draft-ietf-sigtran-m2pa-05.txt   draft-ietf-sigtran-m2pa-06.txt 
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Malleswar Kalla Malleswar Kalla
Telcordia Telcordia
Hanns Juergen Schwarzbauer Hanns Juergen Schwarzbauer
Siemens Siemens
Greg Sidebottom Greg Sidebottom
Ken Morneault Ken Morneault
Cisco Systems Cisco Systems
Brian Bidulock Brian Bidulock
OpenSS7 OpenSS7
Expires November 2002 May 3, 2002 Expires February 2003 August 28, 2002
SS7 MTP2-User Peer-to-Peer Adaptation Layer SS7 MTP2-User Peer-to-Peer Adaptation Layer
<draft-ietf-sigtran-m2pa-05.txt> <draft-ietf-sigtran-m2pa-06.txt>
Status of This Memo Status of This Memo
This document is an Internet-Draft and is in full conformance with all This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026. Internet-Drafts are working provisions of Section 10 of RFC 2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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1.4 Conventions........................................... 6 1.4 Conventions........................................... 6
1.5 Signaling Transport Architecture...................... 6 1.5 Signaling Transport Architecture...................... 6
1.6 Services Provided by M2PA............................. 8 1.6 Services Provided by M2PA............................. 8
1.7 Functions Provided by M2PA............................ 9 1.7 Functions Provided by M2PA............................ 9
1.8 Definition of the M2PA Boundaries.....................10 1.8 Definition of the M2PA Boundaries.....................10
1.9 Differences Between M2PA and M2UA.....................12 1.9 Differences Between M2PA and M2UA.....................12
2. Protocol Elements........................................14 2. Protocol Elements........................................14
2.1 Common Message Header.................................14 2.1 Common Message Header.................................14
2.2 M2PA Header...........................................15 2.2 M2PA Header...........................................15
2.3 M2PA Messages.........................................16 2.3 M2PA Messages.........................................16
3. M2PA Link State Control..................................20 3. M2PA Link State Control..................................19
4. Procedures...............................................23 4. Procedures...............................................23
4.1 Procedures to Support MTP2 Features...................23 4.1 Procedures to Support MTP2 Features...................23
4.2 Procedures to Support the MTP3/MTP2 Interface.........33 4.2 Procedures to Support the MTP3/MTP2 Interface.........33
5. Examples of M2PA Procedures..............................38 4.3 SCTP Considerations...................................37
5.1 Link Initialization (Alignment).......................38 5. Examples of M2PA Procedures..............................39
5.2 Message Transmission and Reception....................40 5.1 Link Initialization (Alignment).......................39
5.3 Link Status Indication................................40 5.2 Message Transmission and Reception....................41
5.4 Link Status Message (Processor Outage)................41 5.3 Link Status Indication................................41
5.5 Level 2 Flow Control..................................42 5.4 Link Status Message (Processor Outage)................42
5.6 MTP3 Signaling Link Congestion........................43 5.5 Level 2 Flow Control..................................43
5.7 Link Deactivation.....................................43 5.6 MTP3 Signaling Link Congestion........................44
5.8 Link Changeover.......................................44 5.7 Link Deactivation.....................................44
6. Security.................................................45 5.8 Link Changeover.......................................45
6.1 Threats...............................................45 6. Security.................................................46
6.2 Protecting Confidentiality............................45 6.1 Threats...............................................46
7. IANA Considerations......................................46 6.2 Protecting Confidentiality............................46
7.1 SCTP Payload Protocol Identifier......................46 7. IANA Considerations......................................47
7.2 M2PA Protocol Extensions..............................46 7.1 SCTP Payload Protocol Identifier......................47
8. Acknowledgements.........................................47 7.2 M2PA Protocol Extensions..............................47
9. References...............................................48 8. Acknowledgements.........................................48
10. Author's Addresses.......................................49 9. References...............................................49
10. Author's Addresses.......................................50
1. Introduction 1. Introduction
1.1 Scope 1.1 Scope
There is a need for Switched Circuit Network (SCN) signaling protocol There is a need for Switched Circuit Network (SCN) signaling protocol
delivery over an IP network. This includes message transfer between delivery over an IP network. This includes message transfer between
the following: the following:
- a Signaling Gateway (SG) and a Media Gateway Controller (MGC) - a Signaling Gateway (SG) and a Media Gateway Controller (MGC)
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--------- ----------- --------- -----------
1 Alignment 1 Alignment
2 Proving Normal 2 Proving Normal
3 Proving Emergency 3 Proving Emergency
4 Ready 4 Ready
5 Processor Outage 5 Processor Outage
6 Processor Outage Ended 6 Processor Outage Ended
7 Busy 7 Busy
8 Busy Ended 8 Busy Ended
9 Out of Service 9 Out of Service
10 In Service
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. These bytes can be used to take SCTP through the slow start bytes. If the optional bytes are used, the format for the message is
period. If the optional bytes are used, the format for the message is
as follows. as follows.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| State | | State |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| filler | | filler |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
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| +--------------------------+ | +--------------------------+
| | (Associate) | | | (Associate) |
V V | V V |
+-----------+ | +-----------+ |
+----------------------->| OOS |<--+ | +----------------------->| OOS |<--+ |
| +-----------+ | Link Configured | | +-----------+ | Link Configured |
| | | | (Associate) | | | | | (Associate) |
| | +-----+ | | | +-----+ |
| | | | | |
| | MTP3 Start | | | MTP3 Start |
| | |
| V | | V |
| +-----------+ | | +-----------+ |
+<-----------------------| AIP |----------------------->+ +<-----------------------| AIP |----------------------->+
| MTP3 Stop +-----------+ SCTP Comm Error | | MTP3 Stop +-----------+ SCTP Comm Error |
| OR T1 Expiry | OR SCTP Comm Lost | | OR T1 Expiry ^ | OR SCTP Comm Lost |
| | | |
| | | |
| +----------------------+ | Send and |
| | | Receive LS Alignment |
| | V |
| | +-----------+ |
+<-----------------------| PROVING |----------------------->+
| | MTP3 Stop +-----------+ SCTP Comm Error |
| | OR Receive LS OOS | OR SCTP Comm Lost |
| | | |
| | | T4 Expiry |
| | V |
| | +-----------+ |
| | | ALIGNED | |
+<-----------------------| READY |----------------------->+
| | MTP3 Stop +-----------+ SCTP Comm Error
| | OR T3 Expiry | OR SCTP Comm Lost
| | OR Receive LS OOS |
| | | Receive LS Ready
| | | OR Receive User Data
| | |
| | V
| | +-----------+
| | | INS |
| | +-----------+
| | | | | |
| | | MTP3 Stop
| | | OR Receive LS OOS
| | | OR SCTP Comm Error
| | | OR SCTP Comm Lost
| | | OR T6 Expiry
| | | OR T7 Expiry
| | | OR M2PA Link Failure
| | | | | |
| | Send and |
| | Receive LS Alignment |
| | | | | |
| V |
| +-----------+ |
+<-----------------------| PROVING |----------------------->+
| MTP3 Stop +-----------+ SCTP Comm Error |
| OR Receive LS OOS | OR SCTP Comm Lost |
| | | | | |
| | T2 Expiry |
| | | | | |
| V | | | V
| +-----------+ | | | MTP3 Start +-----------+
| | ALIGNED | | | +<-------------------| RETRIEVAL |
+<-----------------------| READY |----------------------->+ +<-----------------------+-----------+
| MTP3 Stop +-----------+ SCTP Comm Error Retrieval Complete
| OR T3 Expiry | OR SCTP Comm Lost
| OR Receive LS OOS |
| |
| | Receive LS Ready
| | OR Receive User Data
| |
| V
| +-----------+
| | INS |
| +-----------+
| |
| |
| |
| |
| |
| | MTP3 Stop
| | OR Receive LS OOS
| | OR SCTP Comm Error
| | OR SCTP Comm Lost
| | OR T6 Expiry
| | OR M2PA Link Failure
| |
| V
| +-----------+
+<-----------------------| RETRIEVAL |
Retrieval Complete +-----------+
OR MTP3 Start
Figure 7: M2PA Link State Transition Diagram Figure 7: M2PA Link State Transition Diagram
Figure 8 illustrates state changes in the M2PA management of the SCTP Figure 8 illustrates state changes in the M2PA management of the SCTP
association together with the causing events. Note that some of the association together with the causing events. Note that some of the
error conditions are not shown in the state diagram. error conditions are not shown in the state diagram.
Following is a list of the M2PA Association States and a description Following is a list of the M2PA Association States and a description
of each. of each.
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functionality of MTP2 is not needed. SCTP does not provide functions functionality of MTP2 is not needed. SCTP does not provide functions
related to Link State Control in MTP2. These functions must be related to Link State Control in MTP2. These functions must be
provided by M2PA. provided by M2PA.
4.1.2 MTP and SCTP Entities 4.1.2 MTP and SCTP Entities
This section describes how M2PA relates MTP and SCTP entities. This section describes how M2PA relates MTP and SCTP entities.
Each MTP link corresponds to an SCTP association. To prevent duplicate Each MTP link corresponds to an SCTP association. To prevent duplicate
associations from being established, it is recommended that each associations from being established, it is recommended that each
endpoint know the IP address and port number of both endpoints. SCTP endpoint know the IP address (or IP addresses, if multi-homing is
prevents two associations with the same IP addresses and port numbers used) and port number of both endpoints. SCTP prevents two
from being established. associations with the same IP addresses and port numbers from being
established.
It is necessary for at least one of the endpoints to be listening on It is necessary for at least one of the endpoints to be listening on
the port on which the other endpoint is trying to establish the the port on which the other endpoint is trying to establish the
association. Therefore, at least one of the port numbers should be the association. Therefore, at least one of the port numbers should be the
M2PA registered port. M2PA registered port.
If only one association is to be established between these two IP If only one association is to be established between these two IP
addresses, then the association should be established using the M2PA addresses, then the association should be established using the M2PA
registered port at each endpoint. registered port at each endpoint.
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Multiple Associations Between Two IP Addresses Multiple Associations Between Two IP Addresses
The association shall contain two streams in each direction. Stream 0 The association shall contain two streams in each direction. Stream 0
is designated for Link Status messages. Stream 1 is designated for is designated for Link Status messages. Stream 1 is designated for
User Data messages. User Data messages.
4.1.3 Link Alignment 4.1.3 Link Alignment
The purposes of the alignment procedure are: The purposes of the alignment procedure are:
1. To provide a handshaking procedure so that both endpoints are (1) To provide a handshaking procedure so that both endpoints are
prepared to send SS7 traffic, and to prevent traffic from being prepared to send SS7 traffic, and to prevent traffic from being
sent before the other end is ready. sent before the other end is ready.
2. Verify that the SCTP association is suitable for use as an SS7 (2) To verify that the SCTP association is suitable for use as an
link. SS7 link.
3. Optionally, to overcome the SCTP slow start period.
Link alignment takes place after the association is established. If Link alignment takes place after the association is established. If
SCTP fails to establish the association, and M2PA has received a Start SCTP fails to establish the association, and M2PA has received a Start
Request from its MTP3, then M2PA shall report to MTP3 that the link is Request from its MTP3, then M2PA shall report to MTP3 that the link is
out of service. out of service.
After the association is established, M2PA shall send a Link Status After the association is established, M2PA shall send a Link Status
Out of Service message to its peer. Out of Service message to its peer.
Once the association is established and M2PA has received a Start Once the association is established and M2PA has received a Start
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If timer T1 expires, then M2PA reports to MTP3 that the link is out of If timer T1 expires, then M2PA reports to MTP3 that the link is out of
service. M2PA sends Link Status Out of Service to its peer. M2PA service. M2PA sends Link Status Out of Service to its peer. M2PA
should leave the association established. M2PA waits for MTP3 to should leave the association established. M2PA waits for MTP3 to
initiate the alignment procedure again. initiate the alignment procedure again.
Note: Between the time M2PA sends Link Status Alignment to its peer Note: Between the time M2PA sends Link Status Alignment to its peer
and receives Link Status Alignment from its peer, M2PA may receive and receives Link Status Alignment from its peer, M2PA may receive
Link Status Out of Service from its peer. This message is Link Status Out of Service from its peer. This message is
ignored. After receiving Link Status Alignment from the peer, receipt ignored. After receiving Link Status Alignment from the peer, receipt
of a Link Status Out of Service message causes M2PA to send Out of of a Link Status Out of Service message causes M2PA to send Out of
Service to MTP3 and return to the Out of Serivce state. Service to MTP3 and return to the Out of Service state.
When M2PA has both sent and received the Link Status Alignment When M2PA has both sent and received the Link Status Alignment
message, it has completed alignment and moves to the proving state. message, it has completed alignment and moves to the proving state.
M2PA starts the proving period timer T2. During the proving period, M2PA starts the proving period timer T4. During the proving period,
M2PA sends Link Status Proving messages to its peer at an interval M2PA sends Link Status Proving messages to its peer at an interval
defined by the protocol parameter Proving_Rate. M2PA sends either the defined by the protocol parameter Proving_Rate. M2PA sends either the
Proving Normal or Proving Emergency message, according to the Proving Normal or Proving Emergency message, according to the
Emergency and Emergency Ceases commands from MTP3. M2PA uses the value Emergency and Emergency Ceases commands from MTP3. M2PA uses the value
of T2 corresponding to the Normal or Emergency state. However, if M2PA of T4 corresponding to the Normal or Emergency state. However, if M2PA
receives a Link Status Proving Emergency message from its peer, then receives a Link Status Proving Emergency message from its peer, then
M2PA shall initiate the Emergency proving period value for T2, but it M2PA shall initiate the Emergency proving period value for T4, but it
shall continue to send the Proving message (Normal or Emergency) shall continue to send the Proving message (Normal or Emergency)
determined by its own upper layer MTP3. determined by its own upper layer MTP3.
When the proving period timer T2 expires, M2PA shall start the timer When the proving period timer T4 expires, M2PA shall start the timer
T3 and send Link Status Ready messages to its peer at interval T3 and send Link Status Ready messages to its peer at interval
Status_Interval. These messages are used to verify that both ends have Status_Interval. These messages are used to verify that both ends have
completed proving. completed proving.
M2PA shall stop timer T3 when it receives a Link Status Ready or User M2PA shall stop timer T3 when it receives a Link Status Ready or User
Data message from its peer. If timer T3 expires, then M2PA reports to Data message from its peer. If timer T3 expires, then M2PA reports to
MTP3 that the link is out of service. M2PA sends Link Status Out of MTP3 that the link is out of service. M2PA sends Link Status Out of
Service to its peer. M2PA should leave the association Service to its peer. M2PA should leave the association
established. M2PA waits for MTP3 to initiate the alignment procedure established. M2PA waits for MTP3 to initiate the alignment procedure
again. again.
Note that if M2PA has already received a Link Status Ready message Note that if M2PA has already received a Link Status Ready message
from its peer when its timer T2 expires, there is no need to start from its peer when its timer T4 expires, there is no need to start
timer T3. M2PA can just send Link Status Ready to the peer and timer T3. M2PA can just send Link Status Ready to the peer and
continue along. continue along.
When all of the following are true: When all of the following are true:
(a) M2PA has received a Start Request from MTP3. (a) M2PA has received a Start Request from MTP3.
(b) M2PA's proving period T2 has expired. (b) M2PA's proving period T4 has expired.
(c) M2PA has sent a Link Status Ready to its peer. (c) M2PA has sent a Link Status Ready to its peer.
(d) M2PA has received a Link Status Ready OR User Data (d) M2PA has received a Link Status Ready OR User Data
message from its peer. message from its peer.
(e) M2PA has not received Link Status Out of Service from its peer (e) M2PA has not received Link Status Out of Service from its peer
since it received Link Status Alignment. since it received Link Status Alignment.
then M2PA shall send Link In Service to its MTP3. then M2PA shall send Link In Service to its MTP3.
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Status Processor Outage Ended to its peer. M2PA shall attempt to Status Processor Outage Ended to its peer. M2PA shall attempt to
complete the alignment procedure during the local processor outage complete the alignment procedure during the local processor outage
condition. condition.
If M2PA receives a Link Status Processor Outage during alignment, and If M2PA receives a Link Status Processor Outage during alignment, and
M2PA had received a Start Request from its MTP3, M2PA shall report M2PA had received a Start Request from its MTP3, M2PA shall report
Remote Processor Outage to MTP3. M2PA shall attempt to complete the Remote Processor Outage to MTP3. M2PA shall attempt to complete the
alignment procedure during the remote processor outage condition. alignment procedure during the remote processor outage condition.
If M2PA receives a Stop command from its MTP3 during alignment, M2PA If M2PA receives a Stop command from its MTP3 during alignment, M2PA
shall send Link Status Out of Service to its peer and terminate the shall send Link Status Out of Service to its peer and terminate the
alignment procedure. alignment procedure.
Anomalous messages received during alignment should be
discarded. Examples include:
(a) User Data received before proving begins.
(b) Link Status Alignment received during proving.
Recommended values: Recommended values:
T1 Alignment - Range: 1-60 seconds Default: 10 seconds T1 Alignment - Range: 1-60 seconds Default: 10 seconds
T2 Proving - T4 Proving -
Normal - Range: 1-60 seconds Default: 10 seconds Normal - Range: 1-60 seconds Default: 10 seconds
Emergency - Range: 400-600 milliseconds Default: 500 milliseconds Emergency - Range: 400-600 milliseconds Default: 500 milliseconds
T3 Ready - Range: 1-60 seconds Default: 10 seconds T3 Ready - Range: 1-60 seconds Default: 10 seconds
Status_Interval - implementation dependent. Status_Interval - implementation dependent.
Proving_Rate - implementation dependent. Proving_Rate - implementation dependent.
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it is in receive congestion. it is in receive congestion.
M2PA shall continue transmitting messages while it is in receive M2PA shall continue transmitting messages while it is in receive
congestion. congestion.
When the peer M2PA receives the Link Status Busy message, it shall When the peer M2PA receives the Link Status Busy message, it shall
start the Remote Congestion timer T6. If timer T6 expires, M2PA shall start the Remote Congestion timer T6. If timer T6 expires, M2PA shall
take the link out of service. M2PA sends a Link Status Out of Service take the link out of service. M2PA sends a Link Status Out of Service
message to its peer, and goes to the Retrieval state. message to its peer, and goes to the Retrieval state.
The peer M2PA shall cease transmitting messages to SCTP while its The peer M2PA should continue transmitting messages to SCTP while its
T6 timer is running, i.e., while the other end is Busy. T6 timer is running, i.e., while the other end is Busy.
The peer M2PA shall not fail the link due to expiration of timer T7
excessive delay of acknowledgement (see section 4.2.1 Sending and
receiving messages) while its T6 timer is running, i.e., while the
other end is Busy.
If M2PA is no longer in receive congestion for the association, M2PA If M2PA is no longer in receive congestion for the association, M2PA
shall send a Link Status Busy Ended message to its peer on that shall send a Link Status Busy Ended message to its peer on that
association. association.
When the peer M2PA receives the Link Status Busy Ended message, it When the peer M2PA receives the Link Status Busy Ended message, it
shall stop timer T6. shall stop timer T6.
Recommended value of T6 is 1-6 seconds. Recommended value of T6 is 1-6 seconds.
4.1.6 Error Monitoring 4.1.6 Error Monitoring
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In MTP, Link Status messages have priority over User Data messages In MTP, Link Status messages have priority over User Data messages
([2] Q.703, section 11.2). To achieve this in M2PA, M2PA shall send ([2] Q.703, section 11.2). To achieve this in M2PA, M2PA shall send
Link Status and User Data messages on separate streams in its SCTP Link Status and User Data messages on separate streams in its SCTP
association. All messages are sent using the ordered delivery option. association. All messages are sent using the ordered delivery option.
M2PA SHOULD give higher priority to Link Status messages than to User M2PA SHOULD give higher priority to Link Status messages than to User
Data messages when sending messages to SCTP. Data messages when sending messages to SCTP.
M2PA SHOULD give higher priority to reading the Link Status stream M2PA SHOULD give higher priority to reading the Link Status stream
over the User Data stream. than to reading the User Data stream.
M2PA SHOULD give higher priority to receiving notifications from SCTP M2PA SHOULD give higher priority to receiving notifications from SCTP
over reading either the Link Status stream or the User Data stream. than to reading either the Link Status stream or the User Data stream.
4.1.8 M2PA Version Control 4.1.8 M2PA Version Control
A node upgraded to a newer version of M2PA SHOULD support the older A node upgraded to a newer version of M2PA SHOULD support the older
versions used on other nodes with which it is communicating. If that versions used on other nodes with which it is communicating. If that
is the case, then alignment can proceed normally. is the case, then alignment can proceed normally.
In particular, it is recommended that for future modifications to this In particular, it is recommended that for future modifications to this
protocol: protocol:
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procedures to recognize this and handle it appropriately. procedures to recognize this and handle it appropriately.
In case a newer version of M2PA is incompatible with an older version, In case a newer version of M2PA is incompatible with an older version,
the newer version should recognize this and prevent the alignment of the newer version should recognize this and prevent the alignment of
the link. If a Link Status Alignment message with an unsupported the link. If a Link Status Alignment message with an unsupported
version is received by the newer version, the receiving end's M2PA version is received by the newer version, the receiving end's M2PA
shall not complete the alignment procedure. shall not complete the alignment procedure.
4.2 Procedures to Support the MTP3/MTP2 Interface 4.2 Procedures to Support the MTP3/MTP2 Interface
4.2.1 Sending/receiving messages 4.2.1 Sending and receiving messages
When MTP3 sends a message for transmission to M2PA, M2PA passes the When MTP3 sends a message for transmission to M2PA, M2PA passes the
corresponding M2PA message to SCTP using the SEND primitive. corresponding M2PA message to SCTP using the SEND primitive.
M2PA Link Status messages are passed to SCTP using the SEND primitive. M2PA Link Status messages are passed to SCTP using the SEND primitive.
Link Status and User Data messages shall be sent via SCTP on separate Link Status and User Data messages shall be sent via SCTP on separate
streams. streams.
When M2PA receives a User Data message from SCTP, M2PA passes the When M2PA receives a User Data message from SCTP, M2PA passes the
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next FSN is 0. next FSN is 0.
For message types other than User Data, the Forward Sequence Number is For message types other than User Data, the Forward Sequence Number is
set to the FSN of the last User Data message sent. set to the FSN of the last User Data message sent.
The Backward Sequence Number is set to the FSN of the last User Data The Backward Sequence Number is set to the FSN of the last User Data
message M2PA received from its peer. This serves as an M2PA-level message M2PA received from its peer. This serves as an M2PA-level
acknowledgement of the message. After the link is placed in service acknowledgement of the message. After the link is placed in service
and before a User Data message has been received, the BSN is set to 0. and before a User Data message has been received, the BSN is set to 0.
When M2PA receives a message with Backward Sequence Number equal to When M2PA receives a User Data message with Backward Sequence Number
'n', it may remove all messages with Forward Sequence Number <= n from equal to 'n', it may remove all messages with Forward Sequence Number
its queue. <= n from its queue.
If M2PA receives a User Data message with an FSN that is out of order, If M2PA receives a User Data message with an FSN that is out of order,
M2PA shall fail the link. M2PA shall fail the link.
M2PA may send acknowledgement of a received message in an outgoing M2PA should follow the criterion stated in [2] Q.703, section 5.3.1
User Data or Link Status message. for incorrect BSNs: If any two BSNs in three consecutively received
User Data messages are not the same as the previous one or any of the
FSNs of the User Data messages in the M2PA transmit buffer at the time
they are received, then MTP3 should be informed that the link is
faulty.
If there is no other User Data or Link Status message to be sent when M2PA should ignore the FSN and BSN contained in a Link Status message.
there is a message to acknowledge, M2PA may send a Link Status In
Service message. Note: In all calculations involving FSN and BSN, the programmer should
be aware that the value wraps around to 0 after reaching its maximum
value.
If there is no other User Data message to be sent when there is a
message to acknowledge, M2PA may send a User Data message with no data
payload. The FSN for this empty User Data message is incremented as
with any other User Data message.
Note that since SCTP provides reliable delivery and ordered delivery Note that since SCTP provides reliable delivery and ordered delivery
within the stream, M2PA does not need to perform retransmissions. within the stream, M2PA does not perform retransmissions.
Timer T7 provides an indication of excessive delay of
acknowledgement. If the following conditions are true:
(a) There is at least one message in the M2PA transmit buffer that
has been sent.
(b) The remote M2PA is not in a Busy condition.
(c) M2PA has not received an acknowledgement in the span of T7.
Then M2PA should fail the link.
The recommended range for timer T7 is 0.5-2 seconds.
4.2.2 Link activation and restoration 4.2.2 Link activation and restoration
When MTP3 requests that M2PA activate or restore a link by a Start When MTP3 requests that M2PA activate or restore a link by a Start
Request, M2PA shall follow the alignment procedure in section 4.1.3. Request, M2PA shall follow the alignment procedure in section 4.1.3.
4.2.3 Link deactivation 4.2.3 Link deactivation
When MTP3 requests that M2PA deactivate a link by a Stop command, M2PA When MTP3 requests that M2PA deactivate a link by a Stop command, M2PA
shall send a Link Status Out of Service message to its peer. shall send a Link Status Out of Service message to its peer.
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a gap in the M2PA sequence numbers at the receiving end when the a gap in the M2PA sequence numbers at the receiving end when the
changeover procedure begins. If only the M2PA sequence number is used changeover procedure begins. If only the M2PA sequence number is used
in the XCO/XCA message, there would be a possibility of losing the in the XCO/XCA message, there would be a possibility of losing the
messages in the gap, or duplicating messages after the gap. messages in the gap, or duplicating messages after the gap.
M2PA links with multiple User Data streams would be possible if a M2PA links with multiple User Data streams would be possible if a
multiple-BSNT XCO/XCA message is defined in MTP3, or MTP3 allows multiple-BSNT XCO/XCA message is defined in MTP3, or MTP3 allows
multiple XCO/XCA messages (one for each User Data stream) to be sent multiple XCO/XCA messages (one for each User Data stream) to be sent
during a changeover. This is beyond the scope of this document. during a changeover. This is beyond the scope of this document.
4.3 SCTP Considerations
Some M2PA procedures may be affected by the use of SCTP as a transport
layer. These considerations are discussed in this section.
4.3.1 SCTP Slow Start
SCTP contains a slow start algorithm to control the amount of data
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 slow start under certain conditions, including the following:
(a) Link Alignment. Link alignment takes place after an association
is established. SCTP invokes the slow start algorithm since
transmission is beginning on the association.
(b) Changeover. Messages are retrieved from one link (association)
and transferred to another for transmission. If the second link
had previously been idle, or is in the process of link
alignment, SCTP may invoke the slow start algorithm.
(c) Path failure (multi-homing). If SCTP switches from a failed
path to a new path, and the new path had previously been idle,
SCTP may invoke the slow start algorithm.
(d) Reduced traffic volume. Any time that M2PA sends a low volume
of traffic on a link and then the volume increases, SCTP may
invoke the slow start algorithm.
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 [1][2]. Communications M2PA are named using the MTP terminology [1][2]. Communications
between M2PA and SCTP are named using SCTP terminology. between M2PA and SCTP are named using SCTP terminology.
5.1 Link Initialization (Alignment) 5.1 Link Initialization (Alignment)
An example of the message flow to bring an SS7 link in service is An example of the message flow to bring an SS7 link in service is
shown below. Alignment is done by both ends of the link. To simplify the shown below. Alignment is done by both ends of the link. To simplify
diagram, alignment is shown on one end only. It is assumed in this the diagram, alignment is shown on one end only. It is assumed in this
example that SCTP has been initialized. 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)
skipping to change at page 39, line 16 skipping to change at page 40, line 16
Link Status Alignment Link Status Alignment
------------------------------------> ------------------------------------>
Start timer T1 Start timer T1
Link Status Alignment Link Status Alignment
<------------------------------------ <------------------------------------
Stop timer T1 Stop timer T1
Start timer T2 Start timer T4
Proving period begins. (Messages from remote end not shown.) Proving period begins. (Messages from remote end not shown.)
Link Status Proving Link Status Proving
------------------------------------> ------------------------------------>
------------------------------------> ------------------------------------>
------------------------------------> ------------------------------------>
------------------------------------> ------------------------------------>
------------------------------------> ------------------------------------>
------------------------------------> ------------------------------------>
Timer T2 expires Timer T4 expires
Send Link Status Ready until the remote end completes its proving Send Link Status Ready until the remote end completes its proving
period. period.
Start timer T3 Start timer T3
Link Status Ready Link Status Ready
------------------------------------> ------------------------------------>
------------------------------------> ------------------------------------>
------------------------------------> ------------------------------------>
skipping to change at page 46, line 9 skipping to change at page 47, line 9
Particularly for mobile users, the requirement for confidentiality MAY Particularly for mobile users, the requirement for confidentiality MAY
include the masking of IP addresses and ports. In this case include the masking of IP addresses and ports. In this case
application-level encryption is not sufficient. IPSEC ESP SHOULD be application-level encryption is not sufficient. IPSEC ESP SHOULD be
used instead. Regardless of which level performs the encryption, the used instead. Regardless of which level performs the encryption, the
IPSEC ISAKMP service SHOULD be used for key management. IPSEC ISAKMP service SHOULD be used for key management.
7. IANA Considerations 7. IANA Considerations
7.1 SCTP Payload Protocol Identifier 7.1 SCTP Payload Protocol Identifier
The SCTP (and UDP/TCP) Registered User Port Number Assignment for M2PA The SCTP (and TCP) Registered User Port Number Assignment for M2PA
is TBD. is 3565.
The value assigned by IANA for the Payload Protocol Identifier in the The value assigned by IANA for the Payload Protocol Identifier in the
SCTP Payload Data chunk is SCTP Payload Data chunk is
M2PA 5 M2PA 5
The SCTP Payload Protocol Identifier is included in each SCTP Data The SCTP Payload Protocol Identifier is included in each SCTP Data
chunk, to indicate which protocol the SCTP is carrying. This Payload chunk, to indicate which protocol the SCTP is carrying. This Payload
Protocol Identifier is not directly used by SCTP but may be used by Protocol Identifier is not directly used by SCTP but may be used by
certain network entities to identify the type of information being certain network entities to identify the type of information being
skipping to change at page 48, line 23 skipping to change at page 49, line 23
[3] ANSI T1.111-2000, American National Standard for [3] ANSI T1.111-2000, American National Standard for
Telecommunications - Signaling System Number 7 (SS7) - Telecommunications - Signaling System Number 7 (SS7) -
Message Transfer Part (MTP), 2000. Message Transfer Part (MTP), 2000.
[4] RFC 2719, Framework Architecture for Signaling Transport, [4] RFC 2719, Framework Architecture for Signaling Transport,
October 1999. October 1999.
[5] RFC 2960, Stream Control Transmission Protocol, [5] RFC 2960, Stream Control Transmission Protocol,
October 2000. October 2000.
[6] SS7 MTP2-User Adaptation Layer, draft-ietf-sigtran-m2ua-13.txt, [6] SS7 MTP2-User Adaptation Layer, draft-ietf-sigtran-m2ua-15.txt,
January 2002. February 2002.
[7] ITU-T Recommendation Q.2210, 'Message transfer part level 3 [7] ITU-T Recommendation Q.2210, 'Message transfer part level 3
functions and messages using the services of ITU-T functions and messages using the services of ITU-T
Recommendation Q.2140'. Recommendation Q.2140'.
[8] Bradner, S. "Key words for use in RFCs to Indicate Requirement [8] Bradner, S. "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[9] Telecommunication Technology Committee (TTC) Standard JT-Q704, [9] Telecommunication Technology Committee (TTC) Standard JT-Q704,
'Message Transfer Part Signaling Network Functions', 'Message Transfer Part Signaling Network Functions',
skipping to change at page 49, line 43 skipping to change at page 50, line 43
gregside consulting EMail: gregside@rogers.com gregside consulting EMail: gregside@rogers.com
Kanata, Ontario Kanata, Ontario
Canada Canada
Ken Morneault Tel: +1-703-484-3323 Ken Morneault Tel: +1-703-484-3323
Cisco Systems Inc. EMail: kmorneau@cisco.com Cisco Systems Inc. EMail: kmorneau@cisco.com
13615 Dulles Technology Drive 13615 Dulles Technology Drive
Herndon, VA 20171 Herndon, VA 20171
USA USA
Brian Bidulock Tel +1-972-839-4489 Brian Bidulock Tel +1-780-490-1141
OpenSS7 Project EMail: bidulock@openss7.org OpenSS7 Corporation EMail: bidulock@openss7.org
4701 Preston Park Blvd. #424 1469 Jeffreys Crescent
Plano, TX 75093 Edmonton, AB T6L 6T1
USA Canada
This Internet Draft expires November 2002. This Internet Draft expires February 2003.
 End of changes. 

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