Service Data Adaptation Protocol (SDAP) facilitates implementation of QoS on the New Radio (NR) interface in 5G.
Like LTE, the NR radio protocol stack utilizes protocols such as Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP), and Radio Resource Control (RRC). NR significantly enhances some of these protocols such as PHY and MAC. SDAP is the brand new protocol introduced by 3GPP for the NR air interface. In the downlink, the UPF sends a packet along with QoS Flow Identifier (QFI) to the gNB. This QFI is associated with a certain set of QoS characteristics. The gNB uses the help of SDAP to include QFI in the packet for a suitable Data Radio Bearer (DRB). Thus, SDAP facilitates QoS Flow- DRB mapping. Such DRB receives an appropriate QoS treatment on the air interface. In the uplink, the UE places QFI in the packet using SDAP. The UE also performs Reflective QoS Flow and DRB mapping in the uplink using SDAP. On the N3 interface between the gNB and the UPF, multiple QoS Flows can be mapped onto the same N3 Tunnel. However, these QoS Flows would receive a suitable QoS treatment on the NR air interface based on QFIs, SDAP, and suitable radio resource allocation by the gNB. The QoS Flow receives a suitable packet forwarding treatment in the transport network.