A connection to the switch that allows attempts at establishing calls to be made. A digital station line on a PBX or digital-key system. DTMF Dual Tone Multiple Frequency. Pressing a button on the keypad of a touch-tone phone generates a pair of tones of specified frequency and duration. In analog networks, audible tones generated by the network provide the call progress indications to the user.
Different tones allow the human ear to interpret the progress of the call.
The switch that connects or disconnects the device from the phone line. On a telephone, for example, this is the switch that is automatically activated when a user lifts the receiver from the cradle to get a new dial tone. A telephone whose connection is configured so that no dialing is required. Transmitted within the data stream. See also out of band .