Calls Sporadically don't TX/RX audio

[Blake Carter]

For the past couple months, I have a single remote extension that will sporadically stop TX/RX audio. This is the only remote extension. I have several other clients that have 3cx PBX that are 100% remote extensions, and I have never had this problem. The 3cx PBX is behind a sonicwall router, SIP ALG is disabled, and firewall checker passes everytime. The remote extension is behind an AT&T router/modem combo (home router). I have very little control over this network as it is a private home network, and not the company's network. I have worked with 3cx support multiple times on this and they have been able to offer very little help on this issue, suggesting using the mobile/windows phone client or a SBC to rectify the issue.

The issue happens randomly, and the length of time is sporadic. The user never knows when they answer the phone if they will be able to hear the caller, or if they call someone if they will be able to hear them. Sometimes just simply restarting the phone will resolve the issue for a few days, a week, even a month, then it happens again. Sometimes restarting the phone and reprovisioning 4 or 5 times and its still won't resolve the issue, but after sitting for an hour or two, will resolve the issue itself.

PBX version - 15.5.15502.6
Phone - Yealink T29G
Firmware - 46.83.0.55

Local firewall (sonicwall) has correct ports forwarded, passes firewall checker, and SIP ALG is disabled.
Remote firewall SIP ALG is disabled.

I have attached the screenshots below (modified to protect public IPs) that 3cx had pulled from the support logs and pcap files sent to them.

Wondering if anyone has had a similar issue, or has any suggestions on how to resolve this besides using a SBC for a single phone, or windows/mobile client as that is not a preferred option.

TIA

 

[leejor]

If yo have no other remote extensions to compare to, it is hard to confirm that it is a remote site issue, or not.

Is the router/modem, used at the remote site, one with a built in ATA, to provide phone service from AT&T? if so, then it may be having a conflict with the ports that the 3CX extension is trying to use.

 

[Blake Carter]

I have multiple extensions to compare to if we look at other clients. I have 2 clients that we host the pbx on an esx server, so all of their extension are remote. As for this client I only have the single remote extension. Our in-house PBX that we use has a few remote extensions, and comparing sonicwall settings, all looks to match.

I am not sure if the router/modem has an ata on it, as I mentioned I don't have much control over it. I do have a time slot scheduled tomorrow afternoon to look at the setting on the router/modem, I will definitely check that out.

 

[Blake Carter]

I just had a thought, and double checked the Service groups on the sonicwall, it looks like when we configured the sonicwall we may have missed a port group. I went ahead and added it, will wait and see if this fixes it..

 

[YiannisH_3CX]

Hello @Blake Carter

The capture shows that the phone is requesting audio to a local IP even though it is remote and to a random port. That could mean that either the phone is not provisioned correctly or the modem / router is interfering with the signalling. If the issue can be replicated you could run a capture from the phone's web interface and see what the phone is sending before it hits the modem. That will give you a good idea of where the issue is.

 

[leejor]

...or, perhaps STUN is either misconfigured, or not working properly.

 

[Blake Carter]

I took a detailed look at the modem. It is indeed a modem, an AT&T DSL Modem (B90-755028-15). SIP ALG is disabled on it. I pulled the logs from the modem and am looking through it to see if I can see anything funky happening on that side of things.

 

[leejor]

It then goes to a router?

 

[Blake Carter]

It is a modem/router combo.

 

[leejor]

I was doing a Google search for the device using the part number you listed. Nothing seem to match exactly, a few Netgear units that come close.

 

[Blake Carter]

Sorry made a typo, should be B90-755025-15. It is a Netgear Versa. I found it on Amazon below.


https://www.amazon.com/Genuine-AT-B90-755025-15-Wireless-Gateway/dp/B00WTQZB8O

 

[leejor]

Have the remote set re-boot. Then check the registration in the 3CX Activity Log. Does it show the public IP at the remote end, and the correct local port of the set? Perhaps this is not updating correctly, at times, when re-registering. If it happens again, go back through the Activity Log to find the last re-registration and what information was provided. As I said earlier, it could be either a STUN issue (contacting the STUN server), or a STUN setting, on the set, that is causing this.