draft-ietf-sigtran-m2pa-03.txt

No7信令,我需要交换类似的代码, 请店长审核,谢谢了,急着交换,谢谢

Figure 2 shows an example of M2PA used in a Signaling Gateway
(SG). The SG is an IPSP equipped with both traditional SS7 and IP
network connections.  In effect, the Signaling Gateway acts as a
Signal Transfer Point (STP).  Any of the nodes in the diagram could
have SCCP or other SS7 layers. STPs may or may not be present in the
SS7 path between the SEP and the SG.






















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    ********  SS7   ***************   IP   ********
    * SEP  *--------*     SG      *--------* IPSP *
    ********        ***************        ********

    +------+                               +------+
    | TCAP |                               | TCAP |
    +------+                               +------+
    | SCCP |                               | SCCP |
    +------+        +-------------+        +------+
    | MTP3 |        |    MTP3     |        | MTP3 | 
    +------+        +------+------+        +------+    
    | MTP2 |        | MTP2 | M2PA |        | M2PA |    
    +------+        +------+------+        +------+    
    | MTP1 |        | MTP1 | SCTP |        | SCTP | 
    |      |        |      +------+        +------+
    |      |        |      | IP   |        | IP   |
    +------+        +------+------+        +------+

    SEP   - SS7 Signaling Endpoint

         Figure 2:  M2PA in IP Signaling Gateway


Figure 2 is only an example. Other configurations are possible. For
example, IPSPs without traditional SS7 links could use the protocol
layers MTP3/M2PA/SCTP/IP to route SS7 messages in a network with all
IP links.

Another example, related to Figure 2, is that two SGs could be
connected over an IP network to form an SG mated pair similar to the
way STPs are provisioned in traditional SS7 networks.


1.5.1  Point Code Representation

The MTP specification requires that each node with an MTP3 layer is
identified by an SS7 point code. In particular, each IPSP must have
its own SS7 point code.

1.6 Services Provided by M2PA

The SS7 MTP3/MTP2 (MTP2-User) interface is retained in the IPSP. The
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.

These services are described in the following subsections.

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
[2], [3] and [10], with the addition of support for larger sequence
numbers in [3] and [7].


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Because SCTP uses larger sequence numbers than MTP, the MTP3
Changeover procedure must use the Extended Changeover Order and
Extended Changeover Acknowledgment messages described in [7] and
[3]. This will allow for use of the SCTP stream sequence numbers in
the changeover messages.

Also, the following MTP3/MTP2 primitives must use the larger sequence
numbers:

   - BSNT Confirmation

   - Retrieval Request and FSNC


1.6.2 Support for peer-to-peer communication

In SS7, MTP Level 2 sends three types of messages, known as signal
units: Message Signal Units (MSUs), Link Status Signal Units (LSSUs),
and Fill-In Signal Units (FISUs).

MSUs originate at a higher level than MTP2, and are destined for a
peer at another node. Likewise, M2PA passes these messages from MTP3
to SCTP as data for transport across a link. These are called User
Data messages in M2PA.

LSSUs allow peer MTP2 layers to exchange status information. Analogous
messages are needed for M2PA. The Link Status message serves this
purpose.

FISUs are sent when no other signal units are waiting to be sent. This
purpose is served by the heartbeat messages in SCTP. FISUs also carry
acknowledgment of messages. This function is performed by
SCTP. Therefore, it is unnecessary for M2PA to provide a protocol data
unit like the FISU.

1.7 Functions Provided by M2PA

1.7.1 Support of MTP3/MTP2 Primitives

M2PA receives the primitives sent from MTP3 to its lower layer. M2PA
processes these primitives or maps them to appropriate primitives at
the M2PA/SCTP interface. Likewise, M2PA sends primitives to MTP3 like
those used in the MTP3/MTP2 interface.

1.7.2 MTP2 Functionality

M2PA provides MTP2 functionality that is not provided by SCTP. This
includes







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   - Data retrieval to support the MTP3 changeover procedure

   - Reporting of link status changes to MTP3

   - Processor outage procedure

   - Link alignment procedure


1.7.3 Mapping of SS7 and IP Entities

The M2PA layer must maintain a map of each of its SS7 links to the
corresponding SCTP association.


1.7.4 SCTP Stream Management

SCTP allows a user-specified number of streams to be opened during the
initialization.  It is the responsibility of the M2PA layer to ensure
proper management of the streams allowed within each association.

M2PA uses two streams in each direction for each association. Stream 0
in each direction is designated for Link Status messages. Stream 1 is
designated for User Data and Proving 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
Management functions with IPSPs as with other SS7 nodes.


1.8 Definition of the M2PA Boundaries

1.8.1 Definition of the M2PA / MTP Level 3 boundary

The upper layer primitives provided by M2PA are the same as those
provided by MTP2 to MTP3. These primitives are described in [2], [3],
and [10]. Following is a list of the primitives.

Primitives sent from MTP3 to M2PA:

Data Request - Used to send a Data Message for transmission.

Start Request - Used to activate a link.

Stop Request - Used to deactivate a link.

Retrieve BSNT Request - Request the BSNT for the changeover procedure.



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Retrieval Request and FSNC - Request retrieval of unacknowledged and
unsent messages. This request includes the FSNC received from the
remote end. 

Local Processor Outage Request - Informs M2PA of a local processor
outage condition.

Local Processor Outage Recovered Request - Informs M2PA that a local
processor outage condition has ceased.

Flush Buffers Request - Requests that all transmit and receive
buffers be emptied.

Continue Request - Requests that processing resume after a processor
outage.

Emergency Request - Requests that M2PA use the emergency alignment
procedure.

Emergency Ceases Request - Requests that M2PA use the normal alignment
procedure.


Primitives sent from M2PA to MTP3:

Data Indication - Used to deliver received Data Message to MTP3.

Congestion Indication - Indicates change in congestion status. The
indication includes the congestion status, if the protocol is using the
optional congestion levels. The indication also includes the discard
status.

In Service Indication - Indicates that the link is in service.

Out of Service Indication - Indicates that the link is out of service.

Retrieved Messages Indication - Indicates delivery of unacknowledged
and unsent messages.

Retrieval Complete Indication - Indicates that delivery of
unacknowledged and unsent messages is complete.

BSNT Confirm - Replies to the BSNT Request. The confirmation includes
the BSNT.

BSNT Not Retrievable Confirm - Replies to the BSNT Request when the
BSNT cannot be determined.

Remote Processor Outage Indication - Indicates processor outage at
remote end.

Remote Processor Recovered Indication - Indicates recovery from
processor outage at remote end.


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1.8.2 Definition of the Lower Layer Boundary between M2PA and SCTP

The upper layer primitives provided by SCTP are described in Reference
[5] Section 10 "Interface with Upper Layer".


1.9 Differences Between M2PA and M2UA

The MTP2 User Adaptation Layer (M2UA) [6] also adapts the MTP3 layer
to the SCTP/IP stack. It does so through a backhauling architecture
[4]. This section intends to clarify some of the differences between
the M2PA and M2UA approaches.

A possible M2PA architecture is shown in Figure 3. Here the IPSP's
MTP3 uses its underlying M2PA as a replacement for MTP2. Communication
between the two layers MTP3/M2PA is defined by the same primitives as
in SS7 MTP3/MTP2. M2PA performs functions similar to MTP2.

A comparable architecture for M2UA is shown in Figure 4. In M2UA, the
MGC's MTP3 uses the SG's MTP2 as its lower SS7 layer. Likewise, the
SG's MTP2 uses the MGC's MTP3 as its upper SS7 layer. In SS7,
communication between the MTP3 and MTP2 layers is defined by
primitives. In M2UA, the MTP3/MTP2 communication is defined as M2UA
messages and sent over the IP connection.































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    ********  SS7   ***************   IP   ********
    * SEP  *--------*     SG      *--------* IPSP *
    ********        ***************        ********

    +------+        +-------------+        +------+
    | SCCP |        |    SCCP     |        | SCCP |
    +------+        +-------------+        +------+
    | MTP3 |        |    MTP3     |        | MTP3 | 
    +------+        +------+------+        +------+    
    | MTP2 |        | MTP2 | M2PA |        | M2PA |    
    +------+        +------+------+        +------+    
    | MTP1 |        | MTP1 | SCTP |        | SCTP | 
    |      |        |      +------+        +------+
    |      |        |      | IP   |        | IP   |
    +------+        +------+------+        +------+


         Figure 3:  M2PA in IP Signaling Gateway



    ********  SS7   ***************   IP   ********
    * SEP  *--------*     SG      *--------* MGC  *
    ********        ***************        ********

    +------+                               +------+
    | SCCP |                               | SCCP |
    +------+                               +------+
    | MTP3 |             (NIF)             | MTP3 | 
    +------+        +------+------+        +------+    
    | MTP2 |        | MTP2 | M2UA |        | M2UA |    
    +------+        +------+------+        +------+    
    | MTP1 |        | MTP1 | SCTP |        | SCTP | 
    |      |        |      +------+        +------+
    |      |        |      | IP   |        | IP   |
    +------+        +------+------+        +------+

       NIF   - Nodal Interworking Function


         Figure 4:  M2UA in IP Signaling Gateway












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