RFC 4666
Signaling System 7 (SS7) Message Transfer Part 3 (MTP3) - User Adaptation Layer (M3UA)
4.6. MTP3 Restart
In the case where the MTP3 in the SG undergoes an MTP restart, event communication SHOULD be handled as follows: When the SG discovers SS7 network isolation, the SGPs send an indication to all concerned available ASPs (i.e., ASPs in the ASP- ACTIVE state), using DUNA messages for the concerned destinations. When the SG has completed the MTP Restart procedure, the M3UA layers at the SGPs inform all concerned ASPs in the ASP-ACTIVE state of any available/restricted SS7 destinations, using the DAVA/DRST messages. No message is necessary for those destinations still unavailable after the restart procedure. When the M3UA layer at an ASP receives a DUNA message indicating SS7 destination unavailability at an SG, MTP Users will receive an MTP- PAUSE indication and will stop any affected traffic to this destination. When the M3UA receives a DAVA/DRST message, MTP Users will receive an MTP-RESUME indication and can resume traffic to the newly available SS7 destination, provided that the ASP is in the ASP-ACTIVE state towards this SGP. The ASP MAY choose to audit the availability of unavailable destinations by sending DAUD messages. This would be the case when, for example, an AS becomes active at an ASP and does not have current destination statuses. If MTP restart is in progress at the SG, the SGP returns a DUNA message for that destination, even if it received an indication that the destination became available or restricted. When an ASP becomes active for an AS and the SG is experiencing SS7 network isolation or is performing the MTP Restart procedure for the AS, the SG MAY send a DUNA message for the concerned destinations to the newly active ASP to prevent the ASP from sending traffic. These messages can be sent after receiving the ASP Active, and before sending the ASP Active Ack, to ensure that traffic is not initiated by the ASP to these destinations before the SSNM are received. In addition to DUNA messages, SCON, DRST, and DAVA can also be sent. In the IPSP case, MTP restart could be considered if the IPSP also has connection to an SS7 network. In that case, the same behavior as described above for the SGP would apply to the restarting IPSP. This would also be the case if the IPSPs were perceived as exchanging MTP Peer PDUs, instead of MTP primitives between MTP User and MTP Provider. In other words, M3UA does not provide the equivalent to Traffic Restart Allowed messages indicating the end of the restart procedure between peer IPSPs that would also be connected to an SS7 network.
4.7. NIF Not Available
Implementation Note: Although the NIF is decided to be an implementation dependent function, here are some guidelines that may be useful to follow: - If an SGP is isolated entirely from the NIF, the SGP should send ASP Down Ack to all its connected ASPs. Upon receiving an ASP Up message while isolated from the NIF, the SGP should respond with an Error ("Refused - Management Blocking"). - If an SGP suffers a partial failure (where an SGP can continue to service one or more active AS but due to a partial failure it is unable to service one or more other active AS), the SGP should send ASP Inactive Ack to all its connected ASPs for the affected AS. Upon receiving an ASP Active message for an affected AS while still partially isolated from the NIF, the SGP should respond with an Error ("Refused - Management Blocking"). - If SG is isolated from NIF, it means that each SGP within an SG should follow the procedure mentioned above.4.8. M3UA Version Control
If a message with an unsupported version is received, the receiving end responds with an Error message indicating the version the receiving node supports and notifies Layer Management. This is useful when protocol version upgrades are being performed in a network. A node upgraded to a newer version should support the older versions used on other nodes it is communicating with. Because ASPs initiate the ASP Up procedure, it is likely that the message having an unsupported version is an ASP Up message and therefore that the Error message would normally come from the SGP.4.9. M3UA Termination
Whenever a M3UA node wants to stop the communication with the peer node, it MAY use one of the following procedures: a) Send the sequence of ASP-INACTIVE, DEREG (optionally whenever dynamic registration is used), and ASP-DOWN messages and perform the SCTP Shutdown procedure after that. b) Just do the SCTP Shutdown procedure.
5. Examples of M3UA Procedures
5.1. Establishment of Association and Traffic between SGPs and ASPs
These scenarios show examples of M3UA message flows for the establishment of traffic between an SGP and an ASP or between two IPSPs. In all cases it is assumed that the SCTP association is already set up.5.1.1. Single ASP in an Application Server ("1+0" sparing), No Registration
These scenarios show examples of M3UA message flows for the establishment of traffic between an SGP and an ASP where only one ASP is configured within an AS (no backup).5.1.1.1. Single ASP in an Application Server ("1+0" Sparing), No Registration
SGP ASP1 | | |<-------------ASP Up-----------| |-----------ASP Up Ack--------->| | | |-----NTFY(AS-INACTIVE)(RCn)--->| | | |<------- ASP Active(RCn)-------| RC: Routing Context |-----ASP Active Ack (RCn)----->| (optional) | | |-----NTFY(AS-ACTIVE)(RCn)----->| | | Note: If the ASP Active message contains an optional Routing Context parameter, the ASP Active message only applies for the specified RC value(s). For an unknown RC value, the SGP responds with an Error message.
5.1.1.2. Single ASP in Application Server ("1+0" Sparing), Dynamic Registration
This scenario is the same as for 5.1.1.1 but with the optional exchange of registration information. In this case, the Registration is accepted by the SGP. SGP ASP1 | | |<------------ASP Up------------| |----------ASP Up Ack---------->| | | | | |<----REGISTER REQ(LRCn,RKn)----| LRC: Local Routing | | Key Id |----REGISTER RESP(LRCn,RCn)--->| RK: Routing Key | | RC: Routing Context |----NTFY(AS-INACTIVE)(RCn)---->| | | | | |<------- ASP Active(RCn)-------| |-----ASP Active Ack (RCn)----->| | | |-----NTFY(AS-ACTIVE)(RCn)----->| | | Note: In the case of an unsuccessful registration attempt (e.g., invalid RKn), the Register Response message will contain an unsuccessful indication, and the ASP will not subsequently send an ASP Active message.
5.1.1.3. Single ASP in Multiple Application Servers (Each with "1+0" Sparing), Dynamic Registration (Case 1 - Multiple Registration Requests)
SGP ASP1 | | |<------------ASP Up------------| |----------ASP Up Ack---------->| | | |<----REGISTER REQ(LRC1,RK1)----| LRC: Local Routing | | Key Id |----REGISTER RESP(LRC1,RC1)--->| RK: Routing Key | | RC: Routing Context |---NOTIFY(AS-INACTIVE)(RC1)--->| | | | | |<------- ASP Active(RC1)-------| |-----ASP Active Ack (RC1)----->| | | |----NOTIFY(AS-ACTIVE)(RC1)---->| | | ~ ~ | | |<----REGISTER REQ(LRCn,RKn)----| | | |----REGISTER RESP(LRCn,RCn)--->| | | |---NOTIFY(AS-INACTIVE)(RCn)--->| | | |<------- ASP Active(RCn)-------| |-----ASP Active Ack (RCn)----->| | | |----NOTIFY(AS-ACTIVE)(RCn)---->| | | Note: In the case of an unsuccessful registration attempt (e.g., invalid RKn), the Register Response message will contain an unsuccessful indication, and the ASP will not subsequently send an ASP Active message. Each LRC/RK pair registration is considered independently. It is not necessary to follow a Registration Request/Response message pair with an ASP Active message before sending the next Registration Request. The ASP Active message can be sent at any time after the related successful registration.
5.1.1.4. Single ASP in Multiple Application Servers (each with "1+0" sparing), Dynamic Registration (Case 2 - Single Registration Request)
SGP ASP1 | | |<------------ASP Up------------| |----------ASP Up Ack---------->| | | | | |<---REGISTER REQ({LRC1,RK1}, | | ..., | | {LRCn,RKn}),--| | | |---REGISTER RESP({LRC1,RC1},-->| | ..., | | (LRCn,RCn}) | | | |--NTFY(AS-INACTIVE)(RC1..RCn)->| | | | | |<------- ASP Active(RC1)-------| |-----ASP Active Ack (RC1)----->| | | |----NOTIFY(AS-ACTIVE)(RC1)---->| | | : : : : | | |<------- ASP Active(RCn)-------| |-----ASP Active Ack (RCn)----->| | | |----NOTIFY(AS-ACTIVE)(RCn)---->| | | Note: In the case of an unsuccessful registration attempt (e.g., Invalid RKn), the Register Response message will contain an unsuccessful indication, and the ASP will not subsequently send an ASP Active message. Each LRC/RK pair registration is considered independently. The ASP Active message can be sent at any time after the related successful registration and may have more than one RC.
5.1.2. Two ASPs in Application Server ("1+1" Sparing)
This scenario shows example M3UA message flows for the establishment of traffic between an SGP and two ASPs in the same Application Server, where ASP1 is configured to be in the ASP-ACTIVE state and ASP2 is to be a "backup" in the event of communication failure or the withdrawal from service of ASP1. ASP2 may act as a hot, warm, or cold backup, depending on the extent to which ASP1 and ASP2 share call/transaction state or can communicate call state under failure/withdrawal events. The example message flow is the same whether the ASP Active messages indicate "Override", "Loadshare", or "Broadcast" mode, although typically this example would use an Override mode. SGP ASP1 ASP2 | | | |<--------ASP Up---------| | |-------ASP Up Ack------>| | | | | |--NOTIFY(AS-INACTIVE)-->| | | | | |<----------------------------ASP Up----------------| |----------------------------ASP Up Ack------------>| | | | |--------------------------NOTIFY(AS-INACTIVE)----->| | | | | | | |<-------ASP Active------| | |------ASP Active Ack--->| | | | | |---NOTIFY(AS-ACTIVE)--->| | |--------------------------NOTIFY(AS-ACTIVE)------->| | | |
5.1.3. Two ASPs in an Application Server ("1+1" Sparing, Loadsharing Case)
This scenario shows a case similar to Section 5.1.2, but where the two ASPs are brought to the state ASP-ACTIVE and subsequently loadshare the traffic. In this case, one ASP is sufficient to handle the total traffic load. SGP ASP1 ASP2 | | | |<---------ASP Up--------| | |--------ASP Up Ack----->| | | | | |--NOTIFY(AS-INACTIVE)-->| | | | | |<-----------------------------ASP Up---------------| |----------------------------ASP Up Ack------------>| | | | |--------------------------NOTIFY(AS-INACTIVE)----->| | | | |<--ASP Active (Ldshr)---| | |-----ASP-Active Ack---->| | | | | |---NOTIFY (AS-ACTIVE)-->| | |-----------------------------NOTIFY(AS-ACTIVE)---->| | | | |<---------------------------ASP Active (Ldshr)-----| |------------------------------ASP Active Ack------>| | | |
5.1.4. Three ASPs in an Application Server ("n+k" Sparing, Loadsharing Case)
This scenario shows example M3UA message flows for the establishment of traffic between an SGP and three ASPs in the same Application Server, where two of the ASPs are brought to the state ASP-ACTIVE and subsequently share the load. In this case, a minimum of two ASPs are required to handle the total traffic load (2+1 sparing). SGP ASP1 ASP2 ASP3 | | | | |<------ASP Up------| | | |-----ASP Up Ack--->| | | | | | | |NTFY(AS-INACTIVE)->| | | | | | | |<-------------------------ASP Up-------| | |------------------------ASP Up Ack---->| | | | | | |------------------NOTIFY(AS-INACTIVE)->| | | | | | |<--------------------------------------------ASP Up--------| |--------------------------------------------ASP Up Ack---->| | | | | |--------------------------------------NOTIFY(AS-INACTIVE)->| | | | | | | | | |<--ASP Act (Ldshr)-| | | |----ASP Act Ack--->| | | | | | | | | | | |<-------------------ASP Act. (Ldshr)---| | |----------------------ASP Act Ack----->| | | | | | |--NTFY(AS-ACTIVE)->| | | |--------------------NOTIFY(AS-ACTIVE)->| | |----------------------------------------NOTIFY(AS-ACTIVE)->| | | | | | | | |
5.2. ASP Traffic Failover Examples
5.2.1. 1+1 Sparing, Withdrawal of ASP, Backup Override
Following from the example in Section 5.1.2, ASP1 withdraws from service: SGP ASP1 ASP2 | | | |<-----ASP Inactive------| | |----ASP Inactive Ack--->| | | | | |----NTFY(AS-PENDING)--->| | |-----------------------NTFY(AS-PENDING)----------->| | | | |<----------------------------- ASP Active----------| |-----------------------------ASP Active Ack------->| | | | |----NTFY(AS-ACTIVE)---->| | |-----------------------NTFY(AS-ACTIVE)------------>| Note: If the SGP M3UA layer detects the loss of the M3UA peer (e.g., M3UA heartbeat loss or detection of SCTP failure), the initial ASP Inactive message exchange (i.e., SGP to ASP1) would not occur.5.2.2. 1+1 Sparing, Backup Override
Following on from the example in Section 5.1.2, ASP2 wishes to Override ASP1 and take over the traffic: SGP ASP1 ASP2 | | | |<----------------------------- ASP Active----------| |------------------------------ASP Active Ack------>| |----NTFY(Alt ASP-Act)-->| | | | |
5.2.3. n+k Sparing, Loadsharing Case, Withdrawal of ASP
Following from the example in Section 5.1.4, ASP1 withdraws from service: SGP ASP1 ASP2 ASP3 | | | | |<----ASP Inact.----| | | |---ASP Inact Ack-->| | | | | | | |--NTFY(Ins. ASPs)->| | | |---------------------------------------NOTIFY(Ins. ASPs)-->| | | | | | | | | |<----------------------------------------ASP Act (Ldshr)---| |------------------------------------------ASP Act (Ack)--->| | | | | |-NTFY(AS-ACTIVE)-->| | | |-------------------NOTIFY(AS-ACTIVE)-->| | |---------------------------------------NOTIFY(AS-ACTIVE)-->| | | | | | | | | For the Notify message to be sent, the SG maintains knowledge of the minimum ASP resources required (e.g., if the SG knows that "n+k" = "2+1" for a Loadshare AS and "n" currently equals "1"). Note: If the SGP detects loss of the ASP1 M3UA peer (e.g., M3UA heartbeat loss or detection of SCTP failure), the initial ASP Inactive message exchange (i.e., SGP-ASP1) would not occur.5.3. Normal Withdrawal of an ASP from an Application Server and Teardown of an Association
An ASP that is now confirmed in the state ASP-INACTIVE (i.e., the ASP has received an ASP Inactive Ack message) may now proceed to the ASP-DOWN state, if it is to be removed from service. Following from Section 5.2.1 or 5.2.3, where ASP1 has moved to the "Inactive" state:
SGP ASP1
| |
|<-----ASP Inactive (RCn)------| RC: Routing Context
|----ASP Inactive Ack (RCn)--->|
| |
|<-----DEREGISTER REQ(RCn)-----| See Notes
| |
|---DEREGISTER RESP(LRCn,RCn)->|
| |
: :
| |
|<-----------ASP Down----------|
|---------ASP Down Ack-------->|
| |
Note: The Deregistration procedure will typically be used if the ASP
previously used the Registration procedures for configuration within
the Application Server. ASP Inactive and Deregister messages
exchanges may contain multiple Routing Contexts.
The ASP should be in the ASP-INACTIVE state and should have
deregistered in all its Routing Contexts before attempting to move to
the ASP-DOWN state.
5.4. Auditing Examples
5.4.1. SG State: Uncongested/Available
ASP SGP
--- ---
| -------- DAUD ---------> |
| <------ SCON(0) -------- |
| <------- DAVA ---------- |
5.4.2. SG State: Congested (Congestion Level=2) / Available
ASP SGP
--- ---
| -------- DAUD ---------> |
| <------ SCON(2) -------- |
| <------- DAVA ---------- |
5.4.3. SG State: Unknown/Available
ASP SGP
--- ---
| -------- DAUD ---------> |
| <------- DAVA ---------- |
5.4.4. SG State: Unavailable
ASP SGP --- --- | -------- DAUD ---------> | | <------- DUNA ---------- |5.5. M3UA/MTP3-User Boundary Examples
5.5.1. At an ASP
This section describes the primitive mapping between the MTP3 User and the M3UA layer at an ASP.5.5.1.1. Support for MTP-TRANSFER Primitives at the ASP
5.5.1.1.1. Support for MTP-TRANSFER Request Primitive
When the MTP3-User on the ASP has data to send to a remote MTP3-User, it uses the MTP-TRANSFER request primitive. The M3UA layer at the ASP will do the following when it receives an MTP-TRANSFER request primitive from the M3UA user: - Determine the correct SGP. - Determine the correct association to the chosen SGP. - Determine the correct stream in the association (e.g., based on SLS). - Determine whether to complete the optional fields of the DATA message. - Map the MTP-TRANSFER request primitive into the Protocol Data field of a DATA message. - Send the DATA message to the remote M3UA peer at the SGP, over the SCTP association. SGP ASP | | |<-----DATA Message-------|<--MTP-TRANSFER req. | |5.5.1.1.2. Support for the MTP-TRANSFER Indication Primitive
When the M3UA layer on the ASP receives a DATA message from the M3UA peer at the remote SGP, it will do the following:
- Evaluate the optional fields of the DATA message, if present.
- Map the Protocol Data field of a DATA message into the
MTP-TRANSFER indication primitive.
- Pass the MTP-TRANSFER indication primitive to the user part. In
case of multiple user parts, the optional fields of the Data
message are used to determine the concerned user part.
SGP ASP
| |
|------Data Message------>|-->MTP-Transfer ind.
| |
5.5.1.1.3. Support for ASP Querying of SS7 Destination States
There are situations such as temporary loss of connectivity to the
SGP that may cause the M3UA layer at the ASP to audit SS7 destination
availability/congestion states. Note: there is no primitive for the
MTP3-User to request this audit from the M3UA layer, as this is
initiated by an internal M3UA management function.
SGP ASP
| |
|<----------DAUD-----------|
|<----------DAUD-----------|
|<----------DAUD-----------|
| |
| |
5.5.2. At an SGP
This section describes the primitive mapping between the MTP3-User
and the M3UA layer at an SGP.
5.5.2.1. Support for MTP-TRANSFER Request Primitive at the SGP
When the M3UA layer at the SGP has received DATA messages from its
peer destined to the SS7 network, it will do the following:
- Evaluate the optional fields of the DATA message, if present, to
determine the Network Appearance.
- Map the Protocol data field of the DATA message into an
MTP-TRANSFER request primitive.
- Pass the MTP-TRANSFER request primitive to the MTP3 of the
concerned Network Appearance.
SGP ASP
| |
<---MTP-TRANSFER req.|<---------DATA -----------|
| |
5.5.2.2. Support for MTP-TRANSFER Indication Primitive at the SGP
When the MTP3 layer at the SGP has data to pass its user parts, it
will use the MTP-TRANSFER indication primitive. The M3UA layer at
the SGP will do the following when it receives an MTP-TRANSFER
indication primitive:
- Determine the correct AS, using the distribution function;
- Select an ASP in the ASP-ACTIVE state.
- Determine the correct association to the chosen ASP.
- Determine the correct stream in the SCTP association (e.g.,
based on SLS).
- Determine whether to complete the optional fields of the DATA
message.
- Map the MTP-TRANSFER indication primitive into the Protocol Data
field of a DATA message.
- Send the DATA message to the remote M3UA peer in the ASP, over
the SCTP association.
SGP ASP
| |
--MTP-TRANSFER ind.->|-----------DATA --------->|
| |
5.5.2.3. Support for MTP-PAUSE, MTP-RESUME, MTP-STATUS Indication
Primitives
The MTP-PAUSE, MTP-RESUME, and MTP-STATUS indication primitives from
the MTP3 upper layer interface at the SGP need to be made available
to the remote MTP3 User Part lower-layer interface at the concerned
ASP(s).
5.5.2.3.1. Destination Unavailable
The MTP3 layer at the SGP will generate an MTP-PAUSE indication
primitive when it determines locally that an SS7 destination is
unreachable. The M3UA layer will map this primitive to a DUNA
message. The SGP M3UA layer determines the set of concerned ASPs to
be informed based on internal SS7 network information associated with
the MTP-PAUSE indication primitive indication.
SGP ASP
| |
--MTP-PAUSE ind.-->|---------DUNA----------->|--MTP-PAUSE ind.-->
| |
5.5.2.3.2. Destination Available
The MTP3 at the SGP will generate an MTP-RESUME indication primitive
when it determines locally that an SS7 destination that was
previously unreachable is now reachable. The M3UA layer will map
this primitive to a DAVA message. The SGP M3UA determines the set of
concerned ASPs to be informed based on internal SS7 network
information associated with the MTP-RESUME indication primitive.
SGP ASP
| |
--MTP-RESUME ind.-->|-----------DAVA--------->|--MTP-RESUME ind.-->
| |
5.5.2.3.3. SS7 Network Congestion
The MTP3 layer at the SGP will generate an MTP-STATUS indication
primitive when it determines locally that the route to an SS7
destination is congested. The M3UA layer will map this primitive to
a SCON message. It will determine which ASP(s) to send the SCON
message to, based on the intended Application Server.
SGP ASP
| |
--MTP-STATUS ind.-->|-----------SCON--------->|--MTP-STATUS ind.-->
| |
5.5.2.3.4. Destination User Part Unavailable
The MTP3 layer at the SGP will generate an MTP-STATUS indication
primitive when it receives an UPU message from the SS7 network. The
M3UA layer will map this primitive to a DUPU message. It will
determine which ASP(s) to send the DUPU to based on the intended
Application Server.
SGP ASP
| |
--MTP-STATUS ind.-->|----------DUPU---------->|--MTP-STATUS ind.-->
| |
5.6. Examples for IPSP Communication
These scenarios show a basic example for IPSP communication for the three phases of the connection (establishment, data exchange, disconnection). It is assumed that the SCTP association is already set up. Both single exchange and double exchange behavior are included for illustrative purposes.5.6.1. Single Exchange
IPSP-A IPSP-B | | |-------------ASP Up------------>| |<----------ASP Up Ack-----------| | | |<------- ASP Active(RCb)--------| RC: Routing Context |-----ASP Active Ack (RCb)------>| (optional) | | | | |<========= DATA (RCb) ========>| | | |<-----ASP Inactive (RCb)--------| RC: Routing Context |----ASP Inactive Ack (RCb)----->| (optional) | | |<-----------ASP Down------------| |---------ASP Down Ack---------->| | | Routing Context is previously agreed to be the same in both directions.
5.6.2. Double Exchange
IPSP-A IPSP-B | | |<-------------ASP Up------------| |-----------ASP Up Ack---------->| | | |-------------ASP Up------------>| (optional) |<----------ASP Up Ack-----------| (optional) | | |<------- ASP Active(RCb)--------| RC: Routing Context |-----ASP Active Ack (RCb)------>| (optional) | | |------- ASP Active(RCa)-------->| RC: Routing Context |<-----ASP Active Ack (RCa)------| (optional) | | |<========= DATA (RCa) =========| |========== DATA (RCb) ========>| | | |<-----ASP Inactive (RCb)--------| RC: Routing Context |----ASP Inactive Ack (RCb)----->| | | |------ASP Inactive (RCa)------->| RC: Routing Context |<----ASP Inactive Ack (RCa)-----| | | |<-----------ASP Down------------| |---------ASP Down Ack---------->| | | |------------ASP Down----------->| (optional) |<--------ASP Down Ack-----------| (optional) | | In this approach, only one single exchange of ASP Up message can be considered sufficient since the response by the other peer can be considered a notice that it is in ASP_UP state. For the same reason, only one ASP Down message is needed, since once an IPSP receives ASP_Down ack message it is itself considered to be in the ASP_Down state and not allowed to receive ASPSM messages.6. Security Considerations
Implementations MUST follow the normative guidance of RFC3788 [11] on the integration and usage of security mechanisms in SIGTRAN protocols.
7. IANA Considerations
This document contains no new actions for IANA. The subsections below are retained for historical purposes.7.1. SCTP Payload Protocol Identifier
IANA has assigned an M3UA value for the Payload Protocol Identifier in the SCTP DATA chunk. The following SCTP Payload Protocol Identifier has been registered: M3UA "3" The SCTP Payload Protocol Identifier value "3" SHOULD be included in each SCTP DATA chunk, to indicate that the SCTP is carrying the M3UA protocol. The value "0" (unspecified) is also allowed but any other values MUST not be used. This Payload Protocol Identifier is not directly used by SCTP but MAY be used by certain network entities to identify the type of information being carried in a DATA chunk. The User Adaptation peer MAY use the Payload Protocol Identifier as a way of determining additional information about the data being presented to it by SCTP.7.2. M3UA Port Number
IANA has registered SCTP (and UDP/TCP) Port Number 2905 for M3UA. It is recommended that SGPs use this SCTP port number for listening for new connections. SGPs MAY also use statically configured SCTP port numbers instead.7.3. M3UA Protocol Extensions
This protocol may also be extended through IANA in three ways: - Through definition of additional message classes. - Through definition of additional message types. - Through definition of additional message parameters. The definition and use of new message classes, types, and parameters is an integral part of SIGTRAN adaptation layers. Thus, these extensions are assigned by IANA through an IETF Consensus action as defined in Guidelines for Writing an IANA Considerations Section in RFCs [23]. The proposed extension must in no way adversely affect the general working of the protocol.
7.3.1. IETF-Defined Message Classes
The documentation for a new message class MUST include the following information: (a) A long and short name for the new message class. (b) A detailed description of the purpose of the message class.7.3.2. IETF Defined Message Types
The documentation for a new message type MUST include the following information: (a) A long and short name for the new message type. (b) A detailed description of the structure of the message. (c) A detailed definition and description of intended use for each field within the message. (d) A detailed procedural description of the use of the new message type within the operation of the protocol. (e) A detailed description of error conditions when receiving this message type. When an implementation receives a message type that it does not support, it MUST respond with an Error (ERR) message ("Unsupported Message Type").7.3.3. IETF-Defined Parameter Extension
Documentation of the message parameter MUST contain the following information: (a) Name of the parameter type. (b) Detailed description of the structure of the parameter field. This structure MUST conform to the general type-length-value format described in Section 3.2. (c) Detailed definition of each component of the parameter value. (d) Detailed description of the intended use of this parameter type, and an indication of whether and under what circumstances multiple instances of this parameter type may be found within the same message.8. Acknowledgements
The authors would like to thank Antonio Roque Alvarez, Joyce Archibald, Tolga Asveren, Maria-Cruz Bartolome-Rodrigo, Dan Brendes, Antonio Canete, Nikhil Jain, Roland Jesske, Joe Keller, Kurt Kite, Ming Lin, Steve Lorusso, Naoto Makinae, Howard May, Francois Mouillaud, Barry Nagelberg, Neil Olson, Heinz Prantner, Shyamal
Prasad, Mukesh Punhani, Selvam Rengasami, John Schantz, Ray Singh, Michael Tuexen, Nitin Tomar, Gery Verwimp, Tim Vetter, Kazuo Watanabe, Ben Wilson, and many others for their valuable comments and suggestions.9. Document Contributors
Ian Rytina - Ericsson Guy Mousseau - Nortel Networks Lyndon Ong - Ciena Hanns Juergen Schwarzbauer - Siemens Klaus Gradischnig - Detecon Inc. Mallesh Kalla - Telcordia Normand Glaude - Performance Technologies Brian Bidulock - OpenSS7 John Loughney - Nokia Greg Sidebottom - Signatus Technologies10. References
10.1. Normative References
[1] ITU-T Recommendations Q.761 to Q.767, "Signalling System No.7 (SS7) - ISDN User Part (ISUP)" [2] ANSI T1.113 - "Signaling System Number 7 - ISDN User Part" [3] ETSI ETS 300 356-1 "Integrated Services Digital Network (ISDN); Signalling System No.7; ISDN User Part (ISUP) version 2 for the international interface; Part 1: Basic services" [4] ITU-T Recommendations Q.711 to Q.715, "Signalling System No. 7 (SS7) - Signalling Connection Control Part (SCCP)" [5] ANSI T1.112 "Signaling System Number 7 - Signaling Connection Control Part" [6] ETSI ETS 300 009-1, "Integrated Services Digital Network (ISDN); Signalling System No.7; Signalling Connection Control Part (SCCP) (connectionless and connection-oriented class 2) to support international interconnection; Part 1: Protocol specification" [7] ITU-T Recommendations Q.700 to Q.705, "Signalling System No. 7 (SS7) - Message Transfer Part (MTP)" [8] ANSI T1.111 "Signaling System Number 7 - Message Transfer Part"
[9] ETSI ETS 300 008-1, "Integrated Services Digital Network (ISDN); Signalling System No.7; Message Transfer Part (MTP) to support international interconnection; Part 1: Protocol specification" [10] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [11] Loughney, J., Tuexen, M., and J. Pastor-Balbas, "Security Considerations for Signaling Transport (SIGTRAN) Protocols", RFC 3788, June 2004.10.2. Informative References
[12] Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H., Coene, L., Lin, H., Juhasz, I., Holdrege, M., and C. Sharp, "Framework Architecture for Signaling Transport", RFC 2719, October 1999. [13] ITU-T Recommendation Q.720, "Telephone User Part" [14] ITU-T Recommendations Q.771 to Q.775 "Signalling System No. 7 (SS7) - Transaction Capabilities (TCAP)" [15] ANSI T1.114 "Signaling System Number 7 - Transaction Capabilities Application Part" [16] ETSI ETS 300 287-1, "Integrated Services Digital Network (ISDN); Signalling System No.7; Transaction Capabilities (TC) version 2; Part 1: Protocol specification" [17] 3G TS 25.410 V4.0.0 (2001-04) "Technical Specification - 3rd Generation partnership Project; Technical Specification Group Radio Access Network; UTRAN Iu Interface: General Aspects and Principles" [18] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V. Paxson, "Stream Control Transmission Protocol", RFC 2960, October 2000. [19] ITU-T Recommendation Q.2140 "B-ISDN ATM Adaptation Layer - Service Specific Coordination Function for signalling at the Network Node Interface (SSCF at NNI)" [20] ITU-T Recommendation Q.2110 "B-ISDN ATM Adaptation Layer - Service Specific Connection Oriented Protocol (SSCOP)" [21] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[22] ITU-T Recommendation Q.2210 "Message Transfer Part Level 3 functions and messages using the services of ITU Recommendation Q.2140" [23] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [24] Morneault, K., Dantu, R., Sidebottom, G., Bidulock, B., and J. Heitz, "Signaling System 7 (SS7) Message Transfer Part 2 (MTP2) - User Adaptation Layer", RFC 3331, September 2002. [25] George, T., Bidulock, B., Dantu, R., Schwarzbauer, H., and K. Morneault, "Signaling System 7 (SS7) Message Transfer Part 2 (MTP2) - User Peer-to-Peer Adaptation Layer (M2PA)", RFC 4165, September 2005. [26] Telecommunication Technology Committee (TTC) Standard JT-Q704, "Message Transfer Part Signaling Network Functions", April 28, 1992.
Appendix A
A.1. Signalling Network Architecture
A Signalling Gateway is used to support the transport of MTP3-User signalling traffic received from the SS7 network to multiple distributed ASPs (e.g., MGCs and IP Databases). Clearly, the M3UA protocol is not designed to meet the performance and reliability requirements for such transport by itself. However, the conjunction of distributed architecture and redundant networks provides support for reliable transport of signalling traffic over IP. The M3UA protocol is flexible enough to allow its operation and management in a variety of physical configurations, enabling Network Operators to meet their performance and reliability requirements. To meet the stringent SS7 signalling reliability and performance requirements for carrier grade networks, Network Operators might require that no single point of failure is present in the end-to-end network architecture between an SS7 node and an IP-based application. This can typically be achieved through the use of redundant SGPs or SGs, redundant hosts, and the provision of redundant QOS-bounded IP network paths for SCTP Associations between SCTP End Points. Obviously, the reliability of the SG, the MGC, and other IP-based functional elements also needs to be taken into account. The distribution of ASPs and SGPs within the available Hosts MAY also be considered. As an example, for a particular Application Server, the related ASPs could be distributed over at least two Hosts. One example of a physical network architecture relevant to SS7 carrier grade operation in the IP network domain is shown in Figure A-1, below:
SGs MGCs Host#1 ************** ************** Host#3 * ********__*__________________________*__******** * = * *SGP1.1*__*_____ _______________*__* ASP1 * * MGC1 * ******** * \ / * ******** * * ********__*______\__/________________*__******** * * *SGP2.1*__*_______\/______ _____*__* ASP2 * * * ******** * /\ | | * ******** * * : * / \ | | * : * * ******** * / \ | | * ******** * * * SGPn * * | | | | * * ASPn * * * ******** * | | | | * ******** * ************** | | | | ************** | | \ / Host#2 ************** | | \ / ************** Host#4 * ********__*_____| |______\/_______*__******** * = * *SGP1.2*__*_________________/\_______*__* ASP1 * * MGC2 * ******** * / \ * ******** * * ********__*_______________/ \_____*__******** * * *SGP2.2*__*__________________________*__* ASP2 * * * ******** * * ******** * * : * SCTP Associations * : * * ******** * * ******** * * * SGPn * * * * ASPn * * * ******** * * ******** * ************** ************** SGP1.1 and SGP1.2 are part of SG1 SGP2.1 and SGP2.2 are part of SG2 Figure A-1 - Physical Model In this model, each host may have many application processes. In the case of the MGC, an ASP may provide service to one or more Application Servers, and is identified as an SCTP end point. One or more Signalling Gateway Processes make up a single Signalling Gateway. This example model can also be applied to IPSP-IPSP signalling. In this case, each IPSP may have its services distributed across 2 or more hosts, and may have multiple server processes on each host. In the example above, each signalling process (SGP, ASP, or IPSP) is the end point to more than one SCTP association, leading to more than one other signalling processes. To support this, a signalling process must be able to support distribution of M3UA messages to many simultaneous active associations. This message distribution function
is based on the status of provisioned Routing Keys, the status of the signalling routes to signalling points in the SS7 network, and the redundancy model (active-standby, load sharing, broadcast, n+k) of the remote signalling processes. For carrier grade networks, the failure or isolation of a particular signalling process should not cause stable calls or transactions to be lost. This implies that signalling processes need, in some cases, to share the call/transaction state or be able to pass the call state information between each other. In the case of ASPs performing call processing, coordination may also be required with the related Media Gateway to transfer the MGC control for a particular trunk termination. However, this sharing or communication of call/transaction state information is outside the scope of this document. This model serves as an example. M3UA imposes no restrictions as to the exact layout of the network elements, the message distribution algorithms, and the distribution of the signalling processes. Instead, it provides a framework and a set of messages that allow for a flexible and scalable signalling network architecture, aiming to provide reliability and performance.A.2. Redundancy Models
A.2.1. Application Server Redundancy
At the SGP, an Application Server list contains active and inactive ASPs to support ASP broadcast, loadsharing, and failover procedures. The list of ASPs within a logical Application Server is kept updated in the SGP to reflect the active Application Server Process(es). For example, in the network shown in Figure 1, all messages to DPC x could be sent to ASP1 in Host3 or ASP1 in Host4. The AS list at SGP1 in Host 1 might look like the following: Routing Key {DPC=x) - "Application Server #1" ASP1/Host3 - State = Active ASP1/Host4 - State = Inactive In this "1+1" redundancy case, ASP1 in Host3 would be sent any incoming message with DPC=x. ASP1 in Host4 would normally be brought to the "active" state upon failure of, or loss of connectivity to, ASP1/Host1. The AS List at SGP1 in Host1 might also be set up in loadshare mode:
Routing Key {DPC=x) - "Application Server #1"
ASP1/Host3 - State = Active
ASP1/Host4 - State = Active
In this case, both the ASPs would be sent a portion of the traffic.
For example, the two ASPs could together form a database, where
incoming queries may be sent to any active ASP.
Care might need to be exercised by a Network Operator in the
selection of the routing information to be used as the Routing Key
for a particular AS.
In the process of failover, it is recommended that, in the case of
ASPs supporting call processing, stable calls do not fail. It is
possible that calls in "transition" may fail, although measures of
communication between the ASPs involved can be used to mitigate this.
For example, the two ASPs may share call state via shared memory, or
may use an ASP to ASP protocol to pass call state information. Any
ASP-to-ASP protocol to support this function is outside the scope of
this document.
A.2.2. Signalling Gateway Redundancy
Signalling Gateways may also be distributed over multiple hosts.
Much like the AS model, SGs may comprise one or more SG Processes
(SGPs), distributed over one or more hosts, using an active/backup or
a loadsharing model. Should an SGP lose all or partial SS7
connectivity and other SGPs exist, the SGP may terminate the SCTP
associations to the concerned ASPs.
It is therefore possible for an ASP to route signalling messages
destined to the SS7 network using more than one SGP. In this model,
a Signalling Gateway is deployed as a cluster of hosts acting as a
single SG. A primary/backup redundancy model is possible, where the
unavailability of the SCTP association to a primary SGP could be used
to reroute affected traffic to an alternate SGP. A loadsharing model
is possible, where the signalling messages are loadshared between
multiple SGPs. A broadcast model is also possible, where signalling
messages are sent to each active SGP in the SG. The distribution of
the MTP3-user messages over the SGPs should be done in such a way to
minimize message missequencing, as required by the SS7 User Parts.
It may also be possible for an ASP to use more than one SG to access
a specific SS7 end point, in a model that resembles an SS7 STP mated
pair. Typically, SS7 STPs are deployed in mated pairs, with traffic
loadshared between them. Other models are also possible, subject to
the limitations of the local SS7 network provisioning guidelines.
From the perspective of the M3UA layer at an ASP, a particular SG is capable of transferring traffic to a provisioned SS7 destination X if an SCTP association with at least one SGP of the SG is established, the SGP has returned an acknowledgement to the ASP to indicate that the ASP is actively handling traffic for that destination X, the SGP has not indicated that the destination X is inaccessible, and the SGP has not indicated MTP Restart. When an ASP is configured to use multiple SGPs for transferring traffic to the SS7 network, the ASP must maintain knowledge of the current capability of the SGPs to handle traffic to destinations of interest. This information is crucial to the overall reliability of the service, for active/backup, loadsharing, and broadcast models, in the event of failures and recovery and maintenance activities. The ASP M3UA may also use this information for congestion avoidance purposes. The distribution of the MTP3-user messages over the SGPs should be done in such a way as to minimize message missequencing, as required by the SS7 User Parts.Editors' Addresses
Ken Morneault Cisco Systems Inc. 13615 Dulles Technology Drive Herndon, VA, USA 20171 EMail: kmorneau@cisco.com Javier Pastor-Balbas Ericsson Espana S.A. C/ Retama 1 28045 Madrid - Spain EMail: j.javier.pastor@ericsson.com
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