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

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Paul,

Paul Kyzivat <pkyzivat@xxxxxxxxx>
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.

>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 <ietf.hanserik@xxxxxxxxx> 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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