Overview

In this chapter, we will describe how we have arrived at this electronic global village. Computers, telephones, and wireless devices are being linked by network everywhere in the world of connectivity. We are rapidly coming into an era in which we can find almost anything we want online and reach almost anywhere, anytime. When we collaborate, we are sharing information.

This sharing can be local or remote. Between individual, local communication usually occurs face to face, while remote communication takes place over distance.

Data Communications is the exchange of data between two devices via some form of transmission media such as a wire cable. In other words, we can say that transfer of information or data from one location to another is called data communications. The term Data Communication can generally be defined as the movement of encoded information by means of electrical transmission systems from one computer or device to other computer or device through communication channels (such as cables, wireless media etc.

Five_different_components_of_Data_Communication_SystemFigure 3.1: Five different components of Data Communication System.

Component of Data Communication

There are five components (see figure 3.1) in data communication.

  • Message: The message is the information (data) to be communicated. It can consist of text, number, pictures, sound, video or any combination of these.
  • Sender: The sender is the device that sends the data. It can be computer, workstation, telephone, video camera and so on.
  • Receiver: The receiver is the device that receives the data. It can be computer, workstation, telephone, television and so on.
  • Communication Channel: The Communication channel is the physical path by which a data travels from sender to receiver. It can be a twisted – pair wire, coaxial cable, fiber optic cable, or microwave etc.
  • Encoder and Decoder: The encoder converts digital signals to form, which can pass through transmission medium and decoder again coverts signal from encoded form into digital form, which is understandable for receiver. Without these, two devices may be connected but not communicating, such as a student speaking Urdu cannot understand a student who speaks only German without a translator.

Signals

The electromagnetic or light waves representing data are called signals. These are used to transfer data from one device to another device through a communication medium. Data communication signals can be in analog or digital form.

Analog_signalFigure 3.2: (a) Analog signal

digital_signalFigure 3.2: (b) digital signal

  • Analog: The analogue data signals are continuous electrical signal in the form of wave. This wave is called a carrier wave. Two characteristics of analogue carrier waves that can be altered are frequency and amplitude (figure 3.2.a). Frequency is the number of times a wave repeats during a specific time interval. Amplitude is the height of wave within a given period of time.
  • Digital: A digital signal uses on-off electrical pulses in discontinuous. Or discrete form. Most computers are digital in nature, represent data as patterns of binary numbers (figure 3.2.b).

Type of Data

Data can be represented in different ways such as in data communication, numbers, images, audio, and video etc.

  • Text: The text consists of words, sentences, and paragraphs. Text processing refers to the ability to manipulate words, lines, and pages Typically, the term text refers to text stored as ASCII codes that is, without any formatting. Objects that are not text include graphics, numbers and program code.
  • Numeric: Numeric data consist of digits from 0 to 9, +(positive) or – (negatives)sign and a decimal point. It can be integer type or real type data.
  • Image: This type of data includes chart, graph, pictures and freehand drawings. The information in this form is more comprehensive. The data are sent as contiguous bits, which for transfer, are packed into the 8-bit transfer bytes. The receiving site must store the data as contiguous bits.
  • Audio: Sound is a representation of audio. It is converted into digital code by sampling the sound waves 44,056 times per second and converting each sample into a 16-bit number.
  • Video: Video can be produced either as a continuous entity (by a camera), or it can be a combination of images, each a discrete entity, arrange to convey the idea of motion. Video creates action and movements.

Data Representation

The computer works with binary numbers, binary means two digits. These are 0 and 1. An electrical pulse inside the computer represents each binary number. I is represented by a pulse of electrical inside the computer and 0 by an absence of a pulse. Each binary digit is called bit and it is the smallest element of data.