The Implementation And Delay Optimization Of SIP In Dispatch Client Of Multimedia Trunking System

Wireless trunking communication system plays an important role on manysituations such as public security, airport, harbor and so on. It can help to fightagainst crime and rescue disaster, protecting people’s lives and property safe. Incommercial network, the third generation (3G) or the fourth generation (4G) mobileradio and WiFi-based systems offer enhanced broadband services, including email,web browsing, picture transfer, video streaming, and other wideband services. Butcompared to commercial mobile networks, wireless trunking system is still laggingbehind in China. It can only provide limited narrowband service like voice andmessaging, which cannot meet the growing demand for command and control. TheSIP(Session Initial Protocal) has been chosen as the signaling of the trunking sys-tem. However, SIP was originally designed for Internet, which means the narro w-band system is not taken into consideration at the beginning. As a result, the SIPsession setup delay can be large.In reponse to these problems, a project called Broadband Wireless Trunkinghas been launched in China. The purpose of the this project is to support researches,developments, standardization and applicable evaluation for broadband wirelessprofessional communications, where the major applications focus on future PublicProtection and Disaster Relief (PPDR). In this papar, the implementation and ver i-fication of the SIP module in dispatch client of the system has been shown in detail.The dispatch can not only support the wideband service but also has the function ofcommand and control such as restructing the groups of user, entering the specifiedsession, making the selected equipment out of work temporarily and so on. And thefunction of control and demand is the main role of the dispatch client, which is im-plemented by SIP module. What’s more, the software environment and parameter ofthe diaspatch client has been determined. And oSip/eXosip stack has been chosn toconstruct the SIP module. Base on this stack, the programme and processes of theimplementation have been shown. The validation shows the SIP module constructedin the paper can meet the project rerquirement well.At the end of the paper, the retransmission mechanism and transport protocalsusing by the SIP has been analyzed in detail. Morever, the equations of the sessionsetup delay have been given. These equations demonstrate the sesision setup delayis very large in real narrowband system and the optimization is needed. The sig-naling compression is an effective way and the combination of LZSS and Huffmanalgorithm is the mainstream. Considering the characteristic of the protocol using bythe project, the combination of LZSS and Huffman with pretreatment has been proposed. Fill the dictionary with the commonly used words can improve the per-formance of the compression mechanism, which can decrease the SIP session delayeffectively.