摘要
在网络和多媒体技术的支撑下，远程教学系统得到了蓬勃发展，且作为一种全新的知识传播方式日益受到重视。在线口语训练系统是远程教学系统的一个重要组成部分，同时也是其中较难实现的一部分。本文的主要工作即是实现一套在线口语训练系统的整体框架，重点研究和解决多媒体在网络传输中出现的播放停滞、播放不连续和播放不同步等问题。
本文对现有在线口语训练系统及其相关协议进行了全面深入的分析，针对目前系统中普遍存在的多媒体数据在播放时经常出现播放停滞、播放不连续和播放不同步等问题，提出了一种基于实时传输协议(RTP)的在线口语训练系统的实现方法，即在多媒体数据传输过程中，首先采用MPEG-1标准对多媒体数据进行实时压缩，然后对多媒体数据进行适当调度和实时修复，最后在UDP层之上利用新型的实时传输协议RTP对多媒体数据进行传输控制。通过对补丁流调度算法的研究与分析，提出了适于本系统的选择性补丁流调度算法，并利用该算法对多媒体数据流进行调度。此外，通过前向纠错算法的引入，和视频补偿技术相结合，得到了更适于MPEG-1视频和音频数据的丢包修复算法。通过以上方法能够在一定范围内解决多媒体同步、网络传输中差错恢复和窄带互联网的多媒体传输等技术问题。在整个系统的实现上，本文提出了一个基于实时传输协议(RTP)的具体实施方案，并利用面向对象的方法对在线口语训练系统进行了分析和设计，从而建立了一个完整的应用系统。
在整个系统实现的基础上，通过对在线口语训练系统的各个功能进行测试表明：该系统不仅能很好的满足在线口语训练各方面的要求，而且在多媒体的播放质量上比以往的系统有一定程度的提高。
Under the support of two major technniques of the network and multimedia, remote tutoring system develops vigorously. As one new way of knowledge propagate, it is paid more and more attention .The online spoken language training system is an important component of the remote tutoring system , at the same time it is difficult to realize in the remote tutoring system. The main performance of this thesis is to realize global frame of online spoken language training system, study and solve the problem of playing stop, discontinous playing and the problem of out of step to play in what network appear in transmitting especially.
With the existing online spoken training system deeply analyzed, according to the problem of playing stop, discontinous playing and the problem of out of step to play in what network appear in system, the implementation of online spoken training system base on RTP (real-time transport protocol) is put forward. Namely in the course of transmission of multimedia, at first ,the multimedia data is compressed in real time by MPEG-1 standard; then, the multimedia data is scheduled and repaired in real time ; finally, on UDP layer ,the new-type real time network and transport protocol-RTP/RTCP is adopted to control the transmission of multimedia data. With deeply analyzing algorithm of schedualing patch flow ,the alternative scheduling algorithm that is suitable to the system is put forward to schedual the multimedia data; On the basis of deeply analyzing algorithm of forward error correction (FEC),the repairing algorithm that is suitable for MPEG-1 video and audio is proposed. By means of above process the techniq
ues which include the multi-media synchronism, the recovery of error in network transimission ,the transimission of multi-media in narrow band width are soloved. About realization of the whole system ,in this thesis, the concrete realization scheme which is on the basis of the method of the RTP implementation ,is put forward and applying object- Oriented method,the system is analyzed and designed in detail, then forms the whole application system further.
On the basis of implementation of whole system,by testing each function of this system,it is show that :this system not only greatly responds to the request of the different fields of system, but also improve in more extent than the past system on the quality of playing multimedia.
引文
[1] 戴梅萼，杨川，付良等．一个优化的远程教学系统的设计和研究．北京：清华大学报(自然科学版)，2000，40(9)：74～76
[2] 辉华，周娅，张文辉．现代教育技术的一个重要方向——流媒体技术．桂林电子工业学院学报．2003，23(2)：25～28
[3] 王鹏，许志详．基于IP寻址的多媒体通信．广播电视网络技术，2000(3)：36～39
[4] 高波．基于Internet的流媒体技术．中国远程教育，2002(2)：58～59
[5] 邹华，周强．视频流媒体技术的教学实现．广东广播大学学报，2002(3)：32～36
[6] 陈兴巧．流媒体技术浅析．西部广播电视，2003(2)：13～15
[7] 蔡志军，洪佩琳，李津生．Internet实时多媒体通信高效协议．现代电信科技，1997(8)：5～11
[8] Audio-Video Transport Working Group . RTP: A Transport Protocol for real-time Applications. IETF. RFC1890, 1996(1): 10～15
[9] 吴昱军．多媒体传输协议及在视频传输系统中的应用．微计算机信息，2003，19(10)：75～76
[10] 钟玉琢，王琪，赵黎，土小勤．MPEG-2运动图像压缩编码国际标准及MPEG的新进展．北京：清华大学出版社，2002
[11] 刘益贞，刘滔．Visual C++实现MPEG/JPEG编解码技术．北京：人民邮电出版社，2002(11)：176～182
[12] ISO/IEC International Standard 11172-2 . Coding of Moving Picture and Association Audio for Digital Storage Media at up to about 1.5Mbps. 1994
[13] 钟玉琢，王琪，贺文玉．基于对象的多媒体数据压缩编码国际标准——MPEG-4及其校验模型．北京：科学出版社，2000
[14] 朱广进，祝建．基于非均匀取样的DCT变换[J] ．计算机工程(特刊，上海市计算机学会第五届学术会议)，1997(23)：176～178
[15] 贾志科，崔慧娟，唐昆，冯重熙．用于运动位移估值的新匹配准则，1999，1(1)：43～46
[16] 吴晓蓉，张文俊，杨斌．一种用于H．263的快速块匹配算法．上海大学学报(自然科学版)，2000，6(1)：75～78
[17] 许先斌，安晖，吴国东等．一种基于RTP的MPEG-2实时传输系统．计算机工程，2002，28(10)：167～168
[18] D.hoffman. RTP Payload Format for MPEG1/MPEG2 Video. IETF RFC 2550, 1998(1)
[19] M.Civanlar. RTP Payload Format for Bundled MPEG. IETF RFC 2343 May, 1998
[20] 许长桥，黄明和．MPEG流封装成RTP协议包的具体实现．微型电脑应用，2002，18(9)：54～55
[21] Perkins.C, Hodson.O. Options for repair of streaming media, draft-ietf-avt-info-repair-03, IETF, 1998, 3(13) : 1～5
[22] Dempsey.B.J., Weaver.A.C . On retransmission baseder error control for continuous media traffic in packet switching network. Computer Network and ISN Systems, 1996, 28(5) : 716～736
[23] Hardman, V.Sasse, M.A..Handley. Reliable audio for use over the Internet. 1995. http://www.mice.cs.ucl.ac.uk/multimedia/publicactions/RAT/inet95 -rat.ps
[24] Hung Q.Ngo, Srivatsan, Varadarajan, Jaideep, Sfivastavas . On achieving lower consecutive losses for continuous media streams. http://cs.mnu.edu/tr1999/99-005.ps
[25] Mastromartino.E.A. RTP library. ftp://iasi.rm.cnr.it/pub/RTP. 1998
[26] 张钶，谢忠诚，鞠九滨．基于实时传输协议的丢包实时修复．软件学报．2001，12(07)：1042～1049
[27] 钟玉琢，向哲，沈洪．流媒体和视频服务器．北京：清华大学出版社，2003
[28] Dan A.Sitaram , D.Shahabiddin . Scheduling policies scheme to support pause with batching. Proc ACM Multimedia'94 Conf, 1994
[29] Anthony Jones , Jim Othlund . Network Programming for Microsoft Windows . Washing, U.S.A: Microsoft Press, 2000, 3
[30] 董庆阳等．IP组播技术．数据通信，1998，9(3)：18～21
[31] Almeroth K C, Ammar M H. The use of multicast delivery to provide a scalable and interactive video-on-demand service. IEEE J Selected Areas in Comm, 1994
[32] Golubchik L, Lui J, Muntz R. Adaptive piggybacking : A noval technique for data sharing in video-on-demand storage services. Multimedia Systems, 1996
[33] Kien A Hua, Simon Shen . Skyscraper broadcasting: A new broadcasting scheme for metropolitan video-on-demand System. ProcACM SIGCOMM Conference, Cannes, France, 1997(7)
[34] 赵炯，张树京．一种改进的TCP稳态流吞吐量模型及其性能分析．通信学报．2003，24(1)：52～59
[35] 章程，李建华．实时视频传输的反馈拥塞控制策略．计算机工程．2002，28(2)：56～58
[36] 苏晓丽，郑明春，孟强．多播拥塞控制研究进展．通信学报．2003，24(5)：94～104
[37] John W．Satzinger Robert B．Jackson Stephen D．Burd．系统分析与设计．北京：机械工业出版社，2002
[38] B.J.Cox. Object-Oriented Programming. U.S.A, Addison-Publish Co. ,1986
[39] 刘超，张莉．可视化面向对象建模技术——标准建模语言UML教程．北京：北京航空航天大学出版社．1997
[40] 唐朝京，鲜明，肖顺平，张义荣，赵志超，李华胜．Windows平台上实现多媒体信息实时捕获的几种主要技术研究．计算机应用研究．2003，20(5)：37～39
[41] 胡健，黄丽华，徐至旭，薛华成．面向对象的分析与设计方法的比较研究．计算机工程与应用．1994(12)：4～9
