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  3. Which three statements are true about the operation of a full-duplex Ethernet network, which is being used in the Ezonexam LAN?

Which three statements are true about the operation of a full-duplex Ethernet network, which is being used in the Ezonexam LAN?

admin2009-05-19  54
问题 Which three statements are true about the operation of a full-duplex Ethernet network, which is being used in the Ezonexam LAN? (Choose three)
选项 A、Ethernet hub ports are preconfigured for full-duplex mode.
B、The host network card and the switch port must be capable of operating in full-duplex mode.
C、There are no collisions in full-duplex mode.
D、In a full-duplex environment, the host network card must check for the availability of the network media before transmitting.
E、A dedicated switch port is required for each full-duplex node.
答案B,C,E
解析 Explanation:
Half-duplex Ethernet is defined in the original 802.3 Ethernet and Cisco says you only use one wire pair with a digital signal running in both directions on the wire. It also uses the CSMA/CD protocol to help prevent collisions and to permit retransmitting if a collision does occur. If a hub is attached to a switch, it must operate in half-duplex mode because the end stations must be able to detect collisions.

Half-duplex Ethernet-typically 10BaseT-is only about 30 to 40 percent efficient as Cisco sees it, because a large 10BaseT network will usually only give you 3- to 4Mbps-at most. Full-duplex Ethernet uses two pairs of wires, instead of one wire pair like half duplex. Also, full duplex uses a point-to-point connection between the transmitter of the transmitting device and the receiver of the receiving device, which means that with full-duplex data transfer, you get a faster data transfer compared to half duplex.

And because the transmitted data is sent on a different set of wires than the received data, no collisions occur. The reason you don’t need to worry about collisions is because now Full-duplex Ethernet is like a freeway with multiple lanes instead of the single-lane road provided by half duplex. Full-duplex Ethernet is supposed to offer 100 percent efficiency in both directions; this means you can get 20Mbps with a 10Mbps Ethernet running full duplex, or 200Mbps for FastEthernet.
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