Publishing sensor data in IOT Protocols - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Publishing sensor data with MQTT

What is the output of this MQTT publish command when sending temperature data to topic home/sensor/temperature?

IOT Protocols

mosquitto_pub -h broker.example.com -t home/sensor/temperature -m "22.5"

A Message published successfully to topic home/sensor/temperature

B Syntax error in command

C Connection refused: broker.example.com

D Error: Topic home/sensor/temperature not found

💡 Hint

Check if the command syntax is correct and the broker is reachable.

The command publishes the message '22.5' to the topic 'home/sensor/temperature' on the MQTT broker. If successful, it confirms the message was published.

❓ Configuration

intermediate

Configuring QoS for sensor data publishing

Which MQTT QoS level ensures that the sensor data message is delivered exactly once to the broker?

A QoS 2 - Exactly once

B QoS 1 - At least once

C QoS 3 - Guaranteed delivery

D QoS 0 - At most once

💡 Hint

QoS levels 0, 1, and 2 are standard in MQTT.

QoS 2 guarantees that the message is delivered exactly once by using a four-step handshake between client and broker.

❓ Troubleshoot

advanced

Troubleshooting sensor data not received

A sensor publishes data to topic factory/machine1/status but the subscriber never receives it. Which is the most likely cause?

A Publisher uses QoS 0 and subscriber uses QoS 1

B Subscriber is subscribed to <code>factory/machine1/#</code>

C Subscriber is subscribed to <code>factory/machine1/status</code> but the publisher uses a different topic <code>factory/machine1/state</code>

D Publisher and subscriber use the same client ID

💡 Hint

Check if the topic names exactly match.

If the subscriber listens to a different topic than the publisher sends to, it will never receive the messages.

🔀 Workflow

advanced

Workflow for secure sensor data publishing

Which sequence correctly describes the steps to securely publish sensor data over MQTT?

A 3,1,2,4

B 2,1,3,4

C 1,3,2,4

D 1,2,3,4

💡 Hint

Security steps must happen before publishing data.

First establish a secure connection, then authenticate, publish data, and finally disconnect.

✅ Best Practice

expert

Best practice for sensor data payload format

Which payload format is best for publishing sensor data to ensure interoperability and easy parsing?

A Plain text string with comma-separated values

B JSON object with named fields

C Binary encoded proprietary format

D XML document with nested elements

💡 Hint

Consider readability and support across platforms.

JSON is widely supported, human-readable, and easy to parse in many programming languages, making it ideal for sensor data.