draft-george-sigtran-m2peer-00.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
                                                        Ken Morneault
                                                        Cisco Systems
                                                        Mallesh Kalla
                                                            Telcordia
                                                      Greg Sidebottom
                                                      Nortel Networks
                                                            Ram Dantu
                                                             IPmobile
                                                              
Expires September 2000                                 March 10, 2000


                  SS7 MTP2-User Peer-to-Peer Adaptation Layer
                  <draft-george-sigtran-m2peer-00.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
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ftp.isi.edu (US West Coast).














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Abstract

This Internet Draft defines a protocol for adapting the SS7 MTP2 User
for signaling over an IP connection using the Simple Control
Transmission Protocol (SCTP).  This protocol is used between SS7
Signaling Points equipped with an IP connection (IPSPs). Signaling
points using this protocol are capable of MTP Level 3 routing. This
protocol may be used in a Signaling Gateway (SG). The SG receives SS7
signaling over a standard SS7 interface using the SS7 Message Transfer
Part (MTP) to provide transport, and has the capability to use MTP to
route signaling to IPSPs. The protocol thereby retains the features of
MTP Level 3, including Network Management.








































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                        TABLE OF CONTENTS

1.  Introduction............................................. 4
  1.1  Scope................................................. 4
  1.2  Terminology........................................... 4
  1.3  Signaling Transport Architecture...................... 5
  1.4  Services Provided by the MTP2 User Adaptation Layer... 6
  1.5  Functions Provided by the MTP2 User Adaptation Layer.. 7
  1.6  Definition of the M2UA Boundaries..................... 7
2.  Protocol Elements........................................ 7
  2.1  Common Message Header................................. 8
  2.2  M2UA Messages......................................... 8
3.  Procedures...............................................10
  3.1  Procedures to Support MTP2 Features...................10
  3.2  Procedures to Support the MTP3/MTP2 Interface.........13
4.  Examples of MTP2 User Adaptation (M2UA) Procedures.......14
  4.1  Link Initialization (Alignment).......................15
  4.2  Message Transmission and Reception....................17
  4.3  Link Status Indication................................17
  4.4  Link Status Message (Processor Outage)................18
  4.5  Congestion Notification to Upper layer................19
  4.6  Link Deactivation.....................................20
  4.7  Link Changeover.......................................21
5.  Security.................................................22
6.  Acknowledgements.........................................22
7.  References...............................................22
8.  Author's Addresses.......................................22

























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1. Introduction

1.1 Scope

There is a need for SCN signaling protocol delivery from an Signaling
Gateway (SG) to an IP Signaling Point (IPSP).  In other words, the
Signaling Gateway will transport MTP Level 3 messages to an IPSP.

The delivery mechanism should

*  Support the MTP Level 2 / MTP Level 3 interface boundary
*  Provide for peer-to-peer communication similar to that 
   provided by MTP Level 2.

The SG and IPSP function as traditional SS7 nodes using the IP network
as a new type of SS7 link.  This allows for full MTP Level 3 message
handling and network management capabilities.

Throughout this document, M2UA is used to refer to the MTP 2 User
Peer-to-Peer case. This should not be confused with the MTP 2 User
Backhauling case described in [6].


1.2 Terminology

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

MTP2 - MTP Level 2, the signaling network layer.

MTP3 - MTP Level 3, the MTP signaling link 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
connection used for SS7 over IP. An IPSP may or may not have a
traditional (non-IP) SS7 link.

Signaling Gateway - An SS7 Signaling Point that has both an IP
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].

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


1.3 Signaling Transport Architecture

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

In reference to the SIGTRAN framework architecture [4], this document 
defines a SCN adaptation module that is suitable for the transport of 
SS7 MTP2 User.  The only SS7 MTP2 User is MTP3.

Figure 1 shows the seamless interworking at the MTP3 layer.  MTP3 is
adapted to the SCTP layer using the MTP2 User Adaptation Layer (M2UA).
All the primitives between MTP3 and MTP2 are supported by M2UA.  The
SCTP association acts as an SS7 link between the SG and the IPSP. The
association contains two streams, one in each direction.

In this example, the Signaling Gateway could be an STP.  Any of the
nodes in the diagram could have SCCP or other SS7 user parts. STPs may
or may not be present in the SS7 path between the SEP and the SG. The
IPSP may or may not have a termination to the SS7 network.


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

    +------+                               +-------------+
    | TCAP |                               |    TCAP     |
    +------+                               +-------------+
    | SCCP |                               |    SCCP     |
    +------+        +-------------+        +-------------+
    | MTP3 |        |    MTP3     |        |    MTP3     | 
    +------+        +------+------+        +------+------+    
    | MTP2 |        | MTP2 | M2UA |        | M2UA | MTP2 |    
    +------+        +------+------+        +------+------+    
    | MTP1 |        | MTP1 | SCTP |        | SCTP | MTP1 | 
    |      |        |      +------+        +------+      |
    |      |        |      | IP   |        | IP   |      |
    +------+        +------+------+        +------+------+

    SEP   - SS7 Signaling Endpoint
    IP    - Internet Protocol
    IPSP  - IP Signaling Point
    SCTP  - Simple Control Transmission Protocol  
            (see Reference [5])

         Figure 1:  M2UA Symmetrical Peer-to-Peer Architecture

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Figure 1 is only an example. Other configurations are possible. For
example, IPSPs without traditional SS7 links could use the protocol
layers MTP3/M2UA/SCTP/IP to route SS7 messages in a network with all
IP links.

1.3.1  UDP port

A request will be made to IANA to assign a UDP port for M2UA
peer-to-peer.

1.4 Services Provided by the MTP2 User Adaptation Layer

The SS7 MTP3/MTP2 (MTP2-User) interface is retained at the termination
point in the IP network. The M2UA 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.

1.4.1 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 following exception:

* The interface must support the larger sequence numbers used by 
  SCTP. Reference [7] can be used as a guide for the MTP3 changes.

1.4.2 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, M2UA passes these messages from MTP3
to SCTP as data for transport across a link.

LSSUs allow peer MTP2 layers to exchange status
information. Analogous messages are needed for M2UA.

FISUs are sent when no other signal units are waiting to be sent. It
is unnecessary for M2UA to send FISUs, since their purpose is served
by the heartbeat messages in SCTP.

To perform the function of MTP2 in traditional SS7, the following
protocol element is defined.

Link Status

Provides a means for asychronous notification of link state to an M2UA

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peer.  An example would be the reporting of a local processor outage.


1.5 Functions Provided by the MTP2 User Adaptation Layer

1.5.1 Mapping

The M2UA layer must maintain a map of an SS7 link to an SCTP
association and to a stream within the association. The M2UA layer
must also maintain a map of an SS7 link to its corresponding IP
destination.
 
1.5.2 Flow Control / Congestion

It is possible for the M2UA layer to be informed of IP network
congestion by implementation-dependent means (e.g., an indication from
SCTP).  If the M2UA layer receives this indication, it notifies MTP3
so that MTP3 can invoke its congestion procedures. 

1.5.3 SCTP Stream Management

SCTP allows user specified number of streams to be opened during the
initialization.  It is the responsibility of the M2UA layer to ensure
proper management of the two streams allowed within each association.

1.5.4  Retention of MTP3 in the SS7 Network 

M2UA allows MTP3 to perform all of its Message Handling and Network
Management functions with IPSPs as with other SS7 nodes.


1.6 Definition of the M2UA Boundaries

1.6.1 Definition of the M2UA / MTP Level 3 boundary

The upper layer primitives provided by M2UA are the same as those
provided by MTP2 to MTP3 [2].

1.6.2 Definition of the Lower Layer Boundary between M2UA and SCTP

The upper layer and layer management primitives provided by SCTP are 
described in Reference [5] Section 9.


2.  Protocol Elements

This section describes the format of various messages used in this 
protocol.

All fields in an M2UA message must be transmitted in the network byte
order, i.e., most significant byte first, unless otherwise stated.


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2.1 Common Message Header

The protocol messages for MTP2 User Adaptation require a message
header structure which contains a version, message type and message
length.  This message header is common among all SCN adaptation
layers. The header structure is shown in Figure 2.


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Version    |     Spare     |         Message Type          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Message Length                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |


                 Figure 2:  Common Message Header


2.1.1  Version

The version field (vers) contains the version of the M2UA adapation 
layer.  The supported versions are:

      01   Release 1.0 of M2UA adaptation protocol

2.1.2  Message Type

The valid message types are defined below and the message contents are
described in Section 2.2.  Each message can contain parameters.

The following list contains the message types for the defined messages.