Computer Networks

 1. Introduction

A computer network is a system where two or more computers or devices are connected together to share data, resources, and information.

The main idea is communication and sharing — instead of working alone, computers work together.

2. Need for a Computer Network

Computer networks are important because they allow:

1. Data Sharing: Files, videos, and information can be easily transferred between devices.
2. Resource Sharing: Devices like printers, scanners, and internet connections can be shared.
3. Communication: Enables email, video conferencing, and chatting.
4. Centralized Data Management: Data can be stored and managed from one main computer (server).
5. Cost Efficiency: Reduces hardware and storage costs by sharing resources.

3. Types of Computer Networks

(a) LAN (Local Area Network)

• Covers a small area like a school, office, or building.
• Computers are connected using cables (Ethernet) or Wi-Fi.
• Example: All computers in your school computer lab connected to one server.

Advantages:

• Fast data transfer
• Easy to set up
• Low cost

(b) MAN (Metropolitan Area Network)

• Covers a city or large campus area.
• Connects several LANs together.
• Example: A group of colleges within a city connected through a common network.

Advantages:

• High-speed connection between buildings or campuses
• Covers wider area than LAN

(c) WAN (Wide Area Network)

• Covers a large geographical area, even across countries.
• The Internet is the largest example of WAN.
• Uses satellites, telephone lines, or fiber optics.

Advantages:

• Global communication
• Access to remote data and servers

 4. Components of a Network 

Component	Description	Example
Server	A powerful computer that stores data and manages network resources.	School server
Client	Computers or devices that access data from the server.	Student computers
Network Interface Card (NIC)	Hardware that connects a computer to the network.	Ethernet or Wi-Fi card
Switch / Hub	Devices used to connect multiple computers in a LAN.	Switch in a lab
Router	Connects different networks together and routes data.	Wi-Fi router
Cables / Wireless	Medium for data transfer.	LAN cable, Wi-Fi signals

 5. Types of Network Connections

Wired Connection

• Uses cables (like Ethernet).
• Stable and secure.
• Used in offices or labs.

Wireless Connection

• Uses Wi-Fi, Bluetooth, or radio waves.
• Easier to set up, more flexible.
• Used in homes, smartphones, and laptops.

6. Network Topologies

Network Topologies

Topology refers to how computers are arranged or connected in a network.

Type	Description	Advantage	Disadvantage
Bus Topology	All devices share one communication line (single cable).	Easy setup	Cable fault affects whole network
Star Topology	All computers connect to a central device (hub/switch).	Fast, easy to manage	Central hub failure stops network
Ring Topology	Devices are connected in a circular path.	Equal access	One failure breaks the loop
Mesh Topology	Each device connected to every other device.	Reliable	Expensive and complex

 7. The Internet

The Internet is a global network that connects millions of private, public, academic, and business networks.
It allows access to websites, emails, online learning, and cloud storage.

Key Internet Services:

• Email (Electronic Mail)
• WWW (World Wide Web)
• Social Media
• Cloud Storage (Google Drive, OneDrive)
• Online Learning Platforms

 8. IP Address and Domain Name

IP Address

• A unique numerical label given to every device connected to a network.
• Example: 192.168.1.1
• Works like a home address for computers.

Domain Name

• Human-readable name of a website.
• Example: www.cbse.gov.in
• The domain name maps to an IP address using DNS (Domain Name System).

9. Network Security

To protect data from unauthorized access, hacking, or viruses:

• Use strong passwords
• Install firewalls
• Keep antivirus updated
• Use encryption
• Don’t share personal data online

10. Advantages of Computer Networks

File and resource sharing
Centralized data management
Easy communication
Cost-effective setup
Remote access to data

Summary:

Concept	Meaning
Computer Network	Connection of computers for sharing data & resources
LAN / MAN / WAN	Network types by area covered
Server / Client	Main & user computers in a network
Topology	Structure or layout of connections
IP / Domain	Address and name system for internet
Security	Protection from unauthorized access