As network utilization increases, the distributed data centers can support increasingly Cloud Radio Access Network (Cloud-RAN) and virtual-RAN hub sites, as well as virtualized core Network Functions (NFs). The 5G core network is standardized to define a functional architecture in such a way that the implementation and replacement of further technologies is possible, and the 5G interfaces support much more fluently multivendor scenarios than in previous generations. The most essential new core network concepts in 5G are thus the separation of UP and CP, network slicing, and Service-Based Architecture. The chapter summarize the NFs defined in Release 15. Release 16 has further shaped part of these original NFs. The chapter summarizes the new NFs added in Release 16. Release 16 enhances the support for Multimedia Telephony Service IMS voice and video. Dimensioning of the transport network is one of the essential tasks of 5G operators.