NBC 101 • Unit 515 min read★ Very High Exam Frequency

Network Topologies (Star, Mesh, Ring), OSI Model & Cyber Threats

Q: What is the key difference between a Hub and a Switch in a Star Network?

A Hub is an unintelligent Layer 1 Physical device that broadcasts received data to all connected ports indiscriminately. A Switch is an intelligent Layer 2 Data Link device that reads destination MAC addresses and forwards data packets exclusively to the designated target port. (Examiner Tip: Switches eliminate network collisions and enhance bandwidth efficiency.)

Unit 5: Cyber Security, Emerging Trends & Cloud Computing • Fundamentals of Computer

👨‍🏫 Professor's Mental Model: The Global Postal Delivery System

Computer Network ek international postal service jaisa hai. Jab aap WhatsApp par message bhejte ho, toh data chhote packets me divide hota hai, uspe sender aur receiver ka IP address stamp hota hai, Routers use best raaste se bhejte hain, aur destination par sabhi packets jud kar wapas original message ban jate hain!

1. Network Topologies Architecture

• Star Topology: All nodes connected to a central Hub/Switch. Easy to install, failure of one cable does not affect others, but central switch is single point of failure. • Mesh Topology: Every node connected directly to every other node (Dedicated point-to-point links: n*(n-1)/2 cables). Maximum redundancy and security, highest cabling cost. • Bus Topology: All nodes share a single linear backbone coaxial cable terminated at both ends. Low cost, but cable break stops entire network. • Ring Topology: Each device connected to exactly two neighboring nodes forming a circular loop. Data travels unidirectionally using token passing.

2. Network Types & The 7-Layer OSI Model

• LAN (Local Area Network), MAN (Metropolitan), WAN (Wide Area Network - The Internet). • The 7 Layers of OSI (ISO standard): 7. Application (HTTP, FTP, SMTP, DNS) 6. Presentation (Encryption, Compression, JPEG/ASCII formatting) 5. Session (Session establishment & checkpoints) 4. Transport (End-to-end delivery, TCP/UDP port addressing) 3. Network (Routing & logical IP addressing) 2. Data Link (Framing, error detection, physical MAC addressing) 1. Physical (Raw bit transmission over copper/fiber/radio waves). • Mnemonic: 'All People Seem To Need Data Processing'.

3. Cyber Threats & Defense Mechanisms

• Malware: Virus (attaches to host executables), Worm (self-replicating autonomous network crawler), Trojan Horse (disguised legitimate payload), Ransomware (encrypts storage for ransom). • Cyber Attacks: Phishing (identity spoofing), Denial of Service (DoS / DDoS server flooding), Man-in-the-Middle (MitM). • Defense: Firewalls (packet filtering), Antivirus, Cryptographic Encryption (AES-256, TLS/HTTPS), Multi-Factor Authentication (MFA).

🎯 University Exam Scoring Blueprint

Draw all 4 network topologies (Star, Mesh, Bus, Ring) with clean node diagrams.
Write the mnemonic for 7 OSI layers: 'All People Seem To Need Data Processing' (Application to Physical).
Explain Virus vs Worm (Worms self-replicate without human intervention; Viruses require host file execution).