Client-server vs publish-subscribe models in IOT Protocols - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding communication flow in client-server model

In a client-server model, which statement best describes how communication happens?

A Clients publish messages to a broker, which then forwards to servers.

B Servers broadcast messages to all clients without waiting for requests.

C Clients send requests directly to servers, and servers respond only to those requests.

D Clients and servers communicate through a shared message queue without direct requests.

💡 Hint

Think about who initiates communication and who responds in client-server.

In client-server, clients initiate requests and servers respond directly to those requests. Servers do not broadcast messages unsolicited.

🧠 Conceptual

intermediate

Role of broker in publish-subscribe model

What is the main role of the broker in a publish-subscribe messaging model?

A It stores and forwards messages from publishers to subscribers based on topics.

B It directly connects each publisher to every subscriber without intermediaries.

C It acts as a server that responds to client requests for data.

D It encrypts messages to secure communication between clients.

💡 Hint

Consider how messages reach subscribers in publish-subscribe.

The broker receives messages from publishers and forwards them to subscribers who have expressed interest in specific topics.

💻 Command Output

advanced

Output of MQTT client subscribing to a topic

Given an MQTT client subscribing to topic 'home/temperature', what output will it show when a message '22°C' is published to that topic?

IOT Protocols

mqtt_subscribe('home/temperature')
# Message published: '22°C'

A Received message on 'home/temperature': 22°C

B Error: Topic 'home/temperature' not found

C No messages received

D Received message on 'home/humidity': 22°C

💡 Hint

Think about what happens when you subscribe to a topic and a message is published to it.

The client receives and displays the message published to the subscribed topic.

❓ Troubleshoot

advanced

Troubleshooting message delivery failure in publish-subscribe

An MQTT subscriber is not receiving messages from the broker. Which of the following is the most likely cause?

A Publisher is sending messages to a different protocol.

B Broker is down but subscriber still receives messages.

C Subscriber is sending requests directly to the broker.

D Subscriber did not subscribe to the correct topic.

💡 Hint

Check the topic subscription carefully.

If the subscriber does not subscribe to the correct topic, it will not receive messages published to that topic.

✅ Best Practice

expert

Choosing between client-server and publish-subscribe for IoT devices

For a large network of IoT sensors sending data to multiple monitoring systems, which communication model is best and why?

A Publish-subscribe, because it requires sensors to manage connections to each monitoring system.

B Publish-subscribe, because it decouples senders and receivers and scales well with many clients.

C Client-server, because it allows sensors to broadcast data to all monitoring systems simultaneously.

D Client-server, because it ensures direct communication and reduces message overhead.

💡 Hint

Consider scalability and decoupling in large IoT networks.

Publish-subscribe allows many sensors to send data to a broker, which then distributes messages to multiple subscribers efficiently without sensors managing each connection.