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Networks and the internet: Class 9 Computer Science
Computer networks, their types and topologies, network devices, the internet, the World Wide Web, IP addresses and domain names, common internet services, email and the benefits and risks of networking.
Key points
A computer network is a group of two or more computers and devices connected together so that they can share data, files and resources such as printers and an internet connection. The connection may use cables or wireless signals.
Benefits of networking:
- Resource sharing: many users can use one printer, scanner or storage.
- Fast communication through email and messaging.
- Central storage and easy backup of data.
- Lower cost, because hardware and software are shared.
- Disadvantages are the cost of setup, the risk of viruses and hacking, and loss of work if the main server fails.
Types of network by size:
- LAN (Local Area Network): covers a small area such as a lab, school or office building.
- MAN (Metropolitan Area Network): covers a city.
- WAN (Wide Area Network): covers a large area such as a country or the world. The internet is the largest WAN.
- PAN (Personal Area Network): connects devices around one person, for example a phone and Bluetooth headphones.
Network models:
- Client server: a powerful computer called the server provides services, and the client computers request them. It gives better security and central control.
- Peer to peer: all computers are equal and share resources directly. It is cheap and simple but less secure and suited only to small networks.
Network topology is the layout in which computers are connected:
- Bus: all devices share one main cable. It is cheap, but if the main cable breaks, the network fails.
- Star: every device connects to a central hub or switch. A cable fault affects only one device, but if the centre fails everything stops. It is the most common today.
- Ring: each device connects to two neighbours in a circle and data moves in one direction.
- Mesh: every device connects to many others, so it is very reliable but costly.
Common network devices:
- Network interface card (NIC): the hardware that connects a computer to a network.
- Hub: sends incoming data to all connected devices.
- Switch: sends data only to the device it is meant for, so it is faster and more efficient.
- Router: connects different networks together and finds the best path for data. A home router connects your LAN to the internet.
- Modem: converts digital signals to signals that can travel over phone or cable lines and back.
- Access point: provides Wi-Fi connection.
Communication media carry the data. Wired media include twisted pair cable, coaxial cable and fibre optic cable. Fibre optic cable uses light, is very fast and is not affected by electrical noise. Wireless media include Wi-Fi, Bluetooth and mobile networks.
The internet is a worldwide network of networks. It connects millions of computers using a common set of rules called protocols. The main protocol set is TCP/IP. An Internet Service Provider (ISP) gives users access to the internet.
The World Wide Web (WWW) is a collection of linked web pages and files that are accessed using the internet. The internet and the web are not the same thing: the internet is the network, and the web is a service that runs on it. A web page is written in HTML. A website is a group of related pages. A web browser, such as Chrome or Firefox, is the software used to view web pages.
Addresses on the internet:
- IP address: a unique number given to each device, for example 192.168.1.10 in IPv4.
- URL (Uniform Resource Locator): the full address of a web page, for example https://www.example.com/index.html.
- Domain name: the readable name of a website, such as example.com. The DNS (Domain Name System) turns it into an IP address.
- Common domain endings are .com (commercial), .edu (education), .gov (government), .org (organisation) and .pk (Pakistan).
Common internet services:
- Email: sending messages electronically. An address has the form name@domain.
- Search engines such as Google help to find information.
- Social media and video calls for communication.
- Online banking, shopping and e-learning.
- File transfer (FTP) and cloud storage.
Email works by sending a message from your mail program to your mail server. The server forwards it to the receiver's mail server, where it waits until the receiver opens it. An email contains the To, Cc, Bcc, Subject, message body and optional attachments. Bcc hides the receivers from each other.
Study tip: Make a small table comparing the four topologies with one advantage and one disadvantage each, since this is asked often. Always draw a simple neat diagram when the question mentions a topology. For device questions, link each device to its single main job in one clear sentence.
Definitions and flashcards
Say the meaning first, then open the card to check.
Network
Computers and devices connected to share data and resources.
LAN
A network that covers a small area such as a building.
WAN
A network that covers a large area, such as a country.
Topology
The layout or arrangement of devices in a network.
Router
A device that connects networks and directs data between them.
Protocol
A set of rules for communication between devices.
IP address
A unique number that identifies a device on a network.
URL
The complete address of a web page.
ISP
A company that provides internet access.
Short questions with model answers
These are the kind of questions asked for 2, 3 and 5 marks. Try each one before opening the answer.
Define a computer network and state two advantages. (2 marks)
A computer network is a set of connected computers and devices that can share data and resources. Two advantages are sharing of hardware such as printers, and fast communication through email.
Differentiate between LAN and WAN. (3 marks)
A LAN covers a small area such as a school lab or office, is fast and is usually owned by one organisation. A WAN covers a large area such as a country or the whole world, uses public or leased links, and is slower and costlier. The internet is a WAN.
Explain the star topology with one advantage and one disadvantage. (3 marks)
In a star topology every computer is connected by its own cable to a central hub or switch. An advantage is that the failure of one cable or computer does not stop the rest of the network, and it is easy to add devices. A disadvantage is that if the central hub or switch fails, the entire network stops.
What is the difference between the internet and the World Wide Web? (3 marks)
The internet is the global network of connected computers and the hardware that links them. The World Wide Web is a service that runs on the internet and consists of web pages linked by hyperlinks and viewed with a browser. Email and file transfer are other services that also use the internet.
Describe the functions of a router, a switch and a modem. (5 marks)
A router connects different networks, such as a home LAN to the internet, and chooses the path for data. A switch connects devices in the same network and sends data only to the intended device. A modem converts digital data to signals suitable for a telephone or cable line and converts received signals back to digital data.
What is a domain name and how is it used? (2 marks)
A domain name is the easy-to-remember name of a website, such as example.com. The Domain Name System converts it into the numeric IP address of the server so that the browser can find the website.
Common mistakes
- Saying that the internet and the web are the same. The web is one service on the internet.
- Mixing up a hub and a switch. A hub sends data to everyone, a switch sends it only to the target device.
- Writing that a router and a modem do the same job. A modem connects to the ISP line, a router connects and directs traffic between networks.
- Calling a browser a search engine. Chrome is a browser, Google is a search engine.
- Giving only the name of a topology without a diagram description, advantage or disadvantage.