Understand the difference between the internet and the world wide web

Learning Objective

Students will be able to:

• Distinguish clearly between the Internet and the World‑Wide Web (WWW).
• Explain the architecture of the Internet (TCP/IP model) and the role of each layer.
• Describe how a web page is located, retrieved and displayed.
• Identify key networking concepts required by Cambridge IGCSE 0478 – Topic 5 (e.g., IP addressing, DNS, error‑detection, encryption, cyber‑security).
• Recognise other services that use the Internet but are not part of the Web.

1. Key Definitions

2. Internet Architecture – The TCP/IP Model

The Internet is described by a four‑layer model. Each layer adds its own header (and possibly a trailer) to the data packet before passing it to the layer below.

1. Link layer – Physical media and local‑area networking (Ethernet, Wi‑Fi, fibre). Handles MAC addresses and frames.
2. Internet layer – Routing of packets between networks using the Internet Protocol (IP). Adds the IP header (source & destination IP addresses, TTL, etc.).
3. Transport layer – End‑to‑end data transfer. TCP provides a reliable connection (hand‑shake, sequencing, acknowledgement, retransmission). UDP provides a fast, connection‑less service (used for streaming, gaming).
4. Application layer – Protocols that users interact with (HTTP/HTTPS, FTP, SMTP, DNS, POP3/IMAP, etc.). Adds the application‑layer header (e.g., HTTP request line, status code).

3. Data Transmission Essentials

• Data‑storage units: 1 bit, 1 byte = 8 bits, 1 KiB = 1024 bytes, 1 MiB = 1024 KiB, etc.
• Data compression:
  • Lossless – e.g., Run‑Length Encoding (RLE), Huffman coding.
  • Lossy – e.g., JPEG for images, MP3 for audio.
• Error‑detection methods:
  • Parity bit (simple even/odd check).
  • Checksum (sum of data bytes, used in TCP/UDP).
  • CRC (Cyclic Redundancy Check – used in Ethernet frames).
  • ARQ (Automatic Repeat reQuest) – retransmission on error detection.
• Encryption basics:
  • Symmetric – same key for encryption and decryption (e.g., AES).
  • Asymmetric – public‑key/private‑key pair (e.g., RSA) used for secure key exchange and digital signatures.

4. Network Hardware & Addressing

IP Addressing

• IPv4 – 32‑bit address written as four decimal octets (e.g., 192.168.0.1). Supports ≈4.3 billion addresses.
• IPv6 – 128‑bit address written in hexadecimal groups (e.g., 2001:0db8:85a3::8a2e:0370:7334). Provides a vastly larger address space.
• Static IP – Manually assigned; does not change.
• Dynamic IP – Assigned automatically by DHCP; may change each time the device connects.
• Subnetting (basic) – Divides an IP network into smaller logical networks using a subnet mask (e.g., 255.255.255.0).

5. The Domain Name System (DNS) and URL Anatomy

DNS Lookup Process (simplified flow)

1. Browser checks its cache for the domain‑name‑to‑IP mapping.
2. If not cached, it queries the local DNS resolver (usually provided by the ISP).
3. The resolver contacts a root server, then the appropriate TLD server, and finally the authoritative name server for the domain.
4. The IP address is returned to the browser.

URL (Uniform Resource Locator) Structure

6. HTTP vs HTTPS – Request / Response Model

• HTTP – Port 80; data sent in clear text.
• HTTPS – Port 443; uses TLS/SSL encryption to provide confidentiality and integrity.
• Typical request/response cycle:
  1. Client sends a request line (e.g., GET /index.html HTTP/1.1), request headers and optionally a message body.
  2. Server returns a status line (e.g., HTTP/1.1 200 OK), response headers and the message body (HTML, CSS, etc.).
• Common status codes: 200 OK, 301 Moved Permanently, 403 Forbidden, 404 Not Found, 500 Internal Server Error.

7. Web Browser Functions (Cambridge syllabus wording)

• Enter a URL in the address bar to locate a web page.
• Retrieve and render HTML, CSS and JavaScript to display the page.
• Bookmarks – Save favourite pages for quick access.
• History – List of previously visited pages.
• Tabs – Open multiple pages in a single window.
• Cookies – Small data files; session cookies are deleted when the browser closes, persistent cookies remain until they expire or are deleted.
• Manage security settings (e.g., enable/disable JavaScript, block pop‑ups, control cookie permissions).

8. How a Web Page is Located, Retrieved and Displayed

1. Student types a URL and presses Enter.
2. Browser checks its cache; if the page is not cached, a DNS lookup is performed (see Section 5).
3. Using the obtained IP address, the browser establishes a TCP connection (port 80 for HTTP or 443 for HTTPS).
4. Browser sends an HTTP/HTTPS request to the web server.
5. Server processes the request and returns an HTTP response containing:
   • Status code (e.g., 200 OK).
   • Headers (e.g., Content‑Type, Set‑Cookie).
   • Message body – the HTML document.
6. Browser parses the HTML, automatically requests any linked resources (CSS, JavaScript, images, video).
7. CSS is applied, JavaScript is executed, and the final page is rendered on the screen.

9. Comparison: Internet vs. World‑Wide Web

10. Common Misconceptions

• “The Internet and the Web are the same thing.” – The Internet is the underlying infrastructure; the Web is a service that runs on top of it.
• “All Internet traffic is web traffic.” – Email (SMTP), file transfer (FTP), video calls (VoIP), online gaming, remote access, etc., use the Internet without involving the Web.

11. Practical Uses of the Internet (Beyond the Web)

• Email – SMTP for sending; POP3/IMAP for receiving.
• File sharing – FTP, SFTP, peer‑to‑peer protocols (e.g., BitTorrent).
• Online gaming – Custom protocols, often UDP for low latency.
• Voice over IP (VoIP) – SIP/RTP used by Skype, Zoom, etc.
• Remote access – SSH, Remote Desktop Protocol (RDP), VNC.

12. Cyber‑Security Essentials (Cambridge syllabus)

• Threats:
  • Malware (viruses, worms, ransomware).
  • Phishing and social engineering.
  • Denial‑of‑Service (DoS/DDoS) attacks.
  • Unauthorised access (hacking, password cracking).
• Mitigations:
  • Firewalls – filter incoming/outgoing traffic.
  • Encryption – TLS for web traffic, VPNs for secure remote connections.
  • Authentication – passwords, two‑factor authentication, biometrics.
  • Regular updates & anti‑virus software.
• Legal & ethical issues – copyright, privacy, data protection (e.g., GDPR).

13. Digital Currency & Blockchain (Brief Overview)

• Digital currency – Electronic money that exists only in digital form (e.g., Bitcoin, Ethereum).
• Blockchain – Decentralised, tamper‑evident ledger that records transactions in linked blocks using cryptographic hash functions.
• Relevance to the Internet – Transactions are carried out over the Internet using peer‑to‑peer protocols; security relies on encryption and hashing.

14. Automated Systems, Robotics and Artificial Intelligence

Advantages: increased efficiency, ability to work in hazardous environments, 24 h operation.
Disadvantages: high initial cost, loss of some jobs, ethical concerns.

15. Suggested Diagram (for classroom use)

Summary

The Internet is the worldwide network that provides the underlying connectivity for many services. The World‑Wide Web is one such service, built on top of the Internet and using HTTP/HTTPS to deliver hypertext documents. Understanding the TCP/IP model, IP addressing, DNS, URL structure, the request‑response cycle, and the role of browsers equips students to answer exam questions confidently. In addition, knowledge of error‑detection, encryption, cyber‑security, digital currency, and emerging technologies such as robotics and AI gives a broader context that aligns with the full Cambridge IGCSE 0478 syllabus.