[SIPForum-discussion] Query regarding SIP 183 Session Progress

Tue May 21 14:54:48 UTC 2013

That is incorrect. B must not send Require: 100rel unless 100rel in Supported or 
Require header of INVITE. Per 3262.
Although the first paragraph seems to say that Supported: 100rel is a must, the 
other two imply that Require: 100rel means supported as well.

   A UAS MAY send any non-100 provisional response to INVITE reliably,    so 
long as the initial INVITE request (the request whose provisional    response is 
being sent reliably) contained a Supported header field    with the option tag 
100rel.

If the request did not include either a Supported or Require header    field 
indicating this feature, the UAS MUST NOT send the provisional    response 
reliably.

   The UAS MUST send any non-100 provisional response reliably if the    initial 
request contained a Require header field with the option tag    100rel. 

Stephen James 
sjames_1958 at yahoo.com

We are not princes of the earth, we are the descendants of worms, and any 
nobility must be earned.

________________________________
From: Partha Ray <jubu.partha at gmail.com>
To: Nikash N <nikash.n90 at gmail.com>
Cc: discussion at sipforum.org
Sent: Tue, May 21, 2013 9:48:49 AM
Subject: Re: [SIPForum-discussion] Query regarding SIP 183 Session Progress

Hi NIkas,
Yes , Callee can send it even if no sign from Calller side. But as Srinivas 
mentioned , require embedes the supported itself,hence it is optional to include 
both or just required or even just suported from callee side.

But here is the scenario.
If A calls B. A does support 100 rel but may or may not include it in request, 
and then B includes require, then A would work accordingly (PRACK------).  But 
is if A doesn't support it and B asked for it (require) then A won't send any 
PRACK. But B would expect it. If B doesn't get it with the time (timer set for 
it) then it would terminate the call. This termination again would have multiple 
scenario (B may or may not have responded 200 just after sending 18X with 
required).

BR,
Partha

On Fri, May 17, 2013 at 12:50 AM, Nikash N <nikash.n90 at gmail.com> wrote:

Thank you Srinivas and Partha for your replies. 
>
>
>@Partha
>In your 'Ans for second part', do you mean to say that, an entity (callee) can 
>be configured such that it can send a supported and a required in subsequent 
>messages even if the other entity (caller) does not send a supported header?
>
>
>Is there any relevant RFC or spec for 183? All I'm able to find is the Internet 
>draft released by IETF in 2000. Has there been no updates to it since then?
>
>
>Thank you.
>
>
>
>On Thu, May 16, 2013 at 9:14 PM, Partha Ray <jubu.partha at gmail.com> wrote:
>
>Hi Nikash,
>>
>>
>>Ans for first part:  Basically 'supported' is used by either side 
>>to declare their capability. It is not mandatory but always a good practice if 
>>the B party (in your case includes it). And if it supports precondition too, but 
>>does not want to use it for this session, does it need to specify that in the 
>>supported header?  Ans: If a user doesn't want to use this capability for a 
>>session , you need to configure the entity for that not to include supported 
>>header. You can't make it per session basis. This is a global setting for all 
>>entities.(Either for all session or not  supported at all). You can't have 
>>combination of both at the same time.
>>
>>
>>Ans for second part: Yes callee can do it if configured accordingly. Infact it 
>>is the best practice to include it if supported(declaring your capability). 
>> Callee can send 'required': in any subsequent provisional response. (18X).
>>
>>
>>BR,
>>Partha
>>
>>
>>
>>On Thu, May 16, 2013 at 7:05 AM, Nikash N <nikash.n90 at gmail.com> wrote:
>>
>>Hi
>>>
>>>
>>>I've a scenario here which I'd like to discuss.
>>>
>>>
>>>Caller sends an INVITE with "100rel, timer, precondition" in supported header. 
>>>The Callee responds with a 100 Trying and then a 183 Session Progress, in which 
>>>the require header contains "100rel". Is there a necessity for the 183 to have 
>>>"100rel" in supported header too? And if it supports precondition too, but does 
>>>not want to use it for this session, does it need to specify that in the 
>>>supported header?
>>>
>>>
>>>Alternatively in a different scenario, if an INVITE does not contain a supported 
>>>or a require header, can the callee respond back with a "supported" header 
>>>containing "100rel". And then, if the caller supports 100rel too, and wants to 
>>>use it, in what SIP message can he send a "require" header after these 
>>>exchanges?
>>>
>>>
>>>Thank you.
>>>-- 
>>>
>>>RegardsNikash 
>>>_______________________________________________
>>>This is the SIP Forum discussion mailing list
>>>TO UNSUBSCRIBE, or edit your delivery options, please visit 
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>>>
>>>
>>
>
>
>
>-- 
>
>RegardsNikash 
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