Research And Implementation Of Wireless Terminal System Based On VoIP Technology

Session Initiation Protocol (SIP) is a control protocol carrying on application layer used for multimedia communications at IP network that is proposed and supported to study by the IEEE. SIP combined with SDP (Session Description Protocol) can offer telephone service of more cheaper price, such as data business and multimedia business, this is the VoIP (Voice over IP) that people often talk about. The wireless local area network is the result of the wireless communication technology and computer network technical development. It has been increasing in importance for current years since its abilities to cover a broad area without the need to pinpoint individual connection point. In 1997, the IEEE ratified the 802.11 Wireless LAN standards, establishing a global standard for implementing and deploying Wireless LANS that is got support from numerous network equipment manufacturers.On the foundation of the studying the realization theory of SIP protocol and how-to use the WLAN security mechanism and roaming, switching function established by IEEE802.11b standard ,the reseach work is designing and implementing the software part of the wireless terminal system based on VoIP technology—IP2050. The system breaks the "wired constraint" and makes the audio packets to transmit over 802.11 WLAN. At the same time the system also can connect to Wire Backbone Networks by making use of the small scale base station equipment in the WLAN. According to the system function demand, the IP2050 is composed of six modules, which are MMI, call manager, system manager, signal-processing, real-time transmission, networks interface. The functions of these modules are relatively independent, but also there is the connection between them, forming the vertical level relationship. Among them, the signal-processing module is more important, which is divided into five layers again, including, stack manager layer, dialog layer, transaction layer, transmit layer and packet-parsing layer. And the transaction layer and packet-parsing layer have been taken deeper discussion as key parts.The system has already passed the field test. The result indicates that it can realize all prescriptive system functions.