base station is also being referred to as gNodeB (or shortly gNB). In 5G the gNB functions can be split into sep- arate parts such as centralized unit and distributed unit. Additionally, there is a split of functions into control plane functions (CPFs) and user plane functions (UPFs), and with that decoupling of the control and user planes for higher flexibility in provisioning of new emerging services. In NG-RAN there are gateways for each of the planes, such as the CPF gateway and the UPF gateway, connected with 5G base stations via con- trol plane and user plane interfaces, respectively (Figure 5.5). CPF includes access and mobility management functions (AMFs), which has a similar set of functions as MME in the LTE/LTE-Advanced networks. CPF also includes a session management func- tion (SMF), the authentication server function (AUSF), and the Policy Control Function (PCF), which may be integrated into a single node (e.g. the CPF gateway). Because 5G will certainly coexist with the 4G mobile network during the 2020s and beyond, 3GPP has defined the architecture for interworking of its 5G and 4G mobile networks, which provides seamless handovers (due to the mobility of users) between LTE/LTE-Advanced (as 4G) and New Radio (as 5G). The interworking in the core part can be provided by interfaces between the EPC nodes (on the 4G side) and CN nodes (on the 5G side), such as Nx interface between CPF (5G) and MME (4G), and Xn interface between 4G base stations (eNodeBs) and 5G base stations (gNodeBs). Regarding the 5.2 QoS in 3G Broadband Mobile Networks Operator IP services (IMS, AS, etc.) External IP networks Evolved packet Next generation core (EPC) (AMF, SMF, PCF, NSSF,.. eNodeB eNodeB gNodeB gNodeB E-UTRAN NG-RAN User plane and control plane Control plane only AMF - Access and mobility management function NSSF - Network slice selection function AS - Application server P-GW - Packet data network gateway CPF - Control plane functions PCF - Policy control function E-UTRAN - Evolved UMTS terrestrial radio access net