Our latest release, 5G NR FR1 Reference Design, makes the case for a common, modular architecture for 5G small cell distributed radio units. This work lays the foundations for the development of reference designs focused on delivering greater flexibility and scalability, including the ability to swap out regionally specific RF front end (RFFE) modules. This paper provides the foundational framework for understanding the components and interfaces that make up a 5G NR FR1 small cell distributed radio unit and provides an overview of available solutions, as vendors and deployers increasingly look to have a second or third source of each component.