Fundamentals of computer networks

Welcome to the World of Computer Networks!

In this chapter, we are going to explore how computers "talk" to each other. Whether you are sending a WhatsApp message, playing an online game, or searching for something on Google, you are using a computer network. By the end of these notes, you’ll understand the different types of networks, how they are arranged, and the "rules" they follow to keep our data safe and moving fast.

1. What is a Computer Network?

A computer network is two or more computers (or other devices) connected together so they can communicate and share resources.

Why bother connecting them? (Advantages):
- Sharing Hardware: Everyone in an office can use the same printer.
- Sharing Files: You can work on the same document from different computers.
- Communication: Sending emails or instant messages.
- Centralised Updates: Software can be installed on all computers at once.

The Downsides (Disadvantages):
- Security Risks: Hackers or viruses can spread more easily across a network.
- Cost: You need extra hardware like cables and switches, which can be expensive.
- Management: Large networks often need a specialist person (a network manager) to keep them running.

Quick Review: The Basics

Network: Devices connected to share things.
Main Goal: Communication and resource sharing.

2. Types of Networks: PAN, LAN, and WAN

Not all networks are the same size. We categorise them based on the geographical area they cover.

Personal Area Network (PAN)

A PAN is the smallest type of network. It is used for connecting devices very close to one person. For this course, you only need to think about Bluetooth.
Example: Connecting your wireless headphones to your smartphone.

Local Area Network (LAN)

A LAN covers a small geographical area, like a single house, a school, or an office building.
- Ownership: Usually owned and managed by the person or organisation that uses it (e.g., your school owns its own LAN).
- Hardware: Uses Ethernet cables or Wi-Fi.

Wide Area Network (WAN)

A WAN covers a large geographical area, like a city, a country, or even the whole world.
- Ownership: Often under collective or distributed ownership. They use external equipment like satellites or phone lines.
- The Ultimate Example: The Internet is the world's largest WAN.

Memory Aid:
- PAN = Private (Just me and my gadgets)
- LAN = Local (My building)
- WAN = Wide (The whole world)

Key Takeaway: The main difference between a LAN and a WAN is the geographical area they cover and who owns the hardware.

3. Wired vs. Wireless

Computers can be connected using physical cables or through the air using radio waves.

Wired Connections

- Copper Cable: Uses electrical signals. It’s cheap and common but loses signal over long distances.
- Fibre Optic: Uses pulses of light. It is incredibly fast and can travel very long distances without losing quality. It’s perfect for the "backbone" of the Internet.

Wireless Connections

- Wi-Fi: Uses radio waves to send data.
- Pros: You can move around freely with your laptop or phone.
- Cons: It can be slower than wires and the signal can be blocked by thick walls.

Did you know? Wi-Fi is actually a trademark! The technical term for wireless networking is WLAN (Wireless Local Area Network).

4. Network Topologies (The Layout)

A topology is just a fancy word for how the devices in a network are arranged.

Star Topology

In a Star Topology, every device is connected to a central switch or hub.
- Pro: If one cable breaks, only that device is affected. The rest of the network stays up!
- Con: If the central switch fails, the whole network goes down.

Bus Topology

In a Bus Topology, all devices are connected to a single main cable called the backbone.
- Pro: Very cheap and easy to set up for a few computers.
- Con: If the main backbone cable is cut, the entire network fails. It also gets very slow if too many people use it at once.

Common Mistake: Don't confuse these! In an exam, if you are asked to "select the most appropriate topology," the Star is usually the better choice for modern schools and offices because it is more reliable.

5. Network Protocols (The Rules)

A protocol is a set of rules that governs how data is sent and received. Think of it like a language; if two computers aren't speaking the same protocol, they won't understand each other.

Common Protocols You Need to Know:

- Ethernet: Rules for wired connections in a LAN.
- Wi-Fi: Rules for wireless connections.
- TCP (Transmission Control Protocol): Breaks data into "packets" and ensures they arrive safely and in the right order.
- UDP (User Datagram Protocol): Like TCP, but faster because it doesn't check if data arrived. Great for online gaming or video streaming where speed matters more than perfection.
- IP (Internet Protocol): Handles the "addressing." It makes sure data packets are sent to the right destination on the internet.
- HTTP/HTTPS: Used by web browsers to access websites. The "S" in HTTPS stands for Secure (the data is encrypted).
- FTP (File Transfer Protocol): Used specifically for moving files between computers.
- SMTP (Simple Mail Transfer Protocol): Used to send emails.
- IMAP (Internet Message Access Protocol): Used to receive and manage emails on a server.

Quick Review Box:
Sending Email: SMTP
Receiving Email: IMAP
Web Browsing: HTTP / HTTPS
Fast but "unreliable" data: UDP

6. The 4-Layer TCP/IP Model

To make networking easier to manage, we split the process into layers. Each layer has a specific job. Don't worry if this seems tricky; just think of it like sending a letter through the post office.

1. Application Layer: This is where your apps live (Web browser, Email). Protocols: HTTP, HTTPS, SMTP, IMAP, FTP.
2. Transport Layer: This layer sets up the communication between the two computers. It agrees on things like packet size. Protocols: TCP, UDP.
3. Internet Layer: This layer addresses and routes the data packets across the network. Protocol: IP.
4. Link Layer: This is where the hardware lives (the NIC and cables). It handles the actual physical transfer of data. Protocol: Ethernet.

Analogy: Sending a Letter
- Application: You write the letter.
- Transport: You put it in an envelope.
- Internet: You write the address on the front.
- Link: The postman physically carries it to the destination.

7. Network Security

Because networks are open to many people, we need to protect them. Here are the four main ways:

- Authentication: Checking that a user is who they say they are (usually with a username and password).
- Encryption: Scrambling data so that if a hacker steals it, they can't read it without a special "key."
- Firewall: A piece of software or hardware that monitors traffic entering and leaving a network. It blocks anything suspicious based on a set of rules.
- MAC Address Filtering: Every device has a unique physical "fingerprint" called a MAC address. A network can be set up to only allow specific MAC addresses to connect. It's like having a VIP guest list for your Wi-Fi.

Key Takeaway: These methods work best when used together. A firewall stops intruders, while encryption ensures that even if they get in, the data is useless to them.

Summary: Top Tips for the Exam

1. LAN vs WAN: Remember geographical area and ownership.
2. Protocols: Be ready to explain what specific protocols like SMTP or HTTPS do.
3. Layers: Remember the order (Application, Transport, Internet, Link).
4. Security: Understand that a Firewall is for monitoring traffic, while Authentication is for checking identity.