LTE and 5G NR use similar interface concepts but with different names and some protocol changes. The S1 interface (eNodeB to EPC) becomes the NG interface (gNB to 5GC). The X2 interface (between eNodeBs) becomes Xn (between gNBs). The protocols change from S1AP to NGAP for the control plane, while GTP-U remains for user data transport.