The document discusses data communication and transmission. It defines a Network Interface Card (NIC) as the device that coordinates data transfer. There are two forms of data transmission: analog and digital. Analog transmission sends continuous waveforms while digital transmission uses discrete 'on' or 'off' states represented by 1s and 0s. A modem is used to convert between analog and digital signals for transmission over telephone lines. Data transmission rates are measured in bits per second. There are three transmission modes: simplex for one-way communication, half duplex for two-way communication but only one direction at a time, and full duplex for simultaneous two-way communication.

1. R.D.SIVAKUMAR, M.Sc.,M.Phil.,M.Tech.,
Assistant Professor of Computer Science
Bell Institute
Sivakasi – 626 124.
Mobile: 099440-42243
e-mail : rdsivakumarstaff@gmail.com
DATA COMMUNICATION

2. Coordinating Data Communication
The device that coordinates the data transfer is called Network Interface card(NIC).
Example
Ethernet
 Arcnet and
Token ring

3. Two Forms of Data Transmission
Analog Data
Transmission
• Transmission of data continuous waveform.
• Analog signals are sometimes encoded to represent binary data.
Digital Data
Transmission
• It is Widely used communication system in the world.
• The distinct electrical state of ‘on’ or ‘off’ is represented by 1 or 0.
• It is faster and more efficient than analog.

4. MODEM
MODEM stands for Modulator and Demodulator.
Telephone is used for analog signal
Computer or PC is used for digital signal.
Modem is used to convert analog to digital and vice versa.

5. Data Transmission Rate
The speed at which data travel over a communication channel is called the
communication rate. The rate at which the data are transferred is expressed in
terms of bits per second (bps)

6. When two computers are in communication, data transmission may occur in one
of the three modes
Transmission Mode

7. Simplex mode
The device using the simplex mode of transmission can either send or receive data,
but it cannot do both.
An example is the traditional TV, the transmitter is sent the signal to TV, but TV
is no return any signals to transmitter.
The data can be transmitted back and forth between two stations.
But data can go in any one direction only.
An example is Walky-talky, One can waits of his turn while the other talks.
Half duplex mode
Full duplex mode
The data can be send and receive simultaneously. It is two way bridge.
An example is telephone, two people on the telephone talking and listening.

8. R.D.SIVAKUMAR, M.Sc.,M.Phil.,M.Tech.,
Assistant Professor of Computer Science
Bell Institute
Sivakasi – 626 141.
Mobile: 099440-42243
e-mail : rdsivakumarstaff@gmail.com