Strange One Way Audio Issue

[TagleRock]

We have been having a really weird and specific issue that I have not been able to figure out. The phones in our office are 3CX, its an on-premise system, running on Debian. We use sip.us for the provider. We have a client who is also on 3CX on Debian, and they're using Voxtelesys. When we call them, there is no audio from our side, but there is from their side. No voice, and no DTMF. When we call to our 3CX from theirs, it works normally. They have no issues with any other callers, in either direction, its only our system. I even tried calling them from another 3CX system that is setup on siptrunk.com, which as far as i know, uses the same SIP service, its just a different frontend designed for resellers, and the audio worked.

I've ran firewall tests on both sides and both pass. I've tried disabling and enabling PBX delivers audio in all combinations on the extensions I'm working with. I have it enabled on both sides at the SIP trunk level. I've run captures during test calls and the only thing that really stands out to me so far is a difference in the accept headers.

On the capture from the customer pbx I get: Accept: application/sdp, application/isup, application/dtmf, application/dtmf-relay, multipart/mixed

On the capture from our pbx i get: Accept: application/x-as-feature-event+xml in the first part and Accept: application/sdp in the later part.

Not sure if that makes a difference. Each side appears to have at least one codec in common, and if it was a codec issue i would imagine that it wouldn't work if they called us.

Thanks in advance.

EDIT: To clarify, our system also works with all other callers with no issues. Just when we call to them.

 

[Charles_3CX]

Have you contacted Sip.US? To check if they received the audio from the 3cx system and sent it onward to the provider on the other side of the call?

 

[Kevin@voxtelesys]

Hey @TagleRock,
Just to be clear when you call from your on prem system to the Voxtelesys trunk/number you have issues getting audio back to your on prem system? What if you call into the Voxtelesys trunk/number from a cell phone? It works just fine? If needed you can DM me and I start a ticket on our side.

 

[TagleRock]

Have you contacted Sip.US? To check if they received the audio from the 3cx system and sent it onward to the provider on the other side of the call?

That's a good idea, I have submitted a ticket with them to find out.

 

[TagleRock]

Hey @TagleRock,
Just to be clear when you call from your on prem system to the Voxtelesys trunk/number you have issues getting audio back to your on prem system? What if you call into the Voxtelesys trunk/number from a cell phone? It works just fine? If needed you can DM me and I start a ticket on our side.

The issue is that when we call them, they can't hear us, but we are able to hear them. There is no voice audio or DTMF that makes it from our side to theirs. All other calls to and from their system work without issue, same with ours. Also if someone calls from the Voxtelesys side to our system, the audio works normally.

 

[TagleRock]

Issue is resolved. It was some issue on sip.us' side. I asked them what the issue was but they never responded. Thanks to everyone that replied.