 offers SDN-enabled broadband access (SEBA) and virtual OLT hardware abstraction (VOLTHA) solutions for the broadband networks [228]. Moreover, it provides a central office re-architected as a datacenter (CORD) project to leverage the key 5G enabling technologies, e.g., SDN and NFV, at the network edge. The CORD project provides cloud-native, open, programmable, flexible, and agile services for the MNOs [229]. ONF mobile network projects can be summarized as follows: 1. COMAC: It is an open-source platform built under the CORD project for the RAN and core to provide convergence between the mobile and broadband networks. By leveraging SDN, RAN, core, and edge, COMAC project aims to optimize the QoE for the end-users. 2. SD-RAN: It provides an open-source RAN platform to develop the near-RT RIC entity based on O-RAN architecture (see Sect. 1.2.2.2), in order to control, configure, and manage the RAN by xApps. 3. OMEC: It is an open-source project to offer scalable and virtualized EPC compatible with 3GPP release 13. 4. Aether: It is a 5G open-source edge platform to provide edge computing services and wireless licensed and unlicensed connectivity for enterprises. 1.6 Challenging Issues and Directions Tremendous research works have been conducted, in the literature, on 5G tech- nology to boost the network performance and to fulfill the diverse demands of mobile operators and vertical industry. Herein, several challenging issues and future directions are highlighted on public and private 5G architectures as well as 5G enabling technologies, such as SDN, NFV, network slicing, and MEC. These challenging issues can be summarized as follows: 1. Cloud RAN: A main C-RAN issue is to achieve high QoS. The BBU pool might be placed faraway from some end-user devices which lead to degradation of the QoS. Therefore, efficient frameworks for BBU placement and resource allocations are mandated in order to achieve high QoS for the end-users. Meanwhile, a shared BBU pool demands a universal security and privacy mech- anism. Accordin