Functions, Arrays and Data Structures

Learning Objectives

• Describe LAN, MAN, WAN and PAN in detail.
• Identify network devices and state the function of each.
• Explain how data travels across a network in packets.
• State the benefits of networking in a school.

Starter Scenario

The principal also wants the school's Kuje campus and the Wuse campus in Abuja to share student records. These are two different networking challenges. What kinds of networks would solve each one? The laboratory challenge calls for a Local Area Network, or LAN, that covers one building. The two-campus challenge calls for a wider network, possibly a Metropolitan Area Network, or MAN, or a Wide Area Network, or WAN, depending on the distance and technology used.

Types of Networks in Detail

A computer network is a collection of two or more devices, such as computers, printers, servers and phones, connected together by cables or wireless signals so they can share resources and communicate. Networks can be as small as two phones connected by Bluetooth or as large as the internet connecting billions of devices worldwide. The size and purpose of the network determine its type.

A Local Area Network, or LAN, connects devices in a limited area such as a single room, a building, or a school campus. LANs are the most common type of network in schools and offices. Key features of a LAN include short distances between devices, high data transfer speeds, the use of Ethernet cables or Wi-Fi, and being owned and managed by one organisation. In a typical school LAN, computers in the laboratory connect to a central switch, which connects to a router that provides internet access. A server in the school may store shared files and student accounts.

A Metropolitan Area Network, or MAN, covers a larger area than a LAN but smaller than a WAN, typically spanning a city. For example, a university with campuses in different parts of Abuja might use a MAN to connect them. A Wide Area Network, or WAN, covers a very large area, such as a country or the entire world. The internet is the largest WAN in existence. Companies with offices in different countries often set up private WANs to share data securely. A Personal Area Network, or PAN, is even smaller than a LAN, covering only the space around one person, such as a phone connected to a smartwatch by Bluetooth.

Network Devices

A Network Interface Card, or NIC, is a hardware component that allows a device to connect to a network. Every computer has a NIC, either built into the motherboard or inserted as an expansion card. The NIC converts data into electrical signals for wired networks or radio waves for wireless networks. Without a NIC, a computer cannot join a network at all.

A switch connects devices within a single LAN and directs data to the correct destination. When a switch receives data, it reads the destination address and sends the data only to the intended device. This is faster, more efficient and more secure than a hub. A hub, by contrast, sends data to every connected device regardless of destination, creating unnecessary traffic. Because of this difference, switches have largely replaced hubs in modern networks.

A router forwards data between different networks. When a school's internal LAN needs to reach the internet, the router is the device that connects the two. A modem converts digital data into signals suitable for transmission over telephone lines, cable lines or fibre optic lines, and converts incoming signals back into digital data. An access point allows wireless devices such as phones and tablets to connect to a wired network using Wi-Fi. A server is a powerful computer that stores shared files, runs applications and provides services to other computers on the network. A firewall monitors and filters network traffic to protect against threats.

How Data Travels Across a Network

When data is sent across a network, it follows a series of steps. First, the sending device creates the data, such as a message, file or request. Second, the Network Interface Card converts the data into electrical, optical or radio signals. Third, the data is broken into smaller pieces called packets. Fourth, each packet is labelled with a source address, which is the sender, and a destination address, which is the receiver. Fifth, network devices such as switches and routers read the destination address and forward the packet along the best path. Sixth, when all packets arrive at the destination, they are reassembled into the original message. This process happens in milliseconds and is repeated billions of times every second across networks around the world.

Benefits of Networking

Resource sharing allows one printer, scanner or internet connection to serve many users, reducing cost. Centralised data storage on a server makes files accessible to all authorised users from any device on the network. Fast communication through email, instant messaging and video calls improves collaboration between teachers and learners. Shared software licences reduce the need to install expensive programs on every individual computer. Networked security tools such as firewalls and antivirus software protect all connected devices from threats. Cloud backup and disaster recovery become possible when devices are connected to a reliable network. Networks enable online learning platforms, giving learners access to resources beyond the classroom.

Network Hardware Architectures and Network Terms

The way a network is organised is called its architecture. The two main architectures are client-server and peer-to-peer. In a client-server network, one powerful computer called the server stores files, runs software and shares resources, while the other computers, called clients, request those services. For example, a school laboratory server holds the shared project files and every learner's computer asks the server when it needs a document or a printer.

In a peer-to-peer network, all computers are equal. Every machine can both send and receive files directly to and from the others, with no central server. This architecture works well for small groups such as two or three friends sharing homework files at home, but it becomes harder to manage as the number of computers grows.

Every network also has common terms. A sender is the device that starts a message, a receiver is the device that gets it, the medium is the path the data travels on (a copper cable, a fibre-optic line or radio waves), and a node is any device connected to the network, such as a computer, printer or phone.

Client-server: one server serves many clients; used by banks, schools and offices.

Peer-to-peer: computers share directly without a central server; good for small home networks.

Sender: the device that starts the message.

Receiver: the device that receives the message.

Medium: the cable or wireless signal that carries the data.

Node: any connected device, including printers and phones.

Network Interconnection Devices in Detail

Devices that join different parts of a network together are called interconnection devices. A hub is the simplest. It connects several computers, but when data arrives it sends a copy to every device on the network, which wastes traffic. A switch improves on the hub by reading the destination address and sending data only to the intended computer.

A router connects two or more different networks and chooses the best path for data to travel, which is why a home router joins the local Wi-Fi network to the internet supplied by a provider such as MTN, Glo or Airtel. A modem (short for modulator-demodulator) changes digital signals from the computer into signals that can travel over telephone or cable lines and back again, giving the router its internet connection.

Longer networks need extra help. A repeater receives a weakening signal, strengthens it and sends it onward so that data can travel a longer distance without fading. A bridge connects two separate parts of the same network and only forwards data that is meant for the other side, which reduces unnecessary traffic.

A gateway is the doorway between networks that use different rules, for example a school LAN connecting to the wider internet. In many small networks the router, modem and gateway are combined in a single box. Each interconnection device has a distinct role, as the list below shows.

Hub: connects devices and broadcasts data to every device.

Switch: connects devices and sends data only to the correct device.

Router: joins different networks and routes data between them.

Modem: converts signals between the computer and the internet line.

Repeater: boosts a weakening signal over long distances.

Bridge: joins two parts of the same network and filters traffic.

Gateway: translates between networks that use different rules.

Core Internet Protocols and Addressing

Networks send data using agreed sets of rules called protocols. The most important family is TCP/IP. TCP (Transmission Control Protocol) breaks data into packets, numbers them and reassembles them at the destination, while IP (Internet Protocol) labels each packet with the sender's and receiver's internet addresses so it can be routed across the world.

Application protocols carry the everyday services. HTTP and its secure version HTTPS move web pages between servers and browsers, and HTTPS encrypts the exchange to protect data such as passwords and bank details. FTP (File Transfer Protocol) uploads and downloads files. SMTP (Simple Mail Transfer Protocol) sends email messages between mail servers.

People cannot easily remember long numeric addresses, so the Domain Name System (DNS) acts as the address book of the internet. It translates a name such as www.schoolname.ng into its numeric IP address. The current address system, IPv4, uses addresses such as 192.168.1.1, and the newer IPv6 uses much longer addresses to provide room for billions more devices. Every network device also carries a unique hardware label, its MAC address, which identifies the device on a local network.

TCP/IP: the rule family that fragments, addresses and reassembles data packets.

HTTP and HTTPS: rules for moving web pages; HTTPS adds encryption.

FTP: transfers files between computers.

SMTP: sends email messages between mail servers.

DNS: changes names like www.schoolname.ng into IP addresses.

IPv4 and IPv6: internet address systems; IPv6 is newer and larger.

MAC address: the unique hardware address of each network device.

Practical Work

1. Draw a simple school LAN showing computers, a switch and a router.
2. Make a table comparing LAN, MAN and WAN by area, speed and cost.
3. List the steps by which data travels from one computer to another.
4. List four benefits of networking a school computer laboratory.

Scenario-Based Questions

1. What type of network should the school set up, and what two devices does it need to connect the computers to each other and to the internet?
2. A small printing press has offices in Ikeja and in Victoria Island, both in Lagos. The two offices need to share files daily. What type of network connects them, and how does it differ from a LAN?
3. A bank in Abuja connects branches in Kano, Port Harcourt and Enugu. What type of network is this, and what is one advantage and one limitation compared to a LAN?
4. In a computer lab, a switch receives a data packet addressed to Computer 15. Explain how the switch ensures the packet reaches Computer 15 and not the other 29 computers.
5. A school replaces its old hub with a new switch. A teacher asks why the switch is better. Give two reasons by comparing how a hub and a switch handle incoming data.
6. A small business owner wants to share one internet connection, one printer and one scanner among five staff computers. List the minimum network devices needed and explain the function of each.
7. Two schools in the same street each have their own LAN. They want to share a single high-speed internet link. What device do they need to connect the two LANs together, and what type of network would the combined setup form?

Lesson objectives

By the end of the week, learners should be able to:

1. Define a function and state its input and output parameters.
2. Call a function by passing values correctly.
3. Declare a one-dimensional array and index elements properly.
4. Use an array to store multiple values in sequence.
5. Trace a function call returning a value correctly.

Key vocabulary

• Function: a reusable block performing one computation.
• Parameter: an input variable receiving a passed value.
• Return: giving a value back to the caller after computation.
• Array: a sequence stored in consecutive memory slots.
• Index: the position number of an element in the array.
• One-dimensional array: an array storing values along one axis.
• Reusable block: a section of code called multiple times with different inputs.
• Trace: predicting results by stepping through code.

Common misconceptions

• "Functions replace loops." Functions handle single operations; loops handle repetition.
• "An array stores text." Arrays store homogeneous values; text often sits in a string type separately.
• "Index starts at zero always." Zero-based indexing is common but some languages start elsewhere.

Teacher activities

1. Starter: ask why repeated tasks should use functions rather than duplication.
2. Define a function and give input and output parameters explicitly.
3. Demonstrate calling a function by passing values.
4. Declare a one-dimensional array and index elements step by step.
5. Demonstrate calling a function returning a computed value.
6. Close with the function-trace task and exit question.

Student activities

1. Answer the starter and state the benefit of reusing functions.
2. Define a function in their own words and name input and output parameters.
3. Call a function by passing the correct values.
4. Declare a one-dimensional array and index elements properly.
5. Trace a function call and write the returned value.
6. Answer the exit question comparing functions with loops in one sentence.

Practical / learning evidence

A declared array with indexing exercises, a function call with a returned value, and a function-trace worksheet. Submit all three for marking.

Resources and preparation

Computers with the interpreter, blank arrays and sample tracing cards. Prebuild the interpreter in a read-only folder. Disable Caps Lock before typing. Verify the computer starts reliably.

Assessment for learning

Inspect the array declaration for correct indexing. Check the function return value matches the traced result. Mark the function trace for correct parameter passing. Flag any learner who thinks functions replace loops entirely.

Inclusion and homework

Provide the array template prefilled for learners who need scaffolding and allow oral function calls. Extend confident learners with two arrays and a function that returns an array element. Homework: write a second function that takes an array and returns the sum of its elements.