vents the initiating node from generating additional load during that time. 4 NG-RAN Architecture Since NG-RAN supports connectivity to 5GC, legacy EPC, and both (e.g. in EN-DC) as described in more detail in Chapter 3, the node initiating the E1 Setup procedure signals the type of core network connectivity it supports. Additionally, certain core network network-related information is signaled by the node initiating the E1 Setup procedure, such as list of supported PLMNs and a list of supported slices and cells within that PLMN. This helps resolving potential misconfiguration issues, especially in the early days of 5G deployment and during migration, for example, from NG-RAN deployed with EPC to NG-RAN deployed with 5GC. During the E1 interface operation, both the gNB-CU-CP and the gNB-CU-UP can inform each other about their configuration changes, using the gNB-CU-CP Configuration Update and the gNB-CU-UP Configuration Update procedures, respectively. For example, a gNB-CU-UP may initiate the gNB-CU-UP Configuration Update procedure if the list of supported NR CGIs has changed. The lists of supported PLMNs, cells, and slices in gNB-CU-CP and gNB-CU-UP connected via E1 does not have to match. If it does not, the setup procedure can still succeed, and the gNB-CU-CP will take this information into account for decisions on bearer establishment; for example, by allowing bearer establishment only for UEs requesting access to the PLMN supported by both nodes. These details are, however, not specified in the standard and are left for implementation. Therefore, different implementations may handle these cases differently. 4.4.3.1.2 Bearer Context Management Procedures Bearer context management procedures are arguably the most important aspect of the E1 interface. Using these procedures, a gNB-CU-CP can establish, modify, and release a bearer context in the gNB-CU-UP. There procedures are: Bearer Context Setup Bearer Context Release Bearer Context Modification (gNB-CU-CP initiated) and Bearer Context Modification Required 