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{{T}}
[[Category:English]]
[[Category:Computer Networks and the Internet]]

{{BR}}
= 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 [[English:World Wide Web|Web]], analyze network performance, and reason about common security risks. The course is designed for Grades 9–10 and connects [[English:Computer science|Computer science]], [[English:Information technology|Information technology]], [[English:Digital literacy|Digital literacy]], mathematics, geography, and English communication.

[[File:Structure of the Internet.svg|500px|frameless|center]]

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.

{{#ev:youtube|https://www.youtube.com/watch?v=3QhU9jd03a0|500|center}}

{{BR}}
= From Devices to Networks =

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== 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.

[[File:Router switch in OSI model.png|500px|frameless|center]]

{{BR}}
== 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.

{{BR}}
== 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.

[[File:RJ45 Ethernet Cable.jpg|500px|frameless|center]]

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.

[[File:Submarine cable map umap.png|500px|frameless|center]]

{{#ev:youtube|https://www.youtube.com/watch?v=ZhEf7e4kopM|500|center}}

{{BR}}
= 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.

[[File:Network topology diagram.png|500px|frameless|center]]

{{BR}}
= Addresses: Finding the Right Device =

{{BR}}
== 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.

{{BR}}
== 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.

{{BR}}
= 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.

[[File:DNS schema.svg|500px|frameless|center]]

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.

{{#ev:youtube|https://www.youtube.com/watch?v=5o8CwafCxnU|500|center}}

{{BR}}
= Packets, Switching, and Routing =

{{BR}}
== 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.

[[File:Packet Switching.gif|500px|frameless|center]]

{{BR}}
== 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.

{{#ev:youtube|https://www.youtube.com/watch?v=AYdF7b3nMto|500|center}}

{{BR}}
= 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:
# [[English:Ethernet|Ethernet]]: Common technology for wired local networks.
# [[English:Internet Protocol|IP]]: Provides addressing and packet forwarding between networks.
# [[English:Transmission Control Protocol|TCP]]: Provides a reliable, ordered byte stream between applications.
# [[English:User Datagram Protocol|UDP]]: Sends datagrams with less transport overhead and without TCP-style delivery guarantees.
# [[English:Domain Name System|DNS]]: Maps domain names to information such as IP addresses.
# [[English:Hypertext Transfer Protocol|HTTP]]: Transfers web requests and responses.
# [[English:HTTPS|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.

{{BR}}
= 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:
# [[English:Application layer|Application layer]]: Services used by applications, including protocols such as HTTP and DNS.
# [[English:Transport layer|Transport layer]]: End-to-end transport, including TCP and UDP.
# [[English:Internet layer|Internet layer]]: IP addressing and routing.
# [[English:Link layer|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.

[[File:OSI Model v1.svg|500px|frameless|center]]

{{BR}}
= 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.

{{#ev:youtube|https://www.youtube.com/watch?v=AEaKrq3SpW8|500|center}}

{{BR}}
= Network Performance =

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== 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.

{{BR}}
== 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.

{{BR}}
= Security and Responsible Use =

{{BR}}
== 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.

{{#ev:youtube|https://www.youtube.com/watch?v=ZghMPWGXexs|500|center}}

{{BR}}
== 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.

{{BR}}
= 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.

{{BR}}
= Interactive Tasks =

{{BR}}
== Quiz: Test Your Knowledge ==

{{MC}}

'''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)

{{E}}
<br>

{{MC}}

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

{{E}}
<br>

{{MC}}

'''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)

{{E}}
<br>

{{MC}}

'''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)

{{E}}
<br>

{{MC}}

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

{{E}}
<br>

{{MC}}

'''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)

{{E}}
<br>

{{MC}}

'''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)

{{E}}
<br>

{{MC}}

'''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)

{{E}}
<br>

{{MC}}

'''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)

{{E}}
<br>

{{MC}}

'''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)

{{E}}
<br>

{{BR}}
== Memory Game ==

<div class="memo-quiz">
{|
|-
| 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
|}
{{E}}
<br>

{{BR}}
== Drag and Drop ==

<div class="lueckentext-quiz">

{| class="wikitable"
! 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
|}
{{E}}

<br>
<br />

{{BR}}
== Crossword Puzzle ==

<div class="kreuzwort-quiz">
{|
|-
| 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?
|}
{{E}}
<br>

{{BR}}
== LearningApps ==

<iframe> https://learningapps.org/index.php?s=Computer+Networks+and+the+Internet </iframe>

{{BR}}
== Cloze Text ==

<quiz display=simple>
{'''Complete the text.'''<br>
|type="{}"}
A computer { network } connects devices so that they can communicate and share resources. The global network of networks is called the { Internet }. A { switch } mainly forwards frames inside a local network. A { router } forwards packets between IP networks. The { DNS } helps translate domain names into information such as IP addresses. Internet data is commonly divided into { packets } for transmission. The { TCP } transport protocol provides reliable ordered delivery. Network communication delay is called { latency }. Secure web communication commonly uses { HTTPS }. The World Wide Web is one { service } that uses the Internet.
</quiz>

<br>

{{BR}}
= Open-Ended Tasks =

{{BR}}
=== Easy ===
# [[English:Network Vocabulary Map|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.
# [[English:Home Network Sketch|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.
# [[English:Packet Journey Comic|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.
# [[English:Internet and Web Explanation|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.

{{BR}}
=== Standard ===
# [[English:Latency Experiment|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.
# [[English:Traceroute Investigation|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.
# [[English:Network Professional Interview|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.
# [[English:Protocol Explainer Video|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.

{{BR}}
=== Advanced ===
# [[English:Network Design Challenge|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.
# [[English:Packet Loss Investigation|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.
# [[English:Infrastructure Research Project|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.
# [[English:Network Policy Proposal|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.

{{:Open Task - Create a MOOC}}

{{BR}}
= Learning Assessment =

# [[English:Diagnose a Slow Connection|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.
# [[English:Compare TCP and UDP|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.
# [[English:Trace a Web Request|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.
# [[English:Evaluate Network Resilience|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.
# [[English:Security Reasoning|Security Reasoning]]: Analyze a phishing scenario in which the page uses HTTPS and explain why encryption alone does not make the page trustworthy.
# [[English:Infrastructure Transfer Task|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.

<br>
<br>

{{BR}}
= 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.

<br>
<br>

{{BR}}
= OERs on the Topic =

<iframe> https://en.m.wikipedia.org/wiki/Computer_network </iframe>

<br>

{{BR}}
= 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.

{| align=center
{{:D-Tab}}
'''[[English:Computer Networks and the Internet|Computer Networks and the Internet]]'''
# [[English:Computer network|Computer network]]
# [[English:Internet|Internet]]
# [[English:Network topology|Network topology]]
# [[English:Ethernet|Ethernet]]
# [[English:Router|Router]]
# [[English:Internet Protocol|Internet Protocol]]
# [[English:Domain Name System|Domain Name System]]
# [[English:Transmission Control Protocol|Transmission Control Protocol]]
# [[English:User Datagram Protocol|User Datagram Protocol]]
# [[English:World Wide Web|World Wide Web]]
# [[English:HTTPS|HTTPS]]
# [[English:Cybersecurity|Cybersecurity]]
|}

[[Category:English]]
[[Category:Computer Networks and the Internet]]
[[Category:Computer science]]
[[Category:Information technology]]
[[Category:Digital literacy]]
[[Category:STEM education]]
[[Category:Grades 9-10]]

{{BR}}
= aiMOOC Projects =
[[Category:English]]
[[Category:Computer Networks and the Internet]]
[[Category:Computer science]]
[[Category:Information technology]]
[[Category:Digital literacy]]
[[Category:STEM education]]
[[Category:Grades 9-10]]
[[Category:AI_MOOC]]
[[Category:GPT aiMOOC]]
{{MT}}

English:Computer Networks and the Internet - Versionsgeschichte

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