What is a Computer Network?

A Computer Network is a group of interconnected computers and devices that communicate with each other to share data, resources, and information.

Examples:

• Internet
• School Computer Lab
• Office Network
• Mobile Hotspot Sharing

Types of Computer Networks

1. LAN (Local Area Network)

• Covers a small geographical area
• Used in schools, offices, homes
• High speed network

Features:

• Fast data transfer
• Low cost
• Easy maintenance

2. MAN (Metropolitan Area Network)

• Covers a city or large campus
• Larger than LAN but smaller than WAN

Example:

• Cable TV network in a city

3. WAN (Wide Area Network)

• Covers very large geographical areas
• Connects networks across countries

Example:

• Internet

Features:

• Long-distance communication
• Uses satellites and telecom lines

Network Topologies

1. Bus Topology

• All computers connected to a single cable

Advantage:

• Low cost

Disadvantage:

• Cable failure affects whole network

2. Star Topology

• All devices connected to a central hub/switch

Advantage:

• Easy troubleshooting

Disadvantage:

• Hub failure stops network

3. Ring Topology

• Computers connected in circular form

4. Mesh Topology

• Every device connected to every other device

5. Tree Topology

• Combination of star and bus topology

Network Devices

Hub

• Connects multiple computers
• Works on Physical Layer

Switch

• Smarter than hub
• Sends data to specific device only

Router

• Connects different networks
• Used for internet connection

Modem

• Converts digital signal to analog and vice versa

Repeater

• Boosts weak signals

Transmission Media

Guided Media

Uses physical cables.

Types:

• Twisted Pair Cable
• Coaxial Cable
• Optical Fiber

Unguided Media

Wireless communication.

Examples:

• Radio Waves
• Microwave
• Satellite

Important Networking Protocols

Protocol	Full Form	Use
HTTP	HyperText Transfer Protocol	Web browsing
HTTPS	HyperText Transfer Protocol Secure	Secure websites
FTP	File Transfer Protocol	File transfer
SMTP	Simple Mail Transfer Protocol	Sending emails
POP3	Post Office Protocol v3	Receiving emails
TCP/IP	Transmission Control Protocol/Internet Protocol	Internet communication

IP Address

An IP Address is a unique address of a device on a network.

Types:

• IPv4 → 32-bit
• IPv6 → 128-bit

Example:

• 192.168.1.1

OSI Model (Important for Exams)

Layer	Function
Application	User interaction
Presentation	Data formatting
Session	Session management
Transport	Reliable delivery
Network	Routing
Data Link	Error detection
Physical	Hardware transmission

Advantages of Computer Network

• Resource sharing
• Fast communication
• Data sharing
• Internet access
• Centralized management

Disadvantages

• Security risks
• Virus attacks
• Network failure issues
• Maintenance cost

Important One-Liner Facts

• Internet is the largest WAN.
• Switch works at Data Link Layer.
• Router works at Network Layer.
• Fiber optic cable has highest speed.
• HTTP uses Port 80.
• HTTPS uses Port 443.