# What is 5G? Emerging 5G Mobile Services and Network Requirements
## 6 5G Core Network Architecture and Requirements
The AU-cloud unit (CU) configuration is similar to the conventional radio unit-digital unit (RU-DU) configuration of a cloud radio access network (C-RAN) in the 3 GPP-LTE system. The legacy RUs are remote RF units located at cell-sites, and centralized DUs are connected with these RUs and have relatively heavy functionalities regarding the medium access control (MAC) layer, radio link control (RLC) layer and the packet data convergence protocol (PDCP) layer, compared with RUs. Because the fronthaul data overhead between RUs and DUs is predicted to increase explosively, several functionalities of DUs will be moved into RUs at cell-sites. Thus, we call this modified cell-site unit in the 5G core network the AU, and CUs can be considered as the lightweight DUs. In addition, the mobile edge computing (MEC) entity in the edge cloud provides application developers and content providers with cloud computing capabilities and a 5G service environment at the edge of the 5G mobile networks. In particular, this MEC technology is leveraged to support ultra-low latency and high-bandwidth services. In the 5G core network architecture, the separation of the control plane (CP) and the user plane (UP) is one of the most important features in order to increase operational efficiency, as well as to improve network simplicity and flexibility. Moreover, elaborated management and orchestration of a number of virtualized network resources and slices should essentially be provided in 5G core networks. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multicolumn{2}{c}{**Technical Requirement**} & **Brief Description** \\ \hline F1 & Seamless mobility & Shall support seamless mobility regardless of the cell types and RATs where the macro-cell BSs, small-cell BSs, WLAN APs, and relay stations are mixed and overlapped. \\ \hline F2 & Wired/wireless terminal switching & Shall support terminal and/or session mobility to provide fast handover between wireless and wired terminals \\ \hline F3 & Context-aware best connection & Shall utilize the various context information (device, user, environment, network) to provide always best connection/service \\ \hline F4 & Single ID for multiple access & Shall recognize a mobile terminal as a single entity regardless of its access network \\ \hline A1 & Distributed architecture & Shall support the distributed network architecture to accommodate anticipated 1000 times of traffic \\ \hline A2 & Lightweight signaling & Shall have lightweight signaling to support a variety of terminals such as massive MTC terminal \\ \hline A3 & Multiple RAT interworking & Shall have architecture to support ‘Flow over Multi-RAT’ to provide the high volume service with low cost and guarantee the service continuity in spite of the bandwidth deficiency in a wireless access \\ \hline A4 & Fine-grained location tracking & Shall have function to trace the mobile terminal location in a fine granularity in order to provide advanced location based service \\ \hline O1 & Flexible reconfiguration and upgrade & Shall provide virtualization environment and support to reconfigure and upgrade the core network at low cost without changing the physical network infrastructure \\ \hline O2 & Network on-demand & Shall be able to build the network based on the QoS/QoE, charging, and service characteristics \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Technical requirements for 5G core networks [30]: functional requirements (F), architectural requirements (A) and operational requirements (0). RATs, radio access technologies. Figure 12: Software-centric 5G core and access network architecture.