IGCSE, Edexcel, IB and AP Science Courses | Dr Dabour Hub Academy

Overview

Define an information and communications network and classify LAN, wireless LAN, WAN and the Internet, with the devices that connect them.
Compare client–server with peer-to-peer use of a network, and circuit switching with packet switching.
Read an IPv4 address, explain address exhaustion and DNS, and follow the TCP/IP steps of a transmission.
Explain how a web page and an e-mail travel, calculate transfer time from speed and size, and use cloud services and generative AI correctly.

Computer Networks, Cloud and Prompt Engineering
├── First: networks (concept, types, connection devices)
├── Second: patterns of network use (client-server, peer-to-peer)
├── Third: connection methods (circuit / packet switching)
├── Fourth: IP addresses and domain names (DNS)
├── Fifth: communication protocols and the TCP/IP layers
├── Sixth: how web pages work (URL and browsing steps)
├── Seventh: how e-mail works (SMTP, POP, IMAP)
├── Eighth: data transfer speed and its calculations
├── Ninth: cloud computing and its advantages
└── Tenth: generative AI and prompt engineering

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First: computer networks and their devices

Definitions

An information and communications network is a web-like network that uses communication lines to carry information.
A computer network is a communication system that links information and communication devices — computers and smart phones — so that they exchange data with each other.

Comparison aspect	Main idea	Example	Keywords
LAN	(Local Area Network): links devices inside a limited area	a school or a home	LocalAreaNetworklinks
Wired LAN	data is exchanged through direct connection by cables	—	dataexchangedthroughdirect
Wireless LAN	data is exchanged by radio waves instead of cables	—	dataexchangedradiowaves
WAN	(Wide Area Network): links distant areas and covers a wider range than a LAN	—	WideAreaNetworklinks
The Internet	a world network that connects LANs and WANs to one another	—	worldnetworkconnectsLANs

Comparison aspect	Main idea	Keywords
ISP	(Internet Service Provider): a company that makes Internet access available a contract with one is needed to get the service	InternetServiceProvidercompany
Router	a device that passes data on and re-directs it between different networks	devicepassesdatadirects
Hub	a central connection point to several cables are attached a switch does the same job but forwards each frame only to its destination port	centralconnectionpointseveral
Modem	converts digital data to a signal the line can carry and back again the NIC (network interface card) is the card that puts a device on the network and an access point serves the wireless side of it	convertsdigitaldatasignal

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Second: patterns of using the network

Comparison aspect	Main idea	Keywords
Client–server system	a server is a computer that provides various services to others and the clients are the computers that request those services. Resources and permissions sit centrally so management and security are stronger	computerprovidesvariousservices
Peer-to-peer system	every computer both supplies and consumes resources directly without a dedicated server cheap and simple for a small group but weaker in security and control	everycomputerbothsupplies

Web server→hosts sites and answers browser requests. Mail server sends and stores messages. File server holds shared files. Database server serves queries. Printer server manages one or more printers shared over the network.

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Third: connection methods — circuit and packet switching

Comparison aspect	Main idea	Keywords
Circuit switching	a dedicated connection path is established between the sender and the receiver before transmission starts and the information is exchanged over it — as in a traditional telephone call. The line is reserved even when nothing is being sent	dedicatedconnectionpathestablished
Packet switching	the data is split into packets each travelling independently possibly by different routes and reassembled at the destination. The link is shared and no path is wasted	datasplitpacketstravelling
Why packets	better use of the lines resilience (if one route fails the rest still deliver) and retransmission only of the missing packets	betterlinesresilienceroute
The price of packets	packets may arrive out of order so each carries a header with sequence and address information so the receiver can reorder them	arriveordercarriesheader

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Fourth: IP addresses, domain names and DNS

The IP address

An IP address is a unique identifying number given to every device connected to the Internet; it is the device’s “address” on the network.
IPv4 is divided into four blocks of 8 bits each, separated by a dot and written in decimal from 0 to 255 — for example 192.168.0.1.
Public addresses are reachable on the Internet and are assigned by the authority; private addresses are used inside a local network and are not routable on the Internet.
With the rapid spread of the Internet, new IPv4 addresses are almost exhausted — the solution is IPv6, whose 128-bit addresses give an enormous space, together with address-sharing techniques.

Domain names and DNS

A domain name is the human-readable substitute for an IP address, made of parts read right to left: the top-level (organisation or country), then the second-level name, then the host label such as “www”.
Examples of generic top levels .com commercial, .edu education, .gov government, .org organisation; country codes: .eg Egypt, .jp Japan, .kr South Korea, .cn China.
The DNS (Domain Name System) is the server that translates a domain name into its IP address, and can answer the reverse query.

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Fifth: communication protocols and the TCP/IP model

A protocol is an agreed set of rules that lets devices understand each other; without it two machines cannot communicate.
The TCP/IP suite works in four layers the application layer (the service the user sees, such as HTTP, SMTP, FTP), the transport layer (TCP and UDP: segmentation, ports, reliability), the internet layer (IP: addressing and routing) and the network-access layer (the physical link and its hardware).

Split the data to be sent into packets.
Attach the sender’s and the receiver’s IP addresses in the header of each packet.
Choose the best route for each packet and deliver it to its destination — this is routing.
At the receiving end, if packets are lost their retransmission is requested, then the packets are reordered until the data is complete.

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Sixth: how a web page works

Parts of a URL

The World Wide Web is a system that links an countless number of Internet contents that the user browses as pages.
A URL is read as protocol, then host, then path — in https://www.mext.go.jp/index.html: the protocol https, the host www.mext.go.jp (with the country code jp = Japan), and the requested file /index.html.

The browser asks a DNS server for the IP address matching the domain name.
The DNS server replies with the IP address of the web server.
The browser reaches the web server through that IP address and requests the page.
The web server sends the page data, and it is rendered on the user’s screen.

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Seventh: how e-mail works

E-mail is a system for exchanging messages and data with specific users over the Internet using e-mail addresses.
An address has two parts separated by @ the mailbox (user) name, then the mail server’s domain, e.g. [email protected].

The sender sends the message to his mail server with SMTP.
That server passes the message on to the recipient’s mail server.
The recipient collects it with POP (download and delete from the server) or reads it with IMAP (view what is on the server, messages stay there and synchronise across devices).
Attachments ride as encoded parts of the message, which is why size limits apply to the whole message.

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Eighth: data transfer speed and its calculations

Units and constants

Transfer speed is the number of bits transmitted in one second, measured in bps.
1 Kbps = 1000 bps, 1 Mbps = 1000 Kbps, 1 Gbps = 1000 Mbps.
1 Byte = 8 bits; 1 KB = 1000 B, 1 MB = 1000 KB, 1 GB = 1000 MB.
Transfer time (s) = data size in bits ÷ speed in bps ; data size = speed × time; and actual speed = connection speed × transfer efficiency.

A file of 20 MB over a 40 Mbps link→size = 20 × 1000 × 1000 × 8 = 160,000,000 bits; speed = 40 × 1000 × 1000 = 40,000,000 bps; time = 160,000,000 ÷ 40,000,000 = 4 seconds.

A 1 GB file over a 100 Mbps link whose efficiency is 0.8: actual speed = 100 × 0.8 = 80 Mbps = 80,000,000 bps; size = 1 × 1000 × 1000 × 1000 × 8 = 8,000,000,000 bits; time = 8,000,000,000 ÷ 80,000,000 = 100 seconds.
Always convert megabytes to megabits by multiplying by 8 — forgetting that factor is the classic error.

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Ninth: cloud computing

Comparison aspect	Main idea	Keywords
Cloud computing	is using the Internet to reach files software and data processing without needing heavy local hardware	usingInternetreachfiles
Advantages	access from anywhere and any device no purchase or maintenance of servers automatic backup and recovery on-demand capacity and pay-per-use cost and easy sharing and simultaneous editing	accessanywheredevicepurchase
Points of care	the service needs connectivity speed depends on the provider and the data is held by someone else — so encrypt sensitive files and read the terms	serviceneedsconnectivityspeed
Service models to recognise	infrastructure over the Internet the platform on programs are built and finished software used through a browser	infrastructureoverInternetplatform

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Tenth: generative artificial intelligence

Comparison aspect	Main idea	Keywords
Generative AI	performs mental and cognitive tasks that imitate what a human does using it well improves workflow and raises productivity	performsmentalcognitivetasks
How it works	the model is trained on enormous amounts of text and learns the statistical relations between words then completes new requests by predicting what fits the context	modeltrainedenormousamounts
•	It generates and edits text translates summarises answers questions produces images and writes and debugs program code	generateseditstexttranslates
In learning it acts as a tutor	it explains a difficult concept in simpler words suggests research ideas and turns a lesson into questions for self-testing	explainsdifficultconceptsimpler
•	In programming it can produce a first draft find the error in a snippet and explain the fix — the programmer still verifies and understands the result	programmingproducefirstdraft

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Eleventh: the prompt and prompt engineering

Comparison aspect	Main idea	Keywords
•	A prompt is the instruction you give the model the quality of the output depends on the clarity of the input	promptinstructiongivemodel
A good prompt fixes five things	the role the context the task the constraints (length level language) and the output format (table bullets code block)	rolecontexttaskconstraints
Improve by iteration	give feedback on the first answer and ask for a revised version rather than repeating the same request	givefeedbackfirstanswer
Verify the result	generative models can hallucinate — stating wrong facts and inventing references — so cross-check against trusted sources and never submit generated work as your own without disclosure	generativemodelshallucinatestating

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Exam traps and key takeaways

💡 High-yield traps

In circuit switching the path is reserved before sending; in packet switching no path is reserved and each packet may take another route.
Every IPv4 block is 8 bits and therefore runs 0–255 — a block of 256 is invalid.
Private addresses are not reachable over the Internet; they belong inside the LAN.
DNS does the name → address translation; the router does not.
TCP/IP has four layers, not seven (that is the OSI model).
Transfer speed uses bits while file size is given in bytes multiply the size by 8.
Use 1000, not 1024, for Kbps/Mbps/Gbps and KB/MB/GB in this syllabus.
Actual speed = connection speed × efficiency; a question on “why did the download take longer?” expects this relation.
POP downloads then deletes; IMAP keeps messages on the server — swap them and the answer is wrong.
SMTP sends, it does not receive.
A URL’s country code is the last meaningful label (.eg, .jp); read the domain right to left.
Generative AI predicts text from statistics; it does not look up a verified database of facts.

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Curriculum

ICT (Information and Communication Technology)

Unit 1

Unit 2

Unit 3

Unit 4

Lesson 4: Computer Networks, Cloud Computing and Prompt Engineering