DUPLEXING

What is DuplexingA telecommunications systems where signal can flow in both directions between connected parties Is a system composed of two connected parties or devices which can communicate with one another in both directions. (The term duplex is not used when describing communication between more than two parties or devices.)Duplex systems are employed in nearly all communications networks, either to allow for a communication "two-way street" between two connected parties or to provide a "reverse path" for the monitoring and remote adjustment of equipment in the field.

Types of DuplexingHalf-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.

Half Duplex System

Full-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. A good analogy for a full-duplex system would be a two lane road with one lane for each direction.

Full Duplex EthernetWhile the early coaxial cable based variants of Ethernet were half-duplex by design, all the common variants of twisted pair (10BASE-T, 100BASE-TX and 1000BASE-T) and fiber optic Ethernet provide separate channels for send and receive.To allow use of hubs and for compatibility with existing variants of Ethernet they were initially implemented in a half-duplex manner with the tranceiver (usually by this point integrated into the device) detecting a collision if an attempt was made to transmit and receive simultaneously and looping back data to the host so it could hear itself transmit (as it would on a shared medium).

Full Duplex System

However if both ends of the link are not hubs and the hardware supports it the two channels can be split and used to make a full-duplex link. Unfortunately if autonegotiation is enabled on one end and forced full-duplex on the other, the end with autonegotiation will detect the link as half-duplex causing large numbers of errors due to Duplex_mismatch.

ADSL frequency plan

Autonegotiation (formerly NWay) is an Ethernet procedure by which two connected devices choose common transmission parameters, such as speed and duplex mode. In this process, the connected devices first share their capabilities as for these parameters and then choose the fastest transmission mode they both support.

Duplex Mismatched

In Ethernet, a duplex mismatch is a condition where two connected devices operate in different duplex modes, that is, one operates in half duplex while the other one operates in full duplex. The effect of a duplex mismatch is a network that works but is often much slower than its nominal speed. Duplex mismatch may derive from manually setting two connected network interfaces at different duplex modes, but also derives from connecting a device that performs autonegotiation to one that is manually set to a full duplex mode.