mqtt-v3.1.1-os 29 October 2014
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MQTT Version 3.1.1
OASIS Standard
29 October 2014
Specification URIs
This version:
http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.doc (Authoritative)
http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html
http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.pdf
Previous version:
http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/cos01/mqtt-v3.1.1-cos01.doc (Authoritative)
http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/cos01/mqtt-v3.1.1-cos01.html
http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/cos01/mqtt-v3.1.1-cos01.pdf
Latest version:
http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.doc (Authoritative)
http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.html
http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.pdf
Technical Committee:
OASIS Message Queuing Telemetry Transport (MQTT) TC
Chairs:
Raphael J Cohn (raphael.cohn@stormmq.com), Individual
Richard J Coppen (coppen@uk.ibm.com), IBM
Editors:
Andrew Banks (Andrew_Banks@uk.ibm.com), IBM
Rahul Gupta (rahul.gupta@us.ibm.com), IBM
Related work:
This specification is related to:
MQTT and the NIST Cybersecurity Framework Version 1.0. Edited by Geoff Brown and
Louis-Philippe Lamoureux. Latest version: http://docs.oasis-open.org/mqtt/mqtt-nist-
cybersecurity/v1.0/mqtt-nist-cybersecurity-v1.0.html.
Abstract:
MQTT is a Client Server publish/subscribe messaging transport protocol. It is light weight, open,
simple, and designed so as to be easy to implement. These characteristics make it ideal for use
in many situations, including constrained environments such as for communication in Machine to
Machine (M2M) and Internet of Things (IoT) contexts where a small code footprint is required
and/or network bandwidth is at a premium.
The protocol runs over TCP/IP, or over other network protocols that provide ordered, lossless, bi-
directional connections. Its features include:
Use of the publish/subscribe message pattern which provides one-to-many message
distribution and decoupling of applications.
A messaging transport that is agnostic to the content of the payload.
Three qualities of service for message delivery:
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"At most once", where messages are delivered according to the best efforts of the
operating environment. Message loss can occur. This level could be used, for
example, with ambient sensor data where it does not matter if an individual reading is
lost as the next one will be published soon after.
"At least once", where messages are assured to arrive but duplicates can occur.
"Exactly once", where message are assured to arrive exactly once. This level could
be used, for example, with billing systems where duplicate or lost messages could
lead to incorrect charges being applied.
A small transport overhead and protocol exchanges minimized to reduce network traffic.
A mechanism to notify interested parties when an abnormal disconnection occurs.
Status:
This document was last revised or approved by the membership of OASIS on the above date.
The level of approval is also listed above. Check the “Latest version” location noted above for
possible later revisions of this document. Any other numbered Versions and other technical work
produced by the Technical Committee (TC) are listed at https://www.oasis-
open.org/committees/tc_home.php?wg_abbrev=mqtt#technical.
TC members should send comments on this specification to the TC’s email list. Others should
send comments to the TC’s public comment list, after subscribing to it by following the
instructions at the “Send A Comment” button on the TC’s web page at https://www.oasis-
open.org/committees/mqtt/.
For information on whether any patents have been disclosed that may be essential to
implementing this specification, and any offers of patent licensing terms, please refer to the
Intellectual Property Rights section of the Technical Committee web page (https://www.oasis-
open.org/committees/mqtt/ipr.php).
Citation format:
When referencing this specification the following citation format should be used:
[mqtt-v3.1.1]
MQTT Version 3.1.1. Edited by Andrew Banks and Rahul Gupta. 29 October 2014. OASIS
Standard. http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html. Latest version:
http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.html.
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Notices
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Table of Contents
1 Introduction ........................................................................................................................................... 9
1.1 Organization of MQTT ........................................................................................................................ 9
1.2 Terminology ........................................................................................................................................ 9
1.3 Normative references ....................................................................................................................... 10
1.4 Non normative references ................................................................................................................ 11
1.5 Data representations ........................................................................................................................ 13
1.5.1 Bits ............................................................................................................................................. 13
1.5.2 Integer data values .................................................................................................................... 13
1.5.3 UTF-8 encoded strings .............................................................................................................. 13
1.6 Editing conventions ........................................................................................................................... 15
2 MQTT Control Packet format ............................................................................................................. 16
2.1 Structure of an MQTT Control Packet .............................................................................................. 16
2.2 Fixed header ..................................................................................................................................... 16
2.2.1 MQTT Control Packet type ........................................................................................................ 16
2.2.2 Flags .......................................................................................................................................... 17
2.2.3 Remaining Length ..................................................................................................................... 18
2.3 Variable header ................................................................................................................................ 19
2.3.1 Packet Identifier ......................................................................................................................... 20
2.4 Payload ............................................................................................................................................. 21
3 MQTT Control Packets ....................................................................................................................... 23
3.1 CONNECT – Client requests a connection to a Server .................................................................... 23
3.1.1 Fixed header.............................................................................................................................. 23
3.1.2 Variable header ......................................................................................................................... 23
3.1.3 Payload ...................................................................................................................................... 29
3.1.4 Response .................................................................................................................................. 30
3.2 CONNACK – Acknowledge connection request ............................................................................... 31
3.2.1 Fixed header.............................................................................................................................. 31
3.2.2 Variable header ......................................................................................................................... 31
3.2.3 Payload ...................................................................................................................................... 33
3.3 PUBLISH – Publish message ........................................................................................................... 33
3.3.1 Fixed header.............................................................................................................................. 33
3.3.2 Variable header ......................................................................................................................... 35
3.3.3 Payload ...................................................................................................................................... 36
3.3.4 Response .................................................................................................................................. 36
3.3.5 Actions ....................................................................................................................................... 36
3.4 PUBACK – Publish acknowledgement ............................................................................................. 37
3.4.1 Fixed header.............................................................................................................................. 37
3.4.2 Variable header ......................................................................................................................... 37
3.4.3 Payload ...................................................................................................................................... 37
3.4.4 Actions ....................................................................................................................................... 37
3.5 PUBREC – Publish received (QoS 2 publish received, part 1) ........................................................ 37
3.5.1 Fixed header.............................................................................................................................. 38
3.5.2 Variable header ......................................................................................................................... 38
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3.5.3 Payload ...................................................................................................................................... 38
3.5.4 Actions ....................................................................................................................................... 38
3.6 PUBREL – Publish release (QoS 2 publish received, part 2)........................................................... 38
3.6.1 Fixed header.............................................................................................................................. 38
3.6.2 Variable header ......................................................................................................................... 39
3.6.3 Payload ...................................................................................................................................... 39
3.6.4 Actions ....................................................................................................................................... 39
3.7 PUBCOMP – Publish complete (QoS 2 publish received, part 3) .................................................... 39
3.7.1 Fixed header.............................................................................................................................. 39
3.7.2 Variable header ......................................................................................................................... 40
3.7.3 Payload ...................................................................................................................................... 40
3.7.4 Actions ....................................................................................................................................... 40
3.8 SUBSCRIBE - Subscribe to topics ................................................................................................... 40
3.8.1 Fixed header.............................................................................................................................. 40
3.8.2 Variable header ......................................................................................................................... 40
3.8.3 Payload ...................................................................................................................................... 41
3.8.4 Response .................................................................................................................................. 42
3.9 SUBACK – Subscribe acknowledgement ......................................................................................... 43
3.9.1 Fixed header.............................................................................................................................. 44
3.9.2 Variable header ......................................................................................................................... 44
3.9.3 Payload ...................................................................................................................................... 44
3.10 UNSUBSCRIBE – Unsubscribe from topics ................................................................................... 45
3.10.1 Fixed header............................................................................................................................ 45
3.10.2 Variable header ....................................................................................................................... 45
3.10.3 Payload .................................................................................................................................... 46
3.10.4 Response ................................................................................................................................ 46
3.11 UNSUBACK – Unsubscribe acknowledgement.............................................................................. 47
3.11.1 Fixed header............................................................................................................................ 47
3.11.2 Variable header ....................................................................................................................... 47
3.11.3 Payload .................................................................................................................................... 48
3.12 PINGREQ – PING request ............................................................................................................. 48
3.12.1 Fixed header............................................................................................................................ 48
3.12.2 Variable header ....................................................................................................................... 48
3.12.3 Payload .................................................................................................................................... 48
3.12.4 Response ................................................................................................................................ 48
3.13 PINGRESP – PING response ........................................................................................................ 48
3.13.1 Fixed header............................................................................................................................ 48
3.13.2 Variable header ....................................................................................................................... 49
3.13.3 Payload .................................................................................................................................... 49
3.14 DISCONNECT – Disconnect notification ........................................................................................ 49
3.14.1 Fixed header............................................................................................................................ 49
3.14.2 Variable header ....................................................................................................................... 49
3.14.3 Payload .................................................................................................................................... 49
3.14.4 Response ................................................................................................................................ 49
4 Operational behavior .......................................................................................................................... 51
