Half-duplex data transmission means that data can be transmitted in both directions on a signal carrier, but not at the same time. For example, on a local area network using a technology that has half-duplex transmission, one workstation can send data on the line and then immediately receive data on the line from the same direction in which data was just transmitted. On the other hand, full-duplex transmission implies that data are transmitted in both directions simultaneously.

For example, a walkie-talkie is a half-duplex device because only one party can talk at a time. In contrast, a telephone is a full-duplex device because both parties can talk simultaneously. When two computers communicate over a LAN, data typically travels in only one direction at a time, because the baseband network used for most LANs supports only a single signal. In other words, it is transmitted in half-duplex fashion.

With the right equipment, full-duplex communication is possible on certain types of LANs. The first requirement is a separate channel for traffic running in each direction. Whether this is possible depends on the network medium. Coaxial cable, for example, contains a single conductor and a ground, so there is no physical way that traffic could run in both directions, unless you were to install two cable runs for each connection. Twisted pair cable, on the other hand, contains four separate wire pairs within a single sheath, one of which is dedicated to incoming traffic and one to outgoing. Networks that use this type of cable can therefore theoretically operate in full-duplex mode, and some manufacturers are making Ethernet equipment that makes this possible. Full-duplex Ethernet essentially doubles the throughput of the existing network.

Half Duplex Transmission

Related Terms: Full Duplex