As mentioned above the Session Initiation Protocol (SIP) is a (multimedia) communications protocol. In particular this signalling protocol allows for the establishment of sessions over packet based networks. This protocol has been particularly important in the implementation of IP telephony functionality, which provides for relatively cheap telephone (and other media) connections using the Internet.
Current implementations of SIP generally run atop the TCP and UDP protocols layers (i.e. the Internet), but it can be implemented over ATM, X25, frame relay and carrier pigeon networks without change.
Some of the main characteristics/advantages of this protocol include:
- It includes all the general standard call-forwarding techniques.
- Personal mobility, i.e. it allows a user to be identified by a location independant address
- Setting up of multiparty calls.
- Dynamic feature negotiation.
Competing/related technologies include H.323 and MGCP/Megaco.
References:
http://www.cs.columbia.edu/sip/
http://www.sipcenter.com/