SGP must terminate the SCTP associations to the concerned
ASPs.
It is therefore possible for an ASP to route signalling messages
destined to the SS7 network using more than one SGP. In this model, a
Signalling Gateway is deployed as a cluster of hosts acting as a single
SG. A primary/back-up redundancy model is possible, where the
unavailability of the SCTP association to a primary SGP could be used
to reroute affected traffic to an alternate SGP. A load-sharing model
is possible, where the signalling messages are load-shared between
multiple SGPs.
It may also be possible for an ASP to use more than one SG to access a
specific SS7 end point, in a model that resembles an SS7 STP mated
pair. Typically, SS7 STPs are deployed in mated pairs, with traffic
load-shared between them. Other models are also possible, subject to
the limitations of the local SS7 network provisioning guidelines.
>From the perspective of the M3UA at an ASP, a particular SG is capable
of transferring traffic to an SS7 destination if an SCTP association
with at least one SGP of the SG is established, the SGP has returned an
ASPAC Ack message acknowledging to the ASP M3UA that the ASP is
actively handling traffic for that destination, and the SG has not
indicated that the destination is inaccessible. When an ASP is
configured to use multiple SGs for transferring traffic to the SS7
network, the ASP must maintain knowledge of the current capability of
the SGs to handle traffic to destinations of interest. This
information is crucial to the overall reliability of the service, for
both active/standby and load-sharing model, in the event of failures,
recovery and maintenance activities. The ASP M3UA may also use this
information for congestion avoidance purposes. The distribution of the
MTP3-user messages over the SGs should be done in such a way to
minimize message mis-sequencing, as required by the SS7 User Parts.
1.4.5 Flow Control
Local Management at an ASP may wish to stop traffic across an SCTP
association in order to temporarily remove the association from service
or to perform testing and maintenance activity. The function could
optionally be used to control the start of traffic on to a newly
available SCTP association.
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1.4.6 Congestion Management
The M3UA Layer is informed of local and IP network congestion by means
of an implementation-dependent function (e.g., an implementation-
dependent indication from the SCTP of IP network congestion).
At an ASP or IPSP, the M3UA indicates congestion to local MTP3-Users by
means of an MTP-Status primitive, as per current MTP3 procedures, to
invoke appropriate upper layer responses.
When an SG determines that the transport of SS7 messages to a
Signalling Point Management Cluster (SPMC) is encountering congestion,
the SG should trigger SS7 MTP3 Transfer Controlled management messages
to originating SS7 nodes, as per current MTP3 procedures. The
triggering of SS7 MTP3 Management messages from an SG is an
implementation-dependent function.
The M3UA at an ASP or IPSP should indicate local congestion to an M3UA
peer with an SCON message. When an SG M3UA receives an SCON message
from an ASP, and the SG determines that an SPMC is now encountering
congestion, it should trigger SS7 MTP3 Transfer Controlled management
messages to concerned SS7 destinations according to current MTP
procedures.
1.4.7 SCTP Stream Mapping.
The M3UA at both the SG and ASP also supports the assignment of
signalling traffic into streams within an SCTP association. Traffic
that requires sequencing must be assigned to the same stream. To
accomplish this, MTP3-User traffic may be assigned to individual
streams based on, for example, the SLS value in the MTP3 Routing Label
or the ISUP CIC assignment, subject of course to the maximum number of
streams supported by the underlying SCTP association.
The use of SCTP streams within M3UA is recommended in order to minimize
transmission and buffering delays, therefore improving the overall
performance and reliability of the signalling elements. The
distribution of the MTP3 user messages over the various streams should
be done in such a way to minimize message mis-sequencing, as required
by the SS7 User Parts.
1.4.8 Client/Server Model
The SG takes on the role of server while the ASP is the client. ASPs
MUST initiate the SCTP association to the SG.
In the case of IPSP to IPSP communication, the peer endpoints using
M3UA SHOULD be configured so that one always takes on the role of
client and the other the role of server for initiating SCTP
associations and M3UA messaging.
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The SCTP (and UDP/TCP) Registered User Port Number Assignment for M3UA
is 2905.
1.5 Sample Configurations
1.5.1 Example 1: ISUP message transport
******** SS7 ***************** IP ********
* SEP *---------* SG *--------* ASP *
******** ***************** ********
+------+ +------+
| ISUP | (NIF) | ISUP |
+------+ +------+-+------+ +------+
| MTP3 | | MTP3 | | M3UA | | M3UA |
+------| +------+ +------+ +------+
| MTP2 | | MTP2 | | SCTP | | SCTP |
+------+ +------+ +------+ +------+
| L1 | | L1 | | IP | | IP |
+------+ +------+ +------+ +------+
|_______________| |______________|
SEP - SS7 Signalling End Point
SCTP - Stream Control Transmission Protocol
NIF - Nodal Inter-working Function
In this example, the SG provides an implementation-dependent nodal
inter-working function (NIF) that allows the MGC to exchange SS7
signalling messages with the SS7-based SEP. The NIF within the SG
serves as the interface within the SG between the MTP3 and M3UA. This
nodal inter-working function has no visible peer protocol with either
the MGC or SEP. It also provides network status information to one or
both sides of the network.
For internal SG modeling purposes, at the NIF level, SS7 signalling
messages that are destined to the MGC are received as MTP-TRANSFER
indication primitives from the MTP Level 3 upper layer interface and
are sent to the local M3UA-resident message distribution function for
ongoing routing to the final IP destination. MTP-TRANSFER primitives
received from the local M3UA network address translation and mapping
function are sent to the MTP Level 3 upper layer interface as MTP-
TRANSFER request primitives for on-going MTP Level 3 routing to an SS7
SEP. For the purposes of providing SS7 network status information the
NIF also delivers MTP-PAUSE, MTP-RESUME and MTP-STATUS indication
primitives received from the MTP Level 3 upper layer interface to the
local M3UA-resident management function. In addition, as an
implementation and network option, restricted destinations are
communicated from MTP network management to the local M3UA-resident
management function.
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1.5.2 Example 2: SCCP Transport between IPSPs
******** IP ********
* IPSP * * IPSP *
******** ********
+------+ +------+
|SCCP- | |SCCP- |
| User | | User |
+------+ +------+
| SCCP | | SCCP |
+------+ +------+
| M3UA | | M3UA |
+------+ +------+
| SCTP | | SCTP |
+------+ +------+
| IP | | IP |
+------+ +------+
|________________|
This example shows an architecture where no Signalling Gateway is used.
In this example, SCCP messages are exchanged directly between two IP-
resident IPSPs with resident SCCP-User protocol instances, such as
RANAP or TCAP. SS7 network inter-working is not required, therefore
there is no MTP3 network management status information for the SCCP and
SCCP-User protocols to consider. Any MTP-PAUSE, -RESUME or -STATUS
indications from the M3UA to the SCCP should consider the status of the
SCTP Association and underlying IP network and any congestion
information received from the remote site.
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1.5.3 Example 3: SG resident SCCP layer, with remote ASP
******** SS7 ***************** IP ********
* SEP *---------* *--------* *
* or * * SG * * ASP *
* STP * * * * *
******** ***************** ********
+------+ +---------------+ +------+
| SCCP-| | SCCP | | SCCP-|
| User | +---------------+ | User |
+------+ | _____ | +------+
| SCCP | | | | | | SCCP |
+------+ +------+-+------+ +------+
| MTP3 | | MTP3 | | M3UA | | M3UA |
+------| +------+ +------+ +------+
| MTP2 | | MTP2 | | SCTP | | SCTP |
+------+ +------+ +------+ +------+
| L1 | | L1 | | IP | | IP |
+------+ +------+ +------+ +------+
|_______________| |______________|
STP - SS7 Signalling Transfer Point
In this example, the SG contains an instance of the SS7 SCCP protocol
layer that may, for example, perform the SCCP Global Title Translation
(GTT) function for messages logically addressed to the SG SCCP. If the
result of a GTT for an SCCP message yields an SS7 DPC or DPC/SSN
address an SCCP peer located in the IP domain, the resulting MTP-
TRANSFER request primitive is sent to the local M3UA-resident network
address translation and mapping function for ongoing routing to the
final IP destination.
Similarly, the SCCP instance in an SG can perform the SCCP GTT service
for messages logically addressed to it from SCCP peers in the IP
domain. In this case, MTP-TRANSFER messages are sent from the local
M3UA-resident network address translation and mapping function to the
SCCP for GTT. If the result of the GTT yields the address of an SCCP
peer in the SS7 network then the resulting MTP-TRANSFER request is
given to the MTP3 for delivery to an SS7-resident node.
It is possible that the above SCCP GTT at the SG could yield the
address of an SCCP peer in the IP domain and the resulting MTP-TRANSFER
primitive would be sent back to the M3UA for delivery to an IP
destination.
For internal SG modeling purposes, this may be accomplished with the
use of an implementation-dependent nodal inter-working function within
the SG that effectively sits below the SCCP and routes MTP-TRANSFER
messages to/from both the MTP3 and the M3UA, based on the SS7 DPC or
DPC/SSN
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address information. This nodal inter-working function has no visible
peer protocol with either the ASP or SEP.
Note that the services and interface provided by the M3UA are the same
as in Example 1 and the functions taking place in the SCCP entity are
transparent to M3UA. The SCCP protocol functions are not reproduced in
the M3UA protocol.
1.6 Definition of M3UA Boundaries
1.6.1 Definition of the boundary between M3UA and an MTP3-User.
>From ITU Q.701 [14]:
MTP-TRANSFER request
MTP-TRANSFER indication
MTP-PAUSE indication
MTP-RESUME indication
MTP-STATUS indication
1.6.2 Definition of the boundary between M3UA and SCTP
An example of the upper layer primitives provided by the SCTP are
provided in Reference [13] Section 10.
1.6.3 Definition of the Boundary between M3UA and Layer Management
M-SCTP ESTABLISH request
Direction: LM -> M3UA
Purpose: LM requests ASP to establish an SCTP association with an
SG.
M-STCP ESTABLISH confirm
Direction: M3UA -> LM
Purpose: ASP confirms to LM that it has established an SCTP
association with an SG.
M-SCTP ESTABLISH indication
Direction: M3UA -> LM
Purpose: M3UA informs LM that a remote ASP has established an SCTP
association.
M-SCTP RELEASE request
Direction: LM -> M3UA
Purpose: LM requests ASP to release an SCTP association with SG.
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M-SCTP RELEASE confirm
Direction: M3UA -> LM
Purpose: ASP confirms to LM that it has released SCTP association
with SG.
M-SCTP RELEASE indication
Direction: M3UA -> LM
Purpose: M3UA informs LM that a remote ASP has released an SCTP
Association or the SCTP association has failed.
M-SCTP STATUS request
Direction: LM -> M3UA
Purpose: LM requests M3UA to report the status of an SCTP
association.
M-SCTP STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA reports the status of an SCTP association.
M-ASP STATUS request
Direction: LM -> M3UA
Purpose: LM requests M3UA to report the status of a local or remote
ASP.
M-ASP STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA reports status of local or remote ASP.
M-AS STATUS request
Direction: LM -> M3UA
Purpose: LM requests M3UA to report the status of an AS.
M-AS STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA reports the status of an AS.
M-NOTIFY indication
Direction: M3UA -> LM
Purpose: M3UA reports that it has received a NOTIFY message
from its peer.
M-ERROR indication
Direction: M3UA -> LM
Purpose: M3UA reports that it has received an ERROR message from
its peer or that a local operation has been unsuccessful.
M-ASP UP request
Direction: LM -> M3UA
Purpose: LM requests ASP to start its operation and send an ASP-UP
Message to its peer.
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M-ASP UP confirm
Direction: M3UA -> LM
Purpose: ASP reports that is has received an ASP UP Acknowledgement
message from the SG.
M-ASP UP indication
Direction: M3UA -> LM
Purpose: M3UA reports it has successfully processed an incoming ASP-
UP request from its peer.
M-ASP DOWN request
Direction: LM -> M3UA
Purpose: LM requests ASP to stop its operation and send an ASP-DOWN
Message to its peer.
M-ASP DOWN confirm
Direction: M3UA -> LM
Purpose: ASP reports that is has received an ASP DOWN
Acknowledgement message from the SG.
M-ASP DOWN indication
Direction: M3UA -> LM
Purpose: M3UA reports it has successfully processed an incoming ASP-
DOWN request from its peer.
M-ASP-ACTIVE request
Direction: LM -> M3UA
Purpose: LM requests ASP to send an ASP-ACTIVE message to its peer.
M-ASP ACTIVE confirm
Direction: M3UA -> LM
Purpose: ASP reports that is has received an ASP ACTIVE
Acknowledgement message from the SG.
M-ASP ACTIVE indication
Direction: M3UA -> LM
Purpose: LM reports it has successfully processed an incoming ASP-
ACTIVE request from its peer.
M-ASP-INACTIVE request
Direction: LM -> M3UA
Purpose: LM requests ASP to send an ASP- Inactive message to the SG.
M-ASP INACTIVE confirm
Direction: LM -> M3UA
Purpose: ASP reports that is has received an ASP INACTIVE
Acknowledgement message from the SG.
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M-ASP INACTIVE indication
Direction: M3UA -> LM
Purpose: LM reports it has successfully processed an incoming ASP-
INACTIVE request from its peer.
M-AS ACTIVE indication
Direction: M3UA -> LM
Purpose: LM reports that an AS has moved to the ACTIVE state.
M-AS INACTIVE indication
Direction: M3UA -> LM
Purpose: LM reports that an AS has moved to the INACTIVE state.
M-AS DOWN indication
Direction: M3UA -> LM
Purpose: LM reports that an AS has moved to the DOWN state.
2.0 Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD
NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they appear
in this document, are to be interpreted as described in [RFC2119].
3.0 M3UA Protocol Elements
The general M3UA message format includes a Common Message Header
followed by zero or more parameters as defined by the Message Type.
For forward compatibility, all Message Types may have attached
parameters even if none are specified in this version.
3.1 Common Message Header
The protocol messages for MTP3-User Adaptation require a message header
which contains the adaptation layer version, the message type, and
message length.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Reserved | Message Class | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ /
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All fields in an M3UA message MUST be transmitted in the network byte
order, unless otherwise stated.
3.1.1 M3UA Protocol Version: 8 bits (unsigned integer)
The version field contains the version of the M3UA adaptation layer.
The supported versions are the following:
1 Release 1.0
3.1.2 Message Classes and Types
The following list contains the valid Message Classes:
Message Class: 8 bits (unsigned integer)
The following list contains the valid Message Type Classes:
0 Management (MGMT) Message [IUA/M2UA/M3UA/SUA]
1 Transfer Messages [M3UA]
2 SS7 Signalling Network Management (SSNM) Messages [M3UA/SUA]
3 ASP State Maintenance (ASPSM) Messages [IUA/M2UA/M3UA/SUA]
4 ASP Traffic Maintenance (ASPTM) Messages [IUA/M2UA/M3UA/SUA]
5 Q.921/Q.931 Boundary Primitives Transport (QPTM) Messages
[IUA]
6 MTP2 User Adaptation (MAUP) Messages [M2UA]
7 Connectionless Messages [SUA]
8 Connection-Oriented Messages [SUA]
9 Routing Key Management (RKM) Messages (M3UA)
10 to 127 Reserved by the IETF
28 to 255 Reserved for IETF-Defined Message Class extensions
Message Type: 8 bits (unsigned integer)
The following list contains the message types for the defined
messages.
Management (MGMT) Message
0 Error (ERR)
1 Notify (NTFY)
2 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined MGMT extensions
Transfer Messages
0 Reserved
1 Payload Data (DATA)
2 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined Transfer extensions
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SS7 Signalling Network Management (SSNM) Messages
0 Reserved
1 Destination Unavailable (DUNA)
2 Destination Available (DAVA)
3 Destination State Audit (DAUD)
4 SS7 Network Congestion State (SCON)
5 Destination User Part Unavailable (DUPU)
6 Destination Restricted (DRST)
7 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined SSNM extensions
ASP State Maintenance (ASPSM) Messages
0 Reserved
1 ASP Up (UP)
2 ASP Down (DOWN)
3 Heartbeat (BEAT)
4 ASP Up Ack (UP ACK)
5 ASP Down Ack (DOWN ACK)
6 Heatbeat Ack (BEAT ACK)
7 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined ASPSM extensions
ASP Traffic Maintenance (ASPTM) Messages
0 Reserved
1 ASP Active (ACTIVE)
2 ASP Inactive (INACTIVE)
3 ASP Active Ack (ACTIVE ACK)
4 ASP Inactive Ack (INACTIVE ACK)
5 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined ASPTM extensions
Routing Key Management (RKM) Messages
0 Reserved
1 Registration Request (REG REQ)
2 Registration Response (REG RSP)
3 Deregistration Request (DEREG REQ)
4 Deregistration Response (DEREG RSP)
5 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined ASPTM extensions
3.1.3 Reserved: 8 bits
The Reserved field SHOULD be set to all '0's and ignored by the
receiver.
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3.1.4 Message Length: 32-bits (unsigned integer)
The Message Length defines the length of the message in octets,
including the Common Header. For messages with a final parameter
containing padding, the parameter padding MUST be included in the
Message Length.
Note: A receiver SHOULD accept the message whether or not the final
parameter padding is included in the message length.
3.2 Variable-Length Parameter Format
M3UA messages consist of a Common Header followed by zero or more
variable length parameters, as defined by the message type. All the
parameters contained in a message are defined in a Tag-Length-Value
format as shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Tag | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Parameter Value /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where more than one parameter is included in a message, the parameters
may be in any order, except where explicitly mandated. A receiver
SHOULD accept the parameters in any order.
Parameter Tag: 16 bits (unsigned integer)
The Tag field is a 16-bit identifier of the type of parameter. It
takes a value of 0 to 65534. The parameter Tags defined are as
follows:
0 Reserved
1 Network Appearance
2 Protocol Data 1
3 Protocol Data 2
4 Info String
5 Affected Destinations
6 Routing Context
7 Diagnostic Information
8 Heartbeat Data
9 User/Cause
10 Reason
11 Traffic Mode Type
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12 Error Code
13 Status Type/ID
14 Congestion Indications
15 Concerned Destination
16 Routing Key
17 Registration Result
18 De-registration Result
19 Local_Routing Key Identifier
20 Destination Point Code
21 Service Indicators
22 Subsystem Numbers
23 Originating Point Code List
24 Circuit Range
25 Registration Results
26 De-Registration Results
27 to 65534 Reserved by the IETF
The value of 65535 is reserved for IETF-defined extensions. Values
other than those defined in specific parameter description are
reserved for use by the IETF.
Parameter Length: 16 bits (unsigned integer)
The Parameter Length field contains the size of the parameter in
bytes, including the Parameter Tag, Parameter Length, and Parameter
Value fields. The Parameter Length does not include any padding
bytes.
Parameter Value: variable-length.
The Parameter Value field contains the actual information to be
transferred in the parameter.
The total length of a parameter (including Tag, Parameter Length and
Value fields) MUST be a multiple of 4 bytes. If the length of the
parameter is not a multiple of 4 bytes, the sender pads the
Parameter at the end (i.e., after the Parameter Value field) with
all zero bytes. The length of the padding is NOT included in the
parameter length field. A sender SHOULD NEVER pad with more than 3
bytes. The receiver MUST ignore the padding bytes.
3.3 Transfer Messages
The following section describes the Transfer messages and parameter
contents.
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3.3.1 Payload Data Message (DATA)
The DATA message contains the SS7 MTP3-User protocol data, which is an
MTP-TRANSFER primitive, including the complete MTP3 Routing Label. The
Data message contains the following variable length parameters:
Network Appearance Optional
Protocol Data 1 or 2 Mandatory
The following format MUST be used for the Data Message:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 1 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 3 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Protocol Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance: 32-bits (unsigned integer)
The optional Network Appearance parameter identifies the SS7 network
context for the message, for the purposes of logically separating
the signalling traffic between the SG and the Application Server
Process over a common SCTP Association. An example is where an SG
is logically partitioned to appear as an element in four different
national SS7 networks.
In a Data message, the Network Appearance implicitly defines the SS7
Point Code format used, the SS7 Network Indicator value, and the
MTP3 and possibly the MTP3-User protocol type/variant/version used
within the SS7 network partition. Where an SG operates in the
context of a single SS7 network, or individual SCTP associations are
dedicated to each SS7 network context, the Network Appearance
parameter is not required.
The Network Appearance parameter value is of local significance
only, coordinated between the SG and ASP. Therefore, in the case
where an ASP is connected to more than one SG, the same SS7 network
context may be identified by different Network Appearances depending
over which SG a message is being transmitted/received.
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Where the optional Network Appearance parameter is present, it must
be the first parameter in the message as it defines the format of
the Protocol Data field.
Protocol Data 1 or 2: variable length
One of two possible Protocol Data parameters are included in a DATA
message: Protocol Data 1 or Protocol Data 2.
The Protocol Data 1 parameter contains the original SS7 MTP3
message, including the Service Information Octet and Routing Label.
The Protocol Data 1 parameter contains the following fields:
Service Information Octet. Includes:
Service Indicator,
Network Indicator,
and Spare/Priority codes
Routing Label. Includes:
Destination Point Code,
Originating Point Code,
And Signalling Link Selection Code (SLS)
User Protocol Data. Includes:
MTP3-User protocol elements (e.g., ISUP, SCCP, or TUP
parameters)
The Protocol Data 2 parameter contains all the information in
Protocol Data 1 as described above, plus the MTP2 Length Indicator
octet. The MTP2 Length Indicator (LI) octet appears before the SIO
and Routing Label information. The MTP2 Length Indicator octet is
required for some national MTP variants that use the spare bits in
the LI to carry additional information of interest to the MTP3 and
MTP3-User (e.g., the Japan TTC standard use of LI spare bits to
indicate message priority)
The Payload Data format is as defined in the relevant MTP standards
for the SS7 protocol being transported. The format is either
implicitly known or identified by the Network Appearance parameter.
Note: In the SS7 Recommendations, the format of the messages and
fields within the messages are based on bit transmission order. In
these recommendations the Least Significant Bit (LSB) of each field
is positioned to the right. For this document the received SS7
fields are populated octet by octet as received into the 4-octet
word as shown in the examples below.
For the ANSI protocol example, the Protocol Data field format is
shown below:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SIO | DPC Member | DPC Cluster | DPC Network |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPC Member | OPC Cluster | OPC Network | SLS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Protocol Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB---------------------------------------------------------LSB|
Within each octet the Least Significant Bit (LSB) per the SS7
Recommendations is to the right (e.g., bit 7 of SIO is the LSB).
For the ITU international protocol example, the Protocol Data field
is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SIO | DPC | DPC |OPC| DPC | DPC | OPC |@|
| | Region *| SP *|SP*|Zone*| reg.| Region *| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLS | OPC |$| Protocol |
| *| SP *| | Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* marks LSB of each field; @ = OPC SP MSB; $ = OPC region MSB
3.4 SS7 Signalling Network Management (SSNM) Messages
3.4.1 Destination Unavailable (DUNA)
The DUNA message is sent from the SG to all concerned ASPs to indicate
that the SG has determined that one or more SS7 destinations are
unreachable. It is also sent in response to a message from the ASP to
an unreachable SS7 destination. As an implementation option the SG may
suppress the sending of subsequent "response" DUNAs regarding a certain
unreachable SS7 destination for a certain period in order to give the
remote side time to react. The MTP3-User at the ASP is expected to stop
traffic to the affected destination through the SG initiating the DUNA
as per the defined MTP3-User procedures.
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The DUNA message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
Info String Optional
The format for DUNA Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 1 | Length =8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 5 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected DPC 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected DPC n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance: 32-bit unsigned integer
See Section 3.3.1
Affected Destinations: n x 32-bits
The Affected Destinations parameter contains up to sixteen Affected
Destination Point Code fields, each a three-octet parameter to allow
for 14-, 16- and 24-bit binary formatted SS7 Point Codes. Affected
Point Codes that are less than 24-bits, are padded on the left to
the 24-bit boundary. The encoding is shown below for ANSI and ITU
Point Code examples.
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ANSI 24-bit Point Code:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Network | Cluster | Member |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB-----------------------------------------LSB|
ITU 14-bit Point Code:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask |0 0 0 0 0 0 0 0 0 0|Zone | Region | SP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB--------------------LSB|
It is optional to send an Affected Destinations parameter with more
than one Affected DPC but it is mandatory to receive and process it.
All the Affected DPCs included must be within the same Network
Appearance. Including multiple Affected DPCs may be useful when
reception of an MTP3 management message or a linkset event
simultaneously affects the availability status of a list of
destinations at an SG.
Mask: 8-bits (unsigned integer)
The Mask field associated with each Affected DPC in the Affected
Destinations parameter, used to identify a contiguous range of
Affected Destination Point Codes, independent of the point code
format. Identifying a contiguous range of Affected DPCs may be
useful when reception of an MTP3 management message or a linkset
event simultaneously affects the availability status of a series of
destinations at an SG. For example, if all DPCs in an ANSI cluster
are determined to be unavailable due to local linkset
unavailability, the DUNA could identify potentially 256 Affected
DPCs in a single Affected DPC field.
The Mask parameter represents a bit mask that can be applied to the
related Affected DPC field. The bit mask identifies how many bits
of the Affected DPC field are significant and which are effectively
"wildcarded". For example, a mask of "8" indicates that the least
significant eight bits of the DPC is "wildcarded". For an ANSI 24-
bit Affected DPC, this is equivalent to signalling that all DPCs in
an ANSI Cluster are unavailable. A mask of "3" indicates that the
least significant three bits of the DPC is "wildcarded". For a 14-
bit ITU Affected DPC, this is equivalent to signaling that an ITU
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Internet Draft SS7 MTP3-User Adaptation Layer Feb 2001
Region is unavailable. A mask value equal to the number of bits in
the DPC indicates that the entire network appearance is affected û
this is used to indicate network isolation to the ASP.
Info String: variable length
The optional INFO String parameter can carry any 8-bit ASCII
character string along with the message. Length of the INFO
String parameter is from 0 to 255 characters. No procedures are
presently identified for its use but the INFO String MAY be used by
Operators to identify in text form the location reflected by the
Affected DPC for debugging purposes.
3.4.2 Destination Available (DAVA)
The DAVA message is sent from the SG to all concerned ASPs to indicate
that the SG has determined that one or more SS7 destinations are now
reachable (and not restricted), or in response to a DAUD message if
appropriate. The ASP MTP3-User protocol is allowed to resume traffic to
the affected destination through the SG initiating the DUNA.
The DAVA message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
Info String Optional
The format and description of the Network Appearance, Affected
Destinations and Info String parameters is the same as for the DUNA
message (See Section 3.4.1.)
3.4.3 Destination State Audit (DAUD)
The DAUD message can be sent from the ASP to the SG to audit the
availability/congestion state of SS7 routes to one or more affected
destinations.
The DAUD message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
Info String Optional
The format and description of DAUD Message parameters is the same as
for the DUNA message (See Section 3.4.1.)
3.4.4 SS7 Network Congestion (SCON)
The SCON message can be sent from the SG to all concerned ASPs to
indicate congestion in the SS7 network to one or more destinations, or
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to an ASP in response to a DATA or DAUD message as appropriate. For
some MTP protocol variants (e.g., ANSI MTP) the SCON may be sent when
the SS7 congestion level changes. The SCON message MAY also be sent
from the M3UA of an ASP to an M3UA peer indicating that the M3UA or the
ASP is congested.
The SCON message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
Concerned Destination Optional Congestion Indications
Optional
Info String Optional
The format for SCON Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 1 | Length =8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 5 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected DPC 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected DPC n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 15 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved | Concerned DPC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 14 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Cong. Level* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The format and description of the Network Appearance, Affected
Destinations, and Info String parameters is the same as for the DUNA
message (See Section 3.4.1.)
The Affected Destinations parameter can be used to indicate congestion
of multiple destinations or ranges of destinations. However, an SCON
MUST not be delayed in order to "collect" individual congested
destinations into a single SCON as any delay might affect the timing of
congestion indications to the M3UA Users. One use for including a
range of Congested DPCs is when the SG supports an ANSI cluster route
set to the SS7 network that becomes congested due to outgoing link set
congestion.
Concerned Destination: 32-bits
The optional Concerned Destination parameter is only used if the
SCON is sent from an ASP to the SG. It contains the point code of
the originator of the message that triggered the SCON. The Concerned
Destination parameter contains one Concerned Destination Point Code
field, a three-octet parameter to allow for 14-, 16- and 24-bit
binary formatted SS7 Point Codes. A Concerned Point Code that is
less than 24-bits, is padded on the left to the 24-bit boundary. The
SG sends a Transfer Controlled Message to the Concerned Point Code
using the single Affected DPC contained in the SCON to populate the
(affected) Destination field of the TFC message. Normally the
Affected DPC will be equal to the point code of the ASP.
Congested Indications: 32-bits
The optional Congestion Indications parameter contains a Congestion
Level field. This optional parameter is used to communicate
congestion levels in national MTP networks with multiple congestion
thresholds, such as in ANSI MTP3. For MTP congestion methods
without multiple congestion levels (e.g., the ITU international
method) the parameter is not included.
Congestion Level field: 8-bits (unsigned integer)
The Congestion Level field, associated with all of the Affected
DPC(s) in the Affected Destinations parameter, contains one of the
Following values:
0 No Congestion or Undefined
1 Congestion Level 1
2 Congestion Level 2
3 Congestion Level 3
The congestion levels are defined in the congestion method in the
appropriate national MTP recommendations [14,15].
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3.4.5 Destination User Part Unavailable (DUPU)
The DUPU message is used by an SG to inform an ASP that a remote peer
MTP3-User Part (e.g., ISUP or SCCP) at an SS7 node is unavailable.
The DUPU message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
User/Cause Mandatory
Info String Optional
The format for DUPU Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 1 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 5 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask = 0 | Affected DPC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 9 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause | User |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
User/Cause: 32-bits
The Unavailability Cause and MTP3-User Identity fields, associated
with the Affected DPC in the Affected Destinations parameter, are
encoded as follows:
Unavailability Cause field: 16-bits (unsigned integer)
The Unavailability Cause parameter provides the reason for the
unavailability of the MTP3-User. The valid values for the
Unavailability Cause parameter are shown in the following table.
The values agree with those provided in the SS7 MTP3 User Part
Unavailable message. Depending on the MTP3 protocol used in the
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network appearance, additional values may be used - the
specification of the relevant MTP3 protocol variant/version
recommendation is definitive.
0 Unknown
1 Unequipped Remote User
2 Inaccessible Remote User
MTP3-User Identity field: 16-bits (unsigned integer)
The MTP3-User Identity describes the specific MTP3-User that is
unavailable (e.g., ISUP, SCCP, ...). Some of the valid values for
the MTP3-User Identity are shown below. The values agree with those
provided in the SS7 MTP3 User Part Unavailable message and Service
Indicator. Depending on the MTP3 protocol variant/version used in
the network appearance, additional values may be used. The relevant
MTP3 protocol variant/version recommendation is definitive.
0 to 2 Reserved
3 SCCP
4 TUP
5 ISUP
6 to 8 Reserved
9 Broadband ISUP
10 Satellite ISUP
The format and description of the Affected Destinations parameter is
the same as for the DUNA message (See Section 3.4.1.) except that the
Mask field is not used and only a single Affected DPC is included.
Ranges and lists of Affected DPCs cannot be signaled in a DUPU, but
this is consistent with UPU operation in the SS7 network. The Affected
Destinations parameter in an MTP3 User Part Unavailable message (UPU)
received by an SG from the SS7 network contains only one destination.
The format and description of the Network Appearance and Info String
parameters is the same as for the DUNA message (See Section 3.4.1.).
3.4.6 Destination Restricted (DRST)
The DRST message is optionally sent from the SG to all concerned ASPs
to indicate that the SG has determined that one or more SS7
destinations are now restricted, or in response to a DAUD message if
appropriate. The M3UA at the ASP is expected to send traffic to the
affected destination via an alternate SG of equal priority, but only if
such an alternate route exists and is available. If the affected
destination is currently considered unavailable by the ASP, traffic to
the affected destination through the SG initiating the DRST should be
resumed.
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This message is optional for the SG to send and optional for the ASP to
process. It is for use in the "STP" case described in Section 1.4.2.
The DRST message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
Info String Optional
The format and description of the Network Appearance, Affected
Destinations and Info String parameters is the same as for the DUNA
message (See Section 3.4.1.)
3.5 Application Server Process Maintenance (ASPM) Messages
3.5.1 ASP Up (ASPUP)
The ASP UP (ASPUP) message is used to indicate to a remote M3UA peer
that the Adaptation layer is ready to receive SSNM or ASPM management
messages for all Routing Keys that the ASP is configured to serve.
The ASPUP message contains the following parameters:
INFO String Optional
The format for ASPUP Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.4.1.)
3.5.2 ASP Up Ack
The ASP UP Ack message is used to acknowledge an ASP-Up message
received from a remote M3UA peer.
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The ASPUP Ack message contains the following parameters:
INFO String (optional)
The format for ASPUP Ack Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag =4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.4.1.)
3.5.3 ASP Down (ASPDN)
The ASP Down (ASPDN) message is used to indicate to a remote M3UA peer
that the adaptation layer is NOT ready to receive traffic or
maintenance messages.
The ASPDN message contains the following parameters:
Reason Mandatory
INFO String Optional
The format for the ASPDN message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 10 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag =4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Internet Draft SS7 MTP3-User Adaptation Layer Feb 2001
The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.4.1.)
Reason: 32-bit (unsigned integer)
The Reason parameter indicates the reason that the remote M3UA
adaptation layer is unavailable. The valid values for Reason are
shown in the following table.
0 Unspecified
1 User Unavailable
2 Management Blocking
3.5.4 ASP Down Ack
The ASP Down Ack message is used to acknowledge an ASP-Down message
received from a remote M3UA peer, or to reply to an ASPM message from
an ASP which is locked out for management reasons.
The ASP Down Ack message contains the following parameters:
Reason Mandatory
INFO String Optional
The format for the ASPDN Ack message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 10 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.4.1.)
The format of the Reason parameter is the same as for the ASP-Down
message. (See Section 3.4.3)
3.5.5 Registration Request (REG REQ)
The REG REQ message is sent by an ASP to indicate to a remote M3UA peer
that it wishes to register one or more given Routing Key with the
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Internet Draft SS7 MTP3-User Adaptation Layer Feb 2001
remote peer. Typically, an ASP would send this message to an SGP, and
expects to receive a REG RSP in return with an associated Routing
Context value.
The REG REQ message contains the following parameters:
Routing Key Mandatory
The format for the REG REQ message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 16 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Key 1 /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 16 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Key n /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Routing Key: variable length
The Routing Key parameter is mandatory. The sender of this message
expects that the receiver of this message will create a Routing
Key entry and assign a unique Routing Context value to it, if the
Routing Key entry does not already exist.
The Routing Key parameter may be present multiple times in the same
message. This is used to allow the registration of multiple Routing
Keys in a single message.
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The format of the Routing Key parameter is as follows.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local-RK-Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SI (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSN (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Origination Point Code List (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit Range List (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Local-RK-Identifier: 32-bit integer
The mandatory Local-RK-Identifier field is used to uniquely identify
the registration request. The Identifier value is assigned by the
ASP, and is used to correlate the response in an REG RSP message
with the original registration request. The Identifier value must
remain unique until the REG RSP is received.
The format of the Local-RK-Identifier field is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 19 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local-RK-Identifier value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Destination Point Code:
The Destination Point Code parameter is mandatory, and identifies
the Destination Point Code of incoming SS7 traffic for which the ASP
is registering. The format is the same as described for the
Affected Destination parameter in the DUNA Message (See Section
3.4.1). Its format is:
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Internet Draft SS7 MTP3-User Adaptation Layer Feb 2001
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 20 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask = 0 | Destination Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance:
The optional Network Appearance parameter field identifies the SS7
Network context for the Routing Key, and has the same format as in
the Data message (See Section 3.3.1). Its format is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 1 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Service Indicators (SI): n X 8-bit integers
The SI field contains one or more Service Indicators from the values
as described in the MTP3-User Identity field of the DUPU Message.
The absence of the SI parameter in the Routing Key indicates the use
of any SI values, excluding of course MTP management. Where an SI
parameter does not contain a multiple of four SIs, the parameter is
padded out to 32-byte alignment. An SI value of zero is not valid
in M3UA. The SI format is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 21 | Length = var. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SI #1 | SI #2 | |
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