3GPP 38.300 v19.3.0 — the document's own text
4.7.2 Protocol Stacks
Taught in 4. What NR actually is, in the shape its own document gives it (TSG RAN — the group that specifies the radio, overview).
Fig. 4.7.2-1 shows the protocol stack for F1-U and Fig. 4.7.2-2 shows the protocol stack for F1-C between IAB-DU and IAB-donor-CU. In these figures, F1-U and F1-C are carried over two backhaul hops.
F1-U and F1-C use an IP transport layer between IAB-DU and IAB-donor-CU as defined in TS 38.470 [32]. F1-U and F1-C need to be security-protected as described in TS 33.501 [5] (the security layer is not shown in the Figures 4.7.2-1/2).
On the wireless backhaul, the IP layer is carried over the Backhaul Adaptation Protocol (BAP) sublayer, which enables routing over multiple hops. The IP layer can also be used for non-F1 traffic, such as OAM traffic as defined in TS 38.401 [4].
On each backhaul link, the BAP PDUs are carried by BH RLC channels. Multiple BH RLC channels can be configured on each BH link to allow traffic prioritization and QoS enforcement. The BH-RLC-channel mapping for BAP PDUs is performed by the BAP entities on each IAB-node and the IAB-donor-DU.
Protocol stacks for an IAB-donor with split gNB architecture are specified in TS 38.401 [4].
The IAB-MT further establishes SRBs (carrying RRC and NAS) with the IAB-donor-CU. For IAB-nodes operating in EN-DC, the IAB-MT establishes one or more DRBs with the eNB and one or more DRBs with the IAB-donor-CU, which can be used, e.g., to carry OAM traffic. For SA mode, the establishment of DRBs is optional. These SRBs and DRBs are transported between the IAB-MT and its parent node over Uu access channel(s). The protocol stacks for the SRB is shown in Fig. 4.7.2-3.
