or. LTE connection is the sec- ondary on the connection with the control plane going via the 5G gNB toward the 5G core network. This is suitable for the cases when there is sufficient coverage avail- able for the 5G connection, either building a dense enough network or then using low enough frequency band for a 5G carrier (for at least one of the 5G carriers). This option avoids the need to connect LTE eNB for the 5G core network Option 7, with the LTE eNB being the connection anchor. Now the 5G connection is the secondary on the connection with the control plane going via the LTE eNB toward the 5G core network. This assumes that the LTE eNB is updated to allow connectivity toward the 5G core network. This is suitable for the cases when the LTE coverage is expected to be much better than the available 5G coverage, for example, when using 5G on mmW bands with a relatively small cell radius. Option 7X would then refer to the case when the user plane from the 5G core is routed via the 5G gNB (Figure 5.3). From the architectural point of view, the late drop of Release 15 enables also the pure 5G-5G dual connectivity between two 5G gNBs. There was interest expressed in this 5 5G Architecture Non-standalone with 5G master Non-standalone with LTE master (3GPP option 4) (3GPP option 7x) LTE eNB 5G gNB LTE eNB 5G gNB Control Plane User Plane Figure 5.3 Further 3GPP architecture options part of Release 15 "Late drop." both from the standpoint of using mmW bands together with 5G on lower bands, as well as of considering 5G with low band as the coverage band in dual connectivity with the 2.5 GHz or 3.5 GHz band as the capacity band. The 5G-5G dual connectivity is limited in Release 15 to the synchronized case only, and is to be extended for the asynchronous case part of 5G Phase 2 in Release 16, as covered in Chapter 15 5G Core Network Architecture In recent years, many communication service providers (CSPs) have been virtualizing their EPC, changing the deployment from a series of dedicated physical appliances (specific bla