5.1 Introduction to Computer Networks

Meaning of Computer Network (NCERT Definition)

NCERT defines a computer network as:

A collection of interconnected computers and other devices that are able to communicate with each other and share resources.

In simple terms:

• Two or more computers
• Connected using communication media
• Able to exchange data and resources

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Why Computer Networks are Required

NCERT explains that networks are needed to:

1. Share data

   • Files, documents, databases

2. Share hardware

   • Printers, scanners, storage devices

3. Share software

   • Applications installed on a server

4. Enable communication

   • Email, chat, video conferencing

5. Reduce cost

   • One printer can be shared by many users

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Components of a Computer Network

According to NCERT, a network consists of:

• Nodes

  • Computers, servers, printers

• Transmission media

  • Wired or wireless paths

• Networking devices

  • Switch, router, modem

• Network software

  • Protocols and network operating systems

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Advantages of Computer Networks

NCERT highlights the following advantages:

• Resource sharing
• Fast communication
• Centralised data management
• Improved reliability
• Scalability (easy to add new devices)

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Disadvantages of Computer Networks

NCERT also expects awareness of limitations:

• Security risks (hacking, malware)
• Network failure affects many users
• Setup and maintenance cost
• Requires skilled administration

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5.2 Types of Networks

NCERT classifies networks based on geographical coverage.

5.2.1 PAN – Personal Area Network

Definition A PAN is a network used for communication among personal devices over a short distance.

Examples

• Mobile phone connected to Bluetooth earphones
• Laptop connected to mobile hotspot

Characteristics

• Very small range (a few metres)
• Low cost
• Usually wireless

5.2.2 LAN – Local Area Network

Definition A LAN connects computers within a limited area such as:

• School
• Office
• Building

Examples

• Computer lab in a school
• Office network

Characteristics

• High data transfer speed
• Low error rate
• Privately owned

5.2.3 MAN – Metropolitan Area Network

Definition A MAN covers a larger area than LAN, usually a city.

Examples

• Cable TV network
• City-wide Wi-Fi network

Characteristics

• Covers tens of kilometres
• Higher cost than LAN
• Used by organisations and service providers

5.2.4 WAN – Wide Area Network

Definition A WAN spans a very large geographical area, such as a country or the world.

Examples

• The Internet
• Bank networks connecting branches worldwide

Characteristics

• Uses public communication links
• Slower than LAN
• Very expensive infrastructure

Summary Table (NCERT-Oriented)

Network Type	Coverage Area	Example
PAN	Few metres	Bluetooth devices
LAN	Building	School lab
MAN	City	Cable TV
WAN	Country / World	Internet

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5.3 Network Devices

NCERT introduces network devices as hardware components used to connect computers and manage data flow.

5.3.1 Modem

Full Form: Modulator–Demodulator

Function

• Converts digital signals to analog
• Converts analog signals to digital
• Enables Internet access via telephone/cable lines

Use Case

• Required to connect a computer network to the Internet

5.3.2 Hub

Function

• Connects multiple computers in a network
• Broadcasts data to all connected devices

Limitation

• Inefficient
• No data filtering
• Mostly obsolete today

5.3.3 Switch

Function

• Connects multiple devices in a LAN
• Sends data only to the intended device

Advantages over Hub

• Faster
• More secure
• Reduces network traffic

5.3.4 Router

Function

• Connects different networks
• Routes data packets between networks

Examples

• Home Wi-Fi router
• Office routers

Important Point (NCERT)

• Routers are essential for Internet connectivity

5.3.5 Repeater

Function

• Regenerates weak signals
• Extends network distance

Use Case

• Long-distance communication

5.3.6 Gateway

Function

• Connects networks using different protocols
• Acts as an entry/exit point of a network

Network Devices Summary Table

Device	Main Function
Modem	Internet connectivity
Hub	Broadcast data
Switch	Intelligent data forwarding
Router	Connects networks
Repeater	Signal amplification
Gateway	Protocol conversion

Key Exam Points (Very Important)

NCERT often asks:

• Define PAN, LAN, MAN, WAN
• Differentiate between Hub and Switch
• Explain Router vs Modem
• Advantages and disadvantages of networks

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5.4 Networking Topologies

Meaning of Network Topology (NCERT Definition)

A network topology refers to:

The physical or logical arrangement of computers, cables, and other network components in a network.

In simple words:

• It describes how devices are connected

• It affects:

  • Performance
  • Cost
  • Reliability
  • Scalability

Importance of Network Topology

NCERT highlights that topology selection depends on:

• Size of the network
• Cost involved
• Ease of maintenance
• Fault tolerance

5.4.1 Bus Topology

Description

• All computers are connected to a single central cable called the bus.

Characteristics

• Simple and inexpensive
• Easy to install
• Uses less cable

Disadvantages

• Failure of main cable brings down the entire network
• Performance degrades as more devices are added

Use Case

• Small networks

5.4.2 Star Topology

Description

• All computers are connected to a central device (hub or switch).

Characteristics

• Easy to manage and troubleshoot
• High performance
• Most commonly used topology

Advantages

• Failure of one cable does not affect others
• Easy to add or remove devices

Disadvantage

• Failure of central device stops the network

5.4.3 Ring Topology

Description

• Each computer is connected to two neighbouring devices, forming a ring.

Characteristics

• Data travels in one direction
• Equal access to resources

Disadvantages

• Failure of one node affects entire network
• Difficult to troubleshoot

5.4.4 Mesh Topology

Description

• Every computer is connected to every other computer.

Characteristics

• Very reliable
• High redundancy

Disadvantages

• Very expensive
• Complex installation

Use Case

• Critical networks where reliability is essential

5.4.5 Tree Topology

Description

• Combination of star and bus topology
• Hierarchical structure

Characteristics

• Scalable
• Used in large organisations

Topology Comparison Table (Exam-Oriented)

Topology	Cost	Reliability	Usage
Bus	Low	Low	Small networks
Star	Medium	High	Offices, schools
Ring	Medium	Medium	Rare
Mesh	Very High	Very High	Critical systems
Tree	High	High	Large networks

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5.5 The Internet

Meaning of Internet (NCERT Definition)

The Internet is defined as:

A global network of interconnected computer networks that use standard communication protocols to exchange information.

In simple terms:

• Internet = Network of networks
• It connects millions of computers worldwide

Characteristics of the Internet

According to NCERT:

• Worldwide connectivity
• Decentralised structure
• Uses standard protocols like TCP/IP
• Supports multimedia information

Components of Internet

NCERT identifies the following components:

• Clients

  • Computers requesting services

• Servers

  • Computers providing services

• ISP (Internet Service Provider)

  • Provides Internet access

• Communication media

  • Optical fibre, satellite, cables

Internet Protocols (Conceptual Awareness)

• TCP/IP

  • Core protocol of Internet

• HTTP / HTTPS

  • Used for web communication

• FTP

  • File transfer

• SMTP

  • Email transfer

(Detailed protocol study is not required at this level.)

Advantages of Internet

NCERT highlights:

• Easy access to information
• Global communication
• Online services
• Educational resources
• Entertainment

Limitations of Internet

• Security threats
• Privacy issues
• Misinformation
• Internet addiction

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5.6 Applications of Internet

NCERT categorises Internet applications based on usage areas.

5.6.1 Communication Services

• Email
• Instant messaging
• Video conferencing
• Social networking

These allow fast and low-cost communication.

5.6.2 Information Retrieval

• Search engines
• Online encyclopaedias
• Digital libraries
• News websites

Internet acts as a huge information repository.

5.6.3 E-Commerce

• Online shopping
• Online banking
• Online bill payment

Examples:

• Ticket booking
• Online transactions

5.6.4 E-Learning

• Online courses
• Virtual classrooms
• Educational videos
• Digital study material

Important for students and teachers.

5.6.5 Entertainment

• Online music
• Movies
• Games
• Streaming services

5.6.6 E-Governance

• Online tax filing
• Government portals
• Public service delivery

Improves transparency and efficiency.

Summary: Applications of Internet

Area	Examples
Communication	Email, chat
Education	Online classes
Business	E-commerce
Entertainment	Streaming
Governance	Online services

Key Exam Points (Very Important)

NCERT commonly asks:

• Define network topology
• Explain any two topologies
• What is Internet?
• List applications of Internet
• Advantages and disadvantages of Internet

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5.7 Website

Meaning of Website (NCERT Definition)

A website is defined as:

A collection of interlinked web pages stored on a web server and accessible through the Internet using a common domain name.

In simple words:

• A website is a group of related web pages
• All pages belong to the same domain
• They are accessed using a single web address (URL)

Characteristics of a Website

According to NCERT:

• Has a unique domain name
• Contains multiple web pages
• Stored on a web server
• Accessible through the Internet
• Can contain text, images, audio, video, and links

Examples of Websites

• Educational websites
• Government websites
• Commercial websites
• News websites

Types of Websites (Conceptual Awareness)

NCERT expects basic awareness:

• Static Website

  • Content does not change frequently
  • Simple and fast

• Dynamic Website

  • Content changes based on user interaction
  • Uses databases and server-side processing

5.8 Web Page

Meaning of Web Page (NCERT Definition)

A web page is defined as:

A single document written in HTML that can be displayed in a web browser.

In simple terms:

• A web page is one page of a website
• It contains information displayed on the screen

Characteristics of a Web Page

• Written using HTML

• Can include:

  • Text
  • Images
  • Hyperlinks
  • Multimedia

• Displayed using a web browser

• Each web page has its own URL

Difference Between Website and Web Page (Very Important)

Website	Web Page
Collection of web pages	Single document
Multiple URLs	One URL
Stored on server	Part of a website
Example: School website	Example: Home page

NCERT frequently asks this comparison.

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5.9 Web Server

Meaning of Web Server (NCERT Definition)

A web server is defined as:

A computer system that stores web pages and delivers them to users upon request through the Internet.

In simple terms:

• A web server:

  • Stores websites
  • Responds to client requests
  • Sends web pages to browsers

Functions of a Web Server

NCERT highlights the following functions:

• Stores web pages and website files
• Receives requests from browsers
• Sends requested web pages to users
• Handles multiple users simultaneously

Working of a Web Server (Conceptual Flow)

1. User enters a website address in browser
2. Browser sends request to web server
3. Web server processes the request
4. Web page is sent back to browser
5. Browser displays the web page

Examples of Web Servers (Awareness Only)

• Apache
• IIS
• Nginx

(Names are for awareness; details are not required.)

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5.10 Hosting of a Website

Meaning of Website Hosting

NCERT defines hosting as:

The process of storing a website on a web server so that it can be accessed through the Internet.

In simple words:

• Hosting makes a website available online
• Without hosting, a website cannot be accessed by users

Need for Website Hosting

NCERT explains that hosting is required to:

• Store website files
• Make the website accessible 24×7
• Allow users worldwide to access the site

Types of Web Hosting (Basic Awareness)

• Shared Hosting

  • Multiple websites on one server
  • Low cost

• Dedicated Hosting

  • One server for one website
  • High performance

• Cloud Hosting

  • Website hosted on multiple servers
  • High reliability

Students are expected to know only the idea, not technical details.

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5.11 Browser

Meaning of Web Browser (NCERT Definition)

A web browser is defined as:

A software application used to access, retrieve, and display web pages from the Internet.

In simple terms:

• Browser is used to view websites
• It acts as an interface between user and Internet

Functions of a Web Browser

According to NCERT:

• Requests web pages from web servers
• Displays text, images, and multimedia
• Allows navigation using hyperlinks
• Supports bookmarking and history

Examples of Web Browsers

• Google Chrome
• Mozilla Firefox
• Microsoft Edge
• Safari

Difference Between Web Server and Web Browser (Very Important)

Web Server	Web Browser
Stores websites	Displays websites
Responds to requests	Sends requests
Server-side	Client-side
Example: Apache	Example: Chrome

This comparison is frequently asked in exams.

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Key Exam Points (Very Important)

NCERT commonly asks:

• Define website and web page
• Difference between website and web page
• What is a web server?
• What is website hosting?
• What is a web browser?
• Difference between web server and browser

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