MQTT Specifications
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MQTT is an OASIS standard. The specification is managed by the OASIS MQTT Technical Committee.
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MQTT 5 Specification
is an OASIS Standard. The specification is available as either
> single-page HTML or
> PDF.
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MQTT 3.1.1 Specification
is an older ISO and OASIS Standard. The specification is available as either
> single-page HTML or
> PDF.
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MQTT 3.1 Specification
For historical reference, the specification of MQTT v3.1 is available
> here.
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MQTT-SN v1.2
formerly known as MQTT-S, is available
> here
MQTT for Sensor Networks is aimed at embedded devices on non-TCP/IP networks, such as Zigbee. MQTT-SN is a publish/subscribe messaging protocol for wireless sensor networks (WSN), with the aim of extending the MQTT protocol beyond the reach of TCP/IP infrastructure for Sensor and Actuator solutions.
Read more about it on HiveMQ’s blog.