SDAP is a new layer in 5G NR.
SDAP stands for Service Data Adaption Protocol.
SDAP is a user plane protocol in 5G NR.
The main functions of SDAP are:
1. Mapping between QoS flow and a data radio bearer.
2. Marking of QFI in both UL and DL.
SDAP architecture
> There is no one-to-one mapping between PDU session and SDAP entity.
> A PDU session contains one or more QoS flows and one or more QoS Flow can be mapped to a DRB.
> One or more QoS flow can be configured to one DRB.
> One DRB can be configured to one SDAP.
SDAP data transmission
> A data packet generated by the application layer needs to be mapped twice, once for NAS mapping to process SDF and QoS flow mapping and AS mapping for processing QoS and DRB mapping.
> A UE performing uplink transmission, the mapping rule is based on the mapping rule during downlink transmission (reflective QoS).
Source TS 37.324