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  A Brief History of SIP
  What it does & what it doesn't
  Components in SIP
  SIP Commands
  A typical example
  SIP request
  SIP response
  Types of Responses
  Relation among Call, Dialog, Transaction, Message
  SIP Registration




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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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Last updated: March 1st, 2018