[Serusers] ACK message Via field branch=0 problem

[ks lf]

Thank you Andrei and Jiri for your quick response on this issue, I really like SER project, not only its apache like functions as a sip system, but also you always can get help from so many good heart experts all over the world;

We tried the first suggestion from Andrei by adding syn_branch=no to ser.cfg, it did work - adds the branch id into ACK Via header, but strange thing is it inserted an unknown branch Id which is still not recognized by the termination gateway, and call disconnected after "Recover on Timer Expiry" occur; here is the branch ID I captured ( this time I use SIPURA 2000 as the UA ):

SIPURA -> SER		INVITE		branch=z9hG4bK-d5f36318
SIPURA <- SER		100 trying	branch=z9hG4bK-d5f36318
	  SER -> TermGW	INVITE		branch=z9hG4bK193b.e50217463437115c3052e9a41f0a84b7.0 ( public IP )
					branch=z9hG4bK-d5f36318 ( private IP )
	  SER <- TermGW 100 trying	branch=z9hG4bK193b.e50217463437115c3052e9a41f0a84b7.0
	  SER <- TermGW 183 Session Pro	branch=z9hG4bK193b.e50217463437115c3052e9a41f0a84b7.0
SIPURA <- SER		183 Session Pro	branch=z9hG4bK-d5f36318
	  SER <- TermGW 200 OK		branch=z9hG4bK193b.e50217463437115c3052e9a41f0a84b7.0
SIPURA <- SER		200 OK		branch=z9hG4bK-d5f36318
SIPURA -> SER		ACK		branch=z9hG4bK-3207bbd5 (why new branch id value here ???)
	  SER -> TermGW ACK		branch=z9hG4bK193b.47867d49d7e7231dfc249720f8269f5d.0 ( public IP ) (where new branch id value here ???)
					branch=z9hG4bK-3207bbd5 ( private IP )

We don't know what brand name of the SIP Gateway it's, but will notice the termination partner ( a big carrier ) the valued suggestions all of you contribute, thanks.

Regards,

----- Original Message -----
From: Jiri Kuthan <jiri at iptel.org>
Date: Sat, 17 Jul 2004 11:47:04 +0200
To: Andrei Pelinescu-Onciul <pelinescu-onciul at fokus.fraunhofer.de>,ks lf <ksabc at lycos.com>
Subject: Re: [Serusers] ACK message Via field branch=0 problem

> At 09:58 AM 7/17/2004, Andrei Pelinescu-Onciul wrote:
> >On Jul 16, 2004 at 19:09, ks lf <ksabc at lycos.com> wrote:
> >> Use SER 0.8.12 stable release, enabled nathelper+rtpproxy for NAT traversal, forward 1(xxx)xxx-xxxx to SIp termiantion gateway, when the call was connected, PSTN gateway send 200 OK back, sip client ( behind NAT ) response with ACK ( which has branch value in Via head ), but when SER forward the ACK back to PSTN gateway, in Via header it includes branch=0, PSTN gateway refuse this ACk because it think the branch id is invalid, 
> 
> I don't know if this is the reason why the gateway denies the ACK, but if so,
> you should submit a trouble ticket to the gateway vendor. According to RFC3261,
> ACK for positive replies is a separate transaction and there is no guarantee
> that it would have the same branch id. People who have difficults to understand
> that typically get the "aha" effect when they see a scenario with multiple proxy
> servers as follows:
> 
> 
>            UAC                PROXY1                PROXY2                UAS
>                               (record-routing)      (no rr-ing)
> 
> INVITE     ----------------->     ---------------->      -------------->
> ACK        ----------------->     ------------------------------------->
> 
> in this scenario, only proxy 1 record routes, i.e., subsequent requests such
> as ACK will not visit proxy2. Consequently, proxy2 cannot generate the same
> branch ID as it did for proxy1. UAS will thus see proxy1's branch in the ACK,
> which is different from proxy2's branch in the original INVITE.
> 
> Tell the vendor to match ACKs _DIALOG-WISE_.
> 
> -jiri
> 

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