PPP define different control layers with different interfaces. Moreover, the 5G RAN interfaces have been defined by 3GPP and O-RAN, but some interfaces are still undefined. Besides, we observed that the low physical layer split option has been postponed by 3GPP due to the demand of high transport bandwidth with large antennas. Among the eight deployment scenarios to operate the 5G networks, 3GPP decided to drop scenarios 6 and 8 due to complexities to operate the gNB directly on the EPC. 3. Private 5G networks: We observed that the 3GPP did not define a standard for the NR-U for frequency bands higher than 7 GHz. Moreover, several challenges have been identified due to LBT protocol failure involving the synchronization signals, paging, scheduling, and SO on. Few research works on NR-U have been proposed in the literature to tackle the various challenging issues on efficient and new methods for the channel access procedures. 4. SDN and NFV: The separation of the control and user planes and a centralized SDN controller are foreseen to increase the potential security threats. In addition, a centralized SDN controller has a key challenge of a single point failure and scal- ing limitations. Furthermore, a distributed SDN controller increases the design complexity. In the meanwhile, several challenging issues have been addressed for efficient NFV integration, management, orchestration, and resource optimization A Comprehensive Study on 5G within the 5G networks. In addition, a standardizing of a unified northbound interface for NFV is considered as a challenging issue. Moreover, considering that the network functions will be executed on VMs, the security threat is found to be as a challenging problem for NFV. Accordingly, efficient frameworks for the placement of SDN controllers, unified northbound APIs, fair resource distribution, resource optimization, and security are recommended for future research works on SDN and NFV. 5. Network slicing: The mobility and handover between different RAN in the cellular networks are