INTRODUCTION

Computers are changing the way we do business and the way we live. Business decisions have to be made quickly, and the decision makers require immediate access to accurate information. Before we ask how quickly we can get hooked up, we need to know how networks operate, what types of technology are available, and which design best fills which set of needs. When a company adds a new division, the technology has to be flexible enough to accommodate changing configurations.
When we communicate, we are sharing information. In the context of computer information systems, data are represented by binary information units (or bits) produced and consumed in the form of 0's and 1's. Data communication is the exchange of data between two devices via some form of transmission medium (such as wire cable). Communicating devices must be part of a communication system made up of a combination of hardware and software. The effectiveness of data communication system depends on three characteristics: delivery, accuracy, and timeliness.

A BRIEF HISTORY

The field of communications is certainly not new: people have been communicating since the early days when humans grunted and scratched pictures on cave walls, which are forms of communication based on the auditory and visual senses, where you either hear someone speaking or see letters and symbols that define a message. Communications changed drastically in 1837, after the invention of the Telegraph by Samuel Morse. Telegraph invention made it possible to send information using electrical impulses over a copper wire. Messages were sent by translating each character into a sequence of long or short electrical impulses and transmutation them. Morse code represents a scheme of association of characters with electrical impulses.

In 1937, Howard A. Aliken of Harvard university began work on the design of fully automatic calculating machine using the concepts of Babbage and those used in punch cards in collaboration with the IBM (International Business Machine). Seven years later in January 1944, the design became a reality and was named MARK I. This was considered to be the first digital computer. MARK I could accept data from Punch cards, store them in memory, make calculations by means of automatically controlled electromagnetic relays and arithmetic counters which were mechanical. It could b programmed, that is, given a set of commands to carry out certain operations. l performed arithmetic and logical operations and solved scientific problems. Another event important to communications occurred in 1945 with the invention of the first electronic computer, ENIAC (Electronic Numerical Integrator an Calculator). It contained vacuum tubes, registers, capacitors and switches and was faster than MARK I. Although ENIAC played no direct role in data or compute communications, it did show that calculations and decision making could be don electronically, an important ability in today's communications systems. The relation between computers and communications began to emerge after the invention of transistor in 1947 allowing smaller and cheaper computers to be built. The new generation of computers that emerged during the 1960s made new application such as processing and routing telephone calls economically feasible. Another milestone in computer-networking occurred with the development c ARPANET. It was developed by the US Department of Defense. It was the pioneering network of the Advanced Research Project Agency of the US Department of Defense Operation of ARPANET was started in 1969 and connected over 100 computer spanning half the globe from Hawaii to Norway. The 1970s and 1980s saw the merger of the fields of computer sciences and data communications that profoundly changed the technology, products and companies c the now combined computer-communication industry.

The computer-communications revolution has produced several remarkable fact:
. There is no fundamental difference between data-processing (computing) an data communications (transmission and switching equipment).
. There is no fundamental difference between data, voice, and vide communications. The distinction among single-processor computer, multiprocessor compute local network, metropolitan network and long-haul network has blurred. The 1990s saw the emergence of the World Wide Web, an application that make information from around the world easily accessible from one's desk. With the click of a mouse button, computer users can access files, programs, video clips, and sound bits all over the globe. Computer and communications have progressed to the point where most businesses or schools can no longer function without them. Our almost total dependence on them demands that we understand them and their abilities and limitations.

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