AMQP message transfers (also called deliveries) can occur in either direction, with AMQP links created in pairs from the parent AMQP session.

AMQP defines the following approaches with regard to message transfers (AMQP deliveries):

AMQP deliveries occurring via settled message transfers can be used for a "fire and forget" publishing / subscribing model, as they do not require an explicit acknowledgment.

AMQP publishing occurs when an AMQP application container (Sender) attaches a link to an AMQP node (Receiver) and initiates message deliveries. In the at-most-once model, message deliveries are sent pre-settled by the sender with no expectations of acknowledgment from the receiver.

AMQP subscribing occurs when an AMQP application container (Receiver) attaches a link to an AMQP node (Sender) causing a flow of deliveries from the sender node to the application node. In the at-most-once model, message deliveries are sent pre-settled by the sender with no expectations of acknowledgment from the receiver.

AMQP deliveries occurring via unsettled message transfers require an explicit settlement via acknowledgments, whether initiated by an application container or a broker container.

AMQP publishing occurs when an AMQP application container (Sender) attaches a link to an AMQP node (Receiver) and initiates message deliveries. In the at-least-once model, message deliveries are sent unsettled by the sender with an expectation of acknowledgment from the receiver.

AMQP subscribing occurs when an AMQP application container (Receiver) attaches a link to an AMQP node (Sender) causing a flow of deliveries from the sender node to the application node. In the at-least-once model, message deliveries are sent un-settled by the sender with an expectation of acknowledgment from the receiver. The AMQP source durability configuration indicates whether the durable subscription state should be in-memory or persistent (CONFIGURATION or UNSETTLED_STATE respectively).