Impletement Of H.323System Gatekeeper

With the development of Internet, Multimedia Communication on PacketBased Nework is becoming a hotspot of the research fields. Implementation ofVideo Conferencing System on IP network makes intercommunion easier. ITU-Tadvances H.323protocol, the Recommendation of Packet-Based MultimediaCommunications System provide conference control and describes thecomponents of an H.323system. Implementation of Video Conferencing Systembased COM is inexpensive, and makes prolateness of system easier.In this paper we study the purport of Video Conferencing System and COM,introduce the development status of both them. Introduce H.323protocol andcomponents of H.323system. Provide a Video Conferencing System based COM,discuss the hierarchy and characteristic of system. Principium of COM,Connectable Object and IDispatch Interface are introduced in detail.The main content of this paper is design and realization of four layers,introduce the technology of IP Multicast and programming of Winsock whichused in Bus Layer. Discuss the implementation of TCP Transmit Component,UDP Transmit Component and IP Multicast Component. Discuss the principiumof RAS protocol, Call Signaling protocol and H.245protocol of Channel Layer,introduce the messages of them and their define by C++, discuss COMInterface of RAS, Call Signaling and H.245Channel Component. This paperintroduce the design of H.323Gatekeeper and Terminal, discuss theimplementation of registration, admission functions in Gatekeeper component.And introduce G.711Audio Format, H.261Video Format and Real TransmitProtocol, the implementation of Audio Recorder/Player, Video Recorder/Player isprovided.Finally this paper introduce the design of Gatekeeper Presentation Layer andTerminal Presentation Layer, analyse the result of communication withNetMeeting, the experiment proves good performance. The H.323VideoConferencing System based COM used on LAN can become a product to popularize.