Weird Echo in FreePBX 14 VoIP to VoIP Call

I am having a very weird echo with a single client that has a SIP trunk with VoIP Innovations. They can randomly hear an echo of themselves. The person on the other end has crystal clear audio with no echo. There doesn’t seem to be any rhyme or reason as to what types of calls echo, as it happens for other people on SIP trunks, analog lines, and cell phones. I know that echos are usually associated with calling analog lines, yet it definitely isn’t limited to this as they even had an echo when calling us (we are on VoIP Innovations as well). When a call is established between 2 VoIP Innovations clients, the RTP traffic is routed between the 2 endpoint RTPs without being relayed by the provider, which rules out any issues on the providers end.

I got a packet capture while I was on the phone with them and they said they had a very slight echo. I checked the packets and sure enough, I could ever so slightly hear the caller on the callers inbound RTP stream (me talking). I did not hear any echo on my end while I was on the phone. The packets only show a max jitter of 9.67ms and an average of .37ms.

The PBX is NAT’d behind a Sophos XG firewall with QOS enabled and priority given to SIP and RTP. This client is setup exactly the same as our other clients, with the exception of the Sophos XG UTM. Our other clients are using Sophos UTM 9 products. We’ve never experienced this issue before.

Any ideas on next steps? I’m getting towards the end of my abilities on this one.

Possibly, his send or receive volume is too high, causing normally inaudible echo to be objectionable.

In your test, if the RTP emitted by your phone contains echo, there is no way that could be caused by FreePBX. Most IP phones, when in handset or headset mode, do not do any echo cancellation. Assuming no firmware bug, echo could be caused by acoustic coupling from earpiece to mic (would be more noticeable when the phone is not pressed against your ear) or by acoustic or vibrational coupling within the handset.

What’s the level of the client’s speech in the RTP coming into your phone? If there are frequent peaks within 10 dB of full scale, his transmit volume should be turned down. You can compare that with the level of echo you are sending back. See for what becomes objectionable at different latencies. If you’re below the level where 1% of the people complain, he should probably turn the receive volume down.

How can I measure the DBs of the RTP traffic? I’m not able to find that statistic within wireshark. I agree that I don’t think it’s caused directly by FreePBX. I’m just curious if there’s a way to reduce it from within FreePBX or what the reason would be for it to echo?

Following is a link with a basic flowchart that shows where I am getting the echoes.

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