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 bridge	HTTP bridge
  Device connection is maintained	Connectionless (request/response)
  Full-duplex TCP connection	Half-duplex TCP connection
  JWT is sent in the password field of the CONNECT message	JWT is sent in the Authorization header of the HTTP request
  Telemetry events are pushed to Cloud Pub/Sub	Telemetry events are pushed to Cloud Pub/Sub
  Device connection status is reported	No device connection status reported
  Device configurations are propagated via subscriptions	Device configurations must be explicitly requested (via polling)
  Most recent configuration (whether newer or not) is always received by devices on subscription	Devices can specify that only newer configurations should be received
  Device configurations are acknowledged (ACKed) when using QoS 1	No explicit ACK for device configurations
  Last device heartbeat time is retained	No 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