calling line identification on call waiting (ISDN) (CIDCW)
Calling Line Identification on Call Waiting (CIDCW) is an ISDN service feature that combines two other service features: Calling Line Identification( CLI) and Call Waiting( CW). With Calling Line Identification on Call Waiting, a knocking tone sounds during the call, signaling to the caller that another call is in the waiting to be answered queue. Simultaneously with the beep, the caller's number appears on the display. The called party can switch from the current call to the incoming call by toggling.