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Tuesday, December 22, 2009

Data Communication Modes

Today computer is available in many offices and homes and therefore there is a need to share data and programs among various computers with the advancement of data communication facilities. The communication between computers has increased and it thus it has extended the power of computer beyond the computer room. Now a user sitting at one place can communicate computers of any remote sites through communication channel.

In data communication four basic terms are frequently used. They are :
* Data: A collection of facts in raw forms that become information after processing.
* Signals: Electric or electromagnetic encoding of data.
* Signaling: Propagation of signals across a communication medium.
* Transmission: Communication of data achieved by the processing of signals.

There are three ways for transmitting data from one point to another :
- Simplex :Data only flows in one direction.A good example of simplex
communications is a radio station and your car radio. Simplex is not often
used in computer communications because there is no way to verify when or if data is received. However, simplex communications is a very efficient way to distributed vast amounts of information to a large number of receivers.
- Half Duplex : In this mode, devices allow both transmission and receiving, but not at the same time. Essentially only one device can transmit at a time while all other half-duplex devices receive. RS-485 works in half-duplex mode.
- Full Duplex : In this mode, devices can transmit and receive data at the same time. RS232 and RS422 are examples of Full Duplex communications. There are separate transmit and receive signal lines that allow data to flow in both directions simultaneously.

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