Clear collision occurs when the user and the network simultaneously transfer DISCONNECT messages specifying the same call reference value. When the network receives a DISCONNECT message whilst in the Disconnect Indication state, the network shall stop timer T305 or T306 (whichever is running); disconnect the B-channel (if not disconnected); send a RELEASE message; start timer T308, and enter the Release Request state. Similarly, when the user receives a DISCONNECT message whilst in the Disconnect Request state, the user shall stop timer T305; send a RELEASE message; start timer T308, and enter the Release Request state.
Clear collision can also occur when both sides simultaneously transfer RELEASE messages related to the same call reference value. The entity receiving such a RELEASE message whilst within the Release Request state shall stop timer T308; release the call reference and B-channel and enter the Null state (without sending or receiving a RELEASE COMPLETE message).