Internet, Web, Protocols, HTTP/HTTPS, URLs, Web Browsers, Search Engines, E-Commerce

1. Introduction to the Internet and Web

1.1 Definition and Evolution

• Internet: A global network of interconnected computers and devices using standardized protocols (TCP/IP) to exchange data.
• World Wide Web (WWW): A system of interlinked hypertext documents accessed via the Internet, introduced by Tim Berners-Lee in 1989.
• Key Milestones:
  • 1960s: ARPANET (precursor to the Internet).
  • 1980s: TCP/IP protocol suite adopted.
  • 1990s: WWW popularized with browsers like Netscape and Internet Explorer.

1.2 Internet vs. World Wide Web

1.3 How the Internet Works

The Internet relies on packets, routers, and protocols:

1. Data Packets: Information broken into small chunks for transmission.
2. Routers: Devices that direct packets to their destination using IP addresses.
3. TCP/IP Protocol Suite: Ensures reliable data delivery.

graph TD
    A["User Device"] -->|"HTTP Request"| B["Router 1"]
    B -->|"TCP/IP"| C["ISP Network"]
    C -->|"TCP/IP"| D["Router 2"]
    D -->|"TCP/IP"| E["Web Server"]
    E -->|"HTTP Response"| D
    D -->|"TCP/IP"| C
    C -->|"TCP/IP"| B
    B -->|"HTTP Response"| A

Caption: Packet routing from a user to a web server via ISPs.

2. TCP/IP Protocol Suite

2.1 Layers of TCP/IP

The TCP/IP model has 4 layers (simplified from the OSI 7-layer model):

TCP/IP vs. OSI model comparison (Image: Ardika6879, CC BY-SA 4.0, via Wikimedia Commons)

2.2 Key Protocols

• TCP (Transmission Control Protocol): Ensures reliable, ordered data delivery (used by HTTP).
• UDP (User Datagram Protocol): Faster but unreliable (used for video streaming, VoIP).
• IP (Internet Protocol): Assigns IP addresses (e.g., 192.168.1.1) and routes packets.
• DNS (Domain Name System): Converts domain names (e.g., daraz.com.np) to IP addresses.

Worked Example: DNS Lookup When you type esewa.com.np in a browser:

1. Your device checks the local DNS cache.
2. If not found, it queries the root DNS server.
3. The request follows the DNS hierarchy (.np → esewa.com.np servers).
4. The IP address (e.g., 103.12.219.10) is returned, and the browser connects.

3. HTTP and HTTPS

3.1 HTTP (Hypertext Transfer Protocol)

• Stateless protocol: Each request is independent (no memory of past requests).
• Methods:
  • GET: Retrieve data (e.g., loading a webpage).
  • POST: Send data (e.g., submitting a form).
  • PUT, DELETE, PATCH: Modify server data.
• HTTP Response Codes:
  • 200 OK: Request succeeded.
  • 404 Not Found: Page does not exist.
  • 500 Internal Server Error: Server failure.

3.2 HTTPS (HTTP Secure)

• Encryption: Uses SSL/TLS to encrypt data (prevents eavesdropping).
• How it works:
  1. Client and server exchange public/private keys.
  2. A secure session is established.
  3. All data is encrypted using symmetric encryption (faster).
• Why HTTPS?
  • Protects login credentials (e.g., eSewa, Khalti).
  • Prevents man-in-the-middle attacks.
  • Boosts SEO rankings (Google prioritizes HTTPS sites).

Real-World Example: Khalti Payments When you transfer money via Khalti:

1. Your browser connects to khalti.com via HTTPS.
2. The SSL certificate (issued by a trusted CA like Let’s Encrypt) verifies the site’s identity.
3. Your card details are encrypted and sent securely to Khalti’s servers.

4. Web Browsers and Search Engines

4.1 Web Browsers

• Function: Interpret HTML/CSS/JS and render web pages.
• Popular Browsers:
  • Chrome (Google), Firefox (Mozilla), Edge (Microsoft), Safari (Apple).
• Browser Components:
  • Rendering Engine (Blink in Chrome, Gecko in Firefox).
  • JavaScript Engine (V8 in Chrome).
  • DOM Tree (Document Object Model for dynamic content).

4.2 Search Engines

• How They Work:
  1. Crawling: Bots (e.g., Googlebot) scan the web for new content.
  2. Indexing: Store data in a searchable database.
  3. Ranking: Algorithms (e.g., PageRank) determine relevance.
• Key Search Engines:
  • Google (90% market share), Bing (Microsoft), DuckDuckGo (privacy-focused).

Worked Example: Google Search When you search for "best laptops in Nepal":

1. Google’s crawler indexes pages like daraz.com.np or nepalilaptop.com.
2. The algorithm ranks results based on keywords, backlinks, and user location.
3. You see sponsored ads (paid) and organic results (free).

5. E-Commerce and Web Applications

5.1 E-Commerce Models

5.2 How Daraz Works (B2C Example)

1. User Request: You browse daraz.com.np (HTTPS).
2. Server Processing:
   • The request goes to Daraz’s load balancer.
   • A web server (e.g., Apache/Nginx) handles the request.
   • A database (MySQL) fetches product details.
3. Payment Gateway: Khalti/eSewa integrates via API calls.
4. Order Fulfillment: Inventory system updates stock; logistics (e.g., Ncell Parcel) ships the product.

sequenceDiagram
    User->>Daraz: Requests product page (HTTP)
    Daraz->>Database: Fetches product data
    Database-->>Daraz: Returns data
    Daraz-->>User: Displays page (HTML/CSS)
    User->>Daraz: Clicks "Buy Now" (POST)
    Daraz->>Payment Gateway: Redirects to Khalti
    Khalti-->>Daraz: Confirms payment (HTTPS)
    Daraz->>Logistics: Updates order status

6. Web Security

6.1 Common Threats

6.2 Security Measures

• SSL/TLS Certificates: Encrypts data (e.g., https://esewa.com.np).
• Firewalls: Block unauthorized access.
• Two-Factor Authentication (2FA): Adds an extra verification step (e.g., SMS/OTP).

Real-World Example: Ncell’s Security When you log in to ncell.com.np:

1. The site uses HTTPS to encrypt your credentials.
2. If you enable 2FA, a one-time password (OTP) is sent to your phone.
3. Even if a hacker steals your password, they can’t log in without the OTP.

7. Emerging Web Technologies

7.1 Progressive Web Apps (PWAs)

• Definition: Web apps that work offline and feel like native apps.
• Example: Twitter Lite, PWA version of eSewa.
• Advantages:
  • No app store installation needed.
  • Works on slow networks.

7.2 Web 3.0 (Semantic Web)

• Goal: Machines can understand web content (not just display it).
• Technologies:
  • Blockchain (decentralized apps like Uniswap).
  • AI-driven search (e.g., Google’s BERT).

In the Real World

1. eSewa (Nepal)

   • Uses HTTPS for secure transactions.
   • Relies on APIs to integrate with banks (NMB, Global IME) and telecom (Ncell).
   • Worked Example: When you pay a bill via eSewa, the app sends an encrypted POST request to the bank’s server, which verifies your credentials and deducts the amount.

2. Daraz (Nepal)

   • Uses load balancers to distribute traffic across servers during sales (e.g., Daraz Great Republic Day Sale).
   • Database: MySQL/PostgreSQL stores product inventory, user orders, and reviews.
   • Logistics: Integrates with Ncell Parcel via APIs for real-time tracking.

3. Google (Global)

   • Search Algorithm: Uses PageRank (backlinks) and RankBrain (AI) to rank results.
   • HTTPS: All Google services (Gmail, YouTube) use encryption.
   • CDN: Uses Cloudflare to deliver content faster worldwide.

Exam Tip

What to Expect in TU/PU Exams

1. Short Questions (2-5 marks):

   • Define HTTP vs. HTTPS, TCP vs. UDP, DNS.
   • Explain the 4 layers of TCP/IP.
   • Differentiate B2C vs. B2B e-commerce.

2. Long Questions (10-15 marks):

   • Trace the flow of a web request (user → ISP → server → response).
   • Compare OSI and TCP/IP models in a table.
   • Explain how SSL/TLS works with a diagram.
   • Case Study: "How does Khalti ensure secure payments?" (Cover encryption, APIs, and fraud detection.)

3. Practical Questions:

   • Debugging: "Why does a website show ERR_CONNECTION_REFUSED?"
     • Answer: Firewall blocking port 80/443, server down, or incorrect URL.
   • Configuration: "How would you secure a web server?"
     • Answer: Enable HTTPS, use firewalls, update software, implement 2FA.

Common Mistakes to Avoid

• Mixing OSI and TCP/IP layers: Remember TCP/IP has 4 layers, not 7.
• Ignoring HTTPS: Always mention encryption for security questions.
• Vague answers: Use real examples (e.g., Daraz, eSewa) instead of generic terms.
• Forgetting diagrams: Draw HTTP request-response cycles or TCP/IP layer tables for full marks.

Marks Boosters

• Use bullet points for protocols (TCP, UDP, HTTP methods).
• Relate to Nepal: Mention Ncell, eSewa, Daraz in case studies.
• Include real numbers: E.g., "Google processes 40,000 search queries per second."

Final Note: The Internet and Web are interconnected systems—master the protocols (TCP/IP, HTTP), security (HTTPS, SSL), and real-world applications (e-commerce, search engines). Practice tracing requests and comparing models to excel in exams.