Which statement best describes CSMA/CD operation on an Ethernet network?

• A. A device can transmit whenever it has data to send, regardless of other devices.
• B. All devices listen before transmitting to minimize collisions.
• C. After a collision, devices immediately retransmit with no delay.
• D. The network uses a token to grant transmission rights.

Answer: (B)

CSMA/CD on Ethernet is about listening before transmitting. Each device first senses the network, and only if the channel is idle does it start transmitting. This carrier sensing helps minimize collisions on a shared medium. If two devices happen to transmit at nearly the same time, a collision occurs and is detected by the NICs; all transmitting devices stop, wait for a random period using binary exponential backoff, and then try again. This approach doesn’t guarantee zero collisions, but it reduces them on a shared Ethernet segment. The other ideas—transmitting whenever data is ready without listening, immediately retransmitting after a collision, or using a token to grant rights—don’t describe CSMA/CD.