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draft-agrawal-sip-h323-interworking

落鹤生 发布于 2014-01-26 14:51 点击:次 
This document describes the interworking between SIP and H.323 protocol. It defines the the logical entity known as the SIP-H.323 Interworking Function (SIP-H.323 IWF) that will allow the interworking between the SIP (Session Initiation Protocol) and
TAG: H323  SIP  Interworking  

本RFC草案的完整文档可以在这儿下载到:http://bbs.rosoo.net/thread-15989-1-1.html

Internet Engineering Task Force                       Hemant Agrawal
Internet Draft                               Telverse Communications
draft-agrawal-sip-h323-interworking-01.txt             Radhika R Roy
July 13, 2001                                                   AT&T
Expires: Jan 2002                                      Vipin Palawat
                                                   Cisco Systems Inc
                                                       Alan Johnston
                                                        MCI WorldCom
                                                       Charles Agboh
                                                               Ebone
                                                          David Wang
                                            Nuera Communications Inc
                                                 Henning Schulzrinne
                                                        Kundan Singh
                                                 Columbia University
                                                          Joon Maeng
                                                        ipDialog Inc
 
 
                       SIP-H.323 Interworking
 
Status of this Memo
 
This document is an Internet-Draft and is in full conformance with  all provisions of Section 10 of RFC 2026 [1]. 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 
The list of Internet-Draft Shadow Directories can be accessed at  http://www.ietf.org/shadow.html.
 
This document is a product of the SIP-H.323 Interworking Working 
Group of the Internet Engineering Task Force (IETF).  Comments should  be submitted to the mailing list sip-h323@yahoogroups.com.com.
 
Copyright Notice
 
   Copyright (c) The Internet Society (2000). All Rights Reserved.

Abstract
 
This document describes the interworking between SIP and H.323 protocol. It defines the the logical entity known as the SIP-H.323 Interworking Function (SIP-H.323 IWF) that will allow the interworking between the SIP (Session Initiation Protocol) and H.323  protocol. This includes the call sequence mapping, message parameter mapping, translation between H.245 and SDP, state machines, and handling of different call procedures.

Table of Contents
 
1. Terminology
2. Introduction
3. Background
4. Scope of the document
5. Definitions
6. Overview of IWF Functionality
7. Interworking Requirements for IWF
8.Mapping Between SIP and H.323 in IWF
8.1. Alias Addresses Mapping
8.1.1. Converting SIP Addresses to H.323 Addresses
8.1.2. Converting H.323 Addresses to SIP Addresses
8.2 Message Mapping
8.3 Call Sequence Mapping
8.4 Message Parameters Mapping
8.5 Audio/Video Formats Mapping
9. Basic Message Handling 
9.1 Handling of H.323 Signaling Messages
9.2 Handling of SIP Signaling Messages
10.Interworking Call Scenarios for Different Configurations
11. State Machine
12. Implementation Requirements
13. Activities Planned for Next Phase
14. Security Considerations
15. Known Issues
16. To Be Done
17. Conclusion
 
Appendix A: Calculating common subset of capabilities
Appendix B: Modification in ASN.1 syntax of H.225
Appendix C: Call Flow Message Details
Appendix D: Summary of SIP-H.323 Interworking Requirements
 
References
Acknowledgments
Authors' Addresses
Full Copyright Statement
 
1 Terminology
 
In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [2] and indicate requirement levels for compliant implementations.
 
2. Introduction
 
The primary objective of SIP-H.323 Interworking function (IWF) is to provide protocol conversion between SIP and H.323 protocol. Both of these protocols use similar formats (e.g. RTP) to transfer media (audio/video/data) over the Packet Network. It is, therefore, required to perform the mapping between SIP and H.323 signaling messages only to achieve the interworking between the two protocols. The objective is to transmit media end-to-end directly between the two end systems in H.323 and SIP networks. However, some of the special scenarios may require media to be routed through the IWF using MSF. Such scenarios are out of the scope of the current document.

The logical relationship between the IWF and other SIP and H.323  entities is shown in Figure 1. 
 
 
  H.323 Entity                              SIP Entity
 
+---------------+
| H.323 GK      |                        +----------------+
|               |\                       | SIP |
+---------------+ \                      |    Server      |
                   \                    /+----------------+
                    \                  /
+---------------+    +---------------+/
| H.323 MCU     |----|  Interworking |
| MC,or Terminal|    |   Function    |
+---------------+    +---------------+\
                    /                  \
                   /                    \+----------------+
+---------------+ /                      |     SIP        |
| H.323 Gateway |/                       |  User Agent    |
|               |                        +----------------+
+---------------+
 
Figure 1 : Logical Relationship between IWF and SIP/H.323 entities
 
 
3. Background
 
Two standards are currently popular for IP telephony signaling:  the H.323 protocol suite by ITU-T, and the Session Initiation Protocol (SIP) by IETF. Both of these signaling protocols provide mechanisms for call establishment and teardown, call control and supplementary services, and capability exchange. In terms of functionality and services that can be supported, H.323 version 2 [5] and SIP Version 2 [3] are very similar. However, supplementary services in H.323 are quite different from SIP.
 
H.323 and SIP are improving themselves and the differences between them are diminishing with each new version. At present, H.323 and SIP networks are coexisting with different service providers in many parts of the world as they think to provide services to satisfy their customers' needs.

+-----------+--------+--------+-------+--------+---------+------+
| H.225     |        |        |       |  H.225 | Codecs  |      |
| Call      |  SDP   |  H.245 |  SIP  |  RAS   |-------- | RTCP |
| Signaling |        |        |       |        | RTP     |      |
+-----------+--------+--------+---+---+--------+---------+------+
|                                 |                             |
|          TCP                    |            UDP              |
|                                 |                             |
+-----------+--------+--------+-------+--------+---------+------+
|                                                               |
|                                IP                             |
|                                                               |
+-----------+--------+--------+-------+--------+---------+------+
|                                                               |
|                     Linked and Physical Layer                 |
|                                                               |
+-----------+--------+--------+-------+--------+---------+------+           


       Figure 2: SIP and H.323 Protocol stacks

SIP-H.323 IWF is a solution for those service providers who want to support both H.323 and SIP networks. There are different forums involved in the standardization of SIP-H.323 IWF. The aim of all these forums is to provide an agreed upon specifications so that there will be no interoperability issues between different vendor implementations.
This work is also under progress in ETSI TIPHON and IMTC aHit! forums.
 
4. Scope of this document
 
This document describes interworking between H.323 Version 2.0 [5] and SIP Version 2.0 [3]. However, since H.323v2 terminal may or may not support FastConnect, solutions without using this feature are also detailed in this document. 
 
This Interworking recommendation is being defined in two phases. The  Current (first) phase  defines the basic call establishment, call termination. It also defines the translation between H.245 and SDP for session description. The second phase will include optional messaging of the two protocols, advanced features and services. Both phases have to meet the general requirements specified in the SIP-H323 Interworking Requirement draft [9]. 
 
The support for future versions of H.323 and SIP MAY be addressed in the next phase.
 
5. Definitions
 
 Endpoint (EP): This is an entity from which the media originates or finally terminates. This can either be H.323 terminal or SIP user agent.

H.323 Gatekeeper (GK) : The Gatekeeper (GK) is an OPTIONAL H.323 entity on the network that provides address translation and controls access to the network for H.323 terminals, Gateways and MCUs. The Gatekeeper may also provide other services to the terminals, Gateways and MCUs such as bandwidth management and locating Gateways. 
 
H.323 Terminal:  A H.323 Terminal is an endpoint on the network which provides the real-time, two-way communications with another H.323 terminal, Gateway, or Multipoint Control Unit. This communication consists of control, indications, audio, moving color video pictures, and/or data between the two terminals. A terminal may provide speech only, speech and data, speech and video, or speech, data and video.
 
H.323 Side: The H.323 side of the IWF is the part of the IWF that terminates and originates H.323 signaling from and to the H.323 network respectively.
 
Interworking Function (IWF): It allows interworking between the H.323 and SIP networks.
 
Media Switching Function (MSF): This is an OPTIONAL logical entity present in the IWF, which will perform the task of witching/transcoding RTP from one logical port to other.
   
SIP User Agents (UA): A logical entity which can act as both SIP user  agent client and SIP user agent server.
 
SIP Server: This can be either SIP Proxy, Redirect, Location or Registrar server.
 
SIP Proxy Server: A logical entity which acts as both server and a client. SIP messages will be processed and passed to other SIP entities. A SIP proxy server interprets, and, if necessary, rewrites a SIP message before forwarding it. 
 
SIP Redirect Server: A logical entity which is primarily used for address translation and locating a SIP user. It may take the help of location server for locating a SIP user. SIP redirect server does not accept calls and does not initiate a SIP request on behalf of a calling SIP endpoint. SIP redirect server sends a response to a request for locating a SIP user. 
 
SIP Location Server: A location service is used by a SIP proxy or SIP redirect server to obtain information about the callee's possible location(s).
 
SIP Registrar Server: A SIP registrar is a server that accepts REGISTER requests from SIP endpoints. A SIP registrar is typically co-located with a SIP proxy or SIP redirect server and MAY make its information available through the location server.
 
SIP Side: The SIP side of the IWF is the part of the IWF that terminates and originates SIP signaling from and to the SIP network respectively.
 
6. Overview of IWF Functionality
 
When the IWF receives call signaling messages from an H.323 entity, it performs the necessary translation and sends the corresponding equivalent messages to SIP entity on the SIP side of the IWF and vice versa. The IWF SHALL provide signaling translation for all phases of a call.
 
This IWF does not include media format conversion. However, it MAY include a Media Switching Function for switching RTP packets which is out of scope of this document.

              +---------------------------------------+
              |         +--------------------+        |
              |         |      SIP-H.323     |        |
              |         |    Interworking    |        |
              |         |      Function      |        |
              |         +--------------------+        |
              |           /              \            | 
              |  +---------------+ +---------------+  |
              |  |               | |               |  |
              |  |  H.323 Stack  | |  SIP Stack    |  |
              |  |               | |               |  |
              |  +---------------| +---------------+  |
              +---------------------------------------+
                 /                                 \
        +-------------+                        +------------+
        |             |                        |            |
        |    H.323    |       Media Flow       |    SIP     |
        |   Network   |========================|   Network  |
        +-------------+                        +------------+
         
            Figure 3: Overview of the IWF


 
There are several scenarios where SIP-H.323 IWF can be placed with different network elements in the SIP and H.323 networks. The way the messages are generated during a call establishment between H.323 EP and a SIP UA, is different depending on the scenario.
 
Scenario 1: IWF without H.323 GK and SIP Server
 
+----------+                  +--------+                   +--------+
|          |                  |        |                   |        |
| H.323 EP |<---------------->|   IWF  |<----------------->| SIP UA |
|          |                  |        |                   |        |
+----------+                  +--------+                   +--------+

Scenario 2: IWF with H.323 GK and without SIP Server 
 
+----------+   +----------+   +--------+                  +---------+
|          |   |          |   |        |                  |         |
| H.323 EP |<->| H.323 GK |<->|   IWF  |<---------------->| SIP UA  |
|          |   |          |   |        |                  |         |
+----------+   +----------+   +--------+                  +---------+
 
Scenario 3: IWF with SIP Server and without SIP Server
 
+----------+                  +--------+   +----------+   +---------+
|          |                  |        |   | Proxy or |   |         |
| H.323 EP |<---------------->|   IWF  |<->| Redirect |<->| SIP UA  |
|          |                  |        |   |  Server  |   |         |
+----------+                  +--------+   +----------+   +---------+

Scenario 4: IWF with H.323 Server and SIP Server
+------_---+   +----------+   +--------+   +----------+   +--------+
|          |   |          |   |        |   | Proxy or |   |        |
| H.323 EP |<->| H.323 GK |<->|   IWF  |<->| Redirect |<->| SIP UA |
|          |   |          |   |        |   |  Server  |   |        |
+----------+   +----------+   +--------+   +----------+   +--------+


The IWF can be configured manually similar to SIP servers , H.323 GKs and GWs  or one can use DNS SRV or DNS.

 
7. Interworking Requirements for IWF
 
The requirement for SIP-H.323 IWF has already been addressed in detail in "SIP-H.323 Interworking Requirements" [9]. The summary of SIP-H.323 interworking requirements is given for reference in Appendix D.

(IETF)
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