Data communication apparatus having the function of automatically switching data communication and telephone communication

摘要

A facsimile apparatus sends a quasi-ring back tone to a destination in response to a call from the destination, and detects a CNG from the destination while the apparatus is periodically sending the quasi-ring back tone to the destination. When the apparatus detects a CNG for the first time, the apparatus stops sending the quasi-ring back tone and then performs facsimile communication in response to a second detection of a CNG from the destination, so as to certainly detect the CNG and to quickly shift to facsimile communication.