In simple terms
A friendly intro before the formal notes — no formulas yet.
How Computers Talk to Each Other
A computer network is simply a collection of connected devices that can share resources and data. This communication is governed by a set of rules, called protocols, ensuring that information is sent and received correctly.
Imagine a global postal service. To send a letter, you don't just throw it out the window. You put it in an envelope (a data packet), write the recipient's address (IP address) and your return address, and trust the postal workers (routers and switches) to follow specific procedures (protocols) to deliver it. The network is the entire postal system, from post boxes to delivery vans and sorting offices, all working together to get your message to its destination.
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A device needs to send data. This data is broken down into smaller, manageable chunks called packets.
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Each packet is given a 'header' containing control information, like the source and destination IP addresses, much like an address on an envelope.
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The packets are transmitted over a medium, such as a copper cable, fibre optic line, or wireless radio waves (Wi-Fi).
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Receiving devices collect the packets, check for errors, and reassemble them in the correct order to reconstruct the original data.
Explore the concept
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Full topic notes
Formal explanation with the rigour you need for the exam.
The Building Blocks of a Network
At its core, a network consists of two or more connected computers that can share resources (like printers or a file server), exchange files, or allow electronic communications. The devices on a network can be categorised as clients, which request services, and servers, which provide them. The connection between these devices is managed by specialised hardware and established over a transmission medium.
Clients & Servers: A client (e.g., your laptop) requests information or a service. A server (e.g., a web server) provides that information or service.
Network Interface Card (NIC): A hardware component that connects a computer to a computer network.
Transmission Media: The physical path between transmitter and receiver. This can be wired (e.g., Twisted Pair Cable, Coaxial Cable, Fibre Optic Cable) or wireless (e.g., radio waves for Wi-Fi, microwaves).
Hub: A basic networking device that connects multiple devices in a LAN, broadcasting all data to all ports. Largely obsolete.
Switch: An intelligent device that connects devices in a LAN, forwarding data packets only to the intended recipient's port.
Router: A device that forwards data packets between different computer networks, for example, connecting your home LAN to the internet (a WAN).
Measuring Network Performance
Simply connecting devices is not enough; the performance of the network is critical. We use several key metrics to quantify and evaluate how well a network is performing. The most common are bandwidth, throughput, and latency.
Bandwidth: The theoretical maximum data transfer rate of a network connection. It's measured in bits per second (bps), kilobits per second (kbps), megabits per second (Mbps), or gigabits per second (Gbps). Think of it as the width of a pipe.
Throughput: The actual measured data transfer rate, which is almost always lower than the bandwidth due to factors like network congestion, protocol overhead, and hardware limitations. It's the actual flow of water through the pipe.
Latency: The delay in data communication. It's the time it takes for a single bit of data to travel from the source to the destination. Measured in milliseconds (ms). High latency causes noticeable lag.
Protocols: The Rules of Communication
For devices from different manufacturers to communicate, they must agree on a common set of rules, or protocols. These protocols define everything from how to initiate a connection to how errors are handled. The most dominant suite of protocols is the TCP/IP model, which governs communication on the internet.
TCP (Transmission Control Protocol): A connection-oriented protocol that ensures reliable data delivery. It breaks data into packets, numbers them, and reassembles them at the destination, re-sending any lost packets. Used for web browsing, file transfer, and email.
IP (Internet Protocol): Responsible for addressing and routing packets from the source host to the destination host across one or more networks.
HTTP (Hypertext Transfer Protocol): The foundation of data communication for the World Wide Web. It defines how messages are formatted and transmitted between web browsers and web servers.
FTP (File Transfer Protocol): A standard network protocol used for the transfer of computer files between a client and server on a computer network.
SMTP (Simple Mail Transfer Protocol): The standard protocol for sending email from a client to a mail server.
Examiners love to ask you to differentiate between concepts. Be prepared to explain the difference between: a hub and a switch; a router and a switch; bandwidth and throughput; latency and bandwidth; TCP and UDP (User Datagram Protocol - a connectionless protocol that is faster but less reliable than TCP).
Worked examples
See the formulas applied — reveal one step at a time, like the exam.
A user wants to download a 4 Gigabyte (GB) film. The network connection has a advertised bandwidth of 80 Mbps. Assuming ideal conditions (throughput equals bandwidth), calculate the download time in minutes and seconds. Note: 1 GB = 1024 MB, 1 MB = 1024 KB, 1 KB = 1024 Bytes, and 1 Byte = 8 bits.
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This question requires careful unit conversion. IB exams often use powers of 10 for prefixes (1 GB = 1000 MB), but we will use the binary prefixes (powers of 2) as specified, which is common in OS file sizes.
A real-time online game sends small 128-byte packets of game state information. Network A has a latency of 150 ms and 1 Gbps bandwidth. Network B has a latency of 10 ms and 50 Mbps bandwidth. Which network would provide a better gaming experience and why? Justify your answer by calculating the total time to send one packet for each network.
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The key here is to identify that online gaming is latency-sensitive, not bandwidth-intensive.
How it all connects
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Tap a linked idea to see how it connects back to the main topic — that connection is what examiners reward.
Glossary
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Quick check
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Revision flashcards
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What is a computer network?
A collection of interconnected computing devices that can exchange data and share resources. For example, a Local Area Network (LAN) in a school or a Wide Area Network (WAN) like the internet.
Key takeaways
Review these before you close the topic — retrieval beats re-reading.
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Clients & Servers: A client (e.g., your laptop) requests information or a service. A server (e.g., a web server) provides that information or service.
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Network Interface Card (NIC): A hardware component that connects a computer to a computer network.
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Transmission Media: The physical path between transmitter and receiver. This can be wired (e.g., Twisted Pair Cable, Coaxial Cable, Fibre Optic Cable) or wireless (e.g., radio waves for Wi-Fi, microwaves).
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Hub: A basic networking device that connects multiple devices in a LAN, broadcasting all data to all ports. Largely obsolete.
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Switch: An intelligent device that connects devices in a LAN, forwarding data packets only to the intended recipient's port.
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Router: A device that forwards data packets between different computer networks, for example, connecting your home LAN to the internet (a WAN).
Practice — then mark it
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Test Your Knowledge on Network Fundamentals
Test Your Knowledge on Network Fundamentals
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