Signaling System 7 (SS7) Message Transfer Part 3 (MTP3) - User Adaptation Layer (M3UA)
RFC 4666
| Document | Type |
RFC - Proposed Standard
(September 2006; Errata)
Obsoletes RFC 3332
|
|
|---|---|---|---|
| Authors | Javier Pastor , Ken Morneault | ||
| Last updated | 2015-10-14 | ||
| Replaces | draft-ietf-sigtran-m3ua-implementors-guide, draft-ietf-sigtran-m3ua-v02 | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 4666 (Proposed Standard) | |
| Action Holders |
(None)
|
||
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Jon Peterson | ||
| Send notices to | (None) | ||
Network Working Group K. Morneault, Ed.
Request for Comments: 4666 Cisco Systems
Obsoletes: 3332 J. Pastor-Balbas, Ed.
Category: Standards Track Ericsson
September 2006
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 (2006).
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
Gateway 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. This document obsoletes
RFC 3332.
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RFC 4666 SS7 MTP3-User Adaptation Layer September 2006
Table of Contents
1. Introduction ....................................................6
1.1. Scope ......................................................6
1.2. Terminology ................................................6
1.3. M3UA Overview ..............................................9
1.3.1. Protocol Architecture ...............................9
1.3.2. Services Provided by the M3UA Layer ................10
1.3.2.1. Support for the Transport of
MTP3-User Messages ........................10
1.3.2.2. Native Management Functions ...............11
1.3.2.3. Interworking with MTP3 Network
Management Functions ......................11
1.3.2.4. Support for the Management of SCTP
Associations between the ..................11
1.3.2.5. Support for the Management of
Connections to Multiple SGPs ..............12
1.4. Functional Areas ..........................................12
1.4.1. Signalling Point Code Representation ...............12
1.4.2. Routing Contexts and Routing Keys ..................14
1.4.2.1. Overview ..................................14
1.4.2.2. Routing Key Limitations ...................15
1.4.2.3. Managing Routing Contexts and
Routing Keys ..............................15
1.4.2.4. Message Distribution at the SGP ...........15
1.4.2.5. Message Distribution at the ASP ...........16
1.4.3. SS7 and M3UA Interworking ..........................16
1.4.3.1. Signalling Gateway SS7 Layers .............16
1.4.3.2. SS7 and M3UA Interworking at the SG .......17
1.4.3.3. Application Server ........................17
1.4.3.4. IPSP Considerations .......................18
1.4.4. Redundancy Models ..................................18
1.4.4.1. Application Server Redundancy .............18
1.4.5. Flow Control .......................................18
1.4.6. Congestion Management ..............................19
1.4.7. SCTP Stream Mapping ................................19
1.4.8. SCTP Client/Server Model ...........................19
1.5. Sample Configuration ......................................20
1.5.1. Example 1: ISUP Message Transport ..................20
1.5.2. Example 2: SCCP Transport between IPSPs ............21
1.5.3. Example 3: SGP Resident SCCP Layer, with
Remote ASP .........................................22
1.6. Definition of M3UA Boundaries .............................23
1.6.1. Definition of the Boundary between M3UA and
an MTP3-User .......................................23
1.6.2. Definition of the Boundary between M3UA and SCTP ...23
1.6.3. Definition of the Boundary between M3UA and
Layer Management ...................................24
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2. Conventions ....................................................27
3. M3UA Protocol Elements .........................................28
3.1. Common Message Header .....................................28
3.1.1. M3UA Protocol Version: 8 bits (unsigned integer) ...28
3.1.2. Message Classes and Types ..........................28
3.1.3. Reserved: 8 Bits ...................................30
3.1.4. Message Length: 32-Bits (Unsigned Integer) .........30
3.2. Variable-Length Parameter Format ..........................30
3.3. Transfer Messages .........................................33
3.3.1. Payload Data Message (DATA) ........................33
3.4. SS7 Signalling Network Management (SSNM) Messages .........36
3.4.1. Destination Unavailable (DUNA) .....................36
3.4.2. Destination Available (DAVA) .......................39
3.4.3. Destination State Audit (DAUD) .....................40
3.4.4. Signalling Congestion (SCON) .......................40
3.4.5. Destination User Part Unavailable (DUPU) ...........43
3.4.6. Destination Restricted (DRST) ......................45
3.5. ASP State Maintenance (ASPSM) Messages ....................45
3.5.1. ASP Up .............................................45
3.5.2. ASP Up Acknowledgement (ASP Up Ack) ................46
3.5.3. ASP Down ...........................................47
3.5.4. ASP Down Acknowledgement (ASP Down Ack) ............48
3.5.5. Heartbeat (BEAT) ...................................48
3.5.6. Heartbeat Acknowledgement (BEAT Ack) ...............49
3.6. Routing Key Management (RKM) Messages [Optional] ..........49
3.6.1. Registration Request (REG REQ) .....................49
3.6.2. Registration Response (REG RSP) ....................54
3.6.3. Deregistration Request (DEREG REQ) .................56
3.6.4. Deregistration Response (DEREG RSP) ................57
3.7. ASP Traffic Maintenance (ASPTM) Messages ..................59
3.7.1. ASP Active .........................................59
3.7.2. ASP Active Acknowledgement (ASP Active Ack) ........60
3.7.3. ASP Inactive .......................................61
3.7.4. ASP Inactive Acknowledgement (ASP Inactive Ack) ....62
3.8. Management (MGMT) Messages ................................63
3.8.1. Error ..............................................63
3.8.2. Notify .............................................67
4. Procedures .....................................................70
4.1. Procedures to Support the M3UA-User .......................70
4.1.1. Receipt of Primitives from the M3UA-User ...........70
4.2. Receipt of Primitives from the Layer Management ...........71
4.2.1. Receipt of M3UA Peer Management Messages ...........72
4.3. AS and ASP/IPSP State Maintenance .........................73
4.3.1. ASP/IPSP States ....................................74
4.3.2. AS States ..........................................76
4.3.3. M3UA Management Procedures for Primitives ..........78
4.3.4. ASPM Procedures for Peer-to-Peer Messages ..........79
4.3.4.1. ASP Up Procedures .........................79
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4.3.4.2. ASP-Down Procedures .......................81
4.3.4.3. ASP Active Procedures .....................82
4.3.4.4. ASP Inactive Procedures ...................86
4.3.4.5. Notify Procedures .........................88
4.3.4.6. Heartbeat Procedures ......................89
4.4. Routing Key Management Procedures [Optional] ..............90
4.4.1. Registration .......................................90
4.4.2. Deregistration .....................................92
4.4.3. IPSP Considerations (REG/DEREG) ....................93
4.5. Procedures to Support the Availability or
Congestion Status of SS7 Destination ......................93
4.5.1. At an SGP ..........................................93
4.5.2. At an ASP ..........................................94
4.5.2.1. Single SG Configurations ..................94
4.5.2.2. Multiple SG Configurations ................94
4.5.3. ASP Auditing .......................................94
4.6. MTP3 Restart ..............................................96
4.7. NIF Not Available .........................................97
4.8. M3UA Version Control ......................................97
4.9. M3UA Termination ..........................................97
5. Examples of M3UA Procedures ....................................98
5.1. Establishment of Association and Traffic between
SGPs and ASPs .............................................98
5.1.1. Single ASP in an Application Server ("1+0"
sparing), No Registration ..........................98
5.1.1.1. Single ASP in an Application
Server ("1+0" Sparing), No Registration ...98
5.1.1.2. Single ASP in Application Server
("1+0" Sparing), Dynamic Registration .....99
5.1.1.3. Single ASP in Multiple
Application Servers (Each with "1+0"
Sparing), Dynamic Registration (Case 1
- Multiple Registration Requests) ........100
5.1.1.4. Single ASP in Multiple
Application Servers (each with "1+0"
sparing), Dynamic Registration (Case 2
- Single Registration Request) ...........101
5.1.2. Two ASPs in Application Server ("1+1" Sparing) ....102
5.1.3. Two ASPs in an Application Server ("1+1"
Sparing, Loadsharing Case) ........................103
5.1.4. Three ASPs in an Application Server ("n+k"
Sparing, Loadsharing Case) ........................104
5.2. ASP Traffic Failover Examples ............................105
5.2.1. 1+1 Sparing, Withdrawal of ASP, Backup Override ...105
5.2.2. 1+1 Sparing, Backup Override ......................105
5.2.3. n+k Sparing, Loadsharing Case, Withdrawal of ASP ..106
5.3. Normal Withdrawal of an ASP from an Application Server ...106
5.4. Auditing Examples ........................................107
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5.4.1. SG State: Uncongested/Available ...................107
5.4.2. SG State: Congested (Congestion Level=2) /
Available .........................................107
5.4.3. SG State: Unknown/Available .......................107
5.4.4. SG State: Unavailable .............................108
5.5. M3UA/MTP3-User Boundary Examples .........................108
5.5.1. At an ASP .........................................108
5.5.1.1. Support for MTP-TRANSFER
Primitives at the ASP ....................108
5.5.2. At an SGP .........................................109
5.5.2.1. Support for MTP-TRANSFER Request
Primitive at the SGP .....................109
5.5.2.2. Support for MTP-TRANSFER
Indication Primitive at the SGP ..........110
5.5.2.3. Support for MTP-PAUSE,
MTP-RESUME, MTP-STATUS Indication
Primitives ...............................110
5.6. Examples for IPSP Communication ..........................112
5.6.1. Single Exchange ...................................112
5.6.2. Double Exchange ...................................113
6. Security Considerations .......................................113
7. IANA Considerations ...........................................114
7.1. SCTP Payload Protocol Identifier .........................114
7.2. M3UA Port Number .........................................114
7.3. M3UA Protocol Extensions .................................114
7.3.1. IETF-Defined Message Classes ......................115
7.3.2. IETF Defined Message Types ........................115
7.3.3. IETF-Defined Parameter Extension ..................115
8. Acknowledgements ..............................................115
9. Document Contributors .........................................116
10. References ...................................................116
10.1. Normative References ....................................116
10.2. Informative References ..................................117
Appendix A .......................................................119
A.1. Signalling Network Architecture .............................119
A.2. Redundancy Models ...........................................121
A.2.1. Application Server Redundancy ........................121
A.2.2. Signalling Gateway Redundancy ........................122
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RFC 4666 SS7 MTP3-User Adaptation Layer September 2006
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 [18]. Also,
provision is made for protocol elements that enable a seamless
operation of the MTP3-User peers in the SS7 and IP domains. This
protocol would be used between a Signalling Gateway (SG) and a Media
Gateway Controller (MGC) or IP-resident Database [12], 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 [12]. 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 [13], 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.
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 signalling relation, identified by
an SS7 DPC/OPC. Another example is a virtual database element,
handling all HLR transactions for a particular SS7 SIO/DPC/OPC
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.
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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.
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 to which it belongs. 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
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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 configured either using a configuration
management interface, or by using the routing key management
procedures defined in this document.
Signaling End Point (SEP) - A node in the SS7 network associated with
an originating or terminating local exchange (switch) or a gateway
exchange.
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 (SG) - An SG is a signaling agent that
receives/sends SCN native signaling at the edge of the IP network
[12]. 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.
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.
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Signaling Transfer Point (STP) - A node in the SS7 network that
provides network access and performs message routing, screening and
transfer of signaling messages.
Stream - 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 [12] 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) [13]. TCAP [14,15,16]
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) [18] as the underlying reliable common
signalling transport protocol. This is to take advantage of various
SCTP features, such as:
- Explicit packet-oriented delivery (not stream-oriented)
- Sequenced delivery of user messages within multiple streams,
with an option for order-of-arrival delivery of individual
user messages
- Optional multiplexing of user messages into SCTP datagrams
- Network-level fault tolerance through support of multi-homing
at either or both ends of an association
- Resistance to flooding and masquerade attacks
- 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.
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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.
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, thereby
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
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size. Some configurations (e.g., Broadband MTP [19,20,22]) 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;
- providing an indication to the M3UA layer at an ASP that the routes
to a destination in the SS7 network are restricted; and
- 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 and 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. Also, 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
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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.
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.
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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 it 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, under 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
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
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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
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-octet 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, and SIO found in the MTP3
routing label. Some example Routing Keys are: the DPC alone, the
DPC/OPC combination, or the DPC/OPC/SI 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.
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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. An example of a partial match would be a default
Routing Key that would be the result if there are no other Routing
Keys to which the message belongs. It is not necessary for the
parameter range values within a particular Routing Key to be
contiguous.
1.4.2.3. Managing Routing Contexts and Routing Keys
There are two ways to provision a Routing Key at an SGP. A Routing
Key may be configured statically using an implementation dependent
management interface, or dynamically using the M3UA Routing Key
registration procedure.
When using a management interface to configure Routing Keys, the
message distribution function within the SGP is not limited to the
set of parameters defined in this document. Other implementation-
dependent distribution algorithms may be used.
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.
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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 ASPs, or to drop the
message and provide a notification to layer management. The
treatment of unallocated traffic is implementation dependent.
1.4.2.5. Message Distribution at the ASP
The ASP must choose an SGP to direct a message to the SS7 network.
This is accomplished by observing the Destination Point Code (and
possibly other elements of the outgoing message, such as the SLS
value). 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.
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From an SS7 perspective, it is expected that the Signalling Gateway
transmits and receives SS7 Message Signalling Units (MSUs) over a
standard SS7 network interface, using the SS7 Message Transfer Part
(MTP) [7,8,9].
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) [19,20].
Note: It is also possible for IP-based interfaces to be present,
using the services of the MTP2-User Adaptation Layer (M2UA) [24] or
M2PA [25].
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.
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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 the 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.
1.4.4. Redundancy Models
1.4.4.1 Application Server Redundancy
All MTP3-User messages (e.g., ISUP, SCCP) that 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. Traffic SHOULD be sent after "n" ASPs are active. "k" ASPs MAY
be either active at the same time as "n" or kept inactive until
needed due to 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.
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1.4.6. Congestion Management
The M3UA layer is informed of local and IP network congestion by
means of an implementation-dependent function (e.g., an
implementation-dependent indication from the SCTP of IP network
congestion).
At an ASP or IPSP, the M3UA layer indicates IP network 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 IP network
congestion, the SG MAY trigger SS7 MTP3 Transfer Controlled
management messages to originating SS7 nodes, per the congestion
procedures of the relevant MTP3 standard. The triggering of SS7 MTP3
Management messages from an SG is an implementation-dependent
function.
The M3UA layer at an ASP or IPSP MAY indicate local congestion to an
M3UA peer with an SCON message. When an SG receives a congestion
message (SCON) from an ASP and the SG determines that an SPMC is now
encountering congestion, it MAY trigger SS7 MTP3 Transfer Controlled
management messages to concerned SS7 destinations according to
congestion procedures of the relevant MTP3 standard.
1.4.7. SCTP Stream Mapping
The M3UA layer at both the SGP and ASP also supports the assignment
of signalling traffic into streams within an SCTP association.
Traffic that requires sequencing SHOULD be assigned to the same
stream. To accomplish this, MTP3-User traffic may be assigned to
individual streams based on, for example, the SLS value in the MTP3
Routing Label, subject of course to the maximum number of streams
supported by the underlying SCTP association.
The following rules apply (see Section 3.1.2):
1. The DATA message MUST NOT be sent on stream 0.
2. The ASPSM, MGMT, RKM classes SHOULD be sent on stream 0 (other
than BEAT, BEAT ACK and NTFY messages).
3. The SSNM, ASPTM classes and BEAT, BEAT ACK and NTFY messages can
be sent on any stream.
1.4.8. SCTP 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
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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.
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,
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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.
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 that 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/SI 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 that 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
This section provides a definition of the boundaries of the M3UA
protocol. They consist of SCTP, Layer Management, and the MTP3-User.
+-----------+
| MTP3-User |
+-----------+
|
|
+-----------+ +------------+
| M3UA |-----| Layer Mgmt |
+-----------+ +------------+
|
|
+-----------+
| SCTP |
+-----------+
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 [18], Section 10.
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1.6.3. Definition of the Boundary between M3UA and Layer Management
M-SCTP_ESTABLISH request
Direction: LM -> M3UA
Purpose: LM requests that ASP establish an SCTP association with its
peer.
M-SCTP_ESTABLISH confirm
Direction: M3UA -> LM
Purpose: ASP confirms to LM that it has established an SCTP
association with its peer.
M-SCTP_ESTABLISH indication
Direction: M3UA -> LM
Purpose: M3UA informs LM that a remote ASP has established an SCTP
association.
M-SCTP_RELEASE request
Direction: LM -> M3UA
Purpose: LM requests that ASP 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 that 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 that M3UA report the status of an SCTP
association.
M-SCTP_STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA responds with the status of an SCTP association.
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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 that M3UA report the status of a local or remote
ASP.
M-ASP_STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA reports the status of local or remote ASP.
M-AS_STATUS request
Direction: LM -> M3UA
Purpose: LM requests that M3UA report the status of an AS.
M-AS_STATUS confirm
Direction: M3UA -> LM
Purpose: M3UA reports the status of an AS.
M-NOTIFY indication
Direction: M3UA -> LM
Purpose: M3UA reports that it has received a Notify message
from its peer.
M-ERROR indication
Direction: M3UA -> LM
Purpose: M3UA reports that it has received an Error message from
its peer or that a local operation has been unsuccessful.
M-ASP_UP request
Direction: LM -> M3UA
Purpose: LM requests that ASP start its operation and send an ASP Up
message to its peer.
M-ASP_UP confirm
Direction: M3UA -> LM
Purpose: ASP reports that it has received an ASP UP Ack message from
its peer.
M-ASP_UP indication
Direction: M3UA -> LM
Purpose: M3UA reports that it has successfully processed an incoming
ASP Up message from its peer.
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M-ASP_DOWN request
Direction: LM -> M3UA
Purpose: LM requests that ASP stop its operation and send an ASP Down
message to its peer.
M-ASP_DOWN confirm
Direction: M3UA -> LM
Purpose: ASP reports that it has received an ASP Down Ack message
from its peer.
M-ASP_DOWN indication
Direction: M3UA -> LM
Purpose: M3UA reports that it has successfully processed an incoming
ASP Down message from its peer, or the SCTP association has
been lost/reset.
M-ASP_ACTIVE request
Direction: LM -> M3UA
Purpose: LM requests that ASP send an ASP Active message to its peer.
M-ASP_ACTIVE confirm
Direction: M3UA -> LM
Purpose: ASP reports that it has received an ASP Active
Ack message from its peer.
M-ASP_ACTIVE indication
Direction: M3UA -> LM
Purpose: M3UA reports that it has successfully processed an incoming
ASP Active message from its peer.
M-ASP_INACTIVE request
Direction: LM -> M3UA
Purpose: LM requests that ASP send an ASP Inactive message to its
peer.
M-ASP_INACTIVE confirm
Direction: LM -> M3UA
Purpose: ASP reports that it has received an ASP Inactive
Ack message from its peer.
M-ASP_INACTIVE indication
Direction: M3UA -> LM
Purpose: M3UA reports that 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.
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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 that ASP register RK(s) with its peer by sending
an REG REQ message
M-RK_REG confirm
Direction: M3UA -> LM
Purpose: ASP reports that it has received REG RSP message with a
registration status of 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 that ASP deregister RK(s) with its peer by
sending a DEREG REQ message.
M-RK_DEREG confirm
Direction: M3UA -> LM
Purpose: ASP reports that it has received DEREG REQ message with a
deregistration status of 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
In this document, the keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL
NOT, SHOULD, SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and
OPTIONAL are to be interpreted as described in [21].
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3. M3UA Protocol Elements
The general M3UA message format includes a Common Message Header
followed by zero or more parameters as defined by the Message Type.
For forward compatibility, all Message Types may have attached
parameters even if none are specified in this version.
3.1. Common Message Header
The protocol messages for MTP3-User Adaptation require a message
header that 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 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 as follows:
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
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6 Reserved for Other SIGTRAN Adaptation Layers
7 Reserved for Other SIGTRAN Adaptation Layers
8 Reserved for Other SIGTRAN Adaptation Layers
9 Routing Key Management (RKM) Messages
10 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined Message Class extensions
Message Type: 8 bits (unsigned integer)
The following list contains the message types for the defined
messages.
Management (MGMT) Messages (see Section 3.8)
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)
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7 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined ASPSM extensions
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 octets, if there are any.
Note: A receiver SHOULD accept the message whether or not the final
parameter padding is included in the message length.
3.2. Variable-Length Parameter Format
M3UA messages consist of a Common Header followed by zero or more
variable-length parameters, as defined by the message type. All the
parameters contained in a message are defined in a Tag Length-Value
format, as shown below.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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.
Unless explicitly stated or shown in a message format diagram, only
one parameter of the same type is allowed in a message.
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
Not Used in M3UA 0x000e
Not Used in M3UA 0x000f
Not Used in M3UA 0x0010
ASP Identifier 0x0011
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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
Reserved 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 descriptions
are reserved for use by the IETF. An RFC is required to make use
of parameter values "Reserved by the IETF".
Parameter Length: 16 bits (unsigned integer)
The Parameter Length field contains the size of the parameter in
octets, 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 octets. If the
parameter contains subparameters, the Parameter Length field will
include all the octets of each subparameter, including
subparameter padding octets (if there are any).
Parameter Value: variable length
The Parameter Value field contains the actual information to be
transferred in the parameter.
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The total length of a parameter (including Tag, Parameter Length,
and Value fields) MUST be a multiple of 4 octets. If the length
of the parameter is not a multiple of 4 octets, the sender pads
the Parameter at the end (i.e., after the Parameter Value field)
with all zero octets. The length of the padding is NOT included
in the parameter length field. A sender MUST NOT pad with more
than 3 octets. The receiver MUST ignore the padding octets.
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 Conditional
Protocol Data Mandatory
Correlation Id Optional
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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 if 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 on 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.
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.
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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, which includes
MTP3-User protocol elements (e.g., ISUP, SCCP, or TUP
parameters)
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'.
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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 [26] message
priority bits. The MP bits are aligned to the least significant bit.
Unused bits are coded `0'.
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: variable-length octet string
The User Protocol Data field contains an octet string of MTP-User
information from the original SS7 message, starting with the first
octet of the original SS7 message following the Routing Label
[7][8][26].
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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The DUNA message contains the following parameters:
Network Appearance Optional
Routing Context Conditional
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
The description of Network Appearance in Section 3.3.1 applies,
with the exception that Network Appearance does not have to be the
first parameter in this message.
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Routing Context: n x 32 bits (unsigned integer)
The conditional 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
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 receipt 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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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 receipt 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 are "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 are "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. An INFO String with a zero-length
parameter is not considered an error (a zero length parameter is
one in which the Length field in the TLV will be set to 4).
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 4666 SS7 MTP3-User Adaptation Layer September 2006
The DAVA message contains the following parameters:
Network Appearance Optional
Routing Context Conditional
Affected Point Code Mandatory
INFO String Optional
The format and description of the Network Appearance, Routing
Context, Affected Point Code, and INFO String parameters are 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 Conditional
Affected Point Code Mandatory
INFO String Optional
The format and description of DAUD Message parameters are the same as
for the DUNA message (See Section 3.4.1).
It is recommended that during normal operation (traffic handling) the
mask field of the Affected Point Code parameter in the DAUD message
be kept to a zero value in order to avoid SG overloading.
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 congestion
level of the M3UA layer or the ASP has changed.
IMPLEMENTATION NOTE: An M3UA node may maintain a timer to control
congestion notification validity, if desired. This timer will be
useful in cases where the peer node fails to indicate congestion
abatement.
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The SCON message contains the following parameters:
Network Appearance Optional
Routing Context Conditional
Affected Point Code Mandatory
Concerned Destination Optional
Congestion Indications Optional
INFO String Optional
The format for SCON Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0200 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 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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The format and description of the Network Appearance, Routing
Context, Affected Point Code, and INFO String parameters are 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
The congestion levels are defined in the congestion method in the
appropriate national MTP recommendations [7,8].
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RFC 4666 SS7 MTP3-User Adaptation Layer September 2006
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 Conditional
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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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, etc.). 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
are 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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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 are 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 a route 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 Conditional
Affected Point Code Mandatory
INFO String Optional
The format and description of the Network Appearance, Routing
Context, Affected Point Code, and INFO String parameters are the
same as for the DUNA message (see Section 3.4.1).
3.5. ASP State Maintenance (ASPSM) Messages
3.5.1. ASP Up
The ASP Up message is used to indicate to a remote M3UA peer that
the adaptation layer is ready to receive any ASPSM/ASPTM messages
for all Routing Keys that the ASP is configured to serve.
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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
are the same as for the DUNA message (see Section 3.4.1).
3.5.2. ASP Up Acknowledgement (ASP Up Ack)
The ASP UP Ack message is used to acknowledge an ASP Up message
received from a remote M3UA peer.
The ASP Up Ack message contains the following parameters:
ASP Identifier Optional
INFO String Optional
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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 = 0x0011 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASP Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag =0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The optional ASP Identifier parameter is specifically useful for IPSP
communication. In that case, the IPSP answering the ASP Up message
MAY include its own ASP Identifier value.
The format and description of the optional INFO String parameter are
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 parameter:
INFO String Optional
The format for the ASP Down message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag =0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The format and description of the optional INFO String parameter are
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 parameter:
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 are
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).
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 parameter:
Heartbeat Data Optional
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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 expect to receive a REG RSP message in return with an associated
Routing Context value.
The REG REQ message contains the following parameter:
Routing Key Mandatory
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One or more Routing Key parameters MAY be included. The format for
the REG REQ message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0207 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Key 1 /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0207 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Key n /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Routing Key: variable length
The Routing Key parameter is mandatory. The sender of this
message expects that the receiver of this message will create a
Routing Key entry and assign a unique Routing Context value to it,
if the Routing Key entry does not already exist.
The Routing Key parameter may be present multiple times in the
same message. This is used to allow the registration of multiple
Routing Keys in a single message.
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The format of the Routing Key parameter is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local-RK-Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Routing Context (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Indicators (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating Point Code List (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Point Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Indicators (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating Point Code List (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note: The Destination Point Code, Service Indicators, and
Originating Point Code 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 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.
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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 it
identifies the Destination Point Code of incoming SS7 traffic
for which the ASP is registering. For an alias point code
configuration, the DPC parameter would be repeated for each
point code. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Network Appearance
The optional Network Appearance parameter field identifies the SS7
network context for the Routing Key, and it has the same format as
in the DATA message (see Section 3.3.1) with the exception that it
does not have to be the first parameter in the message. If the
Network Appearance is not specified and the Routing Key applies to
all Network Appearances, then this Routing Key MUST be the only
one registered for the association; that is, Routing Context is
implied, and DATA and SSNM messages are discriminated on Network
Appearance rather than on Routing Context. Where Network
Appearance is not specified and there is only one Network
Appearance, then Network Appearance is implied. 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 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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OPC List
The Originating Point Code List parameter contains one or more SS7
OPC entries, and its format is the same as for the Destination
Point Code parameter. The absence of the OPC List parameter in
the Routing Key indicates the use of any OPC value.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x020e | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Origination Point Code #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Origination Point Code #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ ... /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Origination Point Code #n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.6.2. Registration Response (REG RSP)
The REG RSP message is used as a response to the REG REQ message from
a remote M3UA peer. It contains indications of success/failure for
registration requests and returns a unique Routing Context value for
successful registration requests, to be used in subsequent M3UA
Traffic Management protocol.
The REG RSP message contains the following parameter:
Registration Result Mandatory
One or more Registration Result parameters MUST be included. The
format for the REG RSP message is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0208 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Registration Result 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0208 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Registration Result n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Registration Results
The Registration Result parameter contains the registration result
for a single Routing Key in an REG REQ message. The number of
results in a single REG RSP message MUST be anywhere from one to
the total number of number of Routing Key parameters found in the
corresponding REG REQ message. Where multiple REG RSP messages
are used in reply to REG REQ message, a specific result SHOULD be
in only one REG RSP message. The format of each result is as
follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x020a | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local-RK-Identifier value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0212 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Registration Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Routing Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Local-RK-Identifier: 32-bit integer
The Local-RK-Identifier contains the same value as found in the
matching Routing Key parameter found in the REG REQ message (See
Section 3.6.1).
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Registration Status: 32-bit integer
The Registration Result Status field indicates the success or the
reason for failure of a registration request.
Its values may be:
0 Successfully Registered
1 Error - Unknown
2 Error - Invalid DPC
3 Error - Invalid Network Appearance
4 Error - Invalid Routing Key
5 Error - Permission Denied
6 Error - Cannot Support Unique Routing
7 Error - Routing Key not Currently Provisioned
8 Error - Insufficient Resources
9 Error - Unsupported RK parameter Field
10 Error - Unsupported/Invalid Traffic Handling Mode
11 Error - Routing Key Change Refused
12 Error - Routing Key Already Registered
Routing Context: 32-bit integer
The Routing Context field contains the Routing Context value for
the associated Routing Key if the registration was successful. It
is set to "0" if the registration was not successful.
3.6.3. Deregistration Request (DEREG REQ)
The DEREG REQ message is sent by an ASP to indicate to a remote M3UA
peer that it wishes to deregister a given Routing Key. Typically, an
ASP would send this message to an SGP and expects to receive a DEREG
RSP message in return with the associated Routing Context value.
The DEREG REQ message contains the following parameters:
Routing Context Mandatory
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The format for the DEREG REQ message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Routing Context: n X 32-bit integers
The Routing Context parameter contains (a list of) integers
indexing the Application Server traffic that the sending ASP is
currently registered to receive from the SGP but now wishes to
deregister.
3.6.4. Deregistration Response (DEREG RSP)
The DEREG RSP message is used as a response to the DEREG REQ message
from a remote M3UA peer.
The DEREG RSP message contains the following parameter:
Deregistration Result Mandatory
One or more Deregistration Result parameters MUST be included. The
format for the DEREG RSP message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0209 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Deregistration Result 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0209 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Deregistration Result n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Deregistration Results
The Deregistration Result parameter contains the deregistration
status for a single Routing Context in a DEREG REQ message. The
number of results in a single DEREG RSP message MAY be anywhere
from one to the total number of number of Routing Context values
found in the corresponding DEREG REQ message.
Where multiple DEREG RSP messages are used in reply to DEREG REQ
message, a specific result SHOULD be in only one DEREG RSP
message. The format of each result is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Routing Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0213 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Deregistration Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Routing Context: 32-bit integer
The Routing Context field contains the Routing Context value of
the matching Routing Key to deregister, as found in the DEREG REQ
message.
Deregistration Status: 32-bit integer
The Deregistration Result Status field indicates the success or
the reason for failure of the deregistration.
Its values may be:
0 Successfully Deregistered
1 Error - Unknown
2 Error - Invalid Routing Context
3 Error - Permission Denied
4 Error - Not Registered
5 Error - ASP Currently Active for Routing Context
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3.7. ASP Traffic Maintenance (ASPTM) Messages
3.7.1. ASP Active
The ASP Active message is sent by an ASP to indicate to a remote M3UA
peer that it is ready to process signalling traffic for a particular
Application Server. The ASP Active message affects only the ASP
state for the Routing Keys identified by the Routing Contexts, if
present.
The ASP Active message contains the following parameters:
Traffic Mode Type Optional
Routing Context Optional
INFO String Optional
The format for the ASP Active message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x000b | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Traffic Mode Type: 32-bit (unsigned integer)
The Traffic Mode Type parameter identifies the traffic mode of
operation of the ASP within an AS. The valid values for Traffic
Mode Type are shown in the following table:
1 Override
2 Loadshare
3 Broadcast
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Within a particular Routing Context, Override, Loadshare, and
Broadcast SHOULD NOT be mixed. The Override value indicates that
the ASP is operating in Override mode, in which the ASP takes over
all traffic in an Application Server (i.e., primary/backup
operation), overriding any currently active ASPs in the AS. In
Loadshare mode, the ASP will share in the traffic distribution
with any other currently active ASPs. In Broadcast mode, the ASP
will receive the same messages as any other currently active ASP.
Routing Context: n X 32-bit integers
The optional Routing Context parameter contains (a list of)
integers indexing the Application Server traffic that the sending
ASP is configured/registered to receive.
There is a one-to-one relationship between an index entry and an
SGP Routing Key or AS Name. Because an AS can only appear in one
Network Appearance, the Network Appearance parameter is not
required in the ASP Active message.
An Application Server Process may be configured to process traffic
for more than one logical Application Server. From the
perspective of an ASP, a Routing Context defines a range of
signalling traffic that the ASP is currently configured to receive
from the SGP. For example, an ASP could be configured to support
signalling for multiple MTP3-Users, identified by separate SS7
DPC/OPC/SI ranges.
The format and description of the optional INFO String parameter are
the same as for the DUNA message (see Section 3.4.1).
3.7.2. ASP Active Acknowledgement (ASP Active Ack)
The ASP Active Ack message is used to acknowledge an ASP Active
message received from a remote M3UA peer.
The ASP Active Ack message contains the following parameters:
Traffic Mode Type Optional
Routing Context Optional
INFO String Optional
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The format for the ASP Active Ack message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x000b | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional INFO String parameter are
the same as for the DUNA message (see Section 3.4.1).
The INFO String in an ASP Active Ack message is independent from the
INFO String in the ASP Active message (i.e., it does not have to echo
back the INFO String received).
The format of the Traffic Mode Type and Routing Context parameters is
the same as for the ASP Active message. (See Section 3.7.1.)
3.7.3. ASP Inactive
The ASP Inactive message is sent by an ASP to indicate to a remote
M3UA peer that it is no longer an active ASP to be used from within a
list of ASPs. The ASP Inactive message affects only the ASP state in
the Routing Keys identified by the Routing Contexts, if present.
The ASP Inactive message contains the following parameters:
Routing Context Optional
INFO String Optional
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The format for the ASP Inactive message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Routing Context and INFO
String parameters are the same as for the ASP Active message (see
Section 3.5.5.)
3.7.4. ASP Inactive Acknowledgement (ASP Inactive Ack)
The ASP Inactive Ack message is used to acknowledge an ASP Inactive
message received from a remote M3UA peer.
The ASP Inactive Ack message contains the following parameters:
Routing Context Optional
INFO String Optional
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The format for the ASP Inactive Ack message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional INFO String parameter are
the same as for the DUNA message (see Section 3.4.1).
The INFO String in an ASP Inactive Ack message is independent from
the INFO String in the ASP Inactive message (i.e., it does not have
to echo back the INFO String received).
The format of the Routing Context parameter is the same as for the
ASP Inactive message. (see Section 3.7.3.)
3.8. Management (MGMT) Messages
3.8.1. Error
The Error message is used to notify a peer of an error event
associated with an incoming message. For example, the message type
might be unexpected given the current state, or a parameter value
might be invalid. Error messages MUST NOT be generated in response
to other Error messages.
The Error message contains the following parameters:
Error Code Mandatory
Routing Context Mandatory*
Network Appearance Mandatory*
Affected Point Code Mandatory*
Diagnostic Information Conditional
* Only mandatory for specific Error Codes.
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The format for the Error message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x000c | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag - 0x0012 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected Point Code 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected Point Code n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0200 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0007 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Diagnostic Information /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Error Code: 32 bits (unsigned integer)
The Error Code parameter indicates the reason for the Error
Message. The Error parameter value can be one of the following
values:
0x01 Invalid Version
0x02 Not Used in M3UA
0x03 Unsupported Message Class
0x04 Unsupported Message Type
0x05 Unsupported Traffic Mode Type
0x06 Unexpected Message
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0x07 Protocol Error
0x08 Not Used in M3UA
0x09 Invalid Stream Identifier
0x0a Not Used in M3UA
0x0b Not Used in M3UA
0x0c Not Used in M3UA
0x0d Refused - Management Blocking
0x0e ASP Identifier Required
0x0f Invalid ASP Identifier
0x10 Not Used in M3UA
0x11 Invalid Parameter Value
0x12 Parameter Field Error
0x13 Unexpected Parameter
0x14 Destination Status Unknown
0x15 Invalid Network Appearance
0x16 Missing Parameter
0x17 Not Used in M3UA
0x18 Not Used in M3UA
0x19 Invalid Routing Context
0x1a No Configured AS for ASP
The "Invalid Version" error is sent if a message with an unsupported
version is received. The receiving end responds with an Error
message, indicating the version the receiving node supports, and
notifies layer management.
The "Unsupported Message Class" error is sent if a message with an
unexpected or unsupported Message Class is received. For this error,
the Diagnostic Information parameter MUST be included with the first
40 octets of the offending message.
The "Unsupported Message Type" error is sent if a message with an
unexpected or unsupported Message Type is received. For this error,
the Diagnostic Information parameter MUST be included with the first
40 octets of the offending message.
The "Unsupported Traffic Mode Type" error is sent by a SGP if an ASP
sends an ASP Active message with an unsupported Traffic Mode Type or
a Traffic Mode Type that is inconsistent with the presently
configured mode for the Application Server. An example would be a
case in which the SGP did not support loadsharing.
The "Unexpected Message" error MAY be sent if a defined and
recognized message is received that is not expected in the current
state (in some cases, the ASP may optionally silently discard the
message and not send an Error message). For example, silent discard
is used by an ASP if it received a DATA message from an SGP while it
was in the ASP-INACTIVE state. If the Unexpected message contained
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Routing Contexts, the Routing Contexts SHOULD be included in the
Error message.
The "Protocol Error" error is sent for any protocol anomaly (i.e.,
receipt of a parameter that is syntactically correct but unexpected
in the current situation).
The "Invalid Stream Identifier" error is sent if a message is
received on an unexpected SCTP stream (e.g., a Management message was
received on a stream other than "0").
The "Refused - Management Blocking" error is sent when an ASP Up or
ASP Active message is received and the request is refused for
management reasons (e.g., management lockout). If this error is in
response to an ASP Active message, the Routing Context(s) in the ASP
Active message SHOULD be included in the Error message.
The "ASP Identifier Required" error is sent by an SGP in response to
an ASP Up message that does not contain an ASP Identifier parameter
when the SGP requires one. The ASP SHOULD resend the ASP Up message
with an ASP Identifier.
The "Invalid ASP Identifier" error is sent by an SGP in response to
an ASP Up message with an invalid (i.e., non-unique) ASP Identifier.
The "Invalid Parameter Value" error is sent if a message is received
with an invalid parameter value (e.g., a DUPU message was received
with a Mask value other than "0".
The "Parameter Field Error" would be sent if a message is received
with a parameter having a wrong length field.
The "Unexpected Parameter" error would be sent if a message contains
an invalid parameter.
The "Destination Status Unknown" error MAY be sent if a DAUD is
received at an SG enquiring of the availability/congestion status of
a destination and the SG does not wish to provide the status (e.g.,
the sender is not authorized to know the status). For this error,
the invalid or unauthorized Point Code(s) MUST be included along with
the Network Appearance and/or Routing Context associated with the
Point Code(s).
The "Invalid Network Appearance" error is sent by an SGP if an ASP
sends a message with an invalid (unconfigured) Network Appearance
value. For this error, the invalid (unconfigured) Network Appearance
MUST be included in the Network Appearance parameter.
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The "Missing Parameter" error would be sent if a mandatory parameter
were not included in a message. This error is also sent if a
conditional parameter is not included in the message but is required
in the context of the received message.
The "Invalid Routing Context" error is sent if a message is received
from a peer with an invalid (unconfigured) Routing Context value.
For this error, the invalid Routing Context(s) MUST be included in
the Error message.
The "No Configured AS for ASP" error is sent if a message is received
from a peer without a Routing Context parameter and it is not known
by configuration data which Application Servers are referenced.
Diagnostic Information: variable length
When included, the optional Diagnostic Information can be any
information germane to the error condition, to assist in
identification of the error condition. The Diagnostic Information
SHOULD contain the offending message. A Diagnostic Information
parameter with a zero length parameter is not considered an error
(this means that the Length field in the TLV will be set to 4).
3.8.2. Notify
The Notify message used to provide an autonomous indication of M3UA
events to an M3UA peer.
The Notify message contains the following parameters:
Status Mandatory
ASP Identifier Conditional
Routing Context Optional
INFO String Optional
The format for the Notify message is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x000d | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Type | Status Information |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0011 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASP Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0006 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Status Type: 16 bits (unsigned integer)
The Status Type parameter identifies the type of the Notify
message. The following are the valid Status Type values:
1 Application Server State Change (AS-State_Change)
2 Other
Status Information: 16 bits (unsigned integer)
The Status Information parameter contains more detailed
information for the notification, based on the value of the Status
Type. If the Status Type is AS-State_Change the following Status
Information values are used:
1 Reserved
2 Application Server Inactive (AS-INACTIVE)
3 Application Server Active (AS-ACTIVE)
4 Application Server Pending (AS-PENDING)
These notifications are sent from an SGP to an ASP upon a change
in status of a particular Application Server. The value reflects
the new state of the Application Server.
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If the Status Type is Other, then the following Status Information
values are defined:
1 Insufficient ASP Resources Active in AS
2 Alternate ASP Active
3 ASP Failure
These notifications are not based on the SGP reporting the state
change of an ASP or AS. In the Insufficient ASP Resources case,
the SGP is indicating to an ASP_INACTIVE ASP in the AS that
another ASP is required to handle the load of the AS (Loadsharing
or Broadcast mode). For the Alternate ASP Active case, an ASP is
informed when an alternate ASP transitions to the ASP-ACTIVE state
in Override mode. The ASP Identifier (if available) of the
Alternate ASP MUST be placed in the message. For the ASP Failure
case, the SGP is indicating to ASPs in the AS that one of the
ASPs has failed. The ASP Identifier (if available) of the failed
ASP MUST be placed in the message.
The format and description of the conditional ASP Identifier is the
same as for the ASP Up message (see Section 3.5.1). The format and
description of the Routing Context and Info String parameters are the
same as for the ASP Active message (See Section 3.7.1)
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4. Procedures
The M3UA layer needs to respond to various local primitives it
receives from other layers, as well as to the messages that it
receives from the peer M3UA layer. This section describes the M3UA
procedures in response to these events.
4.1. Procedures to Support the M3UA-User
4.1.1. Receipt of Primitives from the M3UA-User
On receiving an MTP-TRANSFER request primitive from an upper layer at
an ASP/IPSP, or the nodal interworking function at an SGP, the M3UA
layer sends a corresponding DATA message (see Section 3) to its M3UA
peer. The M3UA peer receiving the DATA message sends an MTP-TRANSFER
indication primitive to the upper layer.
The M3UA message distribution function (see Section 1.4.2.1)
determines the Application Server (AS) by comparing the information
in the MTP-TRANSFER request primitive with a provisioned Routing Key.
From the list of ASPs within the AS table, an ASP in the ASP-ACTIVE
state is selected and a DATA message is constructed and issued on the
corresponding SCTP association. If more than one ASP is in the ASP-
ACTIVE state (i.e., traffic is to be loadshared across more than one
ASP), one of the ASPs in the ASP-ACTIVE state is selected from the
list. If the ASPs are in Broadcast Mode, all active ASPs will be
selected, and the message will be sent to each of the active ASPs.
The selection algorithm is implementation dependent but could, for
example, be round robin or based on the SLS or ISUP CIC. The
appropriate selection algorithm must be chosen carefully, as it is
dependent on application assumptions and understanding of the degree
of state coordination between the ASP-ACTIVE ASPs in the AS.
In addition, the message needs to be sent on the appropriate SCTP
stream, again taking care to meet the message sequencing needs of the
signalling application. DATA messages MUST be sent on an SCTP stream
other than stream '0'.
When there is no Routing Key match, or only a partial match, 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 in an
M-ERROR indication primitive. The treatment of unallocated traffic
is implementation dependent.
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4.2. Receipt of Primitives from the Layer Management
On receiving primitives from the local Layer Management, the M3UA
layer will take the requested action and provide an appropriate
response primitive to Layer Management.
An M-SCTP_ESTABLISH request primitive from Layer Management at an ASP
or IPSP will initiate the establishment of an SCTP association. The
M3UA layer will attempt to establish an SCTP association with the
remote M3UA peer by sending an SCTP-ASSOCIATE primitive to the local
SCTP layer.
When an SCTP association has been successfully established, the SCTP
will send an SCTP-COMMUNICATION_UP notification primitive to the
local M3UA layer. At the SGP or IPSP that initiated the request, the
M3UA layer will send an M-SCTP_ESTABLISH confirm primitive to Layer
Management when the association setup is complete. At the peer M3UA
layer, an M-SCTP_ESTABLISH indication primitive is sent to Layer
Management upon successful completion of an incoming SCTP association
setup.
An M-SCTP_RELEASE request primitive from Layer Management initiates
the teardown of an SCTP association. The M3UA layer accomplishes a
graceful shutdown of the SCTP association by sending an SCTP-SHUTDOWN
primitive to the SCTP layer.
When the graceful shutdown of the SCTP association has been
accomplished, the SCTP layer returns an SCTP-SHUTDOWN_COMPLETE
notification primitive to the local M3UA layer. At the M3UA Layer
that initiated the request, the M3UA layer will send an M-
SCTP_RELEASE confirm primitive to Layer Management when the
association shutdown is complete. At the peer M3UA Layer, an M-
SCTP_RELEASE indication primitive is sent to Layer Management upon
abort or successful shutdown of an SCTP association.
An M-SCTP_STATUS request primitive supports a Layer Management query
of the local status of a particular SCTP association. The M3UA layer
simply maps the M-SCTP_STATUS request primitive to an SCTP-STATUS
primitive to the SCTP layer. When the SCTP responds, the M3UA layer
maps the association status information to an M-SCTP_STATUS confirm
primitive. No peer protocol is invoked.
Similar LM-to-M3UA-to-SCTP and/or SCTP-to-M3UA-to-LM primitive
mappings can be described for the various other SCTP Upper Layer
primitives in RFC2960 [18], such as INITIALIZE, SET PRIMARY, CHANGE
HEARTBEAT, REQUEST HEARTBEAT, GET SRTT REPORT, SET FAILURE THRESHOLD,
SET PROTOCOL PARAMETERS, DESTROY SCTP INSTANCE, SEND FAILURE, and
NETWORK STATUS CHANGE. Alternatively, these SCTP Upper Layer
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primitives (and Status as well) can be considered, for modeling
purposes, as a Layer Management interaction directly with the SCTP
Layer.
M-NOTIFY indication and M-ERROR indication primitives indicate to
Layer Management the notification or error information contained in a
received M3UA Notify or Error message, respectively. These
indications can also be generated based on local M3UA events.
An M-ASP_STATUS request primitive supports a Layer Management query
of the status of a particular local or remote ASP. The M3UA layer
responds with the status in an M-ASP_STATUS confirm primitive. No
M3UA peer protocol is invoked.
An M-AS_STATUS request supports a Layer Management query of the
status of a particular AS. The M3UA responds with an M-AS_STATUS
confirm primitive. No M3UA peer protocol is invoked.
M-ASP_UP, M-ASP_DOWN, M-ASP_ACTIVE, and M-ASP_INACTIVE request
primitives allow Layer Management at an ASP to initiate state
changes. Upon successful completion, a corresponding confirm
primitive is provided by the M3UA layer to Layer Management. If an
invocation is unsuccessful, an Error indication primitive is provided
in the primitive. These requests result in outgoing ASP Up, ASP
Down, ASP Active, and ASP Inactive messages to the remote M3UA peer
at an SGP or IPSP.
4.2.1. Receipt of M3UA Peer Management Messages
Upon successful state changes resulting from reception of ASP Up, ASP
Down, ASP Active, and ASP Inactive messages from a peer M3UA, the
M3UA layer MAY invoke corresponding M-ASP_UP, M-ASP_DOWN, M-
ASP_ACTIVE, M-ASP_INACTIVE, M-AS_ACTIVE, M-AS_INACTIVE, and M-AS_DOWN
indication primitives to the local Layer Management.
M-NOTIFY indication and M-ERROR indication primitives indicate to
Layer Management the notification or error information contained in a
received M3UA Notify or Error message. These indications can also be
generated based on local M3UA events.
All non-Transfer and non-SSNM messages, except BEAT and BEAT Ack,
SHOULD be sent with sequenced delivery to ensure ordering. ASPTM
messages MAY be sent on one of the streams used to carry the data
traffic related to the Routing Context(s), to minimize possible
message loss. BEAT and BEAT Ack messages MAY be sent using out-of-
order delivery and MAY be sent on any stream.
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4.3. AS and ASP/IPSP State Maintenance
The M3UA layer on the SGP maintains the state of each remote ASP, in
each Application Server that the ASP is configured to receive
traffic, as input to the M3UA message distribution function.
Similarly, where IPSPs use M3UA in a point-to-point fashion, the M3UA
layer in an IPSP maintains the state of remote IPSPs.
Two IPSP models are defined as follows:
1. IPSP Single Exchange (SE) model. Only a single exchange of ASPTM
and ASPSM messages is needed to change the IPSP states. This
means that a set of requests from one end and acknowledgements
from the other will be enough. The RK must define both sides of
the traffic flow. Each exchange of ASPTM or ASPSM messages can be
initiated by either IPSP. For this exchange, the initiating IPSP
follows the procedures described in Section 4.3.1.
2. IPSP Double Exchange (DE) model. A double exchange of ASPTM and
ASPSM messages is normally needed (ASPSM single exchange is
optional as a simplification). Each exchange of ASPTM or ASPSM
messages can be initiated by either IPSP. The RKs define the
traffic to be directed to the peer as in the AS-SG model.
Therefore, two different RKs are usually used, one installed on
each peer.
When using double exchanges for ASPSM messages, the management of
the connection in the two directions is considered independent.
This means that connections from IPSP-A to IPSP-B is handled
independently of connections from IPSP-B to IPSP-A. Therefore, it
could happen that only one of the two directions is activated or
closed, while the other remains in the same state as it was.
When using single exchange of ASPSM, what is seen as a
simplification, only the activation phase (ASPTM messages) is
independent for each of the two directions. In this case, it
could happen that the sending of the ASPSM from IPSP-A or IPSP-B
could have an effect in the whole communication, as it is defined
in the standard SG-AS communication.
Because of these differences, there should be an agreement on the
way ASPSM messages are being handled before starting DE-IPSP
communication.
In order to ensure interoperability, an M3UA implementation
supporting IPSP communication MUST support the IPSP SE model and MAY
implement the IPSP DE model.
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In Section 4.3.1, ASP/IPSP States are described.
In Section 4.3.2, only the SGP-ASP scenario is described. All of the
procedures referring to an AS served by ASPs are also applicable to
ASes served by IPSPs.
In Section 4.3.3, only the Management procedures for the SGP-ASP
scenario are described. The corresponding Management procedures for
IPSPs are directly implied.
The remaining sections contain specific IPSP Considerations
subsections.
4.3.1. ASP/IPSP States
The state of each remote ASP/IPSP, in each AS that it is configured
to operate, is maintained in the peer M3UA layer (i.e., in the SGP or
peer IPSP, respectively). The state of a particular ASP/IPSP in a
particular AS changes due to events. The events include:
* Receipt of messages from the peer M3UA layer at the ASP/IPSP;
* Receipt of some messages from the peer M3UA layer at other
ASPs/IPSPs in the AS (e.g., ASP Active message indicating
"Override");
* Receipt of indications from the SCTP layer; and
* Local Management intervention.
The ASP/C-IPSP/D-IPSP state transition diagram is shown in Figure 3.
The possible states of an ASP/D-IPSP/C-IPSP are:
ASP-DOWN: The remote M3UA peer at the ASP/IPSP is unavailable, and/or
the related SCTP association is down. Initially, all ASPs/IPSPs will
be in this state. An ASP/IPSP in this state SHOULD NOT be sent any
M3UA messages, with the exception of Heartbeat, ASP Down Ack, and
Error messages.
ASP-INACTIVE: The remote M3UA peer at the ASP/IPSP is available (and
the related SCTP association is up), but application traffic is
stopped. In this state, the ASP/IPSP SHOULD NOT be sent any DATA or
SSNM messages for the AS for which the ASP/IPSP is inactive.
ASP-ACTIVE: The remote M3UA peer at the ASP/IPSP is available and
application traffic is active (for a particular Routing Context or
set of Routing Contexts).
SCTP CDI: The SCTP CDI denotes the local SCTP layer's Communication
Down Indication to the Upper Layer Protocol (M3UA) on an SGP. The
local SCTP layer will send this indication when it detects the loss
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of connectivity to the ASP's peer SCTP layer. SCTP CDI is understood
as either a SHUTDOWN_COMPLETE notification or a COMMUNICATION_LOST
notification from the SCTP layer.
SCTP RI: The local SCTP layer's Restart indication to the upper-layer
protocol (M3UA) on an SG. The local SCTP will send this indication
when it detects a restart from the peer SCTP layer.
+--------------+
| |
+----------------------| ASP-ACTIVE |
| Other ASP/ +-------| |
| IPSP in AS | +--------------+
| Overrides | ^ |
| | ASPAC/ | | ASPIA/
| |[ASPAC-Ack]| | [ASPIA-Ack]
| | | v
| | +--------------+
| | | |
| +------>| ASP-INACTIVE |
| | |
| +--------------+
| ^ |
ASPDN/ | | | ASPDN /
[ASPDN-Ack/]| ASPUP/ | | [ASPDN-Ack /]
SCTP CDI/ | [ASPUP-Ack] | | SCTP CDI/
SCTP RI | | | SCTP RI
| | v
| +--------------+
| | |
+--------------------->| ASP-DOWN |
| |
+--------------+
Figure 3: ASP State Transition Diagram, per AS
The transitions are depicted as a result of the reception of ASP*M
messages or other events. In some of the transitions, there are some
messages in brackets. They mean that for a given node the state
transition will be different, depending on its role: whether or not
it is generating the ASP*M request message (i.e., ASPUP, ASPAC, ASPIA
or ASPDN) or simply receiving it. In a peer-to-peer based
architecture (IPSP), this role may change between the peers.
The transitions not in brackets are valid to track the states of ASPs
and IPSPs that send an ASP*M request message at the peer node.
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The transition in brackets may be used in an ASP or in the IPSP that
receives an ASP*M request to track the peer SGP/IPSP states,
respectively. There may be an SGP per AS state machine at ASPs.
Then, the transitions in brackets can be used for the IPSP DE model
communication (DE-IPSPs) and are related to the special cases when
just one ASP*M messages exchange is needed, as follows:
- ASPSM messages. When ASPSM messages are exchanged using only a
single exchange (only one request and one acknowledgement).
Example (see Section 5.6.2): Whenever a DE-IPSP is taking the
leading role to start communication to a peer DE-IPSP, it sends an
ASP Up message to the peer DE-IPSP. The peer MAY consider the
initiating DE-IPSPs to be in ASP-INACTIVE state, as it already sent
a message, and answer back with ASP Up Ack. Upon receipt of this
answer by the initiating DE-IPSP, it also MAY consider the peer to
be in ASP-INACTIVE state, since it did respond. Therefore, a
second ASP Up message exchange to be started by the peer DE-IPSP
could be avoided. In this case, the receipt of ASP Up Ack will
turn into a state change.
- ASPTM messages. When sending ASPTM messages to activate/deactivate
all the traffic independently of routing keys by not specifying any
RC, a single exchange could be sufficient.
4.3.2. AS States
The state of the AS is maintained in the M3UA layer on the SGPs. The
state of an AS changes due to events. These events include:
* ASP state transitions
* Recovery timer triggers
The possible states of an AS are:
AS-DOWN: The Application Server is unavailable. This state implies
that all related ASPs are in ASP-DOWN state for this AS. Initially
the AS will be in this state. An Application Server is in the AS-
DOWN state when it is removed from a configuration.
AS-INACTIVE: The Application Server is available, but no application
traffic is active. One or more related ASPs are in ASP-INACTIVE
state, and/or the number of related ASPs in ASP-ACTIVE state has not
reached n (n is the number of ASPs required to be in ASP-ACTIVE state
before AS can transition to AS-ACTIVE; n = 1 for Override Traffic
Mode) for this AS. The recovery timer T(r) is not running or has
expired.
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AS-ACTIVE: The Application Server is available and application
traffic is active. The AS moves to this state after being in AS-
INACTIVE and getting n ASPs (n is the number of ASPs required to be
in ASP-ACTIVE state before AS can transition to AS-ACTIVE; n = 1 for
Override Traffic Mode) in ASP-ACTIVE state or after reaching AS-
ACTIVE and keeping one or more ASPs in ASP-ACTIVE state. When one
ASP is considered enough to handle traffic (smooth start), the AS in
AS-INACTIVE MAY reach the AS-ACTIVE as soon as the first ASP moves to
the ASP-ACTIVE state.
AS-PENDING: An active ASP has transitioned to ASP-INACTIVE or ASP
DOWN and it was the last remaining active ASP in the AS. A recovery
timer T(r) SHOULD be started, and all incoming signalling messages
SHOULD be queued by the SGP. If an ASP becomes ASP-ACTIVE before
T(r) expires, the AS is moved to the AS-ACTIVE state, and all the
queued messages will be sent to the ASP.
If T(r) expires before an ASP becomes ASP-ACTIVE, and the SGP has no
alternative, the SGP may stop queuing messages and discard all
previously queued messages. The AS will move to the AS-INACTIVE
state if at least one ASP is in ASP-INACTIVE; otherwise, it will move
to AS-DOWN state.
Figure 4 shows an example AS state machine for the case where the
AS/ASP data is preconfigured and is an n+k redundancy model. In
other cases where the AS/ASP configuration data is created
dynamically, there would be differences in the state machine,
especially at creation of the AS.
+----------+ IA2AC +-------------+
| AS- |---------------------------->| AS- |
| INACTIVE | | ACTIVE |
| |<----------- | |
+----------+ \ +-------------+
^ | \ ^ |
| | IA2DN \ PN2IA | | AC2PN
| | \ | |
DN2IA | | \ PN2AC | |
| v \ | v
+----------+ \ +-------------+
| | ----------| |
| AS-DOWN | | AS-PENDING |
| | PN2DN | (queueing) |
| |<----------------------------| |
+----------+ +-------------+
Figure 4: AS State Transition Diagram
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DN2IA: One ASP moves from ASP-DOWN to ASP-INACTIVE state.
IA2DN: The last ASP in ASP-INACTIVE moves to ASP-DOWN, causing all
the ASPs to be in ASP-DOWN state.
IA2AC: One ASP moves to ASP-ACTIVE, causing the number of ASPs in the
ASP-ACTIVE state to be n. In a special case of smooth start, this
transition MAY be done when the first ASP moves to ASP-ACTIVE state.
AC2PN: The last ASP in ASP-ACTIVE state moves to ASP-INACTIVE or
ASP-DOWN states, causing the number of ASPs in ASP-ACTIVE to drop
below 1.
PN2AC: One ASP moves to ASP-ACTIVE.
PN2IA: T(r) expiry; an ASP is in ASP-INACTIVE state but no ASPs are
in ASP-ACTIVE state.
PN2DN: T(r) expiry; all the ASPs are in ASP-DOWN state.
An AS becomes AS-ACTIVE right after n ASPs reach the ASP-ACTIVE state
during the startup phase (except for smooth start). Once the traffic
is flowing, an AS keeps the AS-ACTIVE state till the last ASP turns
to another state different from ASP-ACTIVE, avoiding unnecessary
traffic disturbances as long as there are ASPs available (this
assumes that the system will not always be exposed to the maximum
load).
There are other cases where the AS/ASP configuration data is created
dynamically. In those cases there would be differences in the state
machine, especially at creation of the AS. For example, where the
AS/ASP configuration data is not created until Registration of the
first ASP, the AS-INACTIVE state is entered directly upon the nth
successful REG REQ from an ASP belonging to that AS. Another example
is where the AS/ASP configuration data is not created until the nth
ASP successfully enters the ASP-ACTIVE state. In this latter case,
the AS-ACTIVE state is entered directly.
4.3.3. M3UA Management Procedures for Primitives
Before the establishment of an SCTP association, the ASP state at
both the SGP and ASP is assumed to be in the state ASP-DOWN.
Once the SCTP association is established (see Section 4.2), assuming
that the local M3UA-User is ready, the local M3UA ASP Maintenance
(ASPM) function will initiate the relevant procedures, using the ASP
Up/ASP Down/ASP Active/ASP Inactive messages to convey the ASP state
to the SGP (see Section 4.3.4).
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If the M3UA layer subsequently receives an SCTP-COMMUNICATION_DOWN or
SCTP-RESTART indication primitive from the underlying SCTP layer, it
will inform the Layer Management by invoking the M-SCTP_STATUS
indication primitive. The state of the ASP will be moved to ASP-
DOWN. At an ASP, the MTP3-User will be informed of the
unavailability of any affected SS7 destinations through the use of
MTP-PAUSE indication primitives.
In the case of SCTP-COMMUNICATION_DOWN, the SCTP client MAY try to
re-establish the SCTP Association. This MAY be done by the M3UA
layer automatically, or Layer Management MAY reestablish using the
M-SCTP_ESTABLISH request primitive.
In the case of an SCTP-RESTART indication at an ASP, the ASP is now
considered to be in the ASP-DOWN state by its M3UA peer. The ASP, if
it is to recover, must begin any recovery with the ASP-Up procedure.
4.3.4. ASPM Procedures for Peer-to-Peer Messages
4.3.4.1. ASP Up Procedures
After an ASP has successfully established an SCTP association to an
SGP, the SGP waits for the ASP to send an ASP Up message, indicating
that the ASP M3UA peer is available. The ASP is always the initiator
of the ASP Up message. This action MAY be initiated at the ASP by an
M-ASP_UP request primitive from Layer Management or MAY be initiated
automatically by an M3UA management function.
When an ASP Up message is received at an SGP and, internally, the
remote ASP is in the ASP-DOWN state and is not considered locked out
for local management reasons, the SGP marks the remote ASP in the
state ASP-INACTIVE and informs Layer Management with an M-ASP_Up
indication primitive. If the SGP is aware, via current configuration
data, which Application Servers the ASP is configured to operate in,
the SGP updates the ASP state to ASP-INACTIVE in each AS that it is a
member.
Alternatively, the SGP may move the ASP into a pool of Inactive ASPs
available for future configuration within Application Servers,
determined in a subsequent Registration Request or ASP Active
procedure. If the ASP Up message contains an ASP Identifier, the SGP
should save the ASP Identifier for that ASP. The SGP MUST send an
ASP Up Ack message in response to a received ASP Up message even if
the ASP is already marked as ASP-INACTIVE at the SGP.
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If for any local reason (e.g., management lockout) the SGP cannot
respond with an ASP Up Ack message, the SGP responds to an ASP Up
message with an Error message with the reason "Refused - Management
Blocking".
At the ASP, the ASP Up Ack message received is not acknowledged.
Layer Management is informed with an M-ASP_UP confirm primitive.
When the ASP sends an ASP Up message, it starts timer T(ack). If the
ASP does not receive a response to an ASP Up message within T(ack),
the ASP MAY restart T(ack) and resend ASP Up messages until it
receives an ASP Up Ack message. T(ack) is provisionable, with a
default of 2 seconds. Alternatively, retransmission of ASP Up
messages MAY be put under control of Layer Management. In this
method, expiry of T(ack) results in an M-ASP_UP confirm primitive
carrying a negative indication.
The ASP must wait for the ASP Up Ack message before sending any other
M3UA messages (e.g., ASP Active or REG REQ). If the SGP receives any
other M3UA messages before an ASP Up message is received (other than
ASP Down; see Section 4.3.4.2), the SGP MAY discard them.
If an ASP Up message is received and, internally, the remote ASP is
in the ASP-ACTIVE state, an ASP Up Ack message is returned, as well
as an Error message ("Unexpected Message"). In addition, the remote
ASP state is changed to ASP-INACTIVE in all relevant Application
Servers, and all registered Routing Keys are considered deregistered.
If an ASP Up message is received and, internally, the remote ASP is
already in the ASP-INACTIVE state, an ASP Up Ack message is returned,
and no further action is taken.
If the ASP receives an unexpected ASP Up Ack message, the ASP should
consider itself in the ASP-INACTIVE state. If the ASP was not in the
ASP-INACTIVE state, it SHOULD send an Error message and then initiate
procedures to return itself to its previous state.
4.3.4.1.1. M3UA Version Control and ASP Up
If an ASP Up message with an unsupported version is received, the
receiving end responds with an Error message, indicating the version
the receiving node supports and notifies Layer Management. See
Section 4.8 for more on this issue.
4.3.4.1.2. IPSP Considerations (ASP Up)
An IPSP may be considered in the ASP-INACTIVE state after an ASP Up
or ASP Up Ack has been received from it. An IPSP can be considered
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in the ASP-DOWN state after an ASP Down or ASP Down Ack has been
received from it. The IPSP may inform Layer Management of the change
in state of the remote IPSP using M-ASP_UP or M-ASP_DN indication or
confirmation primitives.
Alternatively, when using the IPSP DE model, an interchange of ASP Up
messages from each end MUST be performed. Four messages are needed
for completion.
If for any local reason (e.g., management lockout) an IPSP cannot
respond to an ASP Up message with an ASP Up Ack message, it responds
to an ASP Up message with an Error message with the reason "Refused
Management Blocking" and leaves the remote IPSP in the ASP-DOWN
state.
4.3.4.2. ASP-Down Procedures
The ASP will send an ASP Down message to an SGP when the ASP wishes
to be removed from service in all Application Servers that it is a
member and no longer receive any DATA, SSNM or, ASPTM messages. This
action MAY be initiated at the ASP by an M-ASP_DOWN request primitive
from Layer Management or MAY be initiated automatically by an M3UA
management function.
Whether the ASP is permanently removed from any AS is a function of
configuration management. In the case where the ASP previously used
the Registration procedures (see Section 4.4.1) to register within
Application Servers but has not deregistered from all of them prior
to sending the ASP Down message, the SGP MUST consider the ASP
Deregistered in all Application Servers that it is still a member.
The SGP marks the ASP as ASP-DOWN, informs Layer Management with an
M-ASP_Down indication primitive, and returns an ASP Down Ack message
to the ASP.
The SGP MUST send an ASP Down Ack message in response to a received
ASP Down message from the ASP even if the ASP is already marked as
ASP-DOWN at the SGP.
At the ASP, the ASP Down Ack message received is not acknowledged.
Layer Management is informed with an M-ASP_DOWN confirm primitive.
If the ASP receives an ASP Down Ack without having sent an ASP Down
message, the ASP should now consider itself to be in the ASP-DOWN
state.
If the ASP was previously in the ASP-ACTIVE or ASP-INACTIVE state,
the ASP should then initiate procedures to return itself to its
previous state.
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When the ASP sends an ASP Down message, it starts timer T(ack). If
the ASP does not receive a response to an ASP Down message within
T(ack), the ASP MAY restart T(ack) and resend ASP Down messages until
it receives an ASP Down Ack message. T(ack) is provisionable, with a
default of 2 seconds. Alternatively, retransmission of ASP Down
messages MAY be put under control of Layer Management. In this
method, expiry of T(ack) results in an M-ASP_DOWN confirm primitive,
carrying a negative indication.
4.3.4.3. ASP Active Procedures
Anytime after the ASP has received an ASP Up Ack message from the SGP
or IPSP, the ASP MAY send an ASP Active message to the SGP,
indicating that the ASP is ready to start processing traffic. This
action MAY be initiated at the ASP by an M-ASP_ACTIVE request
primitive from Layer Management or MAY be initiated automatically by
an M3UA management function. In the case where an ASP wishes to
process the traffic for more than one Application Server across a
common SCTP association, the ASP Active message(s) SHOULD contain a
list of one or more Routing Contexts to indicate for which
Application Servers the ASP Active message applies. It is not
necessary for the ASP to include all Routing Contexts of interest in
a single ASP Active message, thus requesting to become active in all
Routing Contexts at the same time. Multiple ASP Active messages MAY
be used to activate within the Application Servers independently, or
in sets.
In the case where an ASP Active message does not contain a Routing
Context parameter, the receiver must know, via configuration data,
which Application Server(s) the ASP is a member.
For the Application Servers for which the ASP can be successfully
activated, the SGP or IPSP responds with one or more ASP Active Ack
messages, including the associated Routing Context(s) and reflecting
any Traffic Mode Type value present in the related ASP Active
message. The Routing Context parameter MUST be included in the ASP
Active Ack message(s) if the received ASP Active message contained
any Routing Contexts. Depending on any Traffic Mode Type request in
the ASP Active message, or local configuration data if there is no
request, the SGP moves the ASP to the correct ASP traffic state
within the associated Application Server(s). Layer Management is
informed with an M-ASP_Active indication. If the SGP or IPSP
receives any Data messages before an ASP Active message is received,
the SGP or IPSP MAY discard them. By sending an ASP Active Ack
message, the SGP or IPSP is now ready to receive and send traffic for
the related Routing Context(s). The ASP SHOULD NOT send Data or SSNM
messages for the related Routing Context(s) before receiving an ASP
Active Ack message, or it will risk message loss.
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Multiple ASP Active Ack messages MAY be used in response to an ASP
Active message containing multiple Routing Contexts, allowing the SGP
or IPSP to independently acknowledge the ASP Active message for
different (sets of) Routing Contexts.
The ASP Active message will be responded to in the following way as a
function of the presence/need of the RC parameter:
- If the RC parameter is included in the ASP Active message and the
corresponding RK has been previously defined (by either static
configuration or dynamic registration), the peer node MUST respond
with an ASP Active Ack message. If for any local reason (e.g.,
management lockout) the SGP responds to an ASP Active message with
an Error message with reason "Refused Management Blocking".
- If the RC parameter is included in the ASP Active message and a
corresponding RK has not been previously defined (by either static
configuration or dynamic registration), the peer MUST respond with
an ERROR message with the Error Code "No configured AS for ASP".
- If (1) the RC parameter is not included in the ASP Active message,
(2) there are RKs defined (by either static configuration or
dynamic registration) and (3) RC is not mandatory, the peer node
SHOULD respond with an ASP Active Ack message and activate all the
RKs it has defined for that specific ASP.
- If (!) the RC parameter is not included in the ASP Active message,
(2) there are RKs defined (by either static configuration or
dynamic registration), (3) and RC is mandatory, the peer node MUST
respond with an ERROR message with the Error Code "Missing
Parameter".
- If (1) the RC parameter is not included in the ASP Active message,
(2) there are RKs defined (by either static configuration or
dynamic registration) and (3) RC is not mandatory, the peer node
MUST respond with an ASP Active Ack message if it is ready to
handle traffic; otherwise, it will send an ERROR message with the
Error Code "No Configured AS for ASP" (meaning that it is not ready
to become active).
- If the RC parameter is not included in the ASP Active message and
there are no RKs defined, the peer node SHOULD respond with and
ERROR message with the Error Code "Invalid Routing Context".
Independently of the RC, the SGP MUST send an ASP Active Ack message
in response to a received ASP Active message from the ASP, if the ASP
is already marked in the APS-ACTIVE state.
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At the ASP, the ASP Active Ack message received is not acknowledged.
Layer Management is informed with an M-ASP_ACTIVE confirm primitive.
It is possible for the ASP to receive Data messages before the ASP
Active Ack message as the ASP Active Ack and Data messages from an SG
or IPSP may be sent on different SCTP streams. Message loss is
possible, as the ASP does not consider itself in the ASP-ACTIVE state
until receipt of the ASP Active Ack message.
When the ASP sends an ASP Active message, it starts the timer T(ack).
If the ASP does not receive a response to an ASP Active message
within T(ack), the ASP MAY restart T(ack) and resend ASP Active
messages until it receives an ASP Active Ack message. T(ack) is
provisionable, with a default of 2 seconds. Alternatively,
retransmission of ASP Active messages MAY be put under control of
Layer Management. In this method, expiry of T(ack) results in an M-
ASP_ACTIVE confirm primitive carrying a negative indication.
There are three modes of Application Server traffic handling in the
SGP M3UA layer: Override, Loadshare and Broadcast. When included,
the Traffic Mode Type parameter in the ASP Active message indicates
the traffic handling mode to be used in a particular Application
Server. If the SGP determines that the mode indicated in an ASP
Active message is unsupported or incompatible with the mode currently
configured for the AS, the SGP responds with an Error message
("Unsupported / Invalid Traffic Handling Mode"). If the traffic
handling mode of the Application Server is not already known via
configuration data, then the traffic handling mode indicated in the
first ASP Active message causing the transition of the Application
Server state to AS-ACTIVE MAY be used to set the mode.
In the case of an Override mode AS, receipt of an ASP Active message
at an SGP causes the (re)direction of all traffic for the AS to the
ASP that sent the ASP Active message. Any previously active ASP in
the AS is now considered to be in the state ASP-INACTIVE and SHOULD
no longer receive traffic from the SGP within the AS. The SGP or
IPSP then MUST send a Notify message ("Alternate ASP_Active") to the
previously active ASP in the AS and SHOULD stop traffic to/from that
ASP. The ASP receiving this Notify MUST consider itself now in the
ASP-INACTIVE state, if it is not already aware of this via inter-ASP
communication with the Overriding ASP.
In the case of a Loadshare mode AS, receipt of an ASP Active message
at an SGP or IPSP causes direction of traffic to the ASP sending the
ASP Active message, in addition to all the other ASPs that are
currently active in the AS. The algorithm at the SGP for loadsharing
traffic within an AS to all the active ASPs is implementation
dependent. The algorithm could, for example, be round-robin or based
on information in the Data message (e.g., the SLS, SCCP SSN, or ISUP
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CIC value). An SGP or IPSP, upon receipt of an ASP Active message
for the first ASP in a Loadshare AS, MAY choose not to direct traffic
to a newly active ASP until it determines that there are sufficient
resources to handle the expected load (e.g., until there are "n" ASPs
in state ASP-ACTIVE in the AS). In this case, the SGP or IPSP SHOULD
withhold the Notify (AS-ACTIVE) until there are sufficient resources.
For the n+k redundancy case, ASPs that are in that AS should
coordinate among themselves the number of active ASPs in the AS and
should start sending traffic only after n ASPs are active. All ASPs
within a loadsharing mode AS must be able to process any Data message
received for the AS, to accommodate any potential failover or
rebalancing of the offered load.
In the case of a Broadcast mode AS, receipt of an ASP Active message
at an SGP or IPSP causes direction of traffic to the ASP sending the
ASP Active message, in addition to all the other ASPs that are
currently active in the AS. The algorithm at the SGP for
broadcasting traffic within an AS to all the active ASPs is a simple
broadcast algorithm, where every message is sent to each of the
active ASPs.
At startup or restart phases, an SGP or IPSP, upon receipt of an ASP
Active message for the first ASP in a Loadshare AS, SHOULD NOT direct
traffic to a newly active ASP until it determines that there are
sufficient resources to handle the expected load (e.g., until there
are "n" ASPs in state ASP-ACTIVE in the AS). In this case, the SGP
or IPSP SHOULD withhold the Notify (AS-ACTIVE) until there are
sufficient resources.
An SGP or IPSP, upon receipt of an ASP Active message for the first
ASP in a Broadcast AS, MAY choose not to direct traffic to a newly
active ASP until it determines that there are sufficient resources to
handle the expected load (e.g., until there are "n" ASPs in state
ASP-ACTIVE in the AS). In this case, the SGP or IPSP SHOULD withhold
the Notify (AS-ACTIVE) until there are sufficient resources.
For the n+k redundancy case, ASPs that are in that AS should
coordinate among themselves the number of active ASPs in the AS and
should start sending traffic only after n ASPs are active.
Whenever an ASP in a Broadcast mode AS becomes ASP-ACTIVE, the SGP
MUST tag the first DATA message broadcast in each traffic flow with a
unique Correlation Id parameter. The purpose of this Id is to permit
the newly active ASP to synchronize its processing of traffic in each
traffic flow with the other ASPs in the broadcast group.
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4.3.4.3.1. IPSP Considerations (ASP Active)
Either of the IPSPs can initiate communication. When an IPSP
receives an ASP Active, it should mark the peer as ASP-ACTIVE and
return an ASP Active Ack message. An ASP receiving an ASP Active Ack
message may mark the peer as ASP-Active, if it is not already in the
ASP-ACTIVE state.
Alternatively, when using the IPSP DE model, an interchange of ASP
Active messages from each end MUST be performed. Four messages are
needed for completion.
4.3.4.4. ASP Inactive Procedures
When an ASP wishes to withdraw from receiving traffic within an AS or
the ASP wants to initiate the process of deactivation, the ASP sends
an ASP Inactive message to the SGP or IPSP.
An ASP Inactive message MUST always be responded to by the peer
(although other messages may be sent in the middle) in the following
way:
- If the received ASP Inactive message contains an RC parameter
and the corresponding RK is defined (by either static
configuration or dynamic registration), the SGP/IPSP MUST
respond with an ASP Inactive Ack message.
- If the received ASP Inactive message contains an RC parameter
that is not defined (by either static configuration or dynamic
registration), the SGP/IPSP MUST respond with an ERROR message
with the Error Code "Invalid Routing Context".
- If the received ASP Inactive message does not contain an RC
parameter and the RK is defined (by either static configuration
or dynamic registration), the SGP/IPSP must turn the ASP/IPSP to
ASP-INACTIVE state in all the ASes it serves and MUST respond
with an ASP Inactive Ack message.
- If the received ASP Inactive message does not contain an RC
parameter and the RK is not defined (by either static
configuration or dynamic registration), the SGP/IPSP MUST
respond with an ERROR message with the Error Code "No configured
AS for ASP".
The action of sending the ASP Inactive message MAY be initiated at
the ASP by an M-ASP_INACTIVE request primitive from Layer Management
or MAY be initiated automatically by an M3UA management function. In
the case where an ASP is processing the traffic for more than one
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Application Server across a common SCTP association, the ASP Inactive
message contains one or more Routing Contexts to indicate for which
Application Servers the ASP Inactive message applies.
In the case where an ASP Inactive message does not contain a Routing
Context parameter, the receiver must know, via configuration data,
which Application Servers the ASP is a member of and then move the
ASP to the ASP-INACTIVE state in all Application Servers.
In the case of an Override mode AS, where another ASP has already
taken over the traffic within the AS with an ASP Active ("Override")
message, the ASP that sends the ASP Inactive message is already
considered to be in ASP-INACTIVE state by the SGP. An ASP Inactive
Ack message is sent to the ASP, after ensuring that all traffic is
stopped to the ASP.
In the case of a Loadshare mode AS, the SGP moves the ASP to the
ASP-INACTIVE state, and the AS traffic is reallocated across the
remaining ASPs in the state ASP-ACTIVE, as per the loadsharing
algorithm currently used within the AS. A Notify message
("Insufficient ASP resources active in AS") MAY be sent to all
inactive ASPs, if required. An ASP Inactive Ack message is sent to
the ASP after all traffic is halted, and Layer Management is informed
with an M-ASP_INACTIVE indication primitive.
In the case of a Broadcast mode AS, the SGP moves the ASP to the
ASP-INACTIVE state, and the AS traffic is broadcast only to the
remaining ASPs in the state ASP-ACTIVE. A Notify message
("Insufficient ASP resources active in AS") MAY be sent to all
inactive ASPs, if required. An ASP Inactive Ack message is sent to
the ASP after all traffic is halted, and Layer Management is informed
with an M-ASP_INACTIVE indication primitive.
Multiple ASP Inactive Ack messages MAY be used in response to an ASP
Inactive message containing multiple Routing Contexts, allowing the
SGP or IPSP to independently acknowledge for different (sets of)
Routing Contexts. The SGP or IPSP sends an Error message ("Invalid
Routing Context") message for each invalid or unconfigured Routing
Context value in a received ASP Inactive message.
The SGP MUST send an ASP Inactive Ack message in response to a
received ASP Inactive message from the ASP; the ASP is already marked
as ASP-INACTIVE at the SGP.
At the ASP, the ASP Inactive Ack message received is not
acknowledged. Layer Management is informed with an M-ASP_INACTIVE
confirm primitive. If the ASP receives an ASP Inactive Ack without
having sent an ASP Inactive message, the ASP should now consider
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itself to be in the ASP-INACTIVE state. If the ASP was previously in
the ASP-ACTIVE state, the ASP should then initiate procedures to
return itself to its previous state.
When the ASP sends an ASP Inactive message, it starts the timer
T(ack). If the ASP does not receive a response to an ASP Inactive
message within T(ack), the ASP MAY restart T(ack) and resend ASP
Inactive messages until it receives an ASP Inactive Ack message.
T(ack) is provisionable, with a default of 2 seconds. Alternatively,
retransmission of ASP Inactive messages MAY be put under control of
Layer Management. In this method, expiry of T(ack) results in an M-
ASP_Inactive confirm primitive carrying a negative indication.
If no other ASPs in the Application Server are in the state ASP-
ACTIVE, the SGP MUST send a Notify message ("AS-Pending") to all ASPs
in the AS that are in the state ASP-INACTIVE. The SGP SHOULD start
buffering the incoming messages for T(r) seconds, after which
messages MAY be discarded. T(r) is configurable by the network
operator. If the SGP receives an ASP Active message from an ASP in
the AS before expiry of T(r), the buffered traffic is directed to
that ASP, and the timer is cancelled. If T(r) expires, the AS is
moved to the AS-INACTIVE state.
4.3.4.4.1. IPSP Considerations (ASP Inactive)
An IPSP may be considered in the ASP-INACTIVE state by a remote IPSP
after an ASP Inactive or ASP Inactive Ack message has been received
from it.
Alternatively, when using IPSP DE model, an interchange of ASP
Inactive messages from each end MUST be performed. Four messages are
needed for completion.
4.3.4.5. Notify Procedures
A Notify message reflecting a change in the AS state MUST be sent to
all ASPs in the AS, except those in the ASP-DOWN state, with
appropriate Status Information and any ASP Identifier of the failed
ASP. At the ASP, Layer Management is informed with an M-NOTIFY
indication primitive. The Notify message must be sent whether the AS
state change was a result of an ASP failure or receipt of an ASP
State management (ASPSM) / ASP Traffic Management (ASPTM) message.
In the second case, the Notify message MUST be sent after any related
acknowledgement messages (e.g., ASP Up Ack, ASP Down Ack, ASP Active
Ack, or ASP Inactive Ack).
When an ASP moves from ASP-DOWN to ASP-INACTIVE within a particular
AS, a Notify message SHOULD be sent, by the ASP-UP receptor, after
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sending the ASP-UP-ACK, in order to inform the ASP of the current AS
state.
In the case where a Notify message ("AS-PENDING") message is sent by
an SGP that now has no ASPs active to service the traffic, or where a
Notify ("Insufficient ASP resources active in AS") message is sent in
the Loadshare or Broadcast mode, the Notify message does not
explicitly compel the ASP(s) receiving the message to become active.
The ASPs remain in control of what (and when) traffic action is
taken.
In the case where a Notify message does not contain a Routing Context
parameter, the receiver must know, via configuration data, of which
Application Servers the ASP is a member and take the appropriate
action in each AS.
4.3.4.5.1. IPSP Considerations (NTFY)
Notify works in the same manner as in the SG-AS case. One of the
IPSPs can send this message to any remote IPSP that is not in the
ASP-DOWN state.
4.3.4.6. Heartbeat Procedures
The optional Heartbeat procedures MAY be used when operating over
transport layers that do not have their own heartbeat mechanism for
detecting loss of the transport association (i.e., other than SCTP).
Either M3UA peer may optionally send Heartbeat messages periodically,
subject to a provisionable timer, T(beat). Upon receiving a
Heartbeat message, the M3UA peer MUST respond with a Heartbeat Ack
message.
If no Heartbeat Ack message (or any other M3UA message) is received
from the M3UA peer within 2*T(beat), the remote M3UA peer is
considered unavailable. Transmission of Heartbeat messages is
stopped, and the signalling process SHOULD attempt to re-establish
communication if it is configured as the client for the disconnected
M3UA peer.
The Heartbeat message may optionally contain an opaque Heartbeat Data
parameter that MUST be echoed back unchanged in the related Heartbeat
Ack message. The sender, upon examining the contents of the returned
Heartbeat Ack message, MAY choose to consider the remote M3UA peer as
unavailable. The contents/format of the Heartbeat Data parameter is
implementation-dependent and only of local interest to the original
sender. The contents may be used, for example, to support a
Heartbeat sequence algorithm (to detect missing Heartbeats), and/or a
timestamp mechanism (to evaluate delays).
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Note: Heartbeat-related events are not shown in Figure 3 "ASP state
transition diagram".
4.4. Routing Key Management Procedures [Optional]
4.4.1. Registration
An ASP MAY dynamically register with an SGP as an ASP within an
Application Server using the REG REQ message. A Routing Key
parameter in the REG REQ message specifies the parameters associated
with the Routing Key.
The SGP examines the contents of the received Routing Key parameter
and compares it with the currently provisioned Routing Keys. If the
received Routing Key matches an existing SGP Routing Key entry and
the ASP is not currently included in the list of ASPs for the related
Application Server, the SGP MAY authorize the ASP to be added to the
AS. Or, if the Routing Key does not currently exist and the received
Routing Key data is valid and unique, an SGP supporting dynamic
configuration MAY authorize the creation of a new Routing Key and
related Application Server and add the ASP to the new AS. In either
case, the SGP returns a Registration Response message to the ASP,
containing the same Local-RK-Identifier as provided in the initial
request, and a Registration Result "Successfully Registered". A
unique Routing Context value assigned to the SGP Routing Key is
included. The method of Routing Context value assignment at the SGP
is implementation dependent but must be guaranteed to be unique for
each Application Server or Routing Key supported by the SGP.
If the SGP does not support the registration procedure, the SGP
returns an Error message to the ASP, with an error code of
"Unsupported Message Class".
If the SGP determines that the received Routing Key data is invalid,
or contains invalid parameter values, the SGP returns a Registration
Response message to the ASP, containing a Registration Result "Error
Invalid Routing Key", "Error - Invalid DPC", or "Error - Invalid
Network Appearance", as appropriate.
If the SGP determines that the requested RK partially, but not
exactly, matches an existing RK, and that an incoming signalling
message received at an SGP could possibly match both the requested
and the existing RK, the SGP returns a Registration Response message
to the ASP, with a Registration Status of "Error - "Cannot Support
Unique Routing". An incoming signalling message received at an SGP
should not match against more than one Routing Key.
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If the SGP determines that the received RK was already registered,
fully and exactly, either statically or dynamically, by the sending
ASP, the SGP returns a Registration Response message to the ASP,
containing a Registration Result "Error - Routing Key Already
Registered". This error applies whether the sending ASP/IPSP is in
ASP-ACTIVE or ASP-INACTIVE for the corresponding AS. For this error
code, the RC field in the Registration Response message MUST be
populated with the actual value of RC in SGP corresponding to the
specified RK in the Registration Request message.
An ASP MAY request modification of an existing Routing Key by
including a Routing Context parameter in a Registration Request
message. Upon receipt of a Registration Request message containing a
Routing Context, if the SGP determines that the Routing Context
applies to an existing Routing Key, the SGP MAY adjust the existing
Routing Key to match the new information provided in the Routing Key
parameter. A Registration Response "ERR Routing Key Change Refused"
is returned if the SGP does not support this re-registration
procedure or RC does not exist. Otherwise, a Registration Response
"Successfully Registered" is returned.
If the SGP does not authorize an otherwise valid registration
request, the SGP returns a REG RSP message to the ASP containing the
Registration Result "Error - Permission Denied".
If an SGP determines that a received Routing Key does not currently
exist, and that the SGP does not support dynamic configuration, the
SGP returns a Registration Response message to the ASP, containing a
Registration Result "Error - Routing Key not Currently Provisioned".
If an SGP determines that a received Routing Key does not currently
exist and that the SGP supports dynamic configuration but does not
have the capacity to add new Routing Key and Application Server
entries, the SGP returns a Registration Response message to the ASP,
containing a Registration Result "Error - Insufficient Resources".
If an SGP determines that a received Routing Key does not currently
exist, and the SGP supports dynamic configuration but requires that
the Routing Key first be manually provisioned at the SGP, the SGP
returns a Registration Response message to the ASP, containing a
Registration Result "Error - Routing Key not Currently Provisioned".
If an SGP determines that one or more of the Routing Key parameters
are not supported for the purpose of creating new Routing Key
entries, the SGP returns a Registration Response message to the ASP,
containing a Registration Result "Error - Unsupported RK parameter
field".
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A Registration Response "Error - Unsupported Traffic Handling Mode"
is returned if the Routing Key in the REG REQ contains an Traffic
Handling Mode that is inconsistent with the presently configured mode
for the matching Application Server.
An ASP MAY register multiple Routing Keys at once by including a
number of Routing Key parameters in a single REG REQ message. The
SGP MAY respond to each registration request in a single REG RSP
message, indicating the success or failure result for each Routing
Key in a separate Registration Result parameter. Alternatively the
SGP MAY respond with multiple REG RSP messages, each with one or more
Registration Result parameters. The ASP uses the Local-RK-Identifier
parameter to correlate the requests with the responses.
Upon successful registration of an ASP in an AS, the SGP can now send
related SS7 Signalling Network Management messaging, if this did not
previously start upon the ASP transitioning to state ASP-INACTIVE
4.4.2. Deregistration
An ASP MAY dynamically deregister with an SGP as an ASP within an
Application Server using the DEREG REQ message. A Routing Context
parameter in the DEREG REQ message specifies which Routing Keys to
deregister. An ASP SHOULD move to the ASP-INACTIVE state for an
Application Server before attempting to deregister the Routing Key
(i.e., deregister after receiving an ASP Inactive Ack). Also, an ASP
SHOULD deregister from all Application Servers of which it is a
member before attempting to move to the ASP-Down state.
The SGP examines the contents of the received Routing Context
parameter and validates that the ASP is currently registered in the
Application Server(s) related to the included Routing Context(s). If
validated, the ASP is deregistered as an ASP in the related
Application Server.
The deregistration procedure does not necessarily imply the deletion
of Routing Key and Application Server configuration data at the SG.
Other ASPs may continue to be associated with the Application Server,
in which case the Routing Key data SHOULD NOT be deleted. If a
Deregistration results in no more ASPs in an Application Server, an
SG MAY delete the Routing Key data.
The SGP acknowledges the deregistration request by returning a DEREG
RSP message to the requesting ASP. The result of the deregistration
is found in the Deregistration Result parameter, indicating success
or failure with cause.
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An ASP MAY deregister multiple Routing Contexts at once by including
a number of Routing Contexts in a single DEREG REQ message. The SGP
MAY respond to each deregistration request in a single DEREG RSP
message, indicating the success or failure result for each Routing
Context in a separate Deregistration Result parameter.
4.4.3. IPSP Considerations (REG/DEREG)
The Registration/Deregistration procedures work in the IPSP cases in
the same way as in AS-SG cases. An IPSP may register an RK in the
remote IPSP. An IPSP is responsible for deregistering the RKs that
it has registered.
4.5. Procedures to Support the Availability or Congestion Status of
SS7 Destination
4.5.1. At an SGP
On receiving an MTP-PAUSE, MTP-RESUME or MTP-STATUS indication
primitive from the nodal interworking function at an SGP, the SGP
M3UA layer will send a corresponding SS7 Signalling Network
Management (SSNM) DUNA, DAVA, SCON, or DUPU message (see Section 3.4)
to the M3UA peers at concerned ASPs. The M3UA layer must fill in
various fields of the SSNM messages consistently with the information
received in the primitives.
The SGP M3UA layer determines the set of concerned ASPs to be
informed based on the specific SS7 network for which the primitive
indication is relevant. In this way, all ASPs configured to
send/receive traffic within a particular Network Appearance are
informed. If the SGP operates within a single SS7 Network
Appearance, then all ASPs are informed.
For the particular case that an ASP becomes active for an AS and
destinations normally accessible to the AS are inaccessible,
restricted, or congested, the SG MAY send DUNA, DRST, or SCON
messages for the inaccessible, restricted, or congested destinations
to the ASP newly active for the AS to prevent the ASP from sending
traffic for destinations that it might not otherwise know that are
inaccessible, restricted, or congested. For the newly activating ASP
from which the SGP has received an ASP Active message, these DUNA,
DRST, and SCON messages MAY be sent before sending the ASP Active Ack
that completes the activation procedure.
DUNA, DAVA, SCON, and DRST messages may be sent sequentially and
processed at the receiver in the order sent.
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Sequencing is not required for the DUPU or DAUD messages, which MAY
be sent unsequenced.
4.5.2. At an ASP
4.5.2.1. Single SG Configurations
At an ASP, upon receiving an SS7 Signalling Network Management (SSNM)
message from the remote M3UA Peer, the M3UA layer invokes the
appropriate primitive indications to the resident M3UA-Users. Local
management is informed.
In the case where a local event has caused the unavailability or
congestion status of SS7 destinations, the M3UA layer at the ASP
SHOULD pass up appropriate indications in the primitives to the M3UA
User, as though equivalent SSNM messages were received. For example,
the loss of an SCTP association to an SGP may cause the
unavailability of a set of SS7 destinations. MTP-PAUSE indication
primitives to the M3UA User are appropriate.
4.5.2.2. Multiple SG Configurations
At an ASP, upon receiving a Signalling Network Management message
from the remote M3UA Peer, the M3UA layer updates the status of the
affected route(s) via the originating SG and determines whether or
not the overall availability or congestion status of the affected
destination(s) has changed. If so, the M3UA layer invokes the
appropriate primitive indications to the resident M3UA-Users. Local
management is informed.
Implementation Note: To accomplish this, the M3UA layer at an ASP
maintains the status of routes via the SG, much like an MTP3 layer
maintains route-set status.
4.5.3. ASP Auditing
An ASP may optionally initiate an audit procedure to enquire of an
SGP the availability and (if the national congestion method with
multiple congestion levels and message priorities is used) congestion
status of an SS7 destination or set of destinations. A Destination
Audit (DAUD) message is sent from the ASP to the SGP, requesting the
current availability and congestion status of one or more SS7
Destination Point Codes.
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The DAUD message MAY be sent unsequenced. The DAUD MAY be sent by
the ASP in the following cases:
- Periodic. A Timer originally set upon receipt of a DUNA, SCON,
or DRST message has expired without a subsequent DAVA, DUNA,
SCON, or DRST message updating the availability/congestion
status of the affected Destination Point Codes. The Timer is
reset upon issuing a DAUD. In this case, the DAUD is sent to
the SGP that originally sent the SSNM message.
- Isolation. The ASP is newly ASP-ACTIVE or has been isolated
from an SGP for an extended period. The ASP MAY request the
availability/congestion status of one or more SS7 destinations
to which it expects to communicate.
Implementation Note: In the first of the cases above, the auditing
procedure must not be invoked for the case of a received SCON
message containing a congestion level value of "no congestion" or
"undefined" (i.e., congestion Level = "0").
The SGP SHOULD respond to a DAUD message with the MTP3
availability/congestion status of the routeset associated with each
Destination Point Codes in the DAUD message. The status of each SS7
destination requested is indicated in a DUNA message (if
unavailable), a DAVA message (if available), or a DRST (if restricted
and the SGP supports this feature in national networks). For
national networks, the SGP SHOULD additionally respond with a SCON
message (if the destination is congested) before the DAVA or DRST.
Where the SGP does not maintain the congestion status of the SS7
destination, the response to a DAUD message should always only be a
DAVA, DRST, or DUNA message, as appropriate.
Any DUNA or DAVA message in response to a DAUD message MAY contain a
list of Affected Point Codes.
An SG MAY refuse to provide the availability or congestion status of
a destination if, for example, the ASP is not authorized to know the
status of the destination. The SG MAY respond with an Error Message
(Error Code = "Destination Status Unknown").
An SG SHOULD respond with a DUNA message when DAUD was received with
an unknown Signalling Point Code.
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4.6. MTP3 Restart
In the case where the MTP3 in the SG undergoes an MTP restart, event
communication SHOULD be handled as follows:
When the SG discovers SS7 network isolation, the SGPs send an
indication to all concerned available ASPs (i.e., ASPs in the ASP-
ACTIVE state), using DUNA messages for the concerned destinations.
When the SG has completed the MTP Restart procedure, the M3UA layers
at the SGPs inform all concerned ASPs in the ASP-ACTIVE state of any
available/restricted SS7 destinations, using the DAVA/DRST messages.
No message is necessary for those destinations still unavailable
after the restart procedure.
When the M3UA layer at an ASP receives a DUNA message indicating SS7
destination unavailability at an SG, MTP Users will receive an MTP-
PAUSE indication and will stop any affected traffic to this
destination. When the M3UA receives a DAVA/DRST message, MTP Users
will receive an MTP-RESUME indication and can resume traffic to the
newly available SS7 destination, provided that the ASP is in the
ASP-ACTIVE state towards this SGP.
The ASP MAY choose to audit the availability of unavailable
destinations by sending DAUD messages. This would be the case when,
for example, an AS becomes active at an ASP and does not have current
destination statuses. If MTP restart is in progress at the SG, the
SGP returns a DUNA message for that destination, even if it received
an indication that the destination became available or restricted.
When an ASP becomes active for an AS and the SG is experiencing SS7
network isolation or is performing the MTP Restart procedure for the
AS, the SG MAY send a DUNA message for the concerned destinations to
the newly active ASP to prevent the ASP from sending traffic. These
messages can be sent after receiving the ASP Active, and before
sending the ASP Active Ack, to ensure that traffic is not initiated
by the ASP to these destinations before the SSNM are received. In
addition to DUNA messages, SCON, DRST, and DAVA can also be sent.
In the IPSP case, MTP restart could be considered if the IPSP also
has connection to an SS7 network. In that case, the same behavior as
described above for the SGP would apply to the restarting IPSP. This
would also be the case if the IPSPs were perceived as exchanging MTP
Peer PDUs, instead of MTP primitives between MTP User and MTP
Provider. In other words, M3UA does not provide the equivalent to
Traffic Restart Allowed messages indicating the end of the restart
procedure between peer IPSPs that would also be connected to an SS7
network.
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4.7. NIF Not Available
Implementation Note: Although the NIF is decided to be an
implementation dependent function, here are some guidelines that may
be useful to follow:
- If an SGP is isolated entirely from the NIF, the SGP should send
ASP Down Ack to all its connected ASPs. Upon receiving an ASP Up
message while isolated from the NIF, the SGP should respond with an
Error ("Refused - Management Blocking").
- If an SGP suffers a partial failure (where an SGP can continue to
service one or more active AS but due to a partial failure it is
unable to service one or more other active AS), the SGP should send
ASP Inactive Ack to all its connected ASPs for the affected AS.
Upon receiving an ASP Active message for an affected AS while still
partially isolated from the NIF, the SGP should respond with an
Error ("Refused - Management Blocking").
- If SG is isolated from NIF, it means that each SGP within an SG
should follow the procedure mentioned above.
4.8. M3UA Version Control
If a message with an unsupported version is received, the receiving
end responds with an Error message indicating the version the
receiving node supports and notifies Layer Management.
This is useful when protocol version upgrades are being performed in
a network. A node upgraded to a newer version should support the
older versions used on other nodes it is communicating with. Because
ASPs initiate the ASP Up procedure, it is likely that the message
having an unsupported version is an ASP Up message and therefore that
the Error message would normally come from the SGP.
4.9. M3UA Termination
Whenever a M3UA node wants to stop the communication with the peer
node, it MAY use one of the following procedures:
a) Send the sequence of ASP-INACTIVE, DEREG (optionally whenever
dynamic registration is used), and ASP-DOWN messages and perform
the SCTP Shutdown procedure after that.
b) Just do the SCTP Shutdown procedure.
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5. Examples of M3UA Procedures
5.1. Establishment of Association and Traffic between SGPs and ASPs
These scenarios show examples of M3UA message flows for the
establishment of traffic between an SGP and an ASP or between two
IPSPs. In all cases it is assumed that the SCTP association is
already set up.
5.1.1. Single ASP in an Application Server ("1+0" sparing),
No Registration
These scenarios show examples of M3UA message flows for the
establishment of traffic between an SGP and an ASP where only one ASP
is configured within an AS (no backup).
5.1.1.1. Single ASP in an Application Server ("1+0" Sparing),
No Registration
SGP ASP1
| |
|<-------------ASP Up-----------|
|-----------ASP Up Ack--------->|
| |
|-----NTFY(AS-INACTIVE)(RCn)--->|
| |
|<------- ASP Active(RCn)-------| RC: Routing Context
|-----ASP Active Ack (RCn)----->| (optional)
| |
|-----NTFY(AS-ACTIVE)(RCn)----->|
| |
Note: If the ASP Active message contains an optional Routing Context
parameter, the ASP Active message only applies for the specified RC
value(s). For an unknown RC value, the SGP responds with an Error
message.
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5.1.1.2. Single ASP in Application Server ("1+0" Sparing),
Dynamic Registration
This scenario is the same as for 5.1.1.1 but with the optional
exchange of registration information. In this case, the Registration
is accepted by the SGP.
SGP ASP1
| |
|<------------ASP Up------------|
|----------ASP Up Ack---------->|
| |
| |
|<----REGISTER REQ(LRCn,RKn)----| LRC: Local Routing
| | Key Id
|----REGISTER RESP(LRCn,RCn)--->| RK: Routing Key
| | RC: Routing Context
|----NTFY(AS-INACTIVE)(RCn)---->|
| |
| |
|<------- ASP Active(RCn)-------|
|-----ASP Active Ack (RCn)----->|
| |
|-----NTFY(AS-ACTIVE)(RCn)----->|
| |
Note: In the case of an unsuccessful registration attempt (e.g.,
invalid RKn), the Register Response message will contain an
unsuccessful indication, and the ASP will not subsequently send an
ASP Active message.
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5.1.1.3. Single ASP in Multiple Application Servers (Each
with "1+0" Sparing), Dynamic Registration (Case 1 - Multiple
Registration Requests)
SGP ASP1
| |
|<------------ASP Up------------|
|----------ASP Up Ack---------->|
| |
|<----REGISTER REQ(LRC1,RK1)----| LRC: Local Routing
| | Key Id
|----REGISTER RESP(LRC1,RC1)--->| RK: Routing Key
| | RC: Routing Context
|---NOTIFY(AS-INACTIVE)(RC1)--->|
| |
| |
|<------- ASP Active(RC1)-------|
|-----ASP Active Ack (RC1)----->|
| |
|----NOTIFY(AS-ACTIVE)(RC1)---->|
| |
~ ~
| |
|<----REGISTER REQ(LRCn,RKn)----|
| |
|----REGISTER RESP(LRCn,RCn)--->|
| |
|---NOTIFY(AS-INACTIVE)(RCn)--->|
| |
|<------- ASP Active(RCn)-------|
|-----ASP Active Ack (RCn)----->|
| |
|----NOTIFY(AS-ACTIVE)(RCn)---->|
| |
Note: In the case of an unsuccessful registration attempt (e.g.,
invalid RKn), the Register Response message will contain an
unsuccessful indication, and the ASP will not subsequently send an
ASP Active message. Each LRC/RK pair registration is considered
independently.
It is not necessary to follow a Registration Request/Response message
pair with an ASP Active message before sending the next Registration
Request. The ASP Active message can be sent at any time after the
related successful registration.
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5.1.1.4. Single ASP in Multiple Application Servers (each
with "1+0" sparing), Dynamic Registration (Case 2 - Single
Registration Request)
SGP ASP1
| |
|<------------ASP Up------------|
|----------ASP Up Ack---------->|
| |
| |
|<---REGISTER REQ({LRC1,RK1}, |
| ..., |
| {LRCn,RKn}),--|
| |
|---REGISTER RESP({LRC1,RC1},-->|
| ..., |
| (LRCn,RCn}) |
| |
|--NTFY(AS-INACTIVE)(RC1..RCn)->|
| |
| |
|<------- ASP Active(RC1)-------|
|-----ASP Active Ack (RC1)----->|
| |
|----NOTIFY(AS-ACTIVE)(RC1)---->|
| |
: :
: :
| |
|<------- ASP Active(RCn)-------|
|-----ASP Active Ack (RCn)----->|
| |
|----NOTIFY(AS-ACTIVE)(RCn)---->|
| |
Note: In the case of an unsuccessful registration attempt (e.g.,
Invalid RKn), the Register Response message will contain an
unsuccessful indication, and the ASP will not subsequently send an
ASP Active message. Each LRC/RK pair registration is considered
independently.
The ASP Active message can be sent at any time after the related
successful registration and may have more than one RC.
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5.1.2. Two ASPs in Application Server ("1+1" Sparing)
This scenario shows example M3UA message flows for the establishment
of traffic between an SGP and two ASPs in the same Application
Server, where ASP1 is configured to be in the ASP-ACTIVE state and
ASP2 is to be a "backup" in the event of communication failure or the
withdrawal from service of ASP1. ASP2 may act as a hot, warm, or
cold backup, depending on the extent to which ASP1 and ASP2 share
call/transaction state or can communicate call state under
failure/withdrawal events. The example message flow is the same
whether the ASP Active messages indicate "Override", "Loadshare", or
"Broadcast" mode, although typically this example would use an
Override mode.
SGP ASP1 ASP2
| | |
|<--------ASP Up---------| |
|-------ASP Up Ack------>| |
| | |
|--NOTIFY(AS-INACTIVE)-->| |
| | |
|<----------------------------ASP Up----------------|
|----------------------------ASP Up Ack------------>|
| | |
|--------------------------NOTIFY(AS-INACTIVE)----->|
| | |
| | |
|<-------ASP Active------| |
|------ASP Active Ack--->| |
| | |
|---NOTIFY(AS-ACTIVE)--->| |
|--------------------------NOTIFY(AS-ACTIVE)------->|
| | |
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5.1.3. Two ASPs in an Application Server ("1+1" Sparing,
Loadsharing Case)
This scenario shows a case similar to Section 5.1.2, but where the
two ASPs are brought to the state ASP-ACTIVE and subsequently
loadshare the traffic. In this case, one ASP is sufficient to handle
the total traffic load.
SGP ASP1 ASP2
| | |
|<---------ASP Up--------| |
|--------ASP Up Ack----->| |
| | |
|--NOTIFY(AS-INACTIVE)-->| |
| | |
|<-----------------------------ASP Up---------------|
|----------------------------ASP Up Ack------------>|
| | |
|--------------------------NOTIFY(AS-INACTIVE)----->|
| | |
|<--ASP Active (Ldshr)---| |
|-----ASP-Active Ack---->| |
| | |
|---NOTIFY (AS-ACTIVE)-->| |
|-----------------------------NOTIFY(AS-ACTIVE)---->|
| | |
|<---------------------------ASP Active (Ldshr)-----|
|------------------------------ASP Active Ack------>|
| | |
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5.1.4. Three ASPs in an Application Server ("n+k" Sparing,
Loadsharing Case)
This scenario shows example M3UA message flows for the establishment
of traffic between an SGP and three ASPs in the same Application
Server, where two of the ASPs are brought to the state ASP-ACTIVE and
subsequently share the load. In this case, a minimum of two ASPs are
required to handle the total traffic load (2+1 sparing).
SGP ASP1 ASP2 ASP3
| | | |
|<------ASP Up------| | |
|-----ASP Up Ack--->| | |
| | | |
|NTFY(AS-INACTIVE)->| | |
| | | |
|<-------------------------ASP Up-------| |
|------------------------ASP Up Ack---->| |
| | | |
|------------------NOTIFY(AS-INACTIVE)->| |
| | | |
|<--------------------------------------------ASP Up--------|
|--------------------------------------------ASP Up Ack---->|
| | | |
|--------------------------------------NOTIFY(AS-INACTIVE)->|
| | | |
| | | |
|<--ASP Act (Ldshr)-| | |
|----ASP Act Ack--->| | |
| | | |
| | | |
|<-------------------ASP Act. (Ldshr)---| |
|----------------------ASP Act Ack----->| |
| | | |
|--NTFY(AS-ACTIVE)->| | |
|--------------------NOTIFY(AS-ACTIVE)->| |
|----------------------------------------NOTIFY(AS-ACTIVE)->|
| | | |
| | | |
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5.2. ASP Traffic Failover Examples
5.2.1. 1+1 Sparing, Withdrawal of ASP, Backup Override
Following from the example in Section 5.1.2, ASP1 withdraws from
service:
SGP ASP1 ASP2
| | |
|<-----ASP Inactive------| |
|----ASP Inactive Ack--->| |
| | |
|----NTFY(AS-PENDING)--->| |
|-----------------------NTFY(AS-PENDING)----------->|
| | |
|<----------------------------- ASP Active----------|
|-----------------------------ASP Active Ack------->|
| | |
|----NTFY(AS-ACTIVE)---->| |
|-----------------------NTFY(AS-ACTIVE)------------>|
Note: If the SGP M3UA layer detects the loss of the M3UA peer (e.g.,
M3UA heartbeat loss or detection of SCTP failure), the initial ASP
Inactive message exchange (i.e., SGP to ASP1) would not occur.
5.2.2. 1+1 Sparing, Backup Override
Following on from the example in Section 5.1.2, ASP2 wishes to
Override ASP1 and take over the traffic:
SGP ASP1 ASP2
| | |
|<----------------------------- ASP Active----------|
|------------------------------ASP Active Ack------>|
|----NTFY(Alt ASP-Act)-->| |
| | |
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5.2.3. n+k Sparing, Loadsharing Case, Withdrawal of ASP
Following from the example in Section 5.1.4, ASP1 withdraws from
service:
SGP ASP1 ASP2 ASP3
| | | |
|<----ASP Inact.----| | |
|---ASP Inact Ack-->| | |
| | | |
|--NTFY(Ins. ASPs)->| | |
|---------------------------------------NOTIFY(Ins. ASPs)-->|
| | | |
| | | |
|<----------------------------------------ASP Act (Ldshr)---|
|------------------------------------------ASP Act (Ack)--->|
| | | |
|-NTFY(AS-ACTIVE)-->| | |
|-------------------NOTIFY(AS-ACTIVE)-->| |
|---------------------------------------NOTIFY(AS-ACTIVE)-->|
| | | |
| | | |
For the Notify message to be sent, the SG maintains knowledge of the
minimum ASP resources required (e.g., if the SG knows that "n+k" =
"2+1" for a Loadshare AS and "n" currently equals "1").
Note: If the SGP detects loss of the ASP1 M3UA peer (e.g., M3UA
heartbeat loss or detection of SCTP failure), the initial ASP
Inactive message exchange (i.e., SGP-ASP1) would not occur.
5.3. Normal Withdrawal of an ASP from an Application Server
and Teardown of an Association
An ASP that is now confirmed in the state ASP-INACTIVE (i.e., the ASP
has received an ASP Inactive Ack message) may now proceed to the
ASP-DOWN state, if it is to be removed from service. Following from
Section 5.2.1 or 5.2.3, where ASP1 has moved to the "Inactive" state:
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SGP ASP1
| |
|<-----ASP Inactive (RCn)------| RC: Routing Context
|----ASP Inactive Ack (RCn)--->|
| |
|<-----DEREGISTER REQ(RCn)-----| See Notes
| |
|---DEREGISTER RESP(LRCn,RCn)->|
| |
: :
| |
|<-----------ASP Down----------|
|---------ASP Down Ack-------->|
| |
Note: The Deregistration procedure will typically be used if the ASP
previously used the Registration procedures for configuration within
the Application Server. ASP Inactive and Deregister messages
exchanges may contain multiple Routing Contexts.
The ASP should be in the ASP-INACTIVE state and should have
deregistered in all its Routing Contexts before attempting to move to
the ASP-DOWN state.
5.4. Auditing Examples
5.4.1. SG State: Uncongested/Available
ASP SGP
--- ---
| -------- DAUD ---------> |
| <------ SCON(0) -------- |
| <------- DAVA ---------- |
5.4.2. SG State: Congested (Congestion Level=2) / Available
ASP SGP
--- ---
| -------- DAUD ---------> |
| <------ SCON(2) -------- |
| <------- DAVA ---------- |
5.4.3. SG State: Unknown/Available
ASP SGP
--- ---
| -------- DAUD ---------> |
| <------- DAVA ---------- |
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5.4.4. SG State: Unavailable
ASP SGP
--- ---
| -------- DAUD ---------> |
| <------- DUNA ---------- |
5.5. M3UA/MTP3-User Boundary Examples
5.5.1. At an ASP
This section describes the primitive mapping between the MTP3 User
and the M3UA layer at an ASP.
5.5.1.1. Support for MTP-TRANSFER Primitives at the ASP
5.5.1.1.1. Support for MTP-TRANSFER Request Primitive
When the MTP3-User on the ASP has data to send to a remote MTP3-User,
it uses the MTP-TRANSFER request primitive. The M3UA layer at the
ASP will do the following when it receives an MTP-TRANSFER request
primitive from the M3UA user:
- Determine the correct SGP.
- Determine the correct association to the chosen SGP.
- Determine the correct stream in the association (e.g.,
based on SLS).
- Determine whether to complete the optional fields of the DATA
message.
- Map the MTP-TRANSFER request primitive into the Protocol Data
field of a DATA message.
- Send the DATA message to the remote M3UA peer at the SGP,
over the SCTP association.
SGP ASP
| |
|<-----DATA Message-------|<--MTP-TRANSFER req.
| |
5.5.1.1.2. Support for the MTP-TRANSFER Indication Primitive
When the M3UA layer on the ASP receives a DATA message from the M3UA
peer at the remote SGP, it will do the following:
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- Evaluate the optional fields of the DATA message, if present.
- Map the Protocol Data field of a DATA message into the
MTP-TRANSFER indication primitive.
- Pass the MTP-TRANSFER indication primitive to the user part. In
case of multiple user parts, the optional fields of the Data
message are used to determine the concerned user part.
SGP ASP
| |
|------Data Message------>|-->MTP-Transfer ind.
| |
5.5.1.1.3. Support for ASP Querying of SS7 Destination States
There are situations such as temporary loss of connectivity to the
SGP that may cause the M3UA layer at the ASP to audit SS7 destination
availability/congestion states. Note: there is no primitive for the
MTP3-User to request this audit from the M3UA layer, as this is
initiated by an internal M3UA management function.
SGP ASP
| |
|<----------DAUD-----------|
|<----------DAUD-----------|
|<----------DAUD-----------|
| |
| |
5.5.2. At an SGP
This section describes the primitive mapping between the MTP3-User
and the M3UA layer at an SGP.
5.5.2.1. Support for MTP-TRANSFER Request Primitive at the SGP
When the M3UA layer at the SGP has received DATA messages from its
peer destined to the SS7 network, it will do the following:
- Evaluate the optional fields of the DATA message, if present, to
determine the Network Appearance.
- Map the Protocol data field of the DATA message into an
MTP-TRANSFER request primitive.
- Pass the MTP-TRANSFER request primitive to the MTP3 of the
concerned Network Appearance.
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SGP ASP
| |
<---MTP-TRANSFER req.|<---------DATA -----------|
| |
5.5.2.2. Support for MTP-TRANSFER Indication Primitive at the SGP
When the MTP3 layer at the SGP has data to pass its user parts, it
will use the MTP-TRANSFER indication primitive. The M3UA layer at
the SGP will do the following when it receives an MTP-TRANSFER
indication primitive:
- Determine the correct AS, using the distribution function;
- Select an ASP in the ASP-ACTIVE state.
- Determine the correct association to the chosen ASP.
- Determine the correct stream in the SCTP association (e.g.,
based on SLS).
- Determine whether to complete the optional fields of the DATA
message.
- Map the MTP-TRANSFER indication primitive into the Protocol Data
field of a DATA message.
- Send the DATA message to the remote M3UA peer in the ASP, over
the SCTP association.
SGP ASP
| |
--MTP-TRANSFER ind.->|-----------DATA --------->|
| |
5.5.2.3. Support for MTP-PAUSE, MTP-RESUME, MTP-STATUS Indication
Primitives
The MTP-PAUSE, MTP-RESUME, and MTP-STATUS indication primitives from
the MTP3 upper layer interface at the SGP need to be made available
to the remote MTP3 User Part lower-layer interface at the concerned
ASP(s).
5.5.2.3.1. Destination Unavailable
The MTP3 layer at the SGP will generate an MTP-PAUSE indication
primitive when it determines locally that an SS7 destination is
unreachable. The M3UA layer will map this primitive to a DUNA
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message. The SGP M3UA layer determines the set of concerned ASPs to
be informed based on internal SS7 network information associated with
the MTP-PAUSE indication primitive indication.
SGP ASP
| |
--MTP-PAUSE ind.-->|---------DUNA----------->|--MTP-PAUSE ind.-->
| |
5.5.2.3.2. Destination Available
The MTP3 at the SGP will generate an MTP-RESUME indication primitive
when it determines locally that an SS7 destination that was
previously unreachable is now reachable. The M3UA layer will map
this primitive to a DAVA message. The SGP M3UA determines the set of
concerned ASPs to be informed based on internal SS7 network
information associated with the MTP-RESUME indication primitive.
SGP ASP
| |
--MTP-RESUME ind.-->|-----------DAVA--------->|--MTP-RESUME ind.-->
| |
5.5.2.3.3. SS7 Network Congestion
The MTP3 layer at the SGP will generate an MTP-STATUS indication
primitive when it determines locally that the route to an SS7
destination is congested. The M3UA layer will map this primitive to
a SCON message. It will determine which ASP(s) to send the SCON
message to, based on the intended Application Server.
SGP ASP
| |
--MTP-STATUS ind.-->|-----------SCON--------->|--MTP-STATUS ind.-->
| |
5.5.2.3.4. Destination User Part Unavailable
The MTP3 layer at the SGP will generate an MTP-STATUS indication
primitive when it receives an UPU message from the SS7 network. The
M3UA layer will map this primitive to a DUPU message. It will
determine which ASP(s) to send the DUPU to based on the intended
Application Server.
SGP ASP
| |
--MTP-STATUS ind.-->|----------DUPU---------->|--MTP-STATUS ind.-->
| |
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5.6. Examples for IPSP Communication
These scenarios show a basic example for IPSP communication for the
three phases of the connection (establishment, data exchange,
disconnection). It is assumed that the SCTP association is already
set up. Both single exchange and double exchange behavior are
included for illustrative purposes.
5.6.1. Single Exchange
IPSP-A IPSP-B
| |
|-------------ASP Up------------>|
|<----------ASP Up Ack-----------|
| |
|<------- ASP Active(RCb)--------| RC: Routing Context
|-----ASP Active Ack (RCb)------>| (optional)
| |
| |
|<========= DATA (RCb) ========>|
| |
|<-----ASP Inactive (RCb)--------| RC: Routing Context
|----ASP Inactive Ack (RCb)----->| (optional)
| |
|<-----------ASP Down------------|
|---------ASP Down Ack---------->|
| |
Routing Context is previously agreed to be the same in both
directions.
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5.6.2. Double Exchange
IPSP-A IPSP-B
| |
|<-------------ASP Up------------|
|-----------ASP Up Ack---------->|
| |
|-------------ASP Up------------>| (optional)
|<----------ASP Up Ack-----------| (optional)
| |
|<------- ASP Active(RCb)--------| RC: Routing Context
|-----ASP Active Ack (RCb)------>| (optional)
| |
|------- ASP Active(RCa)-------->| RC: Routing Context
|<-----ASP Active Ack (RCa)------| (optional)
| |
|<========= DATA (RCa) =========|
|========== DATA (RCb) ========>|
| |
|<-----ASP Inactive (RCb)--------| RC: Routing Context
|----ASP Inactive Ack (RCb)----->|
| |
|------ASP Inactive (RCa)------->| RC: Routing Context
|<----ASP Inactive Ack (RCa)-----|
| |
|<-----------ASP Down------------|
|---------ASP Down Ack---------->|
| |
|------------ASP Down----------->| (optional)
|<--------ASP Down Ack-----------| (optional)
| |
In this approach, only one single exchange of ASP Up message can be
considered sufficient since the response by the other peer can be
considered a notice that it is in ASP_UP state.
For the same reason, only one ASP Down message is needed, since once
an IPSP receives ASP_Down ack message it is itself considered to be
in the ASP_Down state and not allowed to receive ASPSM messages.
6. Security Considerations
Implementations MUST follow the normative guidance of RFC3788 [11] on
the integration and usage of security mechanisms in SIGTRAN
protocols.
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7. IANA Considerations
This document contains no new actions for IANA. The subsections
below are retained for historical purposes.
7.1. SCTP Payload Protocol Identifier
IANA has assigned an M3UA value for the Payload Protocol Identifier
in the SCTP DATA chunk. The following SCTP Payload Protocol
Identifier has been registered:
M3UA "3"
The SCTP Payload Protocol Identifier value "3" SHOULD be included in
each SCTP DATA chunk, to indicate that the SCTP is carrying the M3UA
protocol. The value "0" (unspecified) is also allowed but any other
values MUST not be used. This Payload Protocol Identifier is not
directly used by SCTP but MAY be used by certain network entities to
identify the type of information being carried in a DATA chunk.
The User Adaptation peer MAY use the Payload Protocol Identifier as a
way of determining additional information about the data being
presented to it by SCTP.
7.2. M3UA Port Number
IANA has registered SCTP (and UDP/TCP) Port Number 2905 for M3UA. It
is recommended that SGPs use this SCTP port number for listening for
new connections. SGPs MAY also use statically configured SCTP port
numbers instead.
7.3. M3UA Protocol Extensions
This protocol may also be extended through IANA in three ways:
- Through definition of additional message classes.
- Through definition of additional message types.
- Through definition of additional message parameters.
The definition and use of new message classes, types, and parameters
is an integral part of SIGTRAN adaptation layers. Thus, these
extensions are assigned by IANA through an IETF Consensus action as
defined in Guidelines for Writing an IANA Considerations Section in
RFCs [23].
The proposed extension must in no way adversely affect the general
working of the protocol.
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7.3.1. IETF-Defined Message Classes
The documentation for a new message class MUST include the following
information:
(a) A long and short name for the new message class.
(b) A detailed description of the purpose of the message class.
7.3.2. IETF Defined Message Types
The documentation for a new message type MUST include the following
information:
(a) A long and short name for the new message type.
(b) A detailed description of the structure of the message.
(c) A detailed definition and description of intended use for each
field within the message.
(d) A detailed procedural description of the use of the new
message type within the operation of the protocol.
(e) A detailed description of error conditions when receiving this
message type.
When an implementation receives a message type that it does not
support, it MUST respond with an Error (ERR) message ("Unsupported
Message Type").
7.3.3. IETF-Defined Parameter Extension
Documentation of the message parameter MUST contain the following
information:
(a) Name of the parameter type.
(b) Detailed description of the structure of the parameter field.
This structure MUST conform to the general type-length-value
format described in Section 3.2.
(c) Detailed definition of each component of the parameter value.
(d) Detailed description of the intended use of this parameter
type, and an indication of whether and under what
circumstances multiple instances of this parameter type may be
found within the same message.
8. Acknowledgements
The authors would like to thank Antonio Roque Alvarez, Joyce
Archibald, Tolga Asveren, Maria-Cruz Bartolome-Rodrigo, Dan Brendes,
Antonio Canete, Nikhil Jain, Roland Jesske, Joe Keller, Kurt Kite,
Ming Lin, Steve Lorusso, Naoto Makinae, Howard May, Francois
Mouillaud, Barry Nagelberg, Neil Olson, Heinz Prantner, Shyamal
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RFC 4666 SS7 MTP3-User Adaptation Layer September 2006
Prasad, Mukesh Punhani, Selvam Rengasami, John Schantz, Ray Singh,
Michael Tuexen, Nitin Tomar, Gery Verwimp, Tim Vetter, Kazuo
Watanabe, Ben Wilson, and many others for their valuable comments and
suggestions.
9. Document Contributors
Ian Rytina - Ericsson
Guy Mousseau - Nortel Networks
Lyndon Ong - Ciena
Hanns Juergen Schwarzbauer - Siemens
Klaus Gradischnig - Detecon Inc.
Mallesh Kalla - Telcordia
Normand Glaude - Performance Technologies
Brian Bidulock - OpenSS7
John Loughney - Nokia
Greg Sidebottom - Signatus Technologies
10. References
10.1. Normative References
[1] ITU-T Recommendations Q.761 to Q.767, "Signalling System No.7
(SS7) - ISDN User Part (ISUP)"
[2] ANSI T1.113 - "Signaling System Number 7 - ISDN User Part"
[3] ETSI ETS 300 356-1 "Integrated Services Digital Network (ISDN);
Signalling System No.7; ISDN User Part (ISUP) version 2 for the
international interface; Part 1: Basic services"
[4] ITU-T Recommendations Q.711 to Q.715, "Signalling System No. 7
(SS7) - Signalling Connection Control Part (SCCP)"
[5] ANSI T1.112 "Signaling System Number 7 - Signaling Connection
Control Part"
[6] ETSI ETS 300 009-1, "Integrated Services Digital Network (ISDN);
Signalling System No.7; Signalling Connection Control Part
(SCCP) (connectionless and connection-oriented class 2) to
support international interconnection; Part 1: Protocol
specification"
[7] ITU-T Recommendations Q.700 to Q.705, "Signalling System No. 7
(SS7) - Message Transfer Part (MTP)"
[8] ANSI T1.111 "Signaling System Number 7 - Message Transfer Part"
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[9] ETSI ETS 300 008-1, "Integrated Services Digital Network (ISDN);
Signalling System No.7; Message Transfer Part (MTP) to support
international interconnection; Part 1: Protocol specification"
[10] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD
63, RFC 3629, November 2003.
[11] Loughney, J., Tuexen, M., and J. Pastor-Balbas, "Security
Considerations for Signaling Transport (SIGTRAN) Protocols", RFC
3788, June 2004.
10.2. Informative References
[12] Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H., Coene, L.,
Lin, H., Juhasz, I., Holdrege, M., and C. Sharp, "Framework
Architecture for Signaling Transport", RFC 2719, October 1999.
[13] ITU-T Recommendation Q.720, "Telephone User Part"
[14] ITU-T Recommendations Q.771 to Q.775 "Signalling System No. 7
(SS7) - Transaction Capabilities (TCAP)"
[15] ANSI T1.114 "Signaling System Number 7 - Transaction
Capabilities Application Part"
[16] ETSI ETS 300 287-1, "Integrated Services Digital Network (ISDN);
Signalling System No.7; Transaction Capabilities (TC) version 2;
Part 1: Protocol specification"
[17] 3G TS 25.410 V4.0.0 (2001-04) "Technical Specification - 3rd
Generation partnership Project; Technical Specification Group
Radio Access Network; UTRAN Iu Interface: General Aspects and
Principles"
[18] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V. Paxson,
"Stream Control Transmission Protocol", RFC 2960, October 2000.
[19] ITU-T Recommendation Q.2140 "B-ISDN ATM Adaptation Layer -
Service Specific Coordination Function for signalling at the
Network Node Interface (SSCF at NNI)"
[20] ITU-T Recommendation Q.2110 "B-ISDN ATM Adaptation Layer -
Service Specific Connection Oriented Protocol (SSCOP)"
[21] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
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[22] ITU-T Recommendation Q.2210 "Message Transfer Part Level 3
functions and messages using the services of ITU Recommendation
Q.2140"
[23] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[24] Morneault, K., Dantu, R., Sidebottom, G., Bidulock, B., and J.
Heitz, "Signaling System 7 (SS7) Message Transfer Part 2 (MTP2)
- User Adaptation Layer", RFC 3331, September 2002.
[25] George, T., Bidulock, B., Dantu, R., Schwarzbauer, H., and K.
Morneault, "Signaling System 7 (SS7) Message Transfer Part 2
(MTP2) - User Peer-to-Peer Adaptation Layer (M2PA)", RFC 4165,
September 2005.
[26] Telecommunication Technology Committee (TTC) Standard JT-Q704,
"Message Transfer Part Signaling Network Functions", April 28,
1992.
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Appendix A
A.1. Signalling Network Architecture
A Signalling Gateway is used to support the transport of MTP3-User
signalling traffic received from the SS7 network to multiple
distributed ASPs (e.g., MGCs and IP Databases). Clearly, the M3UA
protocol is not designed to meet the performance and reliability
requirements for such transport by itself. However, the conjunction
of distributed architecture and redundant networks provides support
for reliable transport of signalling traffic over IP. The M3UA
protocol is flexible enough to allow its operation and management in
a variety of physical configurations, enabling Network Operators to
meet their performance and reliability requirements.
To meet the stringent SS7 signalling reliability and performance
requirements for carrier grade networks, Network Operators might
require that no single point of failure is present in the end-to-end
network architecture between an SS7 node and an IP-based application.
This can typically be achieved through the use of redundant SGPs or
SGs, redundant hosts, and the provision of redundant QOS-bounded IP
network paths for SCTP Associations between SCTP End Points.
Obviously, the reliability of the SG, the MGC, and other IP-based
functional elements also needs to be taken into account. The
distribution of ASPs and SGPs within the available Hosts MAY also be
considered. As an example, for a particular Application Server, the
related ASPs could be distributed over at least two Hosts.
One example of a physical network architecture relevant to SS7
carrier grade operation in the IP network domain is shown in Figure
A-1, below:
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SGs MGCs
Host#1 ************** ************** Host#3
* ********__*__________________________*__******** * =
* *SGP1.1*__*_____ _______________*__* ASP1 * * MGC1
* ******** * \ / * ******** *
* ********__*______\__/________________*__******** *
* *SGP2.1*__*_______\/______ _____*__* ASP2 * *
* ******** * /\ | | * ******** *
* : * / \ | | * : *
* ******** * / \ | | * ******** *
* * SGPn * * | | | | * * ASPn * *
* ******** * | | | | * ******** *
************** | | | | **************
| | \ /
Host#2 ************** | | \ / ************** Host#4
* ********__*_____| |______\/_______*__******** * =
* *SGP1.2*__*_________________/\_______*__* ASP1 * * MGC2
* ******** * / \ * ******** *
* ********__*_______________/ \_____*__******** *
* *SGP2.2*__*__________________________*__* ASP2 * *
* ******** * * ******** *
* : * SCTP Associations * : *
* ******** * * ******** *
* * SGPn * * * * ASPn * *
* ******** * * ******** *
************** **************
SGP1.1 and SGP1.2 are part of SG1
SGP2.1 and SGP2.2 are part of SG2
Figure A-1 - Physical Model
In this model, each host may have many application processes. In the
case of the MGC, an ASP may provide service to one or more
Application Servers, and is identified as an SCTP end point. One or
more Signalling Gateway Processes make up a single Signalling
Gateway.
This example model can also be applied to IPSP-IPSP signalling. In
this case, each IPSP may have its services distributed across 2 or
more hosts, and may have multiple server processes on each host.
In the example above, each signalling process (SGP, ASP, or IPSP) is
the end point to more than one SCTP association, leading to more than
one other signalling processes. To support this, a signalling
process must be able to support distribution of M3UA messages to many
simultaneous active associations. This message distribution function
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is based on the status of provisioned Routing Keys, the status of the
signalling routes to signalling points in the SS7 network, and the
redundancy model (active-standby, load sharing, broadcast, n+k) of
the remote signalling processes.
For carrier grade networks, the failure or isolation of a particular
signalling process should not cause stable calls or transactions to
be lost. This implies that signalling processes need, in some cases,
to share the call/transaction state or be able to pass the call state
information between each other. In the case of ASPs performing call
processing, coordination may also be required with the related Media
Gateway to transfer the MGC control for a particular trunk
termination. However, this sharing or communication of
call/transaction state information is outside the scope of this
document.
This model serves as an example. M3UA imposes no restrictions as to
the exact layout of the network elements, the message distribution
algorithms, and the distribution of the signalling processes.
Instead, it provides a framework and a set of messages that allow for
a flexible and scalable signalling network architecture, aiming to
provide reliability and performance.
A.2. Redundancy Models
A.2.1. Application Server Redundancy
At the SGP, an Application Server list contains active and inactive
ASPs to support ASP broadcast, loadsharing, and failover procedures.
The list of ASPs within a logical Application Server is kept updated
in the SGP to reflect the active Application Server Process(es).
For example, in the network shown in Figure 1, all messages to DPC x
could be sent to ASP1 in Host3 or ASP1 in Host4. The AS list at SGP1
in Host 1 might look like the following:
Routing Key {DPC=x) - "Application Server #1"
ASP1/Host3 - State = Active
ASP1/Host4 - State = Inactive
In this "1+1" redundancy case, ASP1 in Host3 would be sent any
incoming message with DPC=x. ASP1 in Host4 would normally be brought
to the "active" state upon failure of, or loss of connectivity to,
ASP1/Host1.
The AS List at SGP1 in Host1 might also be set up in loadshare mode:
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Routing Key {DPC=x) - "Application Server #1"
ASP1/Host3 - State = Active
ASP1/Host4 - State = Active
In this case, both the ASPs would be sent a portion of the traffic.
For example, the two ASPs could together form a database, where
incoming queries may be sent to any active ASP.
Care might need to be exercised by a Network Operator in the
selection of the routing information to be used as the Routing Key
for a particular AS.
In the process of failover, it is recommended that, in the case of
ASPs supporting call processing, stable calls do not fail. It is
possible that calls in "transition" may fail, although measures of
communication between the ASPs involved can be used to mitigate this.
For example, the two ASPs may share call state via shared memory, or
may use an ASP to ASP protocol to pass call state information. Any
ASP-to-ASP protocol to support this function is outside the scope of
this document.
A.2.2. Signalling Gateway Redundancy
Signalling Gateways may also be distributed over multiple hosts.
Much like the AS model, SGs may comprise one or more SG Processes
(SGPs), distributed over one or more hosts, using an active/backup or
a loadsharing model. Should an SGP lose all or partial SS7
connectivity and other SGPs exist, the SGP may terminate the SCTP
associations to the concerned ASPs.
It is therefore possible for an ASP to route signalling messages
destined to the SS7 network using more than one SGP. In this model,
a Signalling Gateway is deployed as a cluster of hosts acting as a
single SG. A primary/backup redundancy model is possible, where the
unavailability of the SCTP association to a primary SGP could be used
to reroute affected traffic to an alternate SGP. A loadsharing model
is possible, where the signalling messages are loadshared between
multiple SGPs. A broadcast model is also possible, where signalling
messages are sent to each active SGP in the SG. The distribution of
the MTP3-user messages over the SGPs should be done in such a way to
minimize message missequencing, as required by the SS7 User Parts.
It may also be possible for an ASP to use more than one SG to access
a specific SS7 end point, in a model that resembles an SS7 STP mated
pair. Typically, SS7 STPs are deployed in mated pairs, with traffic
loadshared between them. Other models are also possible, subject to
the limitations of the local SS7 network provisioning guidelines.
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From the perspective of the M3UA layer at an ASP, a particular SG is
capable of transferring traffic to a provisioned SS7 destination X if
an SCTP association with at least one SGP of the SG is established,
the SGP has returned an acknowledgement to the ASP to indicate that
the ASP is actively handling traffic for that destination X, the SGP
has not indicated that the destination X is inaccessible, and the SGP
has not indicated MTP Restart. When an ASP is configured to use
multiple SGPs for transferring traffic to the SS7 network, the ASP
must maintain knowledge of the current capability of the SGPs to
handle traffic to destinations of interest. This information is
crucial to the overall reliability of the service, for active/backup,
loadsharing, and broadcast models, in the event of failures and
recovery and maintenance activities. The ASP M3UA may also use this
information for congestion avoidance purposes. The distribution of
the MTP3-user messages over the SGPs should be done in such a way as
to minimize message missequencing, as required by the SS7 User Parts.
Editors' Addresses
Ken Morneault
Cisco Systems Inc.
13615 Dulles Technology Drive
Herndon, VA, USA 20171
EMail: kmorneau@cisco.com
Javier Pastor-Balbas
Ericsson Espana S.A.
C/ Retama 1
28045 Madrid - Spain
EMail: j.javier.pastor@ericsson.com
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