[OpenSIPS-Users] Bad ACK to negative reply

Bogdan-Andrei Iancu bogdan at opensips.org
Tue Mar 26 03:27:35 EDT 2019

Hi Ben,

OpenSIPS, when doing transaction matching with VIA hdr, is checking the 
branch, transport, host and port parts only , so the "i" param will be 


Bogdan-Andrei Iancu

OpenSIPS Founder and Developer
OpenSIPS Summit 2019

On 03/22/2019 04:34 PM, Ben Newlin wrote:
> Hi,
> I am seeing some strange behavior handling hop-by-hop ACKs to negative 
> replies. A trace of my scenario can be found here: 
> https://pastebin.com/Ve8rnYnu
> The problem is that intermittently the OpenSIPS instance receiving the 
> ACK is not recognizing. t_check_trans is returning false for this ACK.
> The only thing I can see I that the Via header in the ACK is not the 
> same as in the INVITE, which is required by the RFC. The ACK is 
> missing the “i=03ba9232” parameter that was on the Via for the initial 
> INVITE. This parameter was not on the initial INVITE and is being 
> added by the OpenSIPS instance that is forwarding the INVITE. What is 
> this parameter for? Shouldn’t it be included on the ACK? Can anyone 
> see any other reason the ACK would not match?
> Thanks,
> Ben Newlin
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> Users at lists.opensips.org
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