draft-ietf-sigtran-m2pa-02.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

George, et al                                                [Page 14]


Internet Draft  SS7 MTP2-User Peer-to-Peer Adaptation Layer   Mar 2001

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                 ...
   |                     Common Message Header                     |
                                 ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                 ...
   |                         Message Data                          |
                                 ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


2.2.1 User Data 

The User Data is the data sent from the MTP3 in the form of the
contiguous LI, SIO, and SIF octets of the MSU ([2] Q.703, section 2.2
Signal Unit Format). The LI octet includes the two undefined bits
between the SIO and LI fields.

The format for the User Data message is as follows:


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                 ...
   |                            Data                               |
                                 ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


No padding is added to the MTP3 message.

Note that the Data field contains only the LI, SIF, and SIO
octets. The other components of the MTP2 MSU format (the Flag, BSN,
BIB, FSN, FIB, CK) are not included in M2PA.

It is not necessary to put the message length in the LI octet as in
MTP2. The LI octet is included because the two spare bits in the LI
octet are used by MTP3 in a national version of SS7 as a Priority
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.


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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

The MTP2 Link Status message can be sent between M2PA peers to
indicate link status. This message performs a function similar to the
the Link Status Signal Unit in MTP2.


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            State                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The valid values for State are shown in the following table. 

    Value  Description

     1     In Service
     2     Processor Outage
     3     Processor Outage Ended
     4     Busy
     5     Busy Ended


3.  M2PA Link States

The M2PA link moves from one state to another in response to various
events.  The events that may result in a change of state include:

   - MTP3 primitive requests

   - SCTP notifications

   - Receipt of Status messages from the peer M2PA

   - Expiration of certain timers

Figure 6 illustrates state changes together with the causing events.
Note that some of the error conditions are not shown in the state
diagram.

Following is a list of the M2PA Link States and a description of each.

IDLE - State of link during power-up initialization.

OOS - Out Of Service. Power-up initialization is complete. 

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AIP - Alignment In Progress. M2PA is attempting to establish SCTP
association.

INS-LOCAL - In Service Local. Association is established. M2PA is
waiting for peer to verify that it is In Service.

INS - In Service. Link is ready for traffic.

RETRIEVAL - Link no longer carries traffic. M2PA is waiting for
request for message retrieval from MTP3.













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                           +-----------+
                           |   IDLE    |
                           +-----------+
                                 |
                                 | Power On
                                 |
                                 V
                           +-----------+
                  +------->|    OOS    |<---------------------+
                  ^        +-----------+                      |
                  |             | |                           |
                  |  Server AND | | Client AND                |
                  |  MTP3 Start | | MTP3 Start                |
                  |             | |                           |
                  |             V V                           |
                  |        +-----------+                      |
                  |        |    AIP    |--------------------->+
                  |        +-----------+  MTP3 Stop           |
		  |		 |	  OR SCTP Comm Error  |
		  |		 |	  OR SCTP Comm Lost   |
                  |              |                            |
                  |              | SCTP Comm Up	              | 		     
                  |              |                            |              
                  |              V                            |              
                  |        +-----------+	              |		     
                  |        | INS-LOCAL |--------------------->+			     
                  |        +-----------+  MTP3 Stop         	
                  |              |        OR SCTP Comm Error 
                  |              |        OR SCTP Comm Lost  
                  |              |        OR T1 Expiry       
		  |   		 |
                  |              | Link Status		     
                  |              | In Service received	     
                  |              |                                
                  |              V                                
                  |        +-----------+			     
                  |        |    INS    |			     
                  |        +-----------+			     
                  |              |                                
       Retrieval  |              | MTP3 Stop                      
       Complete   |              | OR SCTP Comm Error    
       OR         |              | OR SCTP Comm Lost     
       MTP3 Start |              | OR T6 Expiry       
                  |              |                                
                  |              V                                
                  |        +-----------+                          
                  +<-------| RETRIEVAL |
                           +-----------+


                Figure 6: M2PA Link State Transition Diagram.

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4.  Procedures

4.1 Procedures to Support MTP2 Features

4.1.1 Signal Unit Format, Delimitation, Acceptance

Messages for transmission across the network must follow the format
described in section 2.

SCTP provides reliable, in-sequence delivery. Therefore the related
functionality of MTP2 is not needed. SCTP does not provide functions
related to Link State Control in MTP2. These functions must be
provided by M2PA.


4.1.2 Link Alignment

Link alignment includes the establishment of an SCTP association and a
handshaking procedure between the M2PA peers to verify that the
association is ready to be used as a link.

To prevent duplicate associations from being established, it must be
decided in advance which endpoint initiates the establishment of the
association. In a pair of endpoints, the endpoint that initiates the
establishment of the association is called the client. The other
endpoint is the server. An endpoint may be a client in its
relationship with one endpoint, and a server in its relationship with
another endpoint. The designations of client and server are needed
only to decide which endpoint initiates the establishment of the
association. After that, the endpoints function as peers.

The client initiates the association using the server's IP address and
the M2PA well-known port number as the destination endpoint. In order
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
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 address/port and server IP address/port
(i.e., each association) 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.

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. 


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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
SLCs is implementation dependent.


                IPSP X                        IPSP Y

            +-------------+               +-------------+
            |             |	SCTP      |             |
            |         IPA | association 1 | IPB         |
            |   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






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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      |             |
            |         IPC | association 2 |             |
            |   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








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     +-------------+---------------------------------------+-----+
     | 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