SIP Allows Two End Points to Establish Media Sessions with each other. The main signaling functions of the protocol are as backows:
Location of an end point; Contacting an end point to determine willingness to establish a session; Exchange of media information to allow session to be established; Modification of existing media sessions; Tear-down of existing media sessions.
SIP has also been extended to request and deliver presence information (on-line / off-line status and location information such as that contained in a "buddy" list) as well as instant message sessions These functions include.:
Publishing and uploading of presence information; presence and other event notification; transporting of instant messages.
