Fast connect procedure for Session Initiation Protocol using cached credentials

SIP initiates a call using a three way handshake between User Agents (UAs). Each time a SIP UA initiates a call, it has to perform capability negotiation which involves resolving the caller, selecting an audio codec or a video codec among other things. In this paper, we have proposed a novel scheme for reducing the size of INVITE messages by enabling caching at the UAs. We propose to prevent the transmission of Session Description Protocol messages, which are used for capability negotiation, where-ever possible. Instead, we make UA remember the capabilities of the other end and act upon it intelligently. We have made attempts to make our modification backward compatible and in conformance with SIP RFC 3261. The capabilities will be saved in persistent storage of each UA and will be updated periodically to conform with the in-call INVITE messages. This proposal will effectively reduce the message size of both INVITE and the impending response (180/Ringing or 200/OK) message by half. Under ideal conditions, we get two messages with half the original size. If either end fails to follow to this procedure, SIP codec negotiation will revert back to the original Session Description Protocol exchange without any overhead as described in RFC 3264.