an NST. The NSI is created using the NST and instance-specific information. The concept of network slice subnet instance man- agement is introduced for the purpose of NSI management. For example, for instantiation of an NSI that contains radio access and core network components, these components can be defined and instantiated as two NSSIs denoted by NSSI1 (RAT1) in RAN and NSSI3 in the core network. The targeted NSI will be instantiated by combining the NSSI1 and NSSI3. Another NSI can be instantiated by combining NSSI3 with another RAN NSSI denoted by NSSI2 (RAT2). Depending on the communication service requirements, a communication service can use an existing NSI or trigger the creation of a new NSI. The new NSI may be created exclu- sively for this communication service or it may be created to support multiple communica- tion services with similar network slice requirements. The life cycle of a communication service is related but not dependent on an NSI. The NSI may exist before the communica- tion service uses the NSI and may exist after the communication service stopped using the NSI. An NSI can be created using one or more existing NSSI(s) or initiate the creation of one or more new NSSI(s) depending on the NSI requirements. The new NSSI(s) may be created just for this NSI or it may be created to support multiple NSIs. The life cycle of an NSI is related but not dependent on that of an NSSI. The NSSI may exist before the NSI is created and may exist after the NSI is no longer needed. 1.1.5 Heterogeneous and Ultra-dense Networks Effective network planning is essential to support the increasing number of mobile broad- band data subscribers and bandwidth-intensive services competing for limited radio resources. Network operators have addressed this challenge by increasing the capacity through new spectrum, multi-antenna techniques, and implementing more efficient modula- tion and coding schemes. However, these measures are not adequate in highly populated areas and at the cell edges where performance can sig