ABSTRACT
This chapter describes Session Initiation Protocol (SIP) extensions for presence and instant messaging (IM) based on Requests for Comment 2778, 3856, 3857, 3859, 4975–76, and 5365. For providing IM capabilities, the SIP is extended using another method: MESSAGE. Both page and conferencing modes for IM are discussed. Earlier, we have provided very brief explanations about presence, presentity, and watcher in the context of the SIP event framework. However, we provide more detailed description of these functionalities, including presence user agent, presence agent, edge presence server, and presence Uniform Resource Identifier. However, a full treatment of SIP presence and IM needs a complete separate treatment, and we have not done this for brevity.
