TLS and loud background noise

[almoondsllc]

Today I face out a very strange problem with a Vodia PBX (5.4.1 (Vodia mini PBX (Debian))) and a Snom M300/M65 set. If I enable TLS on the phone I had a very loud background noise before and during the call. All disappear if I use UDP as protocol on the phone instead of the UDP. How that is possible? I attached the audio file I recorded.

[Vodia PBX]

Thats most likely because the SRTP key negotiation failed. You can just manually disable SRTP in the phones to fix the problems. Or upgrade to a recent version of the PBX.

[almoondsllc]

In fact I disabled the TLS on the phone and SRTP, the problem is that I still have 20 snom phones at this customer that now they are working with TLS, but I don't know for how long more it will be ok. How I can check the reason of the SRTP key negotation fails? If the solution is upgrading to a recent version of PBX, is the problem related to some Certificate expiration? If yes, how check when is the expiration? Just to be sure that nothing will happen until that date, thanks.

[Vodia PBX]

The problem is usually that one side proposes optional SRTP and then the other side answers without it, leading to a "one-way" SRTP encryption. If you want to keep the old version you might have to go back to TCP (I would not go to UDP because of the UDP fragmentation problem). 

I don't think the upgrade will make any difference with the certificate. The old snom models did not check the certificate dates anyway.