FXS ports connected to Fax still get ringback when fax is in use when called from Cisco extension. When called from Outside PSTN you will get a busy signal. Some of the other fax machines in the organization are on Cisco analog devices. When they try to fax this machine it will ring even if the fax is in use. Busy Trigger and Max Calls are both set to 1.
Cisco ISR 4321, MGCP Protocol.
