I have configured two of the FXS ports on our UC560, to act as analog ports for fax machines. Each FXS port has been configured with an extension from our publicly routable DID range, and the ports are configured for Loop Start.
However, I am not getting any actual dial tone on the ports, so when I attempt to call into one of the fax numbers, the fax machine (which is set for immediate answer) gets a signal that the analog line is trying to initiate communications and the fax machine initializes itself into receiving mode, but because there isn't any dial tone, the sender's side just continues to ring and ring and ring.
Additionally, when I attempt to fax out from the fax machine, there is never any initial dial tone on the line so the machine dials out and then immediately starts attempting to initiate a fax handshake, but there's still no dial tone on the FXS line at any point during the process.
Am I meant to set something else other than the FXS port setting under Telephony -> Ports and Trunks -> FXS Ports, and then assigning the DIDs under Telephony -> Users/Extensions -> Analog Extensions?