Carrier Sense with Multiple Access with Collision Detection (CSMA/CD)

Carrier Sense with Multiple Access with Collision Detection (CSMA/CD)
Carrier sense multiple access collision detect (CSMA/CD) describes the Ethernet access method.
If a carrier exists, the cable is in use and the device must wait to transmit.
If the deferral counter exceeds a threshold value of 15 retries, the device attempting to transmit
assumes that it will never get access to the cable to transmit the packet.

In this situation, the source device discards the frame. This might happen if there are too many devices on the network, implying that there is not enough bandwidth available.

CSMA/CD process:
1. A device with a frame to send listens until the Ethernet is not busy (in other words, the device cannot sense a carrier signal on the Ethernet segment).
2. When the Ethernet is not busy, the sender begins sending the frame.
3. The sender listens to make sure that no collision occurred.
4. If there was a collision, all stations that sent a frame send a jamming signal to ensure that all stations recognize the collision.
5. After the jamming is complete, each sender of one of the original collided frames randomizes
a timer and waits that long before resending. (Other stations that did not create the collision do not have to wait to send.)
6. After all timers expire, the original senders can begin again with Step 1.