CAN is a 2-wire serial bus, so it cannot carry multiple messages simultaneously. The collision-detection, avoidance, and resolution method it uses is called Carrier Sense Multiple Access/Collision Detection-Collision Resolution (CSMA/CD-CR). Carrier Sense means that nodes wait for a period of time in which there is no bus activity before sending messages. Multiple Access means that every node has an equal opportunity to transmit a message. Collision Detection is needed because a bus collision will occur if two nodes attempt to transmit at the same time. Collision Resolution is essential to avoid bus stalls and traffic jams. CAN uses a non-destructive bitwise arbitration method that does three things: keeps messages intact; sends the highest-priority message uncorrupted and without delay; and subsequently allows retransmissions of lower-priority messages.