draft-ietf-sigtran-m2pa-13.txt   rfc4165.txt 
Network Working Group Tom George Network Working Group T. George
INTERNET-DRAFT Brian Bidulock Request for Comments: 4165 B. Bidulock
OpenSS7 Category: Standards Track OpenSS7
Ram Dantu R. Dantu
University of North Texas University of North Texas
Hanns Juergen Schwarzbauer H. Schwarzbauer
Siemens Siemens
Ken Morneault K. Morneault
Cisco Systems Cisco Systems
September 2005
Expires August 2005 February 18, 2005 Signaling System 7 (SS7) Message Transfer Part 2 (MTP2) -
User Peer-to-Peer Adaptation Layer (M2PA)
Signaling System 7 (SS7) Message Transfer Part 2 (MTP2) - User
Peer-to-Peer Adaptation Layer (M2PA)
<draft-ietf-sigtran-m2pa-13.txt>
Status of This Memo Status of This Memo
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in accordance with RFC 3668.
Abstract This document defines a protocol supporting the transport of
Signaling System Number 7 (SS7) Message Transfer Part (MTP) Level 3
signaling messages over Internet Protocol (IP) using the services of
the Stream Control Transmission Protocol (SCTP). This protocol would
be used between SS7 Signaling Points using the MTP Level 3 protocol.
The SS7 Signaling Points may also use standard SS7 links using the
SS7 MTP Level 2 to provide transport of MTP Level 3 signaling
messages. The protocol operates in a manner similar to MTP Level 2
so as to provide peer-to-peer communication between SS7 endpoints.
This Internet Draft defines a protocol supporting the transport of Table of Contents
Signaling System Number 7 (SS7) Message Transfer Part (MTP) Level 3
signaling messages over Internet Protocol (IP) using the services of
the Stream Control Transmission Protocol (SCTP). This protocol would
be used between SS7 Signaling Points using the MTP Level 3
protocol. The SS7 Signaling Points may also use standard SS7 links
using the SS7 MTP Level 2 to provide transport of MTP Level 3
signaling messages. The protocol operates in a manner similar to MTP
Level 2 so as to provide peer-to-peer communication between SS7
endpoints.
TABLE OF CONTENTS 1. Introduction ....................................................3
1.1. Scope ......................................................3
1.2. Terminology ................................................3
1.3. Abbreviations ..............................................4
1.4. Conventions ................................................5
1.5. Signaling Transport Architecture ...........................5
1.6. Services Provided by M2PA ..................................7
1.7. Functions Provided by M2PA .................................9
1.8. Definition of the M2PA Boundaries .........................10
1.9. Differences Between M2PA and M2UA .........................10
2. Protocol Elements ..............................................12
2.1. Common Message Header .....................................12
2.2. M2PA Header ...............................................13
2.3. M2PA Messages .............................................14
3. State Control ..................................................17
3.1. SCTP Association State Control ............................17
3.2. M2PA Link State Control ...................................18
4. Procedures .....................................................19
4.1. Procedures to Support MTP2 Features .......................19
4.2. Procedures to Support the MTP3/MTP2 Interface .............30
4.3. SCTP Considerations .......................................33
5. Examples of M2PA Procedures ....................................34
5.1. Link Initialization (Alignment) ...........................34
5.2. Message Transmission and Reception ........................37
5.3. Link Status Indication ....................................37
5.4. Link Status Message (Processor Outage) ....................38
5.5. Level 2 Flow Control ......................................42
5.6. MTP3 Signaling Link Congestion ............................44
5.7. Link Deactivation .........................................45
5.8. Link Changeover ...........................................45
6. Security Considerations ........................................47
7. IANA Considerations ............................................47
7.1. SCTP Payload Protocol Identifier ..........................47
7.2. M2PA Protocol Extensions ..................................48
8. Acknowledgements ...............................................49
9. References .....................................................50
9.1. Normative References ......................................50
9.2. Informative References ....................................51
1. Introduction............................................. 4 1. Introduction
1.1 Scope................................................. 4
1.2 Terminology........................................... 4
1.3 Abbreviations......................................... 5
1.4 Conventions........................................... 6
1.5 Signaling Transport Architecture...................... 6
1.6 Services Provided by M2PA............................. 9
1.7 Functions Provided by M2PA............................10
1.8 Definition of the M2PA Boundaries.....................11
1.9 Differences Between M2PA and M2UA.....................11
2. Protocol Elements........................................14
2.1 Common Message Header.................................14
2.2 M2PA Header...........................................15
2.3 M2PA Messages.........................................16
3. State Control............................................20
3.1 SCTP Association State Control........................20
3.2 M2PA Link State Control...............................21
4. Procedures...............................................22
4.1 Procedures to Support MTP2 Features...................22
4.2 Procedures to Support the MTP3/MTP2 Interface.........33
4.3 SCTP Considerations...................................37
5. Examples of M2PA Procedures..............................38
5.1 Link Initialization (Alignment).......................38
5.2 Message Transmission and Reception....................41
5.3 Link Status Indication................................41
5.4 Link Status Message (Processor Outage)................42
5.5 Level 2 Flow Control..................................46
5.6 MTP3 Signaling Link Congestion........................48
5.7 Link Deactivation.....................................48
5.8 Link Changeover.......................................49
6. Security.................................................50
7. IANA Considerations......................................50
7.1 SCTP Payload Protocol Identifier......................50
7.2 M2PA Protocol Extensions..............................51
8. Acknowledgements.........................................54
9. References...............................................54
9.1 Normative..............................................54
9.2 Informative............................................56
10. Author's Addresses.......................................57
11. Full Copyright Statement.................................58
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)
[RFC2719] [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.
networks. SCN signaling nodes would have access to databases and other SCN signaling nodes would have access to databases and other devices
devices in the IP network domain that do not use SS7 signaling in the IP network domain that do not use SS7 signaling links.
links. Likewise, IP telephony applications would have access to SS7 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
"connections". network "connections".
The delivery mechanism described in this document allows for full MTP3 The delivery mechanism described in this document allows for full
message handling and network management capabilities between any two MTP3 message handling and network management capabilities between any
SS7 nodes, communicating over an IP network. An SS7 node equipped with two SS7 nodes communicating over an IP network. An SS7 node equipped
an IP network connection is called an IP Signaling Point (IPSP). The with an IP network connection is called an IP Signaling Point (IPSP).
IPSPs function as traditional SS7 nodes using the IP network instead The IPSPs function as traditional SS7 nodes using the IP network
of SS7 links. instead 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 [Q.700] [Q.701] MTP - The Message Transfer Part of the SS7 protocol [Q.700] [Q.701]
[Q.702] [Q.703] [Q.704] [Q.705] [T1.111]. [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
Level 2. The only MTP2 user is MTP3. The MTP2 user is equivalent to 2. The only MTP2 user is MTP3. The MTP2 user is equivalent to the
the M2PA user. M2PA user.
Signaling End Point (SEP) - An SS7 Signaling Point that originates Signaling End Point (SEP) - An SS7 Signaling Point that originates or
or terminates signaling messages. One example is a central office terminates signaling messages. One example is a central office
switch. [RFC2719] switch. [RFC2719]
IP Signaling Point (IPSP) - An SS7 Signaling Point with an IP IP Signaling Point (IPSP) - An SS7 Signaling Point with an IP network
network connection used for SS7 over IP. 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 [RFC2719]. In this native signaling at the edge of the IP network [RFC2719]. In this
context, an SG is an SS7 Signaling Point that has both an IP network context, an SG is an SS7 Signaling Point that has both an IP network
connection used for SS7 over IP, and a traditional (non-IP) link to an connection used for SS7 over IP, and a traditional (non-IP) link to
SS7 network. an SS7 network.
Signal Transfer Point (STP) - A Signal Transfer Point as defined by MTP Signal Transfer Point (STP) - A Signal Transfer Point as defined by
standards, e.g., [Q.700]. MTP standards, e.g., [Q.700].
Signaling Point (STP) - A Signaling Point as defined by MTP standards, Signaling Point (STP) - A Signaling Point as defined by MTP
e.g., [Q.700]. standards, e.g., [Q.700].
Association - An association refers to an SCTP association Association - An association refers to an SCTP association [RFC2960].
[RFC2960]. The association provides the transport for MTP3 protocol The association provides the transport for MTP3 protocol data units
data units and M2PA adaptation layer peer messages. 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 [RFC791], Appendix B "Data Transmission Order". Endian". See [RFC791], Appendix B "Data Transmission Order".
Stream - A stream refers to an SCTP stream [RFC2960]. Stream - A stream refers to an 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
remote level 2 level 2
LI - Length Indicator LI - Length Indicator
MSU - Message Signal Unit MSU - Message Signal Unit
SCCP - Signaling Connection Control Part SCCP - Signaling Connection Control Part
SCN - Switched Circuit Network SCN - Switched Circuit Network
SCTP - Stream Control Transmission Protocol
SCTP - Stream Control Transmission Protocol SIF - Signaling Information Field
SIF - Signaling Information Field SIO - Service Information Octet
SIO - Service Information Octet SLC - Signaling Link Code
SLC - Signaling Link Code
SS7 - Signaling System Number 7 SS7 - Signaling System Number 7
SSN - Stream Sequence Number SSN - Stream Sequence Number
STP - Signal Transfer Point STP - Signal Transfer Point
1.4 Conventions 1.4. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
"OPTIONAL" in this document are to be interpreted as described in document are to be interpreted as described in [RFC2119].
[RFC2119].
1.5 Signaling Transport Architecture 1.5. Signaling Transport Architecture
The architecture that has been defined [RFC2719] 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. The adaptation layer, known as the MTP2 User Peer-to-peer messages. The adaptation layer, known as the MTP2 User Peer-to-peer
Adaptation Layer (M2PA), provides MTP3 with an interface and services Adaptation Layer (M2PA), provides MTP3 with an interface and services
similar to MTP2. In effect, MTP2 and lower layers of the traditional similar to MTP2. In effect, MTP2 and lower layers of the traditional
SS7 protocol stack are replaced by an IP equivalent. SS7 protocol stack are replaced by an IP equivalent.
Figure 1 shows the seamless interworking at the MTP3 layer. MTP3 is Figure 1 shows the seamless interworking at the MTP3 layer. MTP3 is
adapted to the SCTP layer using the MTP2 User Peer-to-peer Adaptation adapted to the SCTP layer using the MTP2 User Peer-to-peer Adaptation
Layer (M2PA). All the primitives between MTP3 and MTP2 are supported Layer (M2PA). All the primitives between MTP3 and MTP2 are supported
by M2PA. The SCTP association acts as one SS7 link between the IPSPs. by M2PA. The SCTP association acts as one SS7 link between the
An IPSP may have the Signaling Connection Control Part (SCCP) and IPSPs. An IPSP may have the Signaling Connection Control Part (SCCP)
other SS7 layers above MTP3. and other SS7 layers above MTP3.
******** IP ******** ******** IP ********
* IPSP *--------* IPSP * * IPSP *--------* IPSP *
******** ******** ******** ********
+------+ +------+ +------+ +------+
| TCAP | | TCAP | | TCAP | | TCAP |
+------+ +------+ +------+ +------+
| SCCP | | SCCP | | SCCP | | SCCP |
+------+ +------+ +------+ +------+
| MTP3 | | MTP3 | | MTP3 | | MTP3 |
+------+ +------+ +------+ +------+
| 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 [RFC2960] SCTP - Stream Control Transmission Protocol [RFC2960]
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).
(SG). The SG is an IPSP equipped with both traditional SS7 and IP The SG is an IPSP that is equipped with both traditional SS7 and IP
network connections. network connections.
The SEP and the SG communicate through a traditional SS7 link, which The SEP and the SG communicate through a traditional SS7 link, which
follows a protocol such as [Q.702]. The SG and the IPSP communicate follows a protocol such as [Q.702]. The SG and the IPSP communicate
through an IP link using the M2PA protocol. Messages sent from the SEP through an IP link using the M2PA protocol. Messages sent from the
to the IPSP (and vice versa) are routed by the SG. SEP to the IPSP (and vice versa) are routed by the SG.
Any of the nodes in the diagram could have SCCP or other SS7 layers Any of the nodes in the diagram could have SCCP or other SS7 layers
above MTP3. The Signaling Gateway acts as a Signal Transfer Point above MTP3. The Signaling Gateway acts as a Signal Transfer Point
(STP). Other STPs MAY be present in the SS7 path between the SEP and (STP). Other STPs MAY be present in the SS7 path between the SEP and
the SG. the SG.
******** SS7 *************** IP ******** ******** SS7 *************** IP ********
* SEP *--------* SG *--------* IPSP * * SEP *--------* SG *--------* IPSP *
******** *************** ******** ******** *************** ********
+------+ +------+ +------+ +------+
| TCAP | | TCAP | | TCAP | | TCAP |
+------+ +------+ +------+ +------+
| SCCP | | SCCP | | SCCP | | SCCP |
+------+ +-------------+ +------+ +------+ +-------------+ +------+
| MTP3 | | MTP3 | | MTP3 | | MTP3 | | MTP3 | | MTP3 |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
| MTP2 | | MTP2 | M2PA | | M2PA | | MTP2 | | MTP2 | M2PA | | M2PA |
| | | +------+ +------+ | | | +------+ +------+
| | | | SCTP | | SCTP | | | | | SCTP | | SCTP |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
| MTP1 | | MTP1 | IP | | IP | | MTP1 | | MTP1 | 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
stack can be used in place of an MTP2/MTP1 stack. M2PA/SCTP/IP stack can be used in place of an MTP2/MTP1 stack.
1.5.1 Point Code Representation 1.5.1. Point Code Representation
MTP requires that each node with an MTP3 layer is identified by an SS7 MTP requires that each node with an MTP3 layer is identified by an
point code. In particular, each IPSP MUST have its own SS7 point code. SS7 point code. In particular, each IPSP MUST have 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 a set of services to its
services to its user as provided by MTP Level 2 to MTP Level 3. user equivalent to that 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 the This interface is the same as the MTP2/MTP3 interface described in
applicable SS7 standards [Q.703] [Q.704] [T1.111] [Q.2140], with the the applicable SS7 standards [Q.703] [Q.704] [T1.111] [Q.2140], with
addition of support for larger sequence numbers in [T1.111] and the addition of support for the larger sequence numbers found in
[Q.2210]. [T1.111] and [Q.2210].
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
those used in the MTP3/MTP2 interface. similar to those used in the MTP3/MTP2 interface.
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 [Q.2210] and Extended Changeover Acknowledgement messages described in [Q.2210]
[T1.111]. 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
In SS7, MTP Level 2 sends three types of messages, known as signal In SS7, MTP Level 2 sends three types of messages, known as signal
units: Message Signal Units (MSUs), Link Status Signal Units (LSSUs), units: Message Signal Units (MSUs), Link Status Signal Units (LSSUs),
and Fill-In Signal Units (FISUs). and Fill-In Signal Units (FISUs).
MSUs originate at a higher level than MTP2, and are destined for a MSUs originate at a higher level than MTP2, and are destined for a
peer at another node. Likewise, M2PA passes these messages from MTP3 peer at another node. Likewise, M2PA passes these messages from MTP3
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.
messages are needed for M2PA. The Link Status message serves this Analogous messages are needed for M2PA. The Link Status message
purpose. serves this purpose.
FISUs are transmitted continuously when no other signal units are FISUs are transmitted continuously when no other signal units are
waiting to be sent. FISUs also carry acknowledgment of messages. Since waiting to be sent. FISUs also carry acknowledgement of messages.
an IP network is a shared resource, it would be undesirable to have a Since an IP network is a shared resource, it would be undesirable to
message type that is sent continuously as the FISUs are. Furthermore, have a message type that is sent continuously as is the case with
SCTP does not require its upper layer to continuously transmit FISUs. Furthermore, SCTP does not require its upper layer to
messages. Therefore, M2PA does not provide a protocol data unit like continuously transmit messages. Therefore, M2PA does not provide a
the FISU. The M2PA User Data message is used to carry acknowledgment protocol data unit like the FISU. The M2PA User Data message is used
of messages. If M2PA needs to acknowledge a message and it has no MTP3 to carry acknowledgement of messages. If M2PA needs to acknowledge a
message of its own to send, an empty User Data message can be sent. message, and it has no MTP3 message of its own to send, an empty User
Data message can be sent.
1.7 Functions Provided by M2PA 1.7. Functions Provided by M2PA
1.7.1 MTP2 Functionality 1.7.1. MTP2 Functionality
M2PA provides MTP2 functionality that is not provided by SCTP, so that M2PA provides MTP2 functionality that is not provided by SCTP; thus,
together M2PA and SCTP provide functionality similar to that of together M2PA and SCTP provide functionality similar to that of MTP2.
MTP2.
SCTP provides reliable, sequenced delivery of messages. SCTP provides reliable, sequenced delivery of messages.
M2PA functionality includes: M2PA functionality includes:
- Data retrieval to support the MTP3 changeover procedure - Data retrieval to support the MTP3 changeover procedure
- Reporting of link status changes to MTP3 - Reporting of link status changes to MTP3
- Processor outage procedure - Processor outage procedure
- Link alignment procedure - Link alignment procedure
1.7.2 Mapping of SS7 and IP Entities 1.7.2. Mapping of SS7 and IP Entities
The M2PA layer must maintain a map of each of its SS7 links to the The M2PA layer must maintain a map of each of its SS7 links to the
corresponding SCTP association. corresponding SCTP association.
1.7.3 SCTP Association Management 1.7.3. SCTP Association Management
SCTP allows a user-specified number of streams to be opened during the SCTP allows a user-specified number of streams to be opened during
initialization. It is the responsibility of the M2PA layer to ensure the initialization. It is the responsibility of the M2PA layer to
proper management of the streams allowed within each association. ensure proper management of the streams allowed within each
association.
M2PA uses two streams in each direction for each association. Stream 0 M2PA uses two streams in each direction for each association. Stream
in each direction is designated for Link Status messages. Stream 1 is 0 in each direction is designated for Link Status messages. Stream 1
designated for User Data messages, as well as Link Status messages is designated for User Data messages, as well as Link Status messages
that must remain in sequence with the User Data messages. Separating that must remain in sequence with the User Data messages. Separating
the Link Status and User Data messages onto separate streams allows the Link Status and User Data messages into separate streams allows
M2PA to prioritize the messages in a manner similar to MTP2. M2PA to prioritize the messages in a manner similar to MTP2.
Notifications received from SCTP are processed by M2PA or translated Notifications received from SCTP are processed by M2PA or translated
into an appropriate notification to be sent to the upper layer MTP3. into an appropriate notification to be sent to the upper layer MTP3.
1.7.4 Retention of MTP3 in the SS7 Network 1.7.4. 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 it does 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 the provided by MTP2 to MTP3. These primitives are described in the
applicable SS7 standards [Q.703] [Q.704] [T1.111] [Q.2140]. applicable SS7 standards [Q.703] [Q.704] [T1.111] [Q.2140].
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 [RFC2960] The upper layer primitives provided by SCTP are described in
Section 10 "Interface with Upper Layer". [RFC2960] 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) [M2UA] also adapts the MTP3 The MTP2 User Adaptation Layer (M2UA) [M2UA] also adapts the MTP3
layer to the SCTP/IP stack. It does so through a backhauling layer to the SCTP/IP stack. It does so through a backhauling
architecture [RFC2719]. This section is intended to clarify some of architecture [RFC2719]. This section is intended to clarify some of
the differences between the M2PA and M2UA approaches. the differences 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.
between the two layers MTP3/M2PA is defined by the same primitives as Communication between the two layers MTP3/M2PA is defined by the same
in SS7 MTP3/MTP2. M2PA performs functions similar to MTP2. primitives as in SS7 MTP3/MTP2. M2PA performs functions similar to
MTP2.
******** 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 |
| | | +------+ +------+ | | | +------+ +------+
| | | | SCTP | | SCTP | | | | | SCTP | | SCTP |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
| MTP1 | | MTP1 | IP | | IP | | MTP1 | | MTP1 | 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 A comparable architecture for M2UA is shown in Figure 4. In M2UA,
MGC's MTP3 uses the SG's MTP2 as its lower SS7 layer. Likewise, the the MGC's MTP3 uses the SG's MTP2 as its lower SS7 layer. Likewise,
SG's MTP2 uses the MGC's MTP3 as its upper SS7 layer. In SS7, 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 communication between the MTP3 and MTP2 layers is defined by
primitives. In M2UA, the MTP3/MTP2 communication is defined as M2UA primitives. In M2UA, the MTP3/MTP2 communication is defined as M2UA
messages and sent over the IP connection. 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 |
| | | +------+ +------+ | | | +------+ +------+
| | | | SCTP | | SCTP | | | | | SCTP | | SCTP |
+------+ +------+------+ +------+ +------+ +------+------+ +------+
| MTP1 | | MTP1 | IP | | IP | | MTP1 | | MTP1 | 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.
M2UA: MGC transports MTP3/MTP2 primitives between the SG's MTP2 M2UA: MGC transports MTP3/MTP2 primitives between the SG's MTP2
and the MGC's MTP3 (via the NIF) for processing. and the MGC's MTP3 (via the NIF) for processing.
b. M2PA: SG-IPSP connection is an SS7 link. b. M2PA: SG-IPSP connection is an SS7 link.
M2UA: SG-MGC connection is not an SS7 link. It is an M2UA: SG-MGC connection is not an SS7 link. It is an
extension of MTP to a remote entity. extension of MTP to a remote entity.
c. M2PA: SG is an SS7 node with a point code. c. M2PA: SG is an SS7 node with a point code.
M2UA: SG is not an SS7 node and has no point code. M2UA: SG is not an SS7 node and has no point code.
d. M2PA: SG can have upper SS7 layers, e.g., SCCP. d. M2PA: SG can have upper SS7 layers, e.g., SCCP.
M2UA: SG does not have upper SS7 layers since it has no MTP3. M2UA: SG does not have upper SS7 layers since it has no MTP3.
e. M2PA: relies on MTP3 for management procedures. e. M2PA: relies on MTP3 for management procedures.
M2UA: uses M2UA management procedures. M2UA: uses M2UA management procedures.
Potential users of M2PA and M2UA should be aware of these differences Potential users of M2PA and M2UA should be aware of these differences
when deciding how to use them for SS7 signaling transport over IP when deciding how to use them for SS7 signaling transport over IP
networks. networks.
2. Protocol Elements 2. Protocol Elements
This section describes the format of various messages used in this This section describes the format of various messages used in this
protocol. protocol.
All fields in an M2PA message must be transmitted in the network byte All fields in an M2PA message must be transmitted in the network byte
order, i.e., most significant byte first, unless otherwise stated. order, i.e., most significant byte first, unless otherwise stated.
2.1 Common Message Header 2.1. Common Message Header
The protocol messages for M2PA require a message header structure The protocol messages for M2PA require a message header structure
which contains a version, message class, message type, and message that contains a version, message class, message type, and message
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
are: versions are:
Value Value
(decimal) Version (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
The following List contains the valid Message Classes: The following List contains the valid Message Classes:
Value Value
(decimal) Message Class (decimal) Message Class
--------- ------------- --------- -------------
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 Value
(decimal) Message Type (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.
2.2 M2PA Header 2.2. M2PA Header
All protocol messages for M2PA require an M2PA-specific header. The All protocol messages for M2PA require an M2PA-specific header. The
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 (BSN) 2.2.1. Backward Sequence Number (BSN)
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 (FSN) 2.2.2. Forward Sequence Number (FSN)
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.
The FSN and BSN values range from 0 to 16,777,215. The FSN and BSN values range from 0 to 16,777,215.
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.
M2PA message consists of a Common Message Header and M2PA Header An 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 /
\ \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The field "Message Data" contains either: The field "Message Data" contains either:
- a User Data message (section 2.3.1), or
- a Link State message (section 2.3.2)
2.3.1 User Data - a User Data message (Section 2.3.1), or
- a Link State message (Section 2.3.2)
The User Data is the data sent from MTP3. The User Data is an optional 2.3.1. User Data
field. It need not be included in an acknowlegement-only message.
The format for the User Data message is as follows: The User Data is the data sent from MTP3. The User Data is an
optional field. It need not be included in an acknowledgement-only
message.
The format of 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 Unit (MSU):
The Data field contains the following fields of the MTP Message Signal - the Message Priority field (PRI)
Unit (MSU): - Service Information Octet (SIO)
- Signaling Information Field (SIF)
- the Message Priority field (PRI)
- Service Information Octet (SIO)
- Signaling Information Field (SIF)
The MTP MSU is described in Q.703 [Q.703], section 2.2 "Signal Unit The MTP MSU is described in Q.703 [Q.703], Section 2.2, "Signal Unit
Format", and T1.111.3 [T1.111] section 2.2 "Signal Unit Format". Format", and T1.111.3 [T1.111], Section 2.2, "Signal Unit Format".
The Japanese TTC standard uses the PRI field as an MTP3 Message The Japanese TTC standard uses the PRI field as an MTP3 Message
Priority field [JT-Q703]. For versions of MTP that do not use these Priority field [JT-Q703] [JT-Q704]. For versions of MTP that do not
two bits, the entire first octet of the Data field is spare. use these two bits, the entire first octet of the Data field is
spare.
The format of the first octet of the Data field is: The format of the first octet of the Data field 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 [JT-Q703]. PRI - Priority used only in national MTP defined in [JT-Q703] and
Spare for other MTP versions. [JT-Q704]. These bits are spare for other MTP versions.
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
MSU format: MTP 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)
- Length Indicator (LI) - Length Indicator (LI)
- 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.
M2PA SHALL NOT add padding to the MTP3 message. M2PA SHALL NOT add padding to the MTP3 message.
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
positioned to the right. The received SS7 fields are populated octet is positioned to the right. The received SS7 fields are populated
by octet as received into the 4-octet word as shown below. octet 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:
|MSB---------------------------------------------------------LSB| |MSB---------------------------------------------------------LSB|
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PRI| spare | SIO | SIF octet | ... | |PRI| spare | SIO | SIF octet | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ : \ \ \
/ : / / : /
\ : \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | ... | ... | SIF octet | | ... | ... | ... | SIF octet |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Within each octet the Least Significant Bit (LSB) per the SS7 Within each octet, the Least Significant Bit (LSB) per the SS7
Recommendations is to the right (e.g., bit 15 of SIO is the LSB). Recommendations is to the right (e.g., bit 15 of SIO is the LSB).
2.3.2 Link Status 2.3.2. Link Status
The MTP2 Link Status message can be sent between M2PA peers to The MTP2 Link Status message can be sent between M2PA peers to
indicate link status. This message performs a function similar to the indicate link status. This message performs a function similar to
the Link Status Signal Unit in MTP2. The format for the Link Status the Link Status Signal Unit in MTP2. The format of the Link Status
message is as follows: 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| State | | State |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The valid values for State are shown in the following table. The valid values for State are shown in the following table.
Value Value
(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 Recovered 6 Processor Recovered
7 Busy 7 Busy
8 Busy Ended 8 Busy Ended
9 Out of Service (OOS) 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 of 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 /
\ \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 that
varies among the Link Status Proving messages, and that will allow the varies among the Link Status Proving messages, and that allows the
SCTP checksum [RFC3309] to be used to verify the accuracy of SCTP checksum [RFC3309] to be used to verify the accuracy of
transmission. transmission.
3. State Control 3. State Control
3.1 SCTP Association State Control 3.1. SCTP Association State Control
Figure 7 illustrates state changes in the M2PA management of the SCTP Figure 7 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.
ASSOCIATING - M2PA is attempting to establish an SCTP association. ASSOCIATING - M2PA is attempting to establish an SCTP association.
ESTABLISHED - SCTP association is established. ESTABLISHED - SCTP association is established.
+-----------+ +-----------+
| IDLE | | IDLE |
+-----------+ +-----------+
| |
| Associate | Associate
| (Issue SCTP associate) | (Issue SCTP associate)
| |
| +----------------------+ | +----------------------+
| | (Issue SCTP | | | (Issue SCTP |
V V associate) | V V associate) |
+-------------+ | +-------------+ |
| ASSOCIATING |----------------->+ | ASSOCIATING |----------------->+
+-------------+ SCTP Comm Error | +-------------+ SCTP Comm Error |
| | | |
| | | |
| 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 7. M2PA Association State Transition Diagram Figure 7. M2PA Association State Transition Diagram
3.2 M2PA Link State Control 3.2. 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
- Receipt of messages from the peer M2PA - Receipt of messages from the peer M2PA
- Expiration of timers - Expiration of timers
- SCTP notifications - SCTP notifications
These events affect the M2PA link state in a manner similar to MTP2. These events affect the M2PA link state in a manner similar to MTP2.
4. Procedures 4. Procedures
Since M2PA provides MTP3 with an interface and functionality like Because M2PA provides MTP3 with an interface and functionality like
MTP2, its internal functioning is similar to that of MTP2. MTP2, its internal functioning is similar to that of MTP2.
Except as modified in this document, M2PA SHOULD follow the Except as modified in this document, M2PA SHOULD follow the
requirements of the applicable MTP2 specification. These may include requirements of the applicable MTP2 specification. These may include
[Q.703] or [T1.111]. The same standard MUST be followed on both ends [Q.703] or [T1.111]. The same standard MUST be followed on both ends
of the M2PA link. of the M2PA link.
In particular, the the corresponding applicable timer value defaults In particular, the corresponding applicable timer value defaults and
and ranges specified for the applicable MTP2 standard should be used ranges specified for the applicable MTP2 standard should be used for
for the M2PA timers. the M2PA timers.
When referring to MTP2 terminology in this document, the terminology When referring to MTP2 terminology in this document, the terminology
of [Q.703] is used. This does not imply that the requirements of of [Q.703] is used. This does not imply that the requirements of
[Q.703] are to be followed. [Q.703] are to be followed.
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 of user SCTP provides reliable, in-sequence delivery of user messages.
messages. Therefore the related functionality of MTP2 is not Therefore the related functionality of MTP2 is not needed. SCTP does
needed. SCTP does not provide functions related to Link State Control not provide functions related to Link State Control in MTP2. These
in MTP2. These functions must be provided by M2PA. functions must be provided by M2PA.
Since SCTP provides delivery of messages, there is no need for M2PA to Since SCTP provides delivery of messages, there is no need for M2PA
delimit its messages with a flag as in MTP2. Furthermore, M2PA does to delimit its messages with a flag, as is done in MTP2.
not need to perform zero bit insertion and deletion on its messages. Furthermore, M2PA does not need to perform zero bit insertion and
deletion on its messages.
Since SCTP uses a checksum to detect transmission errors, there is no Since SCTP uses a checksum to detect transmission errors, there is no
need for an M2PA checksum as in MTP2. This also eliminates the need need for an M2PA checksum, as is needed in MTP2. This also
for the error rate monitors of MTP2. eliminates the need for the error rate monitors of MTP2.
Since SCTP provides reliable delivery and ordered delivery, M2PA does Since SCTP provides reliable delivery and ordered delivery, M2PA does
not perform retransmissions. This eliminates the need for the forward not perform retransmissions. This eliminates the need for the
and backward indicator bits in MTP2 signal units. forward and backward indicator bits in MTP2 signal units.
Acceptance of a message is indicated by a successful receipt of the Acceptance of a message is indicated by a successful receipt of the
message from SCTP. message from SCTP.
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
associations from being established, it is RECOMMENDED that each duplicate associations from being established, it is RECOMMENDED that
endpoint know the IP address (or IP addresses, if multi-homing is each endpoint know the IP address (or IP addresses, if multi-homing
used) and port number of both endpoints. SCTP prevents two is 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
M2PA registered port. the 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
at the time the SCTP association is established. However, M2PA does created at the time the SCTP association is established. However,
not do any processing based on the SLC. M2PA does 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 8 shows a case with two IPSPs, each with two IP addresses. Two Figure 8 shows a case with two IPSPs, each with two IP addresses.
associations are the links that connect the two IPSPs. Since these Two associations are the links that connect the two IPSPs. Since
links are in the same link set, they MUST have different SLCs. these 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
SLCs is implementation dependent. the SLCs is implementation dependent.
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 |
| | | | | | | |
| | | | | | | |
| | SCTP | | | | SCTP | |
| 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 8. Two IPSPs with Two IP Addresses Each Figure 8. Two IPSPs with Two IP Addresses Each
Table 1. Two IPSPs with Two IP Addresses Each +-------------+---------------------------------------+-----+
| Association | IPSP X | IPSP Y | SLC |
| +------------+------+------------+------+ |
| | IP address | Port | IP address | Port | |
+=============+============+======+============+======+=====+
| 1 | IPA | PW | IPB | PW | a |
+-------------+------------+------+------------+------+-----+
| 2 | IPC | PW | IPD | PW | b |
+-------------+------------+------+------------+------+-----+
+-------------+---------------------------------------+-----+ Table 1. Two IPSPs with Two IP Addresses Each
| Association | IPSP X | IPSP Y | SLC |
| +------------+------+------------+------+ |
| | IP address | Port | IP address | Port | |
+=============+============+======+============+======+=====+
| 1 | IPA | PW | IPB | PW | a |
+-------------+------------+------+------------+------+-----+
| 2 | IPC | PW | IPD | PW | b |
+-------------+------------+------+------------+------+-----+
Figure 9 and Table 2 show an example with three IPSPs. Note that in Figure 9 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,
is possible that the SLC values a and b MAY be equal. it is possible that the SLC 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 |
| | | | | | | |
| | | | | | | |
| | SCTP | | | | SCTP | |
| IPC | association 2 | | | IPC | association 2 | |
| port = PW +-------+ | | | port = PW +-------+ | |
| SLC = b | | | | | SLC = b | | | |
| | | | | | | | | |
| | | | | | | | | |
+-------------+ | +-------------+ +-------------+ | +-------------+
| |
| |
| IPSP Z | IPSP Z
| |
| +-------------+ | +-------------+
| | | | | |
| | IPD | | | IPD |
+-------+ port = PW | +-------+ port = PW |
| SLC = b | | SLC = b |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
+-------------+ +-------------+
IPx = IP address IPx = IP address
PW = Registered port number for M2PA PW = Registered port number for M2PA
Figure 9. One IPSP Connected to Two IPSPs Figure 9. One IPSP Connected to Two IPSPs
Table 2. One IPSP Connected to Two IPSPs
+-------------+---------------------------------------+-----+ +-------------+---------------------------------------+-----+
| Association | IPSP X | IPSP Y/Z | 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 |
+-------------+------------+------+------------+------+-----+ +-------------+------------+------+------------+------+-----+
Figure 10 and Table 3 show two associations between the same IP Table 2. One IPSP Connected to Two IPSPs
addresses. This is accomplished by using different port numbers for
each association at one endpoint.
IPSP X IPSP Y Figure 10 and Table 3 show two associations between the same IP
addresses. This is accomplished by using different port numbers for
each association at one endpoint.
+-------------+ +-------------+ IPSP X IPSP Y
| | SCTP | |
| IPA | association 1 | IPB |
| port = P1 +---------------+ port = PW |
| SLC = a | | SLC = a |
| | | |
| | | |
| | SCTP | |
| IPA | association 2 | IPB |
| port = PW +---------------+ port = PW |
| SLC = b | | SLC = b |
| | | |
| | | |
+-------------+ +-------------+
IPx = IP address +-------------+ +-------------+
P1 = Pre-selected port number | | SCTP | |
PW = Registered port number for M2PA | IPA | association 1 | IPB |
| port = P1 +---------------+ port = PW |
| SLC = a | | SLC = a |
| | | |
| | | |
| | SCTP | |
| IPA | association 2 | IPB |
| port = PW +---------------+ port = PW |
| SLC = b | | SLC = b |
| | | |
| | | |
+-------------+ +-------------+
Figure 10. Multiple Associations Between Two IP Addresses IPx = IP address
P1 = Pre-selected port number
PW = Registered port number for M2PA
Table 3. Multiple Associations Between Two IP Addresses Figure 10. 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 |
+-------------+------------+------+------------+------+-----+ +-------------+------------+------+------------+------+-----+
The association SHALL contain two streams in each direction. Stream 0 Table 3. Multiple Associations Between Two IP Addresses
is designated for Link Status messages. Stream 1 is designated for
User Data messages, as well as Link Status messages that must remain
in sequence with the User Data messages.
The following Link Status messages SHALL be sent on the Link Status The association SHALL contain two streams in each direction. Stream
stream (stream 0): 0 is designated for Link Status messages. Stream 1 is designated for
User Data messages, as well as Link Status messages that must remain
in sequence with the User Data messages.
- Alignment The following Link Status messages SHALL be sent on the Link Status
- Proving Normal stream (stream 0):
- Proving Emergency
- Ready (when sent during alignment)
- Busy
- Busy Ended
- Out of Service
The following Link Status messages SHALL be sent on the User Data - Alignment
stream (stream 1): - Proving Normal
- Proving Emergency
- Ready (when sent during alignment)
- Busy
- Busy Ended
- Out of Service
- Processor Outage The following Link Status messages SHALL be sent on the User Data
- Processor Recovered stream (stream 1):
- Ready (when sent at the end of processor outage)
4.1.3 Link Alignment - Processor Outage
- Processor Recovered
- Ready (when sent at the end of processor outage)
The purposes of the alignment procedure are: 4.1.3. Link Alignment
(1) To provide a handshaking procedure so that both endpoints are The purposes of the alignment procedure are:
prepared to send SS7 traffic, and to prevent traffic from being
sent before the other end is ready.
(2) To verify that the SCTP association is suitable for use as an (1) To provide a handshaking procedure so that both endpoints are
SS7 link. prepared to send SS7 traffic, and to prevent traffic from
being sent before the other end is ready.
Link alignment takes place after the association is established. If (2) To verify that the SCTP association is suitable for use as an
SCTP fails to establish the association, and M2PA has received a Start SS7 link.
Request from its MTP3, then M2PA SHALL report to MTP3 that the link is
out of service.
The Link Status Out of Service message replaces the SIOS message of Link alignment takes place after the association is established. If
MTP2. Unlike MTP2, the message SHOULD NOT be transmitted SCTP fails to establish the association, and M2PA has received a
continuously. After the association is established, M2PA SHALL send a Start Request from its MTP3, then M2PA SHALL report to MTP3 that the
Link Status Out of Service message to its peer. Prior to the beginning link is out of service.
of alignment, M2PA MAY send additional Link Status Out of Service
messages.
The Link Status Alignment message replaces the SIO message of The Link Status Out of Service message replaces the SIOS message of
MTP2. This message is sent to signal the beginning of the alignment MTP2. Unlike MTP2, the message SHOULD NOT be transmitted
procedure. The Link Status Alignment message SHOULD NOT be transmitted continuously. After the association is established, M2PA SHALL send
continuously. M2PA MAY send additional Link Status Alignment until it a Link Status Out of Service message to its peer. Prior to the
receives Link Status Alignment, Link Status Proving Normal, or Link beginning of alignment, M2PA MAY send additional Link Status Out of
Status Proving Emergency from the peer. Service messages.
The Link Status Proving Normal message replaces the SIN message of The Link Status Alignment message replaces the SIO message of MTP2.
MTP2. The Link Status Proving Emergency message replaces the SIE This message is sent to signal the beginning of the alignment
message of MTP2. procedure. The Link Status Alignment message SHOULD NOT be
transmitted continuously. M2PA MAY send additional Link Status
Alignment until it receives Link Status Alignment, Link Status
Proving Normal, or Link Status Proving Emergency from the peer.
The proving period MAY be omitted if this is allowed by the applicable The Link Status Proving Normal message replaces the SIN message of
MTP2 standard (e. g., [Q.2140]). MTP2. The Link Status Proving Emergency message replaces the SIE
message of MTP2.
If proving is performed, then during the proving period (i.e., after The proving period MAY be omitted if this is allowed by the
M2PA starts the proving period timer T4), M2PA SHALL send Link Status applicable MTP2 standard (e.g., [Q.2140]).
Proving messages to its peer at an interval defined by the protocol
parameter Proving_Interval. It is RECOMMENDED that Proving_Interval be
set so that the traffic load generated with the Link Status Proving
messages during the proving period is comparable to the normal traffic
load expected when the link is in service.
The Link Status Ready message replaces the FISU of MTP2 that is sent If proving is performed, then during the proving period (i.e., after
at the end of the proving period. The Link Status Ready message is M2PA starts the proving period timer T4), M2PA SHALL send Link Status
used to verify that both ends have completed proving. When M2PA starts Proving messages to its peer at an interval defined by the protocol
timer T1, it SHALL send a Link Status Ready message to its peer in the parameter Proving_Interval. It is RECOMMENDED that Proving_Interval
case where MTP2 would send a FISU after proving is complete. If the be set so that the traffic load generated with the Link Status
Link Status Ready message is sent, then M2PA MAY send additional Link Proving messages during the proving period is comparable to the
Status Ready messages while timer T1 is running. These Link Status normal traffic load expected when the link is in service.
Ready messages are sent on the Link Status stream.
In the case that MTP2 sends an MSU or SIPO message at the end of The Link Status Ready message replaces the FISU of MTP2 that is sent
proving, M2PA SHALL send (respectively) a User Data or Link Status at the end of the proving period. The Link Status Ready message is
Processor Outage message. used to verify that both ends have completed proving. When M2PA
starts timer T1, it SHALL send a Link Status Ready message to its
peer in the case where MTP2 would send a FISU after proving is
complete. If the Link Status Ready message is sent, then M2PA MAY
send additional Link Status Ready messages while timer T1 is running.
These Link Status Ready messages are sent on the Link Status stream.
4.1.4 Processor Outage In the case that MTP2 sends an MSU or SIPO message at the end of
proving, M2PA SHALL send (respectively) a User Data or Link Status
Processor Outage message.
The Link Status Processor Outage message replaces the SIPO message of 4.1.4. Processor Outage
MTP2. Unlike MTP2, the message SHOULD NOT be transmitted
continuously. M2PA SHALL send a Link Status Processor Outage message
to its peer at the beginning of a processor outage condition where
MTP2 would send SIPO. M2PA MAY send additional Link Status Processor
Outage messages as long as that condition persists. The Link Status
Processor Outage message SHALL be sent on the User Data stream.
While in a local processor outage (LPO) condition: The Link Status Processor Outage message replaces the SIPO message of
MTP2. Unlike MTP2, the message SHOULD NOT be transmitted
continuously. M2PA SHALL send a Link Status Processor Outage message
to its peer at the beginning of a processor outage condition where
MTP2 would send SIPO. M2PA MAY send additional Link Status Processor
Outage messages as long as that condition persists. The Link Status
Processor Outage message SHALL be sent on the User Data stream.
(a) Any User Data messages received from the peer MUST NOT be While in a local processor outage (LPO) condition:
acknowledged and MUST be buffered.
(b) M2PA SHOULD continue to acknowledge User Data messages received (a) Any User Data messages received from the peer MUST NOT be
and accepted by MTP3 before the local processor outage. acknowledged and MUST be buffered.
(c) M2PA SHOULD continue to transmit messages that have been sent (b) M2PA SHOULD continue to acknowledge User Data messages
by its upper layer MTP3. received and accepted by MTP3 before the local processor
outage.
While there is a remote processor outage (RPO) condition: (c) M2PA SHOULD continue to transmit messages that have been sent
by its upper layer MTP3.
(a) M2PA SHOULD continue to acknowledge User Data messages received While there is a remote processor outage (RPO) condition:
and accepted by MTP3 regardless of the remote processor outage.
(b) If any User Data messages received from the peer after the Link (a) M2PA SHOULD continue to acknowledge User Data messages
Status Processor Outage cannot be delivered to MTP3, then these received and accepted by MTP3, regardless of the remote
messages MUST NOT be acknowledged and MUST be buffered. processor outage.
If M2PA receives a Flush command from MTP3, (b) If any User Data messages received from the peer after the
Link Status Processor Outage cannot be delivered to MTP3, then
these messages MUST NOT be acknowledged and MUST be buffered.
(a) M2PA SHALL discard any incoming messages that were queued and If M2PA receives a Flush command from MTP3,
unacknowledged during the processor outage condition.
(b) M2PA SHALL discard messages in the transmit and retransmit (a) M2PA SHALL discard any incoming messages that were queued and
queues as required by MTP2. unacknowledged during the processor outage condition.
If M2PA receives a Continue command from MTP3, M2PA SHALL begin (b) M2PA SHALL discard messages in the transmit and retransmit
processing the incoming messages that were queued and unacknowledged queues as required by MTP2.
during the processor outage condition.
When the local processor outage condition ends, M2PA SHALL send a Link If M2PA receives a Continue command from MTP3, M2PA SHALL begin
Status Processor Recovered message to its peer on the User Data processing the incoming messages that were queued and unacknowledged
stream. This message is used to signal the end of the processor outage during the processor outage condition.
condition, instead of an MSU or FISU as in MTP2. The BSN in the Link
Status Processor Recovered message is set to the FSN of the last User
Data message received (and not discarded) from the peer M2PA. M2PA
SHALL cease transmitting User Data messages after sending the Link
Status Processor Recovered message, until it has received the Link
Status Ready message (see below).
Upon receiving the Link Status Processor Recovered message, the M2PA When the local processor outage condition ends, M2PA SHALL send a
in RPO SHALL respond with a Link Status Ready message on the User Data Link Status Processor Recovered message to its peer on the User Data
stream. The BSN in the Link Status Ready message is set to the FSN of stream. This message is used to signal the end of the processor
the last User Data message received (and not discarded) from the peer outage condition, instead of an MSU or FISU, as is used in MTP2. The
M2PA. BSN in the Link Status Processor Recovered message is set to the FSN
of the last User Data message received (and not discarded) from the
peer M2PA. M2PA SHALL cease transmitting User Data messages after
sending the Link Status Processor Recovered message, until it has
received the Link Status Ready message (see below).
Upon receiving the Link Status Ready message, the M2PA formerly in LPO Upon receiving the Link Status Processor Recovered message, the M2PA
SHALL respond with a Link Status Ready message on the User Data in RPO SHALL respond with a Link Status Ready message on the User
stream. The BSN in the Link Status Ready message is set to the FSN of Data stream. The BSN in the Link Status Ready message is set to the
the last User Data message received (and not discarded) from the peer FSN of the last User Data message received (and not discarded) from
M2PA. the peer M2PA.
M2PA (at both the LPO and RPO ends) uses the BSN value in the received Upon receiving the Link Status Ready message, the M2PA formerly in
Link Status Ready message to resynchronize its sequence numbers, if LPO SHALL respond with a Link Status Ready message on the User Data
this is required by MTP2. M2PA SHALL NOT resume transmitting User Data stream. The BSN in the Link Status Ready message is set to the FSN
messages until it has received the Link Status Ready message. of the last User Data message received (and not discarded) from the
peer M2PA.
During resynchronization, M2PA SHALL NOT discard any received User M2PA (at both the LPO and RPO ends) uses the BSN value in the
Data messages that were sent after the processor outage ended. received Link Status Ready message to resynchronize its sequence
numbers, if this is required by MTP2. M2PA SHALL NOT resume
transmitting User Data messages until it has sent the Link Status
Ready message.
When M2PA experiences a local processor outage, it MAY put the link During resynchronization, M2PA SHALL NOT discard any received User
out of service by sending a Link Status Out of Service message if Data messages that were sent after the processor outage ended.
allowed by the applicable MTP2 standard (e.g., [Q.2140]).
In other respects, M2PA SHOULD follow the same procedures as MTP2 in When M2PA experiences a local processor outage, it MAY put the link
processor outage. out of service by sending a Link Status Out of Service message, if
this is allowed by the applicable MTP2 standard (e.g., [Q.2140]).
4.1.5 Level 2 Flow Control In other respects, M2PA SHOULD follow the same procedures as MTP2 in
processor outage.
The Link Status Busy message replaces the SIB message of MTP2. The 4.1.5. Level 2 Flow Control
message SHOULD NOT be transmitted continuously. M2PA SHALL send a Link
Status Busy message to its peer at the beginning of a receive
congestion condition where MTP2 would send SIB. M2PA MAY send
additional Link Status Busy messages as long as that condition
persists. When the condition ends, M2PA SHALL send a Link Status Busy
Ended message to its peer.
M2PA SHALL continue transmitting messages while it is in receive The Link Status Busy message replaces the SIB message of MTP2. The
congestion, but MUST NOT acknowledge the message that triggered the message SHOULD NOT be transmitted continuously. M2PA SHALL send a
sending of the Link Status Busy message, nor any messages received Link Status Busy message to its peer at the beginning of a receive
before the sending of Link Status Busy Ended. congestion condition where MTP2 would send SIB. M2PA MAY send
additional Link Status Busy messages as long as that condition
persists. When the condition ends, M2PA SHALL send a Link Status
Busy Ended message to its peer.
When the peer M2PA receives the first Link Status Busy message, it M2PA SHALL continue transmitting messages while it is in receive
SHALL start the Remote Congestion timer T6 if there are messages in congestion, but MUST NOT acknowledge the message that triggered the
the retransmission buffer awaiting acknowledgement (i.e., T7 is sending of the Link Status Busy message, nor any messages received
running). In addition, M2PA SHALL stop the T7 timer if it is running. before the sending of Link Status Busy Ended.
Additional Link Status Busy messages received while T6 is running do
not cause T6 to be reset and do not cause T7 to be started. Also,
while T6 is running, T7 SHALL NOT be started.
When the peer M2PA receives the Link Status Busy Ended message and T6 When the peer M2PA receives the first Link Status Busy message, it
has not expired, it SHALL stop T6 if T6 is running and start T7 if SHALL start the Remote Congestion timer T6 if there are messages in
there are messages awaiting acknowledgement in the retransmission the retransmission buffer awaiting acknowledgement (i.e., T7 is
buffer. running). M2PA SHALL stop the T7 timer if it is running. Additional
Link Status Busy messages received while T6 is running do not cause
T6 to be reset and do not cause T7 to be started. While T6 is
running, T7 SHALL NOT be started.
The peer M2PA SHOULD continue receiving and acknowledging messages When the peer M2PA receives the Link Status Busy Ended message and T6
while the other end is busy, but MUST NOT send User Data messages has not expired, it SHALL stop T6 (if T6 is running) and start T7 (if
after receiving Link Status Busy and before receiving Link Status Busy there are messages awaiting acknowledgement in the retransmission
Ended. buffer).
4.1.6 Link Out of Service The peer M2PA SHOULD continue receiving and acknowledging messages
while the other end is busy, but MUST NOT send User Data messages
after receiving Link Status Busy and before receiving Link Status
Busy Ended.
The Link Status Out of Service message replaces the SIOS message of 4.1.6. Link Out of Service
MTP2. Unlike MTP2, the message SHOULD NOT be transmitted
continuously. M2PA SHALL send a Link Status Out of Service message to
its peer at the beginning of a condition where MTP2 would send
SIOS. M2PA MAY send additional Link Status Out of Service messages as
long as that condition persists.
When M2PA places a link in the OUT OF SERVICE state, M2PA SHOULD NOT The Link Status Out of Service message replaces the SIOS message of
terminate the SCTP association. MTP2. Unlike MTP2, the message SHOULD NOT be transmitted
continuously. M2PA SHALL send a Link Status Out of Service message
to its peer at the beginning of a condition where MTP2 would send
SIOS. M2PA MAY send additional Link Status Out of Service messages
as long as that condition persists.
4.1.7 SCTP Association Problems When M2PA places a link in the OUT OF SERVICE state, M2PA SHOULD NOT
terminate the SCTP association.
The SCTP association for a link may become unusable, such as when one 4.1.7. SCTP Association Problems
of the following occurs:
- SCTP sends a Send Failure notification to M2PA. The SCTP association for a link may become unusable, such as when one
of the following occurs:
- SCTP sends a Communication Lost notification to M2PA. - SCTP sends a Send Failure notification to M2PA.
- SCTP sends a Communication Error notification to M2PA. - SCTP sends a Communication Lost notification to M2PA.
- The SCTP association is lost. - SCTP sends a Communication Error notification to M2PA.
If the SCTP association for a link becomes unable to transmit or - The SCTP association is lost.
receive messages, M2PA SHALL report to MTP3 that the link is out of
service and enter the OUT OF SERVICE state.
4.1.8 Transmission and Reception Priorities If the SCTP association for a link becomes unable to transmit or
receive messages, M2PA SHALL report to MTP3 that the link is out of
service and enter the OUT OF SERVICE state.
In MTP, Link Status messages have priority over User Data messages 4.1.8. Transmission and Reception Priorities
([Q.703], section 11.2). To achieve this in M2PA, M2PA uses separate
streams in its SCTP association for Link Status messages and User Data
messages.
M2PA SHALL send all messages using the ordered delivery option of In MTP, Link Status messages have priority over User Data messages
SCTP. ([Q.703], Section 11.2). To achieve this in M2PA, M2PA uses separate
streams in its SCTP association for Link Status messages and User
Data messages.
M2PA SHOULD give higher priority to messages sent on the Link Status M2PA SHALL send all messages using the ordered delivery option of
stream than to messages sent on the User Data stream when sending SCTP.
messages to SCTP.
M2PA SHOULD give higher priority to reading the Link Status stream M2PA SHOULD give higher priority to messages sent on the Link Status
than to reading the User Data stream. stream than to messages sent on the User Data stream when sending
messages to SCTP.
M2PA SHOULD give higher priority to receiving notifications from SCTP M2PA SHOULD give higher priority to reading the Link Status stream
than to reading either the Link Status stream or the User Data stream. than to reading the User Data stream.
4.1.9 M2PA Version Control M2PA SHOULD give higher priority to receiving notifications from SCTP
than to reading either the Link Status stream or the User Data
stream.
A node upgraded to a newer version of M2PA SHOULD support the older 4.1.9. M2PA Version Control
versions used on other nodes with which it is communicating. If that
is the case, then alignment can proceed normally.
In particular, it is recommended that for future modifications to this A node upgraded to a newer version of M2PA SHOULD support the older
protocol: versions used on other nodes with which it is communicating. If that
is the case, then alignment can proceed normally.
- Any newer version SHOULD be able to process the messages from an In particular, it is recommended that for future modifications to
older version. this protocol:
- A newer version of M2PA SHOULD refrain from sending messages to an - Any newer version SHOULD be able to process the messages from an
older version of M2PA messages that the older version cannot older version.
process.
- If an older version of M2PA receives a message that it cannot - A newer version of M2PA SHOULD refrain from sending messages to
process, it SHOULD discard the message. an older version of M2PA messages that the older version cannot
process.
- In cases where different processing is done in two versions for the - If an older version of M2PA receives a message that it cannot
same format of a message, then the newer version SHOULD contain process, it SHOULD discard the message.
procedures to recognize this and handle it appropriately.
In case a newer version of M2PA is incompatible with an older version, - In cases where different processing is done in two versions for
the newer version SHOULD recognize this and prevent the alignment of the same format of a message, then the newer version SHOULD
the link. If a Link Status Alignment message with an unsupported contain procedures to recognize and handle this appropriately.
version is received by the newer version, the receiving end's M2PA
SHOULD reply with a Link Status Out of Service message and not
complete the alignment procedure.
4.2 Procedures to Support the MTP3/MTP2 Interface 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 link. If a Link Status Alignment message with an
unsupported version is received by the newer version, the receiving
end's M2PA SHOULD reply with a Link Status Out of Service message and
not complete the alignment procedure.
4.2.1 Sending and receiving messages 4.2. Procedures to Support the MTP3/MTP2 Interface
When MTP3 sends a message for transmission to M2PA, M2PA passes the 4.2.1. Sending and Receiving Messages
corresponding M2PA message to SCTP using the SEND primitive.
User Data messages SHALL be sent via the User Data stream (stream 1) When MTP3 sends a message for transmission to M2PA, M2PA passes the
of the association. corresponding M2PA message to SCTP using the SEND primitive.
M2PA Link Status messages are passed to SCTP using the SEND primitive. User Data messages SHALL be sent via the User Data stream (stream 1)
of the association.
The following Link Status messages SHALL be sent on the Link Status M2PA Link Status messages are passed to SCTP using the SEND
stream (stream 0): primitive.
- Alignment The following Link Status messages SHALL be sent on the Link Status
- Proving Normal stream (stream 0):
- Proving Emergency
- Ready (when sent during alignment)
- Busy
- Busy Ended
- Out of Service
The following Link Status messages SHALL be sent on the User Data - Alignment
stream (stream 1): - Proving Normal
- Proving Emergency
- Ready (when sent during alignment)
- Busy
- Busy Ended
- Out of Service
- Processor Outage The following Link Status messages SHALL be sent on the User Data
- Processor Recovered stream (stream 1):
- Ready (when sent at the end of processor outage)
If M2PA receives a message from SCTP with an invalid Message Class or - Processor Outage
unsupported Message Type in the Common Message Header, M2PA SHALL - Processor Recovered
discard the message. - Ready (when sent at the end of processor outage)
For message types other than User Data, the Forward Sequence Number is If M2PA receives a message from SCTP with an invalid Message Class or
set to the FSN of the last User Data message sent. unsupported Message Type in the Common Message Header, M2PA SHALL
discard the message.
If M2PA receives a User Data message with an FSN that is out of order, For message types other than User Data, the Forward Sequence Number
M2PA SHALL discard the message. is set to the FSN of the last User Data message sent.
Note: In all calculations involving FSN and BSN, the programmer should If M2PA receives a User Data message with an FSN that is out of
be aware that the value wraps around to 0 after reaching its maximum order, M2PA SHALL discard the message.
value.
When there is a message to acknowledge, M2PA MUST acknowledge the Note: In all calculations involving FSN and BSN, the programmer
message with the next User Data message sent. If there is no User should be aware that the value wraps around to 0 after reaching its
Data message available to be sent when there is a message to maximum value.
acknowledge, M2PA SHOULD generate and send a User Data message with no
data payload, without delay. (In other words, in the case where MTP2
would acknowledge a message with a FISU, M2PA SHOULD acknowledge the
message with an empty User Data message.) The FSN for this empty User
Data message is not incremented. It MUST contain the same FSN as the
most recently sent User Data message containing Data. Delaying of
acknowledgements can result in poor SS7 performance.
If M2PA receives an empty User Data message, it SHALL NOT send an When there is a message to acknowledge, M2PA MUST acknowledge the
acknowledgement of that message. message with the next User Data message sent. If there is no User
Data message available to be sent when there is a message to
acknowledge, M2PA SHOULD generate and send a User Data message with
no data payload, without delay. (In other words, in the case where
MTP2 would acknowledge a message with a FISU, M2PA SHOULD acknowledge
the message with an empty User Data message.) The FSN for this empty
User Data message is not incremented. It MUST contain the same FSN
as the most recently sent User Data message that contains data.
Delaying of acknowledgements can result in poor SS7 performance.
Note that there is no reason to place Link Status messages or empty If M2PA receives an empty User Data message, it SHALL NOT send an
User Data messages in the M2PA retransmit buffer, since these messages acknowledgement of that message.
are not retrieved for changeover and timer T7 does not apply to them.
Note that since SCTP provides reliable delivery and ordered delivery Note that there is no reason to place Link Status messages or empty
within the stream, M2PA does not perform User Data messages in the M2PA retransmit buffer, since these
retransmissions. Nevertheless, M2PA SHALL retain transmitted User Data messages are not retrieved for changeover and timer T7 does not apply
messages in a retransmit queue until they are acknowledged. These to them.
messages are needed in case MTP3 performs data retrieval as part of a
changeover procedure.
Because propagation delays in IP networks are more variable than in Note that since SCTP provides reliable delivery and ordered delivery
traditional SS7 networks, a single T7 timer (excessive delay of within the stream, M2PA does not perform retransmissions.
acknowledgement) as in MTP2 is inadequate. If any message is Nevertheless, M2PA SHALL retain transmitted User Data messages in a
unacknowledged after a period equal to the T7 value, the T7 timer retransmit queue until they are acknowledged. These messages are
SHALL expire. needed in case MTP3 performs data retrieval as part of a changeover
procedure.
4.2.2 MTP3 Signaling Link Congestion Because propagation delays in IP networks are more variable than in
traditional SS7 networks, a single T7 timer (excessive delay of
acknowledgement), as in MTP2, is inadequate. If any message is
unacknowledged after a period equal to the T7 value, the T7 timer
SHALL expire.
M2PA SHALL detect transmit congestion in its buffers according to the 4.2.2. MTP3 Signaling Link Congestion
requirements for signaling link transmit congestion in MTP3, e.g.,
Q.704 [Q.704], section 3.8.
4.2.3 Changeover M2PA SHALL detect transmit congestion in its buffers according to the
requirements for signaling link transmit congestion in MTP3, e.g.,
Q.704 [Q.704], Section 3.8.
The objective of the changeover is to ensure that signaling traffic 4.2.3. Changeover
carried by the unavailable signaling link is diverted to the
alternative signaling link(s) as quickly as possible while avoiding
message loss, duplication, or mis-sequencing. For this purpose, the
changeover procedure includes data retrieval, which is performed
before opening the alternative signaling links to the diverted
traffic. Data retrieval consists of these steps:
(1) buffer updating, i.e., identifying all those User Data The objective of the changeover is to ensure that signaling traffic
messages in the retransmission buffer of the unavailable carried by the unavailable signaling link is diverted to the
signaling link which have not been received by the far end alternative signaling link(s) as quickly as possible while avoiding
M2PA, as well as untransmitted messages, and message loss, duplication, or mis-sequencing. For this purpose, the
changeover procedure includes data retrieval, which is performed
before opening the alternative signaling links to the diverted
traffic. Data retrieval consists of these steps:
(2) transferring those messages to the transmission buffers of the (1) buffer updating, i.e., identifying all those User Data
alternate links. messages in the retransmission buffer of the unavailable
signaling link which have not been received by the far end
M2PA, as well as untransmitted messages, and
Note that only User Data messages containing data are retrieved and (2) transferring those messages to the transmission buffers of the
transmitted over the alternate links. Link Status messages and empty alternate links.
User Data messages SHALL NOT be retrieved and transmitted over the
alternate links.
M2PA's Sequence Numbers are 24 bits long. MTP2's Forward and Backward Note that only User Data messages containing data are retrieved and
Sequence Numbers are only seven bits long. Hence it is necessary for transmitted over the alternate links. Link Status messages and empty
MTP3 to accommodate the larger sequence numbers. This is done through User Data messages SHALL NOT be retrieved and transmitted over the
the use of the Extended Changeover Order (XCO) and Extended Changeover alternate links.
Acknowledgement (XCA) messages instead of the Changeover Order (COO)
and Changeover Acknowledgement (COA) messages. The XCO and XCA
messages are specified in [Q.2210] section 9.8.1 and T1.111.4
[T1.111], section 15.4. Only the XCO and XCA messages from [Q.2210] or
[T1.111] are required. The BSN is placed in the XCO/XCA message as
explained in [Q.2210] and [T1.111].
Also, the following MTP3/MTP2 primitives MUST use the larger sequence M2PA's Sequence Numbers are 24 bits long. MTP2's Forward and
numbers: Backward Sequence Numbers are only seven bits long. Hence, it is
necessary for MTP3 to accommodate the larger sequence numbers. This
is done through the use of the Extended Changeover Order (XCO) and
Extended Changeover Acknowledgement (XCA) messages instead of the
Changeover Order (COO) and Changeover Acknowledgement (COA) messages.
The XCO and XCA messages are specified in [Q.2210] Section 9.8.1 and
T1.111.4 [T1.111], Section 15.4. Only the XCO and XCA messages from
[Q.2210] or [T1.111] are required. The BSN is placed in the XCO/XCA
message as explained in [Q.2210] and [T1.111].
- BSNT Confirmation Also, the following MTP3/MTP2 primitives MUST use the larger sequence
numbers:
- Retrieval Request and FSNC - BSNT Confirmation
If M2PA receives a Retrieval Request and FSNC request from MTP3, M2PA - Retrieval Request and FSNC
SHALL retrieve from its buffers and deliver to MTP3 in order:
(a) any transmitted User Data messages beginning with the first If M2PA receives a Retrieval Request and FSNC request from MTP3, M2PA
unacknowledged message with FSN greater than FSNC. SHALL retrieve from its buffers and deliver to MTP3 in order:
(b) any untransmitted User Data messages. (a) any transmitted User Data messages beginning with the first
unacknowledged message with FSN greater than FSNC.
For emergency changeover, MTP3 retrieves only the unsent messages for (b) any untransmitted User Data messages.
transmission on the alternate link(s). If M2PA receives a Retrieval
Request and FSNC request with no FSNC value, or with an invalid FSNC,
then M2PA SHALL retrieve from its buffers and deliver to MTP3 in
order:
(a) any untransmitted User Data messages. For emergency changeover, MTP3 retrieves only the unsent messages for
transmission on the alternate link(s). If M2PA receives a Retrieval
Request and FSNC request with no FSNC value, or with an invalid FSNC,
then M2PA SHALL retrieve from its buffers and deliver to MTP3 in
order:
The Japanese TTC version of MTP defined in [JT-Q703] has a Retrieval (a) any untransmitted User Data messages.
Request (as well as Retrieval Request and FSNC). The Retrieval Request
allows MTP3 to retrieve both unsent and unacknowleged messages for
transmission on the alternate link(s). In this version of MTP, if M2PA
receives a Retrieval Request, then M2PA SHALL retrieve from its
buffers and deliver to MTP3 in order:
(a) any transmitted but unacknowledged User Data messages. The Japanese TTC version of MTP defined in [JT-Q703] and [JT-Q704]
has a Retrieval Request (as well as Retrieval Request and FSNC). The
Retrieval allows MTP3 to retrieve both unsent and unacknowledged
messages for transmission on the alternate link(s). In this version
of MTP, if M2PA receives a Retrieval Request, then M2PA SHALL
retrieve from its buffers and deliver to MTP3 in order:
(b) any untransmitted User Data messages. (a) any transmitted but unacknowledged User Data messages.
4.2.3.1 Multiple User Data Streams and Changeover (b) any untransmitted User Data messages.
The changeover procedure makes it problematic for M2PA to have 4.2.3.1. Multiple User Data Streams and Changeover
multiple User Data streams in one direction for a link. Buffer
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
XCO/XCA message for sending the last-received sequence number.
Even with sequence numbering of User Data messages at the M2PA layer, The changeover procedure makes it problematic for M2PA to have
it is necessary to perform buffer updating on each stream. Since the multiple User Data streams in one direction for a link. Buffer
M2PA messages would be delivered over multiple streams, there could be updating would have to be done separately for each User Data stream
a gap in the M2PA sequence numbers at the receiving end when the to avoid duplication or loss of messages. But MTP3 provides for only
changeover procedure begins. If only the M2PA sequence number is used one XCO/XCA message for sending the last-received sequence number.
in the XCO/XCA message, there would be a possibility of losing the
messages in the gap, or duplicating messages after the gap.
M2PA links with multiple User Data streams would be possible if a Even with sequence numbering of User Data messages at the M2PA layer,
multiple-BSNT XCO/XCA message is defined in MTP3, or MTP3 allows it is necessary to perform buffer updating on each stream. Since the
multiple XCO/XCA messages (one for each User Data stream) to be sent M2PA messages would be delivered over multiple streams, there could
during a changeover. This is beyond the scope of this document. be a gap in the M2PA sequence numbers at the receiving end when the
changeover procedure begins. If only the M2PA sequence number is
used in the XCO/XCA message, there would be a possibility of losing
the messages in the gap, or duplicating messages after the gap.
4.3 SCTP Considerations M2PA links with multiple User Data streams would be possible if a
multiple-BSNT XCO/XCA message is defined in MTP3, or if MTP3 allows
multiple XCO/XCA messages (one for each User Data stream) to be sent
during a changeover. This is beyond the scope of this document.
Some M2PA procedures may be affected by the use of SCTP as a transport 4.3. SCTP Considerations
layer. These considerations are discussed in this section.
4.3.1 SCTP Slow Start Some M2PA procedures may be affected by the use of SCTP as a
transport layer. These considerations are discussed in this section.
SCTP contains a slow start algorithm to control the amount of data 4.3.1. SCTP Slow Start
being injected into the network. The algorithm allows SCTP to probe
the network to determine the available capacity. The algorithm is
invoked when transmission begins on an association, after a
sufficiently long idle period, or after repairing loss detected by the
SCTP retransmission timer.
It is possible that transmission of M2PA messages MAY be delayed by SCTP contains a slow start algorithm to control the amount of data
SCTP slow start under certain conditions, including the following: being injected into the network. The algorithm allows SCTP to probe
the network to determine the available capacity. The algorithm is
invoked in these cases: when transmission begins on an association,
after a sufficiently long idle period, or after repairing loss
detected by the SCTP retransmission timer.
(a) Link Alignment. Link alignment takes place after an association It is possible that transmission of M2PA messages MAY be delayed by
is established. SCTP invokes the slow start algorithm since SCTP slow start under certain conditions, including the following:
transmission is beginning on the association.
(b) Changeover. Messages are retrieved from one link (association) (a) Link Alignment. Link alignment takes place after an
and transferred to another for transmission. If the second link association is established. SCTP invokes the slow start
had previously been idle, or is in the process of link algorithm since transmission is beginning on the association.
alignment, SCTP may invoke the slow start algorithm.
(c) Path failure (multi-homing). If SCTP switches from a failed (b) Changeover. Messages are retrieved from one link
path to a new path, and the new path had previously been idle, (association) and transferred to another for transmission. If
SCTP may invoke the slow start algorithm. the second link had previously been idle, or is in the process
of link alignment, SCTP may invoke the slow start algorithm.
(d) Reduced traffic volume. Any time that M2PA sends a low volume (c) Path failure (multi-homing). If SCTP switches from a failed
of traffic on a link and then the volume increases, SCTP may path to a new path, and the new path had previously been idle,
invoke the slow start algorithm. SCTP may invoke the slow start algorithm.
Programmers should be aware of this condition and how it may affect (d) Reduced traffic volume. Any time that M2PA sends a low volume
M2PA performance. In some cases, it may be possible to avoid the of traffic on a link and then the volume increases, SCTP may
negative effects of slow start. For example, the Link Status Proving invoke the slow start algorithm.
messages sent during the proving period may be used to complete slow
start before the link is placed in service. Programmers should be aware of this condition and how it may affect
M2PA performance. In some cases, it may be possible to avoid the
negative effects of slow start. For example, the Link Status Proving
messages sent during the proving period may be used to complete slow
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 [Q.700] [Q.701] [Q.702] M2PA are named using the MTP terminology [Q.700] [Q.701] [Q.702]
[Q.703] [Q.704] [Q.705]. Communications between M2PA and SCTP are [Q.703] [Q.704] [Q.705]. Communications between M2PA and SCTP are
named using SCTP terminology. 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 used to bring an SS7 link in service
shown in Figures 11 and 12. Alignment is done by both ends of the is shown in Figures 11 and 12. Alignment is done by both ends of the
link. To simplify the diagram, alignment is shown on one end link. To simplify the diagram, alignment is shown on one end only.
only. Some messages from the remote end are not shown. It is assumed Some messages from the remote end are not shown. It is assumed in
in this example that SCTP has been initialized. this example that SCTP has been initialized.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . . . . . . . .
. Associate . . . . . Associate . . . .
. ------------> . . . . ------------> . . .
. . . . . . . . . . . .
. . (SCTP Association . . . . (SCTP Association . .
. . procedure) . . . . procedure) . .
. . . . . . . . . . . .
. Communication Up Communication Up . . Communication Up Communication Up .
. <------------ ------------> . . <------------ ------------> .
. . . . . . . . . . . .
. Link Status Out of Service . . . Link Status Out of Service . .
. ------------------------------------> . . ------------------------------------> .
. . . . . . . . . . . .
Emergency OR . . . . Emergency OR . . . .
Emergency Ceases . . . . Emergency Ceases . . . .
------------> . . . . ------------> . . . .
. . . . . . . . . . . .
Start . . . . . Start . . . . .
------------> . . . . ------------> . . . .
. . . . . . . . . . . .
. . . . . . . . . . . .
. Link Status Alignment . . . . Link Status Alignment . . .
. ------------------------------------> . . ------------------------------------> .
. . . . . . . . . . . .
. Start timer T2 . . . . Start timer T2 . . .
. . . . . . . . . . . .
. . . Link Status Alignment . . . . Link Status Alignment .
. <------------------------------------ . . <------------------------------------ .
. . . . . . . . . . . .
. Stop timer T2 . . . . Stop timer T2 . . .
. . . . . . . . . . . .
Proving period begins. Proving period begins.
Figure 11. Example: Link Initialization - Alignment Figure 11. Example: Link Initialization - Alignment
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . . . . . . . .
. Start timer T3 . . . . Start timer T3 . . .
. Link Status Proving . . . . Link Status Proving . . .
. ------------------------------------> . . ------------------------------------> .
. . . . . . . . . . . .
. . . Link Status Proving . . . . Link Status Proving .
. <------------------------------------ . . <------------------------------------ .
. . . . . . . . . . . .
. Stop timer T3 . . . . Stop timer T3 . . .
. . . . . . . . . . . .
. Start timer T4 . . . . Start timer T4 . . .
. Link Status Proving . . . . Link Status Proving . . .
. ------------------------------------> . . ------------------------------------> .
. ------------------------------------> . . ------------------------------------> .
. ------------------------------------> . . ------------------------------------> .
. ------------------------------------> . . ------------------------------------> .
. ------------------------------------> . . ------------------------------------> .
. ------------------------------------> . . ------------------------------------> .
. . . . . . . . . . . .
. Timer T4 expires . . . . Timer T4 expires . . .
. . . . . . . . . . . .
Send Link Status Ready (one or more) and wait for the remote end Send Link Status Ready (one or more) and wait for the remote end
to complete its proving period. to complete its proving period.
. . . . . . . . . . . .
. Start timer T1 . . . . Start timer T1 . . .
. . . . . . . . . . . .
. Link Status Ready . . . . Link Status Ready . . .
. ------------------------------------> . . ------------------------------------> .
. . . . . . . . . . . .
. . . . . . . . . . . .
. . . Link Status Ready . . . . Link Status Ready .
. <------------------------------------ . . <------------------------------------ .
. . . . . . . . . . . .
. Stop timer T1 . . . . Stop timer T1 . . .
. . . . . . . . . . . .
In Service . . In Service In Service . . In Service
<------------ . . ------------> <------------ . . ------------>
. . . . . . . . . . . .
MTP3 MAY begin sending data messages. MTP3 MAY begin sending data messages.
Figure 12. Example: Link Initialization - Proving Figure 12. 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
M2PA. Figure 13 shows the case where the Link is In Service. The
message is passed from MTP3 of the source to MTP3 of the destination.
MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ----
. . . . . .
Message for . . . .
transmission . . . .
------------> . . . .
. . . . . .
. Send . . . .
. (Data Message) . . .
. ------------> . . .
. . . . . .
. . (SCTP sends message) . .
. . . . . .
. . . Receive .
. . . ------------> .
. . . . . .
. . . . Received message
. . . . ------------>
. . . . . .
Figure 13. Example: Link Initialization - In Service
5.3 Link Status Indication Messages are transmitted using the Data Request primitive from MTP3
to M2PA. Figure 13 shows the case where the Link is In Service. The
message is passed from MTP3 of the source to MTP3 of the destination.
An example of a Link Status Indication is shown in Figure 14. If SCTP MTP3 M2PA SCTP SCTP M2PA MTP3
sends a Communication Lost primitive to M2PA, M2PA notifies MTP3 that ---- ---- ---- ---- ---- ----
the link is out of service. MTP3 responds in its usual way. . . . . . .
Message for . . . .
transmission . . . .
------------> . . . .
. . . . . .
. Send . . . .
. (Data Message) . . .
. ------------> . . .
. . . . . .
. . (SCTP sends message) . .
. . . . . .
. . . Receive .
. . . ------------> .
. . . . . .
. . . . Received message
. . . . ------------>
. . . . . .
MTP3 M2PA SCTP SCTP M2PA MTP3 Figure 13. Example: Link Initialization - In Service
---- ---- ---- ---- ---- ----
. . . . . .
. Communication Lost . . .
. <------------ . . .
. . . . . .
Out of Service . . . .
<------------ . . . .
. . . . . .
Figure 14. Example: Link Status Indication 5.3. Link Status Indication
5.4 Link Status Message (Processor Outage) An example of a Link Status Indication is shown in Figure 14. If
SCTP sends a Communication Lost primitive to M2PA, M2PA notifies MTP3
that the link is out of service. MTP3 responds in its usual way.
Figure 15 shows how M2PA responds to a local processor outage. M2PA MTP3 M2PA SCTP SCTP M2PA 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 as . . . . . .
in [Q.703]. . Communication Lost . . .
. <------------ . . .
. . . . . .
Out of Service . . . .
<------------ . . . .
. . . . . .
MTP3 M2PA SCTP SCTP M2PA MTP3 Figure 14. Example: Link Status Indication
---- ---- ---- ---- ---- ----
. . . . . .
. M2PA detects . . . .
. Local Processor . . . .
. Outage . . . .
. . . . . .
. Link Status . . . .
. Processor Outage . . .
. ------------------------------------> .
. . . . . .
. . . . Remote Processor
. . . . Outage .
. . . . ------------>
. . . . . .
. Link Status . . .
. Processor . . .
. Recovered . . .
. ------------------------------------> .
. . . . . .
. . . . Remote Processor
. . . . Outage Ceases
. . . . ------------>
. . . . . .
. . . Link Status Ready .
. <------------------------------------ .
. . . . . .
. Link Status Ready . . .
. ------------------------------------> .
. . . . . .
Message for . . . .
transmission . . . .
------------> . . . .
. . . . . .
. User Data . . .
. ------------------------------------> .
. . . . . .
Figure 15. Example: Link Status Message - Processor Outage 5.4. Link Status Message (Processor Outage)
Figure 16 shows an example of processor outage in more detail. All Figure 15 shows how M2PA responds to a local processor outage. M2PA
M2PA messages in this example are sent on the Data stream (stream 1). sends a Link Status message to its peer. The peer M2PA notifies MTP3
of the outage. MTP3 can then follow the processor outage procedures
as in [Q.703].
A B MTP3 M2PA SCTP SCTP M2PA MTP3
---------------------------- ---------------------------- ---- ---- ---- ---- ---- ----
. . . . . .
. M2PA detects . . . .
. Local Processor . . . .
. Outage . . . .
. . . . . .
. Link Status . . . .
. Processor Outage . . .
. ------------------------------------> .
. . . . . .
. . . . Remote Processor
. . . . Outage .
. . . . ------------>
. . . . . .
. Link Status . . .
. Processor . . .
. Recovered . . .
. ------------------------------------> .
. . . . . .
. . . . Remote Processor
. . . . Outage Ceases
. . . . ------------>
. . . . . .
. . . Link Status Ready .
. <------------------------------------ .
. . . . . .
. Link Status Ready . . .
. ------------------------------------> .
. . . . . .
Message for . . . .
transmission . . . .
------------> . . . .
. . . . . .
. User Data . . .
. ------------------------------------> .
. . . . . .
MTP3 M2PA SCTP SCTP M2PA MTP3 Figure 15. Example: Link Status Message - Processor Outage
---- ---- ---- ---- ---- ----
. . . . . .
6 Messages for . . . .
transmission . . . .
------------> . . 6 Messages for
. . . . transmission
. . . . <------------
. User Data FSN=1 . . .
. ------------------------------------> .
. User Data FSN=2 . . .
. ------------------------------------> .
. User Data FSN=3 . . .
. ------------------------------------> .
. . . User Data FSN=11 .
. <------------------------------------ .
. . . User Data FSN=12 .
. <------------------------------------ .
. . . User Data FSN=13 .
. <------------------------------------ .
Side A detects LPO. Figure 16 shows an example of processor outage in more detail. All
M2PA messages in this example are sent on the Data stream (stream 1).
. . . . . . A B
. . . User Data FSN=14 BSN=3 . ---------------------------- ----------------------------
. <------------------------------------ .
. . . User Data FSN=15 BSN=3 .
. <------------------------------------ .
. . . User Data FSN=16 BSN=3 .
. <------------------------------------ .
. LS PO FSN=3 BSN=11 . . .
. ------------------------------------> .
. . . . Remote Processor
. . . . Outage .
. . . . ------------>
While in LPO, A must buffer messages 14-16 without acknowledging MTP3 M2PA SCTP SCTP M2PA MTP3
them. A may continue transmitting messages from MTP3, and ---- ---- ---- ---- ---- ----
acknowledging messages that were received before LPO. . . . . . .
6 Messages for . . . .
transmission . . . .
------------> . . 6 Messages for
. . . . transmission
. . . . <------------
. User Data FSN=1 . . .
. ------------------------------------> .
. User Data FSN=2 . . .
. ------------------------------------> .
. User Data FSN=3 . . .
. ------------------------------------> .
. . . User Data FSN=11 .
. <------------------------------------ .
. . . User Data FSN=12 .
. <------------------------------------ .
. . . User Data FSN=13 .
. <------------------------------------ .
. . . . . . Side A detects LPO.
. User Data FSN=4 BSN=13 . . .
. ------------------------------------> .
. User Data FSN=5 BSN=13 . . .
. ------------------------------------> .
. User Data FSN=6 BSN=13 . . .
. ------------------------------------> .
. . . . . .
While in RPO, B may continue acknowledging messages. Suppose that B . . . . . .
receives message 4, but has not processed 5 and 6 yet. . . . User Data FSN=14 BSN=3 .
. <------------------------------------ .
. . . User Data FSN=15 BSN=3 .
. <------------------------------------ .
. . . User Data FSN=16 BSN=3 .
. <------------------------------------ .
. LS PO FSN=3 BSN=11 . . .
. ------------------------------------> .
. . . . Remote Processor
. . . . Outage .
. . . . ------------>
. . . . . . While in LPO, A must buffer messages 14-16 without acknowledging
. (empty) User Data FSN=16 BSN=4 them. A may continue transmitting messages from MTP3, and
. <------------------------------------ . acknowledging messages that were received before LPO.
LPO ends at A. A flushes 14-16 (the messages that were buffered . . . . . .
without acknowledgement). . User Data FSN=4 BSN=13 . . .
. ------------------------------------> .
. User Data FSN=5 BSN=13 . . .
. ------------------------------------> .
. User Data FSN=6 BSN=13 . . .
. ------------------------------------> .
. . . . . .
. . . . . . While in RPO, B may continue acknowledging messages. Suppose that
. LS PR FSN=6 BSN=13 . . . B receives message 4 and 5, but has not processed 6 yet.
. ------------------------------------> .
. . . . Remote Processor
. . . . Outage Ceases
. . . . ------------>
. . . . . .
A should discard any incoming acknowledgements at this point. They . . . . . .
could have been sent before the LS PR. . (empty) User Data FSN=16 BSN=4
. <------------------------------------ .
. (empty) User Data FSN=16 BSN=5
. <------------------------------------ .
. . . . . . LPO ends at A. A flushes 14-16 (the messages that were buffered
. (empty) User Data FSN=16 BSN=5 without acknowledgement).
. <------------------------------------ .
. (discard) . . . .
. . . . . .
B should not resynchronize its sequence numbers now and start with . . . . . .
FSN=14. If B sent a message now with FSN=14, A might confuse this with . LS PR FSN=6 BSN=13 . . .
a message sent before the LS PR. . ------------------------------------> .
. . . . Remote Processor
. . . . Outage Ceases
. . . . ------------>
. . . . . .
Suppose that B processed message 5, but never processed message 6. B Suppose that B processed message 5, but never processed message 6.
flushes message 6 from its Receive Buffer. B notifies A of this using B flushes message 6 from its Receive Buffer. B notifies A of this
the Link Status Ready message: using the Link Status Ready message setting BSN=5, the last message
that was processed at B.
. . . . . . . . . . . .
. . . LS Ready FSN=16 BSN=5 . . . . . . .
. <------------------------------------ . . . . LS Ready FSN=13 BSN=5 .
. . . . . . . <------------------------------------ .
. . . . . .
B should discard any incoming acknowledgements at this point. They B has completed synchronization of sequence numbers and has sent
could have been sent before B's LS Ready. an LS Ready, so it is able to resume sending data at this point
with the new sequence numbers (starting with FSN=14).
A can use the Link Status Ready information to resynchronize its . . . . . .
sequence numbers to begin with FSN=6 for the next User Data message. . . . . . Message for
. . . . transmission
. . . . <------------
. . . User Data FSN=14 BSN=5 .
. <------------------------------------ .
. . . . . .
. . . . . . A can use the Link Status Ready information to resynchronize its
. LS Ready FSN=5 BSN=13 . . . sequence numbers to begin with FSN=6 in the next User Data message.
. ------------------------------------> .
. . . . . .
. . . . . .
. . . . . .
. . . . . .
B can use this information to resynchronize its sequence numbers to . . . . . .
begin with FSN=14. Each side can resume sending User Data: . LS Ready FSN=5 BSN=13 . . .
. ------------------------------------> .
. . . . . .
. . . . . . A has completed synchronization of sequence number and has both
Message for . . . Message for received and sent an LS Ready, so it is able to resume sending data
transmission . . transmission at this point with the new sequence numbers and acknowledging data
------------> . . <------------ received after receiving LS Ready.
. User Data FSN=6 BSN=13 . . .
. ------------------------------------> .
. . . User Data FSN=14 BSN=5 .
. <------------------------------------ .
. . . . . .
Figure 16. Example: Processor Outage and Recovery . . . . . .
. . . . . .
. User Data FSN=5 BSN=14 (empty) . .
. ------------------------------------> .
. . . . . .
Message for . . . Message for
transmission . . transmission
------------> . . <------------
. User Data FSN=6 BSN=14 . . .
. ------------------------------------> .
. . . User Data FSN=15 BSN=5 .
. <------------------------------------ .
. . . . . .
. . (empty) User Data FSN=15 BSN=6 .
. <------------------------------------ .
. User Data FSN=6 BSN=15 (empty) . .
. ------------------------------------> .
. . . . . .
. . . . . .
. . . . . .
5.5 Level 2 Flow Control Figure 16. Example: Processor Outage and Recovery
Figures 17 and 18 illustrate the Level 2 Flow Control procedure. In 5.5. Level 2 Flow Control
Figure 17, congestion ceases before timer T6 expires. Figure 18 shows
the case where T6 expires.
MTP3 M2PA SCTP SCTP M2PA MTP3 Figures 17 and 18 illustrate the Level 2 Flow Control procedure. In
---- ---- ---- ---- ---- ---- Figure 17, congestion ceases before timer T6 expires. Figure 18
. . . . . . shows the case where T6 expires.
. 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 .
. . . . . .
Figure 17. Example: Level 2 Flow Control - Congestion Ceases 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 .
. . . . . .
MTP3 M2PA SCTP SCTP M2PA MTP3 Figure 17. Example: Level 2 Flow Control - Congestion Ceases
---- ---- ---- ---- ---- ---- MTP3 M2PA SCTP SCTP M2PA MTP3
. . . . . . ---- ---- ---- ---- ---- ----
. Implementation dependent . . . . . . . .
. determination of M2PA . . . Implementation dependent . .
. receive congestion onset . . . determination of M2PA . .
. . . . . . . receive congestion onset . .
. Link Status Busy . . . . . . . . .
. ------------------------------------> . . Link Status Busy . . .
. . . . . . . ------------------------------------> .
. . . . Start . . . . . . .
. . . . Timer T6 . . . . . Start .
. . . . : . . . . . Timer T6 .
. . . . : . . . . . : .
. . . . Timer T6 . . . . . : .
. . . . Expires . . . . . Timer T6 .
. . . . . . . . . . Expires .
. . Link Status Out of Service . . . . . . .
. <------------------------------------ . . . Link Status Out of Service .
. . . . . . . <------------------------------------ .
. . . . Out of Service . . . . . .
. . . . ------------> . . . . Out of Service
. . . . . . . . . . ------------>
. . . . . .
Figure 18. Example: Level 2 Flow Control - Timer T6 Expires Figure 18. Example: Level 2 Flow Control - Timer T6 Expires
5.6 MTP3 Signaling Link Congestion 5.6. MTP3 Signaling Link Congestion
In Figure 19, M2PA notifies MTP3 of congestion onset and In Figure 19, M2PA notifies MTP3 of congestion onset and abatement.
abatement. The notification includes the congestion level, if there The notification includes the congestion level, if there are levels
are levels of congestion defined. of congestion defined.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . . . . . . . .
. Implementation dependent . . . Implementation dependent . .
. determination of M2PA . . . . determination of M2PA . . .
. transmit congestion . . . . transmit congestion . . .
. onset (level) . . . . onset (level) . . .
. . . . . . . . . . . .
Congestion Indication . . . . Congestion Indication . . . .
(level) . . . . . (level) . . . . .
<------------ . . . . <------------ . . . .
. . . . . . . . . . . .
. Implementation dependent . . . Implementation dependent . .
. determination of M2PA . . . . determination of M2PA . . .
. transmit congestion . . . . transmit congestion . . .
. abatement (level) . . . . abatement (level) . . .
. . . . . . . . . . . .
Congestion Indication . . . . Congestion Indication . . . .
(level) . . . . . (level) . . . . .
<------------ . . . . <------------ . . . .
. . . . . . . . . . . .
Figure 19. Example: MTP3 Signalling Link Congestion Figure 19. Example: MTP3 Signaling Link Congestion
5.7 Link Deactivation 5.7. Link Deactivation
Figure 20 shows an example of link deactivation. MTP3 can request that Figure 20 shows an example of link deactivation. MTP3 can request
a link be taken out of service. that a link be taken out of service.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
. . . . . . . . . . . .
Stop . . . . . Stop . . . . .
------------> . . . . ------------> . . . .
. . . . . . . . . . . .
. Link Status Out of Service . . . Link Status Out of Service . .
. ------------------------------------> . . ------------------------------------> .
. . . . . . . . . . . .
Out of Service . . . . Out of Service . . . .
<------------ . . . . <------------ . . . .
. . . . . . . . . . . .
Figure 20. Example: Link Deactivation Figure 20. Example: Link Deactivation
5.8 Link Changeover 5.8. Link Changeover
In Figure 21, MTP3 performs a changeover because the link went out of In Figure 21, MTP3 performs a changeover because the link went out 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.
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 Figure 21. Example: Link Changeover
6. Security 6. Security Considerations
M2PA is designed to carry signaling messages for telephony M2PA is designed to carry signaling messages for telephony services.
services. As such, M2PA MUST involve the security needs of several As such, M2PA MUST involve the security needs of several parties:
parties:
- the end users of the services - the end users of the services
- the network providers - the network providers
- the applications involved - the applications involved
Additional requirements MAY come from local regulation. Additional requirements MAY come from local regulation.
While these parties may have some overlapping security needs, their While these parties may have some overlapping security needs, their
needs may not be identical. Any security solution SHOULD fulfill all needs may not be identical. Any security solution SHOULD fulfill all
of the different parties' needs. of the different parties' needs.
Consult [RFC3788] for a discussion of security requirements and for Consult [RFC3788] for a discussion of security requirements and for
guidance on the use of security protocols. Implementers of M2PA MUST guidance on the use of security protocols. Implementers of M2PA MUST
follow the guidelines in [RFC3788]. follow the guidelines in [RFC3788].
7. IANA Considerations 7. IANA Considerations
7.1 SCTP Payload Protocol Identifier 7.1. SCTP Payload Protocol Identifier
The SCTP Registered User Port Number Assignment for M2PA is 3565. The The SCTP Registered User Port Number Assignment for M2PA is 3565.
TCP Registered User Port Number 3565 is also assigned to M2PA, in case The TCP Registered User Port Number 3565 is also assigned to M2PA, in
a specification for M2PA over TCP is created. case a specification for M2PA over TCP is created.
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
certain network entities to identify the type of information being certain network entities to identify the type of information being
carried in a Data chunk. carried in a Data chunk.
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 [RFC2434]. 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.
The defined values for the message classes, types, and parameters are The defined values for the message classes, types, and parameters are
listed in the Signaling User Adaptation Layer registry listed in the Signaling User Adaptation Layer registry
(sigtran-adapt). (sigtran-adapt).
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.
(b) A detailed description of the purpose of the message class. (b) A detailed description of the purpose of the message class.
7.2.2 IETF Defined Message Types 7.2.2 IETF Defined Message Types
Documentation of the message type MUST contain the following Documentation of the message type MUST contain the following
information: information:
(a) A long and short name for the new message type.
(b) A detailed description of the structure of the message.
(c) A detailed definition and description of the intended use
of each field within the message.
(d) A detailed procedural description of the use of the new
message type within the operation of the protocol.
(e) A detailed description of error conditions when receiving this (a) A long and short name for the new message type.
message type.
When an implementation receives a message type which it does not (b) A detailed description of the structure of the message.
support, it MUST discard the message.
7.2.3 IETF-defined Parameter Extension (c) A detailed definition and description of the intended use of
each field within the message.
Documentation of the message parameter MUST contain the following (d) A detailed procedural description of the use of the new
information: message type within the operation of the protocol.
(a) Name of the parameter type. (e) A detailed description of error conditions when receiving this
message type.
(b) Detailed description of the structure of the parameter field. When an implementation receives a message type that it does not
support, it MUST discard the message.
(c) Detailed definition of each component of the parameter value. 7.2.3. IETF-defined Parameter Extension
(d) Detailed description of the intended use of this parameter type, Documentation of the message parameter MUST contain the following
and an indication of whether and under what circumstances information:
multiple instances of this parameter type may be found within
the same message type.
7.2.4 Defined Values (a) Name of the parameter type.
This section lists the values defined in this document that should be (b) Detailed description of the structure of the parameter field.
included in the Signaling User Adaptation Layer registry
(sigtran-adapt).
The following values for Message Class are defined in this document: (c) Detailed definition of each component of the parameter value.
Value (d) Detailed description of the intended use of this parameter
(decimal) Message Class type, and an indication of whether, and under what
--------- ------------- circumstances, multiple instances of this parameter type may
11 M2PA Messages be found within the same message type.
The following values for Message Type are defined in this document: 7.2.4. Defined Values
Value This section lists the values defined in this document that should be
(decimal) Message Type included in the Signaling User Adaptation Layer registry
--------- ------------- (sigtran-adapt).
1 User Data
2 Link Status
The following values for Version are defined in this document: The following values for Message Class are defined in this document:
Value Value
(decimal) Version (decimal) Message Class
--------- ------- --------- -------------
1 Release 1.0 of M2PA protocol 11 M2PA Messages
The following values for the State parameter are defined in this The following values for Message Type are defined in this document:
document:
Value Value
(decimal) Description (decimal) Message Type
--------- ----------- --------- -------------
1 Alignment 1 User Data
2 Proving Normal 2 Link Status
3 Proving Emergency
4 Ready
5 Processor Outage
6 Processor Recovered
7 Busy
8 Busy Ended
9 Out of Service (OOS)
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, Wayne Davis, Cliff Thomas, comments and suggestions: Brian Tatum, Wayne Davis, Cliff Thomas,
Jeff Copley, Monique Bernard, Malleswar Kalla, Ian Rytina, Jeff Copley, Monique Bernard, Malleswar Kalla, Ian Rytina, Greg
Greg Sidebottom, Al Varney, Jeff Craig, Andrew Booth. Sidebottom, Al Varney, Jeff Craig, and Andrew Booth.
9. References 9. References
9.1 Normative 9.1. Normative References
[JT-Q703] [JT-Q703] TTC, "Message Transfer Part Signalling Link," TTC Standard
TTC, "Message Transfer Part Signalling Link," TTC Standard JT-Q703, Telecommunication Technology Committee (TTC),
JT-Q703, Telecommunication Technology Committee (TTC), version version 3 (April 27, 1994).
3 (April 27, 1994).
[JT-Q704] [JT-Q704] TTC, "Message Transfer Part Signalling Network Functions,"
TTC, "Message Transfer Part Signalling Network Functions," TTC TTC Standard JT-Q704, Telecommunication Technology
Standard JT-Q704, Telecommunication Technology Committee (TTC), Committee (TTC), version 4 (May 30, 2002).
version 4 (May 30, 2002).
[Q.703] [Q.703] ITU, "Signalling System No. 7 - Signalling Link," ITU-T
ITU, "Signalling System No. 7 - Signalling Link," ITU-T Recommendation Q.703, ITU-T Telecommunication
Recommendation Q.703, ITU-T Telecommunication Standardization Standardization Sector of ITU (July 1996).
Sector of ITU (July 1996).
[Q.Imp703] [Q.704] ITU, "Message Transfer Part - Signalling Network Functions
ITU, "Implementors' Guide (03/99) for Recommendation Q.703 and Messages," ITU-T Recommendation Q.704, ITU-T
(07/96)" ITU-T Recommendation Q.Imp703, ITU-T Telecommunication Telecommunication Standardization Sector of ITU (July
Standardization Sector of ITU (March 1999). 1996).
[Q.704] [Q.2140] ITU, "B-ISDN ATM Adaptation Layer - Service Specific
ITU, "Message Transfer Part - Signalling Network Functions and Coordination Function for Signalling at the Network Node
Messages," ITU-T Recommendation Q.704, ITU-T Telecommunication Interface (SSCF at NNI)," ITU-T Recommendation Q.2140,
Standardization Sector of ITU (July 1996). ITU-T Telecommunication Standardization Sector of ITU
(February 1995).
[Q.Imp704] [Q.2210] ITU, "Message Transfer Part Level 3 Functions and Messages
ITU, "Implementors' Guide (12/2000) for Recommendation Q.704 Using the Services of ITU-T Recommendation Q.2140," ITU-T
(07/96)" ITU-T Recommendation Q.Imp704, ITU-T Telecommunication Recommendation Q.2210, ITU-T Telecommunication
Standardization Sector of ITU (December 2000). Standardization Sector of ITU (July 1996).
[Q.2140] [RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
ITU, "B-ISDN ATM Adaptation Layer - Service Specific 1981.
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
1995).
[Q.Imp2140] [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
ITU, "Implementors' Guide (03/99) for Recommendation Q.2140 Requirement Levels", BCP 14, RFC 2119, March 1997.
(02/95)" ITU-T Recommendation Q.Imp2140, ITU-T
Telecommunication Standardization Sector of ITU (March 1999).
[Q.2210] [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
ITU, "Message Transfer Part Level 3 Functions and Messages IANA Considerations Section in RFCs", BCP 26, RFC 2434,
Using the Services of ITU-T Recommendation Q.2140," ITU-T October 1998.
Recommendation Q.2210, ITU-T Telecommunication Standardization
Sector of ITU (July 1996).
[Q.Imp2210] [RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
ITU, "Implementors' Guide (12/99) for Recommendation Q.2210 Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
(07/96)" ITU-T Recommendation Q.Imp2210, ITU-T Zhang, L., and V. Paxson, "Stream Control Transmission
Telecommunication Standardization Sector of ITU (December Protocol", RFC 2960, October 2000.
1999).
[RFC791] [RFC3309] Stone, J., Stewart, R., and D. Otis, "Stream Control
Information Sciences Institute, "Internet Protocol - DARPA Transmission Protocol (SCTP) Checksum Change", RFC 3309,
Internet Program - Protocol Specification," RFC 791, The September 2002.
Internet Society (September 1981).
[RFC2119] [RFC3788] Loughney, J., Tuexen, M., and J. Pastor-Balbas, "Security
S. Bradner, "Key words for use in RFCs to Indicate Requirement Considerations for Signaling Transport (SIGTRAN)
Levels," BCP 14, RFC 2119, Internet Engineering Task Force Protocols", RFC 3788, June 2004.
(March 1997).
[RFC2434] [T1.111] ANSI, "American National Standard for Telecommunications -
T. Narten, H. T. Alvestrand, "Guidelines for Writing an IANA Signaling System Number 7 (SS7) - Message Transfer Part
Considerations Section in RFCs," BCP 26, RFC 2434, The Internet (MTP)," ANSI T1.111-2001, American National Standards
Society (October, 1998). Institute (February 2001).
[RFC2960] 9.2. Informative References
R. Stewart, et. al., "Stream Control Transmission Protocol
(SCTP)," RFC 2960, The Internet Society (February 2000).
[RFC3309] [M2UA] K. Morneault, et. al., "Signaling System 7 (SS7) Message
J. Stone, R. Stewart, and D. Otis, "Stream Control Transmission Transfer Part 2 (MTP2) - User Adaptation Layer," RFC 3331,
Protocol (SCTP) Checksum Change," RFC 3309, The Internet Internet Engineering Task Force - Signalling Transport
Society (September 2002). Working Group (September, 2002).
[RFC3788] [Q.700] ITU, "Introduction to CCITT Signalling System No. 7,"
J. Loughney, M. Tuexen, and J. Pastor-Balbas, "Security ITU-T Recommendation Q.700, ITU-T Telecommunication
Considerations for Signaling Transport (SIGTRAN) Protocols," Standardization Sector of ITU (March 1993).
RFC 3788, The Internet Society (June 2004).
[T1.111] [Q.701] ITU, "Functional Description of the Message Transfer Part
ANSI, "American National Standard for Telecommunications - (MTP) of Signalling System No. 7," ITU-T Recommendation
Signaling System Number 7 (SS7) - Message Transfer Part (MTP)," Q.701, ITU-T Telecommunication Standardization Sector of
ANSI T1.111-2001, American National Standards Institute ITU (March 1993).
(February 2001).
9.2 Informative [Q.702] ITU, "Signalling Data Link," ITU-T Recommendation Q.702,
ITU-T Telecommunication Standardization Sector of ITU
(November 1988).
[M2UA] [Q.705] ITU, "Signalling System No. 7 - Signalling Network
K. Morneault, et. al., "Signaling System 7 (SS7) Message Structure," ITU-T Recommendation Q.705, ITU-T
Transfer Part 2 (MTP2) - User Adaptation Layer," RFC 3331, Telecommunication Standardization Sector of ITU (March
Internet Engineering Task Force - Signalling Transport Working 1993).
Group (September, 2002).
[Q.700] [RFC2719] Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H., Coene,
ITU, "Introduction to CCITT Signalling System No. 7," ITU-T L., Lin, H., Juhasz, I., Holdrege, M., and C. Sharp,
Recommendation Q.700, ITU-T Telecommunication Standardization "Framework Architecture for Signaling Transport", RFC
Sector of ITU (March 1993). 2719, October 1999.
[Q.701] Authors' Addresses
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).
[Q.702] Tom George
ITU, "Signalling Data Link," ITU-T Recommendation Q.702, ITU-T Plano, TX
Telecommunication Standardization Sector of ITU (November USA
1988).
[Q.705] Phone: +1-972-985-4594
ITU, "Signalling System No. 7 - Signalling Network Structure," EMail: tgeorge_tx@verizon.net
ITU-T Recommendation Q.705, ITU-T Telecommunication
Standardization Sector of ITU (March 1993).
[Q.Imp705] Brian Bidulock
ITU, "Implementors' guide (version 09/97) for Q.705 (03/93)" OpenSS7 Corporation
ITU-T Recommendation Q.Imp705, ITU-T Telecommunication 1469 Jeffreys Crescent
Standardization Sector of ITU (September 1997). Edmonton, AB T6L 6T1
Canada
[RFC2719] Phone: +1-780-490-1141
L. Ong, et. al., "Framework Architecture for Signaling EMail: bidulock@openss7.org
Transport," RFC 2719, The Internet Society (October 1999).
10. Author's Addresses Ram Dantu, Ph.D.
Assistant Professor
Department of Computer Science
University of North Texas
Denton, TX 76203
USA
Tom George Telephone: +1-972-985-4594 Phone: +1-940-565-2822
Plano, TX EMail: tgeorge_tx@verizon.net EMail: rdantu@unt.edu
USA
Brian Bidulock Telephone: +1-780-490-1141 Hanns Juergen Schwarzbauer
OpenSS7 Corporation EMail: bidulock@openss7.org SIEMENS AG
1469 Jeffreys Crescent Hofmannstr. 51
Edmonton, AB T6L 6T1 81359 Munich
Canada Germany
Ram Dantu, Ph.D. Telephone: +1-940-565-2822 Phone: +49-89-722-24236
Assistant Professor EMail: rdantu@unt.edu EMail: HannsJuergen.Schwarzbauer@Siemens.com
Department of Computer Science
University of North Texas
Denton, TX 76203
USA
Hanns Juergen Schwarzbauer Telephone: +49-89-722-24236 Ken Morneault
SIEMENS AG EMail: HannsJuergen.Schwarzbauer@Siemens.com Cisco Systems Inc.
Hofmannstr. 51 13615 Dulles Technology Drive
81359 Munich Herndon, VA 20171
Germany USA
Ken Morneault Telephone: +1-703-484-3323 Phone: +1-703-484-3323
Cisco Systems Inc. EMail: kmorneau@cisco.com EMail: kmorneau@cisco.com
13615 Dulles Technology Drive
Herndon, VA 20171
USA
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Internet Society. Internet Society.
This Internet Draft expires August 2005.
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