MQTT Encoding and Decoding - Revision history

Ctreber at 12:49, 13 June 2018

2018-06-13T12:49:21Z

← Older revision		Revision as of 12:49, 13 June 2018
Line 3:		Line 3:
	=MQTT Encoding and Decoding=		=MQTT Encoding and Decoding=

	The MQTT protocol is very lightweight (does not use many bytes to get the message across).		The MQTT protocol is very lightweight. It does not use many bytes to get the message across, and the handshake (sequence of messages) is pretty simple (with user-choosable options ranging from "primitive" to "modestly sophisticated").

	Each MQTT packet consists of:		Each MQTT packet consists of:

	* Fixed header		* Fixed header
	** packet type:byte consisting of MQTT packet type in the higher nibble and flags in the lower nibble		** packet type:byte, consisting of the actual MQTT packet type in the higher nibble and some flags in the lower nibble
	*** b7-4: MQTT packet type		*** b7-4: MQTT packet type
	*** b3: DUP flag (PUBLISH only)		*** b3: DUP flag (PUBLISH only)
	*** b2-1: QoS (PUBLISH only)		*** b2-1: QoS (PUBLISH only)
	*** b0: RETAIN flag (PUBLISH only)		*** b0: RETAIN flag (PUBLISH only)
	** remaining length - this one is a bit tricky and consumes between 1 and 4 bytes. Encoding is least significant bits first in b6-0 while b7 is a "continuation bit" ('1' meaning "another byte follows").		** remaining length - this one is a bit tricky and consumes between 1 and 4 bytes. Encoding is "least significant bits first" in b6-0 while b7 is a "continuation bit" ('1' meaning "another byte follows"). This mechanism ensures that short messages stay short by using the fewest number of bytes needed to encode the length.
	* Variable header (optional), depending on the package type		* Variable header (optional), depending on the package type
	* Payload (optional), depending on the package type		* Payload (optional), depending on the package type

	Type "Array" is binary data, after the number of bytes in the ~~text~~ encoded as two bytes, MSB first.		Type "Array" is binary data, after the number of bytes in the array encoded as two bytes, MSB first.

	Type "String" is like "Array", text encoded in UTF-8 without a terminating "0" byte.		Type "String" is like "Array", with the text encoded in UTF-8 without a terminating "0" byte.

	{\| class="wikitable" style="border: 2px solid"		{\| class="wikitable" style="border: 2px solid"

Ctreber at 12:40, 13 June 2018

2018-06-13T12:40:33Z

← Older revision		Revision as of 12:40, 13 June 2018
Line 8:		Line 8:

	* Fixed header		* Fixed header
	** packet type:byte		** packet type:byte consisting of MQTT packet type in the higher nibble and flags in the lower nibble
	*** b7-4: MQTT packet type		*** b7-4: MQTT packet type
	*** b3: DUP flag (PUBLISH only)		*** b3: DUP flag (PUBLISH only)

Ctreber: /* MQTT Encoding and Decoding */

2017-07-04T08:51:21Z

MQTT Encoding and Decoding

← Older revision		Revision as of 08:51, 4 July 2017
Line 30:		Line 30:
	! Packet Type		! Packet Type
	! Flags		! Flags
	! Msg ID		! Msg ID?
	!		! Content
	\|-		\|-
	\| CONNECT		\| CONNECT
Line 39:		Line 39:
	\| -		\| -
	\|		\|
	* "MQTT"~~:String~~		* protocol name:String (always "MQTT")
	* protocol level (4)~~:byte~~		* protocol level:byte (always 4)
	* connect flags:byte		* connect flags:byte
	** b7: user		** b7: user
Line 46:		Line 46:
	** b4-3: will QoS		** b4-3: will QoS
	** b2: will		** b2: will
	** b1: clean session)		** b1: clean session
	* keep alive:word		* keep alive:word
	\|		\|
Line 64:		Line 64:
	** b0: session present		** b0: session present
	* connect return code:byte		* connect return code:byte
	** 0: connection accepted		** 0: connection accepted (success)
	** 1: unacceptable protocol version		** 1: unacceptable protocol version (fail)
	** 2: identifier rejected		** 2: identifier rejected (fail)
	** 3: server unavailable		** 3: server unavailable (fail)
	** 4: bad user name or password		** 4: bad user name or password (fail)
	** 5: not authorized		** 5: not authorized (fail)
	\| -		\| -
	\|-		\|-
Line 82:		Line 82:
	\|		\|
	* topic name:String		* topic name:String
	* message ID:word (is QoS > 0)		* message ID:word (if QoS > 0)
	\| payload:Array (optional)		\| payload:Array (optional)
	\|-		\|-

Ctreber at 08:48, 4 July 2017

2017-07-04T08:48:11Z

← Older revision		Revision as of 08:48, 4 July 2017
Line 22:		Line 22:

	{\| class="wikitable" style="border: 2px solid"		{\| class="wikitable" style="border: 2px solid"
	! rowspan="2" \| Type		! rowspan="2" \| Packet Type
	~~! rowspan="2" \| Number~~
	! rowspan="2" \| Direction		! rowspan="2" \| Direction
	! rowspan="2" \| ~~Flags~~		! rowspan="1" colspan="2" \| Fixed Header
	! rowspan="1" colspan="2" \| Variable Header		! rowspan="1" colspan="2" \| Variable Header
	! rowspan="2" \| Payload		! rowspan="2" \| Payload
	\|-		\|-
			! Packet Type
			! Flags
	! Msg ID		! Msg ID
	!		!
	\|-		\|-
	\| CONNECT		\| CONNECT
			\| Device to Broker
	\| 1		\| 1
	~~\| Device to Broker~~
	\| 0		\| 0
	\| -		\| -
Line 55:		Line 56:
	\|-		\|-
	\| CONNACK		\| CONNACK
			\| Broker to Device
	\| 2		\| 2
	~~\| Broker to Device~~
	\| 0		\| 0
	\| -		\| -
Line 72:		Line 73:
	\|-		\|-
	\| PUBLISH		\| PUBLISH
			\| Both
	\| 3		\| 3
	~~\| Both~~
	\|		\|
	* b3: DUP		* b3: DUP
Line 85:		Line 86:
	\|-		\|-
	\| PUBACK		\| PUBACK
			\| Both
	\| 4		\| 4
	~~\| Both~~
	\| 0		\| 0
	\| y		\| y
Line 94:		Line 95:
	\|-		\|-
	\| PUBREC		\| PUBREC
			\| Both
	\| 5		\| 5
	~~\| Both~~
	\| 0		\| 0
	\| y		\| y
Line 103:		Line 104:
	\|-		\|-
	\| PUBREL		\| PUBREL
			\| Both
	\| 6		\| 6
	~~\| Both~~
	\| 1 (you may read this as "fixed QoS of 1")		\| 1 (you may read this as "fixed QoS of 1")
	\| y		\| y
Line 112:		Line 113:
	\|-		\|-
	\| PUBCOMP		\| PUBCOMP
			\| Both
	\| 7		\| 7
	~~\| Both~~
	\| 0		\| 0
	\| y		\| y
Line 121:		Line 122:
	\|-		\|-
	\| SUBSCRIBE		\| SUBSCRIBE
			\| Device to Broker
	\| 8		\| 8
	~~\| Device to Broker~~
	\| 1 (you may read this as "fixed QoS of 1")		\| 1 (you may read this as "fixed QoS of 1")
	\| y		\| y
Line 133:		Line 134:
	\|-		\|-
	\| SUBACK		\| SUBACK
			\| Broker to Device
	\| 9		\| 9
	~~\| Broker to Device~~
	\| 0		\| 0
	\| y		\| y
Line 146:		Line 147:
	\|-		\|-
	\| UNSUBSCRIBE		\| UNSUBSCRIBE
			\| Device to Broker
	\| 10		\| 10
	~~\| Device to Broker~~
	\| 1 (you may read this as "fixed QoS of 1")		\| 1 (you may read this as "fixed QoS of 1")
	\| y		\| y
Line 157:		Line 158:
	\|-		\|-
	\| UNSUBACK		\| UNSUBACK
			\| Broker to Device
	\| 11		\| 11
	~~\| Broker to Device~~
	\| 0		\| 0
	\| y		\| y
Line 166:		Line 167:
	\|-		\|-
	\| PINGREQ		\| PINGREQ
			\| Device to Broker
	\| 12		\| 12
	~~\| Device to Broker~~
	\| 0		\| 0
	\| -		\| -
Line 174:		Line 175:
	\|-		\|-
	\| PINGRESP		\| PINGRESP
			\| Broker to Device
	\| 13		\| 13
	~~\| Broker to Device~~
	\| 0		\| 0
	\| -		\| -
Line 182:		Line 183:
	\|-		\|-
	\| DISCONNECT		\| DISCONNECT
			\| Device to Broker
	\| 14		\| 14
	~~\| Device to Broker~~
	\| 0		\| 0
	\| -		\| -

Ctreber: /* MQTT Encoding and Decoding */

2017-07-04T08:43:26Z

MQTT Encoding and Decoding

← Older revision		Revision as of 08:43, 4 July 2017
Line 10:		Line 10:
	** packet type:byte		** packet type:byte
	*** b7-4: MQTT packet type		*** b7-4: MQTT packet type
			*** b3: DUP flag (PUBLISH only)
			*** b2-1: QoS (PUBLISH only)
			*** b0: RETAIN flag (PUBLISH only)
	** remaining length - this one is a bit tricky and consumes between 1 and 4 bytes. Encoding is least significant bits first in b6-0 while b7 is a "continuation bit" ('1' meaning "another byte follows").		** remaining length - this one is a bit tricky and consumes between 1 and 4 bytes. Encoding is least significant bits first in b6-0 while b7 is a "continuation bit" ('1' meaning "another byte follows").
	* Variable header (optional), depending on the package type		* Variable header (optional), depending on the package type
Line 30:		Line 33:
	\|-		\|-
	\| CONNECT		\| CONNECT
	\| 1 ~~(you may read this as "fixed QoS of 1")~~		\| 1
	\| Device to Broker		\| Device to Broker
	\| 0		\| 0

Ctreber at 08:39, 4 July 2017

2017-07-04T08:39:32Z

← Older revision		Revision as of 08:39, 4 July 2017
Line 30:		Line 30:
	\|-		\|-
	\| CONNECT		\| CONNECT
	\| 1		\| 1 (you may read this as "fixed QoS of 1")
	\| Device to Broker		\| Device to Broker
	\| 0		\| 0
Line 78:		Line 78:
	\|		\|
	* topic name:String		* topic name:String
	* message ID:word		* message ID:word (is QoS > 0)
	\| payload:Array (optional)		\| payload:Array (optional)
	\|-		\|-
Line 102:		Line 102:
	\| 6		\| 6
	\| Both		\| Both
	\| 1		\| 1 (you may read this as "fixed QoS of 1")
	\| y		\| y
	\|		\|
Line 120:		Line 120:
	\| 8		\| 8
	\| Device to Broker		\| Device to Broker
	\| 1		\| 1 (you may read this as "fixed QoS of 1")
	\| y		\| y
	\|		\|
Line 145:		Line 145:
	\| 10		\| 10
	\| Device to Broker		\| Device to Broker
	\| 1		\| 1 (you may read this as "fixed QoS of 1")
	\| y		\| y
	\|		\|

Ctreber at 08:37, 4 July 2017

2017-07-04T08:37:27Z

← Older revision		Revision as of 08:37, 4 July 2017
Line 8:		Line 8:

	* Fixed header		* Fixed header
	** b7-4: MQTT ~~Packet Typ, b3-0: Flags~~		** packet type:byte
	** ~~Remaining~~ length - this one is a bit tricky and consumes between 1 and 4 bytes. Encoding is least significant bits first in b6-0 while b7 is a "continuation bit" ('1' meaning "another byte follows").		*** b7-4: MQTT packet type
			** remaining length - this one is a bit tricky and consumes between 1 and 4 bytes. Encoding is least significant bits first in b6-0 while b7 is a "continuation bit" ('1' meaning "another byte follows").
	* Variable header (optional), depending on the package type		* Variable header (optional), depending on the package type
	* Payload (optional), depending on the package type		* Payload (optional), depending on the package type

	~~Text is encoded in UTF-8 without a terminating~~ "0" ~~byte~~, after the number of bytes in the text encoded as two bytes, MSB first.		Type "Array" is binary data, after the number of bytes in the text encoded as two bytes, MSB first.

			Type "String" is like "Array", text encoded in UTF-8 without a terminating "0" byte.

	{\| class="wikitable" style="border: 2px solid"		{\| class="wikitable" style="border: 2px solid"
Line 31:		Line 34:
	\| 0		\| 0
	\| -		\| -
	\| "MQTT":String~~<br/>~~protocol level (4):byte~~<br/>~~connect flags:byte (b7: user, b6: password, b5: will retain, b4-3: will QoS, b2: will, b1: clean session)~~<br/>~~keep alive:word		\|
	\| client ID:String~~<br/>~~will topic:String (if present)~~<br/>~~will payload:Array (if present)~~<br/>~~user name:String (if present)~~<br/>~~password:Array (if present)		* "MQTT":String
			* protocol level (4):byte
			* connect flags:byte
			** b7: user
			** b6: password, b5: will retain
			** b4-3: will QoS
			** b2: will
			** b1: clean session)
			* keep alive:word
			\|
			* client ID:String
			* will topic:String (if present)
			* will payload:Array (if present)
			* user name:String (if present)
			* password:Array (if present)
	\|-		\|-
	\| CONNACK		\| CONNACK
Line 39:		Line 56:
	\| 0		\| 0
	\| -		\| -
	\| connect acknowledge flags:byte (b0: session present~~)<br/>~~connect return code:byte (0: connection accepted, 1: unacceptable		\|
	protocol version, 2: identifier rejected, 3: server unavailable, 4: bad user name or password, 5: not authorized)		* connect acknowledge flags:byte
			** b0: session present
			* connect return code:byte
			** 0: connection accepted
			** 1: unacceptable protocol version
			** 2: identifier rejected
			** 3: server unavailable
			** 4: bad user name or password
			** 5: not authorized
	\| -		\| -
	\|-		\|-
Line 46:		Line 71:
	\| 3		\| 3
	\| Both		\| Both
	\| b3: DUP, b2-1: QoS, b0: RETAIN		\|
			* b3: DUP
			* b2-1: QoS
			* b0: RETAIN
	\| QoS > 0 ? y		\| QoS > 0 ? y
	\| topic name:String~~<br/>~~message ID:word		\|
			* topic name:String
			* message ID:word
	\| payload:Array (optional)		\| payload:Array (optional)
	\|-		\|-
Line 56:		Line 86:
	\| 0		\| 0
	\| y		\| y
	\| message ID of PUBLISH packet:word		\|
			* message ID of PUBLISH packet:word
	\| -		\| -
	\|-		\|-
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	\| 0		\| 0
	\| y		\| y
	\| message ID of PUBLISH packet:word		\|
			* message ID of PUBLISH packet:word
	\| -		\| -
	\|-		\|-
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	\| 1		\| 1
	\| y		\| y
	\| message ID of PUBREC packet:word		\|
			* message ID of PUBREC packet:word
	\| -		\| -
	\|-		\|-
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	\| 0		\| 0
	\| y		\| y
	\| message ID of PUBREL packet:word		\|
			* message ID of PUBREL packet:word
	\| -		\| -
	\|-		\|-
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	\| 1		\| 1
	\| y		\| y
	\| message ID:word		\|
	\| topic filter:String~~<br/>~~requested QoS:byte (b1-0: QoS)~~<br/>(~~repeat sequence one or more times)		* message ID:word
			\|
			* topic filter:String
			* requested QoS:byte (b1-0: QoS)
			repeat sequence one or more times
	\|-		\|-
	\| SUBACK		\| SUBACK
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	\| 0		\| 0
	\| y		\| y
	\| message ID of SUBSCRIBE packet:word		\|
	\| return code:byte (b7: failure, b1-0: maximum QoS~~)<br/>(~~repeat sequence one or more times)		* message ID of SUBSCRIBE packet:word
			\|
			* return code:byte
			** b7: failure
			** b1-0: maximum QoS
			repeat sequence one or more times
	\|-		\|-
	\| UNSUBSCRIBE		\| UNSUBSCRIBE
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	\| 1		\| 1
	\| y		\| y
	\| message ID:word		\|
	\| topic filter:String~~<br/>(~~repeat sequence one or more times)		* message ID:word
			\|
			* topic filter:String
			repeat sequence one or more times
	\|-		\|-
	\| UNSUBACK		\| UNSUBACK
Line 112:		Line 158:
	\| 0		\| 0
	\| y		\| y
	\| message ID of SUBSCRIBE packet:word		\|
			* message ID of SUBSCRIBE packet:word
	\| -		\| -
	\|-		\|-

Ctreber at 08:26, 4 July 2017

2017-07-04T08:26:32Z

← Older revision		Revision as of 08:26, 4 July 2017
Line 15:		Line 15:
	Text is encoded in UTF-8 without a terminating "0" byte, after the number of bytes in the text encoded as two bytes, MSB first.		Text is encoded in UTF-8 without a terminating "0" byte, after the number of bytes in the text encoded as two bytes, MSB first.

	{\|		{\| class="wikitable" style="border: 2px solid"
	! Type		! rowspan="2" \| Type
	! Number		! rowspan="2" \| Number
	! Direction		! rowspan="2" \| Direction
	! Flags		! rowspan="2" \| Flags
	! Variable Header		! rowspan="1" colspan="2" \| Variable Header
	! Payload		! rowspan="2" \| Payload
			\|-
			! Msg ID
			!
	\|-		\|-
	\| CONNECT		\| CONNECT
Line 27:		Line 30:
	\| Device to Broker		\| Device to Broker
	\| 0		\| 0
	\|		\| -
	\|		\| "MQTT":String<br/>protocol level (4):byte<br/>connect flags:byte (b7: user, b6: password, b5: will retain, b4-3: will QoS, b2: will, b1: clean session)<br/>keep alive:word
			\| client ID:String<br/>will topic:String (if present)<br/>will payload:Array (if present)<br/>user name:String (if present)<br/>password:Array (if present)
	\|-		\|-
	\| CONNACK		\| CONNACK
Line 34:		Line 38:
	\| Broker to Device		\| Broker to Device
	\| 0		\| 0
	\|		\| -
	\|		\| connect acknowledge flags:byte (b0: session present)<br/>connect return code:byte (0: connection accepted, 1: unacceptable
			protocol version, 2: identifier rejected, 3: server unavailable, 4: bad user name or password, 5: not authorized)
			\| -
	\|-		\|-
	\| PUBLISH		\| PUBLISH
Line 41:		Line 47:
	\| Both		\| Both
	\| b3: DUP, b2-1: QoS, b0: RETAIN		\| b3: DUP, b2-1: QoS, b0: RETAIN
	\|		\| QoS > 0 ? y
	\|		\| topic name:String<br/>message ID:word
			\| payload:Array (optional)
	\|-		\|-
	\| PUBACK		\| PUBACK
Line 48:		Line 55:
	\| Both		\| Both
	\| 0		\| 0
	\|		\| y
	\|		\| message ID of PUBLISH packet:word
			\| -
	\|-		\|-
	\| PUBREC		\| PUBREC
Line 55:		Line 63:
	\| Both		\| Both
	\| 0		\| 0
	\|		\| y
	\|		\| message ID of PUBLISH packet:word
			\| -
	\|-		\|-
	\| PUBREL		\| PUBREL
Line 62:		Line 71:
	\| Both		\| Both
	\| 1		\| 1
	\|		\| y
	\|		\| message ID of PUBREC packet:word
			\| -
	\|-		\|-
	\| PUBCOMP		\| PUBCOMP
Line 69:		Line 79:
	\| Both		\| Both
	\| 0		\| 0
	\|		\| y
	\|		\| message ID of PUBREL packet:word
			\| -
	\|-		\|-
	\| SUBSCRIBE		\| SUBSCRIBE
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	\| Device to Broker		\| Device to Broker
	\| 1		\| 1
	\|		\| y
	\|		\| message ID:word
			\| topic filter:String<br/>requested QoS:byte (b1-0: QoS)<br/>(repeat sequence one or more times)
	\|-		\|-
	\| SUBACK		\| SUBACK
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	\| Broker to Device		\| Broker to Device
	\| 0		\| 0
	\|		\| y
	\|		\| message ID of SUBSCRIBE packet:word
			\| return code:byte (b7: failure, b1-0: maximum QoS)<br/>(repeat sequence one or more times)
	\|-		\|-
	\| UNSUBSCRIBE		\| UNSUBSCRIBE
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	\| Device to Broker		\| Device to Broker
	\| 1		\| 1
	\|		\| y
	\|		\| message ID:word
			\| topic filter:String<br/>(repeat sequence one or more times)
	\|-		\|-
	\| UNSUBACK		\| UNSUBACK
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	\| Broker to Device		\| Broker to Device
	\| 0		\| 0
	\|		\| y
	\|		\| message ID of SUBSCRIBE packet:word
			\| -
	\|-		\|-
	\| PINGREQ		\| PINGREQ
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	\| Device to Broker		\| Device to Broker
	\| 0		\| 0
			\| -
	\|		\|
	\|		\| -
	\|-		\|-
	\| PINGRESP		\| PINGRESP
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	\| Broker to Device		\| Broker to Device
	\| 0		\| 0
			\| -
	\|		\|
	\|		\| -
	\|-		\|-
	\| DISCONNECT		\| DISCONNECT
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	\| Device to Broker		\| Device to Broker
	\| 0		\| 0
	\|-		\| -
	\|
	\|		\|
			\| -
	\|}		\|}

	[[MQTT]]		[[MQTT]]

Ctreber: Created page with "MQTT =MQTT Encoding and Decoding= The MQTT protocol is very lightweight (does not use many bytes to get the message across). Each MQTT packet consists of: * Fixed head..."

2017-07-03T15:55:09Z

Created page with "MQTT =MQTT Encoding and Decoding= The MQTT protocol is very lightweight (does not use many bytes to get the message across). Each MQTT packet consists of: * Fixed head..."

New page

[[MQTT]]

=MQTT Encoding and Decoding=

The MQTT protocol is very lightweight (does not use many bytes to get the message across).

Each MQTT packet consists of:

* Fixed header
** b7-4: MQTT Packet Typ, b3-0: Flags
** Remaining length - this one is a bit tricky and consumes between 1 and 4 bytes. Encoding is least significant bits first in b6-0 while b7 is a "continuation bit" ('1' meaning "another byte follows").
* Variable header (optional), depending on the package type
* Payload (optional), depending on the package type

Text is encoded in UTF-8 without a terminating "0" byte, after the number of bytes in the text encoded as two bytes, MSB first.

{|
! Type
! Number
! Direction
! Flags
! Variable Header
! Payload
|-
| CONNECT
| 1
| Device to Broker
| 0
|
|
|-
| CONNACK
| 2
| Broker to Device
| 0
|
|
|-
| PUBLISH
| 3
| Both
| b3: DUP, b2-1: QoS, b0: RETAIN
|
|
|-
| PUBACK
| 4
| Both
| 0
|
|
|-
| PUBREC
| 5
| Both
| 0
|
|
|-
| PUBREL
| 6
| Both
| 1
|
|
|-
| PUBCOMP
| 7
| Both
| 0
|
|
|-
| SUBSCRIBE
| 8
| Device to Broker
| 1
|
|
|-
| SUBACK
| 9
| Broker to Device
| 0
|
|
|-
| UNSUBSCRIBE
| 10
| Device to Broker
| 1
|
|
|-
| UNSUBACK
| 11
| Broker to Device
| 0
|
|
|-
| PINGREQ
| 12
| Device to Broker
| 0
|
|
|-
| PINGRESP
| 13
| Broker to Device
| 0
|
|
|-
| DISCONNECT
| 14
| Device to Broker
| 0
|-
|
|
|}

[[MQTT]]