Web Fundamentals, Networking Protocols, and Web Architecture Brief Notes

Internet & World Wide Web Fundamentals

Internet Overview & Key Milestones

• Internet Definition: A decentralized, global network of interconnected computers communicating via standardized protocols.

• Key Pioneers: Vint Cerf and Bob Kahn ("Fathers of the Internet") invented the TCP/IP protocol in 1974.

• Historical Timeline:

  • 1969: Launch of ARPANET (first operational packet-switching network).

  • 1971: Ray Tomlinson sends the first email.

  • 1983: TCP/IP adopted as standard protocol for ARPANET.

  • 1989–1990: Tim Berners-Lee invents the World Wide Web at CERN.

  • 1993: Mosaic, the first graphical web browser, is released; Web opens to the public.

  • 1998: Google is founded.

  • 2007: iPhone introduces widespread mobile Internet access.

Internet vs World Wide Web (WWW)

• Internet: The global physical and logical network infrastructure connecting devices worldwide using TCP/IP.

• World Wide Web: An application running on top of the Internet that uses HTTP/HTTPS to access interconnected hypertext documents via web browsers.

Domain Name System (DNS) & IP Addressing

Domain Name Structure

• Domain Name: Unique, human-readable address corresponding to a server's IP address.

• Hierarchy:

  • Root: .

  • Top-Level Domain (TLD): Categories or regions (e.g., .com, .org, .edu, .in).

  • Second-Level Domain (SLD): Organization name (e.g., example).

  • Subdomain: Specific service or section (e.g., blog, www).

DNS Resolution Process

1. Request: User inputs domain into browser.

2. Cache Check: Browser/OS checks local DNS cache.

3. Recursive Resolver: Query sent to ISP-managed resolver.

4. Root & TLD Servers: Query directed to Root, then TLD server, then Authoritative DNS server.

5. Authoritative Server: Returns real IP address to browser to establish connection.

IP Addressing Protocols

• IPv4:

  • 32-bit address space represented as four decimal octets (e.g., 192.168.1.10).

  • Yields approximately $4.3 \times 10^9$ addresses; requires NAT due to address exhaustion.

• IPv6:

  • 128-bit address space represented in hexadecimal (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334).

  • Massive address capacity, improved routing, built-in security, no NAT required.

Networking Reference Models

OSI Model vs TCP/IP Model

• OSI Reference Model: Developed by ISO based on work by Charles Bachman (1984). Conceptual 7-layer framework:

  1. Physical (Bits)

  2. Data Link (Frames)

  3. Network (Packets)

  4. Transport (Segments)

  5. Session (Data)

  6. Presentation (Data representation/encryption)

  7. Application (Network processes)

• TCP/IP Suite: 4-layer practical protocol standard (1982): Link Layer, Internet Layer, Transport Layer, Application Layer.

Transport Layer Protocols

• TCP (Transmission Control Protocol): Connection-oriented, error-checked, reliable, ordered delivery. Used for web browsing, email, and file transfers.

• UDP (User Datagram Protocol): Connectionless, lightweight, low overhead, no guaranteed delivery. Used for real-time video/voice streaming (VoIP) and DNS.

Application Layer Protocols

HTTP & HTTPS

• HTTP: Transfers plain text web content over port 80 using requests (GET, POST, PUT, DELETE) and responses.

• HTTPS: Encrypts HTTP traffic using SSL/TLS over port 443 to preserve confidentiality, integrity, and authentication.

File & Command Protocols

• FTP: TCP protocol using Port 21 (control channel) and Port 20 (data channel). Supports Active FTP and Passive FTP modes.

• TFTP: Simple, UDP-based file transfer protocol on Port 69 with no authentication; used for booting diskless workstations or loading firmware.

• Telnet: Unencrypted virtual terminal protocol operating on TCP port 23 for remote device access.

Mail & Network Management Protocols

• SMTP: Push protocol operating on TCP port 25 to send and forward email between Mail Transfer Agents (MTAs).

• POP3 / IMAP: Retrieval protocols; POP3 downloads emails to local devices while IMAP synchronizes emails across server and devices.

• DHCP: Dynamic Host Configuration Protocol automatically leases IP addresses, subnet masks, default gateways, and DNS settings to clients.

• SNMP: Application-layer management protocol utilizing SNMP Managers, Agents, and Management Information Bases (MIB) to monitor device status.

Web Architecture & Technologies

Client-Server Architecture Tiers

• Two-Tier: Client directly connects to server containing business logic and database.

• Three-Tier:

  • Presentation Tier: User Interface (Browser, HTML/CSS/JavaScript).

  • Application Tier: Server-side business logic, APIs, and authentication.

  • Data Tier: Isolated database handling data storage and retrieval.

• Multi-Tier (N-Tier): Enterprise distribution across distinct web, application, and database servers.

Page Types & Development Stacks

• Static Web Pages: Fixed HTML/CSS content stored on server; same for every user.

• Dynamic Web Pages: Content generated server-side using scripting languages (PHP, Node.js) connected to databases.

• Active Web Pages: Highly interactive real-time updating without full reloads using client-side scripting (JavaScript, AJAX, React).

• MERN Stack: Full-stack framework comprising MongoDB (Database), Express.js (Backend framework), React.js (Frontend library), and Node.js (JavaScript runtime).