4G Core 5G Core (EPC) (NGC) FIGURE 2-12 Deployment options 1 and 2. Chapter 2 System components, requirements, and interfaces 57 These options show an LTE-only (LTE eNB and LTE EPC) and a 5G-only (5G gNB and 5G NGC) deployment with 4G and 5G standards defining C-plane and U-plane connectivity between the two. Options 3, 3a, and 3x represent Non-Stand Alone (NSA) deployments where the core net- work is LTE (EPC) and both 4G/LTE and 5G/NR RANs are used for wireless access. The dif- ference between the suboptions defines the interconnectivity between the core and the RAN components as well as between the 4G and 5G RAN components. In Option 3, the LTE eNB is connected to the EPC with non-standalone NR. The NR UP connection to the EPC goes via the LTE eNB (Option 3) or directly (Option 3a/3x), refer to Fig. 2-13. Option 3x is a com- bination of 3 and 3a in which user data traffic flows from EPC to gNB from where it is deliv- ered over the 5G/NR air interface or forwarded over the X2 interface to the eNB for transmission over the 4G/LTE air interface. Typically, the forwarded (LTE air interface tar- geted) traffic is voice or another low-bit rate application: Option 3 Option 3a Option 3x 4G Core 4G Core (EPC) 4G Core (EPC) (EPC) LTE eNB 5G gNB LTE eNB 5G gNB LTE eNB 5G gNB FIGURE 2-13 Deployment options 3, 3a, and 3x. Option 4 Option 4a 5G Core 5G Core (NGC) (NGC) 5G gNB LTE eNB 5G gNB LTE eNB FIGURE 2-14 Deployment options 4 and 4a. Option 7 Option 7a Option 7x 5G Core 5G Core (NGC) 5G Core (NGC) (NGC) LTE eNB 5G gNB LTE eNB 5G gNB LTE eNB 5G gNB FIGURE 2-15 Deployment options 7, 7a, and 7x. 58 Open Radio Access Network (O-RAN) Systems Architecture and Design Option 5 Option 6 5G Core 4G Core (NGC) (EPC) LTE eNB FIGURE 2-16 Deployment options 5 and 6. MeNB, S1, NG X2, Xn SeNB, FIGURE 2-17 Dual connectivity in LTE and 5G. LTE, Long-Term Evolution. Options 4 and 4a (Fig. 2-14) are also NSA but use the 5G Core Network (5GC). The dif- ference between 4 and 4a is that in option 4 the LTE U-plane traffic is routed via the 5