Networks: Types, Layering, Protocols and Security
Topic 3 tests how data moves between devices: the kinds of network, the hardware that connects them, the layered model that organizes communication, and the controls that keep traffic trustworthy. Answers score when a protocol or device is matched to a specific requirement in the scenario.
Network types and hardware
PAN, LAN, WLAN, VLAN (logical segmentation of one physical LAN), VPN (encrypted tunnel over a public network), SAN (block-level storage network), intranet (private, internal) versus extranet (controlled access for outsiders) versus the internet. Devices: hub (repeats to every port), switch (forwards by MAC address within a LAN), router (forwards packets between networks using IP addresses), gateway (translates between protocols), NIC, modem, firewall and proxy server.
Protocols and the OSI model
OSI layers, bottom up: physical, data link, network, transport, session, presentation, application. Each layer provides services to the one above and adds its own header - encapsulation. TCP is connection-oriented, preserves order and retransmits lost packets, so it suits email, web and file transfer. UDP is connectionless with low overhead, so it suits streaming and DNS lookups. Well-known ports: HTTP 80, HTTPS 443, FTP 21, SMTP 25, POP3 110, DNS 53, SSH 22.
Worked example
A school adds video-conferencing alongside email. Which transport protocol for each? Video: UDP, because a dropped frame matters less than latency, and retransmission would cause delay and jitter. Email: TCP, because every character must arrive intact and in order. Justify by matching the protocol property to the application's requirement - not by repeating the protocol name.
Traps that cost marks
- Treating a hub, a switch and a router as interchangeable; only the router moves traffic between networks.
- Confusing a VPN (secure tunnel) with a VLAN (logical segmentation).
- Naming an OSI layer without saying what it does.
- Assuming encryption hides that communication took place; it hides content, not the fact of the exchange.