Section: 8.9.13 IP Address Allocation for IAB-nodes
Content: NOTE: The general principles and procedures described in this clause does not apply to ng-eNB. An IAB-node may obtain IP address(es) either from the IAB-donor or from the OAM system. The IP address(es) is(are) used by the IAB-node for F1 and non-F1 traffic exchange via the backhaul. In case IPsec tunnel mode is used to protect this F1 and non-F1 traffic, the IP address(es) refer to the outer tunnel addresses. The allocation of the inner tunnel IP address(es) is outside of 3GPP scope. NOTE: The non-F1 traffic of an IAB-node includes all IP traffic that is not used for the management or transport of F1-C as specified in TS 38.472[ NG-RAN; F1 signalling transport ]  [26] or F1-U as specified in TS 38.474[ NG-RAN; F1 data transport ]  [7]. The non-F1 traffic may include, e.g., OAM traffic if it is transferred using the BH RLC channel. In case of IAB-donor-based IP address allocation, the IP address(es) is(are) allocated by the IAB-donor-CU or IAB-donor-DU. In both cases, the IAB-node requests the IP address(es) via RRC from the IAB-donor-CU. It includes a separate IP address request for each usage, where the usages defined are all traffic, F1-U, F1-C and non-F1. The IAB-donor-CU may initiate the IAB TNL Address Allocation procedure to obtain IP addresses from the IAB-donor-DU. The IAB-donor-CU sends the IP addresses allocated for each usage to the IAB-node via RRC. In case of IAB inter-CU topology management, the F1-terminating IAB-donor-CU may obtain the IP addresses for each usage in the non-F1-terminating IAB-donor-CU’s topology from the non-F1-terminating IAB-donor-CU for the boundary IAB-node and the descendant IAB-nodes of the boundary IAB-node. The IAB-node may be allocated one or multiple IPv6 addresses or one 64-bit IPv6 prefix for each usage and/or one or multiple IPv4 addresses for each usage. Each allocated IP address/IPv6 prefix is unique within the IAB network and routable from the wireline network. In case of OAM-based IP address allocation, the IAB-node informs the IAB-donor-CU via an UL RRC message about the IP address(es) it received for each purpose. This occurs before the IAB node uses the IP address(es) for UL and/or DL traffic. The IAB-donor-CU configures the IAB-donor-DU with mappings between IP header fields and L2 parameters (BAP Routing ID, BH RLC channels) used for DL traffic. Each mapping configuration may hold an IPv4 address, IPv6 address or a 64-bit IPv6 prefix. In case of two mapping entries matching the same IP header where one holds an IPv6 prefix and the other holds a full IPv6 address, the one with full IPv6 address takes precedence at the IAB-donor-DU. In case of IAB-donor-allocated IP addresses, the IAB-node’s IP address(es) can be updated using DL RRC signalling. For F1-C traffic transfer for NSA IAB, the LTE leg and NR leg should use separate IP address pairs {IAB-DU’s IP address, IAB-donor-CU’s IP address}. How the IAB-DU gets the remote IP end point(s) and its own IP address for LTE leg is not specified in this release.