Thank you for the citation.
 
The question is does the defined MUST connection between a new offer and 
increment of the version number works in the opposite way? I.e. the incremented 
version number MUST mean a new offer even if the version change occurred in SDP 
transported in 200 OK?
 
Greetings,
Denis Alexeitsev

 -----Ursprьngliche Nachricht-----
Von: Harpreet S Juneja [mailto:[EMAIL PROTECTED] 
Gesendet: Donnerstag, 26. Juli 2007 15:34
An: Alexeitsev, Denis
Cc: sip-implementors@lists.cs.columbia.edu
Betreff: Re: [Sip-implementors] Relevance of the session version field in SDP 
answer


RFC3264 "An Offer/Answer Model with the Session Description Protocol" (par. 8 
Modifying the Session), specifies that:


"At any point during the session, either participant MAY issue a new
   offer to modify characteristics of the session.  It is fundamental to
   the operation of the offer/answer model that the exact same 
   offer/answer procedure defined above is used for modifying parameters
   of an existing session.

   The offer MAY be identical to the last SDP provided to the other
   party (which may have been provided in an offer or an answer), or it
   MAY be different.  We refer to the last SDP provided as the "previous 
   SDP".  If the offer is the same, the answer MAY be the same as the
   previous SDP from the answerer, or it MAY be different.  If the
   offered SDP is different from the previous SDP, some constraints are 
   placed on its construction, discussed below.

   Nearly all aspects of the session can be modified.  New streams can
   be added, existing streams can be deleted, and parameters of existing
   streams can change.  When issuing an offer that modifies the session, 
   the "o=" line of the new SDP MUST be identical to that in the
   previous SDP, except that the version in the origin field MUST
   increment by one from the previous SDP.  If the version in the origin
   line does not increment, the SDP MUST be identical to the SDP with
   that version number.  The answerer MUST be prepared to receive an 
   offer that contains SDP with a version that has not changed; this is
   effectively a no-op.  However, the answerer MUST generate a valid
   answer (which MAY be the same as the previous SDP from the answerer,
   or MAY be different), according to the procedures defined in Section 
   6."



On 26/07/07, Alexeitsev, D <[EMAIL PROTECTED]> wrote: 

> Hello All
>
> Does the value of the session version field in an answer effectively
> mean anything, or does it only have a meaning in an offer?
>
> The problem is that some UAS increment the version number in the 
> answer and some UACs interpret it as a new offer and try to answer it
> in the ACK. That leads to all kind of mess.
>
> So who is wrong here - UAS incrementing the version number in the
> answer, or UAC interpreting it as a new offer? 
>
> Greetings,
> Denis Alexeitsev
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