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 browsing the web, you are using a computer network. We will look at the different types of networks, how they stay secure, and the "rules" (protocols) they follow to make sure data gets where it needs to go. Don't worry if some of the names sound like alphabet soup—we will break them down piece by piece!

1. What is a Computer Network?

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

Why do we use them? (Advantages)

• Sharing Hardware: Many computers can use the same printer or storage device.
• Communication: People can send emails, instant messages, and video call.
• Sharing Files: You can access your files from different computers on the same network.
• Centralised Updates: Software can be updated on all computers at once from a central server.

What are the downsides? (Disadvantages)

• Security Risks: Hackers can try to break into the network to steal data.
• Cost: Cables, routers, and switches can be expensive to buy and set up.
• Dependency: If the main server goes down, the whole network might stop working.

2. Types of Networks (PAN, LAN, WAN)

Networks are usually classified by how much space they cover. Here are the three you need to know:

PAN (Personal Area Network)

This is for one person. It connects devices over a very short range. Example: Connecting your phone to your wireless headphones via Bluetooth.

LAN (Local Area Network)

A LAN covers a small geographical area, like a single home, a school, or an office. Key Fact: LANs are usually owned and managed by a single person or organization.

WAN (Wide Area Network)

A WAN covers a large geographical area, like a country or even the whole world. Example: The Internet is the biggest example of a WAN. Key Fact: WANs are often under collective or distributed ownership (multiple companies own different parts of the cables and hardware).

Quick Review Box:
• PAN: Just you (Bluetooth).
• LAN: Small area (School/Home).
• WAN: Huge area (The Internet).

3. Wired vs. Wireless Networks

Devices can connect to a network using physical cables (wired) or radio waves (wireless).

Wired Connections

Wired networks use two main types of cables:
1. Copper: Cheap and common, used for short distances.
2. Fibre Optic: Uses light to send data. It is much faster and can cover long distances without losing signal, but it's more expensive.

Wireless Connections (Wi-Fi)

Wireless networks use radio waves to transmit data.
Advantages: You can move around freely, and it’s easy to add new devices without messy cables.
Disadvantages: Speed can be slower than wired, and the signal can be blocked by walls or interfered with by other devices.

4. Network Protocols

A network protocol is a set of rules that defines how data is transmitted between devices on a network. Think of it like a language—if two people don't speak the same language, they can't communicate. Protocols make sure all computers speak the same "language."

The Common Protocols You Must Know:

• TCP (Transmission Control Protocol): Breaks data into small "packets" and makes sure they arrive safely and in the right order.
• IP (Internet Protocol): Handles the "addressing" of data. It makes sure packets are sent to the correct destination on the internet.
• HTTP (Hypertext Transfer Protocol): Used by web browsers to access websites from a server.
• HTTPS (HTTP Secure): An encrypted (secret) version of HTTP. You should always look for this when shopping or banking online!
• SMTP (Simple Mail Transfer Protocol): Used to send emails from your device to a server.
• IMAP (Internet Message Access Protocol): Used to retrieve (access) emails from a server so you can read them.

Mnemonic Aid: To remember email protocols, think SMTP Sends mail; IMAP Inspects (reads) mail.

5. Network Security

Network security is vital to protect data from being stolen or damaged. Here are four common methods:

1. Authentication

Checking that the user is who they say they are. Example: Using a username and password, or a fingerprint scan.

2. Encryption

Scrambling data into a secret code so that if a hacker steals it, they can't read it. Only the person with the "key" can unscramble it.

3. Firewall

A security device that monitors traffic coming in and out of a network. It decides whether to allow or block specific traffic based on security rules. Think of it like a bouncer at a club checking who is allowed to enter.

4. MAC Address Filtering

Every device has a unique physical "ID" called a MAC address. A network can be set up to only allow devices with specific "approved" MAC addresses to connect.

6. The 4-Layer TCP/IP Model

To keep things organized, networking tasks are split into four "layers." Each layer has a specific job. Imagine sending a letter: one person writes it, another puts it in an envelope, another drives it to the city, and another delivers it to the door.

The Layers from Top to Bottom:

1. Application Layer: This is where your apps (like web browsers or email) operate.
Protocols used: HTTP, HTTPS, SMTP, IMAP.

2. Transport Layer: This layer sets up the connection and agrees on settings (like how big the data packets should be). It splits data into packets.
Protocol used: TCP.

3. Internet Layer: This layer adds the destination IP address to the packets and routes them across the network.
Protocol used: IP.

4. Link Layer: This is where the physical hardware lives, like your Network Interface Card (NIC) and cables.
Additional info: This is where OS device drivers operate.

Common Mistake to Avoid: Don't confuse the layers! Remember that TCP lives in the Transport layer and IP lives in the Internet layer. Use the mnemonic: All Tigers In London (Application, Transport, Internet, Link).

Summary Takeaway

Key Takeaway: Networks allow us to share and communicate. They come in different sizes (PAN, LAN, WAN) and can be wired or wireless. They use protocols (rules) like TCP/IP to function and require security (firewalls, encryption) to stay safe. Data travels through four layers: Application, Transport, Internet, and Link.