Section: 6.11.2 Traffic Mapping from Upper Layers to Layer-2
Content: In upstream direction, the IAB-donor-CU configures the IAB-node with mappings between upstream F1 and non-F1 traffic originated at the IAB-node, and the appropriate BAP routing ID, next-hop BAP address and BH RLC channel. A specific mapping is configured: - for each F1-U GTP-U tunnel; - for non-UE associated F1AP messages; - for UE-associated F1AP messages; - for non-F1 traffic. Multiple mappings can contain the same BH RLC channel and/or next-hop BAP address and/or BAP routing ID. In case the IAB-MT is NR-dual-connected (SA mode only), the mapping may include two separate BH RLC channels, where the two BH RLC channels are established toward different parent nodes. In case the IAB-node is configured with multiple IP addresses for F1-C on the NR leg, multiple mappings can be configured for non-UE-associated F1AP messages or UE-associated F1AP messages. The appropriate mapping is selected based on the IAB-node's implementation. These traffic mapping configurations are performed via F1AP. For a boundary IAB-node, the traffic mapping configuration includes information that allows the boundary IAB-node to determine the IAB topology the mapping applies to. During IAB-node integration, a default BH RLC channel and a default BAP routing ID may be configured via RRC, which can be used for non-F1-U traffic. These default configurations may be updated during topology adaptation scenarios as discussed in TS 38.401[ NG-RAN; Architecture description ]  [4]. In downstream direction, traffic mapping occurs internal to the IAB-donor. Transport for IAB-donors that use split-gNB architecture is handled in TS 38.401[ NG-RAN; Architecture description ]  [4].