Section: 16.21.2.2 L2 MP Relay using N3C indirect path
Content: For the multi-path relay using N3C indirect path between the Remote UE and Relay UE, the protocol stacks for the user plane and control plane of L2 MP Relay architecture are illustrated in Figure 16.21.2.2-1 and Figure 16.21.2.2-2. The L2 MP Relay UE and the L2 MP Remote UE are connected via a N3C interface. In the multi-path relay using N3C indirect path, the SRAP sublayer does not exist on the protocol stack. Without the SRAP entity between L2 MP Remote UE and L2 MP Relay UE, the Uu SDAP, PDCP, and RRC are terminated at gNB and L2 MP Remote UE. While RLC, MAC, and PHY are terminated in Uu hop. An UL PDCP PDU in the L2 MP Remote UE can be delivered to a Uu RLC entity and an intended PDCP entity or RLC entity in the L2 MP Relay UE. It is supported for more than one RB over the Uu link of the L2 MP Relay UE by configuring 1:1 bearer mapping between the Radio bearer in the L2 MP Remote UE and Uu Relay RLC channel in the L2 MP Relay UE. The Uu Relay RLC channels for the PDU delivery of the L2 MP Relay UE's local traffic and relay traffic are configured differently. Bearer identification except LCID is not needed in L2 PDU over the Uu link. If the split bearer is configured and the PDCP PDU duplication is activated on the PDCP entity, the duplicated PDCP PDUs are delivered via both direct path and indirect path. Figure 16.21.2.2-1: User plane protocol stack for L2 Multi-path Relay using N3C indirect path Figure 16.21.2.2-2: Control plane protocol stack for L2 Multi-path Relay using N3C indirect path