# Call clearing

To hang up a call, the application builds an ACU_CLEAR_RQ message with the connection ID of the associated call. Receipt of an ACU_CLEAR_CO message confirms that the remote end has hung up. The stack returns to its IDLE state.

The following illustration shows the sequence of messages sent between the ACU and the application when the application initiates a hang up:

If the remote end hangs up first, the application receives an ACU_CLEAR_IN message. The application responds with an ACU_CLEAR_RS (clearing response) message. When the application receives an ACU_CLEAR_CO message, the clearing is confirmed. The stack returns to its IDLE state.

The following illustration shows the sequence of messages sent between the ACU and the application when a hang up is received by the application: