In addition, you can take a look into draft-sawada-sipping-sip-offeranswer-01.txt to find more details about offer-answer negotiation scenarios...
ACK just conveys UAS that answer sent by UAS is been received by UAC and either can start using the negotiated SDPs without any doubt. Also it helps to complete the delayed media negotiation scenarios. Thanks, Nataraju A B > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:sip-implementors- > [EMAIL PROTECTED] On Behalf Of Sameer Sawhney -X (ssawhney - > Flextronics Software at Cisco) > Sent: Tuesday, September 19, 2006 8:56 PM > To: 'Meir Leshem'; [EMAIL PROTECTED]; [email protected] > Subject: Re: [Sip-implementors] ACK is needed ?? > > Hi Meir, > > The example that I suggested was a very crude one in order to help Moin > understand the logic.I think the language might have caused some confusion > to you that the UAC sends a third SDP in the ACK. No actually what I meant > was that a subset of items from the initial offer has to agreed upon by > the > both parties before the media session actually gets started. > > As far as you question about a single chosen codec in the answer,AFAIK the > answer can have a list of codecs chosen from the subset of offer but they > have to be listed in the same order. This helps in assuring that the same > codec is used in > both directions. > > For more details on Offer-Answer,have a look at rfc3264. > > Regards > Sameer > > > > -----Original Message----- > From: Meir Leshem [mailto:[EMAIL PROTECTED] > Sent: Tuesday, September 19, 2006 12:23 AM > To: [EMAIL PROTECTED]; [EMAIL PROTECTED]; > [email protected] > Subject: RE: [Sip-implementors] ACK is needed ?? > > Hi, > Most of the explanation is good and useful, however in the last paragraph > you provided an example with offer (in the Invite) of 10 items from the > UAC, answer in the 200 OK with 5 items from the UAS and a final choose of > one item from the UAC in the ACK. Do you mean that a third SDP (a new > offer?) is sent within the ACK? So how the UAS will send its final answer? > BTW, in telephony (VoIP) calls, I have never seen something else than a > list > of codecs in the "offer" and a single chosen codec in the "answer" > SDP. So this behavior is the only commercial procedure for voip telephony > as > far as I know. Is it correct? > > > Regards > Meir Leshem > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Sameer > Sawhney -X (ssawhney - Flextronics Software at Cisco) > Sent: Monday, September 18, 2006 9:43 PM > To: [EMAIL PROTECTED]; [email protected] > Subject: Re: [Sip-implementors] ACK is needed ?? > > Hi, > > The ACK of 200OK of INVITE serves multiple purpose. The primary purpose of > the ACK is to confirm the reception of the final response of the offer i.e > 200 OK. > If the UAC did not send any offer in the initial INVITE, the 200 OK should > contain the offer and ACK contains the answer of the UAC. > The ACK for a 200 OK response to an INVITE request is considered as a > separate transaction and it completes the three way handshake procedure to > establish a SIP session. > > Consider an imaginary situation where Bob and Alice has to agree on one > aspect of session (like codec to be used for the session). > The whole logic of 3 way handshake can be visualized in this simple > example > where Bob initiates a SIP session towards Alice. Bob sends 10 > aspects/items > which can used in initial INVITE . The UAS (Alice) sends back 200 OK > specifying that it can support 5 items, but you tell me which one would > you > like to use for this session. > Now the final decision is in hand of Bob (UAC) to accept a particular > aspect/item and inform the UAS (Alice) about this. This final decision is > conveyed in an ACK of the INVITE request. > > I hope this a very crude example (ps: this might not be the best way ) > will > help you understand the logic behind the need of ACK for 200 OK. > > For more details on ACK, refer rfc 3261. That will clear all your doubts! > > -sameer > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > [EMAIL PROTECTED] > Sent: Monday, September 18, 2006 9:37 AM > To: [email protected] > Subject: [Sip-implementors] ACK is needed ?? > > Hi, > > What was the intention behind proposing the need for sending ACK after > 200OK > of INVITE under SIP. > > > _______________________________________________ > 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 > _______________________________________________ > 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
