Research And Implementation Of SIP Gateway For Single Channel Communication Between Digital Trunking And Public Network

In the private communication system field, the digital trunking communication system with the advantage of high security and good compatibility and abundant function have been already widely used in many fields of the railway transport, road transport, civil aviation, shipping and so on. In the public communication system, SIP (Session Initiation Protocol) is one of the core protocols for the next-generation Internet, and has the characteristics of simple, efficient and easy expansion, and is widely used in the new emerging network communication and traditional telecom system. Interconnection between SIP and PSTN (Public Switch Telephone Network) has already a corresponding SIP-T specification, the interconnection between digital trunking system and public network can be realized by SIP gateway, in order to greatly expand the function of the digital trunking communication system. Therefore, the study of SIP gateway with the capability of connecting digital trunking with public network has important significance.First of all, based on summaizing the development of digital trunked system and SIP at home and abroad, the components of digital trunking system and the location and the fuction of SIP gateway are analyzed in details in this paper. The second, according to the protocols of digital trunking and public network, registration and calling process of interconnection between digital truking and public network are provided, and SIP gateway is divided into five modules, such as SIP message dealing module, digital trunking PDU dealing module, channel configuration message dealing module, Az dealing module and registration dealing module by the design idea of modularization. At last, the code of SIP gateway is programmed by the osip protocol stack and TPDUGen tool and the GCC compiler in Linux entironment, and the tests of SIP message dealing function and digital trunking PDU dealing function adn channel configuration message dealing fuction and Az dealing function and registration dealing function are made in the unit testing and the system testing. The results of test demonstrate that the single channel communication between digital trunking and public network can be realized by SIP gateway.