Odd one, when you call out from an internal phone you get audio in both directions as expected
An incoming call gets no audio from the PBX or internal phone but can be heard.
I tried setting an inbound route to just play hold music but all I get is 30 seconds of silence then the call hangs up
Have you ever had inbound call audio working? I am going to assume this is a new installation at this location.
You need to see the SIP traffic using a tool such as SNGREP. There are a lot of similar issues like yours that have already been deeply discussed on THIS FORUM. Please search for them.
In most cases the issue is one with the network router or gateway not handling or forwarding the RTP traffic properly in one or both directions. In the simplest of terms, a SIP telephone call begins with a SIP Invitation and Acceptance. In this phase, the caller identifies itself and the receiver responds. They also agree on the RTP port and Codec that will be used to setup the actual audio portion of the call. Your issue is likely with the RTP portion of the call.
It has been working for years, suddenly without any configuration change on the PBX of the firewall it has stopped working without any clue as to why so far. No blocked traffic seen etc…
I will do another search and see if I can find any clues
Check to see if your SIP Trunk provider has altered their RTP port range. If the provider is requesting to initiate RTP on a port that is beyond the port range allowed and forwarded in your router/gateway, then that is your issue.
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