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The difference between half-duplex and full-duplex

What determines if one communicates using half- or full-duplex?

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Half-duplex is used to describe communication where only... one side can talk at a time. Once one side has finished transmitting its data, the other side can respond. Only one node can talk at a time. If both try to talk at the same time, a collision will occur on the network.

As you can understand, this method of communication is not very efficient and requires more time to send/receive larger amounts of data.

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Older networks used to work in half-duplex mode, due to the constraints of the network medium (coax cable) and hardware equipment (hubs).

On the other hand, full-duplex is used to describe communication where both sides are able to send and receive data at the same time. In these cases, there is no danger of a collision and therefore the transfer of data is completed much faster.

Today, all networks make use of switches (rather than hubs) and UTP Ethernet cabling, which allow full-duplex communication between all connected hosts.

For more information:
 View this lesson on half/full duplex communications, hubs and switches.
 See's crash course on understanding duplex conflicts.

This was first published in July 2008

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