On a shared network medium, what is the term for when two transmissions occur simultaneously?

• A. Collision
• B. Interference
• C. Latency
• D. Throughput

Answer: (A)

On a shared network medium, two devices transmitting at the same time cause their signals to collide with each other. This collision is what CSMA/CD handles in Ethernet networks, where stations detect the overlap, send a jam signal to ensure everyone notices, and then back off for a random period before trying again. The idea is that when two transmissions overlap, the data can become garbled, so a collision disrupts both messages and forces a retry rather than two successful deliveries.

Interference is a broader term for any unwanted signal disturbance and isn’t specifically the simultaneous transmission event. Latency is the delay before a transmission begins or between sending and receiving, and throughput is the rate of successful data transfer over time, not the occurrence of two devices transmitting at once. Modern networks reduce or eliminate collisions by using switches and full-duplex links, which isolate each device’s transmissions.