NC Reddy wrote:
> On Thu, Nov 20, 2008 at 9:49 AM, Paul Kyzivat <[EMAIL PROTECTED]> wrote:
>
>>
>> NC Reddy wrote:
>>
>>> I agreed it breaks the SDP offer/answer protocol, but i think it won't
>>> break SIP controlling protocol rules.
>>>
>> The sip controlling protocol rules require that the o/a be completed.
>>
>> The context of the scenario is:
>>> UAC(user) <---------->AS (Announcement Sever)
>>> AS needs to know the RTP IP/port of UAC for to send some announcement
>>> traffic. The RTP traffic is "one way" i.e from AS to UAC. So in the above
>>> context, what's the purpose of sending SDP information (i.e RTP IP and port
>>> ) of AS to UAC?. I can see only to compliant for full fill the offer/answer
>>> model.
>>>
>> In that case, the AS may respond with an answer containing the appropriate
>> m-line, with a=sendonly. The answer provides the necessary data for the
>> exchange of RTCP. Also it is increasingly common for UAs (or something in
>> their network) to require the media to be symmetric, using the address in
>> the answer as a gate for what will be accepted.
>>
>> So why would you not want to send the answer? It costs almost nothing extra
>> in signaling.
>
>
> The requirement is that AS needs to play announcement to the UAC and
> terminate the call (i.e 2xx/non-2xx) with UAC on given call context.
> For AS to play announcement to User, does it possible AS can play
> announcement on UAC RTP IP and Port before sending final resposnses(i.e 2xx
> or non-2xx responses)? without sending announcement server sdp answer.
In theory this is a legal thing to do - early media.
However it seems that many implementations will not accept incoming
media until an answer has been received - in order to prevent getting
media from spurious sources. So while this is *legal* you might not find
it successful.
And it seems that some networks don't allow early media at all except
from certain trusted sources.
> For to emulate one way announcement traffic, does SDP answer from AS should
> have "valid" RTCP ports towards User(UAC)?, can't AS can send some dummy
> answer to UAC to full fill the sdp offer/answer.
You may legally specify your IP as c=0.0.0.0.
But the same considerations above may cause this kind of response to be
less successful than you might like.
Thanks,
Paul
>> Thanks,
>> Paul
>>
>> Thanks in advance.
>>> Regards
>>> Channa
>>>
>>> On Wed, Nov 19, 2008 at 7:46 PM, Paul Kyzivat <[EMAIL PROTECTED]<mailto:
>>> [EMAIL PROTECTED]>> wrote:
>>>
>>> No this isn't valid. The offer must be answered.
>>>
>>> This is the Session Initiation Protocol. Without an answer you have
>>> not initiated a session.
>>>
>>> Paul
>>>
>>> NC Reddy wrote:
>>>
>>> Hi,
>>> I have the following context question:
>>>
>>> UAC <------------->AS(B2BUA)
>>> | ------F1 (INVITE)--->
>>> * SDP-Offer*
>>>
>>> <-----F2: 100 Trying---
>>>
>>> <----F3: 200 OK*(NO-SDP)*---- //Does this step
>>> is valid
>>> without SDP, ?:
>>>
>>> ------F4:ACK------------>
>>>
>>> Questions:
>>>
>>> - Does the 200 OK response without SDP -Answer is a "valid"
>>> sip response
>>> in the above context?.
>>> - If not what are the reason(s)?
>>>
>>> Regards
>>> Channa
>>> _______________________________________________
>>> Sip-implementors mailing list
>>> Sip-implementors@lists.cs.columbia.edu
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>>> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
>>>
>>>
>>>
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