What is Half Duplex and Full Duplex Ethernet Modes?

Half Duplex Ethernet Mode

Ethernet IEEE 802.3 standard defines the half duplex; Cisco describes, it uses a digital signal on a wire pair flowing in both tracks on the wire. Half Duplex always employs the Carrier Sense Multiple Access with Collision Domain (CSMA/CD), so that it can retransmit the transmission if collision occurs. Hub always works in half duplex mode. Half duplex Ethernet is not efficient because it has the limit up to 10BaseT, as Cisco describes 10BaseT is not more than 3 to 4Mbps.

Example of Half Duplex

Full Duplex Ethernet Mode

On the other hand, full duplex Ethernet employs two pairs of wires. Full duplex always works with the point to point connection between the transmitter of source node and the receiver of destination node. So, full duplex provides the fast data transmission, if we compare to half duplex. Collisions do not occur in the full duplex Ethernet mode because source always sent data on different wires than the received data wires. Full duplex Ethernet mode is 100% efficient for both tracks (receivers & transmitters). Full duplex offers the connection speed 10 to 100Mbps. In short, we can run full duplex Ethernet mode with any device except a hub. Full duplex Ethernet mode uses an “auto detect mechanism”. As a full duplex Ethernet port is turned on it connects to the remote node then connects to the other nodes of the Ethernet link. The auto detect mechanism determines the transmission exchange rate, means either it can run at 10Mpbs or 100Mbps. And it also determines that what it have to run full duplex mode or half duplex mode.

Half Duplex Sending Information Full Duplex Receiving Information

We can deploy full duplex Ethernet mode in the following conditions:

• Switch to host connection
• Switch to a switch connection
• Host to host connection by using crossover cable

A few points you must have to remember for deploying full duplex Ethernet mode:

• No collisions in full duplex.
• A dedicated port is necessary for each full duplex device.
• Host’ network identification card and switch port have to able to operate in full duplex mode.

In this article we have covered the differences between half duplex mode and full duplex mode and how half and full duplex modes works at Ethernet and the purpose of auto detect mechanism according to the CCNA 640-802 Cisco Certified Network Associate’ course detail.

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