The Research Of Supplementary By Extending SIP Headers In NGN Architecture

Due to its tremendous advantage, IP telephony is becoming one of the most rapidly developing application technologies.Many organizations of telecommunication and computer in the world are engaging in research on this technology. This leads to two signaling standards of IP telephony,ie ,H.323 and SIP(Session Initial Protocol),which are recommended by ITU-T and IETF respectively.At present, H.323 has applied widely in the IP telephony in China. However, SIP is becoming a focus because of its merits such as simplicity, agility, distributing control and high expansibility, especially 3 GPP uses SIP protocol as the main signaling control protocol in multimedia domain. Now application based on SIP is one of the hotspot in IP telephony.But SIP is new and immature, and not applied on a large scale in telecommunication field. Therefore, the research on IP telephony based on SIP is very significant.The main contributions of this thesis are as follows:Introduces NGN's development briefly: For telecom field, NGN means IP telephone system, which indicates the voice and video communication based IP network, and which means Softswitch sysytem. Currently Softswitch system is replacing the traditional switch system based PSTN network.Introduces SIP protocol briefly: SIP protocol supports name translating and user location, character negotiation, the management for caller or callee and the change of calling character. SIP messages include requiring message and responsing message. Main requiring messages include INVITE, CANCEL, ACK, BYE. Main responsing message include 1^**, 2^**, 3^**, 4^**, 5^** and6^**.Discusses some problems about call forward supplementary server: Call forward means that the callee transfer the calling to another user for some reasons. At present, SIP protocol may support call forward supplement operation, but there are some bugs,for example, it can't limit the forward time, and the caller and the callee can't get forward information.Extends SIP protocol and adds a head^Diversion^to account for the problems about call forward supplementary server.Implements call forward supplementary server and resolves some existent problems: it designed an IP telephone simulation system based SIP protocol in the Microsoft Visual C++ 6.0 development environment, which can implement the call forward operation, and resolve the problems in this operation.The thesis is divided into six chapters.Chapter 1 introduces the current development status of signaling standards of IP telephony;Chapter 2 introduces SIP protocol;Chapter 3 introduces call forward supplementary server based on SIP;Chapter 4 designs an analog system of IP telephony based on SIP in the environment of local area network, which can resolve some problems about call forward supplementary by extending SIP headers;Chapter 5 presents the running and test of the analog system of IP telephony;Chapter 6 summarizes some dificiencies, and prospects the future.