I am having an issue where VoIP phones (Polycom VVX 400) behind my EdgeRouter are not able to answer calls when our Everyone ring group is hit. The phones ring, but neither picking up the handset nor pressing the "Answer" soft key allows the phones to answer.
I have been speaking with support from our hosted PBX, and they told me they were seeing phones registered on the same port as well as frequent port assignment shuffling. Looking at the NAT translations on my EdgeRouter shows the same thing - multiple devices registered to the same Post-NAT port. I did some digging online and found that they recommend a UDP timeout of 300 seconds. Yesterday I set UDP other to 300 and UDP stream to 600, but I am still seeing 2-3 devices on the same Post-NAT port.
I admit I'm new to VoIP (and networking in general), so any help is appreciated. Is there something else I should look at? SIP ALG is disabled, I have upgraded to 1.8.5, and I have tried with offload disabled and enabled.