Re: [Sip-implementors] Question: Does 200 OK(INVITE) without SDP is valid response for INVITE with SDP offer?

[Paul Kyzivat]

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]>> [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---
>>>
>>>>>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
>>>___
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>>>Sip-implementors@lists.cs.columbia.edu
>>>
>>>https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
>>>
>>>
>>>
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Re: [Sip-implementors] Question: Does 200 OK(INVITE) without SDP is valid response for INVITE with SDP offer?

[NC Reddy]

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.
 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.



>
>
>Thanks,
>Paul
>
>  Thanks in advance.
>>  Regards
>> Channa
>>
>>   On Wed, Nov 19, 2008 at 7:46 PM, Paul Kyzivat <[EMAIL PROTECTED]> [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---
>>
>>>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
>>
>>https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
>>
>>
>>
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Re: [Sip-implementors] Question: Does 200 OK(INVITE) without SDP is valid response for INVITE with SDP offer?

[Paul Kyzivat]

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.

Thanks,
Paul

> Thanks in advance.
>  
> Regards
> Channa 
> 
> 
>  
> On Wed, Nov 19, 2008 at 7:46 PM, Paul Kyzivat <[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---
> 
>  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
> ___
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> Sip-implementors@lists.cs.columbia.edu
> 
> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
> 
> 
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Re: [Sip-implementors] Question: Does 200 OK(INVITE) without SDP is valid response for INVITE with SDP offer?

[NC Reddy]

I agreed it breaks the SDP offer/answer protocol, but i think it won't
break SIP controlling protocol rules.
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.

Thanks in advance.

Regards
Channa



On Wed, Nov 19, 2008 at 7:46 PM, Paul Kyzivat <[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---
>>
>> > 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
>> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
>>
>>
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Re: [Sip-implementors] Question: Does 200 OK(INVITE) without SDP is valid response for INVITE with SDP offer?

[Alex Balashov]

Agreed, although it does not seem that the payload data is instrumental 
in the definition of a session per se.

However, if an SDP offer was sent with the initial INVITE, the first 
reliable non-failure response to it must contain an SDP answer.

If no SDP offer was present in the initial INVITE, an initial offer may 
be originated by the UAS in the first reliable non-failure response (the 
200 OK) back to the UAC, in which case the UAC is required to provide 
its answer in the ensuing ACK.

There are some passages in RFC 3261 13.2.1 that seem to support the idea 
that if an offer was present in the INVITE, a non-failure response must 
have an answer - and a provisional response may have an answer:

"If the initial offer is in an INVITE, the answer MUST be in a
 reliable non-failure message from UAS back to UAC which is
 correlated to that INVITE.  For this specification, that is
 only the final 2xx response to that INVITE.  That same exact
 answer MAY also be placed in any provisional responses sent
 prior to the answer."

...

"Concretely, the above rules specify two exchanges for UAs compliant
to this specification alone - the offer is in the INVITE, and the
answer in the 2xx (and possibly in a 1xx as well, with the same
value), or the offer is in the 2xx, and the answer is in the ACK.
All user agents that support INVITE MUST support these two exchanges.


Paul Kyzivat 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---
>>
>> > 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
>> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
>>
> ___
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-- 
Alex Balashov
Evariste Systems
Web: http://www.evaristesys.com/
Tel: (+1) (678) 954-0670
Direct : (+1) (678) 954-0671
Mobile : (+1) (706) 338-8599
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Re: [Sip-implementors] Question: Does 200 OK(INVITE) without SDP is valid response for INVITE with SDP offer?

[Paul Kyzivat]

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---
> 
>  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
> ___
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[Sip-implementors] Question: Does 200 OK(INVITE) without SDP is valid response for INVITE with SDP offer?

[NC Reddy]

Hi,
 I have the following context question:

UAC <->AS(B2BUA)
| --F1 (INVITE)--->
*   SDP-Offer*

<-F2: 100 Trying---



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
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