Agreed, although it does not seem that the payload data is instrumental
in the definition of a session per se.
However, if an SDP offer was sent with the initial INVITE, the first
reliable non-failure response to it must contain an SDP answer.
If no SDP offer was present in the initial INVITE, an initial offer may
be originated by the UAS in the first reliable non-failure response (the
200 OK) back to the UAC, in which case the UAC is required to provide
its answer in the ensuing ACK.
There are some passages in RFC 3261 13.2.1 that seem to support the idea
that if an offer was present in the INVITE, a non-failure response must
have an answer - and a provisional response may have an answer:
"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."
...
"Concretely, the above rules specify two exchanges for UAs compliant
to this specification alone - the offer is in the INVITE, and the
answer in the 2xx (and possibly in a 1xx as well, with the same
value), or the offer is in the 2xx, and the answer is in the ACK.
All user agents that support INVITE MUST support these two exchanges.
Paul Kyzivat wrote:
> No this isn't valid. The offer must be answered.
>
> This is the Session Initiation Protocol. Without an answer you have not
> initiated a session.
>
> Paul
>
> NC Reddy wrote:
>> Hi,
>> I have the following context question:
>>
>> UAC <------------->AS(B2BUA)
>> | ------F1 (INVITE)--->
>> * SDP-Offer*
>>
>> <-----F2: 100 Trying---
>>
>> <----F3: 200 OK*(NO-SDP)*---- //Does this step is valid
>> without SDP, ?:
>>
>> ------F4:ACK------------>
>>
>> Questions:
>>
>> - Does the 200 OK response without SDP -Answer is a "valid" sip response
>> in the above context?.
>> - If not what are the reason(s)?
>>
>> Regards
>> Channa
>> _______________________________________________
>> Sip-implementors mailing list
>> Sip-implementors@lists.cs.columbia.edu
>> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
>>
> _______________________________________________
> Sip-implementors mailing list
> Sip-implementors@lists.cs.columbia.edu
> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
--
Alex Balashov
Evariste Systems
Web : http://www.evaristesys.com/
Tel : (+1) (678) 954-0670
Direct : (+1) (678) 954-0671
Mobile : (+1) (706) 338-8599
_______________________________________________
Sip-implementors mailing list
Sip-implementors@lists.cs.columbia.edu
https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
