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1. Computer Networks - Unit One Lecture Notes Summary

2. What is a Network? • A network is a set of devices (nodes) connected by communication links. • Examples: Computers, printers, smartphones. • Networks can use copper wire, fiber optics, microwaves, infrared, or satellites. • Internet is the largest network of networks.

3. Uses of Computer Networks Business Applications: • Information sharing, client-server model, email, VoIP, desktop sharing, e-commerce. Home Applications: • Peer-to-peer, communication, e-commerce, gaming. Mobile Users: • Texting, smartphones, GPS, m-commerce, NFC. Social Issues: • Privacy, censorship, phishing, botnet attacks.

4. Data Communication Characteristics • Delivery – Correct destination. • Accuracy – Data integrity. • Timeliness – Real-time transmission. • Jitter – Variation in packet arrival time.

5. Data Communication Components 1. Message – Data (text, numbers, images, audio, video). 2. Sender – Device sending data. 3. Receiver – Device receiving data. 4. Transmission Medium – Physical path (wire, fiber, radio). 5. Protocol – Rules for communication.

6. Data Flow Modes • Simplex – One-way (e.g., keyboard to monitor). • Half-Duplex – Alternating send/receive (e.g., walkie-talkies). • Full-Duplex – Simultaneous communication (e.g., telephones).

7. Network Criteria • Performance – Transit and response time. • Reliability – Failure frequency, recovery time, robustness. • Security – Protect data, recovery policies.

8. Network Topologies • Mesh – Each node connected to every other node. • Star – Central hub connects all devices. • Bus – All devices connected to single backbone. • Ring – Devices form a closed loop. • Hybrid – Combination of topologies.

9. Types of Networks • LAN – Local area, small scale, high speed. • MAN – Metropolitan area, covers city. • WAN – Wide area, country/worldwide. • WLAN – Wireless LAN. • PAN – Personal area. • SAN – Storage area.

10. Transmission Media Guided Media: • Twisted Pair (UTP, STP), Coaxial Cable, Fiber Optics. Unguided Media: • Radio Waves, Microwaves, Infrared.

11. Switching Techniques • Circuit Switching – Dedicated path. • Datagram Switching – Connectionless, packets independent. • Virtual Circuit Switching – Hybrid of circuit and datagram.

12. OSI Model 1. Physical – Transmission of bits (cables, hubs). 2. Data Link – Frames, MAC addresses (switches). 3. Network – Packets, IP addressing (routers). 4. Transport – Segments, reliability (TCP/UDP). 5. Session – Connection management. 6. Presentation – Translation, compression, encryption. 7. Application – End-user protocols (HTTP, SMTP, FTP).

13. TCP/IP Model • Application – HTTP, FTP, SMTP, DNS. • Transport – TCP (reliable), UDP (fast, connectionless). • Internet – IP, ICMP, routing packets. • Network Access – Physical + Data link layer.

14. The Internet • Originated from ARPANET in 1969. • Uses TCP/IP protocols. • Composed of ISPs: international, national, regional, local. • Supports business, education, communication, entertainment.