Computer Networks
1. Introduction
We all use computers and mobile devices every day — but have you ever thought about how they connect with each other to share data, access the internet, or print a file from another device? That's where computer networks come in!
A computer network is simply a group of computers and devices that are linked together so they can communicate and share resources. These connections can be wired (using cables) or wireless (like Wi-Fi).
2. Computer Network - A Brief Overview
Imagine your school computers all connected — where you can send files, print notes, or browse the internet from any system. That setup is a computer network.
In technical terms, a computer network helps devices talk to each other, share information, and use common tools like printers or internet connections. These networks can be small (like at home or in school) or large (like the internet).
There are different types of networks based on size:
- LAN (Local Area Network) - within a room, building, or campus
- MAN (Metropolitan Area Network) - covers a city
- WAN (Wide Area Network) - connects cities or countries (e.g., the internet)
2.1 Advantages of Computer Networks
Let's see how networks make life easier:
Easy File Sharing
You can share documents, videos, and images between connected devices in seconds.
Sharing of Hardware
No need for each system to have its own printer or scanner. One printer can serve all!
Better Communication
Chat, email, or video call your friends, teachers, or coworkers easily.
Centralized Storage
Files can be stored in one central system (like a server) and accessed by others safely.
Saves Money
Buying one printer for a network is cheaper than buying one for each system.
Remote Access
You can access your work or files from any location — especially helpful for work from home or online classes!
2.2 Disadvantages of Computer Networks
Even though networks are super useful, they do have some downsides:
Security Risks
If not protected properly, data on a network can be stolen or misused by hackers.
Virus Spreading
A virus on one computer can quickly spread to others on the same network.
High Setup Cost
Installing cables, routers, and servers for big networks can be costly at first.
Requires Skilled Staff
Networks need technical people to fix issues, update software, and keep things running.
Cybercrimes
Sensitive data like passwords and financial info can be at risk if the network is not secure.
3. Evolution of Network
Let's go back in time for a moment…
Computer networks didn't appear overnight. Like humans evolved, networks also evolved step by step to become what they are today — fast, global, and powerful.
Here's a quick look at how it happened:
1960s - The Beginning
- The U.S. Department of Defense created ARPANET, the first experimental network.
- It connected universities and research labs to share information.
1970s - Basic Networking
- Computer scientists developed protocols (rules for communication between computers).
- The idea of sending data in small packets started here.
1980s - Growth of LANs
- Local Area Networks (LANs) became common in schools, colleges, and offices.
- Ethernet technology was introduced — it's still used today.
1990s - Birth of the Internet
- The internet became public.
- The World Wide Web (WWW) was introduced.
- People started browsing websites and sending emails.
2000s to Now - Speed & Mobility
- Wi-Fi and mobile internet made networks wireless.
- Now we use 5G, cloud storage, and Internet of Things (IoT) — where even your fridge can be online!
In short: From military labs to your smartphone, networks have evolved into a daily life essential.
4. How Does the Internet Work?
Ever wondered what happens when you open Google or send a WhatsApp message?
The internet works by connecting many networks together — that's why it's called an "internetwork" or network of networks.
Here's a simple explanation:
- You type a website name (like www.cbse.gov.in) in your browser.
- Your device sends a request through your Wi-Fi or mobile data.
- That request travels through routers and servers.
- The website's server receives the request and sends back data (the page).
- You see the website on your screen.
All of this happens in a few seconds or less — thanks to fast networking!
4.1 Elementary Terminology of Network
Here are some basic network terms every student should know:
| Term | Meaning |
|---|---|
| Node | Any device (computer, printer, phone) connected to a network |
| Server | A powerful computer that provides services or data to other computers |
| Client | The computer that requests data or service from the server |
| IP Address | A unique number given to every device in a network (like a home address) |
| Router | A device that connects different networks and directs data to the right path |
| Switch/Hub | Devices used to connect multiple computers in a network |
| Modem | Converts digital signals to allow internet access from service providers |
| Bandwidth | The maximum amount of data that can pass through a network connection |
| Protocol | A set of rules that define how data is sent and received (e.g., TCP/IP) |
Example:
When you watch a YouTube video, your phone (client) sends a request to the YouTube server. The router helps direct that request, and the server sends the video back to your screen.
5. Components of Data Communication
Whenever data (like a file, message, or image) is shared from one device to another over a network, several key components work together to make it happen.
Let's break it down:
1. Message
The actual data that needs to be sent (like text, audio, video, or file).
2. Sender
The device or computer that creates and sends the message. Example: Your phone when you send a WhatsApp message.
3. Receiver
The device that receives the message. Example: Your friend's phone when they get your message.
4. Transmission Medium
The path or channel through which the data travels.
It can be:
- Wired (like copper cables, fiber optics)
- Wireless (like radio waves, Wi-Fi)
5. Protocol
A set of rules that define how the message will be sent, received, and understood. Example: TCP/IP is a common protocol used on the internet.
6. Different Ways of Sending Data Across a Network
There are different ways to send data from one point to another depending on the type of network and purpose.
One of the major concepts here is Network Switching — how data travels between devices.
6.1 Network Switching and Switching Technology
When you send data over a network, it doesn't travel all at once. It's usually broken into small parts (called packets) and sent through various routes.
This process of transferring data between devices is called Switching, and it is handled by devices called Switches.
There are two main types of switching technologies:
1. Circuit Switching
- A dedicated communication path is established between sender and receiver.
- This path remains reserved during the entire communication session.
- Best for voice calls (like telephone networks).
2. Packet Switching
- The message is divided into small packets.
- Each packet may take a different path to reach the destination.
- At the receiver end, packets are reassembled to form the original message.
- Used in the internet and email communication.
6.2 Difference Between Circuit Switching and Packet Switching
| Feature | Circuit Switching | Packet Switching |
|---|---|---|
| Path Setup | Dedicated path created before communication | No fixed path; each packet takes its own route |
| Speed | Slower to start but constant during call | Faster and more efficient for data |
| Resource Usage | Wastes bandwidth if not used continuously | Efficient use of network resources |
| Example | Telephone calls (landline/mobile) | Internet (email, browsing, file download) |
| Data Loss Risk | Very low during the call | Slightly higher, but protocols manage it |
In simple words:
- Circuit switching is like booking an entire road for your journey.
- Packet switching is like sending parcels through a courier, each one may take a different route but all reach the destination safely.
7. Data Communication Terminologies
Here are some basic terms used in data communication:
| Term | Explanation (Student-Friendly) |
|---|---|
| Bandwidth | Maximum data that can be transferred per second. Like the width of a water pipe. |
| Latency | Time delay between sending and receiving data. Lower is better. |
| IP Address | A unique number given to every device on a network. Like a home address. |
| MAC Address | Hardware address of a device. It's permanent and built into the device. |
| Protocol | A set of rules for communication between devices (e.g., TCP/IP). |
| Throughput | Actual data transferred in a given time. Affected by speed, errors, etc. |
| Packet | A small unit of data sent over the network. |
8. Network Devices
| Device | What it Does (In Simple Words) |
|---|---|
| Router | Connects different networks; used to connect you to the internet. |
| Switch | Connects multiple computers within the same network and forwards data smartly. |
| Hub | Like a switch but slower and sends data to all connected devices. |
| Modem | Converts signals from ISP to your device and vice versa (Modulator + Demodulator). |
| Repeater | Boosts weak signals in long-distance communication. |
| Bridge | Connects two similar networks. |
| Gateway | Connects two different types of networks. |
| Access Point | Allows wireless devices to connect to a wired network (like Wi-Fi hotspot). |
9. Types of Networks
9.1 Personal Area Network (PAN)
- Covers a very small area (1-10 meters)
- Used for personal devices like phones, laptops, Bluetooth devices
- Example: Connecting your smartphone to a Bluetooth speaker
9.2 Local Area Network (LAN)
- Covers a building or campus
- Fast and used in schools, homes, and offices
- Example: School computer lab network
9.3 Metropolitan Area Network (MAN)
- Covers a city or large campus
- Larger than LAN but smaller than WAN
- Example: City-wide cable TV network
9.4 Wide Area Network (WAN)
- Covers a large area — country or the world
- The Internet is the best example of WAN
- Example: Online classes using the internet from different cities
10. Network Topologies
Topology = the physical layout of how devices are connected in a network.
10.1 Mesh Topology
- Every device is connected to every other device
- Reliable but very expensive
- Used in military or high-security areas
10.2 Star Topology
- All devices connect to a central device (switch or hub)
- Easy to manage
- Most common in homes and schools
10.3 Bus (Multipoint) Topology
- All devices share a single communication line (backbone)
- Cheap but one failure affects all
- Used in small networks
10.4 Ring Topology
- Devices form a closed loop
- Data passes in one direction
- Old LAN setups used this
10.5 Tree Topology
- Combination of Star and Bus
- Hierarchical, scalable
- Used in large organizations
11. Communication Media
11.1 Guided Media (Wired)
| Type | Features |
|---|---|
| Twisted Pair Cable | Cheap, used in LANs |
| Coaxial Cable | Used in cable TV, better shielding |
| Optical Fiber | Very fast, used in internet backbone, expensive |
11.2 Unguided Media (Wireless)
| Type | Features |
|---|---|
| Radio Waves | Used in FM, remote controls |
| Microwaves | Used in satellite communication |
| Infrared | Used in remote controls, short-distance |
| Wi-Fi | Wireless LAN, used in homes, cafes |
| Bluetooth | For personal area networking |
12. Network Protocols
Protocols are rules that allow computers to communicate properly.
| Protocol | Use |
|---|---|
| HTTP | Used for web browsing |
| FTP | For file transfer |
| SMTP | For sending emails |
| POP/IMAP | For receiving emails |
| TCP/IP | Core of the internet – ensures data delivery |
| HTTPS | Secure version of HTTP |
13. Introduction to Web Services
Web services allow applications or devices to talk to each other over the internet.
13.1 WWW (World Wide Web)
- A collection of websites and webpages you can access via browsers
- Uses HTTP/HTTPS protocols
- Invented by Tim Berners-Lee
13.2 Hypertext Markup Language (HTML)
- The standard language used to create webpages
- Uses tags to format text, images, and links
- Example: <h1>Welcome</h1> displays a heading
13.3 Extensible Markup Language (XML)
- Designed to store and transport data
- Not for designing, but for organizing data in a readable format
- Used in software and apps to exchange information
13.4 Domain Names
- Easy-to-remember names for websites
- Behind every domain name is an IP address
- Example: www.cbse.gov.in is a domain name
13.5 URL (Uniform Resource Locator)
A URL is the web address you type in the browser to visit a website.
Example: https://www.cbse.gov.in
Parts of a URL:
- https – Protocol
- www.cbse.gov.in – Domain name
- /results/ – Specific path (optional)
Think of a URL like a complete postal address that tells the browser where to go on the internet.
13.6 IP Address
An IP Address (Internet Protocol Address) is a unique number assigned to each device connected to the internet.
Example: 192.168.0.1 or 2401:4900:50a8:abcd::1
There are two types:
- IPv4 – Old format, like 192.168.1.1
- IPv6 – New format, like 2401:abcd:... (used because IPv4 addresses are running out)
Every website and every device on the internet has an IP address.
13.7 Website
A website is a collection of webpages under one domain name. Example: www.tutelage.com is a website.
It may contain:
- Home page
- Contact page
- Notes or blog pages
- Videos or PDF files
13.8 Web Page
A web page is a single page of a website. Example: The "Notes" section of your website is one web page.
Every web page has its own URL, and multiple web pages form a website.
13.9 Web Browser
A web browser is a software used to access websites and web pages.
Popular browsers include:
- Google Chrome
- Mozilla Firefox
- Microsoft Edge
- Safari
Browsers translate HTML code into a viewable format.
13.10 Web Server
A web server is a special computer that stores websites and sends them to users when requested.
When you visit a website, your browser sends a request to a web server, and the server sends the web page to your browser.
13.11 Web Hosting
Web hosting is a service that allows individuals or businesses to store their website on a web server so that it's available on the internet.
Hosting companies provide:
- Storage space
- Server uptime
- Security features
- Support for domains
Without hosting, your website won't be visible to anyone online.
14. Setting Up a Computer Network – An Example
Let's say you want to set up a computer network in a school. Here's how it would be done:
Step 1: Plan the Network
- Decide how many computers will be connected
- Plan whether you need a wired or wireless network
Step 2: Choose Network Devices
- Use switches to connect computers
- Use a router and modem to connect to the internet
- Set up access points for Wi-Fi
Step 3: Cabling and Setup
- Lay Ethernet cables for wired connections
- Install necessary software and drivers
Step 4: Configure IP Addresses
- Assign IP addresses manually or use DHCP
- Ensure all systems can communicate with each other
Step 5: Secure the Network
- Use firewalls and antivirus software
- Set strong passwords and configure router security (WPA2/WPA3)
Step 6: Test the Network
- Check internet access on each system
- Test file sharing, printing, and speed
Real-Life Tip:
In most schools, labs use a Star Topology with a central switch/router. Internet access is often controlled with a firewall.