SIP FAQ : Relationship to Other Protocols :
Why use SIP for presence and instant messaging?
- SIP networks already provide presence information (via REGISTER) as it is needed for session intitiation;
- delivery of presence and notification messages to people is supported on top of existing proxy networks;
- instant messages are often best modeled as a session;
- presence and IM are both parts of a broader communications service that also includes voice, video, shared applications, etc., and it would be nice to smoothly integtrate those together,
- events are needed for a number of session-related functions, thus SIP needs event notification functionality in any event (events are a generalization of presence);
- a requirements analysis showed that much of what's needed for a scalable presence and IM protoco is already offered by SIP.
What port numbers should I use for RTP sessions set up with SIP?