|  | 6.5 | Media Access Control (MAC)
| 6.5.4 | Non-deterministic MAC protocols

Non-deterministic MAC protocols use a first-come, first-served (FCFS) approach. In the late 1970s, the University of Hawaii developed and used a radio communication system (ALOHA) that connected the various Hawaiian Islands. The protocol they used allowed anyone to transmit at will. This led to radio wave collisions that could be detected by listeners during transmissions. However, what started as ALOHA, eventually became a modern MAC protocol called Carrier Sense Multiple Access with Collision Detection (CSMA/CD).

CSMA/CD is a simple system. Everyone on the system listens for quiet, at which time it’s OK to transmit. However, if two people talk at the same time, a collision occurs, and neither person can transmit. Everyone else on the system also hears the collision, waits for silence, and then tries to transmit.