Communication and network technologies
Communication and network technologies tests how data moves between devices: network types and topologies, client–server and peer-to-peer models, packet switching, IP addressing and the protocols that make the internet work. Expect questions that ask you to choose and justify, not just label.
Network types and topologies
A LAN covers one site and is usually owned by the organisation; a WAN links sites across public or leased infrastructure. A WLAN is a LAN using radio (Wi-Fi), typically with CSMA/CA to avoid collisions. In a star topology every device connects to a central switch: a cable fault affects one device, but the switch is a single point of failure. A mesh gives redundant paths at higher cabling cost.
Packet switching and IP addressing
Data is split into packets, each with a header containing source and destination IP addresses and a sequence number. Packets may take different routes and arrive out of order; TCP reassembles them. IPv4 is 32-bit, written as four dotted decimal octets; IPv6 is 128-bit hexadecimal. A subnet mask separates the network and host parts; ANDing the mask with the IP gives the network address.
Protocols
TCP is connection-oriented with acknowledgements and retransmission; UDP is connectionless with lower overhead, used for streaming. HTTP/HTTPS requests web pages, FTP transfers files, SMTP sends mail, IMAP and POP3 retrieve it, DNS resolves names to IP addresses, and DHCP leases addresses automatically.
Worked example
Find the network of 192.168.10.130/26. The mask is 255.255.255.192; block size = 256 − 192 = 64, giving subnets .0, .64, .128, .192. 130 lies between 128 and 191, so the network address is 192.168.10.128, broadcast 192.168.10.191, and usable hosts .129–.190.
Traps
Treating the broadcast address as usable; confusing the default gateway with DNS; saying packet switching guarantees order (TCP does that, not IP); mixing up SMTP and POP3 direction; forgetting that each subnet loses two addresses.