Research And Implementation Of SIP Proxy Server

With the development of the network and communications technology, real-time voice, video and other multimedia applications are popularized rapidly. The signaling control protocol is indispensable for creating, modifying and terminating sessions with one or more participants. Session Initiation Protocol (SIP) that is designed by the IETF organization for the Internet is a new signaling control protocol. Compared with the traditional H.323 protocol suite, SIP is more suitable for session management of the IP-based network. Due to the advantage in complexity, flexibility, scalability and mobility, SIP-based multimedia application has broad space for development. SIP proxies are located in the middle of the whole SIP architecture and it's mainly responsible for routing SIP messages. They are fundamental for the mobility support of SIP intelligent terminals and the deployment of the SIP network.At first the function structure, network elements, implementation principles, message mechanism and signaling flow of SIP protocol are researched with emphases on transaction state machine and layered architecture according to the open source protocol stack. Then a modularized SIP proxy server is described including the architecture, module communication mechanism, the design and implementation of the key modules. After setting up a SIP communication network in the laboratory environment, we test the functionality of the proxy server to verify that it's compliant with the standard. SIP proxy server works in the open and complex Internet environment. There may be various security threats and attacks. The denial of service attack aiming to the proxy server is researched and a state transition defence model is proposed and verified in experimental environment.