Distinguishing between Enforced and Proposed Session Modification in SIP Signalling
Original Publication Date: 2007-May-24
Included in the Prior Art Database: 2007-May-24
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Based on the existing standards for SIP (Session Initiation Protocol), it is possible to modify the session parameters (e.g. media type to be exchanged between peers in a communication session) during an ongoing session by using SIP signaling. Usually, if the session parameters have to be changed, SIP foresees either to use the re-INVITE message or the UPDATE message in order to negotiate the new media types. Both methods allow for the rejection of the proposed media types. Though UPDATE has to be answered immediately, i.e. with no user interaction, the recipient of the message can reject it. However, there exists an enforcement option for the acceptance of sessions that allows the recipient to force off a session invitation to accept the session. This option, which was designed for push to talk services, does not foresee the definition a '"superset" of possible session parameters via the normal SIP negotiation and a subsequent enforced modification of the session within the range of this superset. Also, the caller cannot force the callee to use this option by means of signaling, e.g. by a pre-negotiation prior to the session initiation.