 and overall objectives of the future development of IMT for 2020 and beyond. ITU. 2 Market Drivers Report ITU-R M.2243 (2011). Assessment of the global mobile broadband deployments and forecasts for IMT.ITU. Report ITU-R M.2290 (2013). Future spectrum requirements estimate for terrestrial IMT. ITU. RP-190019 (2019). Support Team Report RAN#83, ETSI MCC. 3GPP. RWS-180004 (2018). The 3GPP submission. 3GPP. 5G System Overview 3.1 Introduction Before diving into the details of NG-RAN (5G Radio Access Network) architecture, it is important to have at least a high-level understanding of the whole 5G System (5GS). To provide such a high-level picture, in the present chapter we describe the functionalities of the physical layer, the protocol stack, the NG-RAN, and the 5G Core (5GC) network. This chapter is not meant to be a definitive guide to either, as each one deserves a separate book in order to describe all the details. Instead, we provide an overview of all the components of 5GS, with emphasis on what is new compared with 4G. Readers who are sufficiently familiar with these can skip this chapter and go directly to the next one, for detailed discussion about NG-RAN architecture. 5G Core Network Sebastian Speicher Qualcomm Wireless LLC, Switzerland 3.2.1 Introduction 5GS consists of the 5G Radio Access Network (RAN), the 5GC, and the user equipment (UE). 1 In the present section we provide a 5GC overview. Like earlier generations of the 3GPP system, the 5GC's tasks include: Storing subscription information, including identifiers, cryptographic information needed for authentication and to derive cipher keys, information about networks a UE may estab- lish data sessions to, and restrictions to specific radio access technologies (RATs) or geo- graphic areas, etc.; Performing mutual authentication between UE and network and subsequent authoriza- tion of the UE; Registering UEs and keeping track of the list of UEs that are registered with the system; 1 5GS may also include non-3GPP Access Networks (ANs). 5G Radio Access 