-AP F1-AP F1-AP PHY/MAC PHY/MAC L1/L2 L1/L2 NR-Uu IPsec IPsec PHY/MAC PHY/MAC PHY/MAC PHY/MAC BH RLC channel BH RLC channel Figure 5.2.6 Protocol stacks for UE-access with two-hop backhaul. Top: User-plane stack. Bottom: Control-plane stack. UE DRB1 VolP BH RLC CH1: UE1 DRB1 BH RLC CH1: UE1 DRB1 UE DRB2 Streaming BH RLC CH2: UE1 DRB2 BH RLC CH2: UE1 DRB2 UE DRB1 VolP BH RLC CH3: UE2 DRB1 BH RLC CH3: UE2 DRB1 UE DRB2 Web browsing BH RLC CH4: UE2 DRB2 BH RLC CH4: UE2 DRB2 donor UE DRB1 VolP BH RLC CH5: UE2 DRB1 BH RLC CH5: UE2 DRB1 UE DRB2 Web browsing BH RLC CH6: UE2 DRB2 BH RLC CH6: UE2 DRB2 UE DRB3 Streaming BH RLC CH7: UE2 DRB3 BH RLC CH7: UE2 DRB3 1:1 mapping between UE bearers and backhaul RLC channels UE DRB1 VolP UE DRB2 Streaming BH RLC CH1: UE1 DRB1 BH RLC CH1: UE1 DRB1 + UE2 DRB1 + UE3 DRB1 + UE2 DRB1 + UE3 DRB1 UE DRB1 VolP BH RLC CH2: UE2 DRB2 BH RLC CH2: UE2 DRB2 UE DRB2 Web browsing + UE3 DRB 2 + UE3 DRB 2 donor BH RLC CH7: UE2 DRB3 BH RLC CH7: UE2 DRB3 UE DRB1 VolP + UE3 DRB3 + UE3 DRB3 UE DRB2 Web browsing UE DRB3 Streaming N:1 mapping between UE bearers and backhaul RLC channels Figure 5.2.7 1:1 and N:1 mapping between UE bearers and backhaul RLC channels for QoS support. 5.2 Wireless Relaying in 5G bearer-specific QoS enforcement, such as guaranteed bitrate for streaming voice or video services. However, 1:1 bearer mapping requires update of RLC channels whenever a UE bearer is established or released. Therefore, IAB further supports N : 1 aggregation of mul- tiple UE bearers onto a common backhaul RLC channel, which still allows traffic priori- tization based, for example, on the traffic's QoS profile (Figure 5.2.7, bottom). Since such aggregated N: 1 mapping can be configured semi-statically, it reduces the signaling over- head compared with 1:1 bearer mapping. The support of both features, 1:1 and N: 1 bearer mappings, was a compromise reached after long discussions in 3GPP. Some companies argued that fine granular QoS support on the backhaul is necessary considering congestion due to traffic 