5.1.5 | THE INTERNET

Topics from the Cambridge IGCSE (9-1) Computer Science 0984 syllabus 2023 - 2025

OBJECTIVES
5.1.5 Describe how web pages are located, retrieved and displayed on a device when a user enters a URL
​Including the role of:
– the web browser
– IP addresses
– domain name server (DNS)
– web server
– HTML

ALSO IN THIS TOPIC
 5.1.1 - 5.1.3 THE INTERNET AND THE WWW
5.1.4 WEB BROWSERS
 YOU ARE HERE | 5.1.5 WEB PROTOCOLS
5.1.6 COOKIES AND SESSIONS
5.2.1 - 5.2.2 DIGITAL CURRENCY
 5.3.1 CYBER SECURITY
5.3.2 KEEPING DATA SAFE
TOPIC 5 REVISION CARDS
TOPIC 5 KEY TERMINOLOGY (CIE)
TOPIC 5 ANSWERS
TOPIC 5 TEACHER RESOURCES

Remember that the World Wide Web and the Internet are two different things. The world wide Web is the protocols, language and webpages we access, whereas the internet is the network that provides a medium for the transfer of data.

SECTION 1 | THE WEB BROWSER

A web browser is the application software we use to view webpages. Web browsers provide a front-end with user friendly features such as scroll bars, refresh and navigation buttons and work back-end to send and receive page requests along with interpreting the HTML that webpage are predominantly written in. Google Chrome and Microsoft Edge are examples of web-browser software. When you type a web address, normally in the bar at the top of the browse you are using the URL.

A URL or Uniform Resource Locator is the address of a webpage, the URL for the homepage of this website is www.computersciencecafe.com. The structure of a url can be broken up into 5 main parts, looking at the url of this page the parts would be:

PART 1 - PROTOCOL: https: - This refers to the protocol used the main two protocols are HTTP and HTTPS
PART 2 - DOMAIN NAME: computersciencecafe.com - This could be further divided into TLD (Top Level Domain) and SLD (Second Level Domain)
PART 3 - PATH OR SUB-DIRECTORY: /gcse/theinternet - This refers to where there page requested is saved
PART 4 - QUERY: ? Used to provided dynamic webpages with custom features for the user.
PART 5: PARAMETERS - Parameters show further breakdown of the query returned

Check out doepud and click on Anatomy of a URL for more information on URLs.

SECTION 2 | IP ADDRESSES

When connected to the internet you will have two IP addresses,  a public IP address and a private IP address. Your internet service provider will issue you with a public IP address and your home/company router will issue you with a private IP address.

Many IP addresses are classed as Version 4 or V4, these are 32 bit (4 x 1 byte)IP addresses that you will see split into 4 sections, each representing a denery value of binary, for example:

192.16.254.1
or in binary:  11000000.00010000.11111110.00000001

With IP V4 being a 32 bit IP address this means that there are only 4294967296 possible unique representations, although part of this problem is solved in IP addressing protocols there was still a need to expand this value so IP V6 is now in use which uses 48 bit (6 x 1 byte) addresses.

SECTION 3 | DOMAIN NAME SEYSTEM

The Domain Name System (DNS) essentially functions as the internet's phone book, translating user-friendly domain names (like www.example.com) into IP addresses that computers use to identify each other on the network. When you type a website address into your browser, the DNS helps your internet-connected device find the website’s IP address. This system is hierarchical and decentralized, meaning the data is distributed across many servers globally, ensuring a robust and resilient network. Various DNS record types, such as Address Records (A) and Canonical Name Records (CNAME), help in mapping different aspects of domain services, ensuring that internet navigation is smooth and efficient.

DNS not only facilitates user access to websites but also plays a vital role in email delivery, network service access, and more, by translating domain names to relevant IP addresses. It uses caching to speed up the domain name resolution process, storing previously searched IP addresses for a specified duration to minimise lookup times for subsequent requests. Furthermore, DNS contributes to internet security through DNS Security Extensions, which authenticate DNS responses, protecting users from malicious activities like DNS spoofing. DNS is pivotal in ensuring that internet users can access resources efficiently, securely, and reliably by seamlessly translating human-readable domain names into machine-recognizable IP addresses.

SECTION 4 | WEB SERVER

A Web Server is a fundamental technology that plays a pivotal role in the functioning of the World Wide Web, acting as a bridge that connects user requests to the content and information they seek online. A web server is a software application or hardware device that uses HTTP (Hypertext Transfer Protocol) and other protocols to communicate with client devices, typically web browsers, to deliver web content and services. Web servers handle the following roles:

Handling Requests and Responses
When a user enters a URL or clicks on a link, a request is sent to the respective web server. The server, in turn, processes this request and sends back the appropriate response. This response can be a web page, an image, or other types of documents. If the requested resource is not available, the server sends an error message, such as "404 Not Found".

Hosting Websites and Web Applications
Web servers store and manage websites, web applications, and their associated databases. They host HTML documents, images, CSS stylesheets, and JavaScript files that collectively form what we perceive as a website. When a user requests a particular webpage, the web server fetches and transmits the corresponding files to the user’s browser, which then renders them as a visually interactive page.

Ensuring Security and Privacy
Web servers are also tasked with ensuring secure data transmission by implementing protocols like HTTPS (Hypertext Transfer Protocol Secure). Through SSL/TLS encryption, web servers safeguard the data being transferred between the server and client, protecting it from potential malicious activities and ensuring privacy and integrity in data communication.

Enabling Dynamic Content and Interactivity
While static content is served as-is, web servers often work in tandem with server-side scripting languages like PHP, Python, or Node.js to generate dynamic content. When a user interacts with a web application (like submitting a form), the web server processes the input using the server-side script and may interact with a database to fetch or store data, thereby creating an interactive user experience.

Load Balancing and Traffic Management
In environments with high traffic, web servers may also distribute incoming requests to multiple servers (a process known as load balancing) to manage high loads and ensure smooth, uninterrupted service. This also provides redundancy, ensuring that if one server fails, others can continue to provide the service.

Logging and Monitoring
Web servers maintain logs of all requests made to them, which can be analysed for various purposes, such as understanding user behaviour, troubleshooting issues, and enhancing user experience. Monitoring tools can also be used to oversee server health, performance, and security.

A web server acts as a gateway that facilitates the seamless interaction between users and the internet, ensuring that they can access, interact with, and receive the online content and services they seek in a secure, efficient, and reliable manner. From hosting websites to managing traffic, ensuring security, and enabling dynamic, interactive web experiences, web servers remain integral to our digital interactions and experiences.

SECTION 5 | THE ROLE OF HTML

HTML, which stands for HyperText Markup Language, is the standard markup language used to create web pages and is a fundamental building block of web content. It provides the structure of a webpage, organizing and formatting content such as text, images, links, and multimedia in a hierarchical and visually coherent manner. HTML achieves this through the use of "tags" and "attributes," which define elements like headings, paragraphs, lists, links, and various media, enabling browsers to interpret and display the content in a user-friendly format. It also allows for the creation of hyperlinks, which are essential for navigating between webpages and websites, thereby enabling the interconnectedness that characterizes the World Wide Web.

SECTION 6 | HOW WEB PAGES ARE LOCATED, RETRIEVED AND DISPLAYED

When a user enters a URL (Uniform Resource Locator) into a web browser, a series of events is triggered to locate, retrieve, and display the web page on the user's device. This process involves multiple technologies and protocols working together to render the webpage. Here’s a simplified step-by-step breakdown of how this process typically works:

1. URL ENTRY

• User input: The user types a URL (e.g., www.example.com) into the address bar of a web browser and presses "Enter".
• Browser Behaviour: The browser parses the URL to identify the protocol (usually HTTP or HTTPS), the domain name, and the path to any specific resource or page.

2. DOMAIN NAME SERVER (DNS) LOOKUP

• Purpose: Convert the human-readable domain name into an IP address.
• Process: The browser communicates with a DNS server to resolve the domain name into an IP address, which uniquely identifies the web server on the Internet.
• Caching: If the browser or the operating system has the IP address cached from previous requests, it skips the DNS lookup.

3. ESTABLISHING A CONNECTION

• Protocol: Typically, HTTP/HTTPS protocols are used.
• Secure Connection: If HTTPS is used, a secure connection is established using TLS/SSL encryption.
• TCP Handshake: The browser establishes a TCP connection with the server using a process known as the "TCP handshake".

4. SENDING AN HTML REQUEST

• Request Components: The browser sends an HTTP request to the server, which includes the method (commonly GET), the path of the requested resource, and additional headers (like cookies and user-agent).
• Data Transmission: If the user submits a form or logs in, the relevant data is also transmitted to the server.

5. SERVER PROCESSING

• Web Server Role: The web server receives the HTTP request and forwards it to the appropriate server-side application (e.g., PHP, Python, Node.js) for processing.
• Data Retrieval: The server-side application may retrieve data from a database or perform other operations.
• Response Creation: The server creates an HTTP response containing the requested web page content, typically in HTML format.
  

6. RECEIVING THE HTTP RESPONCE

• Status Code: The server sends back an HTTP status code (e.g., 200 OK, 404 Not Found).
• Content: The server sends the requested content (HTML, CSS, JavaScript, images, etc.) to the browser.

7. RENDERING THE WEB PAGE

• HTML: The browser parses the HTML to construct the DOM (Document Object Model) tree.
• CSS Styling: CSS is applied to style the visual presentation of the web page.
• JavaScript: JavaScript is executed to dynamically modify the DOM and enable interactive features.
• Media Loading: Images, videos, and other media files are loaded.

8. DISPLAYING THE WEB PAGE

• Rendering: The browser’s rendering engine displays the web page content on the screen, adhering to the applied CSS styling and JavaScript functionality.
• User Interaction: The user can now interact with the web page, clicking links, filling forms, or triggering JavaScript events.

9. CLOSING THE CONNECTION

• Connection Closure: If the "Connection: close" header is sent, the connection is closed.
• Keep-Alive: If the "Connection: keep-alive" header is sent, the connection is kept open for additional requests.

This entire process, from entering the URL to displaying the web page, happens in a matter of seconds, showcasing the efficiency and complexity of web technologies.

ALSO IN THIS TOPIC

5.1.1 - 5.1.3 THE INTERNET AND THE WWW
5.1.4 WEB BROWSERS
5.1.5 WEB PROTOCOLS
5.1.6 COOKIES AND SESSIONS
5.2.1 - 5.2.2 DIGITAL CURRENCY
5.3.1 CYBER SECURITY
5.3.2 KEEPING DATA SAFE
TOPIC 5 REVISION CARDS
TOPIC 5 KEY TERMINOLOGY (CIE)
TOPIC 5 ANSWERS
TOPIC 5 TEACHER RESOURCES