# Clear collision

Clear collision can occur when a call clearing request (ACU_CLEAR_RQ) and a call clearing indication (ACU_CLEAR_IN) for the same call are sent at the same time. In this case, the application must ignore the ACU_CLEAR_IN message, and continue the call clearing as a normal outgoing call clearing (one issued by the application).

Clear collision can take place at the stack level or at the network level. Clear collision at the stack level takes place when a DISCONNECT message is received by the stack directly before it receives an ACU_CLEAR_RQ message from the application. The following illustration shows the sequence of messages exchanged in this situation:

Clear collision at the network level takes place when a DISCONNECT message is received by the network directly after it sends a DISCONNECT message to the stack. The following illustration shows the sequence of messages exchanged in this situation: