CSMA avec compensation exponentielle binaire / CD

Carrier sense multiple access (CSMA / CD）is a network protocol running at the medium access control (MAC) layer. It can sense or listen to whether the shared transmission channel is busy and defer transmission until the channel is idle.

When multiple stations send their frames simultaneously, a collision occurs. The backoff algorithm is a collision resolution mechanism commonly used to schedule retransmissions after Ethernet collisions. The waiting time that the station waits before attempting to retransmit the frame is called the backoff time.

CSMA / CD algorithm

Étapes1）When the frame is ready, the sending station checks whether the channel is idle or busy.

Étapes2）If the channel is busy, the station will wait until the channel becomes idle.

Étapes3）If the channel is idle, the station will start sending and continue to monitor the channel to detect collisions.

Étapes4）If a collision is detected, the work station will initiate the binary exponential compensation algorithm.

Étapes5）the station resets the retransmission counter and completes the frame transmission.

Binary exponential backoff algorithm in the case of collision

Étapes1）the station continues to transmit the current frame and the jam signal within the current time to ensure that all other stations detect the collision.

Étapes2）the station increases the retransmission counter c to indicate the number of collisions.

Étapes3）the station chooses to transmit at 0 and2 ^c – 1Random slot time within the range. For example, in the first collision (i.e., c = 1）after that, the station will wait for 0 or1Slot time. After the second collision (i.e., c = 2），the station will wait for 0 to3Any time between any two slots. After the third collision (i.e., c = 3），the station will wait for 0 to7Any time between any two slots, and so on.

Étapes4）Si le numéro de radio est sélectionné