Re: Is SDP in an unreliable response "the answer" ???

OKUMURA Shinji wrote:
> Paul,
> 
> Paul Kyzivat <[email protected]>
> Tue, 20 Apr 2010 09:47:58 -0400
>> Here is my attempt at summarizing the discussion conclusions:
>>
>> Normative things (stated or implied in existing RFCs):
>>
>> - If the UAC sent an offer in the INVITE, then after it receives SDP 
>> (the answer) in a reliable response to the INVITE, any SDP in subsequent 
>> responses to the INVITE MUST be ignored.
>>
>> - Further, if SDP is received in an unreliable response to the invite 
>> prior to receiving SDP in a reliable response, then it MUST be treated 
>> as the answer for purposes of media processing, but not for purposes of 
>> determining when another offer may be sent or received.
>>
>> - if the UAS receives an offer in the INVITE, it MUST NOT include SDP in 
>> any response it sends until it has determined the intended answer SDP to 
>> the offer.
>>
>> - once the intended answer SDP is determined, it MUST be sent in a 
>> reliable response to the INVITE. It MAY be sent in one or more 
>> *preceding* unreliable provisional responses.
> 
> I agree. But I think one more sentence is necessary.
> - And the SDP in a *preceding* unreliable provisional responses
>   to the INVITE MUST be identical to an answer SDP.

At first I thought your addition to be redundant.
But looking more closely, I guess it is not. My statements did not 
forbid sending sdp other than the answer.

I think there must be a better way to state these things.
But at least we are settling on the necessary behavior, and that it is 
already implicit in the existing RFCs.

	Thanks,	
	Paul

>> Non-normative, best practice suggestions:
>>
>> - if the UAS receives an offer in the invite, once it has sent the 
>> answer in a reliable response, it should not send any SDP in subsequent 
>> responses to the INVITE.
> 
> I agree. And I add one more reason why it is necessary.
> 
> 4. To avoid misunderstanding that UAS is sending new offer.
> 
> Regards,
> Shinji
> 
>> 	Thanks,
>> 	Paul
>>
>> Christer Holmberg wrote:
>>> Hi, 
>>>
>>>>>> Before sending an answer,
>>>>>> - An UAS MAY send unreliable provisional responses with a SDP.
>>>>>> - And the SDP MUST be identical to an answer SDP.
>>>>>>
>>>>>> After sending an answer,
>>>>>> - The UAS should not insert a SDP in any response.
>>>>>>
>>>>>> Is this OK?
>>>>> That text still doesn't say what an SDP inserted after sending the 
>>>>> answer means, only that it should not be sent.
>>>> The SDP means nothing. it is neither an offer nor an answer.
>>> Exactly. In my opinion that is what is important - not whether
>>> the UAS inserts SDP or not.
>>>  
>>>>> I still don't see why we need to make a separation about SDP sent 
>>>>> before and after the answer, because in both cases the SDP must be 
>>>>> identical to the answer.
>>>> 1. RFC3261 says that UAS MAY send it before the answer and
>>>>    doesn't say nothing after the answer.
>>> That is one reason why we are writing the draft - to clarify
>>> things which may not be clear in the specs.
>>>
>>>> 2. The SDP MUST be ignored by UAC. it is meaningless.
>>> I agree, and that is what we must be clear about. Because,
>>> as we know, some people want to send a NEW offer (or updated
>>> answer) in a subsequent response, and that is not allowed.
>>>
>>>
>>>> 3. if another o/a exchange is occured (using UPDATE or PRACK),
>>>>    it is not even a confirmation.
>>>>
>>>> And, again, I know there are many implementations that send 
>>>> a copy of the SDP after the SDP answer has been sent, so instead of 
>>>> saying that it should not be done I think it is much more important to 
>>>> say that, if it is done, it must be identical to the SDP answer. In other 
>>>> words, to make it clear that the UAS can not send a NEW offer (or 
>>>> updated answer) in a subsequent response after the SDP answer has been sent.
>>>>
>>>> Since UAC MUST ignored it, there is no problem on a interworking.
>>>> Why must it be identical to the SDP answer?
>>> Well, if you look at it that way, fine. But, then the important
>>> thing is that the UAC must ignore it - not that the UAS should
>>> not send it.
>>>
>>> Regards,
>>>
>>> Christer
>>>
>>>
>>>
>>>
>>>>> Regards,
>>>>>
>>>>> Christer
>>>>>
>>>>> Hans Erik van Elburg <[email protected]> Mon, 19 Apr 2010 
>>>>> 13:55:41 +0200
>>>>>>> - An UAS MAY insert a SDP body that is identical to the SDP  answer, 
>>>>>>> in an unreliable provisional response before the SDP  answer has 
>>>>>>> been sent.
>>>>>>>
>>>>>>> - The UAS MUST NOT insert a SDP body that is not identical to  the 
>>>>>>> SDP answer, in an unreliable provisional response before  the SDP 
>>>>>>> answer has been sent.
>>>>>>>
>>>>>> This is terribly confusing. Very probabe that noone will get it right.
>>>>>> Triple negation. And talking about sending and answer before  the 
>>>>>> answer has been sent. ???
>>>>>>
>>>>>>
>>>>>>> - The UAS MUST NOT insert a SDP body in any response after the  SDP 
>>>>>>> answer has been sent.
>>>>>>>
>>>>>> This means that you can't send it again after you've send it in an 
>>>>>> unreliable provisional response. Do you want tto say that?
>>>>>>
>>>>>> /Hans Erik van Elburg
> 
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