| rfc3332 Description: Request For Comments
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Network Working Group G. Sidebottom
Request for Comments: 3332 Signatus Technologies
Category: Standards Track K. Morneault
Cisco
J. Pastor-Balbas
Ericsson
Editors
September 2002
Signaling System 7 (SS7) Message Transfer Part 3 (MTP3) -
User Adaptation Layer (M3UA)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This memo defines a protocol for supporting the transport of any SS7
MTP3-User signalling (e.g., ISUP and SCCP messages) over IP using the
services of the Stream Control Transmission Protocol. Also,
provision is made for protocol elements that enable a seamless
operation of the MTP3-User peers in the SS7 and IP domains. This
protocol would be used between a Signalling Gateway (SG) and a Media
Gaway Controller (MGC) or IP-resident Database, or between two IP-
based applications. It is assumed that the SG receives SS7
signalling over a standard SS7 interface using the SS7 Message
Transfer Part (MTP) to provide transport.
Table of Contents
1. Introduction..................................................3
1.1 Scope.........................................................3
1.2 Terminology...................................................4
1.3 M3UA Overview.................................................6
1.4 Functional Areas.............................................10
1.5 Sample Configurations........................................18
1.6 Definition of M3UA Boundaries................................21
2. Conventions..................................................25
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
3. M3UA Protocol Elements.......................................25
3.1 Common Message Header........................................26
3.2 Variable Length Parameter....................................29
3.3 Transfer Messages............................................31
3.4 SS7 Signalling Network Management (SSNM) Messages............35
3.5 ASP State Maintenance (ASPSM) Messages.......................45
3.6 Routing Key Management (RKM) Messages........................48
3.7 ASP Traffic Maintenance (ASPTM) Messages.....................59
3.8 Management (MGMT) Messages...................................63
4. Procedures...................................................69
4.1 Procedures to Support the M3UA-User .........................69
4.2 Procedures to Support the Management of SCTP Associations ...70
4.3 AS and ASP State Maintenance.................................72
4.4 Routing Key Management Procedures............................87
4.5 Procedures to Support the Availability or Congestion Status
of SS7 Destination...........................................89
4.6 MTP3 Restart.................................................92
5. Examples of M3UA Procedures..................................93
5.1 Establishment of Association and Traffic
Between SGs and ASPs.........................................93
5.2 ASP traffic Failover Examples................................99
5.3 Normal Withdrawal of an ASP from an Application Server
and Teardown of an Association..............................100
5.4 M3UA/MTP3-User Boundary Examples............................101
5.5 Examples of IPSP communication..............................105
6. Security Considerations.....................................108
6.1 Introduction................................................108
6.2 Threats.....................................................108
6.3 Protecting Confidentiality..................................108
7. IANA Considerations.........................................109
7.1 SCTP Payload Protocol Identifier............................109
7.2 M3UA Port Number............................................109
7.3 M3UA Protocol Extensions....................................109
8. References...................................................111
8.1 Normative References........................................111
8.2 Informative References......................................111
9. Acknowledgements.............................................113
10. Document Contributors.......................................113
Appendix A......................................................114
A.1 Signalling Network Architecture.............................114
A.2 Redundancy Models...........................................117
Editors' Addresses..............................................119
Full Copyright Statement........................................120
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
1. Introduction
This memo 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 [17]. Also,
provision is made for protocol elements that enable a seamless
operation of the MTP3-User peers in the SS7 and IP domains. This
protocol would be used between a Signalling Gateway (SG) and a Media
Gaway Controller (MGC) or IP-resident Database [11], or between two
IP-based applications.
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 [11]. The delivery
mechanism should meet the following criteria:
* Support for the transfer of all SS7 MTP3-User Part messages (e.g.,
ISUP [1,2,3], SCCP [4,5,6], TUP [12], 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 failover 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 [7,8,9] 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.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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 backup 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 endpoint and may be configured to process signalling
traffic within more than one Application Server.
Association - An association refers to an SCTP association. The
association provides the transport for the delivery of MTP3-User
protocol data units and M3UA adaptation layer peer messages.
IP Server Process (IPSP) - A process instance of an IP-based
application. An IPSP is essentially the same as an ASP, except that
it uses M3UA in a point-to-point fashion. Conceptually, an IPSP does
not use the services of a Signalling Gateway node.
Failover - The capability to reroute 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. Failover also applies
upon the return to service of a previously unavailable Application
Server Process.
Host - The computing platform that the process (SGP, ASP or IPSP) is
running on.
Layer Management - Layer Management is a nodal function that handles
the inputs and outputs between the M3UA layer and a local management
entity.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
Linkset - A number of signalling links that directly interconnect two
signalling points, which are used as a module.
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 is a M3UA local reference
shared by SG and AS (typically an integer) that together with an
Signaling Point Code uniquely identifies an SS7 node by indicating
the specific SS7 network it belongs to. It can be used to distinguish
between signalling traffic associated with different networks being
sent between the SG and the ASP over a common SCTP association. An
example scenario is where an SG appears as an element in multiple
separate national SS7 networks and the same Signaling Point Code
value may be reused in different networks.
Network Byte Order: Most significant byte first, a.k.a Big Endian.
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.
Signalling Gateway Process (SGP) - A process instance of a Signalling
Gateway. It serves as an active, backup, 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 [11]. 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 are assumed to be coordinated into a single management
view to the SS7 network and to the supported Application Servers.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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.
Signalling Point Management Cluster (SPMC) - The complete set of
Application Servers represented to the SS7 network under a single MTP
entity (Signalling Point) in one specific Network Appearance. 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 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.
Stream - A stream refers to an SCTP stream; a unidirectional logical
channel established from one SCTP endpoint to another associated SCTP
endpoint, within which all user messages are delivered in-sequence
except for those submitted to the unordered delivery service.
1.3 M3UA Overview
1.3.1 Protocol Architecture
The framework architecture that has been defined for SCN signalling
transport over IP [11] uses multiple components, including a common
signalling transport protocol and an adaptation module to support the
services expected by a particular SCN signalling protocol from its
underlying protocol layer.
Within the framework architecture, this document defines an MTP3-User
adaptation module suitable for supporting the transfer of messages of
any protocol layer that is identified to the MTP Level 3 as an MTP
User. The list of these protocol layers includes, but is not limited
to, ISDN User Part (ISUP) [1,2,3], Signalling Connection Control Part
(SCCP) [4,5,6] and Telephone User Part (TUP) [12]. TCAP [13,14,15]
or RANAP [16] 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) [17] as the underlying reliable common
signalling transport protocol. This is to take advantage of various
SCTP features such as:
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
- 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 might not be a
requirement and TCP MAY 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 SG, 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 SG.
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.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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.
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, minimizing
missequencing.
The M3UA layer does not impose a 272-octet signalling information
field (SIF) length limit as specified by the SS7 MTP Level 2 protocol
[7,8,9]. 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 interworking 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. The provisioning and configuration of the
SS7 network determines the restriction placed on the maximum block
size. Some configurations (e.g., Broadband MTP [21]) may permit
larger block sizes.
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.
1.3.2.3 Interworking with MTP3 Network Management Functions
At the SGP, the M3UA layer provides interworking 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.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
- 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 (See Section 1.6.3 for a description of
management 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
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.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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 and/or SG, 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.
1.4 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 a local
SCCP layer.
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 [8] 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. Rerouting of traffic between the SGPs MAY 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 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 rerouting through
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
an alternate SG without changing the Destination Point Code Address
of SS7 traffic to the ASP(s).
Where a particular AS can be reached via more than one SGP, the
corresponding Routing Keys in the SGPs should be identical. (Note:
It is possible for the SGP Routing Key configuration data to be
temporarily out-of-sync during configuration updates).
+--------+
| |
+------------+ SG 1 +--------------+
+-------+ | SS7 links | "STP" | IP network | ----
| SEP +---+ +--------+ +---/ \
| or | |* | ASPs |
| STP +---+ +--------+ +---\ /
+-------+ | | | | ----
+------------+ SG 2 +--------------+
| "STP" |
+--------+
Figure 1 Example with mated SGs
* Note:. SG-to-SG communication (i.e., "C-links") is recommended for
carrier grade networks, using an MTP3 linkset or an equivalent, to
allow rerouting between the SGs in the event of route failures. Where
SGPs are used, inter-SGP communication might be used. 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" | |
+-------+ +---------------+
Figure 2 Example with multiple Network
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
1.4.2 Routing Contexts and Routing Keys
1.4.2.1 Overview
The distribution of SS7 messages between the SGP and the Application
Servers is determined by the Routing Keys and their associated
Routing Contexts. A Routing Key is essentially a set of SS7
parameters used to filter SS7 messages, whereas the Routing Context
parameter is a 4-byte value (integer) that is associated to that
Routing Key in a 1:1 relationship. The Routing Context therefore can
be viewed as an index into a sending node's Message Distribution
Table containing the Routing Key entries.
Possible SS7 address/routing information that comprise a Routing Key
entry includes, for example, the OPC, DPC, SIO found in the MTP3
routing label, or MTP3-User specific fields (such as the ISUP CIC,
SCCP subsystem number). 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. 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.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
When using a management interface to configure Routing Keys, the
message distribution function within the SGP is not limited to the
set of parameters defined in this document. Other implementation
dependent distribution algorithms may be used.
1.4.2.4 Message Distribution at the SGP
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 failover 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,
loadsharing 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.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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). The ASP must also take into account whether the related
Routing Context is active or not (See Section 4.3.4.3).
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 failover mechanisms. There is, however, no M3UA messaging
to manage the status of an SGP (e.g., SGP-Up/Down/Active/Inactive
messaging).
Whenever an SCTP association to an SGP exists, the SGP is assumed to
be ready for the purposes of responding to M3UA ASPSM messages (Refer
to Section 3).
1.4.3 SS7 and M3UA Interworking
In the case of SS7 and M3UA interworking, 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) [7,8,9] 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) [18,19].
Note: It is also possible for IP-based interfaces to be present,
using the services of the MTP2-User Adaptation Layer (M2UA) [27] or
M2PA [28].
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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 Interworking at the SG
The SGP provides a functional interworking 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.
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 interworking is not necessary for this model.
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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.
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 failover 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/backup redundancy is a subset of this model. A
simplex "1+0" model is also supported as a subset, with no ASP
redundancy.
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.
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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.
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 and TCP Registered User Port Number Assignment for M3UA is
2905.
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1.5 Sample Configuration
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 Interworking Function
In this example, the SGP provides an implementation-dependent nodal
interworking 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 interworking function has no visible peer protocol with
either the MGC or SEP. It also provides network status information
to one or both sides of the network.
For internal SGP modeling purposes, at the NIF level, SS7 signalling
messages that are destined to the MGC are received as MTP-TRANSFER
indication primitives from the MTP Level 3 upper layer interface,
translated to MTP-TRANSFER request primitives, and sent to the local
M3UA-resident message distribution function for ongoing routing to
the final IP destination. Messages received from the local M3UA
network address translation and mapping function as MTP-TRANSFER
indication primitives are sent to the MTP Level 3 upper layer
interface as MTP-TRANSFER request primitives for ongoing MTP Level 3
routing to an SS7 SEP. For the purposes of providing SS7 network
status information the NIF also delivers MTP-PAUSE, MTP-RESUME and
MTP-STATUS indication primitives received from the MTP Level 3 upper
layer interface to the local M3UA-resident management function. In
addition, as an implementation and network option, restricted
destinations are communicated from MTP network management to the
local M3UA-resident management function.
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1.5.2 Example 2: SCCP Transport between IPSPs
******** IP ********
* IPSP * * IPSP *
******** ********
+------+ +------+
|SCCP- | |SCCP- |
| User | | User |
+------+ +------+
| SCCP | | SCCP |
+------+ +------+
| M3UA | | M3UA |
+------+ +------+
| SCTP | | SCTP |
+------+ +------+
| IP | | IP |
+------+ +------+
|________________|
This example shows an architecture where no Signalling Gateway is
used. In this example, SCCP messages are exchanged directly between
two IP-resident IPSPs with resident SCCP-User protocol instances,
such as RANAP or TCAP. SS7 network interworking 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.
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For internal SGP modeling purposes, this may be accomplished with the
use of an implementation-dependent nodal interworking function within
the SGP that effectively sits below the SCCP and routes MTP-TRANSFER
request/indication messages to/from both the MTP3 and the M3UA layer,
based on the SS7 DPC or DPC/SSN address information. This nodal
interworking 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 [7]:
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 [17] 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.
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M-SCTP_RELEASE request
Direction: LM -> M3UA
Purpose: LM requests ASP to release an SCTP association with its
peer.
M-SCTP_RELEASE confirm
Direction: M3UA -> LM
Purpose: ASP confirms to LM that it has released SCTP association
with its peer.
M-SCTP_RELEASE indication
Direction: M3UA -> LM
Purpose: M3UA informs LM that a remote ASP has released an SCTP
Association or the SCTP association has failed.
M-SCTP_RESTART indication
Direction: M3UA -> LM
Purpose: M3UA informs LM that an SCTP restart indication has been
received.
M-SCTP_STATUS request
Direction: LM -> M3UA
Purpose: LM requests M3UA to report the status of an SCTP
association.
M-SCTP_STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA responds with the status of an SCTP association.
M-SCTP STATUS indication
Direction: M3UA -> LM
Purpose: M3UA reports the status of an SCTP association.
M-ASP_STATUS request
Direction: LM -> M3UA
Purpose: LM requests M3UA to report the status of a local or remote
ASP.
M-ASP_STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA reports status of local or remote ASP.
M-AS_STATUS request
Direction: LM -> M3UA
Purpose: LM requests M3UA to report the status of an AS.
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M-AS_STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA reports the status of an AS.
M-NOTIFY indication
Direction: M3UA -> LM
Purpose: M3UA reports that it has received a Notify message
from its peer.
M-ERROR indication
Direction: M3UA -> LM
Purpose: M3UA reports that it has received an Error message from
its peer or that a local operation has been unsuccessful.
M-ASP_UP request
Direction: LM -> M3UA
Purpose: LM requests ASP to start its operation and send an ASP Up
message to its peer.
M-ASP_UP confirm
Direction: M3UA -> LM
Purpose: ASP reports that is has received an ASP UP Ack message from
its peer.
M-ASP_UP indication
Direction: M3UA -> LM
Purpose: M3UA reports it has successfully processed an incoming ASP
Up message from its peer.
M-ASP_DOWN request
Direction: LM -> M3UA
Purpose: LM requests ASP to stop its operation and send an ASP Down
message to its peer.
M-ASP_DOWN confirm
Direction: M3UA -> LM
Purpose: ASP reports that is has received an ASP Down Ack message
from its peer.
M-ASP_DOWN indication
Direction: M3UA -> LM
Purpose: M3UA reports it has successfully processed an incoming ASP
Down message from its peer, or the SCTP association has
been lost/reset.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
M-ASP_ACTIVE request
Direction: LM -> M3UA
Purpose: LM requests ASP to send an ASP Active message to its peer.
M-ASP_ACTIVE confirm
Direction: M3UA -> LM
Purpose: ASP reports that is has received an ASP Active
Ack message from its peer.
M-ASP_ACTIVE indication
Direction: M3UA -> LM
Purpose: M3UA reports it has successfully processed an incoming ASP
Active message from its peer.
M-ASP_INACTIVE request
Direction: LM -> M3UA
Purpose: LM requests ASP to send an ASP Inactive message to its
peer.
M-ASP_INACTIVE confirm
Direction: LM -> M3UA
Purpose: ASP reports that is has received an ASP Inactive
Ack message from its peer.
M-ASP_INACTIVE indication
Direction: M3UA -> LM
Purpose: M3UA reports it has successfully processed an incoming ASP
Inactive message from its peer.
M-AS_ACTIVE indication
Direction: M3UA -> LM
Purpose: M3UA reports that an AS has moved to the AS-ACTIVE state.
M-AS_INACTIVE indication
Direction: M3UA -> LM
Purpose: M3UA reports that an AS has moved to the AS-INACTIVE state.
M-AS_DOWN indication
Direction: M3UA -> LM
Purpose: M3UA reports that an AS has moved to the AS-DOWN state.
If dynamic registration of RK is supported by the M3UA layer, the
layer MAY support the following additional primitives:
M-RK_REG request
Direction: LM -> M3UA
Purpose: LM requests ASP to register RK(s) with its peer by sending
REG REQ message
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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 deregister 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
deregistration status as successful from its peer.
M-RK_DEREG indication
Direction: M3UA -> LM
Purpose: M3UA informs LM that it has successfully processed an
incoming DEREG REQ from its peer.
2. 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
[20].
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.
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3.1 Common Message Header
The protocol messages for MTP3-User Adaptation require a message
header which contains the adaptation layer version, the message type,
and message length.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Reserved | Message Class | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ /
All fields in an M3UA message MUST be transmitted in the network byte
order, unless otherwise stated.
3.1.1 M3UA Protocol Version: 8 bits (unsigned integer)
The version field contains the version of the M3UA adaptation layer.
The supported versions are the following:
1 Release 1.0
3.1.2 Message Classes and Types
The following list contains the valid Message Classes:
Message Class: 8 bits (unsigned integer)
The following list contains the valid Message Type Classes:
0 Management (MGMT) Messages
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
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Message Type: 8 bits (unsigned integer)
The following list contains the message types for the defined
messages.
Management (MGMT) Messages (See Section 3.8)
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 Signalling Congestion (SCON)
5 Destination User Part Unavailable (DUPU)
6 Destination Restricted (DRST)
7 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined SSNM extensions
ASP State Maintenance (ASPSM) Messages (See Section 3.5)
0 Reserved
1 ASP Up (ASPUP)
2 ASP Down (ASPDN)
3 Heartbeat (BEAT)
4 ASP Up Acknowledgement (ASPUP ACK)
5 ASP Down Acknowledgement (ASPDN ACK)
6 Heartbeat Acknowledgement (BEAT ACK)
7 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined ASPSM extensions
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ASP Traffic Maintenance (ASPTM) Messages (See Section 3.7)
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 3.6)
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. The Message Length MUST include
parameter padding bytes, if any.
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:
Common Parameters. These TLV parameters are common across the
different adaptation layers:
Parameter Name Parameter ID
============== ============
Reserved 0x0000
Not Used in M3UA 0x0001
Not Used in M3UA 0x0002
Not Used in M3UA 0x0003
INFO String 0x0004
Not Used in M3UA 0x0005
Routing Context 0x0006
Diagnostic Information 0x0007
Not Used in M3UA 0x0008
Heartbeat Data 0x0009
Not Used in M3UA 0x000a
Traffic Mode Type 0x000b
Error Code 0x000c
Status 0x000d
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Not Used in M3UA 0x000e
Not Used in M3UA 0x000f
Not Used in M3UA 0x0010
ASP Identifier 0x0011
Affected Point Code 0x0012
Correlation ID 0x0013
M3UA-Specific parameters. These TLV parameters are specific to
the M3UA protocol:
Network Appearance 0x0200
Reserved 0x0201
Reserved 0x0202
Reserved 0x0203
User/Cause 0x0204
Congestion Indications 0x0205
Concerned Destination 0x0206
Routing Key 0x0207
Registration Result 0x0208
Deregistration Result 0x0209
Local_Routing Key Identifier 0x020a
Destination Point Code 0x020b
Service Indicators 0x020c
Reserved 0x020d
Originating Point Code List 0x020e
Circuit Range 0x020f
Protocol Data 0x0210
Reserved 0x0211
Registration Status 0x0212
Deregistration Status 0x0213
Reserved by the IETF 0x0214 to 0xffff
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. Thus, a parameter with a zero-length
Parameter Value field would have a Length field of 4. The
Parameter Length does not include any padding bytes.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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
Routing Context Optional
Protocol Data Mandatory
Correlation Id Optional
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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 = 0x0006 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Routing Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0210 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Protocol Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0013 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Correlation Id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance: 32-bits (unsigned integer)
The Network Appearance parameter identifies the SS7 network
context for the message and implicitly identifies 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 may be
configured to be present for the use of the receiver.
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.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
IMPLEMENTATION NOTE: For simplicity of configuration it may be
desirable to use the same NA value across all nodes sharing a
particular network context.
Routing Context: 32-bits (unsigned integer)
The Routing Context parameter contains the Routing Context value
associated with the DATA message. Where a Routing Key has not
been coordinated between the SGP and ASP, sending of Routing
Context is not required. Where multiple Routing Keys and Routing
Contexts are used across a common association, the Routing Context
MUST be sent to identify the traffic flow, assisting in the
internal distribution of Data messages.
Protocol Data: variable length
The Protocol Data parameter contains the original SS7 MTP3
message, including the Service Information Octet and Routing
Label.
The Protocol Data parameter contains the following fields:
Service Indicator,
Network Indicator,
Message Priority.
Destination Point Code,
Originating Point Code,
Signalling Link Selection Code (SLS).
User Protocol Data. Includes:
MTP3-User protocol elements (e.g., ISUP, SCCP, or TUP
parameters).
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
The Protocol Data parameter is encoded 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SI | NI | MP | SLS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ User Protocol Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Originating Point Code: 32 bits (unsigned integer)
Destination Point Code: 32 bits (unsigned integer)
The Originating and Destination Point Code fields contains the OPC
and DPC from the routing label of the original SS7 message in Network
Byte Order, justified to the least significant bit. Unused bits are
coded `0'.
Service Indicator: 8 bits (unsigned integer)
The Service Indicator field contains the SI field from the original
SS7 message justified to the least significant bit. Unused bits are
coded `0'.
Network Indicator: 8-bits (unsigned integer)
The Network Indicator contains the NI field from the original SS7
message justified to the least significant bit. Unused bits are
coded `0'.
Message Priority: 8 bits (unsigned integer)
The Message Priority field contains the MP bits (if any) from the
original SS7 message, both for ANSI-style and TTC-style [29] message
priority bits. The MP bits are aligned to the least significant bit.
Unused bits are coded `0'.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
Signalling Link Selection: 8 bits (unsigned integer)
The Signalling Link Selection field contains the SLS bits from the
routing label of the original SS7 message justified to the least
significant bit and in Network Byte Order. Unused bits are coded
`0'.
User Protocol Data: (byte string)
The User Protocol Data field contains a byte string of MTP-User
information from the original SS7 message starting with the first
byte of the original SS7 message following the Routing Label.
Correlation Id: 32-bits (unsigned integer)
The Correlation Id parameter uniquely identifies the MSU carried in
the Protocol Data within an AS. This Correlation Id parameter is
assigned by the sending M3UA.
3.4 SS7 Signalling Network Management (SSNM) Messages
3.4.1 Destination Unavailable (DUNA)
The DUNA message is sent from an SGP 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. If there is no alternate route via another SG, the MTP3-User
at the ASP is expected to stop traffic to the affected destination
via the SG as per the defined MTP3-User procedures.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
The DUNA message contains the following parameters:
Network Appearance Optional
Routing Context Optional
Affected Point Code 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 = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0012 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected PC 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected PC n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance: 32-bit unsigned integer
See Section 3.3.1
Routing Context: n x 32-bits (unsigned integer)
The optional Routing Context parameter contains the Routing
Context values associated with the DUNA message. Where a Routing
Key has not been coordinated between the SGP and ASP, sending of
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
Routing Context is not required. Where multiple Routing Keys and
Routing Contexts are used across a common association, the Routing
Context(s) MUST be sent to identify the concerned traffic flows
for which the DUNA message applies, assisting in outgoing traffic
management and internal distribution of MTP-PAUSE indications to
MTP3-Users at the receiver.
Affected Point Code: n x 32-bits
The Affected Point Code parameter contains a list of Affected
Destination Point Code fields, each a three-octet parameter to
allow for 14-, 16- and 24-bit binary formatted SS7 Point Codes.
Affected Point Codes that are less than 24-bits, are padded on the
left to the 24-bit boundary. The encoding is shown below for ANSI
and ITU Point Code examples.
ANSI 24-bit Point Code:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Network | Cluster | Member |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB-----------------------------------------LSB|
ITU 14-bit Point Code:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask |0 0 0 0 0 0 0 0 0 0|Zone | Region | SP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB--------------------LSB|
It is optional to send an Affected Point Code parameter with more
than one Affected PC but it is mandatory to receive it. Including
multiple Affected PCs 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.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
Mask: 8-bits (unsigned integer)
The Mask field can be used to identify a contiguous range of
Affected Destination Point Codes. 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.
The Mask parameter is an integer representing a bit mask that can
be applied to the related Affected PC field. The bit mask
identifies how many bits of the Affected PC field are significant
and which are effectively "wildcarded". For example, a mask of
"8" indicates that the last eight bits of the PC is "wildcarded".
For an ANSI 24-bit Affected PC, this is equivalent to signalling
that all PCs in an ANSI Cluster are unavailable. A mask of "3"
indicates that the last three bits of the PC is "wildcarded". For
a 14-bit ITU Affected PC, this is equivalent to signaling that an
ITU
Region is unavailable. A mask value equal (or greater than) the
number of bits in the PC 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 meaningful UTF-8
[10] character string along with the message. Length of the INFO
String parameter is from 0 to 255 octets. No procedures are
presently identified for its use but the INFO String MAY be used
for debugging purposes.
3.4.2 Destination Available (DAVA)
The DAVA message is sent from an 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. If the ASP M3UA layer previously had no
routes to the affected destinations the ASP MTP3-User protocol is
informed and may now resume traffic to the affected destination. The
ASP M3UA layer now routes the MTP3-user traffic through the SG
initiating the DAVA message.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
The DAVA message contains the following parameters:
Network Appearance Optional
Routing Context Optional
Affected Point Code Mandatory
INFO String Optional
The format and description of the Network Appearance, Routing
Context, Affected Point Code 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 from the SG to one or
more affected destinations.
The DAUD message contains the following parameters:
Network Appearance Optional
Routing Context Optional
Affected Point Code 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 Signalling Congestion (SCON)
The SCON message can be sent from an SGP to all concerned ASPs to
indicate that an SG has determined that there is congestion in the
SS7 network to one or more destinations, or to an ASP in response to
a DATA or DAUD message as appropriate. For some MTP protocol
variants (e.g., ANSI MTP) the SCON message may be sent when the SS7
congestion level changes. The SCON message MAY also be sent from the
M3UA layer of an ASP to an M3UA peer indicating that the M3UA layer
or the ASP is congested.
The SCON message contains the following parameters:
Network Appearance Optional
Routing Context Optional
Affected Point Code Mandatory
Concerned Destination Optional
Congestion Indications Optional
INFO String Optional
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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 = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0012 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected PC 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected PC n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0206 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved | Concerned DPC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0205 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Cong. Level |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
The format and description of the Network Appearance, Routing
Context, Affected Point Code, and INFO String parameters is the same
as for the DUNA message (See Section 3.4.1).
The Affected Point Code parameter can be used to indicate congestion
of multiple destinations or ranges of destinations.
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
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
The congestion levels are defined in the congestion method in the
appropriate national MTP recommendations [7,8].
3.4.5 Destination User Part Unavailable (DUPU)
The DUPU message is used by an SGP to inform concerned ASPs that a
remote peer MTP3-User Part (e.g., ISUP or SCCP) at an SS7 node is
unavailable.
The DUPU message contains the following parameters:
Network Appearance Optional
Routing Context Optional
Affected Point Code 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 = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0012 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask = 0 | Affected PC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0204 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause | User |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
User/Cause: 32-bits
The Unavailability Cause and MTP3-User Identity fields, associated
with the Affected PC in the Affected Point Code parameter, are
encoded as follows:
Unavailability Cause field: 16-bits (unsigned integer)
The Unavailability Cause parameter provides the reason for the
unavailability of the MTP3-User. The valid values for the
Unavailability Cause parameter are shown in the following table.
The values agree with those provided in the SS7 MTP3 User Part
Unavailable message. Depending on the MTP3 protocol used in the
Network Appearance, additional values may be used - the
specification of the relevant MTP3 protocol variant/version
recommendation is definitive.
0 Unknown
1 Unequipped Remote User
2 Inaccessible Remote User
MTP3-User Identity field: 16-bits (unsigned integer)
The MTP3-User Identity describes the specific MTP3-User that is
unavailable (e.g., ISUP, SCCP, ...). Some of the valid values for
the MTP3-User Identity are shown below. The values align with
those provided in the SS7 MTP3 User Part Unavailable message and
Service Indicator. Depending on the MTP3 protocol variant/version
used in the network appearance, additional values may be used.
The relevant MTP3 protocol variant/version recommendation is
definitive.
0 to 2 Reserved
3 SCCP
4 TUP
5 ISUP
6 to 8 Reserved
9 Broadband ISUP
10 Satellite ISUP
11 Reserved
12 AAL type 2 Signalling
13 Bearer Independent Call Control (BICC)
14 Gateway Control Protocol
15 Reserved
The format and description of the Affected Point Code 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
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
included. Ranges and lists of Affected DPCs cannot be signaled 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, Routing
Context, 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 SG, 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 SG with route(s) 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 SG
initiating the DRST message.
This message is optional for the SG 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
Routing Context Optional
Affected Point Code Mandatory
INFO String Optional
The format and description of the Network Appearance, Routing
Context, Affected Point Code and INFO String parameters is the same
as for the DUNA message (See Section 3.4.1).
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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 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 = 0x0011 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASP Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ASP Identifier: 32-bit unsigned integer
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).
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
3.5.2 ASP Up Acknowledgement (ASP Up Ack)
The ASP UP Ack message is used to acknowledge an ASP Up message
received from a remote M3UA peer.
The ASP Up Ack message contains the following parameters:
INFO String (optional)
The format for ASP Up Ack message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag =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
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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 /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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:
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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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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:
Heartbeat Data Optional
The format for the BEAT message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0009 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Heartbeat Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The 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 [Optional]
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.
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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
The REG REQ message contains the following parameters:
Routing Key Mandatory
One or more Routing Key parameters MAY be included. The format for
the REG REQ message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 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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RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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 (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Indicators (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating Point Code List (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit Range List (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Indicators (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating Point Code List (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit Range List (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note: The Destination Point Code, Service Indicators, Originating
Point Code List and Circuit Range List parameters MAY be repeated
as a grouping within the Routing Key parameter, in the structure
shown above.
Local-RK-Identifier: 32-bit unsigned 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.
Sidebottom, et. al. Standards Track [Page 50]
RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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 optional Traffic Mode Type parameter identifies the traffic mode
of operation of the ASP(s) within an Application Server. The format
of the Traffic Mode Type Identifier 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 = 0x000b | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The valid values for Traffic Mode Type are shown in the following
table:
1 Override
2 Loadshare
3 Broadcast
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sidebottom, et. al. Standards Track [Page 51]
RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
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 [7,8] 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.
The SI format is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x020c | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SI #1 | SI #2 | SI #3 | SI #4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ ... /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SI #n | 0 Padding, if necessary |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OPC List:
The Originating Point Code List parameter contains one or more SS7
OPC entries, and its format is the same as the Destination Point
Code parameter. The absence of the OPC List parameter in the
Routing Key indicates the use of any OPC value,
Sidebottom, et. al. Standards Track [Page 52]
RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x020e | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask = 0 | Origination Point Code #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask = 0 | Origination Point Code #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ ... /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask = 0 | Origination Point Code #n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Circuit Range:
An ISUP controlled circuit is uniquely identified by the SS7 OPC,
DPC and CIC value. For the purposes of identifying Circuit Ranges
in an M3UA Routing Key, the optional Circuit Range parameter
includes one or more circuit ranges, each identified by an OPC and
Upper/Lower CIC value. The DPC is implicit as it is mandatory and
already included in the DPC parameter of the Routing Key. The
absence of the Circuit Range parameter in the Routing Key
indicates the use of any Circuit Range values, in the case of
ISUP/TUP traffic. The Origination Point Code is encoded the same
as the Destination Point Code parameter, while the CIC values are
16-bit integers.
Sidebottom, et. al. Standards Track [Page 53]
RFC 3332 SS7 MTP3-User Adaptation Layer September 2002
The Circuit Range format is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x020f | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask = 0 | Origination Point Code #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lower CIC Value #1 | Upper CIC Value #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask = 0 | Origination Point Code #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lower CIC Value #2 | Upper CIC Value #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ ... /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask = 0 | Origination Point Code #n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lower CIC Value #n | Upper CIC Value #n |
+ |
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