Just to confirm:
Kamaili is forwarding the PRAK packet. However, it seems the kamailio ignore the Cseq increase within the PRAK and therefore it ignore the 200 Ok after that. Then, Kamailio re-send 180 again.

Thank,
AS

> Date: Mon, 13 May 2013 11:41:09 -0400
> From: abalashov@evaristesys.com
> To: sr-users@lists.sip-router.org
> Subject: Re: [SR-Users] Does Kamailio support PRACK ?
>
> PRACK is an in-dialog/sequential request, which will be relayed like
> other. So, Kamailio relays it in the same way that it supports any
> sequential request. Is it not necessary for a SIP proxy to do anything
> specific to support PRACK.
>
> The UAC should not be increasing the CSeq when sending a PRACK. My
> guess is that it is the UAS which doesn't like it, rather than
> Kamailiio. From RFC 3262 Section 3 ("UAS Behavior"):
>
> A matching PRACK is defined as one within the same
> dialog as the response, and whose method, CSeq-num, and
> response-num in the RAck header field match, respectively,
> the method from the CSeq, the sequence number from the CSeq,
> and the sequence number from the RSeq of the reliable
> provisional response.
>
> -- Alex
>
> On 05/13/2013 11:37 AM, Alex Solt wrote:
>
> > Hi,
> >
> > Does kamailio support PRACK method ? Any configuration change is needed?
> > It appears Kamailio does not like the PRAK when increasing Cseq.
> > Here is the call flow:
> >
> > A send INVITE --> Kamailio --> proxy the packet to B
> > B send 180 Ringing --> Kamailio -> proxy the packet to A
> > A send PRAK (increase Cseq) --> Kamailio --> proxy the packet to B
> > B send 200 OK --> Kamailio -> proxy the packet to A
> > Kamailio re-send 180 Ringing to A
> >
> >
> > Thanks,
> > AS
> >
> >
> >
> > _______________________________________________
> > SIP Express Router (SER) and Kamailio (OpenSER) - sr-users mailing list
> > sr-users@lists.sip-router.org
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> >
>
>
> --
> Alex Balashov - Principal
> Evariste Systems LLC
> 235 E Ponce de Leon Ave
> Suite 106
> Decatur, GA 30030
> United States
> Tel: +1-678-954-0670
> Web: http://www.evaristesys.com/, http://www.alexbalashov.com/
>
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