What is MQTT
Quick definition
MQTT (Message Queuing Telemetry Transport) is a very lightweight publish/subscribe protocol designed for devices with little CPU, little RAM, and flaky links. It works against a central broker (Mosquitto, HiveMQ, EMQX, AWS IoT Core) and carries most modern industrial IoT traffic.
Why MQTT and not HTTP
Each HTTP request opens TCP, runs a TLS handshake, and ships hundreds of bytes of headers. On NB-IoT or metered IoT, that is expensive. MQTT holds a single TCP connection and messages are binary, not text.
QoS: three levels
QoS 0 (best effort, no ack), QoS 1 (at least once, ack with possible duplicate), QoS 2 (exactly once, double handshake). In industrial IoT, QoS 1 is the norm; QoS 2 only when duplicating a message is unacceptable (billing, critical commands).
FAQ
MQTT 3.1.1 or MQTT 5?+
MQTT 5 if your broker and SDK support it: clear error codes, message properties, better expiry. MQTT 3.1.1 remains the most universally compatible.
Do I need my own broker?+
Not always. AWS IoT Core, Azure IoT Hub, or HiveMQ Cloud handle it for you. For large fleets with private APN, a self-hosted broker on your DC gives more control.
Related terms
What is a static-IP IoT SIM
A static-IP SIM is an IoT card the carrier always assigns the same IP address to, instead of a different dynamic IP per session. It can be public (reachable from the internet) or private (reachable from your private APN or VPN). It is essential whenever a server needs to initiate the connection to the device.
What is a private APN
A private APN is a mobile network access point dedicated to a single company or project. Your IoT traffic never touches the public internet: it exits the carrier straight to your data center over a private tunnel, with your own IP plan, firewall rules, and routing.
What is an IoT VPN
An IoT VPN is an encrypted tunnel between the carrier exit and the customer infrastructure. It lets devices on the cellular network reach private servers without going over the public internet. Typical options are IPSec, WireGuard, and L2TP/IPSec.