What does CSMA/CD stand for, and is it relevant in modern networks?

• A. Carrier Sense Multiple Access with Collision Detection; used on shared Ethernet; largely obsolete in switched networks.
• B. A routing protocol used in LANs.
• C. A wireless access method.
• D. A method to assign IP addresses.

Answer: (A)

CSMA/CD is a method for allowing multiple devices to share a common network segment without stepping on each other’s transmissions. Carrier Sense means a device first listens to the wire before sending. Multiple Access means any device can start transmitting when the line looks free. Collision Detection means if two devices transmit at once, their signals collide and both devices stop, wait a random backoff, and try again. This approach was essential on older Ethernet networks that used hubs or coax, where all devices share a single collision domain and a collision affects everyone on that segment.

In modern networks, switches create separate collision domains for each connection and typically operate in full duplex, so there’s no contention on a link. Because of that, CSMA/CD is largely obsolete in everyday networking, though you might still hear about it in discussions of legacy Ethernet or in basic networking history. It’s not a routing protocol, not a wireless access method, and not a mechanism for IP address assignment.