Hi, >> All, >> >>This was talked before but it still looks not clear: >> >> UAC UAS >> >> ----------->F1 INVITE w/o SDP >> >> <-----------F2 18X w/ SDP1 >> >> ----------->F3 PRACK w/ SDP2 >> >> <-----------F4 200 for PRACK >> >> <-----------F5 200 for INVITE w/ SDP1 >> >> ----------->F6 ACK (w/ SDP2 ???) >> >> >> >> My questions: >> >> 1. Could 200 for INVITE in F5 carry an SDP?
>No. There has already been one o/a in the transaction initiated F1. >There cannot be another offer in the same transaction. As far as I understand, the 200 for INVITE does not carry a new offer. It carries the same answer that was carried in 18x (F2). >In the case where the invite carries an offer sdp, and there is SDP in a >provisional response that same sdp can be in the 200. That wording in >3261 that specifies this is intended for unreliable provisionals, but >has been interpreted to also be possible when there was a reliable >response with an answer. But I can find no rationale for allowing an >offer that was sent in a reliable provisional to be sent again in the >200 response to the invite. Since SIP only allows at most one o/a exchange per SIP transaction, I think the o/a state machine should know that the SDP in 200 is of no meaning - no matter if it's a copy of a previously sent (in a reliable 18x) offer or anwer. It's the same thing if you send an offer, or answer, in a reliable 18x, and then copy it in subsequent reliable 18x responses for the same transaction - from an o/a perspective they have no meaning. >Also I can find no rationale for allowing a *new* offer to be included >in the 200 response to an invite if the initial o/a has been completed. Correct. Again, at most one o/a exchange per SIP transaction. Keeping that in mind will take you pretty far, I think :) >> 2. If 200 in F5 carries the same SDP with that in 18X, should UAC send >> an ACK with SDP? >> >Definitely not. Agree. Regards, Christer _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
