What is MQTT?
A lightweight publish/subscribe messaging protocol designed for IoT and cyber-physical systems.
Why is MQTT considered lightweight?
It has low overhead, small message size, and works well on low bandwidth and unreliable networks.
What communication model does MQTT use?
Publish / Subscribe model.
What are the main components in MQTT?
Client, Broker, Topics, Messages.
What is an MQTT broker?
A server that receives messages from publishers and forwards them to subscribers based on topics.
What is an MQTT client?
Any device or application that publishes or subscribes to messages via a broker.
What is a topic in MQTT?
A hierarchical string that identifies a message (e.g. factory/motor/status).
How are MQTT topics structured?
Hierarchical levels separated by slashes /.
Does the broker understand message content?
No — the broker only filters messages by topic, not content.
What are the three MQTT message types?
Publish, Subscribe, Unsubscribe.
What does Publish mean in MQTT?
Sending a message to a broker on a specific topic.
What does Subscribe mean in MQTT?
Requesting messages from a broker for a specific topic.
What is QoS in MQTT?
Quality of Service — controls how reliably messages are delivered.
MQTT QoS level 0
At most once — no delivery guarantee.
MQTT QoS level 1
At least once — message may be delivered multiple times.
MQTT QoS level 2
Exactly once — highest reliability, most overhead.
What is a retained message?
A message stored by the broker and sent immediately to new subscribers.
Why are retained messages useful?
They ensure new subscribers get the latest known state immediately.
Where does MQTT fit in IoT architecture?
Mainly in the network layer.
What are common security concerns with MQTT?
Eavesdropping, unauthorized access, message tampering.
How can MQTT communication be secured?
TLS, authentication, access control, encryption.
What does TLS provide for MQTT?
Encrypted and secure communication between client and broker.
What is access control in MQTT?
Restricting which clients can publish or subscribe to certain topics.
