DATA FLOW, simplex,half duplex, full-duplex

Simplex:

In simplex mode, the communication is unidirectional, as on a one-way street. Only one

of the two devices on a link can transmit; the other can only receive (see Figure a). Keyboards 

and traditional monitors are examples of simplex devices. The keyboard can only introduce 

input; the monitor can only accept output. The simplex mode can use the entire capacity of the 

channel to send data in one direction.

Half-Duplex:

In half-duplex mode, each station can both transmit and receive, but not at the same time.

When one device is sending, the other can only receive, and vice versa The half-duplex mode is 

like a one-lane road with traffic allowed in both directions.

When cars are traveling in one direction, cars going the other way must wait. In a half-duplex 

transmission, the entire capacity of a channel is taken over by whichever of the two devices is 

transmitting at the time. Walkie-talkies and CB (citizens band) radios are both half-duplex 

systems.

The half-duplex mode is used in cases where there is no need for communication in both 

directions at the same time; the entire capacity of the channel can be utilized for each direction.

Full-Duplex:

In full-duplex both stations can transmit and receive simultaneously (see Figure c). The 

full-duplex mode is like a tW<D-way street with traffic flowing in both directions at the same 

time. In full-duplex mode, si~nals going in one direction share the capacity of the link: with 

signals going in the other din~c~on. This sharing can occur in two ways: Either the link must 

contain two physically separate t:nmsmissiIDn paths, one for sending and the other for receiving; 

or the capacity of the ch:arillilel is divided between signals traveling in both directions. One 

common example of full-duplex communication is the telephone network. When two people are 

communicating by a telephone line, both can talk and listen at the same time. The full-duplex 

mode is used when communication in both directions is required all the time. The capacity of the 

channel, however, must be divided between the two directions.