Subject: [Sip] Questions regarding Offer/Answer model...

From: "Patrick Lam" <[email-masked]>
Date: Mon, 14 Apr 2003 13:09:06 +0800

Dear all:

On p.80 of RFC 3261, it states that:

"If the initial offer is in an INVITE, the answer MUST be in a reliable
non-failure message from UAS back to UAC which is correlated to that INVITE.
For this specification, that is only the final 2xx response to that INVITE.
That same exact answer MAY also be placed in any provisional responses sent
prior to the answer.  The UAC MUST treat the first session description it
receives as the answer, and MUST ignore any session descriptions in
subsequent responses to the initial INVITE."

My questions are:
1.	Is the answer from 1xx valid then???  If so, why does it state that
the answer can only be present in 2xx on one hand, but on the other hand if
the answer is present in 1xx, the answers from 2xx must be ignored??? 
2.	What about the UAS "changes" its mind on the answer after it sends
1xx response (e.g. the callee answers the call from a different UA), and
wants to incorporate the changes into 2xx responses????
3.	Can 100 Trying carry 'answers"?

Thanks very much in advance,

Patrick

---

From: [email-masked]
Date: Mon, 14 Apr 2003 11:52:13 +0530

Response inline...

regds,
srikanth
Hughes Software Systems

"Patrick Lam" <[email-masked]> on 04/14/2003 11:39:06 AM

To:   [email-masked]
cc:    (bcc: Srikanth Sundaragopalan/HSSBLR)

Subject:  [Sip] Questions regarding Offer/Answer model...

Dear all:

non-failure message from UAS back to UAC which is correlated to that
INVITE.

My questions are:
1.   Is the answer from 1xx valid then???  If so, why does it state that
the answer can only be present in 2xx on one hand, but on the other hand if
the answer is present in 1xx, the answers from 2xx must be ignored???
-> Yes,the answer from 1xx is valid,provided that is transmitted reliably.
-> This talks about 2xx response alone because,the RPR's(Reliable
provisional
-> responses)are not part of RFC 3261 and is part of RFC 3262.
-> An Answer can be sent in any RPR(180,182,183) and the same answer can be
-> echoed back in 2xx responses.
2.   What about the UAS "changes" its mind on the answer after it sends
1xx response (e.g. the callee answers the call from a different UA), and
wants to incorporate the changes into 2xx responses????
->UAS *CANNOT* Change the answer when sending 2xx response.If it decides to
change the media
-> parameters it needs to do so by sending a UPDATE Request.(Refer RFC
3311).
3.   Can 100 Trying carry 'answers"?
-> NO.100 Trying is never transmitted reliably,hence cannot contain SDP.
->Moreover its mostly the proxy which sends 100 trying.

Patrick

[Filename: winmail.dat, Content-Type: application/ms-tnef]
The attachment file in the message has been removed as per HSS E-mail
Policy.

_______________________________________________
Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [email-masked] for questions on current sip
Use [email-masked] for new developments on the application of sip