draft-ietf-sigtran-m2pa-06.txt   draft-ietf-sigtran-m2pa-07.txt 
Network Working Group Tom George Network Working Group Tom George
INTERNET-DRAFT Alcatel INTERNET-DRAFT Alcatel
Brian Bidulock
OpenSS7
Ram Dantu Ram Dantu
Netrake Netrake
Malleswar Kalla Malleswar Kalla
Telcordia Telcordia
Hanns Juergen Schwarzbauer Hanns Juergen Schwarzbauer
Siemens Siemens
Greg Sidebottom Greg Sidebottom
Signatus Technologies
Ken Morneault Ken Morneault
Cisco Systems Cisco Systems
Brian Bidulock
OpenSS7
Expires February 2003 August 28, 2002 Expires July 2003 January 17, 2003
SS7 MTP2-User Peer-to-Peer Adaptation Layer SS7 MTP2-User Peer-to-Peer Adaptation Layer
<draft-ietf-sigtran-m2pa-06.txt> <draft-ietf-sigtran-m2pa-07.txt>
Status of This Memo Status of This Memo
This document is an Internet-Draft and is in full conformance with all This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026. Internet-Drafts are working provisions of Section 10 of RFC 2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
skipping to change at page 3, line 16 skipping to change at page 3, line 16
1. Introduction............................................. 4 1. Introduction............................................. 4
1.1 Scope................................................. 4 1.1 Scope................................................. 4
1.2 Terminology........................................... 4 1.2 Terminology........................................... 4
1.3 Abbreviations......................................... 5 1.3 Abbreviations......................................... 5
1.4 Conventions........................................... 6 1.4 Conventions........................................... 6
1.5 Signaling Transport Architecture...................... 6 1.5 Signaling Transport Architecture...................... 6
1.6 Services Provided by M2PA............................. 8 1.6 Services Provided by M2PA............................. 8
1.7 Functions Provided by M2PA............................ 9 1.7 Functions Provided by M2PA............................ 9
1.8 Definition of the M2PA Boundaries.....................10 1.8 Definition of the M2PA Boundaries.....................10
1.9 Differences Between M2PA and M2UA.....................12 1.9 Differences Between M2PA and M2UA.....................11
2. Protocol Elements........................................14 2. Protocol Elements........................................13
2.1 Common Message Header.................................14 2.1 Common Message Header.................................13
2.2 M2PA Header...........................................15 2.2 M2PA Header...........................................15
2.3 M2PA Messages.........................................16 2.3 M2PA Messages.........................................15
3. M2PA Link State Control..................................19 3. M2PA Link State Control..................................19
4. Procedures...............................................23 4. Procedures...............................................23
4.1 Procedures to Support MTP2 Features...................23 4.1 Procedures to Support MTP2 Features...................23
4.2 Procedures to Support the MTP3/MTP2 Interface.........33 4.2 Procedures to Support the MTP3/MTP2 Interface.........32
4.3 SCTP Considerations...................................37 4.3 SCTP Considerations...................................37
5. Examples of M2PA Procedures..............................39 5. Examples of M2PA Procedures..............................39
5.1 Link Initialization (Alignment).......................39 5.1 Link Initialization (Alignment).......................39
5.2 Message Transmission and Reception....................41 5.2 Message Transmission and Reception....................42
5.3 Link Status Indication................................41 5.3 Link Status Indication................................42
5.4 Link Status Message (Processor Outage)................42 5.4 Link Status Message (Processor Outage)................43
5.5 Level 2 Flow Control..................................43 5.5 Level 2 Flow Control..................................44
5.6 MTP3 Signaling Link Congestion........................44 5.6 MTP3 Signaling Link Congestion........................46
5.7 Link Deactivation.....................................44 5.7 Link Deactivation.....................................47
5.8 Link Changeover.......................................45 5.8 Link Changeover.......................................48
6. Security.................................................46 6. Security.................................................50
6.1 Threats...............................................46 6.1 Threats...............................................50
6.2 Protecting Confidentiality............................46 6.2 Protecting Confidentiality............................50
7. IANA Considerations......................................47 7. IANA Considerations......................................51
7.1 SCTP Payload Protocol Identifier......................47 7.1 SCTP Payload Protocol Identifier......................51
7.2 M2PA Protocol Extensions..............................47 7.2 M2PA Protocol Extensions..............................51
8. Acknowledgements.........................................48 8. Acknowledgements.........................................53
9. References...............................................49 9. References...............................................53
10. Author's Addresses.......................................50 10. Author's Addresses.......................................55
1. Introduction 1. Introduction
1.1 Scope 1.1 Scope
There is a need for Switched Circuit Network (SCN) signaling protocol There is a need for Switched Circuit Network (SCN) signaling protocol
delivery over an IP network. This includes message transfer between delivery over an IP network. This includes message transfer between
the following: the following:
- a Signaling Gateway (SG) and a Media Gateway Controller (MGC) - a Signaling Gateway (SG) and a Media Gateway Controller (MGC)
[1] [RFC2719]
- a SG and an IP Signaling Point (IPSP) - a SG and an IP Signaling Point (IPSP)
- an IPSP and an IPSP - an IPSP and an IPSP
This could allow for convergence of some signaling and data This could allow for convergence of some signaling and data
networks. SCN signaling nodes would have access to databases and other networks. SCN signaling nodes would have access to databases and other
devices in the IP network domain that do not use SS7 signaling devices in the IP network domain that do not use SS7 signaling
links. Likewise, IP telephony applications would have access to SS7 links. Likewise, IP telephony applications would have access to SS7
services. There may also be operational cost and performance services. There may also be operational cost and performance
advantages when traditional signaling links are replaced by IP network advantages when traditional signaling links are replaced by IP network
"connections". "connections".
The delivery mechanism described in this document allows for full MTP3 The delivery mechanism described in this document allows for full MTP3
message handling and network management capabilities between any two message handling and network management capabilities between any two
SS7 nodes, communicating over an IP network. An SS7 node equipped with SS7 nodes, communicating over an IP network. An SS7 node equipped with
an IP network connection is called an IP Signaling Point (IPSP). The an IP network connection is called an IP Signaling Point (IPSP). The
IPSPs function as traditional SS7 nodes using the IP network instead IPSPs function as traditional SS7 nodes using the IP network instead
of SS7 links. of SS7 links.
The delivery mechanism should The delivery mechanism SHOULD
- Support seamless operation of MTP3 protocol peers over an IP - Support seamless operation of MTP3 protocol peers over an IP
network connection. network connection.
- Support the MTP Level 2 / MTP Level 3 interface boundary. - Support the MTP Level 2 / MTP Level 3 interface boundary.
- Support management of SCTP transport associations and traffic - Support management of SCTP transport associations and traffic
instead of MTP2 Links. instead of MTP2 Links.
- Support asynchronous reporting of status changes to management. - Support asynchronous reporting of status changes to management.
1.2 Terminology 1.2 Terminology
MTP - The Message Transfer Part of the SS7 protocol [2] [3]. MTP - The Message Transfer Part of the SS7 protocol [Q.700] [Q.701]
[Q.702] [Q.703] [Q.704] [Q.705] [T1.111].
MTP2 - MTP Level 2, the MTP signaling link layer. MTP2 - MTP Level 2, the MTP signaling link layer.
MTP3 - MTP Level 3, the MTP signaling network layer. MTP3 - MTP Level 3, the MTP signaling network layer.
MTP2-User - A protocol that normally uses the services of MTP MTP2-User - A protocol that normally uses the services of MTP
Level 2. The only MTP2 user is MTP3. The MTP2 user is equivalent to Level 2. The only MTP2 user is MTP3. The MTP2 user is equivalent to
the M2PA user. the M2PA user.
Signaling End Point (SEP) - A node in an SS7 network that originates Signaling End Point (SEP) - A node in an SS7 network that originates
or terminates signaling messages. One example is a central office or terminates signaling messages. One example is a central office
switch. switch.
IP Signaling Point (IPSP) - An SS7 Signaling Point with an IP IP Signaling Point (IPSP) - An SS7 Signaling Point with an IP
network connection used for SS7 over IP. network connection used for SS7 over IP.
Signaling Gateway (SG) - A signaling agent that receives/sends SCN Signaling Gateway (SG) - A signaling agent that receives/sends SCN
native signaling at the edge of the IP network [4]. In this context, native signaling at the edge of the IP network [RFC2719]. In this
an SG is an SS7 Signaling Point that has both an IP network connection context, an SG is an SS7 Signaling Point that has both an IP network
used for SS7 over IP, and a traditional (non-IP) link to an SS7 connection used for SS7 over IP, and a traditional (non-IP) link to an
network. SS7 network.
Signaling Transfer Point (STP) - A node in an SS7 network that routes Signaling Transfer Point (STP) - A node in an SS7 network that routes
signaling messages based on their destination point code in the SS7 signaling messages based on their destination point code in the SS7
network. network.
Association - An association refers to a SCTP association [5]. The Association - An association refers to a SCTP association
association provides the transport for MTP3 protocol data units and [RFC2960]. The association provides the transport for MTP3 protocol
M2PA adaptation layer peer messages. data units and M2PA adaptation layer peer messages.
Network Byte Order - Most significant byte first, also known as "Big Network Byte Order - Most significant byte first, also known as "Big
Endian". See [14], Appendix B Data Transmission Order. Endian". See [RFC791], Appendix B "Data Transmission Order".
Stream - A stream refers to a SCTP stream [5]. Stream - A stream refers to a SCTP stream [RFC2960].
1.3 Abbreviations 1.3 Abbreviations
BSNT - Backward Sequence Number to be Transmitted BSNT - Backward Sequence Number to be Transmitted
FSNC - Forward Sequence Number of last message accepted by FSNC - Forward Sequence Number of last message accepted by
remote level 2 remote level 2
LI - Length Indicator LI - Length Indicator
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SSN - Stream Sequence Number SSN - Stream Sequence Number
STP - Signal Transfer Point STP - Signal Transfer Point
1.4 Conventions 1.4 Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they
appear in this document, are to be interpreted as described in appear in this document, are to be interpreted as described in
[8]. [RFC2119].
1.5 Signaling Transport Architecture 1.5 Signaling Transport Architecture
The architecture that has been defined [4] for Switched Circuit The architecture that has been defined [RFC2719] for Switched Circuit
Network (SCN) signaling transport over IP uses multiple components, Network (SCN) signaling transport over IP uses multiple components,
including an IP transport protocol, the Stream Control Transmission including an IP transport protocol, the Stream Control Transmission
Protocol (SCTP), and an adaptation module to support the services Protocol (SCTP), and an adaptation module to support the services
expected by a particular SCN signaling protocol from its underlying expected by a particular SCN signaling protocol from its underlying
protocol layer. protocol layer.
Within this framework architecture, this document defines an SCN Within this framework architecture, this document defines an SCN
adaptation module that is suitable for the transport of SS7 MTP3 adaptation module that is suitable for the transport of SS7 MTP3
messages. messages.
skipping to change at page 7, line 25 skipping to change at page 7, line 25
+------+ +------+ +------+ +------+
| M2PA | | M2PA | | M2PA | | M2PA |
+------+ +------+ +------+ +------+
| SCTP | | SCTP | | SCTP | | SCTP |
+------+ +------+ +------+ +------+
| IP | | IP | | IP | | IP |
+------+ +------+ +------+ +------+
IP - Internet Protocol IP - Internet Protocol
IPSP - IP Signaling Point IPSP - IP Signaling Point
SCTP - Stream Control Transmission Protocol SCTP - Stream Control Transmission Protocol [RFC2960]
(see Reference [5])
Figure 1: M2PA Symmetrical Peer-to-Peer Architecture Figure 1. M2PA Symmetrical Peer-to-Peer Architecture
Figure 2 shows an example of M2PA used in a Signaling Gateway Figure 2 shows an example of M2PA used in a Signaling Gateway
(SG). The SG is an IPSP equipped with both traditional SS7 and IP (SG). The SG is an IPSP equipped with both traditional SS7 and IP
network connections. In effect, the Signaling Gateway acts as a network connections. In effect, the Signaling Gateway acts as a
Signal Transfer Point (STP). Any of the nodes in the diagram could Signal Transfer Point (STP). Any of the nodes in the diagram could
have SCCP or other SS7 layers. STPs may or may not be present in the have SCCP or other SS7 layers. STPs MAY or MAY NOT be present in the
SS7 path between the SEP and the SG. SS7 path between the SEP and the SG.
******** SS7 *************** IP ******** ******** SS7 *************** IP ********
* SEP *--------* SG *--------* IPSP * * SEP *--------* SG *--------* IPSP *
******** *************** ******** ******** *************** ********
+------+ +------+ +------+ +------+
| TCAP | | TCAP | | TCAP | | TCAP |
+------+ +------+ +------+ +------+
| SCCP | | SCCP | | SCCP | | SCCP |
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+------+ +------+------+ +------+ +------+ +------+------+ +------+
| MTP2 | | MTP2 | M2PA | | M2PA | | MTP2 | | MTP2 | M2PA | | M2PA |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
| MTP1 | | MTP1 | SCTP | | SCTP | | MTP1 | | MTP1 | SCTP | | SCTP |
| | | +------+ +------+ | | | +------+ +------+
| | | | IP | | IP | | | | | IP | | IP |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
SEP - SS7 Signaling Endpoint SEP - SS7 Signaling Endpoint
Figure 2: M2PA in IP Signaling Gateway Figure 2. M2PA in IP Signaling Gateway
Figure 2 is only an example. Other configurations are possible. In Figure 2 is only an example. Other configurations are possible. In
short, M2PA uses the SCTP association as an SS7 link. The M2PA/SCTP/IP short, M2PA uses the SCTP association as an SS7 link. The M2PA/SCTP/IP
stack can be used in place of an MTP2/MTP1 stack. stack can be used in place of an MTP2/MTP1 stack.
1.5.1 Point Code Representation 1.5.1 Point Code Representation
The MTP specification requires that each node with an MTP3 layer is The MTP specification requires that each node with an MTP3 layer is
identified by an SS7 point code. In particular, each IPSP must have identified by an SS7 point code. In particular, each IPSP MUST have
its own SS7 point code. its own SS7 point code.
1.6 Services Provided by M2PA 1.6 Services Provided by M2PA
The SS7 MTP3/MTP2 (MTP2-User) interface is retained in the IPSP. The The SS7 MTP3/MTP2 (MTP2-User) interface is retained in the IPSP. The
M2PA protocol layer is required to provide the equivalent set of M2PA protocol layer is required to provide the equivalent set of
services to its user as provided by MTP Level 2 to MTP Level 3. services to its user as provided by MTP Level 2 to MTP Level 3.
These services are described in the following subsections. These services are described in the following subsections.
1.6.1 Support for MTP Level 2 / MTP Level 3 interface boundary 1.6.1 Support for MTP Level 2 / MTP Level 3 interface boundary
This interface is the same as the MTP2/MTP3 interface described in This interface is the same as the MTP2/MTP3 interface described in
[2], [3] and [10], with the addition of support for larger sequence [Q.703], [Q.704], [T1.111], and [Q.2140], with the addition of support
numbers in [3] and [7]. for larger sequence numbers in [T1.111] and [Q.2210].
Because M2PA uses larger sequence numbers than MTP2, the MTP3 Because M2PA uses larger sequence numbers than MTP2, the MTP3
Changeover procedure must use the Extended Changeover Order and Changeover procedure MUST use the Extended Changeover Order and
Extended Changeover Acknowledgment messages described in [7] and [3]. Extended Changeover Acknowledgment messages described in [Q.2210] and
[T1.111].
Also, the following MTP3/MTP2 primitives must use the larger sequence Also, the following MTP3/MTP2 primitives must use the larger sequence
numbers: numbers:
- BSNT Confirmation - BSNT Confirmation
- Retrieval Request and FSNC - Retrieval Request and FSNC
1.6.2 Support for peer-to-peer communication 1.6.2 Support for peer-to-peer communication
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to SCTP as data for transport across a link. These are called User to SCTP as data for transport across a link. These are called User
Data messages in M2PA. Data messages in M2PA.
LSSUs allow peer MTP2 layers to exchange status information. Analogous LSSUs allow peer MTP2 layers to exchange status information. Analogous
messages are needed for M2PA. The Link Status message serves this messages are needed for M2PA. The Link Status message serves this
purpose. purpose.
FISUs are sent when no other signal units are waiting to be sent. This FISUs are sent when no other signal units are waiting to be sent. This
purpose is served by the heartbeat messages in SCTP. FISUs also carry purpose is served by the heartbeat messages in SCTP. FISUs also carry
acknowledgment of messages. This function is performed by the M2PA acknowledgment of messages. This function is performed by the M2PA
User Data and Link Status messages. Therefore, it is unnecessary for User Data message. Therefore, it is unnecessary for M2PA to provide a
M2PA to provide a protocol data unit like the FISU. Furthermore, since protocol data unit like the FISU. Furthermore, since an IP network is
an IP network is a shared resource, it would be undesirable to have a a shared resource, it would be undesirable to have a message type that
message type that is sent continuously as the FISUs are. is sent continuously as the FISUs are.
1.7 Functions Provided by M2PA 1.7 Functions Provided by M2PA
1.7.1 Support of MTP3/MTP2 Primitives 1.7.1 Support of MTP3/MTP2 Primitives
M2PA receives the primitives sent from MTP3 to its lower layer. M2PA M2PA receives the primitives sent from MTP3 to its lower layer. M2PA
processes these primitives or maps them to appropriate primitives at processes these primitives or maps them to appropriate primitives at
the M2PA/SCTP interface. Likewise, M2PA sends primitives to MTP3 like the M2PA/SCTP interface. Likewise, M2PA sends primitives to MTP3 like
those used in the MTP3/MTP2 interface. those used in the MTP3/MTP2 interface.
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1.7.5 Retention of MTP3 in the SS7 Network 1.7.5 Retention of MTP3 in the SS7 Network
M2PA allows MTP3 to perform all of its Message Handling and Network M2PA allows MTP3 to perform all of its Message Handling and Network
Management functions with IPSPs as with other SS7 nodes. Management functions with IPSPs as with other SS7 nodes.
1.8 Definition of the M2PA Boundaries 1.8 Definition of the M2PA Boundaries
1.8.1 Definition of the M2PA / MTP Level 3 boundary 1.8.1 Definition of the M2PA / MTP Level 3 boundary
The upper layer primitives provided by M2PA are the same as those The upper layer primitives provided by M2PA are the same as those
provided by MTP2 to MTP3. These primitives are described in [2], [3], provided by MTP2 to MTP3. These primitives are described in [Q.703],
and [10]. Following is a list of the primitives. [Q.704], [T1.111], and [Q.2140]. Following is a list of the
primitives.
Primitives sent from MTP3 to M2PA: Primitives sent from MTP3 to M2PA:
Data Request - Used to send a Data Message for transmission. Data Request - Used to send a Data Message for transmission.
Start Request - Used to activate a link. Start Request - Used to activate a link.
Stop Request - Used to deactivate a link. Stop Request - Used to deactivate a link.
Retrieve BSNT Request - Request the BSNT for the changeover procedure. Retrieve BSNT Request - Request the BSNT for the changeover
procedure.
Retrieval Request and FSNC - Request retrieval of unacknowledged and Retrieval Request and FSNC - Request retrieval of unacknowledged
unsent messages. This request includes the FSNC received from the and unsent messages. This request includes the FSNC received from
remote end. the remote end.
Local Processor Outage Request - Informs M2PA of a local processor Local Processor Outage Request - Informs M2PA of a local processor
outage condition. outage condition.
Local Processor Outage Recovered Request - Informs M2PA that a local Local Processor Outage Recovered Request - Informs M2PA that a
processor outage condition has ceased. local processor outage condition has ceased.
Flush Buffers Request - Requests that all transmit and receive Flush Buffers Request - Requests that all transmit and receive
buffers be emptied. buffers be emptied.
Continue Request - Requests that processing resume after a processor Continue Request - Requests that processing resume after a
outage. processor outage.
Emergency Request - Requests that M2PA use the emergency alignment Emergency Request - Requests that M2PA use the emergency alignment
procedure. procedure.
Emergency Ceases Request - Requests that M2PA use the normal alignment Emergency Ceases Request - Requests that M2PA use the normal
procedure. alignment procedure.
Primitives sent from M2PA to MTP3: Primitives sent from M2PA to MTP3:
Data Indication - Used to deliver received Data Message to MTP3. Data Indication - Used to deliver received Data Message to MTP3.
Congestion Indication - Indicates change in congestion status. The Congestion Indication - Indicates change in congestion status. The
indication includes the congestion status, if the protocol is using the indication includes the congestion status, if the protocol is using
optional congestion levels. The indication also includes the discard the optional congestion levels. The indication also includes the
status. discard status.
In Service Indication - Indicates that the link is in service. In Service Indication - Indicates that the link is in service.
Out of Service Indication - Indicates that the link is out of service. Out of Service Indication - Indicates that the link is out of
service.
Retrieved Messages Indication - Indicates delivery of unacknowledged Retrieved Messages Indication - Indicates delivery of
and unsent messages. unacknowledged and unsent messages.
Retrieval Complete Indication - Indicates that delivery of Retrieval Complete Indication - Indicates that delivery of
unacknowledged and unsent messages is complete. unacknowledged and unsent messages is complete.
BSNT Confirm - Replies to the BSNT Request. The confirmation includes BSNT Confirm - Replies to the BSNT Request. The confirmation
the BSNT. includes the BSNT.
BSNT Not Retrievable Confirm - Replies to the BSNT Request when the BSNT Not Retrievable Confirm - Replies to the BSNT Request when the
BSNT cannot be determined. BSNT cannot be determined.
Remote Processor Outage Indication - Indicates processor outage at Remote Processor Outage Indication - Indicates processor outage at
remote end. remote end.
Remote Processor Recovered Indication - Indicates recovery from Remote Processor Recovered Indication - Indicates recovery from
processor outage at remote end. processor outage at remote end.
1.8.2 Definition of the Lower Layer Boundary between M2PA and SCTP 1.8.2 Definition of the Lower Layer Boundary between M2PA and SCTP
The upper layer primitives provided by SCTP are described in Reference The upper layer primitives provided by SCTP are described in [RFC2960]
[5] Section 10 "Interface with Upper Layer". Section 10 "Interface with Upper Layer".
1.9 Differences Between M2PA and M2UA 1.9 Differences Between M2PA and M2UA
The MTP2 User Adaptation Layer (M2UA) [6] also adapts the MTP3 layer The MTP2 User Adaptation Layer (M2UA) [M2UA] also adapts the MTP3 layer
to the SCTP/IP stack. It does so through a backhauling architecture to the SCTP/IP stack. It does so through a backhauling architecture
[4]. This section intends to clarify some of the differences between [RFC2719]. This section intends to clarify some of the differences
the M2PA and M2UA approaches. between the M2PA and M2UA approaches.
A possible M2PA architecture is shown in Figure 3. Here the IPSP's A possible M2PA architecture is shown in Figure 3. Here the IPSP's
MTP3 uses its underlying M2PA as a replacement for MTP2. Communication MTP3 uses its underlying M2PA as a replacement for MTP2. Communication
between the two layers MTP3/M2PA is defined by the same primitives as between the two layers MTP3/M2PA is defined by the same primitives as
in SS7 MTP3/MTP2. M2PA performs functions similar to MTP2. in SS7 MTP3/MTP2. M2PA performs functions similar to MTP2.
A comparable architecture for M2UA is shown in Figure 4. In M2UA, the
MGC's MTP3 uses the SG's MTP2 as its lower SS7 layer. Likewise, the
SG's MTP2 uses the MGC's MTP3 as its upper SS7 layer. In SS7,
communication between the MTP3 and MTP2 layers is defined by
primitives. In M2UA, the MTP3/MTP2 communication is defined as M2UA
messages and sent over the IP connection.
******** SS7 *************** IP ******** ******** SS7 *************** IP ********
* SEP *--------* SG *--------* IPSP * * SEP *--------* SG *--------* IPSP *
******** *************** ******** ******** *************** ********
+------+ +-------------+ +------+ +------+ +-------------+ +------+
| SCCP | | SCCP | | SCCP | | SCCP | | SCCP | | SCCP |
+------+ +-------------+ +------+ +------+ +-------------+ +------+
| MTP3 | | MTP3 | | MTP3 | | MTP3 | | MTP3 | | MTP3 |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
| MTP2 | | MTP2 | M2PA | | M2PA | | MTP2 | | MTP2 | M2PA | | M2PA |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
| MTP1 | | MTP1 | SCTP | | SCTP | | MTP1 | | MTP1 | SCTP | | SCTP |
| | | +------+ +------+ | | | +------+ +------+
| | | | IP | | IP | | | | | IP | | IP |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
Figure 3: M2PA in IP Signaling Gateway Figure 3. M2PA in IP Signaling Gateway
A comparable architecture for M2UA is shown in Figure 4. In M2UA, the
MGC's MTP3 uses the SG's MTP2 as its lower SS7 layer. Likewise, the
SG's MTP2 uses the MGC's MTP3 as its upper SS7 layer. In SS7,
communication between the MTP3 and MTP2 layers is defined by
primitives. In M2UA, the MTP3/MTP2 communication is defined as M2UA
messages and sent over the IP connection.
******** SS7 *************** IP ******** ******** SS7 *************** IP ********
* SEP *--------* SG *--------* MGC * * SEP *--------* SG *--------* MGC *
******** *************** ******** ******** *************** ********
+------+ +------+ +------+ +------+
| SCCP | | SCCP | | SCCP | | SCCP |
+------+ +------+ +------+ +------+
| MTP3 | (NIF) | MTP3 | | MTP3 | (NIF) | MTP3 |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
| MTP2 | | MTP2 | M2UA | | M2UA | | MTP2 | | MTP2 | M2UA | | M2UA |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
| MTP1 | | MTP1 | SCTP | | SCTP | | MTP1 | | MTP1 | SCTP | | SCTP |
| | | +------+ +------+ | | | +------+ +------+
| | | | IP | | IP | | | | | IP | | IP |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
NIF - Nodal Interworking Function NIF - Nodal Interworking Function
Figure 4: M2UA in IP Signaling Gateway Figure 4. M2UA in IP Signaling Gateway
M2PA and M2UA are similar in that: M2PA and M2UA are similar in that:
a. Both transport MTP3 data messages. a. Both transport MTP3 data messages.
b. Both present an MTP2 upper interface to MTP3. b. Both present an MTP2 upper interface to MTP3.
Differences between M2PA and M2UA include: Differences between M2PA and M2UA include:
a. M2PA: IPSP processes MTP3/MTP2 primitives. a. M2PA: IPSP processes MTP3/MTP2 primitives.
skipping to change at page 14, line 27 skipping to change at page 14, line 13
length. The header structure is shown in Figure 5. length. The header structure is shown in Figure 5.
0 1 2 3 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 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 | Spare | Message Class | Message Type | | Version | Spare | Message Class | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Length | | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Common Message Header Figure 5. Common Message Header
2.1.1 Version 2.1.1 Version
The version field contains the version of M2PA. The supported versions The version field contains the version of M2PA. The supported versions
are: are:
Value Version Value
----- ------- (decimal) Version
--------- -------
1 Release 1.0 of M2PA protocol 1 Release 1.0 of M2PA protocol
2.1.2 Spare 2.1.2 Spare
The Spare field SHOULD be set to all zeroes (0's) by the sender and The Spare field SHOULD be set to all zeroes (0's) by the sender and
ignored by the receiver. The Spare field SHOULD NOT be used for ignored by the receiver. The Spare field SHOULD NOT be used for
proprietary information. proprietary information.
2.1.3 Message Class 2.1.3 Message Class
skipping to change at page 15, line 21 skipping to change at page 14, line 47
--------- ------------- --------- -------------
11 M2PA Messages 11 M2PA Messages
Other values are invalid for M2PA. Other values are invalid for M2PA.
2.1.4 Message Type 2.1.4 Message Type
The following list contains the message types for the defined The following list contains the message types for the defined
messages. messages.
Value Message Type Value
----- ------------ (decimal) Message Type
--------- -------------
1 User Data 1 User Data
2 Link Status 2 Link Status
Other values are invalid. Other values are invalid.
2.1.5 Message Length 2.1.5 Message Length
The Message Length defines the length of the message in octets, The Message Length defines the length of the message in octets,
including the Common Header. including the Common Header.
skipping to change at page 15, line 46 skipping to change at page 15, line 23
header structure is shown in Figure 6. header structure is shown in Figure 6.
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| unused | BSN | | unused | BSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| unused | FSN | | unused | FSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: M2PA-specific Message Header Figure 6. M2PA-specific Message Header
2.2.1 Backward Sequence Number 2.2.1 Backward Sequence Number
This is the FSN of the message last received from the peer. This is the FSN of the message last received from the peer.
2.2.2 Forward Sequence Number 2.2.2 Forward Sequence Number
This is the M2PA sequence number of the User Data message being sent. This is the M2PA sequence number of the User Data message being sent.
2.3 M2PA Messages 2.3 M2PA Messages
The following section defines the messages and parameter contents. An The following section defines the messages and parameter contents. An
M2PA message consists of a Common Message Header and M2PA Header M2PA message consists of a Common Message Header and M2PA Header
followed by the data appropriate to the message. followed by the data appropriate to the message.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... \ \
| Common Message Header | / Common Message Header /
... \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M2PA-specific Message Header | \ \
/ M2PA-specific Message Header /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... \ \
| Message Data | / Message Data /
... \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.3.1 User Data 2.3.1 User Data
The User Data is the data sent from MTP3. The format for the User Data The User Data is the data sent from MTP3. The User Data is an optional
message is as follows: field. It need not be included in an acknowlegement-only message.
The format for the User Data message is as follows:
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... \ \
| Data | / Data /
... \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Data field contains the following fields of the MTP Message Signal The Data field contains the following fields of the MTP Message Signal
Unit (MSU): Unit (MSU):
- Length Indicator (LI), including the two undefined bits between - Length Indicator (LI), including the two undefined bits between
the SIO and LI fields. the SIO and LI fields.
- Service Information Octet (SIO) - Service Information Octet (SIO)
- Signaling Information Field (SIF) - Signaling Information Field (SIF)
The MTP MSU described in [2] Q.703, section 2.2 Signal Unit Format, The MTP MSU is described in Q.703 [Q.703], section 2.2 "Signal Unit
and [3] T1.111.3 section 2.2 Signal Unit Format. Format", and T1.111.3 [T1.111] section 2.2 "Signal Unit Format".
M2PA does not add padding to the MTP3 message. M2PA does not add padding to the MTP3 message.
Note that the Data field SHALL NOT contain other components of the MTP Note that the Data field SHALL NOT contain other components of the MTP
MSU format: MSU format:
- Flag - Flag
- Backward Sequence Number (BSN) - Backward Sequence Number (BSN)
- Backward Indicator Bit (BIB) - Backward Indicator Bit (BIB)
- Forward Sequence Number (FSN) - Forward Sequence Number (FSN)
- Forward Indicator Bit (FIB) - Forward Indicator Bit (FIB)
- Check bits (CK) - Check bits (CK)
The Data field SHALL be transmitted in the byte order as defined by The Data field SHALL be transmitted in the byte order as defined by
MTP3. MTP3.
It is not necessary to put the message length in the LI octet as in It is not necessary to put the message length in the LI octet as in
MTP2. The LI octet is included because the two spare bits in the LI MTP2. The LI octet is included because the two spare bits in the LI
octet are used by MTP3 in at least one national version of SS7 to octet are used by MTP3 in at least one national version of SS7 to
carry MTP3 information. For example, the Japanese TTC standard uses carry MTP3 information. For example, the Japanese TTC standard uses
these spare bits as an MTP3 Message Priority field. See [9], section these spare bits as an MTP3 Message Priority field. See [JT-Q704],
14 "Common Characteristics of message signal unit formats", section section 14 "Common Characteristics of message signal unit formats",
14.2 (A) Priority Indicator (PRI). For versions of MTP that do not use section 14.2 (A) "Priority Indicator (PRI)". For versions of MTP that
these two bits, the entire octet is spare. do not use these two bits, the entire octet is spare.
Therefore in M2PA the format of the LI octet is: Therefore in M2PA the format of the LI octet is:
0 0
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|PRI| spare | (followed by SIO, SIF) |PRI| spare | (followed by SIO, SIF)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
PRI - Priority used only in national MTP defined in [9]. PRI - Priority used only in national MTP defined in [JT-Q704].
Spare for other MTP versions. Spare for other MTP versions.
Since the LI octet is not used for a message length, there is no need Since the LI octet is not used for a message length, there is no need
to support the expanded LI field in [2], Q.703 Annex A. Therefore the to support the expanded LI field in Q.703 [Q.703] Annex A. Therefore
LI field in M2PA is always one octet. the LI field in M2PA is always one octet.
Note: In the SS7 Recommendations, the format of the messages and Note: In the SS7 Recommendations, the format of the messages and
fields within the messages are based on bit transmission order. In fields within the messages are based on bit transmission order. In
these recommendations the Least Significant Bit (LSB) of each field is these recommendations the Least Significant Bit (LSB) of each field is
positioned to the right. The received SS7 fields are populated octet positioned to the right. The received SS7 fields are populated octet
by octet as received into the 4-octet word as shown below. by octet as received into the 4-octet word as shown below.
As an example, in the ANSI MTP protocol, the Data field format is As an example, in the ANSI MTP protocol, the Data field format is
shown below: shown below:
skipping to change at page 18, line 47 skipping to change at page 18, line 24
(decimal) Description (decimal) Description
--------- ----------- --------- -----------
1 Alignment 1 Alignment
2 Proving Normal 2 Proving Normal
3 Proving Emergency 3 Proving Emergency
4 Ready 4 Ready
5 Processor Outage 5 Processor Outage
6 Processor Outage Ended 6 Processor Outage Ended
7 Busy 7 Busy
8 Busy Ended 8 Busy Ended
9 Out of Service 9 Out of Service (OOS)
2.3.2.1 Link Status Proving 2.3.2.1 Link Status Proving
The Link Status Proving message may optionally carry additional The Link Status Proving message may optionally carry additional
bytes. If the optional bytes are used, the format for the message is bytes. If the optional bytes are used, the format for the message is
as follows. as follows.
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| State | | State |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| filler | \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / filler /
: \ \
:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| filler |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
It is recommended that the length of the Link Status Proving message It is RECOMMENDED that the length of the Link Status Proving message
be similar to the size of the User Data messages that will be carried be similar to the size of the User Data messages that will be carried
on the link. on the link.
It is recommended that the filler field contain a number pattern which It is RECOMMENDED that the filler field contain a number pattern which
varies among the Link Status Proving messages, and that will allow the varies among the Link Status Proving messages, and that will allow the
SCTP checksum to be used to verify the accuracy of transmission. SCTP checksum to be used to verify the accuracy of transmission.
3. M2PA Link State Control 3. M2PA Link State Control
The M2PA link moves from one state to another in response to various The M2PA link moves from one state to another in response to various
events. The events that may result in a change of state include: events. The events that may result in a change of state include:
- MTP3 primitive requests - MTP3 primitive requests
- SCTP notifications - SCTP notifications
- Receipt of Status messages from the peer M2PA - Receipt of Link Status messages from the peer M2PA
- Expiration of certain timers - Expiration of certain timers
Figure 7 illustrates state changes together with the causing events. Figure 7 illustrates state changes together with the causing events.
Note that some of the error conditions are not shown in the state Note that some of the error conditions are not shown in the state
diagram. diagram.
Following is a list of the M2PA Link States and a description of each. Following is a list of the M2PA Link States and a description of each.
IDLE - State of the link during power-up initialization. POWER OFF - State of the link during power-up initialization.
OOS - Out Of Service. Power-up initialization is complete. OUT OF SERVICE (OOS) - Out of service. Power-up initialization is
complete.
AIP - Alignment In Progress. M2PA is attempting to exchange Alignment INITIAL ALIGNMENT - Alignment in Progress. M2PA is attempting to
messages with its peer. exchange Link Status Alignment messages with its peer.
PROVING - M2PA is sending Link Status Proving messages to its peer. PROVING - M2PA is sending Link Status Proving messages to its peer.
ALIGNED READY - Proving is complete. M2PA is waiting until peer ALIGNED READY - Proving is complete. M2PA is waiting until peer
completes proving. completes proving.
INS - In Service. Link is ready for traffic. IN SERVICE (INS) - In service. Link is ready for traffic.
RETRIEVAL - Link no longer carries traffic. M2PA is waiting for ALIGNED NOT READY - A local processor outage condition began before
request for message retrieval from MTP3. the alignment and proving procedure was completed.
PROCESSOR OUTAGE - A local processor outage condition began while
the link was in service.
+-----------+ +-----------+
| IDLE | | POWER |
| OFF |
+-----------+ +-----------+
| |
| Power On | Power On
| |
| +--------------------------+ Flush Buffers | +-------------------------+
| | (Associate) | OR Retrieval | | |
V V | +-------+ | | |
+-----------+ | | | V V |
+----------------------->| OOS |<--+ | | +-----------+ |
+--->| OUT OF | |
+---------------->| SERVICE |<--+ |
| +-----------+ | Link Configured | | +-----------+ | Link Configured |
| | | | (Associate) | | | | | (Associate) |
| | +-----+ | | | +-----+ |
| | | | | |
| | MTP3 Start | | | MTP3 Start |
| V | | V |
| +-----------+ | | +-----------+ |
+<-----------------------| AIP |----------------------->+ | | INITIAL | |
+<----------------| ALIGNMENT |--------------------->+
| MTP3 Stop +-----------+ SCTP Comm Error | | MTP3 Stop +-----------+ SCTP Comm Error |
| OR T1 Expiry ^ | OR SCTP Comm Lost | | OR T2 Expiry | ^ OR SCTP Comm Lost |
| OR Receive LS OOS | | |
| | +-------------------------|--------+
| | LPO/LPR | |
| | | | | | | |
| | Receive LS Align | |
| | | | | | | |
| +----------------------+ | Send and | | V | |
| | | Receive LS Alignment | | +-----------+ LPO/LPR | |
| | V | | | PROVING |<---------------------|--------+
| | +-----------+ | |<----------------| |--------------------->+ |
+<-----------------------| PROVING |----------------------->+ | MTP3 Stop +-----------+ SCTP Comm Error | |
| | MTP3 Stop +-----------+ SCTP Comm Error | | OR T3 Expiry | OR SCTP Comm Lost | |
| | OR Receive LS OOS | OR SCTP Comm Lost | | OR Receive LS OOS | | |
| | T4 Expiry | |
| | Send LS Ready | |
| V | V
| +-----------+ LPO/LPR | +-----------+
| | ALIGNED |<---------------------|->| ALIGNED |
+<----------------| READY |--------------------->+ | NOT READY |
| MTP3 Stop +-----------+ SCTP Comm Error +-----------+
| OR T1 Expiry | OR SCTP Comm Lost | |
| OR Receive LS OOS | | T1 |
| OR Receive LS Align | Receive LS Ready Receive | Expiry|
| | OR Receive User Data LS Ready | OR Rcv|
| | OR Receive | LS |
| | LS PO | Align|
| | | | | | | |
| | | T4 Expiry | | | | |
| | V | | | | |
| | +-----------+ | | V V |
| | | ALIGNED | | | +-----------+ LPO/LPR +-----------+ |
+<-----------------------| READY |----------------------->+ | | IN |<-------------------->| PROCESSOR | |
| | MTP3 Stop +-----------+ SCTP Comm Error | | SERVICE | | OUTAGE | |
| | OR T3 Expiry | OR SCTP Comm Lost | +-----------+ +-----------+ |
| | OR Receive LS OOS | | | | |
| | | Receive LS Ready | MTP3 Stop | MTP3 Stop | |
| | | OR Receive User Data | OR Receive LS OOS | OR Receive LS OOS | |
| | | | OR SCTP Comm Error | OR SCTP Comm Error | |
| | V | OR SCTP Comm Lost | OR SCTP Comm Lost | |
| | +-----------+ | OR T6 Expiry | OR M2PA Link Failure | |
| | | INS | | OR T7 Expiry | OR Receive LS Align | |
| | +-----------+ | OR M2PA Link Failure | | |
| | | | OR Receive LS Align | | |
| | | MTP3 Stop | V V V
| | | OR Receive LS OOS +<----------------------+<---------------------------------+-------+
| | | OR SCTP Comm Error
| | | OR SCTP Comm Lost
| | | OR T6 Expiry
| | | OR T7 Expiry
| | | OR M2PA Link Failure
| | |
| | |
| | |
| | |
| | V
| | MTP3 Start +-----------+
| +<-------------------| RETRIEVAL |
+<-----------------------+-----------+
Retrieval Complete
Figure 7: M2PA Link State Transition Diagram Figure 7. M2PA Link State Transition Diagram
Figure 8 illustrates state changes in the M2PA management of the SCTP Figure 8 illustrates state changes in the M2PA management of the SCTP
association together with the causing events. Note that some of the association together with the causing events. Note that some of the
error conditions are not shown in the state diagram. error conditions are not shown in the state diagram.
Following is a list of the M2PA Association States and a description Following is a list of the M2PA Association States and a description
of each. of each.
IDLE - State of the association during power-up initialization. IDLE - State of the association during power-up initialization.
skipping to change at page 22, line 52 skipping to change at page 22, line 28
| | | |
| | | |
| SCTP Comm Up | | SCTP Comm Up |
| | | |
V | V |
+-------------+ | +-------------+ |
| ESTABLISHED |----------------->+ | ESTABLISHED |----------------->+
+-------------+ SCTP Comm Error +-------------+ SCTP Comm Error
OR SCTP Comm Lost OR SCTP Comm Lost
Figure 8: M2PA Association State Transition Diagram Figure 8. M2PA Association State Transition Diagram
4. Procedures 4. Procedures
4.1 Procedures to Support MTP2 Features 4.1 Procedures to Support MTP2 Features
4.1.1 Signal Unit Format, Delimitation, Acceptance 4.1.1 Signal Unit Format, Delimitation, Acceptance
Messages for transmission across the network must follow the format Messages for transmission across the network must follow the format
described in section 2. described in section 2.
SCTP provides reliable, in-sequence delivery. Therefore the related SCTP provides reliable, in-sequence delivery. Therefore the related
functionality of MTP2 is not needed. SCTP does not provide functions functionality of MTP2 is not needed. SCTP does not provide functions
related to Link State Control in MTP2. These functions must be related to Link State Control in MTP2. These functions must be
provided by M2PA. provided by M2PA.
4.1.2 MTP and SCTP Entities 4.1.2 MTP and SCTP Entities
This section describes how M2PA relates MTP and SCTP entities. This section describes how M2PA relates MTP and SCTP entities.
Each MTP link corresponds to an SCTP association. To prevent duplicate Each MTP link corresponds to an SCTP association. To prevent duplicate
associations from being established, it is recommended that each associations from being established, it is RECOMMENDED that each
endpoint know the IP address (or IP addresses, if multi-homing is endpoint know the IP address (or IP addresses, if multi-homing is
used) and port number of both endpoints. SCTP prevents two used) and port number of both endpoints. SCTP prevents two
associations with the same IP addresses and port numbers from being associations with the same IP addresses and port numbers from being
established. established.
It is necessary for at least one of the endpoints to be listening on It is necessary for at least one of the endpoints to be listening on
the port on which the other endpoint is trying to establish the the port on which the other endpoint is trying to establish the
association. Therefore, at least one of the port numbers should be the association. Therefore, at least one of the port numbers SHOULD be the
M2PA registered port. M2PA registered port.
If only one association is to be established between these two IP If only one association is to be established between these two IP
addresses, then the association should be established using the M2PA addresses, then the association SHOULD be established using the M2PA
registered port at each endpoint. registered port at each endpoint.
If it is desirable to create multiple associations (for multiple If it is desirable to create multiple associations (for multiple
links) between the two IP addresses, different port numbers can be links) between the two IP addresses, different port numbers can be
used for each association. Nevertheless, the M2PA registered port used for each association. Nevertheless, the M2PA registered port
number should be used at one end of each association. number SHOULD be used at one end of each association.
Each combination of IP address/port for the two endpoints (i.e., each Each combination of IP address/port for the two endpoints (i.e., each
association) must be mapped to the same Signaling Link Code (SLC) at association) MUST be mapped to the same Signaling Link Code (SLC) at
each endpoint, so that each endpoint knows which link is being created each endpoint, so that each endpoint knows which link is being created
at the time the SCTP association is established. However, M2PA does at the time the SCTP association is established. However, M2PA does
not do any processing based on the SLC. not do any processing based on the SLC.
Following are examples of the relationships between associations and Following are examples of the relationships between associations and
links. Note that a link is an SCTP association identified by two links. Note that a link is an SCTP association identified by two
endpoints. Each endpoint is identified by an IP address and port endpoints. Each endpoint is identified by an IP address and port
number. Each association is mapped to an SLC. number. Each association is mapped to an SLC.
Figure 9 shows a case with two IPSPs, each with two IP addresses. Two Figure 9 shows a case with two IPSPs, each with two IP addresses. Two
associations are the links that connect the two IPSPs. Since these associations are the links that connect the two IPSPs. Since these
links are in the same link set, they must have different SLCs. links are in the same link set, they MUST have different SLCs.
Table 1 shows the relationships in tabular form. Table 1 is only Table 1 shows the relationships in tabular form. Table 1 is only
conceptual. The actual method for mapping the SCTP associations to the conceptual. The actual method for mapping the SCTP associations to the
SLCs is implementation dependent. SLCs is implementation dependent.
IPSP X IPSP Y IPSP X IPSP Y
+-------------+ +-------------+ +-------------+ +-------------+
| | SCTP | | | | SCTP | |
| IPA | association 1 | IPB | | IPA | association 1 | IPB |
skipping to change at page 24, line 29 skipping to change at page 24, line 29
| IPC | association 2 | IPD | | IPC | association 2 | IPD |
| port = PW +---------------+ port = PW | | port = PW +---------------+ port = PW |
| SLC = b | | SLC = b | | SLC = b | | SLC = b |
| | | | | | | |
| | | | | | | |
+-------------+ +-------------+ +-------------+ +-------------+
IPx = IP address IPx = IP address
PW = Registered port number for M2PA PW = Registered port number for M2PA
Figure 9: Associations and Links - Figure 9. Two IPSPs with Two IP Addresses Each
Two IPSPs with Two IP Addresses Each
Table 1. Two IPSPs with Two IP Addresses Each
+-------------+---------------------------------------+-----+ +-------------+---------------------------------------+-----+
| Association | IPSP X | IPSP Y | SLC | | Association | IPSP X | IPSP Y | SLC |
| +------------+------+------------+------+ | | +------------+------+------------+------+ |
| | IP address | Port | IP address | Port | | | | IP address | Port | IP address | Port | |
+=============+============+======+============+======+=====+ +=============+============+======+============+======+=====+
| 1 | IPA | PW | IPB | PW | a | | 1 | IPA | PW | IPB | PW | a |
+-------------+------------+------+------------+------+-----+ +-------------+------------+------+------------+------+-----+
| 2 | IPC | PW | IPD | PW | b | | 2 | IPC | PW | IPD | PW | b |
+-------------+------------+------+------------+------+-----+ +-------------+------------+------+------------+------+-----+
Table 1: Associations and SLCs -
Two IPSPs with Two IP Addresses Each
Figure 10 and Table 2 show an example with three IPSPs. Note that in Figure 10 and Table 2 show an example with three IPSPs. Note that in
this example, the two links are in different link sets. Therefore, it this example, the two links are in different link sets. Therefore, it
is possible that the values a and b may be equal. is possible that the values a and b MAY be equal.
IPSP X IPSP Y IPSP X IPSP Y
+-------------+ +-------------+ +-------------+ +-------------+
| | SCTP | | | | SCTP | |
| IPA | association 1 | IPB | | IPA | association 1 | IPB |
| port = PW +---------------+ port = PW | | port = PW +---------------+ port = PW |
| SLC = a | | SLC = a | | SLC = a | | SLC = a |
| | | | | | | |
| | | | | | | |
skipping to change at page 25, line 47 skipping to change at page 25, line 47
| | | |
| | | |
| | | |
| | | |
| | | |
+-------------+ +-------------+
IPx = IP address IPx = IP address
PW = Registered port number for M2PA PW = Registered port number for M2PA
Figure 10: Associations and Links - Figure 10. One IPSP Connected to Two IPSPs
One IPSP Connected to Two IPSPs Table 2. One IPSP Connected to Two IPSPs
+-------------+---------------------------------------+-----+ +-------------+---------------------------------------+-----+
| Association | IPSP X | IPSP Y | SLC | | Association | IPSP X | IPSP Y/Z | SLC |
| +------------+------+------------+------+ | | +------------+------+------------+------+ |
| | IP address | Port | IP address | Port | | | | IP address | Port | IP address | Port | |
+=============+============+======+============+======+=====+ +=============+============+======+============+======+=====+
| 1 | IPA | PW | IPB | PW | a | | 1 | IPA | PW | IPB | PW | a |
+-------------+------------+------+------------+------+-----+ +-------------+------------+------+------------+------+-----+
| 2 | IPC | PW | IPD | PW | b | | 2 | IPC | PW | IPD | PW | b |
+-------------+------------+------+------------+------+-----+ +-------------+------------+------+------------+------+-----+
Table 2: Associations and SLCs -
One IPSP Connected to Two IPSPs
Figure 11 and Table 3 show two associations between the same IP Figure 11 and Table 3 show two associations between the same IP
addresses. This is accomplished by using different port numbers for addresses. This is accomplished by using different port numbers for
each association at one endpoint. each association at one endpoint.
IPSP X IPSP Y IPSP X IPSP Y
+-------------+ +-------------+ +-------------+ +-------------+
| | SCTP | | | | SCTP | |
| IPA | association 1 | IPB | | IPA | association 1 | IPB |
| port = P1 +---------------+ port = PW | | port = P1 +---------------+ port = PW |
skipping to change at page 27, line 30 skipping to change at page 26, line 41
| port = PW +---------------+ port = PW | | port = PW +---------------+ port = PW |
| SLC = b | | SLC = b | | SLC = b | | SLC = b |
| | | | | | | |
| | | | | | | |
+-------------+ +-------------+ +-------------+ +-------------+
IPx = IP address IPx = IP address
P1 = Pre-selected port number P1 = Pre-selected port number
PW = Registered port number for M2PA PW = Registered port number for M2PA
Figure 11: Associations and SLCs - Figure 11. Multiple Associations Between Two IP Addresses
Multiple Associations Between Two IP Addresses
Table 3. Multiple Associations Between Two IP Addresses
+-------------+---------------------------------------+-----+ +-------------+---------------------------------------+-----+
| Association | IPSP X | IPSP Y | SLC | | Association | IPSP X | IPSP Y | SLC |
| +------------+------+------------+------+ | | +------------+------+------------+------+ |
| | IP address | Port | IP address | Port | | | | IP address | Port | IP address | Port | |
+=============+============+======+============+======+=====+ +=============+============+======+============+======+=====+
| 1 | IPA | P1 | IPB | PW | a | | 1 | IPA | P1 | IPB | PW | a |
+-------------+------------+------+------------+------+-----+ +-------------+------------+------+------------+------+-----+
| 2 | IPA | PW | IPB | PW | b | | 2 | IPA | PW | IPB | PW | b |
+-------------+------------+------+------------+------+-----+ +-------------+------------+------+------------+------+-----+
Table 3: Associations and SLCs - The association SHALL contain two streams in each direction. Stream 0
Multiple Associations Between Two IP Addresses
The association shall contain two streams in each direction. Stream 0
is designated for Link Status messages. Stream 1 is designated for is designated for Link Status messages. Stream 1 is designated for
User Data messages. User Data messages.
4.1.3 Link Alignment 4.1.3 Link Alignment
The purposes of the alignment procedure are: The purposes of the alignment procedure are:
(1) To provide a handshaking procedure so that both endpoints are (1) To provide a handshaking procedure so that both endpoints are
prepared to send SS7 traffic, and to prevent traffic from being prepared to send SS7 traffic, and to prevent traffic from being
sent before the other end is ready. sent before the other end is ready.
(2) To verify that the SCTP association is suitable for use as an (2) To verify that the SCTP association is suitable for use as an
SS7 link. SS7 link.
Link alignment takes place after the association is established. If Link alignment takes place after the association is established. If
SCTP fails to establish the association, and M2PA has received a Start SCTP fails to establish the association, and M2PA has received a Start
Request from its MTP3, then M2PA shall report to MTP3 that the link is Request from its MTP3, then M2PA SHALL report to MTP3 that the link is
out of service. out of service.
After the association is established, M2PA shall send a Link Status After the association is established, M2PA SHALL send a Link Status
Out of Service message to its peer. Out of Service message to its peer.
Once the association is established and M2PA has received a Start Once the association is established and M2PA has received a Start
Request from MTP3, M2PA sends the Link Status Alignment message to its Request from MTP3, M2PA sends the Link Status Alignment message to its
peer. If M2PA has not already received the Link Status Alignment peer. If M2PA has not already received the Link Status Alignment
message from its peer, then M2PA starts timer T1. message from its peer, then M2PA starts timer T2.
(Note that if the remote M2PA has not received a Start Request from (Note that if the remote M2PA has not received a Start Request from
its MTP3, it will not send the Link Status Alignment message to the its MTP3, it will not send the Link Status Alignment message to the
local M2PA. Eventually timer T1 in the local M2PA will expire. If the local M2PA. Eventually timer T2 in the local M2PA will expire. If the
remote M2PA receives a Start Request from its MTP3 and sends Link remote M2PA receives a Start Request from its MTP3 and sends Link
Status Alignment before the local M2PA's timer T1 expires, the Status Alignment before the local M2PA's timer T2 expires, the
alignment procedure can continue.) alignment procedure can continue.)
M2PA stops timer T1 when it has received the Link Status Alignment M2PA stops timer T2 when it has received the Link Status Alignment
message from its peer. message from its peer.
If timer T1 expires, then M2PA reports to MTP3 that the link is out of If timer T2 expires, then M2PA reports to MTP3 that the link is out of
service. M2PA sends Link Status Out of Service to its peer. M2PA service. M2PA sends Link Status Out of Service to its peer. M2PA
should leave the association established. M2PA waits for MTP3 to SHOULD leave the association established. M2PA waits for MTP3 to
initiate the alignment procedure again. initiate the alignment procedure again.
Note: Between the time M2PA sends Link Status Alignment to its peer Note: Between the time M2PA sends Link Status Alignment to its peer
and receives Link Status Alignment from its peer, M2PA may receive and receives Link Status Alignment from its peer, M2PA may receive
Link Status Out of Service from its peer. This message is Link Status Out of Service from its peer. This message is
ignored. After receiving Link Status Alignment from the peer, receipt ignored. After receiving Link Status Alignment from the peer, receipt
of a Link Status Out of Service message causes M2PA to send Out of of a Link Status Out of Service message causes M2PA to send Out of
Service to MTP3 and return to the Out of Service state. Service to MTP3 and return to the Out of Service state.
When M2PA has both sent and received the Link Status Alignment When M2PA has both sent and received the Link Status Alignment
message, it has completed alignment and moves to the proving state. message, it has completed alignment. M2PA starts the aligned timer T3
and moves to the proving state.
M2PA starts the proving period timer T4. During the proving period, M2PA stops timer T3 when it receives a Proving Normal or Proving
M2PA sends Link Status Proving messages to its peer at an interval Emergency message and starts proving period timer T4.
defined by the protocol parameter Proving_Rate. M2PA sends either the
Proving Normal or Proving Emergency message, according to the If timer T3 expires, then M2PA reports to MTP3 that the link is out of
Emergency and Emergency Ceases commands from MTP3. M2PA uses the value service. M2PA sends Link Status Out of Service to its peer. M2PA
of T4 corresponding to the Normal or Emergency state. However, if M2PA SHOULD leave the association established. M2PA waits for MTP3 to
receives a Link Status Proving Emergency message from its peer, then initiate the alignment procedure again.
M2PA shall initiate the Emergency proving period value for T4, but it
shall continue to send the Proving message (Normal or Emergency)
determined by its own upper layer MTP3.
When the proving period timer T4 expires, M2PA shall start the timer During the proving period (i.e., after M2PA starts the proving period
T3 and send Link Status Ready messages to its peer at interval timer T4), M2PA sends Link Status Proving messages to its peer at an
Status_Interval. These messages are used to verify that both ends have interval defined by the protocol parameter Proving_Interval. M2PA
completed proving. sends either the Proving Normal or Proving Emergency message,
according to the Emergency and Emergency Ceases commands from
MTP3. M2PA uses the value of T4 corresponding to the Normal or
Emergency condition. However, if M2PA receives a Link Status Proving
Emergency message from its peer, then M2PA SHALL initiate the
Emergency proving period value for T4, but it SHALL continue to send
the Proving message (Normal or Emergency) determined by its own upper
layer MTP3.
M2PA shall stop timer T3 when it receives a Link Status Ready or User When the proving period timer T4 expires, M2PA changes to the Aligned
Data message from its peer. If timer T3 expires, then M2PA reports to Ready state. M2PA SHALL start the timer T1 and send a Link Status
Ready message to its peer. These Link Status Ready message is used to
verify that both ends have completed proving. M2PA MAY send additional
Link Status Ready messages while timer T1 is running.
M2PA SHALL stop timer T1 when it receives a Link Status Ready or User
Data message from its peer. If timer T1 expires, then M2PA reports to
MTP3 that the link is out of service. M2PA sends Link Status Out of MTP3 that the link is out of service. M2PA sends Link Status Out of
Service to its peer. M2PA should leave the association Service to its peer. M2PA SHOULD leave the association
established. M2PA waits for MTP3 to initiate the alignment procedure established. M2PA waits for MTP3 to initiate the alignment procedure
again. again.
Note that if M2PA has already received a Link Status Ready message Note that if M2PA has already received a Link Status Ready message
from its peer when its timer T4 expires, there is no need to start from its peer when its timer T4 expires, there is no need to start
timer T3. M2PA can just send Link Status Ready to the peer and timer T1. M2PA can just send Link Status Ready to the peer and
continue along. continue along.
When all of the following are true: When all of the following are true:
(a) M2PA has received a Start Request from MTP3. (a) M2PA has received a Start Request from MTP3.
(b) M2PA's proving period T4 has expired. (b) M2PA's proving period T4 has expired.
(c) M2PA has sent a Link Status Ready to its peer. (c) M2PA has sent a Link Status Ready to its peer.
(d) M2PA has received a Link Status Ready OR User Data (d) M2PA has received a Link Status Ready OR User Data
message from its peer. message from its peer.
(e) M2PA has not received Link Status Out of Service from its peer (e) M2PA has not received Link Status Out of Service from its peer
since it received Link Status Alignment. since it received Link Status Alignment.
then M2PA shall send Link In Service to its MTP3. then M2PA SHALL send Link In Service to its MTP3.
If there is a local processor outage condition during the alignment If there is a local processor outage condition during the alignment
procedure, M2PA sends Link Status Processor Outage to its peer. When procedure, M2PA sends Link Status Processor Outage to its peer. When
the local processor outage condition ends, then M2PA shall send Link the local processor outage condition ends, then M2PA SHALL send Link
Status Processor Outage Ended to its peer. M2PA shall attempt to Status Processor Outage Ended to its peer. M2PA SHALL attempt to
complete the alignment procedure during the local processor outage complete the alignment procedure during the local processor outage
condition. condition.
If M2PA receives a Link Status Processor Outage during alignment, and If M2PA receives a Link Status Processor Outage during alignment, and
M2PA had received a Start Request from its MTP3, M2PA shall report M2PA had received a Start Request from its MTP3, M2PA SHALL report
Remote Processor Outage to MTP3. M2PA shall attempt to complete the Remote Processor Outage to MTP3. M2PA SHALL attempt to complete the
alignment procedure during the remote processor outage condition. alignment procedure during the remote processor outage condition.
If M2PA receives a Stop command from its MTP3 during alignment, M2PA If M2PA receives a Stop command from its MTP3 during alignment, M2PA
SHALL send Link Status Out of Service to its peer, terminate the
alignment procedure, and return to the Out of Service state.
shall send Link Status Out of Service to its peer and terminate the Anomalous messages received during alignment SHOULD be
alignment procedure.
Anomalous messages received during alignment should be
discarded. Examples include: discarded. Examples include:
(a) User Data received before proving begins. (a) User Data received before proving begins.
(b) Link Status Alignment received during proving. (b) Link Status Alignment received before or during proving.
Recommended values: Recommended values:
T1 Alignment - Range: 1-60 seconds Default: 10 seconds T1 Ready - Range: 40-50 seconds. Default: 45 seconds.
T4 Proving -
Normal - Range: 1-60 seconds Default: 10 seconds T2 Not Aligned - Range: 5-150 seconds. Default: 60 seconds.
Emergency - Range: 400-600 milliseconds Default: 500 milliseconds T3 Aligned - Range: 1.0-1.5 seconds. Default: 1.0 seconds.
T3 Ready - Range: 1-60 seconds Default: 10 seconds T4 Normal - Range: 7.5-9.5 seconds. Default: 8 seconds.
Status_Interval - implementation dependent. T4 Emergency - Range: 400-600 milliseconds.
Default: 500 milliseconds.
Proving_Rate - implementation dependent. Proving_Interval - implementation dependent.
4.1.4 Processor Outage 4.1.4 Processor Outage
A processor outage occurs when M2PA cannot transfer messages because A processor outage occurs when M2PA cannot transfer messages because
of a condition at a higher layer than M2PA. of a condition at a higher layer than M2PA.
When M2PA detects a local processor outage, it sends a Link Status When M2PA detects a local processor outage, it sends a Link Status
message to its peer with status Processor Outage. M2PA shall also message to its peer with status Processor Outage. M2PA SHALL also
cease sending User Data messages to SCTP for transmission. M2PA shall cease sending User Data messages to SCTP for transmission. M2PA SHALL
stop receiving incoming messages from SCTP. stop acknowledging received User Data messages.
M2PA should periodically send a Link Status Processor Outage message M2PA MAY send additional Link Status Processor Outage messages as long
as long as there is a local processor outage and the link is in as there is a local processor outage and the link is in service. If
service. If the link is out of service, M2PA should locally mark that the link is out of service, M2PA SHOULD locally mark that it is in
it is in local processor outage. local processor outage.
The peer M2PA, upon receiving the Link Status Processor Outage The peer M2PA, upon receiving the Link Status Processor Outage
message, shall report Remote Processor Outage to its MTP3. The peer message, SHALL report Remote Processor Outage to its MTP3. The peer
M2PA ceases sending User Data messages. M2PA stops the Remote M2PA ceases sending User Data messages. M2PA stops the Remote
Congestion timer T6 (see section 4.1.5 Level 2 Flow Control) if it is Congestion timer T6 (see section 4.1.5 Level 2 Flow Control) if it is
running. running, and timer T7, if it is running.
MTP3 may send a Flush Buffers or Continue command to M2PA as part of MTP3 may send a Flush Buffers or Continue command to M2PA as part of
its processor outage procedure (See section 4.2.4 Flush Buffers, its processor outage procedure (See section 4.2.4 Flush Buffers and
Continue). Alternatively, MTP3 may perform data retrieval as part of a Continue). The use of Flush Buffers and Continue is specified in Q.703
changeover procedure. [Q.703] and T1.111.3 [T1.111].
Alternatively, MTP3 may perform data retrieval as part of a changeover
procedure.
When the processor outage ceases, MTP3 sends a Local Processor When the processor outage ceases, MTP3 sends a Local Processor
Recovered indication to M2PA. The local M2PA notifies its peer by Recovered indication to M2PA. The local M2PA notifies its peer by
sending a Link Status message with status Processor Outage Ended. The sending a Link Status message with status Processor Outage Ended. The
peer uses the Remote Processor Recovered Indication to notify its MTP3 local M2PA SHALL resume receiving and transmitting messages.
that the remote processor outage condition has ceased.
If the peer is in the IN SERVICE state, it uses the Remote Processor
Recovered Indication to notify its MTP3 that the remote processor
outage condition has ceased.
4.1.5 Level 2 Flow Control 4.1.5 Level 2 Flow Control
The determination of receive congestion in M2PA is implementation The determination of receive congestion in M2PA is implementation
dependent. dependent.
If M2PA determines that it is in receive congestion for an If M2PA determines that it is in receive congestion for an
association, M2PA shall send a Link Status Busy message to its peer on association, M2PA SHALL send a Link Status Busy message to its peer on
that association. M2PA shall continue to acknowledge incoming that association. M2PA SHALL continue to acknowledge incoming
messages. messages.
M2PA should periodically send a Link Status Busy message as long as M2PA MAY send additional Link Status Busy messages as long as it is in
it is in receive congestion. receive congestion.
M2PA shall continue transmitting messages while it is in receive M2PA SHALL continue transmitting messages while it is in receive
congestion. congestion.
When the peer M2PA receives the Link Status Busy message, it shall When the peer M2PA receives the first Link Status Busy message, it
start the Remote Congestion timer T6. If timer T6 expires, M2PA shall SHALL start the Remote Congestion timer T6. Additional Link Status
take the link out of service. M2PA sends a Link Status Out of Service Busy messages received while T6 is running do not cause T6 to be
message to its peer, and goes to the Retrieval state. reset.
The peer M2PA should continue transmitting messages to SCTP while its If timer T6 expires, M2PA SHALL take the link out of service. M2PA
sends a Link Status Out of Service message to its peer, and goes to
the Out of Service state.
The peer M2PA SHOULD continue transmitting messages to SCTP while its
T6 timer is running, i.e., while the other end is Busy. T6 timer is running, i.e., while the other end is Busy.
The peer M2PA shall not fail the link due to expiration of timer T7 The peer M2PA SHALL NOT fail the link due to expiration of timer T7
excessive delay of acknowledgement (see section 4.2.1 Sending and excessive delay of acknowledgement (see section 4.2.1 Sending and
receiving messages) while its T6 timer is running, i.e., while the receiving messages) while its T6 timer is running, i.e., while the
other end is Busy. other end is Busy.
If M2PA is no longer in receive congestion for the association, M2PA If M2PA is no longer in receive congestion for the association, M2PA
shall send a Link Status Busy Ended message to its peer on that SHALL send a Link Status Busy Ended message to its peer on that
association. association.
When the peer M2PA receives the Link Status Busy Ended message, it When the peer M2PA receives the Link Status Busy Ended message, it
shall stop timer T6. SHALL stop timer T6.
Recommended value of T6 is 1-6 seconds. Recommended values:
T6 Busy - Range: 1-6 seconds. Default: 4.5 seconds.
4.1.6 Error Monitoring 4.1.6 Error Monitoring
If M2PA loses the SCTP association for a link, M2PA shall report to If M2PA loses the SCTP association for a link, M2PA SHALL report to
MTP3 that the link is out of service. MTP3 that the link is out of service.
4.1.7 Transmission and Reception Priorities 4.1.7 Transmission and Reception Priorities
In MTP, Link Status messages have priority over User Data messages In MTP, Link Status messages have priority over User Data messages
([2] Q.703, section 11.2). To achieve this in M2PA, M2PA shall send ([Q.703], section 11.2). To achieve this in M2PA, M2PA SHALL send
Link Status and User Data messages on separate streams in its SCTP Link Status and User Data messages on separate streams in its SCTP
association. All messages are sent using the ordered delivery option. association. M2PA SHALL send all messages using the ordered delivery
option of SCTP.
M2PA SHOULD give higher priority to Link Status messages than to User M2PA SHOULD give higher priority to Link Status messages than to User
Data messages when sending messages to SCTP. Data messages when sending messages to SCTP.
M2PA SHOULD give higher priority to reading the Link Status stream M2PA SHOULD give higher priority to reading the Link Status stream
than to reading the User Data stream. than to reading the User Data stream.
M2PA SHOULD give higher priority to receiving notifications from SCTP M2PA SHOULD give higher priority to receiving notifications from SCTP
than to reading either the Link Status stream or the User Data stream. than to reading either the Link Status stream or the User Data stream.
4.1.8 M2PA Version Control 4.1.8 M2PA Version Control
A node upgraded to a newer version of M2PA SHOULD support the older A node upgraded to a newer version of M2PA SHOULD support the older
versions used on other nodes with which it is communicating. If that versions used on other nodes with which it is communicating. If that
is the case, then alignment can proceed normally. is the case, then alignment can proceed normally.
In particular, it is recommended that for future modifications to this In particular, it is recommended that for future modifications to this
protocol: protocol:
- Any newer version should be able to process the messages from a - Any newer version SHOULD be able to process the messages from a
lower version. lower version.
- A newer version of M2PA should refrain from sending messages to an - A newer version of M2PA SHOULD refrain from sending messages to an
older version of M2PA messages that the older version cannot older version of M2PA messages that the older version cannot
process. process.
- If an older version of M2PA receives a message that it cannot - If an older version of M2PA receives a message that it cannot
process, it should discard the message. process, it SHOULD discard the message.
- In cases where different processing is done in two versions for the - In cases where different processing is done in two versions for the
same format of a message, then the newer version should contain same format of a message, then the newer version SHOULD contain
procedures to recognize this and handle it appropriately. procedures to recognize this and handle it appropriately.
In case a newer version of M2PA is incompatible with an older version, In case a newer version of M2PA is incompatible with an older version,
the newer version should recognize this and prevent the alignment of the newer version SHOULD recognize this and prevent the alignment of
the link. If a Link Status Alignment message with an unsupported the link. If a Link Status Alignment message with an unsupported
version is received by the newer version, the receiving end's M2PA version is received by the newer version, the receiving end's M2PA
shall not complete the alignment procedure. SHALL NOT complete the alignment procedure.
4.2 Procedures to Support the MTP3/MTP2 Interface 4.2 Procedures to Support the MTP3/MTP2 Interface
4.2.1 Sending and receiving messages 4.2.1 Sending and receiving messages
When MTP3 sends a message for transmission to M2PA, M2PA passes the When MTP3 sends a message for transmission to M2PA, M2PA passes the
corresponding M2PA message to SCTP using the SEND primitive. corresponding M2PA message to SCTP using the SEND primitive.
M2PA Link Status messages are passed to SCTP using the SEND primitive. M2PA Link Status messages are passed to SCTP using the SEND primitive.
Link Status and User Data messages shall be sent via SCTP on separate Link Status and User Data messages SHALL be sent via SCTP on separate
streams. streams.
When M2PA receives a User Data message from SCTP, M2PA passes the When M2PA receives a User Data message from SCTP, M2PA passes the
message to MTP3. message to MTP3.
If M2PA receives a message from SCTP with an invalid Message Class or If M2PA receives a message from SCTP with an invalid Message Class or
unsupported Message Type in the Common Message Header, M2PA shall unsupported Message Type in the Common Message Header, M2PA SHALL
discard the message. discard the message.
The first User Data message sent after the link is placed in service The first User Data message sent after the link is placed in service
is given a Forward Sequence Number (FSN) of 1. is given a Forward Sequence Number (FSN) of 1.
The Forward Sequence Number of the header is incremented by 1 for each The Forward Sequence Number of the header is incremented by 1 for each
User Data message sent. When the FSN reaches the maximum value, the User Data message sent (provided that the message contains a data
next FSN is 0. payload). When the FSN reaches the maximum value, the next FSN is 0.
For message types other than User Data, the Forward Sequence Number is For message types other than User Data, the Forward Sequence Number is
set to the FSN of the last User Data message sent. set to the FSN of the last User Data message sent.
The Backward Sequence Number is set to the FSN of the last User Data The Backward Sequence Number is set to the FSN of the last User Data
message M2PA received from its peer. This serves as an M2PA-level message M2PA received from its peer. This serves as an M2PA-level
acknowledgement of the message. After the link is placed in service acknowledgement of the message. After the link is placed in service
and before a User Data message has been received, the BSN is set to 0. and before a User Data message has been received, the BSN is set to 0.
When M2PA receives a User Data message with Backward Sequence Number When M2PA receives a User Data message with Backward Sequence Number
equal to 'n', it may remove all messages with Forward Sequence Number equal to 'n', it may remove all messages with Forward Sequence Number
<= n from its queue. <= n from its queue.
If M2PA receives a User Data message with an FSN that is out of order, If M2PA receives a User Data message with an FSN that is out of order,
M2PA shall fail the link. M2PA SHALL take the link out of service.
M2PA should follow the criterion stated in [2] Q.703, section 5.3.1 M2PA SHOULD follow the criterion of Q.703 [Q.703], section 5.3.1 for
for incorrect BSNs: If any two BSNs in three consecutively received incorrect BSNs: If any two BSNs in three consecutively received User
User Data messages are not the same as the previous one or any of the Data messages are not the same as the previous one or any of the FSNs
FSNs of the User Data messages in the M2PA transmit buffer at the time of the User Data messages in the M2PA transmit buffer at the time they
they are received, then MTP3 should be informed that the link is are received, then MTP3 SHOULD be informed that the link is faulty.
faulty.
M2PA should ignore the FSN and BSN contained in a Link Status message. M2PA SHOULD ignore the FSN and BSN contained in a Link Status message.
Note: In all calculations involving FSN and BSN, the programmer should Note: In all calculations involving FSN and BSN, the programmer should
be aware that the value wraps around to 0 after reaching its maximum be aware that the value wraps around to 0 after reaching its maximum
value. value.
If there is no other User Data message to be sent when there is a If there is no other User Data message to be sent when there is a
message to acknowledge, M2PA may send a User Data message with no data message to acknowledge, M2PA may send a User Data message with no data
payload. The FSN for this empty User Data message is incremented as payload. The FSN for this empty User Data message is not
with any other User Data message. incremented. It MUST contain the same FSN as the most recently sent
User Data message containing Data.
If M2PA receives an empty User Data message, it SHALL NOT send an
acknowledgement of that message.
Note that there is no reason to place empty User Data messages in the
M2PA retransmit buffer, since the empty messages are not retransmitted
and timer T7 (below) does not apply to them.
Note that since SCTP provides reliable delivery and ordered delivery Note that since SCTP provides reliable delivery and ordered delivery
within the stream, M2PA does not perform retransmissions. within the stream, M2PA does not perform retransmissions.
Timer T7 provides an indication of excessive delay of Timer T7 provides an indication of excessive delay of
acknowledgement. If the following conditions are true: acknowledgement. If the following conditions are true:
(a) There is at least one message in the M2PA transmit buffer that (a) There is at least one message in the M2PA retransmit buffer.
has been sent.
(b) The remote M2PA is not in a Busy condition. (b) The remote M2PA is not in a Busy condition (i.e., the local
timer T6 is not running).
(c) M2PA has not received an acknowledgement in the span of T7. (c) There is a message in the M2PA retransmit buffer that has not
received an acknowledgement in the span of T7 since its last
transmission.
Then M2PA should fail the link. then M2PA SHOULD take the link out of service.
The recommended range for timer T7 is 0.5-2 seconds. Recommended values:
T7 Acknowledgement - Range: 0.5-2 seconds. Default: 1.0 seconds.
4.2.2 Link activation and restoration 4.2.2 Link activation and restoration
When MTP3 requests that M2PA activate or restore a link by a Start When MTP3 requests that M2PA activate or restore a link by a Start
Request, M2PA shall follow the alignment procedure in section 4.1.3. Request, M2PA SHALL follow the alignment procedure in section 4.1.3.
4.2.3 Link deactivation 4.2.3 Link deactivation
When MTP3 requests that M2PA deactivate a link by a Stop command, M2PA When MTP3 requests that M2PA deactivate a link by a Stop command, M2PA
shall send a Link Status Out of Service message to its peer. SHALL send a Link Status Out of Service message to its peer.
The peer M2PA, upon receiving Link Status Out of Service, shall notify The peer M2PA, upon receiving Link Status Out of Service, SHALL notify
its upper layer MTP3 that the link is out of service. its upper layer MTP3 that the link is out of service.
4.2.4 Flush Buffers, Continue 4.2.4 Flush Buffers and Continue
The Flush Buffers and Continue commands allow M2PA to resume normal The Flush Buffers and Continue commands allow M2PA to resume normal
operations (i.e., transmission of messages to SCTP and receiving operations (i.e., transmission of messages to SCTP and receiving
messages from SCTP) after a processor outage (local and/or remote) messages from SCTP) after a processor outage (local and/or remote)
ceases. ceases.
If M2PA receives a Flush Buffers command from MTP3, M2PA: If M2PA receives a Flush Buffers command from MTP3, M2PA:
(a) shall not transmit any messages to SCTP that are currently (a) SHALL NOT transmit any messages to SCTP that are currently
waiting to be transmitted to SCTP. These messages shall be waiting to be transmitted to SCTP. These messages SHALL be
discarded. discarded.
(b) shall discard all messages currently waiting to be passed (b) SHALL discard all messages currently waiting to be passed
to MTP3. to MTP3.
If M2PA receives either a Flush Buffers or Continue command from MTP3,
and the processor outage condition ceases, M2PA shall resume receiving
and transmitting messages.
4.2.5 MTP3 Signaling Link Congestion 4.2.5 MTP3 Signaling Link Congestion
M2PA shall detect transmit congestion in its buffers according to the M2PA SHALL detect transmit congestion in its buffers according to the
requirements for signaling link transmit congestion in [2] Q.704, requirements for signaling link transmit congestion in Q.704 [Q.704],
section 3.8. section 3.8.
M2PA shall use the Congestion Indication primitive to notify its upper M2PA SHALL use the Congestion Indication primitive to notify its upper
layer MTP3 of changes in the signaling link congestion status and the layer MTP3 of changes in the signaling link congestion status and the
signaling link discard status. For national networks with multiple signaling link discard status. For national networks with multiple
congestion threshold levels, M2PA shall notify MTP3 of the congestion congestion threshold levels, M2PA SHALL notify MTP3 of the congestion
and discard status levels. and discard status levels.
4.2.6 Changeover 4.2.6 Changeover
The objective of the changeover is to ensure that signaling traffic The objective of the changeover is to ensure that signaling traffic
carried by the unavailable signaling link is diverted to the carried by the unavailable signaling link is diverted to the
alternative signaling link(s) as quickly as possible while avoiding alternative signaling link(s) as quickly as possible while avoiding
message loss, duplication, or mis-sequencing. For this purpose, the message loss, duplication, or mis-sequencing. For this purpose, the
changeover procedure includes data retrieval, which is performed changeover procedure includes data retrieval, which is performed
before opening the alternative signaling links to the diverted before opening the alternative signaling links to the diverted
skipping to change at page 35, line 40 skipping to change at page 35, line 36
(1) buffer updating, i.e., identifying all those User Data (1) buffer updating, i.e., identifying all those User Data
messages in the retransmission buffer of the unavailable messages in the retransmission buffer of the unavailable
signaling link which have not been received by the far end signaling link which have not been received by the far end
M2PA, as well as untransmitted messages, and M2PA, as well as untransmitted messages, and
(2) transferring those messages to the transmission buffers of the (2) transferring those messages to the transmission buffers of the
alternate links. alternate links.
Note that only User Data messages are retrieved and transmitted over Note that only User Data messages are retrieved and transmitted over
the alternate links. Link Status messages shall not be retrieved and the alternate links. Link Status messages SHALL NOT be retrieved and
transmitted over the alternate links. transmitted over the alternate links.
M2PA's Sequence Numbers are 24 bits long. MTP2's Forward and Backward M2PA's Sequence Numbers are 24 bits long. MTP2's Forward and Backward
Sequence Numbers are only seven bits long. Hence it is necessary for Sequence Numbers are only seven bits long. Hence it is necessary for
MTP3 to accommodate the larger sequence numbers. This is done through MTP3 to accommodate the larger sequence numbers. This is done through
the use of the Extended Changeover Order (XCO) and Extended Changeover the use of the Extended Changeover Order (XCO) and Extended Changeover
Acknowledgement (XCA) messages instead of the Changeover Order (COO) Acknowledgement (XCA) messages instead of the Changeover Order (COO)
and Changeover Acknowledgement (COA) messages. The XCO and XCA and Changeover Acknowledgement (COA) messages. The XCO and XCA
messages are specified in Reference [7] section 9.8.1 and Reference messages are specified in [Q.2210] section 9.8.1 and T1.111.4
[3] T1.111.4, section 15.4. Only the XCO and XCA messages from [7] or [T1.111], section 15.4. Only the XCO and XCA messages from [Q.2210] or
[3] are required. The BSN is placed in the XCO/XCA message as [T1.111] are required. The BSN is placed in the XCO/XCA message as
explained in [7] and [3]. explained in [Q.2210] and [T1.111].
Also, the following MTP3/MTP2 primitives must use the larger sequence Also, the following MTP3/MTP2 primitives MUST use the larger sequence
numbers: numbers:
- BSNT Confirmation - BSNT Confirmation
- Retrieval Request and FSNC - Retrieval Request and FSNC
For data retrieval, MTP3 requests the Backward Sequence Number to be For data retrieval, MTP3 requests the Backward Sequence Number to be
Transmitted (BSNT) from M2PA through the Retrieve BSNT request. M2PA Transmitted (BSNT) from M2PA through the Retrieve BSNT request. M2PA
determines the Forward Sequence Number of the last User Data message determines the Forward Sequence Number of the last User Data message
received from the peer. This value is the BSNT. M2PA sends the BSNT received from the peer. This value is the BSNT. M2PA sends the BSNT
skipping to change at page 36, line 28 skipping to change at page 36, line 21
through the XCO and XCA messages. The BSNT received from the other end through the XCO and XCA messages. The BSNT received from the other end
is called the FSNC. When MTP3 receives the FSNC from the other end, is called the FSNC. When MTP3 receives the FSNC from the other end,
MTP3 retrieves all the unsent and unacknowledged messages starting MTP3 retrieves all the unsent and unacknowledged messages starting
with sequence number (FSNC + 1). This is accomplished through a with sequence number (FSNC + 1). This is accomplished through a
Retrieval Request and FSNC request. After all the messages are sent Retrieval Request and FSNC request. After all the messages are sent
from M2PA to MTP3, M2PA sends a Retrieval Complete indication to MTP3. from M2PA to MTP3, M2PA sends a Retrieval Complete indication to MTP3.
If there are any messages on the M2PA or SCTP receive queues that have If there are any messages on the M2PA or SCTP receive queues that have
not been acknowledged by M2PA, M2PA SHOULD discard these messages. The not been acknowledged by M2PA, M2PA SHOULD discard these messages. The
peer will retransmit them on an alternate link. Any messages peer will retransmit them on an alternate link. Any messages
acknowledged by M2PA MUST NOT be discarded. These messages must be acknowledged by M2PA MUST NOT be discarded. These messages MUST be
delivered to MTP3. delivered to MTP3.
If M2PA receives a Retrieve BSNT request from MTP3, M2PA shall respond If M2PA receives a Retrieve BSNT request from MTP3, M2PA SHALL respond
with the BSNT confirmation. The BSNT value is the Forward Sequence with the BSNT confirmation. The BSNT value is the Forward Sequence
Number of the last User Data message received from the peer. Number of the last User Data message received from the peer.
If M2PA receives a Retrieval Request and FSNC request from MTP3, M2PA If M2PA receives a Retrieval Request and FSNC request from MTP3, M2PA
shall retrieve from its buffers in order and deliver to MTP3: SHALL retrieve from its buffers in order and deliver to MTP3:
(a) any transmitted User Data messages beginning with the first (a) any transmitted User Data messages beginning with the first
unacknowledged message with FSN greater than FSNC. unacknowledged message with FSN greater than FSNC.
(b) any untransmitted User Data messages. (b) any untransmitted User Data messages.
Then M2PA shall send the Retrieval Complete indication to MTP3. Then M2PA SHALL send the Retrieval Complete indication to MTP3.
For emergency changeover, MTP3 retrieves only the unsent messages for For emergency changeover, MTP3 retrieves only the unsent messages for
transmission on the alternate link(s). If M2PA receives a Retrieval transmission on the alternate link(s). If M2PA receives a Retrieval
Request and FSNC request with no FSNC value, or with an invalid FSNC, Request and FSNC request with no FSNC value, or with an invalid FSNC,
then M2PA shall retrieve from its buffers in order and deliver to then M2PA SHALL retrieve from its buffers in order and deliver to
MTP3: MTP3:
(a) any untransmitted User Data messages. (a) any untransmitted User Data messages.
Then M2PA shall send the Retrieval Complete indication to MTP3. Then M2PA SHALL send the Retrieval Complete indication to MTP3.
Note: For the Japanese version of MTP defined in [9], MTP3 retrieves Note: For the Japanese version of MTP defined in [JT-Q704], MTP3
both unsent and unacknowleged messages for transmission on the retrieves both unsent and unacknowleged messages for transmission on
alternate link(s). In this version of MTP, if M2PA receives a Retrieval the alternate link(s). In this version of MTP, if M2PA receives a
Request and FSNC request with no FSNC value, or with an invalid FSNC, Retrieval Request and FSNC request with no FSNC value, or with an
then M2PA shall retrieve from its buffers in order and deliver to invalid FSNC, then M2PA SHALL retrieve from its buffers in order and
MTP3: deliver to MTP3:
(a) any transmitted but unacknowledged User Data messages. (a) any transmitted but unacknowledged User Data messages.
(b) any untransmitted User Data messages. (b) any untransmitted User Data messages.
Then M2PA shall send the Retrieval Complete indication to MTP3. Then M2PA SHALL send the Retrieval Complete indication to MTP3.
4.2.6.1 Multiple User Data Streams and Changeover 4.2.6.1 Multiple User Data Streams and Changeover
The changeover procedure makes it problematic for M2PA to have The changeover procedure makes it problematic for M2PA to have
multiple User Data streams in one direction for a link. Buffer multiple User Data streams in one direction for a link. Buffer
updating would have to be done for each User Data stream separately to updating would have to be done for each User Data stream separately to
avoid duplication or loss of messages. But MTP3 provides for only one avoid duplication or loss of messages. But MTP3 provides for only one
XCO/XCA message for sending the last-received sequence number. XCO/XCA message for sending the last-received sequence number.
Even with sequence numbering of User Data messages at the M2PA layer, Even with sequence numbering of User Data messages at the M2PA layer,
skipping to change at page 38, line 5 skipping to change at page 38, line 5
4.3.1 SCTP Slow Start 4.3.1 SCTP Slow Start
SCTP contains a slow start algorithm to control the amount of data SCTP contains a slow start algorithm to control the amount of data
being injected into the network. The algorithm allows SCTP to probe being injected into the network. The algorithm allows SCTP to probe
the network to determine the available capacity. The algorithm is the network to determine the available capacity. The algorithm is
invoked when transmission begins on an association, after a invoked when transmission begins on an association, after a
sufficiently long idle period, or after repairing loss detected by the sufficiently long idle period, or after repairing loss detected by the
SCTP retransmission timer. SCTP retransmission timer.
It is possible that transmission of M2PA messages may be delayed by It is possible that transmission of M2PA messages MAY be delayed by
SCTP slow start under certain conditions, including the following: SCTP slow start under certain conditions, including the following:
(a) Link Alignment. Link alignment takes place after an association (a) Link Alignment. Link alignment takes place after an association
is established. SCTP invokes the slow start algorithm since is established. SCTP invokes the slow start algorithm since
transmission is beginning on the association. transmission is beginning on the association.
(b) Changeover. Messages are retrieved from one link (association) (b) Changeover. Messages are retrieved from one link (association)
and transferred to another for transmission. If the second link and transferred to another for transmission. If the second link
had previously been idle, or is in the process of link had previously been idle, or is in the process of link
alignment, SCTP may invoke the slow start algorithm. alignment, SCTP may invoke the slow start algorithm.
skipping to change at page 39, line 13 skipping to change at page 39, line 13
start before the link is placed in service. start before the link is placed in service.
5. Examples of M2PA Procedures 5. Examples of M2PA Procedures
In general, messages passed between MTP3 and M2PA are the same as In general, messages passed between MTP3 and M2PA are the same as
those passed between MTP3 and MTP2. M2PA interprets messages from those passed between MTP3 and MTP2. M2PA interprets messages from
MTP3 and sends the appropriate message to SCTP. Likewise, messages MTP3 and sends the appropriate message to SCTP. Likewise, messages
from SCTP are used to generate a meaningful message to MTP3. from SCTP are used to generate a meaningful message to MTP3.
Note that throughout this section, the primitives between MTP3 and Note that throughout this section, the primitives between MTP3 and
M2PA are named using the MTP terminology [1][2]. Communications M2PA are named using the MTP terminology [Q.700] [Q.701] [Q.702]
between M2PA and SCTP are named using SCTP terminology. [Q.703] [Q.704] [Q.705]. Communications between M2PA and SCTP are
named using SCTP terminology.
5.1 Link Initialization (Alignment) 5.1 Link Initialization (Alignment)
An example of the message flow to bring an SS7 link in service is An example of the message flow to bring an SS7 link in service is
shown below. Alignment is done by both ends of the link. To simplify shown in Figures 12 and 13. Alignment is done by both ends of the
the diagram, alignment is shown on one end only. It is assumed in this link. To simplify the diagram, alignment is shown on one end
example that SCTP has been initialized. only. Some messages from the remote end are not shown. It is assumed
in this example that SCTP has been initialized.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . .
. Associate . . . .
. ------------> . . .
. . . . . .
. . (SCTP Association . .
. . procedure) . .
. . . . . .
. Communication Up Communication Up .
. <------------ ------------> .
. . . . . .
. Link Status Out of Service . .
. ------------------------------------> .
. . . . . .
Emergency OR . . . .
Emergency Ceases . . . .
------------> . . . .
. . . . . .
Start . . . . .
------------> . . . .
. . . . . .
. . . . . .
. Link Status Alignment . . .
. ------------------------------------> .
. . . . . .
. Start timer T2 . . .
. . . . . .
. . . Link Status Alignment .
. <------------------------------------ .
. . . . . .
. Stop timer T2 . . .
. Start timer T4 . . .
. . . . . .
Associate Proving period begins.
------------>
(SCTP Association
procedure)
Communication Up Communication Up
<------------ ------------>
Link Status Out of Service
------------------------------------>
Emergency OR
Emergency Ceases
------------>
Start Figure 12. Example: Link Initialization - Alignment
------------>
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . .
. Link Status Proving . . .
. ------------------------------------> .
. ------------------------------------> .
. ------------------------------------> .
. ------------------------------------> .
. ------------------------------------> .
. ------------------------------------> .
. . . . . .
. Timer T4 expires . . .
. . . . . .
Link Status Alignment Send Link Status Ready (one or more) and wait for the remote end
------------------------------------> to complete its proving period.
Start timer T1
Link Status Alignment
<------------------------------------
Stop timer T1
Start timer T4
Proving period begins. (Messages from remote end not shown.)
Link Status Proving
------------------------------------>
------------------------------------>
------------------------------------>
------------------------------------>
------------------------------------>
------------------------------------>
Timer T4 expires
Send Link Status Ready until the remote end completes its proving
period.
Start timer T3
Link Status Ready
------------------------------------>
------------------------------------>
------------------------------------>
------------------------------------>
Link Status Ready
<------------------------------------
Stop timer T3 . . . . . .
. Start timer T1 . . .
. . . . . .
. Link Status Ready . . .
. ------------------------------------> .
. . . . . .
. . . . . .
. . . Link Status Ready .
. <------------------------------------ .
. . . . . .
. Stop timer T1 . . .
. . . . . .
In Service . . In Service
<------------ . . ------------>
. . . . . .
In Service In Service MTP3 MAY begin sending data messages.
<------------ ------------>
At this point, MTP3 may begin sending data messages. Figure 13. Example: Link Initialization - Proving
5.2 Message Transmission and Reception 5.2 Message Transmission and Reception
Messages are transmitted using the Data Request primitive from MTP3 to Messages are transmitted using the Data Request primitive from MTP3 to
M2PA. The diagram shows the case where the Link is In Service. The M2PA. Figure 14 shows the case where the Link is In Service. The
message is passed from MTP3 of the source to MTP3 of the destination. message is passed from MTP3 of the source to MTP3 of the destination.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . .
Message for . . . .
transmission . . . .
------------> . . . .
. . . . . .
. Send . . . .
. (Data Message) . . .
. ------------> . . .
. . . . . .
. . (SCTP sends message) . .
. . . . . .
. . . Receive .
. . . ------------> .
. . . . . .
. . . . Received message
. . . . ------------>
. . . . . .
Message for Figure 14. Example: Link Initialization - In Service
transmission
------------>
Send
(Data Message)
------------>
(SCTP sends message)
Receive
------------>
Received message
------------>
5.3 Link Status Indication 5.3 Link Status Indication
If SCTP sends a Communication Lost primitive to M2PA, M2PA notifies An example of a Link Status Indication is shown in Figure 15. If SCTP
MTP3 that the link is out of service. MTP3 responds in its usual way. sends a Communication Lost primitive to M2PA, M2PA notifies MTP3 that
the link is out of service. MTP3 responds in its usual way.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . .
. Communication Lost . . .
. <------------ . . .
. . . . . .
Out of Service . . . .
<------------ . . . .
. . . . . .
Communication Lost Figure 15. Example: Link Status Indication
<------------
Out of Service
<------------
5.4 Link Status Message (Processor Outage) 5.4 Link Status Message (Processor Outage)
This example shows how M2PA responds to a local processor outage. M2PA Figure 16 shows how M2PA responds to a local processor outage. M2PA
sends a Link Status message to its peer. The peer M2PA notifies MTP3 sends a Link Status message to its peer. The peer M2PA notifies MTP3
of the outage. MTP3 can then follow the processor outage procedures in of the outage. MTP3 can then follow the processor outage procedures in
[2]. [Q.703].
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . .
. M2PA detects . . . .
. Local Processor . . . .
. Outage . . . .
. . . . . .
. Link Status . . . .
. Processor Outage . . .
. ------------> . . .
. . . . . .
. . (SCTP sends message) . .
. . . . . .
. . . Receive . .
. . . ------------> .
. . . . . .
. . . . Remote Processor
. . . . Outage .
. . . . ------------>
. . . . . .
. Link Status . . .
. Processor Outage . . .
. Ended . . .
. ------------> . . .
. . . . . .
. . (SCTP sends message) . .
. . . . . .
. . . Receive . .
. . . ------------> .
. . . . . .
. . . . Remote Processor
. . . . Outage Ceases
. . . . ------------>
. . . . . .
M2PA detects Figure 16. Example: Link Status Message - Processor Outage
Local Processor
Outage
Link Status
Processor Outage
------------>
(SCTP sends message)
Receive
------------>
Remote Processor
Outage
------------>
Link Status
Processor Outage
Ended
------------>
(SCTP sends message)
Receive
------------>
Remote Processor
Outage Ceases
------------>
5.5 Level 2 Flow Control 5.5 Level 2 Flow Control
This illustrates the Level 2 Flow Control procedure. In the first Figures 17 and 18 illustrate the Level 2 Flow Control procedure. In
diagram, congestion ceases before timer T6 expires. The second diagram Figure 17, congestion ceases before timer T6 expires. Figure 18 shows
shows the case where T6 expires. the case where T6 expires.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . .
. Implementation dependent . .
. determination of M2PA . .
. receive congestion onset . .
. . . . . .
. Link Status Busy . . .
. ------------------------------------> .
. . . . . .
. . . . Start .
. . . . Timer T6 .
. . . . . .
. Implementation dependent . .
. determination of M2PA . .
. receive congestion abatement . .
. . . . . .
. Link Status Busy Ended . . .
. ------------------------------------> .
. . . . . .
. . . . Stop .
. . . . Timer T6 .
. . . . . .
Implementation dependent Figure 17. Example: Level 2 Flow Control - Congestion Ceases
determination of M2PA
receive congestion onset
Link Status Busy
------------------------------------>
Start
Timer T6
Implementation dependent
determination of M2PA
receive congestion abatement
Link Status Busy Ended
------------------------------------>
Stop
Timer T6
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . .
. Implementation dependent . .
. determination of M2PA . .
. receive congestion onset . .
. . . . . .
. Link Status Busy . . .
. ------------------------------------> .
. . . . . .
. . . . Start .
. . . . Timer T6 .
. . . . : .
. . . . : .
. . . . Timer T6 .
. . . . Expires .
. . . . . .
. . Link Status Out of Service .
. <------------------------------------ .
. . . . . .
. . . . Out of Service
. . . . ------------>
. . . . . .
Implementation dependent Figure 18. Example: Level 2 Flow Control - Timer T6 Expires
determination of M2PA
receive congestion onset
Link Status Busy
------------------------------------>
Start
Timer T6
:
:
Timer T6
Expires
Link Status Out of Service
<------------------------------------
Out of Service
------------>
5.6 MTP3 Signaling Link Congestion 5.6 MTP3 Signaling Link Congestion
In this example, M2PA notifies MTP3 of congestion onset and In Figure 19, M2PA notifies MTP3 of congestion onset and
abatement. The notification includes the congestion level, if there abatement. The notification includes the congestion level, if there
are levels of congestion defined. are levels of congestion defined.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . .
. Implementation dependent . .
. determination of M2PA . . .
. transmit congestion . . .
. onset (level) . . .
. . . . . .
Congestion Indication . . . .
(level) . . . . .
<------------ . . . .
. . . . . .
. Implementation dependent . .
. determination of M2PA . . .
. transmit congestion . . .
. abatement (level) . . .
. . . . . .
Congestion Indication . . . .
(level) . . . . .
<------------ . . . .
. . . . . .
Implementation dependent Figure 19. Example: MTP3 Signalling Link Congestion
determination of M2PA
transmit congestion
onset (level)
Congestion Indication
(level)
<------------
Implementation dependent
determination of M2PA
transmit congestion
abatement (level)
Congestion Indication
(level)
<------------
5.7 Link Deactivation 5.7 Link Deactivation
The MTP3 can request that a SS7-IP link be taken out of service. Figure 20 shows an example of link deactivation. MTP3 can request that
a link be taken out of service.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . .
Stop . . . . .
------------> . . . .
. . . . . .
. Link Status Out of Service . .
. ------------------------------------> .
. . . . . .
Out of Service . . . .
<------------ . . . .
. . . . . .
Stop Figure 20. Example: Link Deactivation
------------>
Link Status Out of Service
------------------------------------>
Out of Service
<------------
5.8 Link Changeover 5.8 Link Changeover
In this example, MTP3 performs a changeover because the link went out In Figure 21, MTP3 performs a changeover because the link went out of
of service. MTP3 selects a different link to retransmit the service. MTP3 selects a different link to retransmit the
unacknowledged and unsent messages. unacknowledged and unsent messages.
Note that in this example, the sequence numbers and messages requested Note that in this example, the sequence numbers and messages requested
by MTP3 are sent from SCTP to M2PA in the Communication Lost by MTP3 are sent from SCTP to M2PA in the Communication Lost
primitive. In general, the retrieval of sequence numbers and messages primitive. In general, the retrieval of sequence numbers and messages
is implementation dependent. is implementation dependent.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . .
Communication Lost . Communication Lost . . .
<------------ . <------------ . . .
. . . . . .
Out of Service Out of Service . . . .
<------------ <------------ . . . .
. . . . . .
Retrieve BSNT Retrieve BSNT . . . .
------------> ------------> . . . .
. . . . . .
BSNT Confirmation BSNT Confirmation . . . .
<------------ <------------ . . . .
. . . . . .
XCO (BSNT) on another link XCO (BSNT) on another link . . .
------------------------------------------------------------> ------------------------------------------------------------>
. . . . . .
Retrieve BSNT . . . . Retrieve BSNT
<------------ . . . . <------------
. . . . . .
BSNT Confirmation . . . . BSNT Confirmation
------------> . . . . ------------>
. . . . . .
XCA (BSNT) . . . . . XCA (BSNT)
<------------------------------------------------------------ <------------------------------------------------------------
. . . . . .
Retrieval Request Retrieval Request . . . .
and FSNC and FSNC . . . . .
------------> ------------> . . . .
. . . . . .
Retrieved Message Retrieved Message . . . .
<------------ <------------ . . . .
: . : . . . . .
: . : . . . . .
<------------ <------------ . . . .
. . . . . .
Retrieval Complete Retrieval Complete . . . .
<------------ <------------ . . . .
. . . . . .
Send messages on another link. Send messages on another link.
Figure 21. Example: Link Changeover
6. Security 6. Security
M2PA is designed to carry signaling messages for telephony M2PA is designed to carry signaling messages for telephony
services. As such, M2PA MUST involve the security needs of several services. As such, M2PA MUST involve the security needs of several
parties: the end users of the services, the network providers, and the parties: the end users of the services, the network providers, and the
applications involved. Additional requirements MAY come from local applications involved. Additional requirements MAY come from local
regulation. While having some overlapping security needs, any regulation. While having some overlapping security needs, any
security solution SHOULD fulfill all of the different parties' needs. security solution SHOULD fulfill all of the different parties' needs.
6.1 Threats 6.1 Threats
There is no quick-fix, one-size-fits-all solution for security. As a There is no quick-fix, one-size-fits-all solution for security. As a
transport protocol, M2PA has the following security objectives: transport protocol, M2PA has the following security objectives:
- Availability of reliable and timely user data transport. - Availability of reliable and timely user data transport.
- Integrity of user data transport. - Integrity of user data transport.
- Confidentiality of user data. - Confidentiality of user data.
M2PA runs on top of SCTP. SCTP [5] provides certain transport related M2PA runs on top of SCTP. SCTP [RFC2960] provides certain transport
security features, such as: related security features, such as:
- Blind Denial of Service Attacks - Blind Denial of Service Attacks
- Flooding - Flooding
- Masquerade - Masquerade
- Improper Monopolization of Services - Improper Monopolization of Services
When M2PA is running in professionally managed corporate or service When M2PA is running in professionally managed corporate or service
provider network, it is reasonable to expect that this network provider network, it is reasonable to expect that this network
includes an appropriate security policy framework. The "Site Security includes an appropriate security policy framework. The "Site Security
Handbook" [11] SHOULD be consulted for guidance. Handbook" [RFC2196] SHOULD be consulted for guidance.
When the network in which M2PA runs involves more than one party When the network in which M2PA runs involves more than one party
(e.g., a non-private network), it MAY NOT be reasonable to expect that (e.g., a non-private network), it MAY NOT be reasonable to expect that
all parties have implemented security in a sufficient manner. In such all parties have implemented security in a sufficient manner. In such
a case, it is recommended that IPSEC be used to ensure confidentiality a case, it is recommended that IPSEC be used to ensure confidentiality
of user payload. Consult [12] for more information on configuring of user payload. Consult [RFC2401] for more information on configuring
IPSEC services. IPSEC services.
6.2 Protecting Confidentiality 6.2 Protecting Confidentiality
Particularly for mobile users, the requirement for confidentiality MAY Particularly for mobile users, the requirement for confidentiality MAY
include the masking of IP addresses and ports. In this case include the masking of IP addresses and ports. In this case
application-level encryption is not sufficient. IPSEC ESP SHOULD be application-level encryption is not sufficient. IPSEC ESP SHOULD be
used instead. Regardless of which level performs the encryption, the used instead. Regardless of which level performs the encryption, the
IPSEC ISAKMP service SHOULD be used for key management. IPSEC ISAKMP service SHOULD be used for key management.
7. IANA Considerations 7. IANA Considerations
7.1 SCTP Payload Protocol Identifier 7.1 SCTP Payload Protocol Identifier
The SCTP (and TCP) Registered User Port Number Assignment for M2PA The SCTP (and UDP/TCP) Registered User Port Number Assignment for M2PA
is 3565. is 3565.
The value assigned by IANA for the Payload Protocol Identifier in the The value assigned by IANA for the Payload Protocol Identifier in the
SCTP Payload Data chunk is SCTP Payload Data chunk is
M2PA 5 M2PA 5
The SCTP Payload Protocol Identifier is included in each SCTP Data The SCTP Payload Protocol Identifier is included in each SCTP Data
chunk, to indicate which protocol the SCTP is carrying. This Payload chunk, to indicate which protocol the SCTP is carrying. This Payload
Protocol Identifier is not directly used by SCTP but may be used by Protocol Identifier is not directly used by SCTP but may be used by
skipping to change at page 47, line 32 skipping to change at page 51, line 32
The User Adaptation peer may use the Payload Protocol Identifier as a The User Adaptation peer may use the Payload Protocol Identifier as a
way of determining additional information about the data being way of determining additional information about the data being
presented to it by SCTP. presented to it by SCTP.
7.2 M2PA Protocol Extensions 7.2 M2PA Protocol Extensions
This protocol may be extended through IANA in three ways: This protocol may be extended through IANA in three ways:
- through definition of additional message classes, - through definition of additional message classes,
- through definition of additional message types, and - through definition of additional message types, and
- through definition of additional message parameters. - through definition of additional message parameters.
The definition and use of new message classes, types, and parameters The definition and use of new message classes, types, and parameters
is an integral part of SIGTRAN adaptation layers. Thus, these is an integral part of SIGTRAN adaptation layers. Thus, these
extensions are assigned by IANA through an IETF Consensus action as extensions are assigned by IANA through an IETF Consensus action as
defined in [13]. defined in [RFC2434].
The proposed extension must in no way adversely affect the general The proposed extension must in no way adversely affect the general
working of the protocol. working of the protocol.
7.2.1 IETF Defined Message Classes 7.2.1 IETF Defined Message Classes
The documentation for a new message class MUST include the following The documentation for a new message class MUST include the following
information: information:
(a) A long and short name for the message class. (a) A long and short name for the message class.
skipping to change at page 49, line 7 skipping to change at page 53, line 13
the same message type. the same message type.
8. Acknowledgements 8. Acknowledgements
The authors would like to thank the following for their valuable The authors would like to thank the following for their valuable
comments and suggestions: Brian Tatum, Jeff Copley, Monique Bernard, comments and suggestions: Brian Tatum, Jeff Copley, Monique Bernard,
Wayne Davis, Cliff Thomas, Ian Rytina, Al Varney. Wayne Davis, Cliff Thomas, Ian Rytina, Al Varney.
9. References 9. References
[1] ITU-T Recommendation Q.700, 'Introduction To ITU-T Signalling [JT-Q704]
System No. 7 (SS7)'. TTC, "Message Transfer Part Signalling Network Functions," TTC
Standard JT-Q704, Telecommunication Technology Committee (TTC)
(April 28, 1992).
[2] ITU-T Recommendation Q.701-Q.705, 'Signalling System No. 7 [M2UA]
(SS7) - Message Transfer Part (MTP)'. K. Morneault, et. al., "Signaling System 7 (SS7) Message
Transfer Part 2 (MTP2) - User Adaptation Layer," RFC 3331,
Internet Engineering Task Force - Signalling Transport Working
Group (September, 2002).
[3] ANSI T1.111-2000, American National Standard for [Q.700]
Telecommunications - Signaling System Number 7 (SS7) - ITU, "Introduction to CCITT Signalling System No. 7," ITU-T
Message Transfer Part (MTP), 2000. Recommendation Q.700, ITU-T Telecommunication Standardization
Sector of ITU (March 1993).
[4] RFC 2719, Framework Architecture for Signaling Transport, [Q.701]
October 1999. ITU, "Functional Description of the Message Transfer Part (MTP)
of Signalling System No. 7," ITU-T Recommendation Q.701, ITU-T
Telecommunication Standardization Sector of ITU (March 1993).
[5] RFC 2960, Stream Control Transmission Protocol, [Q.702]
October 2000. ITU, "Signalling Data Link," ITU-T Recommendation Q.702, ITU-T
Telecommunication Standardization Sector of ITU (March 1993).
[6] SS7 MTP2-User Adaptation Layer, draft-ietf-sigtran-m2ua-15.txt, [Q.703]
February 2002. ITU, "Signalling System No. 7 - Signalling Link," ITU-T
Recommendation Q.703, ITU-T Telecommunication Standardization
Sector of ITU (March 1993).
[7] ITU-T Recommendation Q.2210, 'Message transfer part level 3 [Q.704]
functions and messages using the services of ITU-T ITU, "Message Transfer Part - Signalling Network Functions and
Recommendation Q.2140'. Messages," ITU-T Recommendation Q.704, ITU-T Telecommunication
Standardization Sector of ITU (March 1993).
[8] Bradner, S. "Key words for use in RFCs to Indicate Requirement [Q.705]
Levels", BCP 14, RFC 2119, March 1997. ITU, "Signalling System No. 7 - Signalling Network Structure,"
ITU-T Recommendation Q.705, ITU-T Telecommunication
Standardization Sector of ITU (March 1993).
[9] Telecommunication Technology Committee (TTC) Standard JT-Q704, [Q.2140]
'Message Transfer Part Signaling Network Functions', ITU, "B-ISDN ATM Adaptation Layer - Service Specific
April 28, 1992. Coordination Function for Signalling at the Network Node
Interface (SSCF at NNI)," ITU-T Recommendation Q.2140, ITU-T
Telecommunication Standardization Sector of ITU (February
1996).
[10] ITU-T Recommendation Q.2140, 'B-ISDN ATM Adaptation Layer', [Q.2210]
February 1995. ITU, "Message Transfer Part Level 3 Functions and Messages
Using the Services of ITU-T Recommendation Q.2140," ITU-T
Recommendation Q.2210, ITU-T Telecommunication Standardization
Sector of ITU (July 1996).
[11] RFC 2196, Site Security Handbook, September 1997. [RFC791]
Information Sciences Institute, "Internet Protocol - DARPA
Internet Program - Protocol Specification," RFC 791, The
Internet Society (September 1981).
[12] RFC 2401, Security Architecture for the Internet Protocol, [RFC2119]
November 1998. S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels," BCP 14, RFC 2119, Internet Engineering Task Force
(March 1997).
[13] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA [RFC2196]
Considerations Section in RFCs", BCP 26, RFC 2434, October B. Y. Frazer, "Site Security Handbook," RFC 2196, Internet
1998. Engineering Task Force (September 1997).
[14] RFC 791, Internet Protocol, September 1981. [RFC2401]
S. Kent, R. Atkinson, "Security Architecture for the Internet
Protocol," RFC 2401, Internet Engineering Task Force (November
1998).
[RFC2434]
T. Narten, H. T. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs," BCP 26, RFC 2434, The Internet
Society (October, 1998).
[RFC2719]
L. Ong, et. al., "Framework Architecture for Signaling
Transport," RFC 2719, The Internet Society (October 1999).
[RFC2960]
R. Stewart, et. al., "Stream Control Transmission Protocol
(SCTP)," RFC 2960, The Internet Society (February 2000).
[T1.111]
ANSI, "American National Standard for Telecommunications -
Signaling System Number 7 (SS7) - Message Transfer Part (MTP),"
ANSI T1.111-2000, American National Standards Institute (2000).
10. Author's Addresses 10. Author's Addresses
Tom George Tel: +1-972-519-3168 Tom George Tel: +1-972-519-3168
Alcatel USA, Inc. EMail: Tom.George@alcatel.com Alcatel USA, Inc. EMail: Tom.George@alcatel.com
1000 Coit Road 1000 Coit Road
Plano, TX 75075 Plano, TX 75075
USA USA
Brian Bidulock Tel +1-780-490-1141
OpenSS7 Corporation EMail: bidulock@openss7.org
1469 Jeffreys Crescent
Edmonton, AB T6L 6T1
Canada
Ram Dantu, Ph.D. Tel: +1-214-291-1111 Ram Dantu, Ph.D. Tel: +1-214-291-1111
Netrake Corporation EMail: rdantu@netrake.com Netrake Corporation EMail: rdantu@netrake.com
3000 Technology Drive, Suite 100 3000 Technology Drive, Suite 100
Plano 75074 Plano 75074
USA USA
Malleswar Kalla Tel: +1-973-829-5212 Malleswar Kalla Tel: +1-973-829-5212
Telcordia Technologies EMail: kalla@research.telcordia.com Telcordia Technologies EMail: kalla@research.telcordia.com
MCC 1J211R MCC 1J211R
445 South Street 445 South Street
Morristown, NJ 07960 Morristown, NJ 07960
USA USA
Hanns Juergen Schwarzbauer Tel: +49-89-722-24236 Hanns Juergen Schwarzbauer Tel: +49-89-722-24236
SIEMENS AG HannsJuergen.Schwarzbauer@icn.siemens.de SIEMENS AG HannsJuergen.Schwarzbauer@icn.siemens.de
Hofmannstr. 51 Hofmannstr. 51
81359 Munich 81359 Munich
Germany Germany
Greg Sidebottom Greg Sidebottom
gregside consulting EMail: gregside@rogers.com Signatus Technologies EMail: greg@signatustechnologies.com
Kanata, Ontario Kanata, Ontario
Canada Canada
Ken Morneault Tel: +1-703-484-3323 Ken Morneault Tel: +1-703-484-3323
Cisco Systems Inc. EMail: kmorneau@cisco.com Cisco Systems Inc. EMail: kmorneau@cisco.com
13615 Dulles Technology Drive 13615 Dulles Technology Drive
Herndon, VA 20171 Herndon, VA 20171
USA USA
Brian Bidulock Tel +1-780-490-1141 This Internet Draft expires July 2003.
OpenSS7 Corporation EMail: bidulock@openss7.org
1469 Jeffreys Crescent
Edmonton, AB T6L 6T1
Canada
This Internet Draft expires February 2003.
 End of changes. 

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