Core Issue
The Foreign Exchange Station (FXS) port does not disconnect quickly after a fax, which results in a fast busy tone for other inbound callers.
Resolution
In order to resolve this problem, issue the disconnect-ack command under the voice port in order to remove the line power, which is the DC voltage that is provided by the FXS battery on the ring. This can be detected by the fax machine as an off-hook condition.
Refer to Cisco VG224 Voice Gateway Configuration Example for a sample configuration.
