| draft-ietf-sigtran-m3ua-08 Description: Request For Comments
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Network Working Group Greg Sidebottom
INTERNET-DRAFT Guy Mousseau
Nortel Networks
Lyndon Ong
Ciena
Ian Rytina
Ericsson
Hanns Juergen Schwarzbauer
Siemens
Klaus Gradischnig
NeuStar
Ken Morneault
Cisco
Mallesh Kalla
Telcordia
Normand Glaude
Performance Technologies
Brian Bidulock
OpenSS7
Expires in six months Jul 2001
SS7 MTP3-User Adaptation Layer (M3UA)
<draft-ietf-sigtran-m3ua-08.txt>
Status of This Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026. Internet-Drafts are working
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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
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operation of the MTP3-User peers in the SS7 and IP domains. This
protocol would be used between a Signalling Gateway (SG) and a Media
Gateway Controller (MGC) or IP-resident Database. It is assumed that
the SG receives SS7 signalling over a standard SS7 interface using the
SS7 Message Transfer Part (MTP) to provide transport.
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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........................................21
1.6 Definition of M3UA Boundaries................................24
2. Conventions.......................................................28
3. M3UA Protocol Elements............................................28
3.1 Common Message Header........................................28
3.2 Variable-Length Parameter....................................31
3.3 Transfer Messages............................................32
3.4 SS7 Signalling Network management (SSNM) Messages............35
3.5 ASP State Maintenance (ASPM) Messages........................43
3.6 Routing Key Management (RKM) Messages........................46
3.7 ASP Traffic Maintenance (ASPTM) Messages.....................55
3.8 Management(MGMT) Messages....................................60
4. Procedures........................................................64
4.1 Procedures to Support the M3UA-User and Layer Management
Layers.......................................................64
4.2 Procedures to Support the Management of SCTP Associations
with M3UA Peers..............................................67
4.3 Procedures to support the Unavailability or Congestion
Status of SS7 Destinations...................................81
4.4 MTP3 Restart.................................................83
5. Examples of M3UA Procedures.......................................84
5.1 Establishment of Association and Traffic
Between SGs and ASPs.........................................84
5.2 ASP traffic Fail-over Examples...............................89
5.3 Normal Withdrawal of an ASP from an Application Server
and Tear-down of an Association..............................90
5.4.M3UA/MTP3-User Boundary Examples.............................91
6. Security..........................................................95
6.1 Introduction.................................................95
6.2 Threats......................................................95
6.3 Protecting Confidentiality...................................95
7. IANA Considerations...............................................96
7.1 SCTP Payload Protocol Identifier.............................96
7.2 M3UA Protocol Extensions.....................................96
8. Acknowledgements..................................................97
9. References........................................................97
10. Bibliography....................................................99
11. Author's Addresses..............................................99
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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 SIO/DPC/OPC/CIC_range. Another example is a
virtual database element, handling all HLR transactions for a
particular SS7 DPC/OPC/SCCP_SSN combination. The AS contains a set of
one or more unique Application Server Processes, of which one or more
is normally actively processing traffic. Note that there is a 1:1
relationship between an AS and a Routing Key.
Application Server Process (ASP) - A process instance of an Application
Server. An Application Server Process serves as an active or back-up
process of an Application Server (e.g., part of a distributed virtual
switch or database). Examples of ASPs are processes (or process
instances) of MGCs, IP SCPs or IP HLRs. An ASP contains an SCTP end-
point and may be configured to process signalling traffic within more
than one Application Server.
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Association - An association refers to an SCTP association. The
association provides the transport for the delivery of MTP3-User
protocol data units and M3UA adaptation layer peer messages.
IP Server Process (IPSP) - A process instance of an IP-based
application. An IPSP is essentially the same as an ASP, except that it
uses M3UA in a point-to-point fashion. Conceptually, an IPSP does not
use the services of a Signalling Gateway.
Signalling Gateway Process (SGP) - A process instance of a Signalling
Gateway. It serves as an active, back-up, load-sharing or broadcast
process of a Signalling Gateway.
Signalling Gateway - An SG is a signaling agent that receives/sends SCN
native signaling at the edge of the IP network [1]. An SG appears to
the SS7 network as an SS7 Signalling Point. An SG contains a set of one
or more unique Signalling Gateway Processes, of which one or more is
normally actively processing traffic. Where an SG contains more than
one SGP, the SG is a logical entity and the contained SGPs might
typically be coordinated into a single management view to the SS7
network and to the supported Application Servers.
Signalling Process - A process instance that uses M3UA to communicate
with other signalling processes. An ASP, an SGP and an IPSP are all
signalling processes.
Routing Key: A Routing Key describes a set of SS7 parameters and
parameter values that uniquely define the range of signalling traffic
to be handled by a particular Application Server. Parameters within the
Routing Key cannot extend across more than a single Signalling Point
Management Cluster.
Routing Context - A value that uniquely identifies a Routing Key.
Routing Context values are either configured using a configuration
management interface, or by using the routing key management procedures
defined in this document.
Fail-over - The capability to re-route signalling traffic as required
to an alternate Application Server Process, or group of ASPs, within an
Application Server in the event of failure or unavailability of a
currently used Application Server Process. Fail-over also applies upon
the return to service of a previously unavailable Application Server
Process.
Signalling Point Management Cluster (SPMC) - The complete set of
Application Servers represented to the SS7 network under a single MTP
entity (Signalling Point). SPMCs are used to aggregate the
availability, congestion, and user part status of an MTP entity
(Signalling Point) that is distributed in the IP domain, for the purpose
of supporting MTP3 management procedures towards the SS7 network. In
some
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cases, the SG itself may also be a member of the SPMC. In this case,
the SG availability/congestion/User_Part status should also be taken
into account when considering any supporting MTP3 management actions.
MTP - The Message Transfer Part of the SS7 protocol.
MTP3 - MTP Level 3, the signalling network layer of SS7
MTP3-User - Any protocol normally using the services of the SS7 MTP3
(e.g., ISUP, SCCP, TUP, etc.).
Network Appearance - The Network Appearance uniquely identifies an SS7
entity (Point Code) into an SS7 network, as presented by the SG. It is
used for the purposes of logically separating the signalling traffic
between the SG and the Application Server Processes over a common SCTP
association. This partitioning is necessary where an SG is logically
partitioned to appear as end node elements in multiple separate SS7
networks, in which case there is a separate network appearance for each
point code in the SS7 networks. It is also necessary when an SG is
configured as an STP hosting multiple point codes, or when configured
as multiple end nodes within the same network, in which case each point
code is a separate network appearance.between the SG and the
Application Server Processes over a common SCTP Association. An
example is where an SG is logically partitioned to appear as an element
in four separate national SS7 networks. A Network Appearance
implicitly defines the SS7 Point Code(s), Network Indicator and MTP3
protocol type/variant/version used within a separate SS7 network.
Network Byte Order: Most significant byte first, a.k.a Big Endian.
Layer Management - Layer Management is a nodal function that handles
the inputs and outputs between the M3UA layer and a local management
entity.
Host - The computing platform that the process (SGP, ASP or IPSP) is
running on.
Stream - A stream refers to an SCTP stream; a uni-directional logical
channel established from one SCTP endpoint to another associated SCTP
endpoint, within which all user messages are delivered in-sequence
except for those submitted to the un-ordered delivery service.
1.3 M3UA Overview
1.3.1 Protocol Architecture.
The framework architecture that has been defined for SCN signalling
transport over IP [1] uses multiple components, including a common
signalling transport protocol and an adaptation module to support the
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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 as an MTP User.
The list of these protocol layers include, but is not limited to, ISDN
User Part (ISUP) [2,3,4], Signalling Connection Control Part (SCCP)
[5,6,7] and Telephone User Part (TUP) [8]. TCAP [9,10,11] or RANAP [12]
messages are transferred transparently by the M3UA protocol as SCCP
payload, as they are SCCP-User protocols.
It is recommended that M3UA use the services of the Stream Control
Transmission Protocol (SCTP) [13] as the underlying reliable common
signalling transport protocol. This is to take advantage of various
SCTP features such as:
- Explicit packet-oriented delivery (not stream-oriented),
- Sequenced delivery of user messages within multiple streams,
with an option for order-of-arrival delivery of individual
user messages,
- Optional multiplexing of user messages into SCTP datagrams,
- Network-level fault tolerance through support of multi-homing
at either or both ends of an association,
- Resistance to flooding and masquerade attacks, and
- Data segmentation to conform to discovered path MTU size.
Under certain scenarios, such as back-to-back connections without
redundancy requirements, the SCTP functions above MAY NOT be a
requirement and TCP can be used as the underlying common transport
protocol.
1.3.2 Services Provided by the M3UA Layer
The M3UA Layer at an ASP or IPSP provides the equivalent set of
primitives at its upper layer to the MTP3-Users as provided by the MTP
Level 3 to its local MTP3-Users at an SS7 SEP. In this way, the ISUP
and/or SCCP layer at an ASP or IPSP is unaware that the expected MTP3
services are offered remotely from an MTP3 Layer at an SGP, and not by
a local MTP3 layer. The MTP3 layer at an SGP may also be unaware that
its local users are actually remote user parts over M3UA. In effect,
the M3UA extends access to the MTP3 layer services to a remote IP-based
application. The M3UA layer does not itself provide the MTP3 services.
However, in the case where an ASP is connected to more than one SGP,
the M3UA layer at an ASP should maintain the status of configured SS7
destinations and route messages according to the availability and
congestion status of the routes to these destinations via each SGP.
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The M3UA layer may also be used for point-to-point signalling between
two IP Server Processes (IPSPs). In this case, the M3UA layer provides
the same set of primitives and services at its upper layer as the MTP3.
However, in this case the expected MTP3 services are not offered
remotely from an SGP. The MTP3 services are provided but the
procedures to support these services are a subset of the MTP3
procedures due to the simplified point-to-point nature of the IPSP to
IPSP relationship.
1.3.2.1 Support for the Transport of MTP3-User Messages
The M3UA layer provides the transport of MTP-TRANSFER primitives across
an established SCTP association between an SGP and an ASP or between
IPSPs.
The MTP-TRANSFER primitive information is encoded as in MTP3-User
messages. In this way, the User Part messages received from the
SS7 network by the SGP are not re-encoded into a different format for
transport between the M3UA peers. The MTP3 Service Information Octet
(SIO) and Routing Label (OPC, DPC, and SLS) are included, encoded as
expected by the MTP3 and MTP3-User protocol layer.
At an ASP, in the case where a destination is reachable via multiple
SGPs, the M3UA layer must also choose via which SGP the message is to
be routed or support load balancing across the SGPs, ensuring that no
missequencing occurs.
The M3UA layer does not impose a 272-octet signalling information field
(SIF) length limit as specified by the SS7 MTP Level 2 protocol [14]
[15] [16]. Larger information blocks can be accommodated directly by
M3UA/SCTP, without the need for an upper layer segmentation/re-assembly
procedure as specified in recent SCCP or ISUP versions. However, in
the context of an SG, the maximum 272-octet block size must be followed
when inter-working to a SS7 network that does not support the transfer
of larger information blocks to the final destination. This avoids
potential ISUP or SCCP fragmentation requirements at the SGPs.
However, if the SS7 network is provisioned to support the Broadband MTP
[20] to the final SS7 destination, the information block size limit MAY
be increased past 272 octets.
1.3.2.2 Native Management Functions
The M3UA layer provides the capability to indicate errors associated
with received M3UA messages and to notify, as appropriate, local
management and/or the peer M3UA.
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1.3.2.3 Inter-working with MTP3 Network Management Functions
At the SGP, the M3UA layer must also provide inter-working with MTP3
management functions to support seamless operation of the user SCN
signalling applications in the SS7 and IP domains. This includes:
- Providing an indication to MTP3-Users at an ASP that a destination
in the SS7 network is not reachable.
- Providing an indication to MTP3-Users at an ASP that a destination
in the SS7 network is now reachable.
- Providing an indication to MTP3-Users at an ASP that messages to a
destination in the SS7 network are experiencing SS7 congestion.
- Providing an indication to the M3UA layer at an ASP that the routes
to a destination in the SS7 network are restricted.
- Providing an indication to MTP3-Users at an ASP that a MTP3-User
peer is unavailable.
The M3UA layer at an ASP keeps the state of the routes to remote SS7
destinations and may initiate an audit of the availability, the
restricted or the congested state of remote SS7 destinations. This
information is requested from the M3UA layer at the SGP.
The M3UA layer at an ASP may also indicate to the SG that the M3UA
layer itself or the ASP or the ASP's Host is congested.
1.3.2.4 Support for the Management of SCTP Associations between the SGP
and ASPs.
The M3UA layer at the SGP maintains the availability state of all
configured remote ASPs, to manage the SCTP Associations and
the traffic between the M3UA peers. As well, the active/inactive and
congestion state of remote ASPs is maintained.
The M3UA layer MAY be instructed by local management to establish an
SCTP association to a peer M3UA node. This can be achieved using the
M-SCTP_ESTABLISH primitives to request, indicate and confirm the
establishment of an SCTP association with a peer M3UA node. In order
to avoid redundant SCTP associations between two M3UA peers, one side
(client) SHOULD be designated to establish the SCTP association, or
M3UA configuration information maintained to detect redundant
associations (e.g., via knowledge of the expected local and remote SCTP
endpoint addresses).
Local management MAY request from the M3UA layer the status of the
underlying SCTP associations using the M-SCTP_STATUS request and
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confirm primitives. Also, the M3UA MAY autonomously inform local
management of the reason for the release of an SCTP association,
determined either locally within the M3UA layer or by a primitive from
the SCTP.
Also the M3UA layer MAY inform the local management of the change in
status of an ASP or AS. This MAY 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 SGPs
As shown in Figure 1 an ASP may be connected to multiple SGPs. In such
a case a particular SS7 destination may be reachable via more than one
SGP, i.e., via more than one route. As MTP3 users only maintain status
on a destination and not on a route basis, the M3UA layer must maintain
the status (availability, restriction, and/or congestion of route to
destination) of the individual routes, derive the overall availability
or congestion status of the destination from the status of the
individual routes, and inform the MTP3 users of this derived status
whenever it changes.
1.3.3 Signalling Network Architecture
A Signalling Gateway is used to support the transport of MTP3-User
signalling traffic received from the SS7 network to multiple
distributed ASPs (e.g., MGCs and IP Databases). Clearly, the M3UA
protocol is not designed to meet the performance and reliability
requirements for such transport by itself. However, the conjunction of
distributed architecture and redundant networks does allow for a
sufficiently reliable transport of signalling traffic over IP. The
M3UA protocol is flexible enough to allow its operation and management
in a variety of physical configurations, enabling Network Operators to
meet their performance and reliability requirements.
To meet the stringent SS7 signalling reliability and performance
requirements for carrier grade networks, Network Operators SHOULD
ensure that no single point of failure is present in the end-to-end
network architecture between an SS7 node and an IP-based application.
This can typically be achieved through the use of redundant SGPs or
SGs, redundant hosts, and the provision of redundant QOS-bounded IP
network paths for SCTP Associations between SCTP End Points. Obviously,
the reliability of the SG, the MGC and other IP-based functional
elements also needs to be taken into account. The distribution of ASPs
and SGPs within the available Hosts MAY also be considered. As an
example, for a particular Application Server, the related ASPs SHOULD
be distributed over at least two Hosts.
One example of a physical network architecture relevant to SS7 carrier-
grade operation in the IP network domain is shown in Figure 1 below:
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SG MGC
Host#1 ************** ************** Host#3
= * ********__*__________________________*__******** * =
* * SGP1 *__*_____ _______________*__* ASP1 * * MGC1
* ******** * \ / * ******** *
* ********__*______\__/________________*__******** *
* * SGP2 *__*_______\/______ _____*__* ASP2 * *
* ******** * /\ | | * ******** *
* : * / \ | | * : *
* ******** * / \ | | * ******** *
* * SGPn * * | | | | * * ASPn * *
* ******** * | | | | * ******** *
************** | | | | **************
| | \ /
Host#2 ************** | | \ / ************** Host#4
= * ********__*_____| |______\/_______*__******** * =
* * SGP1 *__*_________________/\_______*__* ASP1 * * MGC2
* ******** * / \ * ******** *
* ********__*_______________/ \_____*__******** *
* * SGP2 *__*__________________________*__* ASP2 * *
* ******** * * ******** *
* : * SCTP Associations * : *
* ******** * * ******** *
* * SGPn * * * * ASPn * *
* ******** * * ******** *
************** **************
Figure 1 - Physical Model
In this model, each host MAY have many application processes. In the
case of the MGC, an ASP may provide service to one or more Application
Servers, and is identified as an SCTP end point. A pair of Signalling
Gateway Processes MAY represent, as an example, a single Signalling
Gateway, serving a signalling point management cluster.
This example model can also be applied to IPSP-IPSP signalling. In
this case, each IPSP MAY have its services distributed across 2 hosts
or more, and may have multiple server processes on each host.
In the example above, each signalling process (SGP, ASP or IPSP) is the
end point to more than one SCTP association, leading to more than one
other signalling processes. To support this, a signalling process must
be able to support distribution of M3UA messages to many simultaneous
active associations. This message distribution function is based on
the status of provisioned Routing Keys, the status of the signalling
routes to signalling points in the SS7 network , and the redundancy
model (active-standby, load-sharing, broadcast, 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
For example, within an SS7 network, a Signalling Gateway might be
charged with representing a set of nodes in the IP domain into the SS7
network for routing purposes. The SG itself, as a signalling point in
the SS7 network, might also be addressable with an SS7 Point Code for
MTP3 Management purposes. The SG Point Code might also be used for
addressing any local MTP3-Users at the SG such as an SG-resident SCCP
function.
An SG may be logically partitioned to operate in multiple SS7 network
appearances. In such a case, the SG could be addressable with a Point
Code in each network appearance, and represents a set of nodes in the
IP domain into each SS7 network. Alias Point Codes [15] may also be
used within an SG network appearance.
Where an SG contains more than one SGP, the MTP3 routeset, SPMC and
remote AS/ASP states of each SGP SHOULD be coordinated across all the
SGPs. Re-routing of traffic between the SGPs SHOULD also be supported.
Application Servers can be represented under the same Point
Code of the SG, their own individual Point Codes or grouped with other
Application Servers for Point Code preservation purposes. A single
Point Code may be used to represent the SG and all the Application
Servers together, if desired.
If an ASP or group of ASPs is available to the SS7 network via more
than one SG, each with its own Point Code, the ASP(s) will typically be
represented by a Point Code that is separate from any SG Point Code.
This allows, for example, these SGs to be viewed from the SS7 network as
"STPs", each
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having an ongoing "route" to the same ASP(s). Under failure conditions
where the ASP(s) become(s) unavailable from one of the SGs, this
approach enables MTP3 route management messaging between the SG and SS7
network, allowing simple SS7 re-routing through an alternate SG without
changing the Destination Point Code Address of SS7 traffic to the
ASP(s).
Where an AS can be reached via more than one SGP the corresponding
Routing Keys in the involved SGPs should be identical. (Note: It is
possible for the SGP Routing Key configuration data to be temporarily
out-of-synch during configuration updates).
+--------+
| |
+------------+ SG 1 +--------------+
+-------+ | SS7 links | "STP" | IP network | ----
| SEP +---+ +--------+ +---/ \
| or | * | ASPs |
| STP +---+ +--------+ +---\ /
+-------+ | | | | ----
+------------+ SG 2 +--------------+
| "STP" |
+--------+
* Note:. SG-to -SG communication is recommended for carrier grade
networks, using an MTP3 linkset or an equivalent, to allow re-routing
between the SGs in the event of route failures. Where SGPs are used,
inter-SGP communication is recommended. Inter-SGP protocol is outside
of the scope of this document.
The following example shows a signalling gateway partitioned into two
network appearances.
SG
+-------+ +---------------+
| SEP +--------------| SS7 Ntwk |M3UA| ----
+-------+ SS7 links | "A" | | / \
|__________| +-----------+ ASPs |
| | | \ /
+-------+ | SS7 Ntwk | | ----
| SEP +--------------+ "B" | |
+-------+ +---------------+
1.4.2 Routing Contexts and Routing Keys
1.4.2.1 Overview
The distribution of SS7 messages between the SGP and the Application
Servers is determined by the Routing Keys and their associated Routing
Contexts. A Routing Key is essentially a set of SS7 parameters used to
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filter SS7 messages, whereas the Routing Context parameter is a 4-byte
value (integer) that is associated to that Routing Key in a 1:1
relationship. The Routing Context therefore can be viewed as an index
into a sending node's Message Distribution Table containing the Routing
Key entries.
Possible SS7 address/routing information that comprise a Routing Key
entry includes, for example, the OPC, DPC, SIO found in the MTP3
routing label, or MTP3-User specific fields (such 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 ASP Inactive management messages, the
signalling traffic to be started or stopped is discriminated by the
Routing Context parameter. At an ASP, the Routing Context parameter
uniquely identifies the range of signalling traffic associated with
each Application Server that the ASP is configured to receive.
1.4.2.2 Routing Key Limitations
Routing Keys SHOULD be unique in the sense that each received SS7
signalling message SHOULD have a full or partial match to a single
routing result to an Application Server. It is not necessary for the
parameter range values within a particular Routing Key to be contiguous.
For example, an AS could be configured to support call processing for
multiple ranges of PSTN trunks that are not represented by contiguous
CIC values.
1.4.2.3 Managing Routing Contexts and Routing Keys
There are two ways to provision a Routing Key at an SGP. A
Routing Key may be configured statically using an implementation
dependent management interface, or dynamically using the M3UA Routing
Key registration procedure.
When using a management interface to configure Routing Keys, the
message distribution function within the SGP is not limited to the set
of parameters defined in this document. Other implementation dependent
distribution algorithms may be used.
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1.4.2.4 Message Distribution at the SGP
To direct messages received from the SS7 MTP3 network to the
appropriate IP destination, the SGP must perform a message distribution
function using information from the received MTP3-User message.
To support this message distribution, the SGP might, for example,
maintain the equivalent of a network address translation table, mapping
incoming SS7 message information to an Application Server for a
particular application and range of traffic. This could be accomplished
by comparing elements of the incoming SS7 message to currently defined
Routing Keys in the SGP. These Routing Keys could in turn map directly
to an Application Server that is enabled by one or more ASPs. These
ASPs provide dynamic status information regarding their availability,
traffic handling capability and congestion to the SGP using various
management messages defined in the M3UA protocol.
The list of ASPs in an AS is assumed to be dynamic, taking into account
the availability, traffic handling capability and congestion status of
the individual ASPs in the list, as well as configuration changes and
possible fail-over mechanisms.
Normally, one or more ASPs are active (i.e., currently processing
traffic) in the AS but in certain failure and transition cases it is
possible that there may be no active ASP available. Broadcast, load-
sharing and backup scenarios are supported.
When there is no matching Routing Key entry for an incoming SS7
message, a default treatment MAY be specified. Possible solutions are
to provide a default Application Server at the SGP that directs all
unallocated traffic to a (set of) default ASP(s), or to drop the message
and provide a notification to layer management. The treatment of
unallocated traffic is implementation dependent.
1.4.2.5 Message Distribution at the ASP
The ASP must choose an SGP to direct a message to the SS7 network. This
is accomplished by observing the Destination Point Code (and possibly
other elements of the outgoing message such as the SLS value).
Implementation Note: Where more than one route (or SGP) is
possible for routing to the SS7 network, the ASP could, for example,
maintain a dynamic table of available SGP routes for the SS7
destinations, taking into account the SS7 destination
availability/restricted/congestion status received from the SGP(s), the
availability status of the individual SGPs and configuration changes and
fail-over mechanisms. There is, however, no M3UA messaging to manage the
status of an SGP (e.g., SGP-Up/Down/Active/Inactive messaging).
Whenever an SCTP
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association to an SGP exists, the SGP is assumed to be ready for the
purposes of responding to M3UA ASPSM messages (Refer to Section 3).
Every SGP of one SG ASP regarding one AS provides identical SS7
connectivity to this ASP.
1.4.3 SS7 and M3UA Interworking
In the case of SS7 and M3UA inter-working, the M3UA adaptation layer is
designed to provide an extension of the MTP3 defined user primitives.
1.4.3.1 Signalling Gateway SS7 Layers
The SG is responsible for terminating MTP Level 3 of the SS7 protocol,
and offering an IP-based extension to its users.
>From an SS7 perspective, it is expected that the Signalling Gateway
transmits and receives SS7 Message Signalling Units (MSUs) to and
from the PSTN over a standard SS7 network interface, using the SS7
Message Transfer Part (MTP) [14,15,16] to provide reliable transport of
the messages.
As a standard SS7 network interface, the use of MTP Level 2 signalling
links is not the only possibility. ATM-based High Speed Links can also
be used with the services of the Signalling ATM Adaptation Layer (SAAL)
[17,18].
Note: It is also possible for IP-based interfaces to be present, using
the services of the MTP2-User Adaptation Layer (M2UA) [26] or M2PA [27].
These could be terminated at a Signalling Transfer Point (STP) or
Signalling End Point (SEP). Using the services of MTP3, the SG could be
capable of communicating with remote SS7 SEPs in a quasi-associated
fashion, where STPs may be present in the SS7 path between the SEP and
the SG.
1.4.3.2 SS7 and M3UA Inter-Working at the SG
The SGP provides a functional inter-working of transport functions
between the SS7 network and the IP network by also supporting the M3UA
adaptation layer. It allows the transfer of MTP3-User signalling
messages to and from an IP-based Application Server Process where the
peer MTP3-User protocol layer exists.
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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.
MTP3 management messages (such as TFPs or TFAs received from the SS7
network) MUST NOT be encapsulated as Data message Payload Data and sent
either from SG to ASP or from ASP to SG. The SG MUST terminate these
messages and generate M3UA messages as appropriate.
1.4.3.3 Application Server
A cluster of application servers is responsible for providing the
overall support for one or more SS7 upper layers. From an SS7
standpoint, a Signalling Point Management Cluster (SPMC) provides
complete support for the upper layer service for a given point code.
As an example, an SPMC providing MGC capabilities could provide complete
support for ISUP (and any other MTP3 user located at the point code of
the SPMC) for a given point code.
In the case where an ASP is connected to more than one SGP, the M3UA
layer must maintain the status of configured SS7 destinations and route
messages according to availability/congestion/restricted status of the
routes to these SS7 destinations.
1.4.3.4 IPSP Considerations
Since IPSPs use M3UA in a point-to-point fashion, there is no concept
of routing of messages beyond the remote end. Therefore, SS7 and M3UA
inter-working is not necessary for this model.
1.4.4 Redundancy Models
1.4.4.1 Application Server Redundancy
All MTP3-User messages (e.g., ISUP, SCCP) which match a provisioned
Routing Key at an SGP are mapped to an Application Server.
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The Application Server is the set of all ASPs associated with a specific
Routing Key. Each ASP in this set may be active inactive or unavailable.
Active ASPs handle traffic; inactive ASPs might be used when active ASPs
become unavailable.
The fail-over model supports an "n+k" redundancy model, where "n" ASPs
is the minimum number of redundant ASPs required to handle traffic and
"k" ASPs are available to take over for a failed or unavailable ASP. A
"1+1" active/back-up redundancy is a subset of this model. A simplex
"1+0" model is also supported as a subset, with no ASP redundancy.
At the SGP, an Application Server list contains active and inactive
ASPs to support ASP broadcast, load-sharing and fail-over procedures.
The list of ASPs within a logical Application Server is kept updated in
the SGP to reflect the active Application Server Process(es).
For example, in the network shown in Figure 1, all messages to DPC x
could be sent to ASP1 in Host3 or ASP1 in Host4. The AS list at SGP1 in
Host 1 might look like the following:
Routing Key {DPC=x) - "Application Server #1"
ASP1/Host3 - State = Active
ASP1/Host4 - State = Inactive
In this "1+1" redundancy case, ASP1 in Host3 would be sent any incoming
message with DPC=x. ASP1 in Host4 would normally be brought to the
"active" state upon failure of, or loss of connectivity to, ASP1/Host1.
The AS List at SGP1 in Host1 might also be set up in load-share mode:
Routing Key {DPC=x) - "Application Server #1"
ASP1/Host3 - State = Active
ASP1/Host4 - State = Active
In this case, both the ASPs would be sent a portion of the traffic.
For example the two ASPs could together form a database, where incoming
queries may be sent to any active ASP.
Care might need to be exercised by a Network Operator in the selection
of the routing information to be used as the Routing Key for a
particular AS.
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For example, where Application Servers are defined using ranges of ISUP
CIC values, the Operator is implicitly splitting up control of the
related circuit groups. Some CIC value range assignments may interfere
with ISUP circuit group management procedures.
In the process of fail-over, it is recommended that in the case of ASPs
supporting call processing, stable calls do not fail. It is possible
that calls in "transition" MAY fail, although measures of communication
between the ASPs involved can be used to mitigate this. For example,
the two ASPs MAY share call state via shared memory, or MAY use an ASP
to ASP protocol to pass call state information. Any ASP-to-ASP
protocol to support this function is outside the scope of this
document.
1.4.4.2 Signalling Gateway Redundancy
Signalling Gateways MAY also be distributed over multiple hosts. Much
like the AS model, SGs may comprise one or more SG Processes (SGPs),
distributed over one or more hosts, using an active/back-up or a load-
sharing model. Also, every SGP within an SG communicating with an ASP
provides identical SS7 connectivity to this ASP. Should an SGP lose all
or partial SS7 connectivity and other SGPs exist, the SGP MUST
terminate the SCTP associations to the concerned ASPs.
It is therefore possible for an ASP to route signalling messages
destined to the SS7 network using more than one SGP. In this model, a
Signalling Gateway is deployed as a cluster of hosts acting as a single
SG. A primary/back-up redundancy model is possible, where the
unavailability of the SCTP association to a primary SGP could be used
to reroute affected traffic to an alternate SGP. A load-sharing model
is possible, where the signalling messages are load-shared between
multiple SGPs. A broadcast model is also possible, where signalling
messages are sent to each active SGP in the SG. The distribution of the
MTP3-user messages over the SGPs should be done in such a way to
minimize message mis-sequencing, as required by the SS7 User Parts.
It may also be possible for an ASP to use more than one SG to access a
specific SS7 end point, in a model that resembles an SS7 STP mated
pair. Typically, SS7 STPs are deployed in mated pairs, with traffic
load-shared between them. Other models are also possible, subject to
the limitations of the local SS7 network provisioning guidelines.
>From the perspective of the M3UA layer at an ASP, a particular SG is
capable of transferring traffic to an SS7 destination if an SCTP
association with at least one SGP of the SG is established, the SGP has
returned an acknowledgement to the ASP to indicate that the ASP is
actively handling traffic for that destination, and the SGP has not
indicated that the destination is inaccessible. When an ASP is
configured to use multiple SGPs for transferring traffic to the SS7
network, the ASP must maintain knowledge of the current capability of
the SGPs to handle traffic to destinations of interest. This
information is crucial to the overall reliability of the service, for
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active/back-up, load-sharing and broadcast models, in the event of
failures, recovery and maintenance activities. The ASP M3UA may also
use this information for congestion avoidance purposes. The
distribution of the MTP3-user messages over the SGPs should be done in
such a way to minimize message mis-sequencing, as required by the SS7
User Parts.
1.4.5 Flow Control
Local Management at an ASP may wish to stop traffic across an SCTP
association to temporarily remove the association from service
or to perform testing and maintenance activity. The function could
optionally be used to control the start of traffic on to a newly
available SCTP association.
1.4.6 Congestion Management
The M3UA layer is informed of local and IP network congestion by means
of an implementation-dependent function (e.g., an implementation-
dependent indication from the SCTP of IP network congestion).
At an ASP or IPSP, the M3UA layer indicates congestion to local MTP3-
Users by means of an MTP-STATUS primitive, as per current MTP3
procedures, to invoke appropriate upper layer responses.
When an SG determines that the transport of SS7 messages to a
Signalling Point Management Cluster (SPMC) is encountering congestion,
the SG MAY trigger SS7 MTP3 Transfer Controlled management messages
to originating SS7 nodes, per the congestion procedures of the relevant
MTP3 standard. The triggering of SS7 MTP3 Management messages from an
SG is an implementation-dependent function.
The M3UA layer at an ASP or IPSP MAY indicate local congestion to an
M3UA peer with an SCON message. When an SG receives a congestion
message (SCON) from an ASP, and the SG determines that an SPMC is now
encountering congestion, it MAY trigger SS7 MTP3 Transfer Controlled
management messages to concerned SS7 destinations according to
congestion procedures of the relevant MTP3 standard.
1.4.7 SCTP Stream Mapping.
The M3UA layer at both the SGP and ASP also supports the assignment of
signalling traffic into streams within an SCTP association. Traffic
that requires sequencing SHOULD be assigned to the same stream. To
accomplish this, MTP3-User traffic may be assigned to individual
streams based on, for example, the SLS value in the MTP3 Routing Label
or the ISUP CIC assignment, subject of course to the maximum number of
streams supported by the underlying SCTP association.
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1.4.8 Client/Server Model
It is recommended that the SGP and ASP be able to support both client
and server
operation. The peer endpoints using M3UA SHOULD be configured so that
one always
takes on the role of client and the other the role of server for
initiating SCTP
associations. The default orientation would be for the SGP to take on
the role
of server while the ASP is the client. In this case, ASPs SHOULD
initiate the
SCTP association to the SGP
In the case of IPSP to IPSP communication, the peer endpoints using
M3UA SHOULD be configured so that one always takes on the role of
client and the other the role of server for initiating SCTP
associations.
The SCTP Registered User Port Number Assignment for M3UA is 2905.
1.5 Sample Configurations
1.5.1 Example 1: ISUP Message Transport
******** SS7 ***************** IP ********
* SEP *---------* SGP *--------* ASP *
******** ***************** ********
+------+ +---------------+ +------+
| ISUP | | (NIF) | | ISUP |
+------+ +------+ +------+ +------+
| MTP3 | | MTP3 | | M3UA | | M3UA |
+------| +------+-+------+ +------+
| MTP2 | | MTP2 | | SCTP | | SCTP |
+------+ +------+ +------+ +------+
| L1 | | L1 | | IP | | IP |
+------+ +------+ +------+ +------+
|_______________| |______________|
SEP - SS7 Signalling End Point
SCTP - Stream Control Transmission Protocol
NIF - Nodal Inter-working Function
In this example, the SGP provides an implementation-dependent nodal
inter-working function (NIF) that allows the MGC to exchange SS7
signalling messages with the SS7-based SEP. The NIF within the SGP
serves as the interface within the SGP between the MTP3 and M3UA. This
nodal inter-working function has no visible peer protocol with either
the MGC or SEP. It also provides network status information to one or
both sides of the network.
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For internal SGP modeling purposes, at the NIF level, SS7 signalling
messages that are destined to the MGC are received as MTP-TRANSFER
indication primitives from the MTP Level 3 upper layer interface,
translated to MTP-TRANSFER request primitives, and sent to the local
M3UA-resident message distribution function for ongoing routing to the
final IP destination. Messages received from the local M3UA network
address translation and mapping function as MTP-TRANSFER indication
primitives are sent to the MTP Level 3 upper layer interface as MTP-
TRANSFER request primitives for on-going MTP Level 3 routing to an SS7
SEP. For the purposes of providing SS7 network status information the
NIF also delivers MTP-PAUSE, MTP-RESUME and MTP-STATUS indication
primitives received from the MTP Level 3 upper layer interface to the
local M3UA-resident management function. In addition, as an
implementation and network option, restricted destinations are
communicated from MTP network management to the local M3UA-resident
management function.
1.5.2 Example 2: SCCP Transport between IPSPs
******** IP ********
* IPSP * * IPSP *
******** ********
+------+ +------+
|SCCP- | |SCCP- |
| User | | User |
+------+ +------+
| SCCP | | SCCP |
+------+ +------+
| M3UA | | M3UA |
+------+ +------+
| SCTP | | SCTP |
+------+ +------+
| IP | | IP |
+------+ +------+
|________________|
This example shows an architecture where no Signalling Gateway is used.
In this example, SCCP messages are exchanged directly between two IP-
resident IPSPs with resident SCCP-User protocol instances, such as
RANAP or TCAP. SS7 network inter-working is not required, therefore
there is no MTP3 network management status information for the SCCP and
SCCP-User protocols to consider. Any MTP-PAUSE, MTP-RESUME or MTP-
STATUS indications from the M3UA layer to the SCCP layer should
consider the status of the SCTP Association and underlying IP network
and any congestion information received from the remote site.
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1.5.3 Example 3: SGP Resident SCCP Layer, with Remote ASP
******** SS7 ***************** IP ********
* SEP *---------* *--------* *
* or * * SGP * * ASP *
* STP * * * * *
******** ***************** ********
+------+ +---------------+ +------+
| SCCP-| | SCCP | | SCCP-|
| User | +---------------+ | User |
+------+ | _____ | +------+
| SCCP | | | | | | SCCP |
+------+ +------+-+------+ +------+
| MTP3 | | MTP3 | | M3UA | | M3UA |
+------| +------+ +------+ +------+
| MTP2 | | MTP2 | | SCTP | | SCTP |
+------+ +------+ +------+ +------+
| L1 | | L1 | | IP | | IP |
+------+ +------+ +------+ +------+
|_______________| |______________|
STP - SS7 Signalling Transfer Point
In this example, the SGP contains an instance of the SS7 SCCP protocol
layer that may, for example, perform the SCCP Global Title Translation
(GTT) function for messages logically addressed to the SG SCCP. If the
result of a GTT for an SCCP message yields an SS7 DPC or DPC/SSN
address of an SCCP peer located in the IP domain, the resulting MTP-
TRANSFER request primitive is sent to the local M3UA-resident network
address translation and mapping function for ongoing routing to the
final IP destination.
Similarly, the SCCP instance in an SGP can perform the SCCP GTT service
for messages logically addressed to it from SCCP peers in the IP
domain. In this case, MTP-TRANSFER indication primitives are sent from
the local M3UA-resident network address translation and mapping
function to the SCCP for GTT. If the result of the GTT yields the
address of an SCCP peer in the SS7 network then the resulting MTP-
TRANSFER request primitive is given to the MTP3 for delivery to an SS7-
resident node.
It is possible that the above SCCP GTT at the SGP could yield the
address of an SCCP peer in the IP domain and the resulting MTP-TRANSFER
request primitive would be sent back to the M3UA layer for delivery to
an IP destination.
For internal SGP modeling purposes, this may be accomplished with the
use of an implementation-dependent nodal inter-working function within
the SGP that effectively sits below the SCCP and routes MTP-TRANSFER
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request/indication messages to/from both the MTP3 and the M3UA layer,
based on the SS7 DPC or DPC/SSN address information. This nodal inter-
working function has no visible peer protocol with either the ASP or
SEP.
Note that the services and interface provided by the M3UA layer are the
same as in Example 1 and the functions taking place in the SCCP entity
are transparent to the M3UA layer. The SCCP protocol functions are not
reproduced in the M3UA protocol.
1.6 Definition of M3UA Boundaries
1.6.1 Definition of the Boundary between M3UA and an MTP3-User.
>From ITU Q.701 [14]:
MTP-TRANSFER request
MTP-TRANSFER indication
MTP-PAUSE indication
MTP-RESUME indication
MTP-STATUS indication
1.6.2 Definition of the Boundary between M3UA and SCTP
An example of the upper layer primitives provided by the SCTP are
provided in Reference [13] Section 10.
1.6.3 Definition of the Boundary between M3UA and Layer Management
M-SCTP_ESTABLISH request
Direction: LM -> M3UA
Purpose: LM requests ASP to establish an SCTP association with its
peer.
M-STCP_ESTABLISH confirm
Direction: M3UA -> LM
Purpose: ASP confirms to LM that it has established an SCTP
association with its peer.
M-SCTP_ESTABLISH indication
Direction: M3UA -> LM
Purpose: M3UA informs LM that a remote ASP has established an SCTP
association.
M-SCTP_RELEASE request
Direction: LM -> M3UA
Purpose: LM requests ASP to release an SCTP association with its
peer.
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M-SCTP_RELEASE confirm
Direction: M3UA -> LM
Purpose: ASP confirms to LM that it has released SCTP association
with its peer.
M-SCTP_RELEASE indication
Direction: M3UA -> LM
Purpose: M3UA informs LM that a remote ASP has released an SCTP
Association or the SCTP association has failed.
M-SCTP RESTART indication
Direction: M3UA -> LM
Purpose: M3UA informs LM that an SCTP restart indication has been
received.
M-SCTP_STATUS request
Direction: LM -> M3UA
Purpose: LM requests M3UA to report the status of an SCTP
association.
M-SCTP_STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA responds with the status of an SCTP association.
M-SCTP STATUS indication
Direction: M3UA -> LM
Purpose: M3UA reports the status of an SCTP association.
M-ASP_STATUS request
Direction: LM -> M3UA
Purpose: LM requests M3UA to report the status of a local or remote
ASP.
M-ASP_STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA reports status of local or remote ASP.
M-AS_STATUS request
Direction: LM -> M3UA
Purpose: LM requests M3UA to report the status of an AS.
M-AS_STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA reports the status of an AS.
M-NOTIFY indication
Direction: M3UA -> LM
Purpose: M3UA reports that it has received a Notify message
from its peer.
M-ERROR indication
Direction: M3UA -> LM
Purpose: M3UA reports that it has received an Error message from
its peer or that a local operation has been unsuccessful.
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M-ASP_UP request
Direction: LM -> M3UA
Purpose: LM requests ASP to start its operation and send an ASP Up
message to its peer.
M-ASP_UP confirm
Direction: M3UA -> LM
Purpose: ASP reports that is has received an ASP UP Ack message from
its peer.
M-ASP_UP indication
Direction: M3UA -> LM
Purpose: M3UA reports it has successfully processed an incoming ASP
Up message from its peer.
M-ASP_DOWN request
Direction: LM -> M3UA
Purpose: LM requests ASP to stop its operation and send an ASP-Down
message to its peer.
M-ASP_DOWN confirm
Direction: M3UA -> LM
Purpose: ASP reports that is has received an ASP Down
Ack message from its peer.
M-ASP_DOWN indication
Direction: M3UA -> LM
Purpose: M3UA reports it has successfully processed an incoming ASP
Down message from its peer, or the SCTP association has
been lost/reset.
M-ASP_ACTIVE request
Direction: LM -> M3UA
Purpose: LM requests ASP to send an ASP Active message to its peer.
M-ASP_ACTIVE confirm
Direction: M3UA -> LM
Purpose: ASP reports that is has received an ASP Active
Ack message from its peer.
M-ASP_ACTIVE indication
Direction: M3UA -> LM
Purpose: M3UA reports it has successfully processed an incoming ASP
Active message from its peer.
M-ASP_INACTIVE request
Direction: LM -> M3UA
Purpose: LM requests ASP to send an ASP Inactive message to its
peer.
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M-ASP_INACTIVE confirm
Direction: LM -> M3UA
Purpose: ASP reports that is has received an ASP Inactive
Ack message from its peer.
M-ASP_INACTIVE indication
Direction: M3UA -> LM
Purpose: M3UA reports it has successfully processed an incoming ASP
Inactive message from its peer.
M-AS_ACTIVE indication
Direction: M3UA -> LM
Purpose: M3UA reports that an AS has moved to the AS-ACTIVE state.
M-AS_INACTIVE indication
Direction: M3UA -> LM
Purpose: M3UA reports that an AS has moved to the AS-INACTIVE state.
M-AS_DOWN indication
Direction: M3UA -> LM
Purpose: M3UA reports that an AS has moved to the AS-DOWN state.
If dynamic registration of RK is supported by the M3UA layer, the layer
MAY support the following additional primitives:
M-RK_REG request
Direction: LM -> M3UA
Purpose: LM requests ASP to register RK(s) with its peer by sending
REG REQ message
M-RK_REG confirm
Direction: M3UA -> LM
Purpose: ASP reports that it has received REG RSP message with
registration status as successful from its peer.
M-RK_REG indication
Direction: M3UA -> LM
Purpose: M3UA informs LM that it has successfully processed an
incoming REG REQ message.
M-RK_DEREG request
Direction: LM -> M3UA
Purpose: LM requests ASP to de-register RK(s) with its peer by
sending DEREG REQ message.
M-RK_DEREG confirm
Direction: M3UA -> LM
Purpose: ASP reports that it has received DEREG REQ message with de-
registration status as successful from its peer.
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M-RK_DEREG indication
Direction: M3UA -> LM
Purpose: M3UA informs LM that it has successfully processed an
incoming DEREG REQ from its peer.
2.0 Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD
NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they appear
in this document, are to be interpreted as described in [RFC2119].
3. M3UA Protocol Elements
The general M3UA message format includes a Common Message Header
followed by zero or more parameters as defined by the Message Type.
For forward compatibility, all Message Types may have attached
parameters even if none are specified in this version.
3.1 Common Message Header
The protocol messages for MTP3-User Adaptation require a message header
which contains the adaptation layer version, the message type, and
message length.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Reserved | Message Class | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ /
All fields in an M3UA message MUST be transmitted in the network byte
order, unless otherwise stated.
3.1.1 M3UA Protocol Version: 8 bits (unsigned integer)
The version field contains the version of the M3UA adaptation layer.
The supported versions are the following:
1 Release 1.0
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3.1.2 Message Classes and Types
The following list contains the valid Message Classes:
Message Class: 8 bits (unsigned integer)
The following list contains the valid Message Type Classes:
0 Management (MGMT) Message
1 Transfer Messages
2 SS7 Signalling Network Management (SSNM) Messages
3 ASP State Maintenance (ASPSM) Messages
4 ASP Traffic Maintenance (ASPTM) Messages
5 Reserved for Other Sigtran Adaptation Layers
6 Reserved for Other Sigtran Adaptation Layers
7 Reserved for Other Sigtran Adaptation Layers
8 Reserved for Other Sigtran Adaptation Layers
9 Routing Key Management (RKM) Messages
10 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined Message Class extensions
Message Type: 8 bits (unsigned integer)
The following list contains the message types for the defined
messages.
Management (MGMT) Messages (See Section 3.6)
0 Error (ERR)
1 Notify (NTFY)
2 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined MGMT extensions
Transfer Messages (See Section 3.3)
0 Reserved
1 Payload Data (DATA)
2 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined Transfer extensions
SS7 Signalling Network Management (SSNM) Messages (See Section
3.4)
0 Reserved
1 Destination Unavailable (DUNA)
2 Destination Available (DAVA)
3 Destination State Audit (DAUD)
4 SS7 Network Congestion (SCON)
5 Destination User Part Unavailable (DUPU)
6 Destination Restricted (DRST)
7 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined SSNM extensions
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ASP State Maintenance (ASPSM) Messages (See Section 3.5)
0 Reserved
1 ASP Up (ASPUP)
2 ASP Down (ASPDN)
3 Heartbeat (BEAT)
4 ASP Up Acknowledgement (ASPUP ACK)
5 ASP Down Acknowledgement (ASPDN ACK)
6 Heatbeat Acknowledgement (BEAT ACK)
7 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined ASPSM extensions
ASP Traffic Maintenance (ASPTM) Messages (See Section 3.5)
0 Reserved
1 ASP Active (ASPAC)
2 ASP Inactive (ASPIA)
3 ASP Active Acknowledgement (ASPAC ACK)
4 ASP Inactive Acknowledgement (ASPIA ACK)
5 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined ASPTM extensions
Routing Key Management (RKM) Messages (See Section 3.7)
0 Reserved
1 Registration Request (REG REQ)
2 Registration Response (REG RSP)
3 Deregistration Request (DEREG REQ)
4 Deregistration Response (DEREG RSP)
5 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined RKM extensions
3.1.3 Reserved: 8 bits
The Reserved field SHOULD be set to all '0's and ignored by the
receiver.
3.1.4 Message Length: 32-bits (unsigned integer)
The Message Length defines the length of the message in octets,
including the Common Header. For messages with a final parameter
containing padding, the parameter padding MUST be included in the
Message Length.
Note: A receiver SHOULD accept the message whether or not the final
parameter padding is included in the message length.
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3.2 Variable-Length Parameter Format
M3UA messages consist of a Common Header followed by zero or more
variable length parameters, as defined by the message type. All the
parameters contained in a message are defined in a Tag-Length-Value
format as shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Tag | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Parameter Value /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where more than one parameter is included in a message, the parameters
may be in any order, except where explicitly mandated. A receiver
SHOULD accept the parameters in any order.
Parameter Tag: 16 bits (unsigned integer)
The Tag field is a 16-bit identifier of the type of parameter. It
takes a value of 0 to 65534. Common parameters used by adaptation
layers are in the range of 0x00 to 0x3f. M3UA-specific parameters
have Tags in the range 0x0200 to 0x02ff. The parameter Tags defined
are as follows:
0x0000 Reserved
0x0200 Network Appearance
0x0201 Protocol Data 1
0x0202 Protocol Data 2
0x0004 INFO String
0x0203 Affected Destinations
0x0006 Routing Context
0x0007 Diagnostic Information
0x0009 Heartbeat Data
0x0204 User/Cause
0x000a Reason
0x000b Traffic Mode Type
0x000c Error Code
0x000d Status
0x000e ASP Identifier
0x0205 Congestion Indications
0x0206 Concerned Destination
0x0207 Routing Key
0x0208 Registration Result
0x0209 De-registration Result
0x020a Local_Routing Key Identifier
0x020b Destination Point Code
0x020c Service Indicators
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0x02 Subsystem Numbers
0x020e Originating Point Code List
0x020f Circuit Range
0x0210 to 0xffff...Reserved by the IETF
The value of 65535 is reserved for IETF-defined extensions. Values
other than those defined in specific parameter description are
reserved for use by the IETF.
Parameter Length: 16 bits (unsigned integer)
The Parameter Length field contains the size of the parameter in
bytes, including the Parameter Tag, Parameter Length, and Parameter
Value fields. The Parameter Length does not include any padding
bytes.
Parameter Value: variable-length.
The Parameter Value field contains the actual information to be
transferred in the parameter.
The total length of a parameter (including Tag, Parameter Length and
Value fields) MUST be a multiple of 4 bytes. If the length of the
parameter is not a multiple of 4 bytes, the sender pads the
Parameter at the end (i.e., after the Parameter Value field) with
all zero bytes. The length of the padding is NOT included in the
parameter length field. A sender SHOULD NOT pad with more than 3
bytes. The receiver MUST ignore the padding bytes.
3.3 Transfer Messages
The following section describes the Transfer messages and parameter
contents.
3.3.1 Payload Data Message (DATA)
The DATA message contains the SS7 MTP3-User protocol data, which is an
MTP-TRANSFER primitive, including the complete MTP3 Routing Label. The
DATA message contains the following variable length parameters:
Network Appearance Optional
Protocol Data 1 or 2 Mandatory
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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 = 0x0200 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0201 or 0x0202 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Protocol Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance: 32-bits (unsigned integer)
The optional Network Appearance parameter identifies the SS7 network
context for the message, for the purposes of logically separating
the signalling traffic between the SGP and the ASP over a common
SCTP association. An example is where an SG is logically
partitioned to appear as an element in four different national SS7
networks.
In a DATA message, the Network Appearance implicitly defines the SS7
Point Code format used, the SS7 Network Indicator value, and the
MTP3 and possibly the MTP3-User protocol type/variant/version used
within the specific SS7 network. Where an SG operates in the
context of a single SS7 network, or individual SCTP associations
are dedicated to each SS7 network context, the Network Appearance
parameter is not required. In other cases the parameter MUST be
included.
The Network Appearance parameter value is of local significance
only, coordinated between the SGP and ASP. Therefore, in the case
where an ASP is connected to more than one SGP, the same SS7 network
context may be identified by different Network Appearance values
depending over which SGP a message is being transmitted/received.
Where the optional Network Appearance parameter is present, it must
be the first parameter in the message as it defines the format of
the Protocol Data field
One of two possible Protocol Data parameters are included in a DATA
message: Protocol Data 1 or Protocol Data 2.
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Protocol Data 1 or 2: variable length
The Protocol Data 1 parameter contains the original SS7 MTP3
message, including the Service Information Octet and Routing Label.
The Protocol Data 1 parameter contains the following fields:
Service Information Octet. Includes:
Service Indicator,
Network Indicator,
and Spare/Priority codes.
Routing Label. Includes:
Destination Point Code,
Originating Point Code,
And Signalling Link Selection Code (SLS).
User Protocol Data. Includes:
MTP3-User protocol elements (e.g., ISUP, SCCP, or TUP
parameters).
The Protocol Data 2 parameter contains all the information in
Protocol Data 1 as described above, plus the MTP2 Length Indicator
octet. The MTP2 Length Indicator (LI) octet appears before the SIO
and Routing Label information. The MTP2 Length Indicator octet is
required for some national MTP variants that use the spare bits in
the LI to carry additional information of interest to the MTP3 and
MTP3-User (e.g., the Japan TTC standard use of LI spare bits to
indicate message priority)
The Payload Data format is as defined in the relevant MTP standards
for the SS7 protocol being transported. The format is either
implicitly known or identified by the Network Appearance parameter.
Note: In the SS7 Recommendations, the format of the messages and
fields within the messages are based on bit transmission order. In
these recommendations the Least Significant Bit (LSB) of each field
is positioned to the right. The received SS7 fields are populated
octet by octet as received into the 4-octet word as shown in the two
examples below.
For the ANSI protocol example, the Protocol Data 1 field format is
shown below:
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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 (with the 3/8/3 Point
Code format), the Protocol Data 1 field is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SIO | DPC | DPC |OPC| DPC | DPC | OPC |@|
| | Region *| SP *|SP*|Zone*| reg.| Region *| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLS | OPC |$| Protocol |
| *|Zone*| | Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* marks LSB of each field; @ = OPC SP MSB; $ = OPC region MSB
3.4 SS7 Signalling Network Management (SSNM) Messages
3.4.1 Destination Unavailable (DUNA)
The DUNA message is sent from all SGPs in an SG to all concerned ASPs
to indicate that the SG has determined that one or more SS7
destinations are unreachable. It is also sent by an SGP in response to
a message from the ASP to an unreachable SS7 destination. As an
implementation option the SG may suppress the sending of subsequent
"response" DUNA messages regarding a certain unreachable SS7
destination for a certain period to give the remote side time
to react. The MTP3-User at the ASP is expected to stop traffic to the
affected destination through the SGPs initiating the DUNA message as
per the defined MTP3-User procedures.
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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 = 0x0200 | Length =8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0203 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected DPC 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected DPC n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance: 32-bit unsigned integer
See Section 3.3.1
Affected Destinations: n x 32-bits
The Affected Destinations parameter contains up to sixteen Affected
Destination Point Code fields, each a three-octet parameter to allow
for 14-, 16- and 24-bit binary formatted SS7 Point Codes. Affected
Point Codes that are less than 24-bits, are padded on the left to
the 24-bit boundary. The encoding is shown below for ANSI and ITU
Point Code examples.
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ANSI 24-bit Point Code:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Network | Cluster | Member |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB-----------------------------------------LSB|
ITU 14-bit Point Code:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask |0 0 0 0 0 0 0 0 0 0|Zone | Region | SP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB--------------------LSB|
It is optional to send an Affected Destinations parameter with more
than one Affected DPC but it is mandatory to receive and process it.
All the Affected DPCs included must be within the same Network
Appearance. Including multiple Affected DPCs may be useful when
reception of an MTP3 management message or a linkset event
simultaneously affects the availability status of a list of
destinations at an SG.
Mask: 8-bits (unsigned integer)
The Mask field associated with each Affected DPC in the Affected
Destinations parameter, used to identify a contiguous range of
Affected Destination Point Codes, independent of the point code
format. Identifying a contiguous range of Affected DPCs may be
useful when reception of an MTP3 management message or a linkset
event simultaneously affects the availability status of a series of
destinations at an SG. For example, if all DPCs in an ANSI cluster
are determined to be unavailable due to local linkset
unavailability, the DUNA could identify potentially 256 Affected
DPCs in a single Affected DPC field.
The Mask parameter represents a bit mask that can be applied to the
related Affected DPC field. The bit mask identifies how many bits
of the Affected DPC field are significant and which are effectively
"wildcarded". For example, a mask of "8" indicates that the least
significant eight bits of the DPC is "wildcarded". For an ANSI 24-
bit Affected DPC, this is equivalent to signalling that all DPCs in
an ANSI Cluster are unavailable. A mask of "3" indicates that the
least significant three bits of the DPC is "wildcarded". For a 14-
bit ITU Affected DPC, this is equivalent to signaling that an ITU
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Region is unavailable. A mask value equal to the number of bits in
the DPC indicates that the entire network appearance is affected -
this is used to indicate network isolation to the ASP.
INFO String: variable length
The optional INFO String parameter can carry any 8-bit ASCII
character string along with the message. Length of the INFO
String parameter is from 0 to 255 characters. No procedures are
presently identified for its use but the INFO String MAY be used by
Operators to identify in text form the location reflected by the
Affected DPC for debugging purposes.
3.4.2 Destination Available (DAVA)
The DAVA message is sent from the SGP to all concerned ASPs to indicate
that the SG has determined that one or more SS7 destinations are now
reachable (and not restricted), or in response to a DAUD message if
appropriate. The ASP MTP3-User protocol is informed and may now resume
traffic to the affected destination. The ASP M3UA layer routes the
MTP3_user traffic through the SGP(s) initiating the DAVA message.
The DAVA message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
INFO String Optional
The format and description of the Network Appearance, Affected
Destinations and INFO String parameters is the same as for the DUNA
message (See Section 3.4.1).
3.4.3 Destination State Audit (DAUD)
The DAUD message MAY be sent from the ASP to the SGP to audit the
availability/congestion state of SS7 routes to one or more affected
destinations.
The DAUD message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
INFO String Optional
The format and description of DAUD Message parameters is the same as
for the DUNA message (See Section 3.4.1).
3.4.4 SS7 Network Congestion (SCON)
The SCON message can be sent from the SGP to all concerned ASPs to
indicate congestion in the SS7 network to one or more destinations, or
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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 message may be
sent when the SS7 congestion level changes. The SCON message MAY also
be sent from the M3UA layer of an ASP to an M3UA peer indicating that
the M3UA layer or the ASP is congested.
The SCON message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
Concerned Destination Optional
Congestion Indications Optional
INFO String Optional
The format for SCON Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0200 | Length =8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0203 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected DPC 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected DPC n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0206 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved | Concerned DPC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0205 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Cong. Level |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the Network Appearance, Affected
Destinations, and INFO String parameters is the same as for the DUNA
message (See Section 3.4.1).
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The Affected Destinations parameter can be used to indicate congestion
of multiple destinations or ranges of destinations. However, an SCON
message MUST not be delayed to "collect" individual congested
destinations into a single SCON message as any delay might affect the
timing of congestion indications to the M3UA Users. One use for
including a range of Congested DPCs is when the SG supports an ANSI
cluster route set to the SS7 network that becomes congested due to
outgoing link set congestion.
Concerned Destination: 32-bits
The optional Concerned Destination parameter is only used if the
SCON message is sent from an ASP to the SGP. It contains the point
code of the originator of the message that triggered the SCON
message. The Concerned Destination parameter contains one Concerned
Destination Point Code field, a three-octet parameter to allow for
14-, 16- and 24-bit binary formatted SS7 Point Codes. A Concerned
Point Code that is less than 24-bits is padded on the left to the
24-bit boundary. Any resulting Transfer Controlled (TFC) message
from the SG is sent to the Concerned Point Code using the single
Affected DPC contained in the SCON message to populate the
(affected) Destination field of the TFC message
Congested Indications: 32-bits
The optional Congestion Indications parameter contains a Congestion
Level field. This optional parameter is used to communicate
congestion levels in national MTP networks with multiple congestion
thresholds, such as in ANSI MTP3. For MTP congestion methods
without multiple congestion levels (e.g., the ITU international
method) the parameter is not included.
Congestion Level field: 8-bits (unsigned integer)
The Congestion Level field, associated with all of the Affected
DPC(s) in the Affected Destinations parameter, contains one of the
Following values:
0 No Congestion or Undefined
1 Congestion Level 1
2 Congestion Level 2
3 Congestion Level 3
The congestion levels are defined in the congestion method in the
appropriate national MTP recommendations [14,15].
3.4.5 Destination User Part Unavailable (DUPU)
The DUPU message is used by an SGP to inform an ASP that a remote peer
MTP3-User Part (e.g., ISUP or SCCP) at an SS7 node is unavailable.
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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 = 0x0200 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0203 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask = 0 | Affected DPC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0204 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause | User |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
User/Cause: 32-bits
The Unavailability Cause and MTP3-User Identity fields, associated
with the Affected DPC in the Affected Destinations parameter, are
encoded as follows:
Unavailability Cause field: 16-bits (unsigned integer)
The Unavailability Cause parameter provides the reason for the
unavailability of the MTP3-User. The valid values for the
Unavailability Cause parameter are shown in the following table.
The values agree with those provided in the SS7 MTP3 User Part
Unavailable message. Depending on the MTP3 protocol used in the
Network Appearance, additional values may be used - the
specification of the relevant MTP3 protocol variant/version
recommendation is definitive.
0 Unknown
1 Unequipped Remote User
2 Inaccessible Remote User
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MTP3-User Identity field: 16-bits (unsigned integer)
The MTP3-User Identity describes the specific MTP3-User that is
unavailable (e.g., ISUP, SCCP, ...). Some of the valid values for
the MTP3-User Identity are shown below. The values align with those
provided in the SS7 MTP3 User Part Unavailable message and Service
Indicator. Depending on the MTP3 protocol variant/version used in
the network appearance, additional values may be used. The relevant
MTP3 protocol variant/version recommendation is definitive.
0 to 2 Reserved
3 SCCP
4 TUP
5 ISUP
6 to 8 Reserved
9 Broadband ISUP
10 Satellite ISUP
11 Reserved
12 AAL type 2 Signalling
13 Bearer Independent Call Control (BICC)
14 Gateway Control Protocol
15 Reserved
The format and description of the Affected Destinations parameter is
the same as for the DUNA message (See Section 3.4.1.) except that the
Mask field is not used and only a single Affected DPC is included.
Ranges and lists of Affected DPCs cannot be signalled in a DUPU
message, but this is consistent with UPU operation in the SS7 network.
The Affected Destinations parameter in an MTP3 User Part Unavailable
message (UPU) received by an SGP from the SS7 network contains only one
destination.
The format and description of the Network Appearance and INFO String
parameters is the same as for the DUNA message (See Section 3.4.1).
3.4.6 Destination Restricted (DRST)
The DRST message is optionally sent from the SGP to all concerned ASPs
to indicate that the SG has determined that one or more SS7
destinations are now restricted from the point of view of the SGP, or
in response to a DAUD message if appropriate. The M3UA layer at the ASP
is expected to send traffic to the affected destination via an
alternate SGP of equal priority, but only if such an alternate route
exists and is available. If the affected destination is currently
considered unavailable by the ASP, The MTP3-User should be informed
that traffic to the affected destination can be resumed. In this case,
the M3UA layer should route the traffic through the SGP initiating the
DRST message.
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This message is optional for the SGP to send and it is optional for the
ASP to act on any information received in the message. It is for use in
the "STP" case described in Section 1.4.1.
The DRST message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
INFO String Optional
The format and description of the Network Appearance, Affected
Destinations and INFO String parameters is the same as for the DUNA
message (See Section 3.4.1).
3.5 ASP State Maintenance (ASPSM) Messages
3.5.1 ASP Up
The ASP Up message is used to indicate to a remote M3UA peer that the
adaptation layer is ready to receive any SSNM or ASPSM/ASPTM messages
for all Routing Keys that the ASP is configured to serve.
The ASP Up message contains the following parameters:
ASP Identifier Optional
INFO String Optional
The format for ASP Up message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x000e | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASP Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The optional ASP Identifier parameter contains a unique value that is
locally significant among the ASPs that support an AS. The SGP should
save the ASP Identifier to be used, if necessary, with the Notify
message (see Section 3.8.2).
The format and description of the optional INFO String parameter is the
same as for the DUNA message (See Section 3.4.1).
3.5.2 ASP Up Acknowledgement (ASP Up Ack)
The ASP UP Ack message is used to acknowledge an ASP Up message
received from a remote M3UA peer.
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The ASP Up Ack message contains the following parameters:
INFO String (optional)
The format for ASP Up Ack message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag =0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional INFO String parameter is the
same as for the DUNA message (See Section 3.4.1). The INFO String in
an ASP Up Ack message is independent from the INFO String in the ASP Up
message (i.e., it does not have to echo back the INFO String received).
3.5.3 ASP Down
The ASP Down message is used to indicate to a remote M3UA peer that the
adaptation layer is NOT ready to receive DATA, SSNM, RKM or ASPTM
messages.
The ASP Down message contains the following parameters:
INFO String Optional
The format for the ASP Down message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag =0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The format and description of the optional INFO String parameter is the
same as for the DUNA message (See Section 3.4.1).
3.5.4 ASP Down Acknowledgement (ASP Down Ack)
The ASP Down Ack message is used to acknowledge an ASP Down message
received from a remote M3UA peer.
The ASP Down Ack message contains the following parameters:
Reason Mandatory
INFO String Optional
The format for the ASP Down Ack message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional INFO String parameter is the
same as for the DUNA message (See Section 3.4.1).
The INFO String in an ASP Down Ack message is independent from the INFO
String in the ASP Down message (i.e., it does not have to echo back the
INFO String received).
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3.5.5 Heartbeat (BEAT)
The BEAT message is optionally used to ensure that the M3UA peers
are still available to each other. It is recommended for use when the
M3UA runs over a transport layer other than the SCTP, which has its own
heartbeat.
The BEAT message contains the following parameters:
Heatbeat Data Optional
The format for the BEAT message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0009 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Heartbeat Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Heartbeat Data parameter contents are defined by the sending node.
The Heartbeat Data could include, for example, a Heartbeat Sequence
Number and/or Timestamp. The receiver of a BEAT message does not
process this field as it is only of significance to the sender. The
receiver MUST respond with a BEAT Ack message.
3.5.6 Heartbeat Acknowledgement (BEAT Ack)
The BEAT Ack message is sent in response to a received BEAT
message. It includes all the parameters of the received BEAT
message, without any change.
3.6 Routing Key Management (RKM) Messages
3.6.1 Registration Request (REG REQ)
The REG REQ message is sent by an ASP to indicate to a remote M3UA peer
that it wishes to register one or more given Routing Keys with the
remote peer. Typically, an ASP would send this message to an SGP, and
expects to receive a REG RSP message in return with an associated
Routing Context value.
The REG REQ message contains the following parameters:
Routing Key Mandatory
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One or more Routing Key parameters MAY be included. The format for the
REG REQ message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0207 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Key 1 /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0207 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Key n /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Routing Key: variable length
The Routing Key parameter is mandatory. The sender of this message
expects that the receiver of this message will create a Routing
Key entry and assign a unique Routing Context value to it, if the
Routing Key entry does not already exist.
The Routing Key parameter may be present multiple times in the same
message. This is used to allow the registration of multiple Routing
Keys in a single message.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SI (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSN (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Origination Point Code List (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit Range List (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Local-RK-Identifier: 32-bit integer
The mandatory Local-RK-Identifier field is used to uniquely identify
the registration request. The Identifier value is assigned by the
ASP, and is used to correlate the response in an REG RSP message
with the original registration request. The Identifier value must
remain unique until the REG RSP message is received.
The format of the Local-RK-Identifier field is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x020a | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local-RK-Identifier value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Traffic Mode Type: 32-bit (unsigned integer)
The Traffic Mode Type parameter is mandatory and identifies the
traffic mode of operation of the ASP(s) within an Application
Server. The valid values for Traffic Mode Type are shown in the
following table:
1 Over-ride
2 Load-share
3 Broadcast
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If the receiver of the REG REQ creates a new Routing Key entry, then
the Traffic Mode Type sets the traffic mode for the new Application
Server. If the receiver of the REG REQ determines that a matching
Routing Key already exists, the Traffic Mode Type MUST match the
existing traffic mode for the AS.
Destination Point Code:
The Destination Point Code parameter is mandatory, and identifies
the Destination Point Code of incoming SS7 traffic for which the ASP
is registering. The format is the same as described for the
Affected Destination parameter in the DUNA message (See Section
3.4.1). Its format is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x020b | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask = 0 | Destination Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance:
The optional Network Appearance parameter field identifies the SS7
network context for the Routing Key, and has the same format as in
the DATA message (See Section 3.3.1). The absence of the Network
Appearance parameter in the Routing Key indicates the use
of any Network Appearance value, Its format is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0200 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Service Indicators (SI): n X 8-bit integers
The optional SI field contains one or more Service Indicators from
the values as described in the MTP3-User Identity field of the DUPU
message. The absence of the SI parameter in the Routing Key
indicates the use of any SI value, excluding of course MTP
management. Where an SI parameter does not contain a multiple of
four SIs, the parameter is padded out to 32-byte alignment. An
SI value of zero is not valid in M3UA. The SI format is:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x020c | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SI #1 | SI #2 | SI #3 | SI #4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ ... /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
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