tion, and activation: During instantiation/configuration, all shared/dedicated resources associated with the NSI have been created and configured and the NSI is ready for operation. The activation step includes any actions that make the NSI active such as routing traffic to it, provisioning databases (if dedicated to the network slice, otherwise this takes place in the preparation phase), and instantiation, configuration, and activation of other shared and/or non-shared NF(s). Run-time: In this phase, the NSI is capable of traffic handling and supports certain types of communication services. The run-time phase includes supervision/reporting, as well as activities related to modification. Modification of the workflows related to runtime tasks may include upgrade, reconfiguration, NSI scaling, changes of NSI capacity, changes of NSI topology, and association and disassociation of NFs with NSI. Decommissioning: This step includes deactivation by taking the NSI out of active state as well as the retrieval of dedicated resources (e.g., termination or reuse of NFs) and configuration of shared/dependent resources. Following this phase, the NSI does not exist anymore. An NSI is complete in the sense that it includes all functionalities and resources necessary to support certain set of communication services. The NSI contains NFs belonging to the access and the core networks. Lifecycle of a network slice instance Preparation Instantiation, configuration, and activation Run-time Decommissioning Supervision Design Pre-provision Instantiation/ Activation Modification De-activation Termination configuration Network environment preparation Reporting Figure 1.19 Life cycle phases of an NSI [7] 46 Chapter 1 If the NFs are interconnected, the 3GPP management system contains the information rele- vant to connections between these NFs including the topology of connections, and individ- ual link requirements such as QoS attributes. The NSI is realized via the required physical and logical resources. A network slice is described by 