Computer Networks and the Internet

Introduction

Every time you send a message, stream a video, play an online game, or open a website, computers exchange data across networks. A computer network is a group of connected devices that can communicate and share resources. The Internet is a global network of networks: many independently operated networks use common standards so that data can travel between them.

In this aiMOOC, you will learn how devices connect, how data is divided into packets, how addresses and names help information reach the right destination, and how protocols make communication reliable and secure. You will also learn to distinguish the Internet from the Web, analyze network performance, and reason about common security risks. The course is designed for Grades 9–10 and connects Computer science, Information technology, Digital literacy, mathematics, geography, and English communication.

The diagram above shows that the Internet is not one single machine or company. It is built from access networks, Internet service providers, Internet exchange points, and many interconnected autonomous networks.

From Devices to Networks

End Devices and Network Devices

An end device or host is a device that sends or receives data, such as a laptop, smartphone, server, printer, or game console. Between end devices are network devices that forward traffic.

A switch connects devices within a local network and forwards Ethernet frames toward the correct port. A router connects different IP networks and forwards packets toward their destination. A wireless access point lets wireless devices join a network, while a home router often combines routing, switching, Wi-Fi, and other services in one box.

You can think of these devices as having different jobs. Hosts create and consume data. Switches organize traffic inside a local network. Routers move traffic between networks.

Network Size and Scope

A local area network or LAN covers a limited area such as a classroom, home, office, or school building. A wide area network or WAN connects networks across larger geographic areas. The Internet is the largest example of interconnected networks, but it is not controlled as one giant LAN.

Networks may be connected by copper cable, fiber-optic cable, radio waves, microwave links, or satellite links. Different media have different capacities, ranges, costs, and delays.

Physical Media: Copper, Fiber, and Wireless

Copper Ethernet cables carry electrical signals. Fiber-optic cables carry pulses of light and can transmit very large amounts of data over long distances. Wi-Fi uses radio waves, which makes mobility possible but also means that walls, distance, interference, and shared airtime can affect performance.

Large parts of international Internet traffic travel through fiber-optic cables on land and under the sea. Wireless connections are important at the edges of the Internet, but long-distance global links still depend heavily on physical infrastructure.

Network Topologies

A network topology describes how devices and links are arranged. In a star topology, devices connect to a central switch or access point. In a bus topology, devices share one main communication path. In a ring topology, each device is linked in a circular pattern. Real networks can use combinations of these structures.

Topology affects cost, reliability, troubleshooting, and how failures spread. A star network is common in modern Ethernet LANs because one cable failure usually affects only one device, although failure of the central switch can affect many devices.

Addresses: Finding the Right Device

MAC Addresses

An Ethernet network uses MAC addresses at the data-link level. A switch learns which MAC addresses are reachable through which ports and uses this information to forward frames inside the local network.

A MAC address is useful for local delivery, but Internet communication needs an addressing system that works across many connected networks.

IP Addresses

The Internet Protocol or IP provides logical addressing and forwarding across networks. An IP address identifies an interface on an IP network. Routers examine destination IP addresses to decide where to send packets next.

IPv4 addresses are 32 bits long. Because the number of Internet-connected devices grew enormously, techniques such as private addressing and network address translation became common. IPv6 uses 128-bit addresses and provides a vastly larger address space.

You do not need to memorize address ranges for this course. What matters is understanding that an IP address is used for routing packets between networks, while a MAC address is mainly used for delivery on a local link.

Domain Names and DNS

Humans prefer names such as example.org to long numerical addresses. The Domain Name System or DNS is a distributed naming system that helps translate domain names into information such as IP addresses.

DNS is hierarchical. A lookup may involve a recursive resolver and authoritative DNS servers. Caching allows previously obtained answers to be reused for a limited time, which can make later lookups faster and reduce repeated traffic.

A useful analogy is a contact list: you remember a person's name, while the system finds the number needed to reach them. The analogy is not perfect because DNS is distributed and hierarchical rather than one central directory.

Packets, Switching, and Routing

Why Data Is Divided into Packets

Instead of reserving one complete path for one conversation, Internet data is usually divided into smaller units called packets. Each packet carries control information as well as part of the data being transmitted.

Packet switching lets many users share network links efficiently. Packets from different conversations can be interleaved on the same links. They may experience different delays, and in some situations packets can be lost or arrive out of order.

Datei:Packet Switching.gif

Routing and Hops

A router forwards an IP packet from one network toward another. The packet may pass through several routers, called hops, before reaching its destination. Routers use routing information to choose a next hop; they do not need a complete physical map inside each individual packet.

If a link or route becomes unavailable, routing systems may eventually choose another path. This ability contributes to resilience, although it does not guarantee that every failure is invisible to users.

Protocols: Rules for Communication

A protocol is an agreed set of rules for communication. Networks work because different devices and software systems follow compatible protocols.

Important examples include:

Ethernet: Common technology for wired local networks.
IP: Provides addressing and packet forwarding between networks.
TCP: Provides a reliable, ordered byte stream between applications.
UDP: Sends datagrams with less transport overhead and without TCP-style delivery guarantees.
DNS: Maps domain names to information such as IP addresses.
HTTP: Transfers web requests and responses.
HTTPS: Uses HTTP over TLS so that web traffic can be encrypted and authenticated in transit.

Protocols work together. For example, a browser may use DNS to find an address, IP to move packets across networks, TCP or another transport mechanism to carry application data, and HTTPS to protect communication with a web server.

Layered Models

Engineers use layers to separate networking tasks into manageable parts. The TCP/IP model describes the practical protocol suite used by the Internet. The OSI model is a seven-layer conceptual reference model often used for learning, design discussions, and troubleshooting.

A simplified comparison is useful:

Application layer: Services used by applications, including protocols such as HTTP and DNS.
Transport layer: End-to-end transport, including TCP and UDP.
Internet layer: IP addressing and routing.
Link layer: Local delivery over technologies such as Ethernet or Wi-Fi.

The models are not identical, and real implementations do not always fit perfectly into neat boxes. The value of layering is that you can reason about one part of communication without treating the entire network as one undivided problem.

Datei:OSI Model v1.svg

The Internet and the World Wide Web

The Internet is the global networking infrastructure and protocol system that connects networks. The World Wide Web is one service that uses the Internet. The Web consists of linked resources accessed with technologies such as URLs, HTTP, HTTPS, browsers, and web servers.

Other Internet services include email, voice and video calling, multiplayer games, file transfer, cloud applications, and many machine-to-machine services. Saying that the Internet and the Web are the same is therefore incorrect.

Network Performance

Bandwidth, Throughput, and Latency

Bandwidth describes a link's capacity to carry data, usually expressed in bits per second. Throughput is the useful rate actually achieved during a transfer. Throughput can be lower than the theoretical bandwidth because of congestion, protocol overhead, interference, device limits, server limits, or other traffic.

Latency is the delay between sending information and receiving a response or result. A high-bandwidth connection can still have noticeable latency. Online games, voice calls, and remote control systems can be especially sensitive to delay.

Packet Loss and Jitter

Packet loss occurs when some packets do not reach their destination. Jitter is variation in packet delay over time. Real-time applications can be affected by both. TCP can retransmit missing data, which supports reliability but can increase delay. Some real-time applications use UDP because timely delivery can matter more than retransmitting every missing unit.

When diagnosing performance, do not assume that one speed-test number explains everything. Consider bandwidth, throughput, latency, loss, Wi-Fi conditions, server location, congestion, and the application itself.

Security and Responsible Use

Encryption and HTTPS

When a website uses HTTPS, TLS is used to protect data in transit between your browser and the server. Encryption helps prevent outsiders on the path from easily reading the content. Authentication helps your browser verify the server's identity through certificates.

HTTPS does not prove that a website is trustworthy in every way. A malicious site can also use HTTPS. You still need to check the domain name, think critically about requests for personal information, and follow school or workplace security rules.

Common Risks and Good Habits

Common risks include phishing, malware, weak or reused passwords, unsafe downloads, insecure software, and accidental sharing of sensitive information. Good habits include using strong unique passwords, enabling multi-factor authentication where available, keeping software updated, checking links and domain names carefully, and reporting suspicious activity through the correct channel.

When you perform networking experiments for this course, use only your own devices, a school lab, or systems your teacher has explicitly approved. Do not scan, probe, or attempt to bypass access controls on networks you do not have permission to test.

A Packet's Journey: Putting the Ideas Together

Imagine that you enter a secure website address in a browser:

Your device connects to a local network through Ethernet or Wi-Fi.
DNS helps your device obtain an IP address for the website's service.
Your device creates application data and passes it through transport and Internet protocols.
The data is divided into packets and placed into frames for the local link.
A switch or wireless access point helps move local traffic toward the router.
Routers forward packets across multiple networks using destination IP addresses.
The destination server processes the request and sends response data back.
HTTPS protects the application exchange in transit when TLS is correctly established.

This sequence is simplified, but it connects the central ideas: physical links carry signals, link technologies handle local delivery, IP supports internetwork routing, transport protocols support application communication, DNS handles names, and application protocols define what the communicating programs are trying to do.

Interactive Tasks

Quiz: Test Your Knowledge

What best describes the Internet? (A global network of interconnected networks) (!A single worldwide computer) (!Only the collection of all websites) (!A private network inside one building)

Which device mainly forwards packets between different IP networks? (Router) (!Keyboard) (!Monitor) (!Printer)

What is the main purpose of DNS? (To map domain names to information such as IP addresses) (!To increase screen resolution) (!To charge a laptop battery) (!To compress every Internet packet)

Why is data commonly divided into packets on the Internet? (To let traffic share network links efficiently) (!To make every message follow one permanent cable) (!To remove the need for addresses) (!To guarantee zero delay)

Which protocol provides logical addressing and packet forwarding across networks? (IP) (!HTML) (!USB) (!JPEG)

Which statement about TCP is correct? (It provides reliable ordered transport) (!It is a type of fiber optic cable) (!It replaces all IP addresses with names) (!It is the same thing as Wi Fi)

What does latency describe? (Delay in network communication) (!The physical color of a cable) (!The number of files on a server) (!The size of a keyboard)

What is the relationship between the Web and the Internet? (The Web is a service that uses the Internet) (!The Web is the physical cable inside every router) (!The Internet is only one website) (!The Web and the Internet are always identical terms)

What does HTTPS mainly add to HTTP communication? (Protection using TLS) (!A larger computer screen) (!A guarantee that every website is honest) (!A replacement for all routers)

Which statement best compares bandwidth and throughput? (Bandwidth is capacity while throughput is the rate actually achieved) (!Bandwidth is a password while throughput is a username) (!Bandwidth is a domain name while throughput is an IP address) (!Bandwidth and throughput always have exactly the same value)

Memory Game

Router	Forwards packets between IP networks
Switch	Forwards frames within a local network
DNS	Resolves domain names to network information
Latency	Delay in communication
Packet	Small unit of data sent through a network
Fiber	Medium that carries data using light

Drag and Drop

Match the correct terms.	Topic
MAC address	Local link identification
IP address	Logical network addressing
DNS	Domain name resolution
TCP	Reliable ordered transport
HTTPS	Protected web communication

Crossword Puzzle

Ethernet	Which common wired LAN technology sends frames across local links?
Router	Which device forwards packets between IP networks?
Packet	What small unit carries part of a message across a packet-switched network?
Protocol	What is an agreed set of communication rules called?
Latency	What term means communication delay?
Firewall	What security system can filter network traffic according to rules?

LearningApps

Cloze Text

A computer

connects devices so that they can communicate and share resources. The global network of networks is called the

. A

mainly forwards frames inside a local network. A

forwards packets between IP networks. The

helps translate domain names into information such as IP addresses. Internet data is commonly divided into

for transmission. The

transport protocol provides reliable ordered delivery. Network communication delay is called

. Secure web communication commonly uses

. The World Wide Web is one

that uses the Internet.

Open-Ended Tasks

Easy

Network Vocabulary Map: Create a one-page concept map using at least ten course terms and draw labeled connections between devices, addresses, protocols, and services.
Home Network Sketch: Draw a privacy-safe diagram of a typical home or classroom network using generic labels rather than real passwords, account names, or sensitive addresses.
Packet Journey Comic: Produce a six-panel comic showing how a browser request can travel from a device through a local network and routers to a web server.
Internet and Web Explanation: Write a short explanation for a younger student that clearly distinguishes the Internet from the World Wide Web and includes two examples of non-Web Internet services.

Standard

Latency Experiment: With teacher approval, use a standard ping tool on approved public hosts, record several round-trip times, calculate a simple average, and explain why the results may vary.
Traceroute Investigation: With teacher approval, run traceroute or tracert to an approved destination, describe the visible sequence of hops, and explain what the tool can and cannot prove about the physical route.
Network Professional Interview: Interview a school IT staff member or another network professional about reliability, security, and troubleshooting, then summarize three insights in your own words.
Protocol Explainer Video: Create a two-minute video that explains how DNS, IP, TCP or UDP, and HTTPS can work together when a user accesses an online service.

Advanced

Network Design Challenge: Design a network for a small school club room, justify your choice of wired and wireless connections, and explain how your design addresses performance, reliability, security, and cost.
Packet Loss Investigation: Build a teacher-approved simulation or use a classroom network simulator to compare reliable and real-time traffic under packet loss, then explain the trade-offs you observe.
Infrastructure Research Project: Research one submarine fiber-optic cable or Internet exchange point from trustworthy sources and present how geography, redundancy, ownership, and maintenance influence connectivity.
Network Policy Proposal: Write a concise acceptable-use and security proposal for a fictional school network, defending your choices with technical reasoning about passwords, updates, permissions, encryption, and incident reporting.

Learning Assessment

Diagnose a Slow Connection: Given a scenario with high bandwidth but high latency and packet loss, explain which symptoms users may notice and propose a justified troubleshooting sequence.
Compare TCP and UDP: Choose suitable transport behavior for file transfer and live voice communication, explain the trade-offs, and state why no single choice is best for every application.
Trace a Web Request: Explain how local networking, DNS, IP routing, transport, and HTTPS cooperate from the moment a user enters a web address until a response arrives.
Evaluate Network Resilience: Compare two hypothetical topologies after a link or central-device failure and argue which design better fits a stated school use case.
Security Reasoning: Analyze a phishing scenario in which the page uses HTTPS and explain why encryption alone does not make the page trustworthy.
Infrastructure Transfer Task: Explain how the same networking principles apply to a new context such as a hospital, factory, sports venue, or remote research station, identifying at least three design priorities.

Evidence of Learning

Strong evidence of learning includes accurate use of networking vocabulary; a correct distinction between the Internet and the Web; the ability to explain the roles of hosts, switches, routers, access points, DNS, IP, TCP, UDP, HTTP, HTTPS, and TLS; and the ability to reason about packet switching, routing, addressing, bandwidth, throughput, latency, packet loss, and security.

Your products can include network diagrams, concept maps, experiment records, interview summaries, videos, research presentations, and design proposals. High-quality work shows that you can connect ideas rather than list isolated facts, interpret evidence from simple network measurements, communicate technical explanations clearly, follow permission and privacy rules during practical work, and transfer networking principles to unfamiliar real-world situations.

OERs on the Topic

Linked Learning Areas

The topic connects physical infrastructure, digital communication, software protocols, mathematics, cybersecurity, geography, and communication skills. Understanding these links helps you move from simply using online services to explaining how networked systems function and how design choices affect reliability, speed, access, and safety.

Computer Networks and the Internet