The present document is an introduction to the 3GPP TS 38.46x series of technical specifications that define the E1 interface. The E1 interface provides means for interconnecting a gNB-CU-CP and a gNB-CU-UP of a gNB-CU within an NG-RAN@ or for interconnecting a gNB-CU-CP and a gNB-CU-UP of an en-gNB within an E-UTRAN.