draft-ietf-sigtran-m2pa-01.txt   draft-ietf-sigtran-m2pa-02.txt 
Network Working Group Tom George Network Working Group Tom George
INTERNET-DRAFT Alcatel INTERNET-DRAFT Alcatel
Ram Dantu Ram Dantu
IPmobile Cisco Systems
Malleswar Kalla Malleswar Kalla
Telcordia Telcordia
Hanns Juergen Schwarzbauer Hanns Juergen Schwarzbauer
Siemens Siemens
Greg Sidebottom Greg Sidebottom
Nortel Networks Nortel Networks
Ken Morneault Ken Morneault
Cisco Systems Cisco Systems
Expires May 2001 November 22, 2000 Expires September 2001 March 2, 2001
SS7 MTP2-User Peer-to-Peer Adaptation Layer SS7 MTP2-User Peer-to-Peer Adaptation Layer
<draft-ietf-sigtran-m2pa-01.txt> <draft-ietf-sigtran-m2pa-02.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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protocol. The SS7 Signaling Points may also employ standard SS7 links protocol. The SS7 Signaling Points may also employ standard SS7 links
using the SS7 Message Transfer Part (MTP) Layer 2 to provide transport using the SS7 Message Transfer Part (MTP) Layer 2 to provide transport
of MTP Layer 3 signaling messages. of MTP Layer 3 signaling messages.
TABLE OF CONTENTS TABLE OF CONTENTS
1. Introduction............................................. 4 1. Introduction............................................. 4
1.1 Scope................................................. 4 1.1 Scope................................................. 4
1.2 Terminology........................................... 4 1.2 Terminology........................................... 4
1.3 Abbreviations......................................... 5 1.3 Abbreviations......................................... 5
1.4 Conventions........................................... 5 1.4 Conventions........................................... 6
1.5 Signaling Transport Architecture...................... 6 1.5 Signaling Transport Architecture...................... 6
1.6 Services Provided by M2PA............................. 7 1.6 Services Provided by M2PA............................. 7
1.7 Functions Provided by M2PA............................ 8 1.7 Functions Provided by M2PA............................ 8
1.8 Definition of the M2PA Boundaries..................... 9 1.8 Definition of the M2PA Boundaries..................... 9
1.9 Differences Between M2PA and M2UA.....................10 1.9 Differences Between M2PA and M2UA.....................11
2. Protocol Elements........................................12 2. Protocol Elements........................................13
2.1 Common Message Header.................................12 2.1 Common Message Header.................................13
2.2 M2PA Messages.........................................13 2.2 M2PA Messages.........................................14
3. M2PA Link States.........................................15 3. M2PA Link States.........................................16
4. Procedures...............................................17 4. Procedures...............................................19
4.1 Procedures to Support MTP2 Features...................17 4.1 Procedures to Support MTP2 Features...................19
4.2 Procedures to Support the MTP3/MTP2 Interface.........21 4.2 Procedures to Support the MTP3/MTP2 Interface.........26
5. Examples of M2PA Procedures..............................24 5. Examples of M2PA Procedures..............................31
5.1 Link Initialization (Alignment).......................24 5.1 Link Initialization (Alignment).......................31
5.2 Message Transmission and Reception....................26 5.2 Message Transmission and Reception....................33
5.3 Link Status Indication................................26 5.3 Link Status Indication................................33
5.4 Link Status Message (Processor Outage)................27 5.4 Link Status Message (Processor Outage)................34
5.5 Congestion Notification to Upper layer................28 5.5 Level 2 Flow Control..................................35
5.6 Link Deactivation.....................................29 5.6 MTP3 Signaling Link Congestion........................37
5.7 Link Changeover.......................................30 5.7 Link Deactivation.....................................38
6. Security.................................................32 5.8 Link Changeover.......................................39
7. IANA Considerations......................................32 6. Security.................................................41
8. Acknowledgements.........................................32 7. IANA Considerations......................................42
9. References...............................................33 8. Acknowledgements.........................................42
10. Author's Addresses.......................................34 9. References...............................................43
10. Author's Addresses.......................................44
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 delivery from a Signalling delivery over an IP network. This includes delivery from a Signalling
Gateway (SG) to a Media Gateway Controller (MGC) or IP Signaling Gateway (SG) to a Media Gateway Controller (MGC) or IP Signaling
Point, as described in the Framework Architecture for Signalling Point, as described in the Framework Architecture for Signalling
Transport [1]. This could allow for convergence of some signaling Transport [1]. This could allow for convergence of some signaling and
and data networks. SCN Signaling nodes would have access to databases data networks. SCN signaling nodes would have access to databases and
and other devices in the IP network domain that do not employ SS7 other devices in the IP network domain that do not employ SS7
signaling links. There may also be operational cost and performance signaling links. Likewise, IP telephony applications would have access
to SS7 services. There may also be operational cost and performance
advantages when traditional signaling links are replaced by IP network advantages when traditional signaling links are replaced by IP network
"connections". "connections".
The delivery mechanism described in this document allows for full MTP3 The delivery mechanism described in this document allows for full MTP3
message handling and network management capabilities between any two message handling and network management capabilities between any two
SS7 nodes, communicating over an IP network. An SS7 node equipped with SS7 nodes, communicating over an IP network. An SS7 node equipped with
an IP network connection is called an IP Signaling Point (IPSP). The an IP network connection is called an IP Signaling Point (IPSP). The
IPSPs function as traditional SS7 nodes using the IP network instead IPSPs function as traditional SS7 nodes using the IP network instead
of SS7 links. of SS7 links.
The delivery mechanism should The delivery mechanism should
* Support seamless operation of MTP3 protocol peers over an IP - Support seamless operation of MTP3 protocol peers over an IP
network connection. network connection.
* Support the MTP Level 2 / MTP Level 3 interface boundary. - Support the MTP Level 2 / MTP Level 3 interface boundary.
* Support management of SCTP transport associations and traffic - Support management of SCTP transport associations and traffic
instead of MTP2 Links. instead of MTP2 Links.
* Support asynchronous reporting of status changes to management. - Support asynchronous reporting of status changes to management.
1.2 Terminology 1.2 Terminology
MTP - The Message Transfer Part of the SS7 protocol [2]. MTP - The Message Transfer Part of the SS7 protocol [2].
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 Level MTP2-User - A protocol that normally uses the services of MTP Level
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1.6 Services Provided by M2PA 1.6 Services Provided by M2PA
The SS7 MTP3/MTP2 (MTP2-User) interface is retained in the IPSP. The The SS7 MTP3/MTP2 (MTP2-User) interface is retained in the IPSP. The
M2PA protocol layer is required to provide the equivalent set of M2PA protocol layer is required to provide the equivalent set of
services to its user as provided by MTP Level 2 to MTP Level 3. services to its user as provided by MTP Level 2 to MTP Level 3.
These services are described in the following subsections. These services are described in the following subsections.
1.6.1 Support for MTP Level 2 / MTP Level 3 interface boundary 1.6.1 Support for MTP Level 2 / MTP Level 3 interface boundary
This interface is the same as the MTP2/MTP3 interface described in This interface is the same as the MTP2/MTP3 interface described in [2]
[2], with the addition of support for larger sequence numbers in and [10], with the addition of support for larger sequence numbers in
[7]. [7].
Because SCTP uses larger sequence numbers than MTP, the MTP3 Because SCTP uses larger sequence numbers than MTP, the MTP3
Changeover procedure must use the Extended Changeover Order and Changeover procedure must use the Extended Changeover Order and
Extended Changeover Acknowledgment messages described in [7]. This Extended Changeover Acknowledgment messages described in [7]. This
will allow for use of the SCTP stream sequence numbers in the will allow for use of the SCTP stream sequence numbers in the
changeover messages. changeover messages.
Also, the following MTP3/MTP2 primitives must use the larger sequence
numbers:
- BSNT Indication
- 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.
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- Processor outage procedure - Processor outage procedure
- Link alignment procedure - Link alignment procedure
1.7.3 Mapping of SS7 and IP Entities 1.7.3 Mapping of SS7 and IP Entities
For each IP link, the M2PA layer must maintain a map of the SS7 link For each IP link, the M2PA layer must maintain a map of the SS7 link
to its SCTP association and its corresponding IP destination. to its SCTP association and its corresponding IP destination.
1.7.3 SCTP Stream Management 1.7.4 SCTP Stream 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 the
initialization. It is the responsibility of the M2PA layer to ensure initialization. It is the responsibility of the M2PA layer to ensure
proper management of the streams allowed within each association. proper management of the streams allowed within each association.
1.7.4 Retention of MTP3 in the SS7 Network M2PA uses two streams in each direction in each association. Stream 0
in each direction is designated for Link Status messages. Stream 1 is
designated for User Data messages. Separating the Link Status and User
Data messages onto separate stream allows M2PA to prioritize the
messages in a manner similar to MTP2.
1.7.5 Retention of MTP3 in the SS7 Network
M2PA allows MTP3 to perform all of its Message Handling and Network M2PA allows MTP3 to perform all of its Message Handling and Network
Management functions with IPSPs as with other SS7 nodes. Management functions with IPSPs as with other SS7 nodes.
1.8 Definition of the M2PA Boundaries 1.8 Definition of the M2PA Boundaries
1.8.1 Definition of the M2PA / MTP Level 3 boundary 1.8.1 Definition of the M2PA / MTP Level 3 boundary
The upper layer primitives provided by M2PA are the same as those The upper layer primitives provided by M2PA are the same as those
provided by MTP2 to MTP3. Following is a list of these primitives. provided by MTP2 to MTP3. These primitives are described in [2] and
[10]. Following is a list of the primitives.
Primitives sent from MTP3 to M2PA: Primitives sent from MTP3 to M2PA:
Data Request - Used to send a Data Message for transmission. Data Request - Used to send a Data Message for transmission.
Start Request - Used to establish a link. Start Request - Used to establish a link.
Stop Request - Used to release a link. Stop Request - Used to release a link.
Retrieve BSNT Request - Request the BSNT for the changeover procedure. Retrieve BSNT Request - Request the BSNT for the changeover procedure.
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Emergency Request - This is ignored by M2PA. Emergency Request - This is ignored by M2PA.
Emergency Ceases Request - This is ignored by M2PA. Emergency Ceases Request - This is ignored by M2PA.
Primitives sent from M2PA to MTP3: Primitives sent from M2PA to MTP3:
Data Indication - Used to deliver received Data Message to MTP3. Data Indication - Used to deliver received Data Message to MTP3.
Congestion Indication - Indicates change in congestion level. The Congestion Indication - Indicates change in congestion level. The
indication includes the congestion level, if the protocol is using the indication includes the congestion level, if the protocol is using the
optional congestion levels. optional congestion levels. The indication also includes the discard
level.
In Service Indication - Indicates that the link is in service. In Service Indication - Indicates that the link is in service.
Out of Service Indication - Indicates that the link is out of service. Out of Service Indication - Indicates that the link is out of service.
Retrieved Messages Indication - Indicates delivery of unacknowledged Retrieved Messages Indication - Indicates delivery of unacknowledged
and unsent messages. and unsent messages.
Retrieval Complete Indication - Indicates that delivery of Retrieval Complete Indication - Indicates that delivery of
unacknowledged and unsent messages is complete. unacknowledged and unsent messages is complete.
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| Version | Spare | Message Type | | Version | Spare | 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 (vers) contains the version of the M2PA adapation The version field contains the version of the M2PA adapation layer.
layer. The supported versions are: The supported versions are:
01 Release 1.0 of M2PA protocol 01 Release 1.0 of M2PA protocol
2.1.2 Message Type 2.1.2 Message Type
The valid message types are defined below and the message contents are The valid message types are defined below and the message contents are
described in Section 2.2. Each message can contain parameters. described in Section 2.2. Each message can contain parameters.
The following list contains the message types for the defined messages. The following list contains the message types for the defined messages.
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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 |
... ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
No padding is added to the MTP3 message. No padding is added to the MTP3 message.
Note that the Data field contains only the LI, SIF, and SIO Note that the Data field contains only the LI, SIF, and SIO
octets. The other components of the message transmitted by MTP2 (the octets. The other components of the MTP2 MSU format (the Flag, BSN,
Flag, BSN, BIB, FSN, FIB, CK) are not included in M2PA. BIB, FSN, FIB, CK) are not included in M2PA.
Note: The two spare bits in the LI octet are used in a national It is not necessary to put the message length in the LI octet as in
version of SS7 by MTP3 as a Priority field. See [9], section 14 MTP2. The LI octet is included because the two spare bits in the LI
"Common Characteristics of message signal unit formats", section 14.2 octet are used by MTP3 in a national version of SS7 as a Priority
(A) Priority Indicator (PRI). field. See [9], section 14 "Common Characteristics of message signal
unit formats", section 14.2 (A) Priority Indicator (PRI). Therefore
the format of the LI octet is:
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| spare |PRI| (followed by SIO, SIF)
+-+-+-+-+-+-+-+-+
PRI - Priority used only in national MTP defined in [9].
Spare for other MTP versions.
Since the LI octet is not used for a message length, there is no need
to support the expanded LI field in [2], Q.703 Annex A. Therefore the
LI field in M2PA is always one octet.
2.2.2 Link Status 2.2.2 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
the Link Status Signal Unit in MTP2. the Link Status Signal Unit in MTP2.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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request for message retrieval from MTP3. request for message retrieval from MTP3.
+-----------+ +-----------+
| IDLE | | IDLE |
+-----------+ +-----------+
| |
| Power On | Power On
| |
V V
+-----------+ +-----------+
+------->| OOS |---------+ +------->| OOS |<---------------------+
^ +-----------+ |
| | | |
| Server AND | | Client AND |
| MTP3 Start | | MTP3 Start |
| | | |
| V V |
| +-----------+ | | +-----------+ |
| | AIP |--------------------->+
| +-----------+ MTP3 Stop |
| | OR SCTP Comm Error |
| | OR SCTP Comm Lost |
| | | | | |
| | Client AND | Server AND | | SCTP Comm Up |
| | MTP3 Start | MTP3 Start
| | | | | |
| V | | V |
| +-----------+ | | +-----------+ |
| | AIP |<--------+ | | INS-LOCAL |--------------------->+
| +-----------+ | +-----------+ MTP3 Stop
| | | | OR SCTP Comm Error
| | SCTP | | OR SCTP Comm Lost
| | Communication Up | | OR T1 Expiry
| |
| V
| +-----------+
| | INS-LOCAL |
| +-----------+
| | | |
| | Link Status | | Link Status
| | In Service received | | In Service received
| | | |
| V | V
| +-----------+ | +-----------+
| | INS | | | INS |
| +-----------+ | +-----------+
| | | |
Retrieval | | MTP3 Stop Retrieval | | MTP3 Stop
Complete | | OR SCTP Communication Error Complete | | OR SCTP Comm Error
| | OR SCTP Communication Lost OR | | OR SCTP Comm Lost
| | OR T6 Expiration MTP3 Start | | OR T6 Expiry
| | | |
| V | V
| +-----------+ | +-----------+
+--------| RETRIEVAL | +<-------| RETRIEVAL |
+-----------+ +-----------+
Figure 6: M2PA Link State Transition Diagram. Figure 6: M2PA Link State Transition Diagram.
4. Procedures 4. Procedures
4.1 Procedures to Support MTP2 Features 4.1 Procedures to Support MTP2 Features
4.1.1 Signal Unit Format, Delimitation, Acceptance 4.1.1 Signal Unit Format, Delimitation, Acceptance
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relationship with one endpoint, and a server in its relationship with relationship with one endpoint, and a server in its relationship with
another endpoint. The designations of client and server are needed another endpoint. The designations of client and server are needed
only to decide which endpoint initiates the establishment of the only to decide which endpoint initiates the establishment of the
association. After that, the endpoints function as peers. association. After that, the endpoints function as peers.
The client initiates the association using the server's IP address and The client initiates the association using the server's IP address and
the M2PA well-known port number as the destination endpoint. In order the M2PA well-known port number as the destination endpoint. In order
to allow for multiple links between the two endpoints, the client uses to allow for multiple links between the two endpoints, the client uses
a different local port number for each link. It must be decided in a different local port number for each link. It must be decided in
advance which local ports are used by the client. Each of these client advance which local ports are used by the client. Each of these client
ports must be known to the server. Each combination of client IP ports must be known to the server.
address/port and server IP address/port must be mapped to the same
Signaling Link Code (SLC) in the client and server, so that each
endpoint knows which link is being created at the time the SCTP
association is established. However, M2PA does not do any processing
based on the SLC.
An example of the relationships between the associations and the SLCs Each combination of client IP address/port and server IP address/port
is shown in Figure 7 and Table 1. Note that a link is an SCTP (i.e., each association) must be mapped to the same Signaling Link
association identified by two endpoints, in this case a client and Code (SLC) in the client and server, so that each endpoint knows which
server. Each endpoint is identified by an IP address and port link is being created at the time the SCTP association is
number. Each association is mapped to an SLC. Table 1 is only established. However, M2PA does not do any processing based on the
SLC.
Following are examples of the relationships between associations and
links. Note that a link is an SCTP association identified by two
endpoints, in this case a client and server. Each endpoint is
identified by an IP address and port number. Each association is
mapped to an SLC.
Figure 7 shows a case with two IPSPs, each with two IP addresses. Two
associations are the links that connect the two IPSPs. Since 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
conceptual. The actual method for mapping the SCTP associations to the conceptual. The actual method for mapping the SCTP associations to the
SLCs is implementation dependent. SLCs is implementation dependent.
Client Server IPSP X IPSP Y
IPA IPB
+-------------+ +-------------+ +-------------+ +-------------+
| | SCTP | | | | SCTP | |
| SLC = a | association 1 | SLC = a | | IPA | association 1 | IPB |
| port = P1 +---------------+ port = PW | | port = PW +---------------+ port = PW |
| SLC = a | | SLC = a |
| Client | | Server |
| | | | | | | |
| | SCTP | |
| IPC | association 2 | IPD |
| port = PW +---------------+ port = PW |
| SLC = b | | SLC = b |
| Client | | Server |
| | | | | | | |
+-------------+ +-------------+
IPx = IP address
PW = Well-known port number for M2PA
Figure 7: Associations and Links -
Two IPSPs with Two Endpoints Each
+-------------+---------------------------------------+-----+
| Association | Client | Server | SLC |
| +------------+------+------------+------+ |
| | IP address | Port | IP address | Port | |
+=============+============+======+============+======+=====+
| 1 | IPA | PW | IPB | PW | a |
+-------------+------------+------+------------+------+-----+
| 2 | IPC | PW | IPD | PW | b |
+-------------+------------+------+------------+------+-----+
Table 1: Associations and SLCs -
Two IPSPs with Two Endpoints Each
Figure 8 and Table 2 show an example with three IPSPs. Note that in
this example, the two links are in different link sets. Therefore, it
is possible that the values a and b may be equal.
IPSP X IPSP Y
+-------------+ +-------------+
| | SCTP | |
| IPA | association 1 | IPB |
| port = PW +---------------+ port = PW |
| SLC = a | | SLC = a |
| Client | | Server |
| | | | | | | |
| | SCTP | | | | SCTP | |
| SLC = b | association 2 | SLC = b | | IPC | association 2 | |
| port = P2 +---------------+ port = PW | | port = PW +-------+ | |
| SLC = b | | | |
| Client | | | |
| | | | |
+-------------+ | +-------------+
|
|
| IPSP Z
|
| +-------------+
| | |
| | IPD |
+-------+ port = PW |
| SLC = b |
| Server |
| |
| |
| |
| |
| |
| |
| |
+-------------+
IPx = IP address
PW = Well-known port number for M2PA
Figure 8: Associations and Links -
One IPSP Connected to Two IPSPs
+-------------+---------------------------------------+-----+
| Association | Client | Server | SLC |
| +------------+------+------------+------+ |
| | IP address | Port | IP address | Port | |
+=============+============+======+============+======+=====+
| 1 | IPA | PW | IPB | PW | a |
+-------------+------------+------+------------+------+-----+
| 2 | IPC | PW | IPD | PW | b |
+-------------+------------+------+------------+------+-----+
Table 2: Associations and SLCs -
One IPSP Connected to Two IPSPs
Figure 9 and Table 3 show two associations between the same
endpoints. This is accomplished by using different port numbers for
each association at the client.
IPSP X IPSP Y
+-------------+ +-------------+
| | SCTP | |
| IPA | association 1 | IPB |
| port = P1 +---------------+ port = PW |
| SLC = a | | SLC = a |
| Client | | Server |
| | | | | | | |
| | SCTP | |
| IPA | association 2 | IPB |
| port = PW +---------------+ port = PW |
| SLC = b | | SLC = b |
| Client | | Server |
| | | | | | | |
+-------------+ +-------------+ +-------------+ +-------------+
IPA = IP address of Client IPx = IP address
IPB = IP address of Server
P1, P2 = Pre-selected port numbers for Client P1, P2 = Pre-selected port numbers for Client
PW = Well-known port number for M2PA PW = Well-known port number for M2PA
Figure 7: Associations and SLCs Figure 9: Associations and SLCs -
Multiple Associations Between Endpoints
+-------------+---------------------------------------+-----+ +-------------+---------------------------------------+-----+
| Association | Client | Server | SLC | | Association | Client | Server | 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 | P2 | IPB | PW | b | | 2 | IPA | P2 | IPB | PW | b |
+-------------+------------+------+------------+------+-----+ +-------------+------------+------+------------+------+-----+
Table 1: Associations and SLCs Table 3: Associations and SLCs -
Multiple Associations Between Endpoints
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.
If the SCTP association is not established, the client M2PA sends the If the SCTP association is not established, the client M2PA sends the
ASSOCIATE primitive to SCTP. The client should attempt to establish ASSOCIATE primitive to SCTP. The client should attempt to establish
the association periodically until it is successful. the association periodically until it is successful.
If SCTP fails to establish the association, and M2PA had received a If SCTP fails to establish the association, and M2PA had received a
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Processor Recovered, then M2PA sends Link Status Processor Processor Recovered, then M2PA sends Link Status Processor
Outage Ended to its peer, followed by Link Status In Service. Outage Ended to its peer, followed by Link Status In Service.
If M2PA has not received a Link Status In Service from its peer at the If M2PA has not received a Link Status In Service from its peer at the
time it sends the Link Status In Service, M2PA starts timer T1. Timer time it sends the Link Status In Service, M2PA starts timer T1. Timer
T1 is stopped when M2PA receives Link Status In Service from its T1 is stopped when M2PA receives Link Status In Service from its
peer. If M2PA does not receive Link Status In Service from its peer peer. If M2PA does not receive Link Status In Service from its peer
before T1 expires, then M2PA reports to MTP3 that the link is out of before T1 expires, then M2PA reports to MTP3 that the link is out of
service. Then M2PA uses the ABORT primitive to end the association. service. Then M2PA uses the ABORT primitive to end the association.
Recommended value of T1 is 5-150 seconds. Recommended value of T1 is 5-50 seconds.
Note that if the server M2PA has not received a Start Request from its Note that if the server M2PA has not received a Start Request from its
MTP3, it will not send the Link Status In Service message to the MTP3, it will not send the Link Status In Service message to the
client. Eventually the client will ABORT the association. The client client. Eventually the client will ABORT the association. The client
will then attempt to establish the association. will then attempt to establish the association.
When the association is established, M2PA has sent Link Status In When the association is established, M2PA has sent Link Status In
Service to its peer, and has received Link Status In Service from its Service to its peer, and has received Link Status In Service from its
peer, and there is no local processor outage condition, then M2PA peer, and there is no local processor outage condition, then M2PA
sends Link In Service to its MTP3. sends Link In Service to its MTP3.
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M2PA shall ignore the Emergency and Emergency Ceases commands from M2PA shall ignore the Emergency and Emergency Ceases commands from
MTP3. MTP3.
4.1.3 Processor Outage 4.1.3 Processor Outage
A processor outage occurs when M2PA cannot transfer messages because A processor outage occurs when M2PA cannot transfer messages because
of a condition at a higher layer than M2PA. of a condition at a higher layer than M2PA.
When M2PA detects a local processor outage, it sends a Link Status When M2PA detects a local processor outage, it sends a Link Status
message to its peer with status Processor Outage. M2PA shall discard message to its peer with status Processor Outage. M2PA shall discard
any User Data messages received. M2PA shall also cease sending User any User Data messages received. M2PA shall also cease sending User
Data messages to SCTP for transmission. Data messages to SCTP for transmission.
The peer M2PA, upon receiving the Link Status Processor Outage The peer M2PA, upon receiving the Link Status Processor Outage
message, shall report Remote Processor Outage to its MTP3. M2PA ceases message, shall report Remote Processor Outage to its MTP3. M2PA ceases
sending User Data messages. sending User Data messages.
When the processor outage ceases, MTP3 sends a Local Processor MTP3 sends a Flush Buffers or Continue command to M2PA. When the
Recovered indication to M2PA. The local M2PA notifies its peer by processor outage ceases, MTP3 sends a Local Processor Recovered
sending a Link Status message with status Processor Outage Ended. The indication to M2PA. The local M2PA notifies its peer by sending a Link
peer notifies its MTP3 that the remote processor outage has ceased. Status message with status Processor Outage Ended. The peer notifies
its MTP3 that the remote processor outage has ceased.
4.1.4 Level 2 Flow Control 4.1.4 Level 2 Flow Control
Notification of receive congestion from SCTP to M2PA is implementation Notification of receive congestion from SCTP to M2PA is implementation
dependent. This section assumes that there is some form of receive dependent. This section assumes that there is some form of receive
congestion notification from SCTP to M2PA. congestion notification from SCTP to M2PA. Since SCTP has its own
congestion control, the purpose of the M2PA level 2 flow control is to
monitor the association and decide if it should be aborted.
If M2PA receives notification from its lower layer SCTP that SCTP is If M2PA receives notification from its lower layer SCTP that SCTP is
in receive congestion for an association, M2PA shall send a Link in receive congestion for an association, M2PA shall send a Link
Status Busy message to its peer on that association. Status Busy message to its peer on that association.
When the peer M2PA receives the Link Status Busy message, it shall When the peer M2PA receives the Link Status Busy message, it shall
cease transmitting User Data messages from its upper layer MTP3. (User start the Remote Congestion timer T6. If timer T6 expires, M2PA shall
Data messages already given to the lower layer SCTP are transmitted as use the ABORT primitive to end the association and take the link out
the SCTP protocol allows.) M2PA shall start the Remote Congestion of service.
timer T6. If timer T6 expires, M2PA shall use the ABORT primitive to
end the association and take the link out of service. The peer M2PA shall continue transmitting messages to SCTP while its
T6 timer is running, i.e., while the other end is Busy.
If M2PA receives notification from its lower layer SCTP that SCTP is If M2PA receives notification from its lower layer SCTP that SCTP is
no longer in receive congestion for the association, M2PA shall send a no longer in receive congestion for the association, M2PA shall send a
Link Status Busy Ended message to its peer on that association. Link Status Busy Ended message to its peer on that 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 and resume transmitting User Data messages from shall stop timer T6.
its upper layer MTP3.
Recommended value of T6 is 1-6 seconds. Recommended value of T6 is 1-6 seconds.
4.1.5 Error Monitoring 4.1.5 Error Monitoring
If M2PA loses the SCTP association for a link, M2PA shall report to If M2PA loses the SCTP association for a link, M2PA shall report to
MTP3 that the link is out of service. MTP3 that the link is out of service.
As long as the SCTP association is up, M2PA shall regularly invoke the
SCTP GETSRTTREPORT primitive to determine the Smooth Round Trip Time
(SRTT) from SCTP. If the the SRTT exceeds the maximum acceptable
value, the link is considered failed and taken out of service. The
interval between successive SRTT requests and the maximum acceptable
SRTT value are determined by the parameters:
SRTT_measurement_interval
Range: 1 - 1000 seconds.
Default: 5 seconds.
SRTT_max
Range: 0-65,535 milliseconds.
Default: 1000 milliseconds.
4.1.6 Transmission Priorities 4.1.6 Transmission Priorities
In MTP, Link Status messages have priority over User Data messages In MTP, Link Status messages have priority over User Data messages
([2] Q.703, section 11.2). To achieve this in M2PA, Link Status and ([2] Q.703, section 11.2). To achieve this in M2PA, Link Status and
User Data messages shall be sent via SCTP on separate streams. All User Data messages shall be sent via SCTP on separate streams. All
messages are sent using the ordered delivery option. messages are sent using the ordered delivery option.
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. over 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. over reading either the Link Status stream or the User Data stream.
Implementation Note: If the SCTP implementation allows streams to have Implementation Note: If the SCTP implementation allows streams to have
different priorities for sending messages, then M2PA should set the different priorities for sending messages, then M2PA SHOULD set the
Link Status stream to a higher priority than the User Data stream. Link Status stream to a higher priority than the User Data stream. See
[13] for a possible extension to SCTP to allow for stream priorities.
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/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.
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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 4.1.2. Request, M2PA shall follow the alignment procedure in section 4.1.2.
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 an ABORT primitive to SCTP. shall send an ABORT primitive to SCTP.
4.2.4 Flush buffers 4.2.4 Flush Buffers, Continue
The Flush Buffers and Continue commands allow M2PA to resume normal
operations (i.e., transmission of messages to SCTP and receiving
messages from SCTP) after a processor outage (local and/or remote)
ceases.
If M2PA receives a Flush Buffers command from MTP3, M2PA: If M2PA receives a Flush Buffers command from MTP3, M2PA:
(a) shall not transmit any messages to SCTP that are currently (a) shall not transmit any messages to SCTP that are currently
waiting to be transmitted to SCTP. waiting to be transmitted to SCTP. These messages shall be
discarded.
(b) shall discard all messages currently waiting to be passed (b) shall discard all messages currently waiting to be passed
to MTP3. to MTP3.
If M2PA receives either a Flush Buffers or Continue command from MTP3,
and the processor outage condition ceases, M2PA shall resume receiving
and transmitting messages.
4.2.5 MTP3 Signaling Link Congestion 4.2.5 MTP3 Signaling Link Congestion
Notification of transmit congestion from SCTP to its upper layer Notification of transmit congestion from SCTP to its upper layer
(M2PA) is implementation dependent. Nevertheless, M2PA should receive (M2PA) is implementation dependent. Nevertheless, M2PA should receive
notification from SCTP adequate to allow MTP3 to meet its requirements notification from SCTP adequate to allow MTP3 to meet its requirements
for signaling link transmit congestion in [2] Q.704, section 3.8. for signaling link transmit congestion in [2] Q.704, section 3.8.
M2PA shall notify its upper layer MTP3 when transmit buffer occupancy M2PA shall use the Congestion Indication primitive to notify its upper
layer MTP3 when transmit buffer occupancy crosses the congestion
onset, discard, and abatement thresholds. For national networks with
multiple congestion threshold levels, M2PA shall notify MTP3 when
transmit buffer occupancy crosses each level of the congestion onset,
discard, and abatement thresholds.
crosses the congestion onset, discard, and abatement thresholds. For Note: M2PA does not discard messages because of transmit
national networks with multiple congestion threshold levels, M2PA congestion. Discarding of messages due to transmit congestion is
shall notify MTP3 when transmit buffer occupancy crosses each level of performed by MTP3.
the congestion onset, discard, and abatement thresholds.
4.2.6 Changeover 4.2.6 Changeover
The objective of the changeover is to ensure that signaling traffic The objective of the changeover is to ensure that signaling traffic
carried by the unavailable signaling link is diverted to the carried by the unavailable signaling link is diverted to the
alternative signaling link(s) as quickly as possible while avoiding alternative signaling link(s) as quickly as possible while avoiding
message loss, duplication, or mis-sequencing. For this purpose, the message loss, duplication, or mis-sequencing. For this purpose, the
changeover procedure includes data retrieval, which is performed changeover procedure includes data retrieval, which is performed
before opening the alternative signaling links to the diverted before opening the alternative signaling links to the diverted
traffic. Data retrieval consists of these steps: traffic. Data retrieval consists of these steps:
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Numbers must be used in place of the Forward and Backward Sequence Numbers must be used in place of the Forward and Backward Sequence
Numbers (FSN/BSN) of SS7. Numbers (FSN/BSN) of SS7.
Stream Sequence Numbers used by SCTP are 16 bits long. MTP2's Forward Stream Sequence Numbers used by SCTP are 16 bits long. MTP2's Forward
and Backward Sequence Numbers are only seven bits long. Hence it is and Backward Sequence Numbers are only seven bits long. Hence it is
necessary for MTP3 to accomodate the larger SSNs. This is done through necessary for MTP3 to accomodate the larger SSNs. This is done through
the use of the Extended Changeover Order (XCO) and Extended Changeover the use of the Extended Changeover Order (XCO) and Extended Changeover
Acknowledgement (XCA) messages instead of the Changeover Order (COO) Acknowledgement (XCA) messages instead of the Changeover Order (COO)
and Changeover Acknowledgement (COA) messages. The XCO and XCA and Changeover Acknowledgement (COA) messages. The XCO and XCA
messages are specified in Reference [7] section 9.8.1. Only the XCO messages are specified in Reference [7] section 9.8.1. Only the XCO
and XCA messages from [7] are used. These messages have a 24-bit field and XCA messages from [7] are required. These messages have a 24-bit
for the sequence number. The upper 8 bits of the 24 bit field should field for the sequence number. The upper 8 bits of the 24 bit field
be set to 0, and the SSN placed in the lower 16 bits. should be set to 0, and the SSN placed in the lower 16 bits.
(Note that the Stream Sequence Numbers are used instead of the (Note that the Stream Sequence Numbers are used instead of the
Transmission Sequence Numbers. The Transmission Sequence Numbers are Transmission Sequence Numbers. The Transmission Sequence Numbers are
32 bits long, and therefore would not fit in the XCO and XCA 32 bits long, and therefore would not fit in the XCO and XCA
messages.) messages.)
For data retrieval, MTP3 requests Backward Sequence Number (BSN) from Also, the following MTP3/MTP2 primitives must use the larger sequence
M2PA. This is the sequence number of the last message received by the numbers:
local end. Normally, SCTP delivers ordered messages to the
application. However, during congestion or failure condition, the - BSNT Indication
sequence numbers of the acknowledged messages may have gaps. In
particular, the SACK (selective acknowledgement message) message can - Retrieval Request and FSNC
have several of these gaps. Hence, it is important to scan through
these gaps and find the sequence number before the first gap. This is For data retrieval, MTP3 requests the Backward Sequence Number to be
the number from which the remote end has to transmit the messages. So Transmitted (BSNT) from M2PA through the Retrieve BSNT
this is the number considered as the Backward Sequence Number and request. Normally, SCTP receives messages in order, in which case the
communicated to the remote end. In a similar way, the remote end also BSNT is the last message received by SCTP. However, because of
detects the BSN and indicates to the local end. As soon as the MTP3 of congestion or a failure condition, the sequence numbers of the
the local end receives this BSN, MTP3 retrieves all the unacknowledged acknowledged messages may have gaps. In particular, the SCTP SACK
messages starting from BSN. This is accomplished through a Retrieval (selective acknowledgement message) message can have several of these
Request and FSNC request. After all the messages are sent from M2PA gaps. In this case, it is necessary to scan through these gaps and
to MTP3, a Retrieval Complete indication is sent. find the sequence number before the first gap. This is the number
considered as the BSNT and communicated to MTP3. M2PA sends the BSNT
value to MTP3 in the BSNT indication. In the same way, the remote end
also detects its BSNT. The MTP3 layers exchange BSNT values through
the XCO/XCA messages. The BSNT received from the other end is called
the FSNC. When MTP3 receives the FSNC from the other end, MTP3
retrieves all the unsent and unacknowledged messages starting with
sequence number (FSNC + 1). This is accomplished through a Retrieval
Request and FSNC request. After all the messages are sent from M2PA to
MTP3, M2PA sends a Retrieval Complete indication to MTP3.
As an example of how the BSNT is determined, suppose the following
SSNs had been received by SCTP on the Data Stream when it is time to
do the changeover procedure: 1-10, 13, 14, 16. Then M2PA tells its
upper layer that the last message it received (the BSNT) was 10. SCTP
has not delivered 13, 14, and 16 to M2PA because to do so would
violate ordered delivery within the stream. The value of 10 is
transmitted to the remote end by MTP3 in the XCO/XCA message. So the
remote end will retransmit 11-16 on an alternate link.
If there are any messages on the SCTP receive queue, M2PA SHOULD
receive these messages and deliver them to MTP3. Note that SCTP does
not deliver incoming messages after the first gap (if any) in the
SSNs, since this would violate ordered delivery within the stream. In
the example above, this would mean that messages 1-10 SHOULD be
received. Otherwise, these unreceived messages might be lost, since
SCTP might have acknowledged them.
Note that the sequence numbers and messages requested by MTP3 may be Note that the sequence numbers and messages requested by MTP3 may be
obtained by M2PA from SCTP via the Communication Lost primitive [5]. obtained by M2PA from SCTP via the Communication Lost primitive [5].
Retrieval of messages is an optional feature in SCTP. To perform data Retrieval of messages is an optional feature in SCTP. To perform data
retrieval, it is necessary that this option be implemented, and that retrieval, it is necessary that this option be implemented, and that
the SSNs of the messages are identified. SCTP must retain the messages the SSNs of the messages are identified. SCTP must retain the messages
for retrieval by MTP3/M2PA whenever an association is aborted. SCTP for retrieval by MTP3/M2PA whenever an association is aborted. SCTP
must be able to return messages to M2PA so that M2PA can perform must be able to return messages to M2PA so that M2PA can perform
retrieval for MTP3. There are various ways that this can be retrieval for MTP3. There are various ways that this can be
implemented, such as: implemented, such as:
(1) SCTP provides a way for M2PA to request retrieval of messages (1) SCTP provides a way for M2PA to request retrieval of messages
for a specified stream and SSN(s). for a specified stream and SSN(s).
(2) SCTP retrieves all messages and identifies the stream and SSN (2) SCTP retrieves all messages and identifies the stream and SSN
of each message. M2PA then must select the appropriate messages of each message. M2PA then must select the appropriate messages
to pass up to MTP3. to pass up to MTP3.
If M2PA receives a Retrieve BSNT request from MTP3, M2PA responds with M2PA must be able to respond to the BSNT request from MTP3. There are
the BSNT indication. The BSNT value is the SCTP stream sequence number various ways of implementing this, such as having SCTP provide the
of the last message received by SCTP User Data stream before any gaps BSNT.
in the stream sequence numbers.
It is helpful for M2PA to have access to the first and last SSN in
SCTP's transmission queue. This information could be used to determine
if the FSNC received from the remote end is a valid value.
If M2PA receives a Retrieve BSNT request from MTP3, M2PA shall respond
with the BSNT indication. The BSNT value is the SCTP stream sequence
number of the last message received by SCTP User Data stream before
any gaps in the stream sequence numbers.
(Note that any messages with stream sequence number greater than this (Note that any messages with stream sequence number greater than this
BSNT value have been acknowledged by the receiving SCTP, but have not BSNT value have been acknowledged by the receiving SCTP, but have not
been passed up to M2PA. These messages are discarded by the receiving been passed up to M2PA. These messages are discarded by the receiving
SCTP and are not delivered to the upper layer M2PA. Therefore these SCTP and are not delivered to the upper layer M2PA. Therefore these
messages should be retransmitted by the far end on the alternate messages should be retransmitted by the far end on the alternate
link.) link.)
If M2PA receives a Retrieval Request and FSNC request from MTP3, M2PA If M2PA receives a Retrieval Request and FSNC request from MTP3, M2PA
retrieves from SCTP: shall retrieve from SCTP in order and deliver to MTP3:
(a) any transmitted messages beginning with the first (a) any transmitted User Data messages beginning with the first
unacknowledged message with stream sequence number greater unacknowledged message with stream sequence number greater
than FSNC, and than FSNC.
(b) any untransmitted messages in SCTP. (b) any untransmitted User Data messages in SCTP.
Each of these messages is sent to MTP3, first (a), then (b). Then M2PA (c) any untransmitted User Data messages M2PA has not delivered
sends the Retrieval Complete indication to MTP3. to SCTP for transmission.
Then M2PA shall send the Retrieval Complete indication to MTP3.
For emergency changover, 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 SCTP in order and deliver to MTP3:
(a) any untransmitted User Data messages in SCTP.
(b) any untransmitted User Data messages M2PA has not delivered
to SCTP for transmission.
Then M2PA shall send the Retrieval Complete indication to MTP3.
Note: The changeover procedure makes it impossible for M2PA to have Note: The changeover procedure makes it impossible for M2PA to have
multiple User Data streams in a direction for one link. Buffer multiple User Data streams in a direction for one link. Buffer
updating would have to be done for each User Data stream separately to updating would have to be done for each User Data stream separately to
avoid duplication of messages. But MTP3 provides for only one XCO avoid duplication of messages. But MTP3 provides for only one XCO
message for sending the last-received SSN. message for sending the last-received SSN.
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
skipping to change at page 28, line 5 skipping to change at page 35, line 5
(SCTP sends message) (SCTP sends message)
Receive Receive
------------> ------------>
Remote Processor Remote Processor
Outage Ceases Outage Ceases
------------> ------------>
5.5 Congestion Notification to Upper layer 5.5 Level 2 Flow Control
MTP3 expects notification of link congestion. In this example, it is This illustrates the Level 2 Flow Control procedure. In the first
assumed that SCTP notifies M2PA of congestion onset and abatement. The diagram, congestion ceases before timer T6 expires. The second diagram
notification includes the congestion level, if there are levels of shows the case where T6 expires.
congestion defined.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
Implementation dependent Implementation dependent
indication of congestion indication of receive
onset (level) congestion onset
<------------
Link Status Busy
------------------------------------>
Start
Timer T6
Implementation dependent
indication of receive
congestion abatement
<------------
Link Status Busy Ended
------------------------------------>
Stop
Timer T6
MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ----
Implementation dependent
indication of receive
congestion onset
<------------
Link Status Busy
------------------------------------>
Start
Timer T6
:
:
Timer T6
Expires
Abort
<------------
Comm Lost
------------>
Out of Service
------------>
5.6 MTP3 Signaling Link Congestion
In this example, it is assumed that SCTP notifies M2PA of congestion
onset and abatement. The notification includes the congestion level,
if there are levels of congestion defined.
MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ----
Implementation dependent
indication of transmit
congestion onset (level)
<------------ <------------
Congestion Indication Congestion Indication
(level) (level)
<------------ <------------
Implementation dependent Implementation dependent
indication of congestion indication of transmit
abatement (level) congestion abatement (level)
<------------ <------------
Congestion Indication Congestion Indication
(level) (level)
<------------ <------------
5.6 Link Deactivation 5.7 Link Deactivation
The MTP3 can request that a SS7-IP link be taken out-of-service. M2PA The MTP3 can request that a SS7-IP link be taken out-of-service. M2PA
uses the Abort message as shown below. uses the Abort message as shown below.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
Stop Stop
------------> ------------>
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(SCTP performs its (SCTP performs its
termination procedure) termination procedure)
Communication Lost Communication Lost
<------------ <------------
Out of Service Out of Service
<------------ <------------
5.7 Link Changeover 5.8 Link Changeover
In this example, MTP3 performs a changeover because the link went out In this example, MTP3 performs a changeover because the link went out
of service. MTP3 selects a different link for retransmitting the of service. MTP3 selects a different link for retransmitting the
unacknowledged messages. unacknowledged and unsent messages.
Note that in this example, the sequence numbers and messages requested Note that in this example, the sequence numbers and messages requested
by MTP3 are sent from SCTP to M2PA in the Communication Lost by MTP3 are sent from SCTP to M2PA in the Communication Lost
primitive. In general, the retrieval of sequence numbers and messages primitive. In general, the retrieval of sequence numbers and messages
is implementation dependent. is implementation dependent.
MTP3 M2PA SCTP SCTP M2PA MTP3 MTP3 M2PA SCTP SCTP M2PA MTP3
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
Communication Lost Communication Lost
<------------ <------------
Out of Service Out of Service
<------------ <------------
Retrieve BSN Retrieve BSNT
------------> ------------>
(M2PA locates (M2PA locates
first gap in first gap in
received messages) received messages)
Indicate BSN BSNT Indication
<------------ <------------
XCO (BSN) on another link XCO (BSNT) on another link
------------------------------------------------------------> ------------------------------------------------------------>
Retrieve BSN Retrieve BSNT
<------------ <------------
Indicate BSN BSNT Indication
------------> ------------>
XCA (BSN) XCA (BSNT)
<------------------------------------------------------------ <------------------------------------------------------------
Retrieval Request Retrieval Request
and FSNC (FSNC = and FSNC
BSN from XCA message)
------------> ------------>
(M2PA locates (M2PA locates
first gap in first gap in
acknowledgements) acknowledgements)
Retrieved Message Retrieved Message
<------------ <------------
Retrieved Message Retrieved Message
<------------ <------------
Retrieval Complete Retrieval Complete
<------------ <------------
Send messages on another link. Send messages on another link.
6. Security 6. Security
SCN adaptation layers rely on SCTP to provide security. M2PA is designed to carry signaling messages for telephony
services. As such, M2PA MUST involve the security needs of several
parties: the end users of the services, the network providers, and the
applications involved. Additional requirements MAY come from local
regulation. While having some overlapping security needs, any
security solution SHOULD fulfill all of the different parties' needs.
6.1 Threats
There is no quick-fix, one-size-fits-all solution for security. As a
transport protocol, M2PA has the following security objectives:
- Availability of reliable and timely user data transport.
- Integrity of user data transport.
- Confidentiality of user data.
M2PA runs on top of SCTP. SCTP [5] provides certain transport related
security features, such as:
- Blind Denial of Service Attacks
- Flooding
- Masquerade
- Improper Monopolization of Services
When M2PA is running in professionally managed corporate or service
provider network, it is reasonable to expect that this network
includes an appropriate security policy framework. The "Site Security
Handbook" [11] SHOULD be consulted for guidance.
When the network in which M2PA runs involves more than one party, it
MAY NOT be reasonable to expect that all parties have implemented
security in a sufficient manner. In such a case, it is recommended
that IPSEC be used to ensure confidentiality of user payload. Consult
[12] for more information on configuring IPSEC services.
6.2 Protecting Confidentiality
Particularly for mobile users, the requirement for confidentiality MAY
include the masking of IP addresses and ports. In this case
application-level encryption is not sufficient. IPSEC ESP SHOULD be
used instead. Regardless of which level performs the encryption, the
IPSEC ISAKMP service SHOULD be used for key management.
7. IANA Considerations 7. IANA Considerations
The SCTP (and UDP/TCP) Registered User Port Number Assignment for M2PA The SCTP (and UDP/TCP) Registered User Port Number Assignment for M2PA
is TBD. is TBD.
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 TBD M2PA TBD
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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.
8. Acknowledgements 8. Acknowledgements
The authors would like to thank Brian Tatum and Ian Rytina for their The authors would like to thank the following for their valuable
valuable comments and suggestions. comments and suggestions: Brian Tatum, Ian Rytina, Al Varney.
9. References 9. References
[1] ITU-T Recommendation Q.700, 'Introduction To ITU-T Signalling [1] ITU-T Recommendation Q.700, 'Introduction To ITU-T Signalling
System No. 7 (SS7)' System No. 7 (SS7)'
[2] ITU-T Recommendation Q.701-Q.705, 'Signalling System No. 7 [2] ITU-T Recommendation Q.701-Q.705, 'Signalling System No. 7
(SS7) - Message Transfer Part (MTP)' (SS7) - Message Transfer Part (MTP)'
[3] Bellcore GR-246-CORE 'Bell Communications Research Specification [3] ANSI T1.111-2000, American National Standard for
of Signaling System Number 7', Volume 1, December 1995 Telecommunications - Signaling System Number 7 (SS7) -
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-05.txt, [6] SS7 MTP2-User Adaptation Layer, draft-ietf-sigtran-m2ua-07.txt,
November 2000 February 2001
[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',
April 28, 1992. April 28, 1992.
[10] ITU-T Recommendation Q.2140, 'B-ISDN ATM Adaptation Layer',
February 1995
[11] RFC 2196, Site Security Handbook, September 1997
[12] RFC 2401, Security Architecture for the Internet Protocol,
November 1998
[13] SCTP Stream Based Flow Limiting Methods,
draft-ietf-sigtran-srwnd-sctp-00.txt, January 31, 2001
10. Author's Addresses 10. Author's Addresses
Tom George Tel: +1-972-519-3168 Tom George Tel: +1-972-519-3168
Alcatel USA EMail: tom.george@usa.alcatel.com Alcatel USA EMail: tom.george@usa.alcatel.com
1000 Coit Road 1000 Coit Road
Plano, TX 75075 Plano, TX 75075
USA USA
Ram Dantu, Ph.D. Tel: +1-972-234-6070 extension 211 Ram Dantu, Ph.D. Tel: +1-469-255-0716
IPmobile EMail: rdantu@ipmobile.com Cisco Systems Inc. EMail: rdantu@cisco.com
1651 North Glenville, Suite 216 17919 Waterview Parkway
Richardson, TX 75081 Dallas, TX 75252
USA USA
Malleswar Kalla Tel: +1-973-829-5212 Malleswar Kalla Tel: +1-973-829-5212
Telcordia Technologies EMail: kalla@research.telcordia.com Telcordia Technologies EMail: kalla@research.telcordia.com
MCC 1J211R MCC 1J211R
445 South Street 445 South Street
Morristown, NJ 07960 Morristown, NJ 07960
USA USA
Hanns Juergen Schwarzbauer Tel: +49-89-722-24236 Hanns Juergen Schwarzbauer Tel: +49-89-722-24236
skipping to change at page 34, line 44 skipping to change at page 44, line 44
3685 Richmond Rd, 3685 Richmond Rd,
Nepean, Ontario Nepean, Ontario
Canada K2H5B7 Canada K2H5B7
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
This Internet Draft expires May 2001. This Internet Draft expires September 2001.
 End of changes. 

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