Implement of system control part in a multimedia communication terminal

This paper presents how to realize the system control part of a multimedia communication terminal on a LAN. The system control part is the core of the terminal. The design partly refers to ITU-T H.323. System control is composed of call control and H.245 control. Call control signals are used for call establishment, disconnect and other call control functions. H.225.0 defines the syntax of call-signal messages. We use C language to achieve encode and decode of those messages. TCP/IP network protocols serve as a friendly interface to the LAN. We establish a TCP channel (at 1720 port) to transfer those messages to finish the call control process. Through call control negotiation, we establish another TCP channel for H.245 control. Master/slave determination, capability exchange, logical channel signalling and close logical channel procedures are finished at the H.245 control channel through a message exchange method. Abstract syntax notation one (ASN.1) serves as a structured data specification language. It is widely used in H.225.0 and H.245 protocols. It is very important to finish the ASN.1 language to C language translation. A compiler translates the ASN.1 notations into C language sources, which function as the encoder and decoder for the ASN.1 notations according to X.691 (packed encoding rules or PER). Other parts of the terminal are H.263 video codec, G.723.1 audio codec and RTP (real-time protocol). The terminal can run perfectly point-point multimedia communication on the LAN. It can also interoperate with Microsoft NetMeeting for video and audio communication.