In an Ethernet network, under what two scenarios can devices transmit? (Choose two.)
The correct answers are D. when the medium is idle and C. when they detect no other devices are sending.
Explanation: In an Ethernet network, the devices follow the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol to avoid collisions on the network. This protocol governs when devices can transmit data.
CSMA/CD is a contention-based protocol where all devices on the network share the same communication medium, and multiple devices may try to transmit data at the same time. To avoid collisions, devices follow the following rules:
Carrier sense: Devices listen to the network to determine if any other device is currently transmitting data. If they detect a carrier (i.e., a signal indicating that another device is transmitting), they wait until the carrier is gone before trying to transmit.
Multiple access: Multiple devices share the same communication medium, and they can all try to transmit data. However, only one device can transmit at a time.
Collision detection: If two devices transmit data at the same time, their signals collide and become garbled. When this happens, both devices detect the collision and stop transmitting. They then wait for a random amount of time before trying to transmit again.
With this in mind, we can see that options A and E are not correct. There is no special token or server access granted in Ethernet networks.
Option B is partially correct, as devices do need to detect a carrier before transmitting. However, they also need to wait until the carrier is gone before transmitting, which is covered in option D.
Option D is correct because devices can only transmit when the medium is idle, meaning no other device is currently transmitting data.
Option C is also correct because devices need to make sure that no other device is sending data before they can start transmitting. Once they determine that the medium is idle, they can start transmitting.