The CCNA Basic: Half-duplex and full-duplex

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The CCNA Basic: Half-duplex and full-duplex
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In telecommunications, a duplex communication system is a point-to-point system of two devices, which can communicate with each other in two directions. There are two types of duplex communication systems in an Ethernet environment:

Half duplex-ports can only send data when data is not received. In other words, it cannot send and receive data at the same time. The network hub runs in half-duplex mode to prevent conflicts. Because hubs are rare in modern LAN, half-duplex systems are no longer widely used in Ethernet.

Full-duplex - All nodes can be sent and received on their ports at the same time. There is no conflict in full-duplex mode, but host NIC and switch ports must support full-duplex mode. All duplex Ethernet uses two pairs of lines at the same time, not one pair like half-duplex.

The following picture illustrates the concept:

Because the hub can only run in half-duplex mode, the switch and hub will negotiate the use of half-duplex mode, which means that only one device can send data at that time. The workstation on the right supports full duplex, so the link between the switch and the workstation will use full-duplex, and both devices will send data at the same time.

Each nic and switch port has a duplex setting. For all links between host and switch or between the switch, full-duplex mode shall be used. however, for all links connected to the LAN hub, the half-duplex mode should be used to prevent duplex mismatches that may cause network performance degradation.

In Windows, you can set up duplex settings in the Properties window of your network adapter:

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