 slices are defined. Furthermore, the self-organizing network (SON) concept evolves with 5G to address new radio (NR) technology and incorporates the concept of multi-domain optimization. SON evolution is driven by the evolution of 3GPP network management techniques for RAN and core network domains. 6.5.2 Key Ideas In LTE, the management architecture is defined in terms of logical network nodes: Net- work Elements (NEs) and Element Managers (EMs). In 5G, a service-based management architecture has been introduced. This is in line with the overall approach for describing the 5GC in the standards. 3GPP defines management information models, which are decoupled from the commu- nication protocols (such as NETCONF and YANG) used to access the OAM information in a model. Management models defined in 3GPP cover all NG-RAN architecture options: monolithic gNB and various split NG-RAN architectures, described in Chapter 4. PM is an important part of the OAM framework, which consists of generation of perfor- mance measurements (e.g. by NG-RAN), their collection, and the corresponding man- agement actions based on the collected measurements. The OAM framework supports network slicing through the Network Slice Instance (NSI) and Network Slice Subnet Instance (NSSI) models. The SON concept in 5G evolves from the 4G SON functionality and adds E2E aspects covering not just NG-RAN, but also 5GC and the transport network. Furthermore, the 5G SON framework has been extended to cover slicing, new QoS requirements, NG-RAN split architectures, and more. 6.5 Operations, Administration, and Management 6.5.3 Service-Based Management Architecture The 3G and 4G network management reference model is illustrated in Figure 6.5.1 (3GPP TS 32.101 clause 5.1.1). The model includes managed NEs, such as Node-Bs (3G) and eNBs (4G), and manage- ment functions such as (EMs, domain managers (DMs), and network managers (NMs). The Type 1 and Type 2 interface categories are defined. One of the innovations in the 3GPP Release-15 is a transition to servic