| H.323 protocol, Packet-based multimedia communications systems, was mapped out by ITU-T. It is a frame protocol, working with H.225 protocol, H.245 protocol and many audio/video codec protocols. All of those compose H.323 protocol stack. This project aims at the implementation of H.323 protocol stack independent of any operation system and hardware. The protocol stack should work under any environment through transplanting. For the convenience of display, this project implements H.323 terminal and makes it work under WinXP operation system.This paper puts out the scheme of H.323 protocol stack firstly and then mainly describes the detailed design and software achievement of H.245 protocol and bandwidth control. Finally It is supplied that test for H.245 protocol and bandwidth control. H.245 control starts after the finish of call signalling. It implements capability exchange, master-slave determination between two communication terminals by signalling message. It's also in charge of opening logical channels used to transmit audio/video streams. The adjustment of audio/video codec and maintenance loop during the course of communication can also be achieved by H.245 control signalling.About bandwidth control, this paper brings forward the application and implementation of RSVP, Resource ReserVation Protocol in H.323. The function of RSVP is transmitting signalling among terminals and routers, setting aside some bandwidth for audio/video stream in advance and ensuring quality of service when the total bandwidth is not enough.In all, There are some special difficulties on the design of H.245 protocol and bandwidth control. The first is PER of signalling messages. The second is to find reasonable data structure store complex terminal capability set. The third is to finish fast singalling procedures cooperating with faststart and tunneling. And the last is to draw out SDL diagram for RSVP implements. These difficulties are resolved well in this paper.
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