One-way audio after picking up a call that was on Hold or Parked

I am having an intermittent issue with the outside party not being able to hear the PBX side when a call that has been Parked or put on Hold is picked back up. It does not happen often, but just fairly randomly.

The PBX server is a co-located server with a public internet IP.

All extensions (10 of them) are remote and on the same LAN together. All of them connect to the server using a VPN. (And it is all done through the Extension Manager.) Phones are Yealink T46U.

Again, everything else seems to be working great. For incoming and outgoing calls, both parties can hear each other just fine – until someone is parked or put on hold. When that call is picked back up, sometimes (again, not always) the other party cannot hear the extension/PBX party. When that happens, if you park the call again and pick it back up, usually, they can hear just fine again!

I know the common “one way audio is almost always NAT”, but it seems very different in this case – especially since all of the phones are connected via VPN to the PBX server. There really shouldn’t be any NAT issues in that case.

The only other thing I can find that might relate was mention of there being an issue with the codec used for the MOH if there isn’t a matching codec. I am using Twilio was my provider and the trunks are all set to only ulaw (as recommended by Twilio). The MOH is encoded in multiple formats – including ulaw. So, I wouldn’t expect that to be it, but I’m mentioning it just in case. :slight_smile:

Open to suggestions. Thanks!

Is this happening between remote extension to extension calls as well?

I do not know. They do VERY little extension-to-extension calls in this office. That is why I actually decided to do the remote server. (If an office has more than 5 extensions, I normally do an on-site FreePBX server, but since this office pretty much never does ext-to-ext, I did it off-site.)

I can try to do some testing on Monday and see. Again, it is very intermittent. They might park and pick up 10 calls no problem – and then we suddenly have one where you pick it up and the caller can’t hear the extension. But the just park that call and pick it right back up – and it works fine again. Very inconsistent.

This is the first time I’m using VPNs for all of the phones. Just for testing, I might try removing the VPN temporarily on Monday also just to try to eliminate it from the equation.

Thanks for any suggestions!

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