SDAP is responsible for QoS Flow handling across the 5G air interface. In particular, SDAP will map a specific QoS Flow within a PDU Session to a corresponding Data Radio Bearer (which has been established with the appropriate level of QoS). In addition, SDAP will mark the transmitted packets with the correct QFI (QoS Flow ID), ensuring that the packet receives the correct forwarding treatment as it traverses the 5G System.
For each PDU Session, a single protocol entity of SDAP will be configured. The exception to this is Dual Connectivity, whereby the Master Cell Group and Secondary Cell Group will each have a separate SDAP configuration on the device.