Calling party control

Calling Party Control or forward disconnect is a telecommunication signal sent from a central office to the telephone subscriber's equipment to indicate that the calling party has hung up. This indicates that answering machines should stop recording, notifies conference call bridges that a participant has left or removes an abandoned call from a hold queue or interactive voice response menu.

• Open Loop Disconnect (battery drop) is most commonly used to provide disconnect supervision from a central office. When the caller hangs up, the battery voltage to the called party's line is disconnected for a fraction of a second to signal the end of the call.
• Battery reversal is used by some voice over IP adapters to indicate call status. Instead of removing the battery voltage, the polarity of the DC power on the line is briefly reversed.

An analogue telephone line may send tones such as a busy signal, reorder tone or dial tone to indicate a call has ended.

Some digital trunks, such as SS7, use out-of-band signaling to indicate termination of a call.

See also

• Disconnect tone