result of comparison, certain actions can be performed by the C-SON system on the network nodes, 6.5 Operations, Administration, and Management using the provisioning services. Closed loop optimization therefore includes network mon- itoring, analysis of the monitoring outcome, followed by execution of necessary actions. Unlike 4G SON, the 5G C-SON is connected to both RAN and core network, SO that the data collection and actions can be performed on both. With the addition of the transport network, this provides the SON algorithm with E2E visibility of the network and allows E2E service optimization. This approach can be also used for optimization of network slicing, if NSI-level KPIs are used. E2E service assurance (e.g. for video quality indicators) is beneficial for the 5G networks; however, implementation of this requires support for cross-domain service optimization in SON. In addition to classic SON inputs, such as NE-level KPIs and performance mea- surements, the E2E SON additionally uses Quality of Experience (QoE) indicators and key quality indicators (KQIs). Figure 6.5.8 shows the principles of the cross-domain service optimization function, in which E2E SON is connected to multiple network domains: NG-RAN, MBH, 5GC, Gi-LAN, IP services, NFV, and transport. E2E SON collects performance data and sends configura- tion commands to these domains, with the goal of achieving the optimization targets, for example, to monitor and optimize the SLAs for different services such as IoT, video, and voice, in an automated closed loop manner. The reports collected from multiple domains, which may be related, for example, to the video data flows crossing all network domains, are aggregated into E2E QoS indicators. These indicators can be computed with granularity of the individual UEs (QoS flows), which can be further aggregated at the level of subnetwork or network slice. Analysis of the E2E QoS indicators may cause the E2E SON to execute certain actions performed on NFs in one or several domains. Network performance 