Re: [Sip-implementors] To tag in 180 but not in final response

[Sergey Sitnikov]

Hi Doug!   You can't receive response without to tag. See p. 15.2(page 78 ) in bis-03.   15.2 Callee Issues Response .... Additionally, the responding UAS MUST add the tag parameter to the To field in the response .....   Note, that each response with different to tag represents different CallLeg. And only successful responses creates CallLeg.   SY. Sergey Sitnikov   Coretek   ----- Original Message ----- Hi,    I have a scenario in which a UAC sends an INVITE and then receives    a 180. The 180 includes a to header with a tag. After the 180 is received    a "408 Request Timeout" final response is received.  The 408 final response    does have a to header tag.    I was under the impression that the UAS would send the same to tag once    it sent the to tag.  Without the to tag in the 408 final response the UAC cannot    tell if the 408 is from the same proxy or from a proxy which received a forked    copy of the INVITE.    If the UAS sends the 408 with a tag it will be accepted by the UAC even if    the 180 was never received by the UAC.  This would occur as the final response    would be the first response with a tag for the transaction.    Are there valid cases in which the UAC should accept a subsequent response    without a to header tag once a response is received with a to header tag?