Hi Priya IMO, the version number in the 'o' line of SDP can be used to determine whether the SDP is a new offer or a session refresh request.
Consider the following excerpt from RFC 3264, Modifying the Session The offer MAY be identical to the last SDP provided to the other party (which may have been provided in an offer or an answer), or it MAY be different. We refer to the last SDP provided as the "previous SDP". If the offer is the same, the answer MAY be the same as the previous SDP from the answerer, or it MAY be different. If the offered SDP is different from the previous SDP, some constraints are placed on its construction, discussed below. Nearly all aspects of the session can be modified. New streams can be added, existing streams can be deleted, and parameters of existing streams can change. When issuing an offer that modifies the session, the "o=" line of the new SDP MUST be identical to that in the previous SDP, except that the version in the origin field MUST increment by one from the previous SDP. If the version in the origin line does not increment, the SDP MUST be identical to the SDP with that version number. The answerer MUST be prepared to receive an offer that contains SDP with a version that has not changed; this is effectively a no-op. Thus - If UPDATE is received with SDP having the same version in 'o' line, you can consider it as a session refresh request. - If the version number is incremented by 1, consider it as a new offer. Regards, Tarun Gupta Aricent -----Original Message----- From: sip-implementors-boun...@lists.cs.columbia.edu [mailto:sip-implementors-boun...@lists.cs.columbia.edu] On Behalf Of Priya Arya Sent: Monday, November 08, 2010 9:33 AM To: sip-implementors@lists.cs.columbia.edu Subject: [Sip-implementors] Identifying Session Refresh UPDATE Hi, I have one query regarding the Session Refresh UPDATE. - Just by looking at PDU of UPDATE in a session, can it be idenitified that if this UPDATE is for session refresh or for updating the SDP parameters in the session. Actually RFC 4028 recommends the following : " It is RECOMMENDED that the UPDATE request not contain an offer [4<http://tools.ietf.org/html/rfc4028#ref-4>], but a re-INVITE SHOULD contain one, even if the details of the session have not changed." But if UPDATE is received from UAS containing SDP in it, then can the session version number in the "o-line" be used to identify if this UPDATE is for updating the SDP parameters only. Thanks in advance. Regards Priya Arya ________________________________ "DISCLAIMER: This message is proprietary to Aricent and is intended solely for the use of the individual to whom it is addressed. It may contain privileged or confidential information and should not be circulated or used for any purpose other than for what it is intended. If you have received this message in error, please notify the originator immediately. If you are not the intended recipient, you are notified that you are strictly prohibited from using, copying, altering, or disclosing the contents of this message. Aricent accepts no responsibility for loss or damage arising from the use of the information transmitted by this email including damage from virus." _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors "DISCLAIMER: This message is proprietary to Aricent and is intended solely for the use of the individual to whom it is addressed. It may contain privileged or confidential information and should not be circulated or used for any purpose other than for what it is intended. If you have received this message in error, please notify the originator immediately. If you are not the intended recipient, you are notified that you are strictly prohibited from using, copying, altering, or disclosing the contents of this message. Aricent accepts no responsibility for loss or damage arising from the use of the information transmitted by this email including damage from virus." _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
