[SIPForum-discussion] PRACK

[Stephen James]

If the 200 ok has Required: timer this means that the original INVITE indicated support for timer and the UAS supports timer as well and is instructing the UAC to perform the refresher role. 

Sent from my iPhone

On Nov 13, 2012, at 22:32, Abhisek Acharya <abhisek.acharya at gmail.com> wrote:

> Hi Moh,
> 
> First of all good morning and I hope everything going well in PCCW HONGKONG and USA.I will answer your question in a detailed way with few points.
> 
> 
> 1.100 rel stands for the support of PRACK method is SIP protocol.rel stands for reliability and 100 stands for provisional response. 100rel is called as option tags.No option tag is mandatory but the use of the same can be very very tricky.
> 
> 2.100 rel option tag has nothing to do with 200 OK response but it has everything to do with the 18x response.If 100 rel is missing from the 200 OK response then it should not have any impact on the call theoretically. 
> 
> 3.Supported and Require headers have a bigger role to play in the use of 100 rel.If initial INVITE contains a Supported:100 rel then if the UAS wants the 18x responses to be acknowledged then it MUST add a Require:100 rel option-tag with a Rseq header which will act as a Reliable sequence number and UAC will acknowledge that with a PRACK message with a Rack header which will replicate the Rseq number.
> 
> 4.As long as the above process is working fine then there is no reason of call failure.
> 
> 
> 5.Now coming back to your question regarding the Require:timer header in 200 OK response then my answer is yes.200 OK response can contain Require:timer header as this signifies the kicking off the Session-Refresher mechanism and this is a completely different mechanism to PRACK.
> 
> 
> Please send me a call trace with all the necessary information and IP details so that I can take a look and put my points.Also please let me know if something is not clear on the above explanation.Please remember that 100 rel and timer are two different option tags and used for two different purposes in SIP.
> 
> Regards
> Abhisek Acharya
> 
> 
> 
> 
> On Thu, Nov 8, 2012 at 12:50 PM, Moh, Yee-Kuang <ykmoh at pccwglobal.com> wrote:
>> Hi SIPForum,
>> 
>>  
>> 
>> Greeting!
>> 
>>  
>> 
>> 1.      I would like to know isn’t that “100rel” has to presence or mandatory in header of the 2nd 200ok (note: it is used for responding to INVITE)?
>> 
>> 2.      What happen if “100rel” was missing in this 200ok header?    
>> 
>> 3.      Does 2nd 200ok has to follow the same header with “Request:100rel” when “183 Session Progress” is having “Request: 100rel”? I experience some GW respond “200ok” contain “Request: timer\r\n” the call was disconnected after picking up the phone.
>> 
>>  
>> 
>>  
>> 
>> Thank you very much.
>> 
>>  
>> 
>> Regards
>> 
>> moh
>> 
>> 
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