Topic 3 covers how computers communicate: network types (LAN, WAN, VPN), transmission media, protocols and standards, layered models, packet switching, and how to calculate transfer times.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you are ready.
Networks are grouped by scale and purpose:
Data travels over different media:
Tap an item, then the category it belongs to.
On packet-switched networks, data is split into packets. Each packet carries the source and destination addresses and a sequence number, and may travel a different route. The receiver reassembles them in order and requests any that are lost.
Advantages: efficient shared use of links, resilience (packets reroute around failures). The alternative, circuit switching, reserves a whole path for the call.
A protocol is an agreed set of rules for communication. Protocols provide data integrity, flow control, congestion management and error checking. Standard protocols let different vendors interoperate.
Communication is organised into layers. The OSI model has 7 layers; the practical TCP/IP model has 4. Layering lets each level be designed and changed independently.
Tap a job on the left, then the protocol that does it.
On a shared wired medium, CSMA/CD (carrier sense multiple access with collision detection) lets a device listen before sending; if two transmit at once a collision is detected and both back off for a random time before retrying.
Wireless networks are convenient but the medium is shared and exposed, so encryption (WPA2/WPA3) is essential for security.
Communication is split into layers, each with one job, so parts can be designed and changed independently. The OSI model has 7 layers (physical, data link, network, transport, session, presentation, application); the practical TCP/IP model has 4 (link, internet, transport, application). As data goes down the stack each layer encapsulates it by adding a header.
A VPN creates an encrypted tunnel across a public network, so remote users appear to be on the private network securely. Wireless networks are exposed, so they use encryption (WPA2/WPA3) and authentication to keep traffic private.
Types: LAN (one site), WAN (wide area), PAN, VPN, WLAN
Media: twisted pair, coaxial, fibre-optic, wireless
Packet switching: addressed packets, different routes, reassembled in order
Protocols: integrity, flow control, congestion, error checking; OSI (7) and TCP/IP (4) layers
CSMA/CD: listen, detect collisions, random back-off
Transfer time: file size in bits divided by speed in bits per second
You have covered the key ideas in Topic 3 — networks. Press Finish to see your score.
You have worked through Networks. 🎉
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Next: test yourself in the Verify stage.