MQTT-SN for sensor networks in IOT Protocols - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the MQTT-SN client ID.

IOT Protocols

client.setClientId("[1]")

Drag options to blanks, or click blank then click option'

AsensorNode01

Bconnect

Cpublish

Dsubscribe

Attempts:

3 left

💡 Hint

Common Mistakes

Using MQTT actions like 'connect' or 'publish' as client ID.

The client ID uniquely identifies the MQTT-SN client in the network.

2fill in blank

medium

Complete the code to connect the MQTT-SN client to the gateway.

IOT Protocols

client.[1]()

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Aconnect

Bpublish

Cdisconnect

Dsubscribe

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'disconnect' or 'publish' instead of 'connect' here.

The 'connect' method establishes a connection between the client and the MQTT-SN gateway.

3fill in blank

hard

Fix the error in the publish command to send sensor data.

IOT Protocols

client.publish("sensor/data", [1])

Drag options to blanks, or click blank then click option'

Adisconnect

Bconnect

Csubscribe

Dtemperature

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names like 'connect' or 'subscribe' as data payload.

The publish method requires the data payload, here the variable 'temperature' holds the sensor reading.

4fill in blank

hard

Fill both blanks to subscribe to a topic and set the callback function.

IOT Protocols

client.[1]("sensor/alerts")
client.[2] = alertHandler

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Asubscribe

Bpublish

ConMessage

Dconnect

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'publish' instead of 'subscribe' or wrong handler property.

Subscribe listens to a topic, and onMessage sets the function to handle incoming messages.

5fill in blank

hard

Fill all three blanks to create a dictionary of sensor readings filtered by value.

IOT Protocols

filtered = [1]: [2] for [3] in readings if readings[[3]] > 50}

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Asensor

Breadings[sensor]

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names or values in comprehension.

This dictionary comprehension creates a new dict with sensors and their readings above 50.

Practice

1. What is the main advantage of using MQTT-SN in sensor networks?

easy

A. It requires sensors to have large memory for storing messages

B. It encrypts all messages with complex algorithms

C. It uses less power and bandwidth by using UDP and short topic IDs

D. It only works with wired sensor networks

Solution

1. Step 1: Understand MQTT-SN design goals

   MQTT-SN is designed for small sensors with limited power and bandwidth.

2. Step 2: Identify protocol features

   It uses UDP and short topic IDs to reduce message size and save resources.

3. Final Answer:

   It uses less power and bandwidth by using UDP and short topic IDs -> Option C

4. Quick Check:

   Lightweight + UDP = less power [OK]

Hint: Remember MQTT-SN is lightweight for small sensors [OK]

Common Mistakes:

• Thinking MQTT-SN encrypts all messages
• Assuming MQTT-SN needs large memory
• Believing MQTT-SN only works wired

2. Which of the following is the correct way to specify a topic ID in MQTT-SN?

easy

A. A MAC address of the gateway

B. A long string topic name like 'sensor/temperature/room1'

C. An IP address of the sensor

D. A short numeric topic ID like 0x01 or 0x0A

Solution

1. Step 1: Recall MQTT-SN topic format

   MQTT-SN uses short numeric topic IDs to save bandwidth.

2. Step 2: Compare options

   Only a short numeric topic ID like 0x01 or 0x0A shows a short numeric topic ID format.

3. Final Answer:

   A short numeric topic ID like 0x01 or 0x0A -> Option D

4. Quick Check:

   Short numeric topic ID = correct MQTT-SN topic [OK]

Hint: MQTT-SN uses short numeric IDs, not long strings [OK]

Common Mistakes:

• Choosing long string topic names like MQTT
• Confusing topic ID with IP or MAC addresses
• Assuming topic ID is a sensor address

3. Given this MQTT-SN message snippet, what is the topic ID used?

TopicId: 0x05
Payload: 23.5

medium

A. Topic ID 0x05

B. Sensor ID 0x05

C. Payload value 23.5

D. Topic name 'temperature'

Solution

1. Step 1: Identify the topic ID field

   The message shows 'TopicId: 0x05' which is the numeric topic identifier.

2. Step 2: Differentiate topic ID from other fields

   Payload is data (23.5), sensor ID is not shown here, topic name is not used in MQTT-SN messages.

3. Final Answer:

   Topic ID 0x05 -> Option A

4. Quick Check:

   TopicId field = 0x05 [OK]

Hint: Look for 'TopicId' field for topic identifier [OK]

Common Mistakes:

• Confusing payload with topic ID
• Assuming topic name is sent instead of ID
• Mixing sensor ID with topic ID

4. You try to send an MQTT-SN message but the sensor does not receive it. Which of these is a likely cause?

medium

A. Using TCP instead of UDP for MQTT-SN messages

B. Using short topic IDs instead of long topic names

C. Sending messages with QoS level 0

D. Using the correct gateway address

Solution

1. Step 1: Understand MQTT-SN transport protocol

   MQTT-SN uses UDP, not TCP, for lightweight communication.

2. Step 2: Analyze the problem

   Using TCP instead of UDP can cause message delivery failure in MQTT-SN.

3. Final Answer:

   Using TCP instead of UDP for MQTT-SN messages -> Option A

4. Quick Check:

   MQTT-SN requires UDP, TCP causes failure [OK]

Hint: MQTT-SN always uses UDP, not TCP [OK]

Common Mistakes:

• Thinking short topic IDs cause failure
• Believing QoS 0 blocks delivery
• Ignoring gateway address correctness

5. You want to optimize a sensor network using MQTT-SN. Which combination best reduces power and bandwidth usage?

hard

A. Use TCP transport, long topic names, and QoS level 2

B. Use UDP transport, short topic IDs, and QoS level 1

C. Use UDP transport, long topic names, and QoS level 0

D. Use TCP transport, short topic IDs, and QoS level 0

Solution

1. Step 1: Identify MQTT-SN features for efficiency

   MQTT-SN uses UDP and short topic IDs to save power and bandwidth.

2. Step 2: Consider QoS levels

   QoS 1 ensures message delivery with minimal overhead, better than QoS 0 for reliability.

3. Step 3: Evaluate options

   The combination of UDP transport, short topic IDs, and QoS level 1 best balances efficiency and reliability.

4. Final Answer:

   Use UDP transport, short topic IDs, and QoS level 1 -> Option B

5. Quick Check:

   UDP + short IDs + QoS1 = optimized MQTT-SN [OK]

Hint: Combine UDP, short IDs, and QoS 1 for best efficiency [OK]

Common Mistakes:

• Choosing TCP which wastes power
• Using long topic names increasing bandwidth
• Ignoring QoS impact on reliability