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Protocols (MQTT & HTTP)

OmniCore supports two protocols for device connection and communication: MQTT and HTTP. Devices communicate with OmniCore across a "bridge" — either the MQTT bridge or the HTTP bridge. The MQTT/HTTP bridge is a central component of OmniCore, as shown in the components overview. When you create a device registry, you select protocols to enable: MQTT, HTTP, or both.

  • MQTT is a standard publish/subscribe protocol that is frequently used and supported by embedded devices, and is also common in machine-to-machine interactions.

  • HTTP is a "connectionless" protocol: with the HTTP bridge, devices do not maintain a connection to OmniCore. Instead, they send requests and receive responses. OmniCore supports HTTP 1.1 only (not 2.0).

    The following table compares how the two protocols work in OmniCore:

    MQTT bridgeHTTP bridge
    Device connection is maintainedConnectionless (request/response)
    Full-duplex TCP connectionHalf-duplex TCP connection
    JWT is sent in the password field of the CONNECT messageJWT is sent in the Authorization header of the HTTP request
    Telemetry events are pushed to Cloud Pub/SubTelemetry events are pushed to Cloud Pub/Sub
    Device connection status is reportedNo device connection status reported
    Device configurations are propagated via subscriptionsDevice configurations must be explicitly requested (via polling)
    Most recent configuration (whether newer or not) is always received by devices on subscriptionDevices can specify that only newer configurations should be received
    Device configurations are acknowledged (ACKed) when using QoS 1No explicit ACK for device configurations
    Last device heartbeat time is retainedNo device heartbeat data

You might also want to consider the following general features of each protocol:

MQTT​

  • Lower bandwidth usage
  • Lower latency
  • Higher throughput
  • Supports raw binary data

HTTP​

  • Lighter weight (easy to get started; simple curl commands)
  • Fewer firewall issues
  • Binary data must be base64-encoded, which requires more network and CPU resources