CSMA/CD

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)is a protocol used for network control. This ensures that only a single network node transmits on the Ethernet wire at any given time in the Ethernet network.

Carrier Sense is the responsiveness of each Ethernet device to the activity that goes on in Ethernet wires before transmission attempts. The device will delay transmission if it observes transmission activity from another device.

Multiple Access is two or more Ethernet devices sensing (observation and waiting before transmitting) at any given time.

Collision Detection is the ability of different Ethernet devices to perceive the error when transmitting simultaneously.

Collision Occurrence in CSMA/CD

Assume that an Ethernet network is comprised of only two nodes. Each independent node opts to send the other an Ethernet frame. Both nodes observe the Ethernet wire and perceive that there is no carrier present. Both nodes then transmit at the same time, triggering a collision. Both nodes sense the collision and each delays the transmission for a random period of time.

Ethernet network collisions are usual, and a small number of collisions are typical to the protocol design.

Collision detection methods depend on the media. A comparison of transmitted information with the received information detects collisions for an electrical bus like the Ethernet. If the data differs and another transmitter overlays the other’s signal, the transmission is terminated immediately. This causes the sending of a jam signal, which sets transmitters back by random durations, consequently decreasing the probability of collision.

Logically, if numerous nodes transmit in an Ethernet network, the collision level can escalate to an insupportable extent. This means loss of accessible bandwidth in a network because retransmission wastes much bandwidth.

To optimize bandwidth and further reduce the marginal concerns with the CSMA/CD protocol, networks also utilize Ethernet switches.