Re: [MMUSIC] [RFC4566] Increment of SDP session version when NO modification is made to the session data

On 3/15/16 10:36 AM, Brett Tate wrote:
>> I am a new in SIP/SDP and I have a question
>
> The following list may be helpful for future sip related questions.
>
> https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors

Yes, that is the best place for this sort of query.

>> If session data is NOT made any change, is session-version
>> acceptable to increase or it is NOT?
>
> As far as I know, RFC 4028 section 7.4 provides the only related mandate.
> For interoperability reasons, I recommend being lenient when receiving.
>
> Section 7.4:
>
> "It is RECOMMENDED that the UPDATE request not contain an
> offer [4], but a re-INVITE SHOULD contain one, even if the details of
> the session have not changed.  In that case, the offer MUST indicate
> that it has not changed.  In the case of SDP, this is accomplished by
> including the same value for the origin field as did previous SDP
> messages to its peer.  The same is true for an answer exchanged as a
> result of a session refresh request; if it has not changed, that MUST
> be indicated."

Note that 4028 is only concerned with session timers. IMO its language 
is confusing and possibly deceptive in some regards. It is *not* 
intended to refine how offer/answer works - only to comment on how 
standard O/A rules might best be used for signaling triggered by session 
timer.

AFAIK it is not *invalid* to increase the SDP session-version when 
nothing else in the SDP has changed. But doing so may cause the other 
side to do more work. (It might have an optimization for the case where 
the version isn't changed.)

	Thanks,
	Paul