Section: 5.35.6 IAB operation involving EPC
Content: When the IAB-donor gNB has connection to both EPC and 5GC, based on PLMN configuration, there are two possible operation modes: - the IAB-node connects to a 5GC via the IAB-donor gNB, while the UEs served by the IAB-node connect to EPC with Dual Connectivity as defined in TS 37.340[ Evolved Universal Terrestrial Radio Access (E-UTRA) and NR; Multi-connectivity; Overall Description; Stage-2 ]  [31]. In this operation mode, the IAB-donor gNB has connection to an eNB, and the 5GC is restricted for IAB-node access only; and - the IAB-node connects to an EPC via the IAB-donor gNB with Dual Connectivity as defined in TS 37.340[ Evolved Universal Terrestrial Radio Access (E-UTRA) and NR; Multi-connectivity; Overall Description; Stage-2 ]  [31], while the UEs served by the IAB-node connect to the 5GC. In this operation mode, the EPC is restricted for IAB-node access only. To support the above operation modes, the IAB-UE shall be configured to select only a specific PLMN (as defined in TS 23.122[ Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode ]  [17]) and whether it needs to connect to 5GC or EPC. NOTE: For a particular PLMN, it is expected that only one of the modes would be deployed in a known region.