Internet of Things
This domain tests how connected devices sense, communicate, and are managed, and where they fail. CET questions cover architecture layers, sensors and actuators, wireless protocols, edge versus cloud processing, and the security and lifecycle risks of constrained devices.
Core rules and concepts
- Architecture: perception/device layer (sensors, actuators), network layer (gateways, connectivity), processing layer (edge or cloud analytics), application layer (dashboards, business logic).
- Sensors vs actuators: sensors convert physical conditions into data; actuators convert commands into physical action.
- Protocol fit: MQTT is lightweight publish/subscribe through a broker and offers QoS levels; CoAP is request/response over UDP for constrained devices; LoRaWAN is long-range, low-bandwidth, low-power; Zigbee and BLE suit short-range personal or building networks.
- Edge processing: filtering or aggregating near the device reduces bandwidth, latency, and cloud cost.
- Lifecycle: provision identity, rotate credentials, support over-the-air updates, monitor, and decommission securely. Default passwords and unsigned firmware are recurring weaknesses.
Worked example
A farm needs soil-moisture readings every 15 minutes from fields several kilometers from power and Wi-Fi. Devices must run for years on small batteries and send only summary data.
Reasoning: the range rules out BLE and Zigbee mesh for wide fields; Wi-Fi is unavailable and power-hungry. LoRaWAN fits long range, low power, and low payload. Sending every raw reading wastes energy, so an edge rule should average or threshold readings and transmit summaries. The design should also include unique device credentials and signed OTA updates, because physical accessibility makes tampering likely.
Traps
Do not choose a high-bandwidth protocol for a battery-limited sensor. MQTT is not a database and does not guarantee delivery by itself; QoS is a setting, not a network. Edge computing does not replace security. 'Cloud is always better' ignores latency, connectivity, and cost. Confusing sensors with actuators, or gateways with brokers, costs marks.