Incoming Calls Dropped Within 30 Seconds

[Frank86]

Started having issues this morning.
Incoming calls only are dropped within 30 seconds. 3CX activity log shows the following:

03/04/2022 11:01:28 AM - [CM503021]: Call(C:19): ACK is not received from sip:+1{incoming phone number}@fl.gg

Running 3CX 18.0 update 2 (build 315) on Windows Server 2016 with Flowroute as the provider.

Problem started today.

 

[ChrisC_3CX]

From the looks of it the 3CX PBX never receives the ACK SIP for the 200 OK it sent when you answered the call. If this is the case, it's actually expected that the call is dropped 32 seconds later which explains the behavior you're experiencing.

First things I'd do is make absolutely sure that you've configured the SIP Trunk as per our guide:
https://www.3cx.com/docs/usa-sip-trunk-flowroute/

Also, make absolutely sure that you've forwarded all required ports to the PBX and that it can still pass the firewall checker 100%.

If the issue persists after the above has been confirmed to be in order, you might actually need to reach out to the SIP Provider to find out if they are indeed sending the ACK or not so that you can identify where the issue might be.

Should you need to see the SIP flow for yourself, I'd suggest running a packet capture and then place an inbound call, wait to it to drop, and then save and check the packet capture with a tool such as wireshark to see what's happening. You can then use this information when speaking with the SIP provider.

For this you might want to also check out our basic troubleshooting 3CX Academy course: https://www.3cx.com/3cxacademy/videos/advanced/basic-troubleshooting/

Hope this helps!

 

[Frank86]

Yes, I'll check but I'm pretty sure the SIP trunk is configured correctly since it's been working great for years until this morning, and also the firewall ports are all forward correctly. I've opened a ticket with the SIP trunk provider.

 

[ChrisC_3CX]

and also the firewall ports are all forward correctly. I've opened a ticket with the SIP trunk provider.

Info from the SIP Provider should shed some light on the matter but I do recommend running the firewall checker too in the meantime just in case.

Note: Running the firewall checker will temporarily stop certain 3CX Services and hence may drop calls. I recommend running it during out of office hours and generally when downtime is tolerable.

 

[Frank86]

Sounds good. I have an active outgoing call. As soon as there are no calls, I'll run the firewall checker.

 

[Frank86]

Ran the firewall checker a few times. It fails one or two ports under the media server (9000-10999), never the same port, though. Could be 9213 or 9218 or 9298. I also updated 3CX to the latest version 18.0 Update 3 (build 450).

 

[Frank86]

I just ran the firewall checker again, and it passes it, but incoming calls are still cut off after 32 seconds. Waiting to hear back from Flowroute.