This chapter focuses on standards-based NG-Radio Access Network (NG-RAN) architectures, but one must understand that unlike the standards-based NR Uu (air) interface, NG-RAN network standards are not as rigorous. It describes various split architectures defined in relevant standards development organizations and industry fora. The chapter discusses the gNB-CU/DU split architecture, which is equivalent to option 2 from the 5G study. It describes the NG-RAN architecture in which a gNB is split into two (high-level and low-level) logical nodes, with a standardized F1 interface between them. The chapter also describes multi-radio dual connectivity, which is different as gNB functionality is split across two fully functional base stations, which are otherwise capable of serving user equipment by themselves, that is, also without the cooperation of another base station. It also discusses the characteristics of physical layer functions, and the challenges separating these functions into separate network nodes.