基于IP可视电话的MCU的设计与实现
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摘要
视频会议是利用计算机，电视或其他终端召集会议的一种通信方法，融计算机技术、通信网络技术、微电子技术等于一体的产物，它利用各种网络进行实时传输并能使用户间进行友好的信息交流。
近年来，视频会议在实用化方面取得了迅速的发展，并在军事，经济，文化等领域发挥了显著的作用。顺应三网合一的发展趋势，由于交互式多媒体通信所依附的传输网络基础，由电路交换式的ISDN和专线网络向分组交换式的IP网络过渡，针对的市场目标将由大型公司、政府机构的会议室向小型化的工作组会议室、个人化的桌面延伸，并最终发展到家庭，功能也已由原先单纯的电视会议功能发展成远程教学系统、远程监控系统、远程医疗系统等多方面的综合业务。因此，视频会议技术势必要进入一个新的发展阶段。在此转型期间，尽管视频会议的发展不会以一种形式取代另一种形式，而是同时存在着多种解决方案，基于H.323协议的可视电话视频会议系统将是视频会议系统发展的热点。正是在这种背景下，我们设计了H.323协议下支持可视电话多点会议的MCU(多点控制单元)。
本文首先在第一章介绍了视频会议的发展历史，类型和所遵循的标准；第二章将从系统部件组成和协议栈结构两个角度出发，介绍H.323框架协议；在第三章中，详细介绍了本系统的硬件平台以及底层通信协议，这是本系统构造和运行的基础；在第四章中，将介绍本系统实现的视频编解码标准，视频编解码器以及MCU视频拼接部分的实现；第五章将介绍本系统实现的音频编解码标准，音频编解码器以及MCU音频合成部分的实现；第六章将介绍MCU功能模块的设计实现，由于MCU的设计牵涉到很多功能模块，文章中将撇开许多实现的细节，而着重介绍实现的关键点及所采取的一些实现技巧；最后，第七章总结了这个项目的实际意义，同时展望了在已经完成的工作的基础上，进一步完善本系统的方向。
Video conference is a technology using computer or TV or other terminals to have a meeting. This technology is the combination of computer technology, communication network technology and microelectronics technology. It makes peoples can exchange messages friendly through the digitization of multimedia data and the real time transportation of multimedia data using networks.
Recently, video conference has improved rapidly in practice and been used widely in military affairs, economy and culture. As the communication net work of which it is based is changing from circuit switching based ISDN and DDN to packet switching based IP network, the object market will change from large cooperation and government to little work group and personal desktop conference, and finally to family, the function has developed from the simple Video Conference to integrated services such as remote learning system, remote monitoring system and remote medical system etc, video conference will be in a new development generation.
In this changing period, there will be many kinds of Video Conference system existing at the same time. Even though it is impossible for one kind to be absolute advantaged, the H.323 based videophone conference system will be the hottest spot in the development of Video Conference system. Under this background, we designed this H.323 based MCU to support multipoint conference for videophone conference system.
In this paper, chapter one describe briefly the history, types and standards of Video Conference. Chapter two, the components and protocol structure of H.323 protocol. The hardware environment and the low-layer communication protocol is introduced in chapter three. Chapter four and chapter five introduce the encoder and decoder for audio and video. The main part of the software design and the implement of MCU are discussed in chapter six. At last, we point out what we should do in the near future to optimize our product in chapter seven.
近年来，视频会议在实用化方面取得了迅速的发展，并在军事，经济，文化等领域发挥了显著的作用。顺应三网合一的发展趋势，由于交互式多媒体通信所依附的传输网络基础，由电路交换式的ISDN和专线网络向分组交换式的IP网络过渡，针对的市场目标将由大型公司、政府机构的会议室向小型化的工作组会议室、个人化的桌面延伸，并最终发展到家庭，功能也已由原先单纯的电视会议功能发展成远程教学系统、远程监控系统、远程医疗系统等多方面的综合业务。因此，视频会议技术势必要进入一个新的发展阶段。在此转型期间，尽管视频会议的发展不会以一种形式取代另一种形式，而是同时存在着多种解决方案，基于H.323协议的可视电话视频会议系统将是视频会议系统发展的热点。正是在这种背景下，我们设计了H.323协议下支持可视电话多点会议的MCU(多点控制单元)。
本文首先在第一章介绍了视频会议的发展历史，类型和所遵循的标准；第二章将从系统部件组成和协议栈结构两个角度出发，介绍H.323框架协议；在第三章中，详细介绍了本系统的硬件平台以及底层通信协议，这是本系统构造和运行的基础；在第四章中，将介绍本系统实现的视频编解码标准，视频编解码器以及MCU视频拼接部分的实现；第五章将介绍本系统实现的音频编解码标准，音频编解码器以及MCU音频合成部分的实现；第六章将介绍MCU功能模块的设计实现，由于MCU的设计牵涉到很多功能模块，文章中将撇开许多实现的细节，而着重介绍实现的关键点及所采取的一些实现技巧；最后，第七章总结了这个项目的实际意义，同时展望了在已经完成的工作的基础上，进一步完善本系统的方向。
Video conference is a technology using computer or TV or other terminals to have a meeting. This technology is the combination of computer technology, communication network technology and microelectronics technology. It makes peoples can exchange messages friendly through the digitization of multimedia data and the real time transportation of multimedia data using networks.
Recently, video conference has improved rapidly in practice and been used widely in military affairs, economy and culture. As the communication net work of which it is based is changing from circuit switching based ISDN and DDN to packet switching based IP network, the object market will change from large cooperation and government to little work group and personal desktop conference, and finally to family, the function has developed from the simple Video Conference to integrated services such as remote learning system, remote monitoring system and remote medical system etc, video conference will be in a new development generation.
In this changing period, there will be many kinds of Video Conference system existing at the same time. Even though it is impossible for one kind to be absolute advantaged, the H.323 based videophone conference system will be the hottest spot in the development of Video Conference system. Under this background, we designed this H.323 based MCU to support multipoint conference for videophone conference system.
In this paper, chapter one describe briefly the history, types and standards of Video Conference. Chapter two, the components and protocol structure of H.323 protocol. The hardware environment and the low-layer communication protocol is introduced in chapter three. Chapter four and chapter five introduce the encoder and decoder for audio and video. The main part of the software design and the implement of MCU are discussed in chapter six. At last, we point out what we should do in the near future to optimize our product in chapter seven.
引文
[1] ITU-T Recommendation H.323 v2(1998), Packet-based multimedia communications systems.
[2] ITU-T Recommendation H.225.0(1998), Call signalling protocols and media stream packetization for packet based multimedia communication systems.
[3] ITU-T Recommendation H.245(1998), Control protocol for multimedia communication.
[4] CCITT Recommendation G.711(1988), Pulse Code Modulation(PCM) of voice frequencies.
[5] CCITT Recommendation G.722(1988), 7kHz audio-coding within 64 kbit/s.
[6] ITU-T Recommendation G.723.1(1996), Speech coders: Dual rate speech coder for multimedia communications transmitting at 5.3 and 6.3 kbit/s.
[7] CCITT Recommendation G.728(1992), Coding of speech at 16kbit/s using low-delay code excited linear prediction.
[8] ITU-T Recommendation G.729(1996), Coding of speech at 8kbit/s using Conjugate Structure Algebraic-Code-Excited Linear-Prediction(CS-ACELP).
[9] ITU-T Recommendation H.261(1993), Video codec for audiovisual services at p×64 kbit/s.
[10] ITU-T Recommendation H.263(1996), Video coding for low bit rate communication.
[11] ITU-T Recommendation T.120(1996), Data protocols for multimedia conferencing.
[12] ITU-T Recommendation H.320(1997), Narrow-band visual telephone systems and terminal equipment.
[13] ITU-T Recommendation H.321(1996), Adaptation of H.320 visual telephone terminals to B-ISDN environments.
[14] ITU-T Recommendation H.322(1996), Visual telephone systems and terminal equipment for local area networks which provide a guaranteed quality of service.
[15] ITU-T Recommendation H.324(1996), Terminal for low bit rate multimedia communication.
[16] ITU-T Recommendation H.310(1996), Broadband audiovisual communication systems and terminals.
[17] ITU-T Recommendation Q.931(1993), ISDN user-network interface layer 3 specification for basic call control.
[18] ITU-T Recomnendation E.164(1997), The internationalpublic telecommunication numbering plan.
[19] 艾浩军 胡瑞敏等，H．323多点处理器任务调度策略。计算机工程与应用，2001／8
[20] 施可为 蔡安妮，H．323视频会议终端的软件实现。北京邮电大学学报，2000／3
[21] 齐飞 赵帅锋，T．120与H．323融合方案的探讨。世界网络与多媒体，2000／5
[22] 游明星 刘立柱，基于H．323协议的实时IP传真的实现。数据通信，200／3
[23] 贺梁 顾君忠，基于H．323协议的QoS实现技术。计算机工程，2000／8
[24] 胡绍海 赵帅锋等，基于H．323的多点视听会议系统的实现。北方交通大学学报，2000／6
[25] 黄东霖，基于IP的多媒体通信平台(H．323系统)的发展。有线电视技术，2000／10
[26] 姜海尔 胡绍海，H．323系统中关守的功能及实现。数据通信，1999／4
[27] 姜海尔 胡绍海，基于H．323多媒体通信平台的开发与实现。世界网络与多媒体，2000／1
[28] 蔡婷婷，朱秀昌，H．323中RTP／RTCP协议的分析与实现。世界网络与多媒体，2001
[2] ITU-T Recommendation H.225.0(1998), Call signalling protocols and media stream packetization for packet based multimedia communication systems.
[3] ITU-T Recommendation H.245(1998), Control protocol for multimedia communication.
[4] CCITT Recommendation G.711(1988), Pulse Code Modulation(PCM) of voice frequencies.
[5] CCITT Recommendation G.722(1988), 7kHz audio-coding within 64 kbit/s.
[6] ITU-T Recommendation G.723.1(1996), Speech coders: Dual rate speech coder for multimedia communications transmitting at 5.3 and 6.3 kbit/s.
[7] CCITT Recommendation G.728(1992), Coding of speech at 16kbit/s using low-delay code excited linear prediction.
[8] ITU-T Recommendation G.729(1996), Coding of speech at 8kbit/s using Conjugate Structure Algebraic-Code-Excited Linear-Prediction(CS-ACELP).
[9] ITU-T Recommendation H.261(1993), Video codec for audiovisual services at p×64 kbit/s.
[10] ITU-T Recommendation H.263(1996), Video coding for low bit rate communication.
[11] ITU-T Recommendation T.120(1996), Data protocols for multimedia conferencing.
[12] ITU-T Recommendation H.320(1997), Narrow-band visual telephone systems and terminal equipment.
[13] ITU-T Recommendation H.321(1996), Adaptation of H.320 visual telephone terminals to B-ISDN environments.
[14] ITU-T Recommendation H.322(1996), Visual telephone systems and terminal equipment for local area networks which provide a guaranteed quality of service.
[15] ITU-T Recommendation H.324(1996), Terminal for low bit rate multimedia communication.
[16] ITU-T Recommendation H.310(1996), Broadband audiovisual communication systems and terminals.
[17] ITU-T Recommendation Q.931(1993), ISDN user-network interface layer 3 specification for basic call control.
[18] ITU-T Recomnendation E.164(1997), The internationalpublic telecommunication numbering plan.
[19] 艾浩军 胡瑞敏等，H．323多点处理器任务调度策略。计算机工程与应用，2001／8
[20] 施可为 蔡安妮，H．323视频会议终端的软件实现。北京邮电大学学报，2000／3
[21] 齐飞 赵帅锋，T．120与H．323融合方案的探讨。世界网络与多媒体，2000／5
[22] 游明星 刘立柱，基于H．323协议的实时IP传真的实现。数据通信，200／3
[23] 贺梁 顾君忠，基于H．323协议的QoS实现技术。计算机工程，2000／8
[24] 胡绍海 赵帅锋等，基于H．323的多点视听会议系统的实现。北方交通大学学报，2000／6
[25] 黄东霖，基于IP的多媒体通信平台(H．323系统)的发展。有线电视技术，2000／10
[26] 姜海尔 胡绍海，H．323系统中关守的功能及实现。数据通信，1999／4
[27] 姜海尔 胡绍海，基于H．323多媒体通信平台的开发与实现。世界网络与多媒体，2000／1
[28] 蔡婷婷，朱秀昌，H．323中RTP／RTCP协议的分析与实现。世界网络与多媒体，2001