This paper provides an overview of external and internal interfaces of a 5G base station (gNB). The New Radio gNB is connected to the Access and Mobility Management Function (AMF) and the User Plane Function (UPF) in the 5G Core Network (5GC). A new Xn interface inter-connects gNBs that are connected to the 5GC. The 5G RAN internal structure has been discussed heavily in the standardization process of 5G. Different split options that are under discussion are also introduced in this paper. Eventually, the eCPRI specification that was released a few days ago is introduced.