SIP(Session Initiation Protocol) is a protocol, including transport layer, transaction layer, session layer (transaction user layer), for establishment, modification and termination of a multimedia session or call. Multimedia sessions can be applications as multimedia meeting, distant education and IP Phone. SIP can be easily extended in order to support improved functions. SIP-BCP-T(or SIP-T) is part of the extension of SIP, which addresses the communication between MGCs. It also supports synchronization between different MGCs and communication with ISUP. SIP enables users to be reachable by means of IP networks as wired LAN and WAN, Public Internet Skeleton Network, Mobile 2.5G and 3G , Wi-Fi and IP devices as telephone, PC, PDA and Mobile Phones.

SIP is a client-server protocol in text form. The client generates a request and then the server makes a response to the request. This is very similar to SMTP (Simple Mail Transmission Protocol ) and HTTP (Hyper- Text Transmission Protocol ). SIP holds the features of simplicity, unlimited extension and close relation with applications of current Internet.

SIP offers a framework for development. With this framework you can develop lots of IP telecommunication services which are applicable to the 3G mobile telecommunication. This technology makes Internet be able to link with mobile phones through a consistent protocol and enables future mobile endpoints and other equipments to link with the Internet to communicate with each other more directly through IP data-stream. It means that more services as voice, short message and e-mail can be provided to users through mobile phones in a more intelligent way. At the age of whole IP technology, plentiful new applications can be realized with SIP.