Cisco Certified Network Associate (CCNA) Practice Exam

What media access method is used by Gigabit Ethernet?

1. CSMA/CA

2. Token passing

3. Point-to-point

4. CSMA/CD

The correct answer is: CSMA/CD

Gigabit Ethernet uses the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) media access method, which is designed to manage how devices on a shared medium transmit data. The CSMA/CD protocol allows devices to listen to the channel before transmitting data. If the channel is clear, the device can send its data. However, if two devices transmit simultaneously, resulting in a collision, the protocol allows each device to detect the collision and back off before attempting to retransmit after a random time delay. In the context of Gigabit Ethernet, while it uses a switched medium where collisions are largely eliminated through full-duplex technology, the underlying principles of CSMA/CD were essential in earlier Ethernet standards. In switched Gigabit Ethernet networks, each device has a dedicated connection to the switch, thus avoiding collisions. However, the reference to CSMA/CD is more about the technology's historical roots and provides context for Ethernet's evolution. Other methods, such as token passing, are not used in Ethernet networks, as they rely on different mechanisms to control access (like in Token Ring networks). CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is typically used in wireless networks, while point-to-point refers to direct communication between two devices rather than