 have been addressed briefly in [3, 7, 11] and [16-19]. Unlike these research works, herein, the concept, architectural frameworks, challenges, and recent research works on the key 5G enabling technologies are addressed in depth. 1.1.2 Contributions and Chapter Organization The main scope of this chapter is the 5G E2E architectures for public and private net- works considering the standards of 3GPP, 5GPPP, and O-RAN alliance. In addition, SDN, NFV, and network slicing, artificial intelligence/machine learning (AI/ML), and MEC technologies have been investigated comprehensively. Furthermore, we review the R&D progress on 5G technology to deliver E2E services including projects and simulators. Despite our comprehensive study on the NG-RAN, some technologies for the NG-RAN, e.g., massive MIMO and beamforming, are out of the scope of this chapter. The contributions of this chapter are manifold as follows: 1. Investigating and comparing the 5G architectures for centralized and partially cloud-RAN (C-RAN), heterogeneous C-RAN (H-CRAN), virtualized C-RAN (V-CRAN), and fog C-RAN (F-CRAN) considering benefits, limitations, and deployment scenarios provided by 3GPP for public networks. 1 A Comprehensive Study on 5G 2. An in-depth study on the 5G E2E architecture proposed by 3GPP, O-RAN, and 5GPPP involving MEC and O-RAN deployment scenarios. 3. Exploring the private 5G networks for vertical industries including architectural frameworks and spectrum options. 4. A comprehensive review on the key 5G enabling technologies, i.e., SDN, NFV, network slicing, AI/ML methods, and MEC, including concept, standards, architectural frameworks, and recent research works. 5. Addressing the 5G R&D software and projects for RAN and core including features, benefits, and limitations. 6. Summary on the challenging issues for 5G deployment. This chapter is organized as follows: Section 1.2 presents several architectural frameworks for the public 5G networks involving the concept, standards, benefits, and limitations. The explored 5G archi- tec