Re: [sipcore] Dialog state - Scope in draft-ietf-sipcore-reinvite

[Gonzalo Camarillo <[e-mail]>]

Hi Gao,

the successful completion of any offer/answer exchange without
preconditions means commitment. In your example, offer/answer 1 already
means commitment.

Cheers,

Gonzalo


On 22/07/2010 10:33 AM, [e-mail] wrote:
> 
> Hi Gonzalo,
> 
> 
>> > 3.3:
>> >
>> >     A change to the session state is considered to have been executed if
>> >     an offer/answer without preconditions [RFC4032] for the stream has
>> >     completed successfully or the UAs have exchanged media using the new
>> >
>> > "exchanged" is a tricky word here, and could use some added definition.
>>
>> I have done the following:
>>
>> OLD:
>> ...or the UAs have exchanged media using the new parameters
>>
>> NEW:
>> ...or the UA have sent or received media using the new parameters
>>
>>
>> > A UA can know if it has *sent* media, and it can know if it has
>> > *received* media. If media has been received (and can be distinguished
>> > from the media that would have been received had the change not
>> > occurred) then that UA knows media has been exchanged. But it doesn't
>> > know if the other UA knows media has been exchanged. We want both sides
>> > to reach the same conclusion regarding the exchange of media, but I'm
>> > not sure how to assure that.
>>
>> You cannot do this in a simple way. For RTP over UDP media, you would
>> need to look at the RTCP information. For TCP media, you would need to
>> look into the TCP data (unless the media stream itself provided some
>> type of acks). So, I think this is the best we can do without adding a
>> level of complexity that nobody would really implement just to resolve
>> corner cases.
>>
>> > So, from the perspective of one of the UAs, how do you propose that
> this
>> > decision be made? Is it just "I have received media according to the
> new
>> > sdp"?
>>
>> I have received or sent media (or both) using the new sdp.
>>
>> > What about cases where no media is expected to be exchanged as a result
>> > of the new O/A?  E.g. Suppose the change was simply from
> "a=sendrecv" to
>> > "a=inactive". Is the absence of packets for some period of time
> evidence
>> > that this is in effect?
>>
>> To cover all these cases, the UAs can perform a new offer/answer
>> exchange without preconditions, as described in that section. That is
>> the more general way to indicate that the session parameters are in use.
> 
> I'd like to check that do you mean only the new(subsequent) O/A exchange
> with out precondition means commitment?
> 
> as a example:
> 
> Offer1/Answer1(without precondition), then the Offer2/Answer2 with the
> same SDP. Only the Offer2/Answer2 means commitment?
> 
> then, I think the following sentence might not be proper. As this should
> be a defintion for the new (subsequent) O/A exchange behavior.
> 
> As indicated above, the successful
>    completion of an offer/answer exchange without preconditions
>    indicates that the new parameters for the media stream are already
>    considered to be in use.
> 
> Thanks,
> 
> Gao
> 
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