One way audio

[lizarazo]

Hello guys, I have a strange issue with an analog GSM gateway that when I call through the IPO, the audio only works in one direction. The phones from which the calls are being made are digital, so the calls do not go through the client's LAN network. I also tried removing the SIM cards and testing them directly in a mobile phone and I have no audio issues. I brought the client's equipment to my office and did the same test and here I did not present any audio failure, I tested with analog, digital, and IP phones and it worked perfectly. I already changed the VCM board and the complete chassis of the control unit and the result at the client's site is the same. The client also acquired a GSM IP gateway and the result was the same, that is, the audio continues to fail in one direction. Has anyone else experienced this and can give me any idea of what else I can try?

 

[Travis Harper]

I have never had any experience with the GSM gateway, but the problem you are describing sounds like a NAT issue. I ran your question through ChatGPT and this is what I got back.

It sounds like a tricky issue, especially since the problem is only occurring at the client's site. Here are a few areas you could investigate further:

1. Network or Firewall Settings: Even though the phones are digital and the calls don’t go through the client's LAN, it’s worth checking if there are any network firewalls or routers that could be blocking or interfering with RTP (audio) streams. Sometimes SIP signaling works, but the RTP streams get blocked.

2. Codecs Mismatch: Check if there are codec mismatches between the IPO and the GSM gateway. Ensure that both devices are using compatible codecs like G.711 or G.729.

3. Echo Cancellation or Silence Suppression: Some GSM gateways have echo cancellation or silence suppression features that could be misconfigured, causing one-way audio. You might want to try disabling these features temporarily to see if it makes a difference.

4. Clock Synchronization: Sometimes, clock synchronization issues between the IPO and the gateway can lead to one-way audio. You might want to verify the synchronization settings between devices.

5. SIP Trunk Settings (for the IP Gateway): If you're using SIP with the GSM IP gateway, make sure the SIP trunk settings on the Avaya IPO are correctly configured. You can try adjusting things like NAT settings or STUN server configurations.

 

[lizarazo]

Hello Travis, I want to clarify a few things that came up from the options you sent me: 1. I rule out a network issue since the client's phones are not IP, they are analog and digital connected directly to the IPO or the phone expansion module 8. The GSM gateways are also analog and are connected directly to the phone expansion 8, meaning none of the equipment goes through the client's LAN. 2. I rule out the issue of codecs because the communication is going via analog. 3. The gateway does not have silence suppression or similar. 4. It also does not have clock synchronization to configure. 5. It is not a SIP trunk, so I rule out network issues. What stands out to me is that with this same configuration at the client it fails and in my office it works, I am starting to think it could be the cell antenna it connects to.

 

[Travis Harper]

Thanks for the clarification. I guess since it works at your location, but does not work at the clients location, and otherwise all things being equal, you are likely on the right path.
The issue could be related to signal strength or interference from other wireless devices at the client's location as well.

This is a tricky one.