[pheitkemper]

We have implemented a service which registers as an extension to 3CX. I have sucessfully called to this service from various softphones and a Cisco 504G. It works great.

The problem comes when I try to use a Grandstream 4104 on our house PBX to call this service. When I call from the analog side, the invite occurs. My service sends a 100Trying, 180 Ringing, and 200 OK messages. However, does not ACK my 200, and 3CX continues to send me invite requests. These occur with the time-doubling you would expect if the PBX has not received the 200 msg. Using Wireshark, I can see that the machine always receives these packets.

The other interesting aspect comes when I replace my service with a soft phone (3CXPhone, Phonerlite) configured for the same extension. The call works perfectly. This also occurs when I change the forwarding rules to forward to another extension, be it softphone or the Cisco 504G mentioned before.

Why would my service work perfectly with 3CX and a softphone, but not with 3CX and a Grandstream? That would suggest a configuration error on the Grandstream. But I can make calls to anything else besides my service.

This is repeatable behavior. I have also had the same results using a Patton 4114 Smartnode. Also, I have used this service before with this PBX and Grandstream device (and our house analog PBX for that matter).

Please help me understand what's happening. How do I go about debugging this?

Thanks,
Paul

[danhriscanu]

Hi,

Please see http://www.3cx.com/voip-gateways/Grands ... 44108.html

[pheitkemper]

Hi,

Please see http://www.3cx.com/voip-gateways/Grands ... 44108.html

I used this to set up the gateway in the first place. What am I missing?

[danhriscanu]

Did you also try to activate "PBX Delivers Audio" in Advance tab of Grandstream device?

[SY]

It looks like that the response 200 OK, which is replied by your service, is malformed in this call scenario...