The BrokerTransportQualityOfService Enumeration DataType is formally defined in Table 71.
The mapping of quality of service to the broker transport specific implementation is defined in 7.3.4.5 for AMQP and 7.3.5.5 for MQTT.
Table 69 – BrokerTransportQualityOfService Values
|
Value |
Description |
|
NotSpecified_0 |
The value is not specified and the value of the parent object shall be used. |
|
BestEffort_1 |
The transport shall make the best effort to deliver a message. Worst case this means data loss or data duplication are possible. |
|
AtLeastOnce_2 |
The transport guarantees that the message shall be delivered at least once, but duplication is possible. Readers must de-duplicate based on message id or sequence number. |
|
AtMostOnce_3 |
The transport guarantees that the message shall be sent once, but if it is lost it is not sent again. |
|
ExactlyOnce_4 |
The transport handshake guarantees that the message shall be delivered to the broker exactly once and not more or less. |