KS3 Computing — Internet, Protocols & the WWW

Study revision notes for KS3 Computing — Internet, Protocols & the WWW

KS3 Computing — Study Pack

Topic: The Internet, Protocols & the World Wide Web

Year 7–9 | Networks | UK National Curriculum

Overview

People frequently use "the internet" and "the World Wide Web" as if they mean the same thing — they do not. Understanding this distinction is one of the most important concepts in this topic. This pack also covers how data travels across networks in packets, how addresses work, and the protocols (agreed rules) that allow billions of different devices to communicate reliably.

Section 1: The Internet vs the World Wide Web

The Internet

The Internet is the global infrastructure — the physical and logical network of interconnected networks spanning the entire planet. It consists of:

Undersea fibre optic cables crossing oceans
Overland cables connecting countries
Routers directing traffic across the network
Servers providing services
The physical connections between billions of devices

Think of the internet as the road network — the roads, motorways, and junctions that exist everywhere.

The World Wide Web (WWW)

The WWW is a service that runs on top of the internet. It is the collection of web pages, websites, images, and other media that are linked together using hyperlinks and accessed using the HTTP/HTTPS protocol via a web browser.

Think of the WWW as the cars and lorries that travel on the road network — they use the roads (internet) but are not the same thing as the roads.

Other Services That Run on the Internet

The internet carries many services — the WWW is just one of them:

Service	Protocol used	What it does
World Wide Web	HTTP / HTTPS	Browsing web pages
Email	SMTP, IMAP, POP3	Sending and receiving emails
File transfer	FTP	Uploading/downloading files
Video streaming	RTSP / HTTP	Netflix, YouTube
Online gaming	TCP/UDP	Real-time game data
Video calls	WebRTC / SIP	Zoom, Teams

Key point: When you send an email, you are using the internet but NOT the WWW. When you browse Wikipedia, you are using both the internet (to carry the data) and the WWW (the web page itself).

Section 2: Addressing — IP Addresses, Domain Names, and DNS

IP Addresses

Every device connected to the internet has a unique IP (Internet Protocol) address — a numerical identifier that allows routers to direct data to the correct destination.

IPv4: The original format. Written as four groups of numbers separated by dots, each 0–255.

Example: 192.168.1.1 or 66.220.149.25
Uses 32 bits → approximately 4.3 billion unique addresses
Problem: the world has run out of IPv4 addresses (more devices than addresses)

IPv6: The replacement format, designed to solve address exhaustion.

Example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
Uses 128 bits → approximately 340 undecillion (3.4 × 10³⁸) unique addresses
Gradually being adopted alongside IPv4

Domain Names

IP addresses like 172.217.169.68 are difficult for humans to remember. Domain names provide human-readable addresses:

www.bbc.co.uk
www.google.com
www.educationwebsite.org

Anatomy of a domain name:

   www    .    bbc    .    co    .    uk
   |           |           |          |
subdomain    second-    domain    country-
             level      type      code

DNS — Domain Name System

The DNS is the system that translates domain names into IP addresses. It acts like a phone book for the internet — you provide a name and it gives you the number (IP address).

Without DNS, you would need to memorise the IP address of every website you want to visit.

DNS Resolution — Step by Step:

Step 1: User types "www.bbc.co.uk" in browser

Step 2: Browser checks its LOCAL CACHE
        → Has it looked up this address recently?
        → If yes: use cached IP address (fast)
        → If no: proceed to Step 3

Step 3: Browser contacts the DNS SERVER
        (provided by ISP or configured manually e.g. 8.8.8.8 = Google DNS)
        → "What is the IP address for www.bbc.co.uk?"

Step 4: DNS SERVER responds
        → "www.bbc.co.uk is at 151.101.0.81"

Step 5: Browser contacts the WEB SERVER at that IP address
        → "Please send me the home page"

Step 6: Web server sends the HTML, CSS, images back to browser

Step 7: Browser renders and displays the web page

ASCII DNS Resolution Flow Diagram

[USER]
  |
  | Types: www.bbc.co.uk
  v
[BROWSER]
  |
  |---(1) Is it in cache?---> YES ---> [IP known, skip to step 5]
  |
  | NO
  v
[DNS SERVER]  <---(2) "What IP for www.bbc.co.uk?"
  |
  |---(3) Returns: 151.101.0.81
  v
[BROWSER]
  |
  |---(4) HTTP request to 151.101.0.81
  v
[WEB SERVER at bbc.co.uk]
  |
  |---(5) Returns HTML, CSS, images
  v
[BROWSER renders page for USER]

Section 3: Packets and Packet Switching

What are Packets?

When you send a file, email, or load a web page, the data is not sent as one continuous stream. Instead, it is broken into small chunks called packets.

Each packet contains:

+------------------------------------------+
|  HEADER                                  |
|  - Source IP address (where it came from)|
|  - Destination IP address (where to go)  |
|  - Sequence number (packet 3 of 10)      |
|  - Protocol information                  |
+------------------------------------------+
|  PAYLOAD                                 |
|  - The actual chunk of data              |
|  (e.g. part of a web page, part of file) |
+------------------------------------------+
|  TRAILER                                 |
|  - Error checking (checksum)             |
+------------------------------------------+

Packet Switching

Packet switching is the method used to send packets across the internet. Key characteristics:

Different routes: each packet in a message may travel via a completely different route through the network
Independent decisions: each router decides the best path for each packet at that moment, based on network conditions
Reassembly: at the destination, packets are reassembled into the correct order using the sequence numbers

Packet Switching Diagram

SOURCE (sending a 3-packet message A, B, C)
|
|  Packet A ---> Router 1 ---> Router 3 ---> DESTINATION
|  Packet B ---> Router 1 ---> Router 2 ---> Router 4 --> DESTINATION
|  Packet C ---> Router 2 ---> Router 4 ---> DESTINATION

All three packets arrive at DESTINATION:
Packet A (arrived 1st), Packet C (arrived 2nd), Packet B (arrived 3rd)

REASSEMBLED in correct order using sequence numbers: A, B, C

Benefits of Packet Switching

Benefit	Explanation
Efficient use of network	No dedicated line is reserved between sender and receiver — many users share the same network infrastructure simultaneously
Fault tolerant	If a router fails, packets automatically reroute around the problem — the message still arrives
Scalable	Works for billions of simultaneous connections
No wasted bandwidth	Lines are only used when actually carrying a packet

Section 4: Protocols

A protocol is a set of agreed rules that define how data is formatted, transmitted, and received. Protocols allow different devices (different manufacturers, different operating systems) to communicate reliably.

Key Protocols Reference Table

Protocol	Full Name	Port	Purpose
HTTP	HyperText Transfer Protocol	80	Transfers web pages from server to browser; data sent in plain text (unsecured)
HTTPS	HTTP Secure	443	HTTP with SSL/TLS encryption; data encrypted in transit; padlock shown in browser
TCP	Transmission Control Protocol	—	Splits data into packets; ensures all packets arrive; requests retransmission of lost packets; reliable
IP	Internet Protocol	—	Handles routing of packets across networks using IP addresses
TCP/IP	Combined protocol suite	—	Foundation of internet communication; TCP + IP working together
DNS	Domain Name System	53	Translates domain names to IP addresses
SMTP	Simple Mail Transfer Protocol	25/587	Sends email from client to mail server or between servers
IMAP	Internet Message Access Protocol	143/993	Receives email; messages stay on server; accessible from multiple devices
POP3	Post Office Protocol v3	110/995	Receives email; messages downloaded to device and deleted from server
FTP	File Transfer Protocol	20/21	Transfers files between computers

HTTP vs HTTPS — The Critical Difference

HTTP (port 80):

Data is transmitted as plain text
Anyone intercepting the data can read it
Suitable only for public, non-sensitive content
No padlock in the browser address bar

HTTPS (port 443):

Data is encrypted using SSL/TLS before transmission
Even if intercepted, the data appears as meaningless ciphertext
Required for any login page, banking, shopping, or personal data
Shows a padlock icon in the browser
The server has an SSL/TLS certificate proving its identity

TCP/IP — The Internet's Foundation

TCP (Transmission Control Protocol) handles the reliable delivery of data:

Breaks data into packets
Numbers each packet (sequence numbers)
Ensures all packets arrive at the destination
Requests retransmission of any lost packets
Reassembles packets in the correct order

IP (Internet Protocol) handles routing:

Each packet has a source and destination IP address
Routers read the IP address and forward the packet toward its destination
Each router makes an independent decision about the next hop

Together, TCP/IP ensures that data gets from A to B accurately, regardless of the route taken or the hardware involved.

Key Vocabulary

Term	Definition
Internet	The global physical and logical infrastructure — the network of interconnected networks
WWW (World Wide Web)	A service running on the internet — the collection of linked web pages accessed via HTTP/HTTPS
IP address	A unique numerical identifier assigned to every device on a network
IPv4	32-bit IP address format; approximately 4.3 billion unique addresses (now largely exhausted)
IPv6	128-bit IP address format; designed to replace IPv4 with vastly more addresses
Domain name	A human-readable address for a website (e.g. www.bbc.co.uk)
DNS	Domain Name System — translates domain names into IP addresses
Packet	A small chunk of data (with header, payload, and trailer) sent across a network
Packet switching	Method of sending packets independently via different routes; reassembled at destination
Protocol	A set of agreed rules for how data is formatted and transmitted between devices
HTTP	Protocol for transferring web pages; data is unencrypted
HTTPS	Secure version of HTTP; data is encrypted using SSL/TLS
TCP	Protocol that splits data into packets, ensures reliable delivery, and reassembles them
IP	Protocol that handles routing of packets across networks using IP addresses
SMTP	Protocol for sending email
IMAP	Protocol for receiving email; keeps messages on the server
FTP	Protocol for transferring files between computers
SSL/TLS	Encryption protocols used by HTTPS to secure data in transit
Cache	Temporary storage of previously accessed data (e.g. DNS records) to speed up future requests
Sequence number	Number in each packet's header that allows correct reassembly at the destination

Common Misconceptions

Misconception	Correction
"The internet and the World Wide Web are the same thing"	The internet is the physical infrastructure (cables, routers, servers). The WWW is a service — just one of many — that runs on the internet. Email also uses the internet but is not part of the WWW.
"HTTP and HTTPS are completely different protocols"	HTTPS is HTTP with SSL/TLS encryption added on top. The underlying protocol is the same; HTTPS simply encrypts the data before sending it.
"All packets in a message travel the same route"	In packet switching, each packet may take a completely different route through the network, depending on traffic and router decisions. They are reassembled in the correct order at the destination.
"DNS stores the actual web page content"	DNS only stores the mapping between domain names and IP addresses — a "phone book" entry. The actual web content is stored on web servers.
"IPv4 and IPv6 work the same way — IPv6 is just bigger"	While both are IP addressing schemes, IPv6 was redesigned with a much larger address space (128-bit vs 32-bit) and includes additional features. They are not directly compatible without translation mechanisms.
"A web browser is the internet"	A browser (Chrome, Firefox, Safari) is a program that accesses the WWW. The internet exists independently of any browser.

Diagrams / ASCII Art

The Internet vs WWW — Conceptual Model

+---------------------------------------------------------------+
|                        THE INTERNET                           |
|  (Physical cables, routers, servers, fibre, satellites)       |
|                                                               |
|   +------------------+  +-----------+  +------------------+  |
|   |  WORLD WIDE WEB  |  |   EMAIL   |  | VIDEO STREAMING  |  |
|   |  (HTTP/HTTPS)    |  |   (SMTP   |  |   (RTSP/HTTP)    |  |
|   |  Web pages,      |  |    IMAP)  |  |   Netflix,       |  |
|   |  hyperlinks      |  |           |  |   YouTube        |  |
|   +------------------+  +-----------+  +------------------+  |
|                                                               |
|   +------------------+  +-----------+                        |
|   |   FILE TRANSFER  |  |  GAMING   |                        |
|   |      (FTP)       |  |  (UDP)    |                        |
|   +------------------+  +-----------+                        |
+---------------------------------------------------------------+

Packet Header Structure

PACKET 3 of 7:
+---------------------------+
| Source IP: 192.168.1.5    |  <- Where did this packet come from?
| Dest. IP:  151.101.0.81   |  <- Where is it going?
| Seq. No:   3              |  <- This is packet number 3
| Checksum:  A4F2           |  <- Error checking
+---------------------------+
| PAYLOAD: ...data chunk... |  <- The actual content
+---------------------------+
| TRAILER: error check bits |
+---------------------------+

Exam-Style Questions

Q1 [2 marks] State one similarity and one difference between the internet and the World Wide Web.

Q2 [3 marks] Explain how DNS resolves a domain name. Your answer should include what information is sent and what is returned.

Q3 [4 marks] Explain what is meant by packet switching. In your answer, explain:

what a packet is
what packet switching means
one benefit of packet switching

Q4 [2 marks] Explain why a website that handles bank account details should use HTTPS rather than HTTP.

Q5 [6 marks] Trace the steps that occur from a user typing www.example.com into their browser to the web page appearing on screen. You should include: DNS, IP address, HTTP request, web server, and packet delivery.

MCQ Which protocol is used to send email?

A) HTTP B) FTP C) SMTP D) DNS

Fill in the blanks Data sent across the internet is broken into small chunks called __________. Each chunk contains a __________, which includes the source and destination __________ addresses, and a sequence number used for __________. This method, where each chunk may travel via a different __________, is called packet switching.

Model Answers

Q1:

Similarity: both the internet and the WWW involve transferring data between computers (1).
Difference: the internet is the physical global infrastructure (cables, routers, servers), whereas the WWW is a service (collection of web pages) that runs on top of the internet (1). [2 marks]

Q2: The user's browser sends a request to a DNS server containing the domain name (1). The DNS server looks up the domain name in its database and finds the matching IP address (1). The DNS server returns the IP address to the browser, which then contacts the web server at that IP address (1). [3 marks]

Q3:

A packet is a small chunk of data that includes a header (containing source IP, destination IP, and sequence number), a payload (the actual data), and a trailer (error checking) (1).
Packet switching is a method where the data is broken into packets and each packet may travel via a different route through the network (1).
Packets are reassembled in the correct order at the destination using sequence numbers (1).
Benefit: if one router fails, packets can be rerouted automatically around the failure, making the system fault tolerant / the network is used efficiently because no dedicated line is reserved (1). [4 marks]

Q4: HTTPS encrypts the data using SSL/TLS before it is transmitted (1). This means that even if an attacker intercepts the data, they cannot read the account details — it appears as meaningless ciphertext (1). HTTP sends data as plain text, which anyone intercepting the connection could read. [2 marks]

Q5: Award 1 mark per correct step, up to 6 marks:

User types www.example.com — browser checks local DNS cache for the IP address
If not cached, browser sends a DNS query to the DNS server asking for the IP address of www.example.com
DNS server returns the IP address (e.g. 93.184.216.34) to the browser
Browser sends an HTTP/HTTPS request (a packet) to the web server at that IP address, asking for the web page
The request and response are broken into packets; each packet travels via routers across the internet, potentially via different routes, and is reassembled at the destination
The web server at www.example.com sends back the HTML, CSS, and image files; the browser renders these and displays the page

MCQ: C — SMTP

Fill in the blanks: packets / header / IP / reassembly / route

Revision Checklist

I can explain the difference between the internet and the WWW with an example
I can name three services that use the internet other than the WWW
I can describe what an IP address is and why it is needed
I can state one difference between IPv4 and IPv6
I can explain what DNS does and why it is needed
I can describe the DNS resolution process step by step
I can explain what a packet is and name three parts of a packet
I can explain what packet switching means
I can state two benefits of packet switching
I can state the purpose of HTTP and HTTPS and explain the difference
I can explain why HTTPS is more secure than HTTP
I can state the purpose of TCP/IP, SMTP, IMAP, and FTP
I can explain what a protocol is and why protocols are needed

Practice this topic