QOS Impact in MQT

The MQTT QoS parameter is applicable for communication between device and mqtt broker. The communication between MQTT broker and SCS A/S is http. Therefore, QoS is not guaranteed for entire path from Device, and then mqtt broker, and then application.

The following table describes different QOS available in MQTT:

Table 2-18 Different QOS available in MQTT

QOS	Description
QoS 0 At most once delivery	The message is delivered according to the capabilities of the underlying network. No response is sent by the receiver and no retry is performed by the sender. The message arrives at the receiver either once or never.
QoS 1 At least once delivery	This quality of service ensures that the message arrives at the receiver at least once. Duplication of messages are possible.
QoS 2 Exactly once delivery	This is the highest quality of service that does not accept loss and duplication of messages. There is an increased overhead associated with this quality of service.

For more information about QOS, refer to MQTT 3.1.1 Specification.