On a shared Ethernet segment, what event occurs when two devices transmit at the same time?

• A. Collision
• B. Interference
• C. Latency
• D. Packet loss

Answer: (A)

On a shared Ethernet segment, when two devices transmit at the same time, their signals collide. This happens because the medium is shared and there’s no central arbiter in half‑duplex environments, so both transmissions overlap and corrupt each other. The network cards use CSMA/CD to manage this: they listen before sending (carrier sense), and if a collision is detected during transmission, they stop, send a jam to ensure all devices detect the collision, and then each device waits for a random backoff period before attempting to retransmit. This mechanism is what makes a collision the defining event on a shared segment. Interference is general noise on the line, latency is the delay incurred in transmission, and packet loss can result from collisions but is not the event itself. In modern networks with switches and full duplex, collisions are largely eliminated because each link is its own collision domain.