As said try also with a soft phone connected (and with another VOIP service on a trial basis). This way you can connect directly from the Airband ONT port removing your router and ATA from the equation to simplify fault finding
Thank you for your suggestions, they are appreciated.
The problem is very intermittent so to be meaningful any test has to be for weeks, and thus has to be compatible with maintaining both incoming landline and full house Wi-Fi.
The initial VOIP setup was using Airband supplied router, this quickly showed the incoming call problem and after a few days we went back to just the landline. I then setup the openWRT router and went back to VOIP. We had about 10 days error free use, but then 3 days with around 50% unconnected calls. ( we get around 3-4 calls per day). Since installing the Nathelper-extra package we have had 3 days of error free service. We also have had 3 evening of buffering free iPlayer/Netflix. After 3 days is this significant?.
If the problem is not fixed I plan as a temporary test I plan to try using the SPA122 as the router. This would eliminate my router.
The Airband fibre comes through the wall and terminated in one of These
, I assume this is the same as an ONT, then a cat5e to the router. Would it work if I put a gigabit switch in this line and connected both the router and the SPA122 or slaptop with softphone? I wonder if Airband supports multiple sessions?
I am also concerned about oddities around the public IP. Tarka-the-otter reports IP address changing with time, In late Dec I definitely saw that the external IP when logged into a VPS using ssh showed as 1 different to that shown by speedtest.net.
The last 3 days I have had a script running checking the public IP using both ssh (port 22) and https (port 443), both have remained the same and constant.