Random problem with phone calls

[Matt Stephens]

Hello everyone and thank you in advance for your input.

We have had an ongoing issue here for a while, and I can't figure out what's causing it. It happens on outgoing and incoming calls, but never when calling local extensions.

Basically, once a call is answered we cannot hear the other person. We only hear our own voice coming back through the phone like an echo. This is very random and doesn't happen often, maybe once every hundred calls, sometimes more. Usually if we just hang up and call back it will be fine.

I have told the staff to let me know whenever it happens, and I am able to go find the recording and hear the problem myself. It's so random though, that I can't really perform a packet capture because then I'll have the capture running for hours waiting for it to happen again.

I've tried checking "PBX delivers audio" and that did not help.

I can also confirm it happens on IP phones and Windows client, so it isn't a problem with the phones. Just in case you were wondering though, all our phones are Yealink t46s except for one t48s

We are up to date on V15 SP5 and all the phones are on supported firmware.

Has anyone heard of this issue before? Any advice?

 

[dandenson]

following

 

[leejor]

You don't say how your "system' is set up. Are the sets local or remote to the server? If remote, do you use STUN, or an SBC, or VPN? If STUN, how many sets at that location?

What type of trunking do you use? Only one trunk group?

 

[Matt Stephens]

Mostly local, same subnet as the PBX. There are 6 remote phones using STUN, but not in the same locations. I have had reports of this issue from the remote phones as well.

We have only one trunk, coming in on a dedicated T1 line.

 

[craigreilly]

Perhaps the RTP Ports in use by 3cx are not the same as the ports used by the firewall?
Early on, without a dedicated T1 or anything like that - I had the same complaint.
I found that the PBX RTP Ports were 9000-9500 but the firewall was restricted to 9000-9250. So on occasion a call would end up outside of the 9250 range.

Not sure if this issue would be the same with a dedicated link - you say T1 - not sure if you mean a Data T1 - or a T1 for voice going into a Gateway.

 

[Matt Stephens]

Craig, I don't have that exact issue with the firewall, however you did make me think to check for overlapping rules. I found there are two other services that use one port in the 9000-9500 range. Unfortunately those rules aren't commented on and I have no idea what they're for... infuriating..

Anyway... that seems like it could be a possible cause and thanks for making me look that direction. I'll try and figure out what those rules are for and if I can change the ports they use or just disable them.

 

[Matt Stephens]

Actually, scratch that last reply. There are services listed but they aren't reference by any NAT policies. They were just default services built in with the firewall that never got used for anything. I suspect the firewall would be smart enough not to allow overlapping rules like that anyway