基于SIP的视频会议终端及其与H.323终端 -(2)

目 录

摘 要 .............................................................................................................................................. I ABSTRACT ................................................................................................................................... II 第1章

引言 ............................................................................................................................... 1

1.1 课题的研究背景 ................................................................................................................... 1 1.1.1 课题的提出 .................................................................................................................... 1 1.1.2 研究的意义 .................................................................................................................... 1 1.2 国内外发展现状 ................................................................................................................... 2 1.2.1 视频会议系统的发展现状 ............................................................................................ 2 1.2.2 SIP视频会议终端的发展现状 ..................................................................................... 3 1.3 本文的主要工作 ................................................................................................................... 4 1.4 本章小结 ............................................................................................................................... 5 第2章

视频会议系统相关技术 ............................................................................................... 6

2.1 视频会议系统的简介 ........................................................................................................... 6 2.2 SIP协议 ................................................................................................................................ 6 2.2.1 SIP的概述 ..................................................................................................................... 6 2.2.2 SIP的技术特点 ............................................................................................................. 9 2.2.3 SIP消息[1] .................................................................................................................... 10 2.2.4 SIP建立通信的过程 ................................................................................................... 12 2.2.5 SIP相关协议的简介 ................................................................................................... 14 2.3 H.323协议 .......................................................................................................................... 16 2.3.1 H.323协议的概述 ....................................................................................................... 16 2.3.2 H.323系统结构 ........................................................................................................... 17 2.3.3 H.323的相关协议 ....................................................................................................... 18 2.4 SIP与H.323的比较 .......................................................................................................... 19 2.5 本章小结 ............................................................................................................................. 20 第3章

基于SIP视频会议终端的设计与实现...................................................................... 21

3.1 基于SIP的视频会议终端的概述 ..................................................................................... 21 3.2 基于SIP的视频会议终端的设计 ..................................................................................... 22 3.2.1 视频终端的总体结构 .................................................................................................. 22 3.2.2 用户控制模块 .............................................................................................................. 23 3.2.3 多媒体处理模块 .......................................................................................................... 24 3.2.4 SIP协议栈 ................................................................................................................... 25 3.3 基于SIP的视频会议终端的实现 ..................................................................................... 30 3.3.1 SIP视频会议的基本流程 ........................................................................................... 30 3.3.2 用户控制模块的实现 .................................................................................................. 32

第 I 页

3.3.3 多媒体模块的实现...................................................................................................... 33 3.3.4 在SIP视频会议中发言权控制的实现 ...................................................................... 37 3.4 本章小结............................................................................................................................. 42 第4章

SIP视频会议终端与H.323终端互通的研究与实现 .............................................. 43

4.1 H.323协议和SIP在互通条件下的比较 .......................................................................... 43 4.1.1 基于H.323协议的视频会议终端.............................................................................. 43 4.1.2 H.323协议和SIP在互通条件下的比较 ................................................................... 44 4.2 IWF的研究与设计 ............................................................................................................ 44 4.2.1 IWF的研究 ................................................................................................................. 45 4.2.2 IWF设计方案 ............................................................................................................. 49 4.2.3 地址解析...................................................................................................................... 50 4.2.4 消息映射...................................................................................................................... 52 4.2.5 终端媒体类型描述...................................................................................................... 53 4.3 SIP视频终端与H.323视频终端互通的实现 .................................................................. 54 4.3.1 IWF的实现 ................................................................................................................. 54 4.3.2 呼叫连接过程.............................................................................................................. 55 4.4 对SIP视频会议终端与H.323终端互通的测试 ............................................................. 60 4.4.1 测试环境...................................................................................................................... 60 4.4.2 测试过程...................................................................................................................... 60 4.4.3 测试结果及分析.......................................................................................................... 61 4.5 本章小节............................................................................................................................. 61 第5章

总结与展望 ................................................................................................................. 62

5.1 论文工作总结..................................................................................................................... 62 5.2 下一步工作的展望............................................................................................................. 62 致 谢........................................................................................................................................... 63 参考文献....................................................................................................................................... 64 附录一：攻读硕士期间科研工作和发表论文情况................................................................... 67 附录二：缩略语........................................................................................................................... 68

第 II 页

摘 要

视频会议系统是一种支持人们远距离进行实时信息交流、开展协同工作的应用系统。目前用于支持视频会议的协议主要有ITU的H.323协议和IETF的SIP。H.323协议较为完善，自颁布以来就得到了广泛的应用；SIP以其简单、易于实现、功能扩展性好的特点为开发各种增值业务和会议呼叫提供了很大的方便，也越来越受到关注。目前，SIP视频会议系统及其与H.323视频会议系统的互通也逐渐成为了研究热点。

本文首先针对在视频会议系统中如何简便地发起会话、便于参与者进行视频通讯，如何有效地利用共享资源，如何实现多协议下视频终端的互通，开展了对SIP和H.323协议的研究工作，并对二者进行了详细的比较。

然后详细给出了基于SIP视频会议系统终端的总体设计；实现了可通过SIP建立视频会议连接，进行视音频双向传输的会议终端；在SIP视频会议系统中用SIP_FC算法实现了发言权控制，解决了在SIP视频会议中不提供floor control而引起的对共享资源强占的问题。

最后分析了SIP视频会议终端和H.323视频会议终端互通的原理，对RFC4123中定义的支持SIP和H.323协议互通的IWF进行了研究，在此基础上，进一步研究分析了实现IWF的关键技术，重点主要集中在地址转换、消息映射、终端媒体能力协商及互通呼叫的流程控制等问题上。结合已有的H.323视频会议系统，设计了独立的IWF来实现了两个协议下视频终端的互通。

关键词：视频会议，终端，SIP，H.323，互通，IWF

第 I 页

ABSTRACT

The videoconference system is a sort of application that supports the real-time information exchange and cooperation among the people. At present, the protocols supporting videoconferences are H.323 of ITU and SIP of IETF. The H.323 protocol is relatively more consummate, which is applied broadly since it has been promulgated; the SIP provides prodigious conveniences for the development of all kinds of increment services and the conference calling, which attains increasing attention with the virtues such as simple, easy to be implemented and good expansibility. At present, videoconference system which based on the SIP and communicatied with the H.323 video conference system gradually have become the research hotspot.

The paper studies SIP and H.323 protocol about how to initiate conversation and carry through video communication among participants, how to share the resources effectively and how to implement the communication with multi-protocols in the video terminal systems. We also compared the SIP with H.323 protocol in detail.

The main framework of videoconference system terminal based on SIP is introduced; a conference terminal which is able to be connected by the SIP is implemented, and carry on bidirectional transmission of the audio and video; we implement the voice control in the SIP video conference system using the SIP_FC algorithm, which solves the accroach of shared resource resulted from the lack of floor control in SIP videoconference.

At last, the theory of the communication between SIP videoconference terminal and H.323 videoconference terminal is analyzed, and the IWF of communication between SIP and H.323 defined in RFC4123 by IETF is studied. On Based on the analysis above , the core technology of IWF , the emphasis of which are on address conversion , message mapping , terminal media capacity and flow control of communication call, are farther studied. Based on the former H.323 videoconference system, an independent IWF is designed to achieve the connectedness of the terminals under the two protocols.。

Keywords: videoconference, Terminal, SIP, H.323, Interworking, IWF

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