[Serusers] rfc 3262 support

Greger V. Teigre greger at teigre.com
Mon Oct 23 10:15:01 CEST 2006


Thanks, Klaus. That made me actually read the 3262 :-)

For the sake of closure, I'll summarize:
- 100 Trying is hop-by-hop and is NOT possible to do reliable

- RFC3262: "An element that can act as a proxy can also send reliable 
provisional
   responses.  In this case, it acts as a UAS for purposes of that
   transaction.  However, it MUST NOT attempt to do so for any request
   that contains a tag in the To field.  That is, a proxy cannot
   generate reliable provisional responses to requests sent within the
   context of a dialog."
As SER does not have specific support for provisional responses, 181 
Call Is Being Forwarded and 181 Queued cannot be sent to the UAC reliably

- Any other reliable provisional messages will go between UAC and UAS, 
and SER will not interfere

g-)

Klaus Darilion wrote:
> Greger V. Teigre wrote:
>> I think the idea is that a proxy can send a provisional response to 
>> the UAC and thus take responsibility for the transaction towards the 
>> (real) UAS, just like sending a 100 Trying... before forwarding. The 
>> UAS has not yet received the INVITE (or whatever message we are 
>> talking about) and thus to tag is not yet set.
>
> This is the standard transaction stateful call setup - there is no 
> reliability of provisional responses.
>
> regards
> klaus
>
>> g-)
>>
>> Klaus Darilion wrote:
>>> Hi Kamal!
>>>
>>> I reconsidered by previous answer and found that there is no Cseq 
>>> Problem as CSeq may have gap.
>>>
>>> But reading your snippet: I've never seen any client yet sending 
>>> provisional responses without to-tag. Thus, even if the proxy could 
>>> generate reliable responses it wouldn't be used often.
>>>
>>> regards
>>> klaus
>>>
>>> Kamal.Mann at t-systems.com wrote:
>>>> Hi Darilion
>>>> Please check the following snippet from rfc-3262
>>>> "An element that can act as a proxy can also send reliable provisional
>>>> responses.  In this case, it acts as a UAS for purposes of that
>>>> transaction.  However, it MUST NOT attempt to do so for any request 
>>>> that
>>>> contains a tag in the To field.  That is, a proxy cannot generate
>>>> reliable provisional responses to requests sent within the context 
>>>> of a
>>>> dialog.  Of course, unlike a UAS, when the proxy element receives a
>>>> PRACK that does not match any outstanding reliable provisional 
>>>> response,
>>>> the PRACK MUST be proxied."
>>>>
>>>> Regards
>>>> Kamal Mann
>>>>
>>>> -----Original Message-----
>>>> From: Klaus Darilion [mailto:klaus.mailinglists at pernau.at] Sent: 
>>>> Thursday, October 19, 2006 3:03 PM
>>>> To: Greger V. Teigre
>>>> Cc: Mann, Kamal; serusers at lists.iptel.org
>>>> Subject: Re: [Serusers] rfc 3262 support
>>>>
>>>> AFAIK PRACK is a client feature and is end to end. Thus, ser 
>>>> supports PRACK as any other generic SIP request.
>>>>
>>>> Maybe you could fake PRACK requests or responses between a PRACK 
>>>> capable
>>>>
>>>> client and the proxy, but this will cause end-to-end CSeq mismatch 
>>>> and would require a dialog stateful proxy to adapt the CSeqs.
>>>>
>>>> regards
>>>> klaus
>>>>
>>>> Greger V. Teigre wrote:
>>>>> AFAIK, this RFC is not implemented yet. As for a list, there is 
>>>>> none right now, but it's on the to-do list :-)
>>>>> g-)
>>>>>
>>>>> Kamal.Mann at t-systems.com wrote:
>>>>>> Hi All
>>>>>>
>>>>>> Do SER supports 'rfc 3262 Reliability of Provisional Responses in 
>>>>>> SIP'? Is there any list of standards supported by SER available??
>>>>>>
>>>>>>  
>>>>>>
>>>>>> Regards
>>>>>>
>>>>>> Kamal Mann
>>>>>>
>>>>>>  
>>>>>>
>>>>>>
>>>> ------------------------------------------------------------------------ 
>>>>
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>>>>>>   
>>>>>
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>>>>
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>>>
>>>
>
>



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