A communication apparatus that accurately measure a time period T0 required for line connection in IPFAX, and optimizes the timing with which a T.38 CNG command is sent out. An AT command that is a dial request is converted into a SIP command that is a session-establishment request, and the SIP command is sent. When there is a provisional response or a session-establishment response to the sent SIP command, a T0 timer which clocks the time period T0 is caused to start counting.