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SIP Makes Your Presence Known: Page 3 of 8

These extensions use a PA (presence agent), a SIP-based software package like Microsoft's Live Communication Server 2005. The PA accepts and stores information about the target user. It also can send notifications to subscribers--when a user goes offline, for example. PAs are logical entities, meaning they are collocated with a SIP proxy server, and also come in standalone PSs (presence servers). (You can use the same URI as any other SIP request, such as sip:[email protected]).


The Skinny on SIP Presence

These are the IETF standards-track and informational RFCs (Request for Comments) on SIP-based presence.

RFC 2778: A Model for Presence and Instant Messaging

RFC 2779: Instant Messaging/Presence Protocol Requirements