work RAN - Radio access network IMS - IP Multimedia subsystem S-GW - Serving gateway MME - Mobility management entity SMF - Session management function NG-RAN - Next generation radio access network UPF - User plane functions Figure 5.5 5G mobile network architecture. user plane, the EPC user plane nodes S-GW and P-GW are replaced in 5G with UPF nodes (different UPF nodes are interconnected via the N9 interface). In the longer term the EPC can be removed and eNodeBs can be connected with direct interfaces to CPF and UPF nodes in the 5G CN. QoS in 3G Broadband Mobile Networks Mobile broadband access in fact started with 3G mobile networks. However, these net- works were based on a hybrid approach, that is circuit-switching used for voice and packet-switching (IP connectivity) used for Internet access service. However, the main 5 QoS for Mobile Ultra-Broadband representative of 3G mobile networks, the UMTS, had well-defined QoS support from the beginning. For the packet-switching traffic (i.e. IP traffic) in UMTS, four different traffic (i.e. QoS) classes are defined: Conversational class. This is targeted at services with requirements for low delay and preserved time variation between different IP packets, i.e. very low delay variation. This scheme is targeted at carrier-grade real-time services over IP, such as VoIP, video telephony (based on VoIP), and conferencing tools (based on VoIP). Streaming class. This is targeted at traffic which requires preserved time variation between IP packets within a given flow, but it does not have certain strict require- ments on low transfer delay. Hence, this class is suitable for streaming services (audio and video). Interactive class. This is targeted for non-real-time services which have certain requirements on transfer delay (which is however not as strict as for real-time ser- vices) based on request-response use by the end-user. This class refers to interactive client-server services/applications, such as Web, database retrieval, etc. The key QoS parameters are low round 