Two popular architecture options for 5G deployments are Non-Standalone New Radio (NSA NR) with the Evolved Packet Core (EPC) and Standalone NR (SA NR) with the 5G Core (5GC).
In the NSA NR with the EPC architecture, the 5G UE can simultaneously do data transfer with the LTE Master eNB and 5G Secondary gNB. Furthermore, the gNB cannot stand on its own feet; it needs help of the MeNB.
In the SA NR with the 5GC architecture, the gNB can directly exchange signaling as well as user traffic with the UE; the gNB does not need to rely on an eMB…it can work by itself (that’s why the name STANDALONE!).