CSMA/CD stands for Carrier sense multiple access / Collision detection.
CSMA/CD is a technique used in sharing ethernet in which the sending computer has exclusive use of the cable during the transmission of the frame.
- All computers attached to Ethernet use CSMA/CD to co-ordinate their activities.
- A computer wishing to transmit checks for electrical activity in the cable. This electrical activity is known as carrier.
- If there is no carrier computer transmits the frames. If there is it waits.
- However it is possible that two computers might simultaneously start the transmission. This interference is called collision.
- Sending computer monitors the signal on the cable and if it is different from the one it is transmitting it indicates that collision has occured and transmission stops immediately.
- Computer waits for the cable to become ideal before retransmission.
- For no further collision standard decides the maximum delay of d. Each computer chooses any random value less than d.
- In case collision occurs again delay becomes 2d, 4d and so on. This technique is called binary exponential backoff.