draft-ietf-sigtran-m2pa-01.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

Network Working Group                                      Tom George
INTERNET-DRAFT                                                Alcatel
                                                            Ram Dantu
                                                             IPmobile
                                                      Malleswar Kalla
                                                            Telcordia
                                           Hanns Juergen Schwarzbauer
                                                              Siemens
                                                      Greg Sidebottom
                                                      Nortel Networks
                                                        Ken Morneault
                                                        Cisco Systems

                                                              
Expires May 2001                                    November 22, 2000


             SS7 MTP2-User Peer-to-Peer Adaptation Layer
                  <draft-ietf-sigtran-m2pa-01.txt>


Status of This Memo

This document is an Internet-Draft and is in full conformance with all 
provisions of Section 10 of RFC 2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups.  Note that other groups may also distribute
working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as 'work in progress.'

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

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To learn the current status of any Internet-Draft, please check the
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munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or
ftp.isi.edu (US West Coast).











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Abstract

This Internet Draft defines a protocol supporting the transport of SS7
MTP Layer 3 signaling messages over IP using the services of the
Stream Control Transmission Protocol (SCTP).  This protocol would be
used between SS7 Signaling Points employing the MTP Level 3
protocol. The SS7 Signaling Points may also employ standard SS7 links
using the SS7 Message Transfer Part (MTP) Layer 2 to provide transport
of MTP Layer 3 signaling messages.










































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                        TABLE OF CONTENTS

1.  Introduction............................................. 4
  1.1  Scope................................................. 4
  1.2  Terminology........................................... 4
  1.3  Abbreviations......................................... 5
  1.4  Conventions........................................... 5
  1.5  Signaling Transport Architecture...................... 6
  1.6  Services Provided by M2PA............................. 7
  1.7  Functions Provided by M2PA............................ 8
  1.8  Definition of the M2PA Boundaries..................... 9
  1.9  Differences Between M2PA and M2UA.....................10
2.  Protocol Elements........................................12
  2.1  Common Message Header.................................12
  2.2  M2PA Messages.........................................13
3.  M2PA Link States.........................................15
4.  Procedures...............................................17
  4.1  Procedures to Support MTP2 Features...................17
  4.2  Procedures to Support the MTP3/MTP2 Interface.........21
5.  Examples of M2PA Procedures..............................24
  5.1  Link Initialization (Alignment).......................24
  5.2  Message Transmission and Reception....................26
  5.3  Link Status Indication................................26
  5.4  Link Status Message (Processor Outage)................27
  5.5  Congestion Notification to Upper layer................28
  5.6  Link Deactivation.....................................29
  5.7  Link Changeover.......................................30
6.  Security.................................................32
7.  IANA Considerations......................................32
8.  Acknowledgements.........................................32
9.  References...............................................33
10. Author's Addresses.......................................34


















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1. Introduction

1.1 Scope

There is a need for Switched Circuit Network (SCN) signaling protocol
delivery over an IP network.  This includes delivery from a Signalling
Gateway (SG) to a Media Gateway Controller (MGC) or IP Signaling
Point, as described in the Framework Architecture for Signalling
Transport [1]. This could allow for convergence of some signaling
and data networks. SCN Signaling nodes would have access to databases
and other devices in the IP network domain that do not employ SS7
signaling links. There may also be operational cost and performance
advantages when traditional signaling links are replaced by IP network
"connections".

The delivery mechanism described in this document allows for full MTP3
message handling and network management capabilities between any two
SS7 nodes, communicating over an IP network. An SS7 node equipped with
an IP network connection is called an IP Signaling Point (IPSP). The
IPSPs function as traditional SS7 nodes using the IP network instead
of SS7 links.

The delivery mechanism should

   * Support seamless operation of MTP3 protocol peers over an IP
     network connection.

   * Support the MTP Level 2 / MTP Level 3 interface boundary.

   * Support management of SCTP transport associations and traffic
     instead of MTP2 Links.

   * Support asynchronous reporting of status changes to management.


1.2 Terminology

MTP - The Message Transfer Part of the SS7 protocol [2]. 

MTP2 - MTP Level 2, the MTP signaling link layer.

MTP3 - MTP Level 3, the MTP signaling network layer.

MTP2-User - A protocol that normally uses the services of MTP Level
2. The only MTP2 user is MTP3.

Signaling End Point (SEP) - A node in an SS7 network that originates
or terminates signaling messages.  One example is a central office
switch.

IP Signaling Point (IPSP) - An SS7 Signaling Point with an IP
network connection used for SS7 over IP. 

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Signaling Gateway (SG) - A signaling agent that receives/sends SCN
native signaling at the edge of the IP network [4]. In this context,
an SG is an SS7 Signaling Point that has both an IP network connection
used for SS7 over IP, and a traditional (non-IP) link to an SS7
network.

Signaling Transfer Point (STP) - A node in an SS7 network that routes
signaling messages based on their destination point code in the SS7
network.

Association - An association refers to a SCTP association [5]. The
association provides the transport for MTP3 protocol data units and
M2PA adaptation layer peer messages.

Network Byte Order - Most significant byte first, also known as "Big
Endian".

Stream - A stream refers to a SCTP stream [5].  


1.3 Abbreviations

BSNT   - Backward Sequence Number to be Transmitted

FSNC   - Forward Sequence Number of last message accepted by 
         remote level 2

MSU    - Message Signal Unit

SCN    - Switched Circuit Network

SCTP   - Stream Control Transmission Protocol

SIF    - Signaling Information Field

SIO    - Service Information Octet

SLC    - Signaling Link Code

SS7    - Signaling System 7

SSN    - Stream Sequence Number


1.4 Conventions

The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they
appear in this document, are to be interpreted as described in
[8].


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1.5 Signaling Transport Architecture

The architecture that has been defined [4] for Switched Circuit
Network (SCN) signaling transport over IP uses multiple components,
including an IP transport protocol, the Stream Control Transmission
Protocol (SCTP), and an adaptation module to support the services
expected by a particular SCN signaling protocol from its underlying
protocol layer.

Within this framework architecture, this document defines an SCN
adaptation module that is suitable for the transport of SS7 MTP3
messages.

Figure 1 shows the seamless interworking at the MTP3 layer.  MTP3 is
adapted to the SCTP layer using the MTP2 User Peer-to-peer Adaptation
Layer (M2PA).  All the primitives between MTP3 and MTP2 are supported
by M2PA.  The SCTP association acts as one SS7 link between the IPSPs.



            ********   IP   ********
            * IPSP *--------* IPSP *
            ********        ********
            		    
            +------+        +------+
            | MTP3 |        | MTP3 | 
            +------+        +------+    
            | M2PA |        | M2PA |    
            +------+        +------+    
            | SCTP |        | SCTP | 
            +------+        +------+
            | IP   |        | IP   |
            +------+        +------+

    IP    - Internet Protocol
    IPSP  - IP Signaling Point
    SCTP  - Stream Control Transmission Protocol
            (see Reference [5])

         Figure 1:  M2PA Symmetrical Peer-to-Peer Architecture


An IPSP may have SCCP and other SS7 layers above MTP3. Figure 2 shows
an example. The Signaling Gateway is an IPSP equipped with both
traditional SS7 and IP network connections.  In effect, the Signaling
Gateway acts as an 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
represented 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], with the addition of support for larger sequence numbers in
[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]. This
will allow for use of the SCTP stream sequence numbers in the
changeover messages.

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 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

   - Data retrieval to support the MTP3 changeover procedure

   - Reporting of link status changes to MTP3

   - Processor outage procedure

   - Link alignment procedure




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1.7.3 Mapping of SS7 and IP Entities

For each IP link, the M2PA layer must maintain a map of the SS7 link
to its SCTP association and its corresponding IP destination.
 
1.7.3 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.

1.7.4  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. Following is a list of these primitives.

Primitives sent from MTP3 to M2PA: