Computer Networks – SS1 Digital Technologies Lesson Note (Second Term)

A computer network is a collection of computers and devices connected together so they can share resources, such as a printer, and information, such as a file or an email.

Behavioural objectives

1. Define a computer network.
2. State three reasons for connecting computers.
3. Distinguish between LAN, MAN and WAN and give an example of each.
4. Describe the server, the client, the network interface card (NIC) and transmission media.
5. Explain the roles of a hub, a switch and a router.

What is a computer network?

A computer network is a group of computers and devices linked together to share resources and information.

• Resource: something that can be shared, such as a printer, a scanner or an Internet connection.
• Information: data that can be sent across the link, such as a file, a photo or an email.
• Everyday idea: a network of friends stays in touch to share news. A computer network does the same with machines.

Why do we connect computers?

1. Resource sharing: one printer can serve ten offices instead of buying ten printers.
2. Communication: users send emails and instant messages and make video calls.
3. Data sharing: a file is sent over the network instead of being copied to a flash drive and carried to another room.

What are the advantages and disadvantages of a network?

• Advantage, saves money: shared hardware and software reduce cost.
• Advantage, saves time: files and messages reach other users at once.
• Disadvantage, set-up cost: cables, switches and routers must be bought and installed.
• Disadvantage, security risk: viruses and hackers can spread from one connected computer to others.
• Disadvantage, server failure: if the main server breaks down, many users lose access.

What are the types of computer network?

There are three main types of computer network, grouped by the area they cover: LAN, MAN and WAN.

What is a LAN (Local Area Network)?

A LAN is a network that covers a small area such as a room, a house or a school computer laboratory.

• Speed: usually very fast.
• Ownership: usually private, owned by one person or organisation.
• Example: the computers linked together in your school’s computer laboratory.

What is a MAN (Metropolitan Area Network)?

A MAN is a network that covers a whole city or a large campus.

• Make-up: it is usually several LANs joined together.
• Example: a bank with five branches across Lagos, all connected to each other.

What is a WAN (Wide Area Network)?

A WAN is a network that covers very long distances, such as countries and continents.

• Links used: telephone lines, satellites and undersea cables.
• Example: the Internet is the largest WAN in the world.

How do LAN, MAN and WAN compare?

What are the hardware components of a network?

A network needs four main hardware components besides the computers themselves: the server, the client, the NIC and transmission media.

• Server: a powerful computer that provides data or services to the other computers.
• Client: an ordinary computer or phone that requests data or services from the server.
• Network Interface Card (NIC): a small circuit board or chip in a computer that lets it connect to the network.
• Transmission media: the paths along which data travels, either wired or wireless.

What are the types of transmission media?

There are two types of transmission media: wired (cables) and wireless (radio waves).

• Twisted-pair cable: wired, the common Ethernet cable used in school laboratories and offices.
• Coaxial cable: wired, a cable with a central copper core, used for cable television.
• Fibre-optic cable: wired, carries data as light and works over long distances.
• Wi-Fi and radio waves: wireless, used by phones, laptops and routers.
• Satellite: wireless, carries data over very long distances.

What do hubs, switches and routers do?

Hubs, switches and routers are devices that direct data between computers and between networks.

What is a hub?

• Job: sends incoming data to every computer connected to it.
• Weakness: it is not selective, so it wastes capacity. It is an older device.

What is a switch?

• Job: sends data only to the computer it is meant for.
• Advantage: it is smarter and faster than a hub.

What is a router?

• Job: connects different networks together, such as a school LAN and the Internet.
• Role: it works like a gatekeeper that chooses the path data takes between networks.

How do a hub, a switch and a router differ?

How does a WhatsApp message travel across a network?

A WhatsApp message travels from your phone (the client) through a router and across a WAN to a server.

1. Your phone, the client, sends the message through its network connection.
2. A router passes the data from your local network towards the Internet.
3. The data crosses the WAN (the Internet) over cables, radio links or satellites.
4. A server receives the message and passes it on to the other person’s phone.

Evaluation

1. If you wanted to connect all the schools in one city, would you use a LAN or a MAN?
2. What is the main job of a server?
3. Why is the Internet considered a WAN?
4. If your computer has no NIC, can it join a network? Give a reason.
5. Name two examples of wired transmission media.

Assignment

1. Draw a table showing the full meaning of LAN, MAN and WAN with one example of each. Then explain in one or two sentences each the difference between a hub, a switch and a router.