For further clarification, the Contact header is not relevant at all (so not used) for routing current request (no matter is ACK or something else). No Contact never results in misrouting. As Alex pointed, only a full sip trace can reveal the problem.

Cheers,
Daniel

On 11/27/13 8:31 PM, Alex Balashov wrote:
The only way to diagnose this is to get a full packet capture. In all likelihood, there is a problem with the ACK. 4.0 does not, in principle, mishandle ACKs, no, but loose-routing and NAT problems related to their handling are not uncommon.


Adnan <112linuxstockholm@gmail.com> wrote:
Hi,

We are migrating from our openser 1.4 to kamailio 4.0.3 and have run into a couple of issues. One of them is described below and we need to know if it is a known bug or not.

Kamailio receives an INVITE from a gateway and finally responds with 200 OK. Then an ACK is generated by the gateway towards the Kamailio that some how does not get relayed to the next hop.

The only special aspect here is that the ACK does not contain a Contact header. Is that something that could confuse kamailio and make it unable to relay?

According to SIP RFC, a contact header in ACK is not a must have. Our case is the one where ACK  is sent by the UAC after receiving a 200 OK final response. Everything else about the ACK looks OK e.g. ACK has a branch different from the the branch value in the UAC INVITE.

Is it a a known bug in 4.0.3?

In the configuration, we handle ACK as below:

if (is_method("ACK")) {
                                if (t_check_trans()) {
                                        t_relay();
                                        exit;
                                } else {                        
                                        exit;
                                }
                       
Br
Adnan

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Alex Balashov - Principal
Evariste Systems LLC
235 E Ponce de Leon Ave
Suite 106
Decatur, GA 30030
United States
Tel: +1-678-954-0671
Web: http://www.evaristesys.com/, http://www.alexbalashov.com 

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