CSMA (carrier sense multiple access) is a probabilistic media access control protocol, which verifies the absence of traffic before transmitting on a shared transmission medium.
Carrier Sense: the transmitter check whether another transmission is in progress before initiating a transmission.
Multiple access: the shared medium can be accessed by multiple senders and receivers. Transmission by one node is generally received by all nodes connected to the medium.
CSMA access mode
1-persistence: if transmission medium is idle, transmits immediately. if busy, it senses the transmission medium continuously until it becomes idle, then transmits with a probability of 1.
Non-persistence: if transmission medium is idle, transmits immediately. if busy, it waits for a random period of time and then restarts the logic cycle (sense and transmit)
p-persistence: if transmission medium is idle, transmits immediately. if busy, it senses the transmission medium continuously until it becomes idle, then transmits with a probability of p.
O-persistence: A supervisory node orders the transmission to each node.