Gamma - 200 OK does not get acknowledged

[commercial1]

We use a self hosted 3cx pbx, with gamma as a sip provider. Currently on version 18.0 update 7 using Fanvil x4u handsets and 3cx smartphone app. At random times of the day outbound calls can not be made from the smart app or the desk phones. I have raised a ticket with Gamma as i felt it was a SIP issue they have come back with the following response "I have reviewed the call examples provided and can see that the 200 OK does not get acknowledged, you need to send an ACK and not another Invite to the 200 OK" Could anyone advise what i need to change on the system in order to send the ACK and explain to me why this would only occur randomly and not on all calls.

Many Thanks

 

[YiannisH_3CX]

Hi @commercial1

For a call to be considered established you need an initial Invite, a 200 OK from the recipient and an ACK message from the initiator.
From Gammas reply I see that 3CX does not receive the 200 OK (since we sent another Invite instead of an ACK) so we never send an ACK message.
This can happen for a few reasons but most commonly, the Gamma IP the 200 OK is coming from is blacklisted in 3CX or the 200 OK is sent to the wrong IP address thus never received.
Gamma specifically requires that the public IP is always sent in the VIA header so that's the first thing you should check.
Open your trunk settings and navigate to "Options". Make sure that the option "Put Public IP in SIP VIA Header" is enabled and that the correct public IP is set there.

Since the issue is intermittent however I would guess that one of Gammas IP is in your IP blacklist. If the issue persists then you will need to run some packet captures to identify the issue.

 

[commercial1]

Thanks for the information, i have checked and the public IP is enabled and correct. I will have to try and run some packet captures to get further information, although this is a little tricky as it happens for about 5 minute period a couple of times a day at random times.

 

[YiannisH_3CX]

You can run tshark if you are running a self hosted environment. You can google the commands. It can run all day and create smaller files which will not impact the performance of the system. Once the issue is replicated you can stop it and get the latest files to check. The rest you delete.