Topics and topic hierarchy in IOT Protocols - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a 'topic' in IoT messaging protocols like MQTT?

A topic is a label or address used to organize and route messages between devices. It acts like a channel name where messages are published and subscribed.

beginner

How does a topic hierarchy help in IoT communication?

A topic hierarchy organizes topics in a tree-like structure, allowing devices to subscribe to broad or specific message categories easily.

beginner

What symbol is commonly used as a separator in topic hierarchies?

The forward slash '/' is used to separate levels in a topic hierarchy, like folders in a file system.

intermediate

What does subscribing to 'home/+/temperature' mean in MQTT?

It means subscribing to all topics that have 'home' as the first level, any single word as the second level, and 'temperature' as the third level. The '+' is a wildcard for one level.

intermediate

What is the difference between '+' and '#' wildcards in topic subscriptions?

'+' matches exactly one level in the topic hierarchy, while '#' matches all remaining levels, including zero or more levels.

Which character is used to separate levels in an MQTT topic hierarchy?

A /

B .

C -

D _

The forward slash '/' separates topic levels, similar to folders in a file path.

What does the MQTT topic 'sensors/+/humidity' subscribe to?

A All humidity data from any sensor

B Only humidity data from sensor named '+'

C All sensors with 'humidity' as the first level

D All topics starting with 'sensors/humidity'

The '+' wildcard matches any single level, so it subscribes to humidity data from all sensors.

What does the '#' wildcard represent in MQTT topic subscriptions?

A Matches exactly one level

B Matches only the root topic

C Matches zero or more levels

D Matches no levels

'#' matches all remaining topic levels, including zero or more.

Why use a topic hierarchy in IoT messaging?

A To reduce message size

B To encrypt messages

C To speed up device hardware

D To organize messages for easier filtering

Topic hierarchies help organize messages so devices can subscribe to relevant data easily.

Which topic would match the subscription 'home/#'?

A office/kitchen/temperature

B Both C and D

C home

D home/kitchen/temperature

'home/#' matches 'home' and any subtopics like 'home/kitchen/temperature'.

Explain what a topic hierarchy is and how it helps in IoT messaging.

Think of it like folders and subfolders organizing files.

Describe the difference between '+' and '#' wildcards in MQTT topic subscriptions.

One is for a single folder, the other for many folders.