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A
duplex
communication system is a system composed of two connected parties or devices that
can communicate with one another in both directions.
Half Duplex:
A
half-duplex
system provides for communication in both directions, but only one direction at a
time (not simultaneously). Typically, once a party begins receiving a signal, it must wait for the
transmitter to stop transmitting, before replying.
Full Duplex:
A
full-duplex
, or sometimes
double-duplex
system, allows communication in both directions, and,
unlike half-duplex, allows this to happen simultaneously. Land-line telephone networks are full-
duplex, since they allow both callers to speak and be heard at the same time.
Loopback Test
A loopback test is a test in which a signal in sent from a communications device and returned
(looped back) to it as a way to determine whether the device is working right or as a way to pin
down a failing node in a network. One type of loopback test is performed using a special plug,
called a
wrap plug
that is inserted in a port on a communications device. The effect of a wrap
plug is to cause transmitted (output) data to be returned as received (input) data, simulating a
complete communications circuit using a single computer.
Auto MDI-MDIX
Auto-MDIX (automatic medium-dependent interface crossover) is a computer networking
technology that automatically detects the required cable connection type (straight-through or
crossover) and configures the connection appropriately, thereby removing the need for crossover
cables to interconnect switches or connecting PCs peer-to-peer. When it is enabled, either type
of cable can be used or the interface automatically corrects any incorrect cabling. For Auto-
MDIX to operate correctly, the speed on the interface and duplex setting must be set to "auto".
Auto-MDIX was developed by HP engineers Dan Dove and Bruce Melvin.
Auto Negotiation
Auto (auto-negotiation) allows one port to negotiate with a peer port automatically to obtain the
connection speed and duplex mode that both ends support. When auto-negotiation is turned on,
a port on the Switch negotiates with the peer automatically to determine the connection speed
and duplex mode.
