Internet, Networking & Protocols

Internet एक global public network of interconnected networks है जो TCP/IP protocol का उपयोग करता है।

Key Characteristics:

• Global coverage
• Public access
• No single owner
• Uses TCP/IP protocols
• Connects billions of devices

Major Internet Services:

• World Wide Web (WWW)
• E-mail
• FTP (File Transfer Protocol)
• VoIP (Voice over IP)
• Video conferencing
• Instant messaging
• Cloud services

• Intranet — इंट्रानेट: Internet technologies पर आधारित private organisational network। Only authorised members (employees, faculty) can access। Example: University internal portal.
• Extranet — एक्स्ट्रानेट: Private network जिसमें selected outsiders (vendors, collaborators) को भी authorised access दिया जाता है। Example: University portal accessed by authorised vendors.

• Internet: Physical और logical network infrastructure connecting devices worldwide. (Infrastructure)
• World Wide Web (WWW): Internet पर उपलब्ध interlinked web pages और resources की service। (Service running on the infrastructure)

Exam Trap: Internet और WWW समान concepts नहीं हैं। WWW, Internet की services में से एक है।

Computer Network: Interconnected computers का set जो resources share और communicate करते हैं।

Key Components:

• Nodes: Devices connected to the network (computers, printers, routers)
• Links: Connections between nodes (wired or wireless)
• Protocols: Rules for communication (TCP/IP, HTTP, FTP)
• Bandwidth: Data carrying capacity of the network
• Latency: Delay in data transmission

• PAN (Personal Area Network): एक व्यक्ति के आसपास छोटी range (Bluetooth, smartphone-earbuds)
• LAN (Local Area Network): छोटे geographical area (office, building, university department)
• MAN (Metropolitan Area Network): City या metropolitan area तक
• WAN (Wide Area Network): Large geographical area (country, world) — Internet is a WAN
• WLAN (Wireless LAN): Wireless version of LAN (Wi-Fi)

• Bus Topology: All devices connected to a single central cable (bus). Simple but single point of failure.
• Star Topology: All devices connected to a central hub/switch. Most common in LANs.
• Ring Topology: Devices connected in a circular loop. Data travels in one direction.
• Mesh Topology: Every device connected to every other device. Most reliable but expensive.
• Tree Topology: Hierarchical structure combining bus and star topologies.

Exam Point: Star topology is the most widely used in modern LANs.

• Hub: Broadcasts data to all devices in the network. (Layer 1 - Physical layer)
• Switch: Connects devices within a network; forwards data only to the intended device. (Layer 2 - Data Link layer)
• Router: Connects different networks; routes data between networks. (Layer 3 - Network layer)
• Modem: Converts digital to analog (and vice versa) for transmission over telephone/cable lines.
• Bridge: Connects two LAN segments.
• Gateway: Connects networks with different protocols.
• Access Point (AP): Allows wireless devices to connect to a wired network (Wi-Fi).

OSI (Open Systems Interconnection) Model: A reference model for understanding how data travels across a network.

7 Layers (Bottom to Top):

• 7. Application: User interface (HTTP, FTP, SMTP, DNS)
• 6. Presentation: Data formatting, encryption, compression
• 5. Session: Connection establishment, management, termination
• 4. Transport: End-to-end communication, error control (TCP, UDP)
• 3. Network: Routing, addressing (IP)
• 2. Data Link: Framing, error detection (MAC addresses)
• 1. Physical: Physical transmission of raw bits

Memory Formula: All People Seem To Need Data Processing (Application, Presentation, Session, Transport, Network, Data Link, Physical)

TCP/IP Model: The actual protocol suite used by the Internet.

4 Layers:

• Application: HTTP, FTP, SMTP, DNS, etc.
• Transport: TCP, UDP
• Internet: IP (addressing and routing)
• Network Access/Link: Physical and data link layers

OSI vs TCP/IP:

• OSI has 7 layers; TCP/IP has 4 layers
• OSI is conceptual; TCP/IP is practical/implemented
• TCP/IP is the actual model used on the Internet

IP Address: Unique identifier for each device on a network.

IPv4: 32-bit address, 4 octets (e.g., 192.168.1.1). About 4.3 billion addresses.

• Class A: 0.0.0.0 to 127.255.255.255 (Large networks)
• Class B: 128.0.0.0 to 191.255.255.255 (Medium networks)
• Class C: 192.0.0.0 to 223.255.255.255 (Small networks)
• Class D: 224.0.0.0 to 239.255.255.255 (Multicast)
• Class E: 240.0.0.0 to 255.255.255.255 (Reserved)

IPv6: 128-bit address, 8 groups of 4 hexadecimal digits (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334). Developed to solve IPv4 address exhaustion.

Public vs Private IP:

• Public: Routable on the Internet
• Private: Used within local networks (192.168.x.x, 10.x.x.x, 172.16.x.x to 172.31.x.x)

Protocol: A set of rules that govern communication between devices on a network.

Major Protocol Categories:

• Application Layer: HTTP, HTTPS, FTP, SMTP, POP3, IMAP, DNS, DHCP
• Transport Layer: TCP, UDP
• Network Layer: IP

• HTTP (Hypertext Transfer Protocol): Transfers web pages from server to browser. Port 80. No encryption (not secure).
• HTTPS (Hypertext Transfer Protocol Secure): Encrypted version of HTTP using SSL/TLS. Port 443. Secure.

Exam Trap: HTTPS adds encryption; it does not guarantee that every website is trustworthy.

• FTP (File Transfer Protocol): Transfers files between computers. Ports 20 (data), 21 (control). No encryption.
• SFTP (Secure File Transfer Protocol): Secure version of FTP using SSH. Encrypted file transfer.

Exam Point: FTP is used for file transfer; SFTP is the secure version.

• SMTP (Simple Mail Transfer Protocol): Sending e-mail from client to server and between servers. Port 25.
• POP3 (Post Office Protocol Version 3): Retrieving e-mail from server to client. Downloads and removes from server (usually). Port 110.
• IMAP (Internet Message Access Protocol): Synchronising and managing e-mail on the server. Keeps messages on server; syncs across devices. Port 143.

POP3 vs IMAP: POP3 downloads to one device; IMAP syncs across multiple devices.

DNS translates human-readable domain names (e.g., google.com) into IP addresses (e.g., 142.250.185.46).

Key Points:

• Port 53
• Distributed hierarchical system
• Cache stores translations for faster access
• Essential for using domain names instead of numeric IPs

DHCP automatically assigns IP addresses to devices on a network.

Key Points:

• Reduces manual configuration
• Manages IP address pool
• Assigns temporary/leased IP addresses
• Essential for large networks

Exam Trap: UDP का fast होना यह नहीं दर्शाता कि वह TCP से अधिक reliable है।

• Trap 1: Internet and WWW are not synonymous.
• Trap 2: Router = connects devices within a network → ❌ Router connects networks; Switch connects devices.
• Trap 3: SMTP = receiving e-mail → ❌ SMTP sends e-mail; POP3/IMAP retrieve/access it.
• Trap 4: DNS = assigns IP addresses → ❌ DNS translates domain names to IP addresses; DHCP assigns IP addresses.
• Trap 5: HTTP = secure → ❌ HTTP is not secure; HTTPS is secure.
• Trap 6: UDP = more reliable than TCP → ❌ TCP is more reliable; UDP is faster.
• Trap 7: LAN = large network → ❌ LAN is local; WAN is large.
• Trap 8: POP3 = syncs across devices → ❌ IMAP syncs across devices; POP3 downloads to one device.

A university portal accessible only to employees and registered faculty members is an example of:

• A. Internet
• B. Intranet
• C. Extranet
• D. World Wide Web

Explanation: Restricted organisational network for internal members.

Which protocol is used to send e-mail?

• A. POP3
• B. IMAP
• C. SMTP
• D. FTP

Explanation: SMTP is used for sending e-mail. POP3 and IMAP are for receiving/accessing e-mail.

Which protocol translates domain names to IP addresses?

• A. DHCP
• B. DNS
• C. HTTP
• D. FTP

Explanation: DNS translates domain names to IP addresses. DHCP assigns IP addresses automatically.

Which network topology is most commonly used in modern LANs?

• A. Bus
• B. Ring
• C. Star
• D. Mesh

Explanation: Star topology is the most widely used in modern LANs, with all devices connected to a central switch.

Which device connects different networks and routes data between them?

• A. Hub
• B. Switch
• C. Router
• D. Modem

Explanation: A router connects different networks and routes data between them. A switch connects devices within a network.

Which layer of the OSI model is responsible for routing and addressing?

• A. Data Link
• B. Transport
• C. Network
• D. Application

Explanation: The Network layer (Layer 3) handles routing and addressing (IP).

What is the default port for HTTPS?

• A. 80
• B. 443
• C. 21
• D. 25

Explanation: HTTPS uses port 443; HTTP uses port 80; FTP uses port 21; SMTP uses port 25.

OSI Layers (Memory): All People Seem To Need Data Processing (Application, Presentation, Session, Transport, Network, Data Link, Physical)

Exam Formula:

UGC NET में Internet, Networking & Protocols के questions protocol functions, port numbers, network types, devices और OSI model पर based होते हैं।