Fundamentals

A computer network is simply a group of computers and devices that are connected together so they can share information and resources with each other.

Think of it like this: imagine you and your friends live in different houses, but you have a string telephone connecting all your houses. You can talk to each other through those strings. A computer network works the same way, just with cables or wireless signals instead of strings.

Why Do We Need a Network?

We use networks for many everyday reasons:

To share files between computers, like sending a document to a friend
To share resources, like one printer used by many computers in an office
To communicate through email, video calls, and messages
To access the internet
To play online games with other people

Types of Networks by Size

Networks come in different sizes, depending on how big an area they cover:

PAN (Personal Area Network) - A very small network, just around you. Like your phone connected to your Bluetooth earphones. It covers only a few meters.
LAN (Local Area Network) - A small network that covers one home, school, or office building.
MAN (Metropolitan Area Network) - A network that covers a whole city or a large campus, like a network connecting several office branches in the same city.
WAN (Wide Area Network) - A very large network that can cover whole countries or even the entire world. The internet is the biggest WAN of all.

Basic Networking Terms You Should Know

These are the most common words used in networking. Think of this section as your networking dictionary.

IP Address

Every device on a network has its own unique address called an IP address (Internet Protocol Address). It works like a home address for your computer, so when data is sent to you, it knows exactly where to go.

Example: 192.168.1.1

MAC Address

MAC stands for Media Access Control. It is a permanent address built into your network card (the hardware) by the company that made it. Unlike an IP address, which can change, a MAC address never changes.

Example: 00:1A:2B:3C:4D:5E

You can think of it like your Aadhaar card number - unique to you and never changing.

Bandwidth

Bandwidth is how much data can travel through a network connection at one time. Think of it like a water pipe: a wider pipe lets more water flow through. The more bandwidth you have, the more data can flow at once. It is measured in bits per second (bps, Kbps, Mbps, Gbps).

Latency

Latency is the delay when data travels from one place to another. It is similar to shouting at someone far away - there is a small gap before they hear you. Lower latency means a faster response, which matters a lot in online games and video calls.

Protocol

A protocol is a set of rules that computers follow so they can talk to each other. Just like humans follow rules during a conversation, such as taking turns and speaking one at a time, computers follow protocols. Some examples are HTTP, TCP/IP, FTP, and DNS.

Server and Client

A server is a powerful computer that provides services to other computers, called clients. For example, when you visit a website, a server sends you that website’s files. A client is any device, like your laptop or phone, that asks the server for that data or service.

Packet

Data is not sent in one big chunk. Instead, it is broken into small pieces called packets. Each packet travels on its own, and they are all put back together once they reach the destination. It is similar to sending a big book to someone page by page through the mail.

DNS (Domain Name System)

DNS works like the phone book of the internet. It changes website names, like google.com, into IP addresses, like 142.250.182.46, that computers can understand. Without DNS, you would have to remember the IP address of every single website you want to visit.

Port

A port is like a door or channel on your computer through which specific types of data enter or leave. Your computer has thousands of ports, numbered from 0 to 65535. Some common ones are:

Port 80 - HTTP (normal websites)
Port 443 - HTTPS (secure websites)
Port 22 - SSH (remote login)
Port 25 - SMTP (sending email)

Firewall

A firewall acts like a security guard for your network. It checks all the data coming in and going out, and blocks anything that looks suspicious or dangerous.

HTTP and HTTPS

HTTP (HyperText Transfer Protocol) is the language your browser uses to talk to websites. HTTPS is the secure version of it, where the “S” stands for Secure, meaning the data is encrypted.

Router, Switch, and Hub (Quick Look)

These three devices come up a lot in networking, so here is a quick introduction. We will go into more detail on all hardware devices a bit later in this page.

Router - connects your home network to the internet and decides which path data should take
Switch - connects multiple devices in the same network and sends data only to the device it is meant for
Hub - an older device that sends data to every connected device, even if the message is meant for only one of them

What is the Web?

The Web (World Wide Web) is a collection of websites and web pages that you can visit through a browser, like Chrome or Firefox, using the internet.

Here is how it works, in simple steps:

You type a web address (URL) into your browser, like www.google.com
Your browser asks DNS, “What is the IP address of google.com?”
DNS replies with the IP address, something like 142.250.182.46
Your browser connects to Google’s server using that IP address
Google’s server sends back the web page files (HTML, CSS, images)
Your browser reads those files and shows you the web page

A few more terms worth knowing:

URL (Uniform Resource Locator) - the full address of a web page, like https://www.example.com/about
Browser - the app you use to view websites, such as Chrome, Firefox, Edge, or Safari
HTML - the language used to build web pages
Web Server - the computer that stores and sends out website files

Web vs Internet: What’s the Difference?

This confuses a lot of people, so here is a simple way to understand it.

	Internet	Web (World Wide Web)
What it is	The physical network of cables, routers, and connections all over the world	A service that runs on top of the internet
Simple meaning	The road or highway	The vehicles (websites and apps) that drive on that road
Examples	Email, FTP, VoIP, WhatsApp, and the Web itself	Websites like YouTube, Google, and Wikipedia
Who uses it	Anyone connected to any network	People browsing websites through a browser

In short, the internet is the infrastructure - the roads. The web is just one of many things you can do using that infrastructure. Email also runs on the internet but is not part of the web. WhatsApp calls use the internet too, but again, not the web.

Types of Transmission Media

Transmission media is simply the medium that data travels through to go from one device to another. It is similar to how sound travels through the air when you talk, or through a string in a tin can phone.

There are two main categories: wired media, which uses physical cables, and wireless media, which sends data through the air.

Wired Media
Wireless Media

1. Twisted Pair Cable

This is the most common cable used in homes and offices. It has two copper wires twisted together, and the twisting helps reduce interference. There are two types:

UTP (Unshielded Twisted Pair) - no extra protection, cheaper, used in most home and office networks
STP (Shielded Twisted Pair) - has a metal shield to block interference, used in places with a lot of electrical noise

Speed can go up to 10 Gbps, depending on the cable category (Cat5, Cat6, Cat7).

2. Coaxial Cable

This is a thick cable with a copper wire in the center, wrapped in insulation and a metal shield. It is similar to the cable that connects your TV to the set-top box. It used to be common for cable internet and TV connections, and it holds up well over longer distances.

3. Fibre Optic Cable

This cable uses light instead of electricity to send data. It is made of glass or plastic fibers thinner than a human hair. It is extremely fast, can carry data close to the speed of light, and is not affected by electrical interference. It is used for internet backbone connections and undersea cables between countries. It costs more, but it is very fast and reliable.

Network Devices Explained

These are the hardware devices that make a network actually work:

NIC (Network Interface Card) - a card inside your computer that lets it connect to a network. Every computer has one, sometimes built into the motherboard, and it has its own unique MAC address.
Hub - connects multiple devices in a network but sends data to every connected device, which is wasteful and slow. It is old technology and is not really used anymore.
Switch - smarter than a hub. It sends data only to the specific device it is meant for. It is used in offices to connect computers within a building and works at Layer 2 (Data Link Layer) of the OSI model.
Router - connects different networks together. Your home router connects your home network (LAN) to the internet (WAN). It reads IP addresses and decides where to send data. It works at Layer 3 (Network Layer).
Modem - short for Modulator-Demodulator. It converts digital data from your computer into signals that can travel over phone lines or cable lines, and converts them back again. Your internet provider gives you a modem to connect to their network.
Access Point (AP) - creates a wireless network (Wi-Fi) by connecting to a wired network. This is often the Wi-Fi box in your home, sometimes combined with the router.
Bridge - connects two network segments together. It is smarter than a hub and can filter traffic, though it has mostly been replaced by switches now.
Repeater - boosts a weak signal so it can travel further, similar to a Wi-Fi range extender in your home.
Gateway - connects networks that use different protocols, acting as a translator between two very different types of networks.

Unicast, Broadcast, and Multicast

These terms describe how data is sent from one device to others.

Unicast - One to One

Data is sent from one sender to one specific receiver, like sending a text message to a single friend. For example, when you load a website, the server sends that page only to your device.

Broadcast - One to All

Data is sent from one sender to every device on the network, like a teacher making an announcement to the whole class. For example, ARP requests, which ask “who has this IP address?”, are sent to every device. The downside is that too much broadcast traffic can slow the network down.

Multicast - One to Many (but Not All)

Data is sent from one sender to a specific group of devices that have signed up to receive it, like a group WhatsApp message that only the people in the group get. For example, in live video streaming, the video is sent to all viewers at once, instead of sending a separate copy to each person.

Network Topology (How Devices Are Laid Out)

Topology just means the layout, or how computers and devices are arranged and connected in a network. Think of it like how you arrange chairs and tables in a room, since there are different ways to set them up.

Mesh

Every device is connected to every other device. If one connection fails, data can still take another path. This makes it very reliable, but also very expensive because of all the cables needed. It is used in networks where reliability really matters, like military or banking networks.

graph TD A((A)) --- B((B)) A --- C((C)) A --- D((D)) B --- C B --- D C --- D

Star

All devices connect to one central device, usually a switch or a hub. This is the most common setup in homes and offices, where your Wi-Fi router acts as the center. If the central device fails, the whole network goes down, but it is easy to add new devices.

graph TD Switch((Switch)) --- A((A)) Switch --- B((B)) Switch --- C((C)) Switch --- D((D))

Bus

All devices connect to one single cable, called the bus, and data travels along this cable in both directions. If the main cable breaks, the whole network fails. This is old technology and is not used much today.

graph LR A((A)) --- B((B)) --- C((C)) --- D((D)) --- E((E))

Ring

Devices are connected in a circle, and data travels around the ring in one direction. Each device passes the data along to the next one until it reaches its destination. If one device fails, the whole ring breaks, unless it is a dual ring setup.

graph LR A((A)) --> B((B)) B --> C((C)) C --> D((D)) D --> A

Tree

This is a combination of star topologies connected in a hierarchy, like a tree with branches. The main switch connects to smaller switches, which then connect to individual computers. This setup is common in large organizations with many departments.

graph TD Root((Root Switch)) --> SA((Switch A)) Root --> SB((Switch B)) SA --> C((C)) SA --> D((D)) SA --> E((E)) SB --> F((F)) SB --> G((G)) SB --> H((H))

Comparison:

Topology	Cost	Reliability	Used For
Mesh	Very High	Very High	Critical networks
Star	Medium	Medium	Homes, offices
Bus	Low	Low	Old systems
Ring	Medium	Medium	Old token ring networks
Tree	Medium-High	High	Large organizations

LAN vs MAN vs WAN

	LAN	MAN	WAN
Full Form	Local Area Network	Metropolitan Area Network	Wide Area Network
Coverage	One building or campus	One city	Countries or worldwide
Example	Your home Wi-Fi, office network	City-wide cable TV network	The Internet
Speed	Very fast (up to 10 Gbps+)	Fast	Slower (depends on distance)
Cost	Low	Medium	High
Who manages it	You or your organization	Local service provider	Telecom companies, ISPs

Here’s a simple way to remember them:

LAN - your Living room network
MAN - your Metro city network
WAN - your World-wide network