Incoming PSTN call drops before hearing audio prompt

[lello213]

I have a self hosted 3CX where a grandstream GXW 4104 voice gateway is connected using sip registration. Both Inbound and outbound calls to PSTN are working fine except for this one scenario.

I have setup a queue so that when PSTN users dial in, they will be redirected to the queue but first they will have to hear a prompt, as soon as they hear the first word of the prompt, the call ends from the called entity side but the line remains busy from the voice gateway side and 3CX agents are still able to receive the call knowing that the other party’s call has already ended abruptly.

 

[leejor]

Is it only incoming calls, to the queue, that drop? Do they go direct to the queue?
What happens if you call the queue number from an extension?
Is it the queue recording/announcement that the caller is hearing?
Did this just begin, or is this a new install?
Are the Gateway and PBX on the same LAN?

If you have access, check the 3CX Activity Log set to Verbose. that will show you any errors, and which end/device is dropping the call. Maybe no ACK?

 

[lello213]

Is it only incoming calls, to the queue, that drop?
-Yes this is only for incoming calls

Do they go direct to the queue?
-Yes the call goes directly to the queue, they should be hearing a welcome prompt before being forwarded to the queue. Even if the caller’s call ends, after 15 seconds (the duration of the prompt), the agents receive the call as if nothing happened but they can’t answer it obviously becaue the other party is not present.

What happens if you call the queue number from an extension?
-It works normally, when we remove the prompt before the queue when calling from PSTN, it works normally.

Is it the queue recording/announcement that the caller is hearing?
-Yes correct

Did this just begin, or is this a new install?
Are the Gateway and PBX on the same LAN?
-This is a new setup, PBX and gateway are in different networks.

There is no significant alarming 3CX Activity Log, we have also created a support case with 3CX but they blamed the gateway not the PBX saying that the call is ended from there.

 

[lello213]

Additionally, this scenario works one out of 10 or 15 times on its own without modifying any settings.

 

[leejor]

The fact that the Gateway and the PBX are on different networks, might be the problem. However, since other incoming calls to destinations other than the queue are working, and this is an intermittent problem, then this would seem to make this less likely.

When you say that the caller receives a prompt, do you mean that they go to an IVR first, then choose which queue to route to?
If this is the case, then do all incoming callers to an IVR, have an issue, even if the call routes to an extension and not a queue?

Intermittent problems are a pain to diagnose.

I assume that you don't have any other incoming trunks (VoIP?) to test this scenario on.

What I would do, it to compare a working call to a failed call in the Activity Log, or using something like Wireshark, if you have access. Pay attention to the SIP messages. For the call to end, one side (3CX, or the gateway) will send a message to end the call, or drop it because of something like no ACK, assuming the other end has dropped. Find which side is actually ending the call.

Even if the caller’s call ends, after 15 seconds (the duration of the prompt), the agents receive the call as if nothing happened but they can’t answer it obviously becaue the other party is not present.

What this tells me is that 3CX still thinks the call is up, so perhaps it didn't drop it, and it was the gateway that did. The Activity Log should confirm if this is the case.

I have not used that particular gateway before, but you might check to see if it has any internal logs that you can access

 

[fxbastler]

Are the Gateway and PBX on the same LAN?
-This is a new setup, PBX and gateway are in different networks.

That is usually the problem, even with problems that only occur intermittently.