3GPP. Available at: www.3gpp.org (accessed May 22, 2020). 3GPP Technical Specification 38.415 (2019). NG-RAN; PDU Session User Plane protocol. 3GPP. Available at: www.3gpp.org (accessed May 22, 2020). 3GPP Technical Specification 38.423 (2019). NG-RAN; Xn Application Protocol (XnAP). 3GPP. Available at: www.3gpp.org (accessed May 22, 2020). 3GPP Technical Specification 38.424 (2019). NG-RAN; Xn data transport. 3GPP. Available at: www.3gpp.org (accessed May 22, 2020). 3GPP Technical Specification 38.425 (2019). NG-RAN; NR user plane protocol. 3GPP. Available at: www.3gpp.org (accessed May 22, 2020). 802.11-2016 IEEE Standard for Information technology - Telecommunications and information exchange between systems Local and metropolitan area networks - Specific requirements - Part 11 (2016). Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications IETF RFC 4960, Stream Control Transmission Protocol. Internet Engineering Task Force. 3 5G System Overview 3.4 NR Protocol Stack Sudeep Palat Intel Corporation, UK 3.4.1 Introduction As mentioned above, 5GS architecture is functionally split into 5GC and RAN (NR) func- tionalities similar to older cellular technologies. 5GC functionality is responsible for the overall user registrations and session management functions, while NR provides the radio access-related functionalities. 5GC functionality is discussed in more detail in Section 3.2. NG-RAN provides the connectivity over the radio interface between the network and the UE with the user-plane functions providing the required QoS for the data over the radio interface. While the network aspects of NG-RAN are explained in Section 3.3, in the present section we focus on the air interface protocol stack, specifically: The NR protocol stack consists of user-plane and control-plane parts: the user plane han- dles the transfer of data across the radio interface with the required QoS, while the control plane handles the configuration of the radio interface connection. In the non-split NG-RAN architecture