Content for  TS 38.401  Word version:  18.1.0

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8.2.5  Intra-CU Backhaul RLF recovery for IAB-nodes in SA mode |R16|p. 54

The intra-CU backhaul RLF recovery procedure for IAB-nodes in SA mode enables migration of an IAB-node to another parent node underneath the same IAB-donor-CU, when the IAB-MT declares a backhaul RLF. The declaration of backhaul RLF is described in TS 38.331.
Figure 8.2.5-1 shows an example of the BH RLF recovery procedure for an IAB-node in SA mode. In this example, the IAB-node changes from its initial parent node to a new parent node, where the new parent node is served by an IAB-donor-DU different than the one serving its initial parent node.
Reproduction of 3GPP TS 38.401, Fig. 8.2.5-1: IAB intra-CU backhaul RLF recovery procedure for an IAB-node in SA mode
Step 1.
The IAB-MT declares BH RLF for the MCG as described in clause of TS 38.331.
Step 2.
The IAB-MT undergoing recovery from RLF conducts the RRC re-establishment procedure at the new parent node, as defined in clause 8.7. In this procedure, the IAB-donor-CU may provide new TNL address(es), which is(are) anchored at the new IAB-donor-DU, to the IAB-MT via RRC signalling. Furthermore, the IAB-donor-CU may also provide a new default UL mapping which includes a default BH RLC channel and a default BAP Routing ID for UL F1-C/non-F1 traffic on the target path, to the IAB-node undergoing recovery from RLF via RRCReconfiguration message in this procedure.
Step 3.
The remaining part of the procedure follows the steps 11-15 of the intra-CU topology adaptation procedure defined in clause
Descendant node(s) of the IAB-node undergoing recovery from RLF may also need to switch to new TNL address(es) anchored in the target-path IAB-donor-DU following the same mechanism as described for IAB intra-CU topology adaptation procedure in clause The descendant node(s) may also be provided with new default UL mapping via RRC, after the IAB-node undergoing recovery from RLF connects the IAB-donor-CU via the recovery path.

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