Sip-based Distance Learning Communications Technology Research

With the expanding of applied of multimedia on Internet,the demand of multimedia data-flows especially the transmission of realtime data-flows become bigger,related applied such as the distance teaching,the VOD(Video-On-Demand)etc.The multimedia control signaling which is accepted extensively includes series of ITU-T H.323 and SIP which was brought forth by TETENow,the multimedia distance teaching systems based on IP network were put forward according to the H.323 of ITU-T,the development of H.323 is more mature and can guarantee a certain quality of service.SIP is another communication protocol which can develop multimedia teaching on IP network.It adopts the method of calls control and links a control,at the same time the call control news and medium control news are sending in the meantime,and it can adjust state and modify conversation attribute dynamic,such as conversation bandwidth requirements,type of transmission media,the media encoding and decoding formats,as well as the support of the Multicast,etc,and it is suitable for the characteristics of data transmission on IP network.So it has a brighter future.SIP(Session Initiation Protocol)is a control protocol in application layer which was put forward by IETF,and independent of the underlying transport protocol TCP/UDP/SCTP.It can be used to establish,revise,and cease the multimedia conversation of two or more parties.The SIP system includes four parts of user Agent,SIP proxy server, Redirection server,SIP register server.This thesis briefly.introduces the basic function of SIP and framework of the protocols,studies the entity of user agent,SIP proxy server,Redirection server,SIP register server and location server.It describes the session processes and information description of SIP protocol,parameters consultation meeting,SIP affairs and dialogue,SIP registration system and SIP message format,deeply and comparatively analyzes between SIP protocol and H.323 protocol from various angles of the architecture,reliability, extensible,complexity of protocol.In this paper,we analyze and study the distance teaching systems,put forward the model of remote synchronization teaching system based on SIP,analyze and the working principle and workflow of system model,describe teaching process and its' functions of the remote synchronization Teaching System.At last,analyze the key technique which is involved such as multicast,protocol SDP of Session description,RTP/RTCP etc.This thesis introduces the Concrete process of the synchronous distance experiment teaching system:The software and hardware environment and the configuration of LCS; Describes the principle of e-board and carries to the DCOM server and DCOM client of e-board;Analyzes the function of on-line answer question mold,introduces the key technique which is involved such as the technique of FTP,the technique of formula edit, the key document and algorism of creation of index files.Describes the basic frame of instant communication,analyzes to class and configuration files of the server needs,and gives source code,analyzes designment and realization of sound video mold,finishes data collection of sound video,RTP transmission of the sound video,receive and play of the sound video,synchronous processing of the sound video.At last,we carry on a related test and simple analysis.