In Ethernet networking, which of the following statements about full-duplex and half-duplex operation is correct?

Introduction / Context:
Ethernet local area networks can operate in either half-duplex or full-duplex mode. Understanding how many wire pairs are used and how traffic flows in each direction is important for troubleshooting collisions, performance issues, and cabling design in modern switched networks.

Given Data / Assumptions:

• We are considering standard twisted-pair Ethernet links, such as Fast Ethernet or Gigabit Ethernet over copper.
• Full-duplex allows simultaneous sending and receiving of frames.
• Half-duplex allows sending or receiving at one time, but not both simultaneously.
• We assume a typical point-to-point link between a switch port and a host network interface card.

Concept / Approach:
On twisted-pair Ethernet, the physical medium uses separate wire pairs for transmit and receive. In full-duplex mode, one pair is dedicated to sending data and another pair is dedicated to receiving data. This separation removes the need for collision detection and improves throughput. In half-duplex mode, the medium is logically shared for send and receive, and the device must use carrier sense multiple access with collision detection to avoid and recover from collisions. The key idea is that full-duplex relies on two independent paths, one in each direction.

Step-by-Step Solution:
1. Recall that a twisted-pair Ethernet cable contains multiple wire pairs.2. In standard full-duplex Ethernet over copper, one pair is used to transmit data from device A to device B.3. Another separate pair is used to transmit data from device B back to device A.4. Because the transmit and receive paths are independent, both devices can send and receive at the same time.5. Therefore, the correct statement is that full-duplex Ethernet uses two separate pairs of wires, one for each direction of communication.

Verification / Alternative check:
You can verify this by looking at standard Ethernet pinouts. For example, on a typical RJ-45 connector for 100 Mbps Ethernet, one pair of pins is used for transmit and another pair for receive. Network documentation and cabling diagrams also show separate transmit and receive pairs for full-duplex links.

Why Other Options Are Wrong:
Option A is incorrect because using only one pair for both sending and receiving would force half-duplex operation. Option C is incorrect because half-duplex cannot send and receive at the same time and does not typically use two independent pairs for simultaneous traffic. Option D is incorrect because full-duplex Ethernet does not use three pairs; the common implementation uses two pairs for data, and any additional pairs are unused or reserved for other purposes depending on the standard.

Common Pitfalls:
A common mistake is to confuse the number of pairs in the cable with how many are actually used for data transmission. Many Ethernet cables have four pairs, but not all pairs are used by every Ethernet standard. Another pitfall is assuming that full-duplex only changes software behavior; in reality, it also depends on how the physical medium is wired and used.

Final Answer:
Full-duplex Ethernet uses two separate pairs of wires, one for transmitting and one for receiving.