IBM MQ Telemetry Transport protocol

The IBM® MQ Telemetry Transport (MQTT) v3 protocol is designed for exchanging messages between small devices on low bandwidth, or expensive connections, and to send messages reliably. It uses TCP/IP.

The MQTT protocol is published; see IBM MQ Telemetry Transport format and protocol. Version 3 of the protocol uses publish/subscribe, and supports three qualities of service: fire and forget, at least once, and exactly once.

The small size of the protocol headers, and the byte array message payload, keeps messages small. The headers comprise a 2 byte fixed header, and up to 12 bytes of additional variable headers. The protocol uses 12 byte variable headers to subscribe and connect, and only 2 byte variable headers for most publications.

With three qualities of service, you can trade off between low-latency and reliability; see Qualities of service provided by an MQTT client. Fire and forget uses no persistent device storage, and only one transmission to send or receive a publication. At least once, and exactly once require persistent storage on the device to maintain the protocol state and save a message until it is acknowledged.