Publish-subscribe architecture in IOT Protocols - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to publish a message to a topic using MQTT.

IOT Protocols

client.publish('[1]', 'Hello World')

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

Ahome/livingroom/temperature

Bconnect

Csubscribe

Ddisconnect

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names like 'connect' or 'subscribe' as the topic name.

Leaving the topic name blank or using invalid strings.

The publish method requires the topic name as the first argument. Here, home/livingroom/temperature is a valid topic.

2fill in blank

medium

Complete the code to subscribe to a topic to receive messages.

IOT Protocols

client.[1]('home/kitchen/humidity')

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

Apublish

Bsubscribe

Cconnect

Ddisconnect

Attempts:

3 left

💡 Hint

Common Mistakes

Using publish instead of subscribe to listen for messages.

Confusing connection methods with subscription.

The subscribe method is used to listen for messages on a topic.

3fill in blank

hard

Fix the error in the code to correctly connect to the MQTT broker.

IOT Protocols

client.[1]('mqtt.example.com', 1883)

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

Aconnect

Bpublish

Csubscribe

Ddisconnect

Attempts:

3 left

💡 Hint

Common Mistakes

Using publish or subscribe instead of connect to connect.

Omitting the port number or using wrong method names.

The connect method is used to establish a connection to the MQTT broker with the host and port.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps topics to their message lengths for topics with messages longer than 5 characters.

IOT Protocols

{topic: len(message) for topic, message in messages.items() if len(message) [1] [2]

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

A>

B5

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using < or == instead of >.

Swapping the number and operator positions.

The condition len(message) > 5 filters messages longer than 5 characters.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase topic names to message sizes for messages with size greater than 10.

IOT Protocols

{ [1]: [2] for topic, message in data.items() if len(message) [3] 10 }

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

Atopic.upper()

Blen(message)

C>

Dtopic

Attempts:

3 left

💡 Hint

Common Mistakes

Using the original topic name instead of uppercase.

Using wrong comparison operators or values.

The comprehension maps uppercase topic names (topic.upper()) to message lengths (len(message)) for messages longer than 10 characters (> 10).

Practice

1. What is the main role of a broker in a publish-subscribe architecture?

easy

A. To receive messages from publishers and forward them to subscribers

B. To directly connect publishers and subscribers

C. To store all messages permanently

D. To encrypt messages between devices

Solution

1. Step 1: Understand the broker's function

   The broker acts as a middleman that receives messages from publishers.

2. Step 2: Identify message forwarding role

   The broker forwards these messages to subscribers interested in specific topics.

3. Final Answer:

   To receive messages from publishers and forward them to subscribers -> Option A

4. Quick Check:

   Broker forwards messages [OK]

Hint: Broker forwards messages, it doesn't connect devices directly [OK]

Common Mistakes:

• Thinking broker connects devices directly
• Assuming broker stores messages permanently
• Confusing broker with encryption service

2. Which of the following is the correct way to describe a topic in publish-subscribe?

easy

A. A label used to organize messages for subscribers

B. A direct connection between two devices

C. A security protocol for message encryption

D. A device that publishes messages

Solution

1. Step 1: Define what a topic is

   A topic is a label or category that organizes messages so subscribers receive only relevant ones.

2. Step 2: Eliminate incorrect options

   Topics are not connections, security protocols, or devices.

3. Final Answer:

   A label used to organize messages for subscribers -> Option A

4. Quick Check:

   Topic organizes messages [OK]

Hint: Topics organize messages, not devices or connections [OK]

Common Mistakes:

• Confusing topics with device connections
• Thinking topics are security features
• Mixing up topics with publishers

3. Given this scenario: A device publishes messages to topic home/temperature. Which device will receive the messages?

medium

A. All devices on the network

B. Any device subscribed to home/humidity

C. Any device subscribed to home/temperature

D. Only the publishing device

Solution

1. Step 1: Identify the topic published to

   The device publishes to home/temperature.

2. Step 2: Determine which subscribers get the message

   Only devices subscribed to home/temperature receive the messages.

3. Final Answer:

   Any device subscribed to home/temperature -> Option C

4. Quick Check:

   Subscribers to topic get messages [OK]

Hint: Subscribers to the exact topic get messages [OK]

Common Mistakes:

• Assuming all devices get messages
• Thinking publishing device receives its own messages
• Confusing similar topic names

4. A subscriber is not receiving messages from the broker. Which of these is a likely cause?

medium

A. Publisher is sending messages to the subscriber directly

B. Subscriber is publishing messages instead of subscribing

C. Broker is encrypting messages incorrectly

D. Subscriber is not subscribed to the correct topic

Solution

1. Step 1: Check subscription correctness

   If the subscriber is not subscribed to the right topic, it won't get messages.

2. Step 2: Rule out other causes

   Publishers don't send messages directly; encryption issues or wrong roles are less common causes here.

3. Final Answer:

   Subscriber is not subscribed to the correct topic -> Option D

4. Quick Check:

   Correct topic subscription needed [OK]

Hint: Check subscriber's topic subscription first [OK]

Common Mistakes:

• Thinking publisher sends messages directly
• Blaming encryption without evidence
• Confusing subscriber and publisher roles

5. In a large IoT system using publish-subscribe, how can you ensure that only devices in the 'factory/floor1' area receive temperature alerts without affecting others?

hard

A. Publish all alerts to factory/temperature and let devices filter messages locally

B. Publish temperature alerts to topic factory/floor1/temperature and have devices subscribe to it

C. Send alerts directly to each device's IP address

D. Use a single topic temperature for all devices

Solution

1. Step 1: Use topic hierarchy for targeted messaging

   Publishing to factory/floor1/temperature targets only devices subscribed to that specific area.

2. Step 2: Avoid broad topics or direct device addressing

   Broad topics or direct IP messaging reduce scalability and flexibility.

3. Final Answer:

   Publish temperature alerts to topic factory/floor1/temperature and have devices subscribe to it -> Option B

4. Quick Check:

   Use specific topics for targeted delivery [OK]

Hint: Use detailed topic paths for precise message delivery [OK]

Common Mistakes:

• Using broad topics causing unwanted message delivery
• Trying direct device IP messaging in pub-sub
• Ignoring topic hierarchy benefits