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    IoT Platform:Optimized device-cloud interactions

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    IoT Platform:Optimized device-cloud interactions

    Last Updated:Jun 21, 2023

    This topic describes optimized device-cloud interactions in MQTT 5.0 supported by IoT Platform.

    Feature description

    MQTT 5.0 is designed to improve the interoperability and messaging transparency between devices and servers. In MQTT 5.0, the following device-cloud interactions are optimized:

    Feedback on connection establishment

    Feedback on connection establishment is a negotiation mechanism between devices and the server. When a connection is being established between a device and the server, the device sends connection parameters in the request, and the server returns a CONNACK packet as the feedback. The CONNACK packet is a connect acknowledgment that includes the values of request parameters and the features that are available to the device.

    CONNACK property

    Description and value range

    Response from IoT Platform

    Retain Available

    • 1: Retained messages are supported.

    • 0: Retained messages are not supported.

    1

    Wildcard Subscription Available

    • 1: Wildcard Subscriptions are supported.

    • 0: Wildcard Subscriptions are not supported.

    1

    Subscription Identifiers Available

    • 1: Subscription Identifiers are supported.

    • 0: Subscription Identifiers are not supported.

    0

    Shared Subscription Available

    • 1: Shared Subscriptions are supported.

    • 0: Shared Subscriptions are not supported.

    1

    Topic Alias

    • 1: The server accepts Topic Aliases on this connection.

    • 0: The server does not accept Topic Aliases on this connection.

    1

    Maximum QoS

    • 2: QoS 2.

    • 1: QoS 1.

    • 0: QoS 0.

    1

    Server Keep Alive

    The server continues to send heartbeat packets or data packets during the keep-alive period. Otherwise, the connection is disrupted. This property specifies the keep-alive period.

    Valid values: 30 to 1200.

    IoT Platform returns the keep-alive period that the device specifies in the connection parameters.

    If the value that is set by the device is beyond the value range, the connection is disrupted.

    Session Expiry Interval

    This property specifies the retention period of the session after the connection is disrupted.

    Valid values: 0 to 0xFFFFFFFF.

    IoT Platform returns the retention period that the device specifies in the connection parameters.

    If the device did not specify this period, the default value 0 is used.

    Maximum Packet Size

    Valid values: 0 to 0xFFFFFFFF.

    IoT Platform always returns 262144, which indicates 256 KB.

    Topic Alias Maximum

    Valid values: 0 to 0xFFFFFFFF.

    IoT Platform always returns 20.

    Server-sent DISCONNECT packets

    In MQTT 3.1.1, if a device violates a rule, the server directly closes the device connection without explaining why the connection closed.

    In MQTT 5.0, the server can close the connection to a device, and sends a DISCONNECT packet to the device. The DISCONNECT packet contains a reason code and a reason string that explains why the connection closed. The DISCONNECT packet simplifies troubleshooting.

    Enhancements in error codes

    Enhancement

    MQTT 3.1

    MQTT 5.0

    Quantity increase

    5 error codes

    20 error codes

    Reason string

    Not supported

    The Reason String property is added to specify the detailed error cause for debugging and troubleshooting.

    Error codes for more types of packets

    Error codes are returned for only CONNECT packets.

    Error codes are returned for CONNECT, UNSUBACK, PUBACK, DISCONNECT and other packets.

    Error codes

    Decimal

    Hexadecimal

    Name

    Packet type

    0

    0x00

    Success

    CONNACK, PUBACK, PUBREC, PUBREL, PUBCOMP, UNSUBACK, and AUTH

    128

    0x80

    Unspecified error

    CONNACK, PUBACK, PUBREC, SUBACK, UNSUBACK, and DISCONNECT

    129

    0x81

    Malformed Packet

    CONNACK and DISCONNECT

    130

    0x82

    Protocol Error

    CONNACK and DISCONNECT

    132

    0x84

    Unsupported Protocol Version

    CONNACK

    136

    0x88

    Server unavailable

    CONNACK

    137

    0x89

    Server busy

    CONNACK and DISCONNECT

    138

    0x8A

    Banned

    CONNACK

    140

    0x8C

    Bad authentication method

    CONNACK and DISCONNECT

    141

    0x8D

    Keep Alive timeout

    DISCONNECT

    144

    0x90

    Topic Name invalid

    CONNACK, PUBACK, PUBREC, and DISCONNECT

    147

    0x93

    Receive Maximum exceeded

    DISCONNECT

    148

    0x94

    Topic Alias invalid

    DISCONNECT

    149

    0x95

    Packet too large

    CONNACK and DISCONNECT

    150

    0x96

    Message rate too high

    DISCONNECT

    151

    0x97

    Quota exceeded

    CONNACK, PUBACK, PUBREC, SUBACK, and DISCONNECT

    152

    0x98

    Administrative action

    DISCONNECT

    153

    0x99

    Payload format invalid

    PUBACK, PUBREC, and DISCONNECT

    154

    0x9A

    Retain not supported

    CONNACK and DISCONNECT

    155

    0x9B

    QoS not supported

    CONNACK and DISCONNECT

    156

    0x9C

    Use another server

    CONNACK and DISCONNECT

    157

    0x9D

    Server moved

    CONNACK and DISCONNECT

    158

    0x9E

    Shared Subscription not supported

    SUBACK and DISCONNECT

    159

    0x9F

    Connection rate exceeded

    CONNACK and DISCONNECT