Errata exists for this version of the document.

A writer negotiates the delivery guarantees for its link using the snd-settle-mode settlement policy (settled, unsettled, mixed) it will use, and the desired rcv-settle-mode (first, second) of the broker.

Vice versa, the reader negotiates delivery guarantees using its rcv-settle-mode (first, second) and the desired snd-settle-mode (settled, unsettled) of the broker.

This matches to the BrokerTransportQualityOfService values as follows:

• AtMostOnce_1 – messages are pre-settled at the sender endpoint and not sent again. Messages may be lost in transit.  This is the default setting.
• AtLeastOnce_2 – messages are received and settled at the receiver without waiting for the sender to settle.
• ExactlyOnce_3 – messages are received, the sender settles and then the receiver settles.