CWISE Sample Questions & Answers

Class C devices have continuously open receive windows, closing only when transmitting. This allows for low-latency downlink communication initiated by the server at any time. Class A only receives after a transmission. Class B opens receive windows at scheduled intervals (beacons), which has higher latency than Class C. Class C consumes the most power but meets the low-latency downlink requirement.

BLE utilizes 40 channels (3 advertising, 37 data) spaced 2 MHz apart in the 2.4 GHz ISM band. Bluetooth Classic uses 79 channels spaced 1 MHz apart.

BLE is optimized for short bursts of data transmission followed by long sleep periods, enabling extremely low power consumption suitable for coin-cell operation. Bluetooth Classic is connection-oriented and designed for continuous data streams like audio.

QoS 0 is 'fire and forget'. The message is delivered at most once, meaning it might be lost, but it will never be duplicated. This matches the requirement where missing a message is acceptable but duplicates are not. QoS 1 guarantees delivery but may result in duplicates. QoS 2 guarantees exactly once delivery but has higher overhead.

The 6LoWPAN adaptation layer performs two critical functions: Header Compression (HC) to reduce the IPv6 header size, and Fragmentation/Reassembly to split IPv6 packets (MTU 1280 bytes) into 802.15.4 frames (max payload ~127 bytes). NAT64 is for translation between IPv6 and IPv4. DHCPv6 handles addressing, not sizing.

RSL = Tx Power - Cable Loss + Tx Antenna Gain - FSPL + Rx Antenna Gain - Cable Loss (assuming split or total). Using total cable loss: RSL = 20 dBm - 2 dB + 10 dBi - 100 dB + 10 dBi = 38 - 100 = -62 dBm.

Calculation:
Tx Power: +20
Total Cable Loss: -2
Total Antenna Gain: +20 (10+10)
FSPL: -100
Total: 20 - 2 + 20 - 100 = -62 dBm.

BLE 5.1 with AoA provides sub-meter accuracy (meeting the 1-2m requirement), has excellent battery life, and can be deployed using battery-powered anchor points (reducing cabling needs). While it operates in 2.4 GHz, modern BLE uses frequency hopping to coexist with Wi-Fi. Active RFID at 433 MHz has good penetration but typically lower accuracy (3-10m). Wi-Fi RTLS consumes too much tag battery. UWB offers high accuracy but requires expensive infrastructure and extensive cabling.

The CoAP OBSERVE option (RFC 7641) allows a client to register interest in a resource. The server then sends notifications (responses) whenever the resource state changes. This eliminates the need for inefficient polling in constrained networks. GET is a standard method, Block-wise transfer handles large payloads, and Discovery is for finding resources.

The output of a certificate signing request generation command is the CSR file itself, typically named with a .csr extension (e.g., gateway.csr). The private key is specified by -keyout.

Industrial microwaves and large heating elements often operate in the ISM band and create broadband noise that covers the entire 2.4 GHz spectrum. The duty cycle (on for 10 seconds, off for 2 minutes) is characteristic of a heating cycle. Wi-Fi would look like specific channels. Bluetooth is hopping and narrowband. Fluorescent lights cause interference but usually at line frequency (50/60Hz) harmonics, not broadband sweeping.

Time-Series Databases (TSDB) like InfluxDB are specifically optimized for writing and querying high volumes of time-stamped data. They offer superior compression and query performance for range-based lookups compared to RDBMS or Key-Value stores. Graph databases are for relationships, not time-series telemetry.