SIP supports five facets

SIP supports five facets of establishing and terminating multimedia

communications:

User location: determination of the end system to be used for

communication;

User capabilities: determination of the media and media parameters to

be used;

User availability: determination of the willingness of the called

party to engage in communications;

Call setup: "ringing", establishment of call parameters at both

called and calling party;

Call handling: including transfer and termination of calls.