In simple terms
A friendly intro before the formal notes — no formulas yet.
Sending Data Like a Jigsaw Puzzle
Packet switching is the method computers use to send large files over a network by breaking them into smaller, manageable pieces called packets. These packets are sent independently and reassembled at the destination, making the transfer efficient and robust.
Imagine you need to send a very large, rare book to a friend. Instead of risking sending the whole book in one box (which could get lost), you photocopy each page, put each page in a separate, numbered envelope with your friend's address, and post them all. Even if some envelopes take a different route or arrive out of order, your friend can use the page numbers to reassemble the entire book. Packet switching works in a very similar way for digital data.
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A large file is broken down into smaller chunks of data.
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Each chunk is placed into a 'packet' with a header containing the destination address, source address, and its sequence number.
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The packets are sent across the network, potentially taking different routes to the destination.
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At the destination, the packets are reassembled in the correct order using their sequence numbers to recreate the original file.
Explore the concept
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Full topic notes
Formal explanation with the rigour you need for the exam.
Modes of Data Transmission
Before data can be sent, the communicating devices must agree on the rules of transmission. These rules can be categorised by directionality (how data flows) and by the number of bits sent simultaneously.
Furthermore, data can be sent bit-by-bit or in groups:
Simplex: One-way communication. Think of a radio broadcast. Data flows from the transmitter to the receiver, but not back.
Half-Duplex: Two-way communication, but only one direction at a time. Walkie-talkies are a classic example; you must say 'over' to signal the other person can speak.
Full-Duplex: Two-way communication, happening simultaneously. A modern phone call allows both parties to speak and be heard at the same time.
Serial Transmission: Bits are sent one after another down a single channel. This is slower but more reliable over long distances as there's no risk of bits arriving out of sync ('skew'). USB (Universal Serial Bus) is a prime example.
Parallel Transmission: Multiple bits are sent simultaneously over multiple channels. This is much faster for short distances but is expensive and susceptible to interference and skew over longer distances, as the bits may not arrive at the exact same time.
Packet Switching: The Internet's Postal Service
Large files are not sent as a single, continuous stream. Instead, they are broken down using a method called packet switching. This process is managed by protocols, most famously the TCP/IP suite. Each packet is like a small parcel containing a piece of the overall message. It has a header with crucial information like the destination IP address, source IP address, and a sequence number. The main data is called the payload. A trailer may be added for error checking.
Wireless Networking Essentials
Wireless Local Area Networks (WLANs), commonly known as Wi-Fi, allow devices to connect to a network without physical cables. This convenience comes with security challenges. Several components work together to manage a wireless network.
SSID (Service Set Identifier): This is the network's name that is broadcast to users. It can be hidden for a minor security improvement, but it is not a robust security measure on its own.
MAC Address Filtering: Every network-capable device has a unique MAC address. A router can be configured to only allow devices with specific MAC addresses to connect. This provides a layer of security, but MAC addresses can be 'spoofed' (imitated) by determined attackers.
Encryption: This is the most critical part of wireless security. Data is scrambled before transmission and unscrambled by the receiver. WPA2 (Wi-Fi Protected Access 2) is a strong and widely used encryption standard. Its successor, WPA3, offers even more robust security. Older standards like WEP are insecure and should not be used.
In exam questions involving calculations, always show your working clearly, step-by-step. Pay very close attention to units (e.g., bits vs bytes, Mb vs MB, KiB vs KB). 1 byte = 8 bits. 'b' usually means bits (e.g., Mbps = megabits per second), while 'B' usually means bytes (e.g., MB = megabytes). Be precise!
Worked examples
See the formulas applied — reveal one step at a time, like the exam.
A 2 MiB image file is transmitted using packet switching. Each packet has a payload size of 1024 bytes and a header size of 40 bytes. Calculate the total amount of data transmitted, including all headers, in KiB. (Note: 1 MiB = 1024 KiB, 1 KiB = 1024 bytes).
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Convert file size to bytes:
Calculate the theoretical minimum time, in seconds, to download a 450 MiB file over a network connection with a speed of 80 Mbps. (Note: 1 MiB = bytes, 1 Mbps = bits per second).
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Convert file size from MiB to bits:
How it all connects
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Glossary
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Quick check
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Revision flashcards
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What is Simplex data transmission?
Data transmission in one direction only. For example, from a computer to a printer, or a radio broadcast.
Key takeaways
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Simplex: One-way communication. Think of a radio broadcast. Data flows from the transmitter to the receiver, but not back.
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Half-Duplex: Two-way communication, but only one direction at a time. Walkie-talkies are a classic example; you must say 'over' to signal the other person can speak.
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Full-Duplex: Two-way communication, happening simultaneously. A modern phone call allows both parties to speak and be heard at the same time.
Practice — then mark it
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Test Your Knowledge on Data Transmission
Test Your Knowledge on Data Transmission
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Checkpoint
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