Arbitration

Arbitration

In event-driven bus systems such as CAN, every ECU checks if the bus is available (idle) before it starts to transmit a message. This process of "listening before transmitting" is called Carrier Sense (CS). Arbitration is necessary when several ECUs have access to the bus (MA = Multiple Access) and want to start sending a message at the same time. That results in a collision. Arbitration is a procedure that solves this collision. There are CSMA/CD (CD = Collision Detection) and CSMA/CA (CA = Collision Avoidance). Time-triggered bus systems such as LIN use TDMA (Time Division Multiple Access) as bus access where arbitration is not necessary.