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Communicate with DPS using the MQTT protocol

  • Artikkeli

Azure IoT Device Provisioning Service (DPS) enables devices to communicate with the DPS device endpoint using:

DPS isn't a full-featured MQTT broker and doesn't support all the behaviors specified in the MQTT v3.1.1 standard. This article describes how devices can use supported MQTT behaviors to communicate with DPS.

All device communication with DPS must be secured using TLS/SSL. Therefore, DPS doesn't support nonsecure connections over port 1883.

Note

DPS does not currently support devices using TPM attestation mechanism over the MQTT protocol.

Connecting to DPS

A device can use the MQTT protocol to connect to a DPS instance using any of the following options.

Using the MQTT protocol directly (as a device)

If a device can't use the device SDKs, it can still connect to the public device endpoints using the MQTT protocol on port 8883. In the CONNECT packet, the device should use the following values:

  • For the ClientId field, use registrationId.

  • For the Username field, use {idScope}/registrations/{registration_id}/api-version=2019-03-31, where {idScope} is the ID scope of the DPS and {registration_id} is the Registration ID for your device.

    Note

    If you use X.509 certificate authentication, the registration ID is provided by the subject common name (CN) of your device leaf (end-entity) certificate. {registration_id} in the Username field must match the common name.

  • For the Password field, use a SAS token. The format of the SAS token is the same as for both the HTTPS and AMQP protocols:

    SharedAccessSignature sr={URL-encoded-resourceURI}&sig={signature-string}&se={expiry}&skn=registration The resourceURI should be in the format {idScope}/registrations/{registration_id}. The policy name (skn) should be set to registration.

    Note

    If you use X.509 certificate authentication, SAS token passwords are not required.

    For more information about how to generate SAS tokens, see the security tokens section of Control access to DPS.

The following list contains DPS implementation-specific behaviors:

  • DPS doesn't support persistent sessions. It treats every session as non-persistent, regardless of the value of the CleanSession flag. We recommend setting CleanSession to true.

  • When a device app subscribes to a topic with QoS 2, DPS grants maximum QoS level 1 in the SUBACK packet. After that, DPS delivers messages to the device using QoS 1.

TLS/SSL configuration

To use the MQTT protocol directly, your client must connect over TLS 1.2. Attempts to skip this step fail with connection errors.

Registering a device

To register a device through DPS, a device should subscribe using $dps/registrations/res/# as a Topic Filter. The multi-level wildcard # in the Topic Filter is used only to allow the device to receive more properties in the topic name. DPS doesn't allow the usage of the # or ? wildcards for filtering of subtopics. Since DPS isn't a general-purpose pub-sub messaging broker, it only supports the documented topic names and topic filters.

The device should publish a register message to DPS using $dps/registrations/PUT/iotdps-register/?$rid={request_id} as a Topic Name. The payload should contain the Device Registration object in JSON format. In a successful scenario, the device receives a response on the $dps/registrations/res/202/?$rid={request_id}&retry-after=x topic name where x is the retry-after value in seconds.

Polling for registration operation status

The device must poll the service periodically to receive the result of the device registration operation. Assuming that the device has already subscribed to the $dps/registrations/res/# topic, it can publish a get operation status message to the $dps/registrations/GET/iotdps-get-operationstatus/?$rid={request_id}&operationId={operationId} topic name. The operation ID in this message should be the value received in the RegistrationOperationStatus response message in the previous step. In the successful case, the service responds on the $dps/registrations/res/200/?$rid={request_id} topic. The payload of the response contains the RegistrationOperationStatus object. The device should keep polling the service if the response code is 202 after a delay equal to the retry-after period. The device registration operation is successful if the service returns a 200 status code.

Connecting over Websocket

When connecting over Websocket, specify the subprotocol as mqtt. Follow RFC 6455.

Next steps

To learn more about the MQTT protocol, see the MQTT documentation.

To browse sample MQTT code, see MQTT application samples.

To further explore the capabilities of DPS, see:

What is Azure IoT Hub Device Provisioning Service?