I recently switched from plain DSL to Comcast cable internet. Faxing worked fine before - I sent 100s of pages without a problem using a OBi202. Voice calls on port 1 are reasonable quality and I have one Google Voice line. Trying to fax on port 2 from a new HP 7740 (aka the big guy) just get communication errors. Same results if plugged into port 1. Also tried my Epson ET-4750 tank printer with the same results. I have customer owned Arris SBG6950AC2 modem so I turned SIP off and rebooted the router. Same problem. Turned SIP back on. Haven't tried inbound fax as I never gotten one in years. Strange thing - with a laptop connected to the OBi202 a speed test download varies from 8-22 while a desktop hooked to the same upstream switch is a solid 29 Mbps download. Both uploads are +2 Mbps. To troubleshoot I attached the OBi202 directly to the router but had the same failures.
HELP!!!!
Just to be clear. I tested with the OBi202 both directly attached to the Arris and with it in it's normal configuration behind one of two newer high-end routers attached to the Arris and then everything off them and thru newer powerline adapters or wireless repeaters as my office is in a detached garage. If I can get it to work directly attached to the Arris I can work out any other networking issues with the equipment I have.
Arris of course just punted the problem to Obihai even though the real change is their modem. Oh well - just one of the joys of mostly being retired.
On your fax machine try turning the speed down and the error correction off. (Yes, off.)