abling Technologies Table 6.5.6 Legacy SON functionality. Release-8 Release-9 Release-10 Release-11 Automatic Mobility Coverage and capacity Handover optimization inventory robustness/hand over optimization optimization Automatic RACH optimization Enhanced inter-cell Coverage and capacity software download interference optimization coordination Automatic Load balancing Cell outage detection Coordination between neighbor relation optimization and compensation various SON functions Automatic Inter-cell interference Self-healing functions physical cell ID coordination (PCI) assignment Minimization of drive testing Network energy saving Coordination between the C-SON and D-SON; SON for Active Antenna System (AAS)-based deployments; Trace and Minimization of the Drive Test (MDT); Mobility robustness optimization; NG-RAN energy saving. Many of the D-SON features mentioned above have been defined in Release-16, with work to be continued in Release-17 to specify the remaining ones (3GPP SON/MDT enhance- ments). Naturally, the legacy SON features being introduced into 5G are extended to support NR technology specifics, such as flexible numerology, massive MIMO, beamforming, and network slicing. 6.5.9.3 Multi-Domain SON with E2E Optimization In contrast to 4G, which primarily supported RAN SON, the SON in 5G covers also the core network domain and, to some extent, the transport network; the latter including backhaul and fronthaul connections (see Section 6.6 for details about the transport network). 3GPP TS 28.861 defines three SON variants: C-SON, which is fully based on OAM; D-SON, which is based on control-plane messages exchanged between NG-RAN nodes; Hybrid SON combines both C-SON and D-SON. Figure 6.5.7 shows C-SON architecture, which is the primary focus of this section. As mentioned above, in the C-SON solution, the SON algorithm is running in the NMS. The management system collects network performance data and computes the KPIs. The received values are compared with the targets set by the network operator. As the 