Functions of SIP

SIP is limited to only the setup, modification and termination of sessions. It serves four major purposes

• SIP allows for the establishment of user location (i.e. translating from a user's name to their current network address).
• SIP provides for feature negotiation so that all of the participants in a session can agree on the features to be supported among them.
• SIP is a mechanism for call management - for example adding, dropping, or transferring participants.
• SIP allows for changing features of a session while it is in progress.

All of the other key functions are done with other protocols. Yes! this does indeed mean that SIP is not a session description protocol, and that SIP does not do conference control. SIP is not a resource reservation protocol and it has nothing to do with quality of service (QoS). SIP can work in a framework with other protocols to make sure these roles are played out - but SIP does not do them. SIP can function with SOAP, HTTP, XML, VXML , WSDL, UDDI, SDP and others. Everyone has a role to play!
With all that said, SIP is still one of the most important protocols. Better learn about the SIP components.

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