Expedited resource negotiation in sip

Abstract

A method of expediting resource negotiation in a modified Session Initiation Protocol (SIP) reduces the number of messages exchanged for resource negotiation, thereby reducing the latencies involved in session setup. The method entails sending an INVITE message having a modified SIP header containing an indication that the originator's terminal seeks a fast session setup. The INVITE message further contains a list of all codecs available at the originator's terminal and how many each type of media component are required. These codecs can be provided in an order of preference. The answerer selects the codecs for the requested media types from the list of available codecs without engaging in a back-and-forth resource negotiation for the codecs. The result is that the session can be set up with fewer messages which provides quicker session setup than in the prior art.

1 . A method of operating a communication terminal as an originating terminal to originate a communication session with another communication terminal operating as an answering terminal, the method comprising:
 sending, to the answering terminal, an offer message communicating a prioritized list of media capabilities and numbers of media streams required to set up the communication session and corresponding numbers of media streams;   reserving, at the originating terminal, resources corresponding to the media capabilities sent in the offer message;   receiving, from the answering terminal, an answer message communicating at least one media capability selected from the media capabilities communicated in the offer message; and   releasing, from reservation, resources corresponding to any unselected media capabilities on receipt of the answer message.   
     
     
         2 . The method of  claim 1 , further comprising:
 reserving at least one media capability of the originating terminal before sending the offer message; and   releasing, from reservation at the originating terminal, any unselected media capability on receipt of the answer message communicating the selected at least one media capability.   
     
     
         3 . The method of  claim 1 , wherein the offer message comprises a list of media capabilities in order of preference. 
     
     
         4 . The method of  claim 1 , wherein the offer message comprises an INVITE message. 
     
     
         5 . The method of  claim 4 , wherein the INVITE message comprises a modified session description protocol message. 
     
     
         6 . The method of  claim 1 , wherein the offer message is a I:XX message. 
     
     
         7 . The method of  claim 1 , wherein the offer message comprises a list of media capabilities in order of preference.