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.
Types
Types of network
Networks are grouped by scale and purpose:
LAN (local area network) — one site, e.g. a school or office.
WAN (wide area network) — geographically spread; the internet is the largest WAN.
PAN (personal area network) — around one person, e.g. Bluetooth devices.
VPN (virtual private network) — a secure, encrypted tunnel across a public network.
WLAN — a wireless LAN using Wi-Fi.
Quick check
LAN or WAN?
?A single company office connects its computers and printer over its own cabling in one building. What type of network is this?
Media
Transmission media
Data travels over different media:
Twisted-pair (copper) — cheap, common in LANs, limited speed and distance.
Coaxial — better shielding than twisted pair.
Fibre-optic — light in glass; very high bandwidth, long distance, immune to electrical interference.
Wireless (radio) — convenient and mobile, but shared, slower and less secure.
Quick check
Best medium
?A backbone link must carry huge bandwidth over many kilometres with no electrical interference. Which medium is best?
Sort it
Sort the network terms
Tap an item, then the category it belongs to.
🖧 Network type
🔌 Transmission medium
📡 Protocol
Packets
Packet switching
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.
Quick check
Packet switching
?Which statement about packet switching is correct?
Protocols
Protocols and layered models
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.
Match it
Match the protocol
Tap a job on the left, then the protocol that does it.
Job
Protocol
CSMA
CSMA/CD and wireless
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.
Quick check
CSMA/CD
?What is the purpose of CSMA/CD on a shared wired network?
Calculate
Transfer time
1A 2 MB file is sent over a link with a speed of 8 Mbps (megabits per second). Assuming 1 byte = 8 bits, how many seconds does the transfer take?
s
Hint: 2 MB = 16 megabits; 16 divided by 8.
Calculate
Usable hosts
2A network uses a /24 subnet mask, leaving 8 host bits. The number of addresses is 2 to the power 8, but two are reserved (network and broadcast). How many usable host addresses are there?
hosts
Hint: 2 to the power 8 is 256, then subtract 2.
Layers
OSI and TCP/IP layered models
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.
Quick check
Why layers
?What is the main benefit of organising network communication into layers?
Security
VPN and wireless security
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.
Quick check
VPN
?What does a VPN provide?
Recap
The big ideas to know
Types: LAN (one site), WAN (wide area), PAN, VPN, WLAN