Design And Implementation Of Microcontroller-based H.323 Terminal

With the rapid development of Internet and IP technology, packetized telephone service has gradually taken a mainstream role in the evolution of telecommunication networks, in result VoIP technology is undergoing an unparalleled development. Various VoIP products have been injected into markets and are changing people's life-style; meanwhile, the getting rid of the stale and bringing forth the fresh of VoIP technology has became a hotspot absorbing world eyes. Although suffering impact from SIP, undoubted, H.323 recommendations are still most matured standards, have gained a majority of markets, and are most compliant for setting up various dimension IP networks. With the continuous development of VoIP technology, H.323 is also making progress by assimilating advantages from other relevant standards, showing a strong vitality. Many people think that H.323 will continue to be the de facto industry standard.There are some paragraphs in this paper for discussing the system structure of the H.323 standards, which relate to the survey and constitution of H.323 protocols, RTP/RTCP protocols, composing entities of H.323 system, call processes of H.323 communication. It is very important that we master these technologies, because what is useful for modifying, customizing and enhancing the protocols stack in order to conforming it to our national standards.Describing the procedure of implementing a H.323 terminal based on a SCM (Single Chip Micyoco) is the main motive in this paper. The terminal is designed for telecommunication services provider and business users. As conforming with the H.323v2 and relevant national standards, the terminal has high interoperability with other H.323 device, and has some main function units defined by standards such as System Control unit, H.225 Layer unit, LAN interface unit, and Audio Codec unit. This paper has firstly introduced the environment of developing this terminal, which includes PA1688 controller platform, PA1688 API functions libraries, SCM C language and C51 compiler. According to the demanded functions of the terminal, this paper has gave the total designs for hardware and software, then has specifically described function of every module composing terminal software. Continuing, this paper has detailedly presented all writer have achieved works, which involve designing and implementing audio data assignment function, software on-line upgradefunction, real time clock driver programme, user input process function, and testing the terminal's interoperability with some other H.323 devices. At the end of this paper, the conclusion has characterized writer's works and has proposed some advices about improvement of the terminal.