Hi, I summarised offer/answer exchange a few days ago in this mailing list. If my summary is correct, I can answer your questions as follows;
> > Hi, > > I have couple of questions regarding the use of UPDATE method. > > 1. Can UPDATE be used to send an answer SDP ? > Consider the following scenario: > - INVITE was sent without SDP > - 18x is received with Offer SDP > - There is no PRACK exchange because 18x does not contain a > Require:100rel header > Now can UPDATE be used to send answer SDP?? > No. SDP in a non-reliable 18x response is officially not an answer. This must be the same as an answer which would be received in the subsequence first reliable non-failure response, which may be provisional or may be 2xx. At any time, in my understanding, UPDATE request can not send "offer". > 2. As per RFC 3311, UPDATE method should be used only if dialog is > established. > If INVITE/18x exchange happened without PRACK, can both ends treat this > as early dialog and feel free to use UPDATE ? > No. Establishing an early dialog does not necessarily mean completion of offer/answer exchange. INVITE/18x exchange without PRACK, which would mean 18x is not a reliable provisional response, I assume, can not complete offer/answer exchange. Before sending an "official" answer or receiving an "officail" answer, both ends can not send new offer in UPDATE. > 3. Is 18x send/recv over TCP considered reliable ? > In the following scenario: > - INVITE with offer sdp sent > - 18x over TCP with answer sdp recvd (No PRACK exchange happened) > Now can the caller/calleee use UPDATE ? > No. Basically, SIP application is indepent from the transport layer. Actually, using TCP to the first hop does not guarantee that TCP is used in all the way through the end. Regards, Takuya > Appreciate any responses. > Thanks, > Kasam > > > > _______________________________________________ > Sip-implementors mailing list > [EMAIL PROTECTED] > http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors > -------- Takuya Sawada KDDI Corporation (KDDI) Garden Air Tower, 3-10-10 Iidabashi Chiyoda-ku Tokyo 102-8460, Japan Tel: +81-3-6678-2997 Fax: +81-3-6678-0285 [EMAIL PROTECTED] _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
