Computer · Chapter 05

🌐 Internet & Networking

Protocols, IP, DNS, OSI model and network types.

🌐 Connecting the World

The Internet is a global network of interconnected computers. The World Wide Web (WWW) is a service that runs on the Internet — invented by Tim Berners-Lee in 1989 at CERN.

Key protocols:
• HTTP/HTTPS — HyperText Transfer Protocol. Used for web pages. HTTPS = secure (SSL/TLS encrypted).
• FTP — File Transfer Protocol. Transfer files between computers.
• SMTP — Simple Mail Transfer Protocol. Send emails.
• POP3/IMAP — Receive emails. POP3 downloads and deletes from server. IMAP syncs with server.
• TCP/IP — Transmission Control Protocol/Internet Protocol. Foundation of the Internet.
• DNS — Domain Name System. Converts domain names (google.com) to IP addresses.

IP Address — unique address of each device on network. IPv4: 32-bit (e.g., 192.168.1.1). IPv6: 128-bit (e.g., 2001:0db8::1). MAC Address — hardware address of network card (48-bit, unique).

🔌 Network types and topologies

LAN (Local Area Network) — within a building/campus. Fast. Low cost. Office Wi-Fi, school lab.
MAN (Metropolitan Area Network) — city-wide. Cable TV networks.
WAN (Wide Area Network) — across countries. The Internet is the largest WAN.
PAN (Personal Area Network) — Bluetooth devices around a person.
Topologies: Bus (single cable), Star (hub at center, most common), Ring (circle), Mesh (every device connected to every other), Tree (hierarchical), Hybrid.

📧 Internet terms — SSC/CCC exam

URL (Uniform Resource Locator) — web address. https://www.example.com/page
Browser — Chrome, Firefox, Safari, Edge. Renders web pages.
ISP (Internet Service Provider) — Jio, Airtel, BSNL, ACT.
Bandwidth — data transfer rate (Mbps, Gbps).
Modem — modulates/demodulates analog signals for digital data.
Router — routes data packets between networks.
Cookies — small files stored by browser to remember your preferences.
Cache — stored copies of web pages for faster loading.

🎬

How the Internet Works

Animation
INTERNET PROTOCOLS — CLICK EACH TO LEARN 🌐 HTTP/HTTPS Web pages Port 80 / 443 📁 FTP File Transfer Port 20/21 📤 SMTP Send emails Port 25/587 📥 POP3 / IMAP Receive emails Port 110 / 143 NETWORK REQUEST JOURNEY 💻 Your Computer DNS query 📡 Router/ISP IP packets ☁️ INTERNET TCP/IP 🖥️ Web Server 📄 Web Page (HTML) OSI MODEL (7 LAYERS) 7. Application — HTTP, FTP, SMTP (User-facing protocols) 6. Presentation — SSL/TLS encryption, data formatting 5. Session — manages connections between systems 4. Transport — TCP/UDP — ports, error checking 3. Network — IP addressing, routing (routers) 2. Data Link — MAC addresses, switches, frames 1. Physical — cables, Wi-Fi signals, bits over medium CLICK A PROTOCOL ABOVE FOR DETAILS

Every website visit involves DNS lookup, TCP handshake, HTTP request, server response — all in milliseconds.

💻

Network Concepts Explorer

Interactive
IPv432-bit — 192.168.1.1 — 4 billion addresses
IPv6128-bit — 2001:db8::1 — 340 undecillion addresses
Localhost127.0.0.1 — your own computer
Private IP ranges192.168.x.x, 10.x.x.x, 172.16-31.x.x
MAC Address48-bit hardware ID — AA:BB:CC:DD:EE:FF
Practice (CCC/O-Level): What is the difference between TCP and UDP? When is each used?
TCP (Transmission Control Protocol):
• Connection-oriented — establishes connection before data transfer (3-way handshake: SYN, SYN-ACK, ACK)
• Reliable — guarantees delivery, maintains order, retransmits lost packets
• Slower due to overhead
• Used for: HTTP/HTTPS (web), Email (SMTP, IMAP), FTP, SSH

UDP (User Datagram Protocol):
• Connectionless — sends data without establishing connection first
• Unreliable — no guarantee of delivery, no order maintenance
• Much faster — low overhead
• Used for: Video streaming (YouTube), Online gaming, VoIP (WhatsApp calls), DNS queries, Live TV

Analogy:
TCP = Registered post — confirmed delivery, acknowledgment
UDP = Regular post — fast, no delivery confirmation

Why use UDP for video streaming? If a few frames are lost, it is better to skip them and continue than to wait and retransmit (that would cause stuttering). Speed and continuity matters more than perfect delivery.

Port numbers: HTTP uses TCP port 80, DNS uses UDP port 53.
Practice (SSC): What is the difference between a Hub, Switch, and Router?
Hub:
• Operates at Physical Layer (Layer 1)
• Broadcasts data to ALL connected devices
• Dumb device — no intelligence
• Security risk — any connected device can see all traffic
• Rarely used today — replaced by switches

Switch:
• Operates at Data Link Layer (Layer 2)
• Sends data only to the specific destination device (using MAC address table)
• Smart — learns which device is on which port
• Efficient — reduces unnecessary traffic
• Used in LANs — connects computers in an office

Router:
• Operates at Network Layer (Layer 3)
• Connects different networks — routes data between them
• Uses IP addresses to make routing decisions
• Your home Wi-Fi device is a router (+ switch + modem combined)
• Routes your home network to the internet via ISP

Summary: Hub = flood everyone, Switch = smart delivery in LAN, Router = connects different networks.
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