Computer Networks & Security - Complete Guide
Last Updated: August 19, 2026 | Marks Weightage: ~12 Marks | BPSC CS Teacher
Master Computer Networks and Security with this comprehensive guide for the BPSC Computer Science Teacher exam.
1. Evolution of Networks
- ARPANET: First packet-switching network (1960s)
- NSFNET: National Science Foundation Network
- Internet: Global network of networks
2. OSI Model (7 Layers)
User interface (HTTP, FTP)
Data formatting, encryption
Session management
End-to-end communication (TCP, UDP)
Routing (IP)
Frame transmission (MAC, LLC)
Bits transmission (Cables, signals)
3. TCP/IP Model (4 Layers)
- Application: HTTP, FTP, SMTP, DNS
- Transport: TCP, UDP
- Internet: IP, ICMP, ARP
- Network Access: Ethernet, Wi-Fi
4. Transmission Media
🔌 Guided (Wired)
- Twisted Pair: Ethernet cables
- Co-axial: Cable TV
- Fiber Optic: High-speed internet
📡 Unguided (Wireless)
- Radio: Wi-Fi, Bluetooth
- Microwave: Satellite
- Infrared: Remote controls
5. Network Devices
🔄 Hub
Broadcasts data to all ports
🔄 Switch
Intelligent device, sends data to specific port
🔄 Router
Connects networks, routes data
🔄 Bridge
Connects two LAN segments
🔄 Gateway
Connects different network types
🔄 Modem
Modulates/demodulates signals
6. Network Topologies
⭐ Star
All devices connect to central hub
🚌 Bus
All devices share a single cable
🔗 Ring
Devices form a circle
🕸️ Mesh
Every device connects to every other
🌳 Tree
Hierarchical structure
7. Types of Networks
- PAN: Personal Area Network (Bluetooth)
- LAN: Local Area Network (Home/Office)
- MAN: Metropolitan Area Network (City)
- WAN: Wide Area Network (Internet)
8. Protocols
🌐 Application Layer
- HTTP/HTTPS: Web browsing
- FTP: File transfer
- SMTP: Email sending
- POP3/IMAP: Email receiving
- DNS: Domain name resolution
🌐 Transport & Network
- TCP: Reliable, connection-oriented
- UDP: Fast, connectionless
- IP: Addressing and routing
- DHCP: Dynamic IP assignment
- VoIP: Voice over IP
9. Wireless & Mobile
- GSM: 2G digital mobile network
- GPRS: 2.5G data service
- 3G: Mobile broadband
- 4G: High-speed mobile internet
- 5G: Ultra-fast, low latency
10. Security Threats
⚠️ Malware
- Virus: Self-replicating, attaches to files
- Worm: Self-replicating, spreads via network
- Trojan: Disguised as legitimate software
- Ransomware: Encrypts files, demands ransom
⚠️ Attacks
- Phishing: Fake emails for credentials
- DDoS: Overwhelming a server
- Man-in-the-Middle: Intercepting communication
- SQL Injection: Attacking databases
11. Security Measures
🛡️ Defenses
- Firewall: Blocks unauthorized access
- Encryption: Converts data to unreadable format
- Digital Signature: Verifies authenticity
- VPN: Secure, encrypted connection
🛡️ Intrusion Systems
- IDS: Intrusion Detection System (Monitors)
- IPS: Intrusion Prevention System (Blocks)
12. Cyber Laws
- Indian IT Act 2000: Legal framework for cyber security
- Digital Privacy: Data protection rights
- Cyber Crimes: Hacking, identity theft, cyber fraud
13. Frequently Asked Questions
❓ What is the difference between OSI and TCP/IP?
OSI has 7 layers, TCP/IP has 4 layers. TCP/IP is more practical.
❓ What is the difference between Hub and Switch?
Hub broadcasts data to all ports; Switch sends data to specific ports.
❓ What is the difference between TCP and UDP?
TCP is reliable and connection-oriented; UDP is fast and connectionless.
❓ What is a Firewall?
A network security device that monitors and controls incoming/outgoing traffic.