Extensions of session initiation protocol for next generation services

The IETF's session initiation protocol (SIP) is a flexible, yet simple tool for establishing interactive connections across the Internet. It was originally developed for initiation of multimedia sessions. SIP, Internet multimedia, voice over IP and IP telephony have become quite popular, both within IETF and other standard groups, and the applications of SIP have grown. Result of this popularity has been a continual flood of suggestions for SIP modifications and extensions. One of SIP's most important features is flexibility, i.e. ease of its extension (with new methods, new header fields, new body types, and new parameters). There have been countless proposals to do just that. The intention of this paper is to give a short overview of some of the most interesting extensions of SIP protocol.