Computer Networking Courses

Unit 1 : Introduction to Computer Networks

Introduction
Computer workloads are continuously being decentralized. The need for communicating among the geographically dispersed computers has evolved computer networks. In this unit, preliminary ideas of computer networks are introduced. Classification of computer networks and their topologies are also presented in this unit.

Lesson 1 : Computer Networks
1.1. Learning Objectives
On completion of this lesson you will be able to :

i) grasp the elementary idea of computer networks

ii) understand the goals of computer networks

iii) grasp the idea of message transmission over a computer network

1.2. What is a Computer Network?
A computer network is an interconnected collection of autonomous computers. An autonomous computer is one whose start, stop and control do not depend on any other computer. Two computers are said to be interconnected if they are able to exchange information. This connection between two computers may be using copper wire, fiber optics, microwaves, and communication satellites.

1.3. Computer Networks and Distributed Systems
There is a considerable confusion between a computer network and a distributed system. In a computer network, users explicitly log onto one computer, explicitly submit jobs remotely, explicitly move files around and generally handle all the network management personally. A computer network is an interconnected collection of autonomous computers.

In a distributed system, the existence of multiple autonomous computers is not visible to the user. A user can type a command to run a program, and it runs. It is up to the operating system to select best processor, find and transport all the input files to that processor, and put the results in the appropriate place. In a distributed system, nothing has to be done explicitly, it is all automatically done by the system without the user’s knowledge. In effect, a distributed system is a software system built on top of a computer network.

1.4. Goals of Computer Networks
Computer networks have the following goals :
(i) Resource sharing : Programs, equipment, and data available to anyone on the network can be shared without regard to the physical location of resource and the user.
(ii) High reliability : Alternative sources of resource supply provide high reliability. For example, files could be placed on two or three computers, so if one of them is unavailable due to a hardware failure, the other copies could be used. In addition, for presence of multiple CPUs, if one goes down the other may be able to take over its work.
(iii) Saving money : Resource sharing provides considerable saving of money.
(iv) Salability : Computer network provides ability to increase system performance gradually as the workload grows just by adding more processor in the network.
(v) Communication medium : A computer network provides a powerful communication medium among widely separated people. For example, it is easy for two or more people who live far apart to write a report using a computer network.

1.5. Message Transmission over a Computer Network
A message in a computer network is a single unit of communication. For example, in an e-mail system, a message would consist of a document sent from one user to another. A message in an image transmission system could be a single figure, image, or diagram.
To transmit a message over a computer network, it is usually represented as a string of bits. Transmitting long message as one complete unit is generally not done for various reasons. Long messages are normally broken up into shorter bit strings called packets. These packets are then sent through the network as individual units and are reassembled into complete message at the destination computer.