ecessary information for anybody wanting to deploy a timing solution for 5G mobile. The principles behind the 5G system architecture are based on the fundamental vision that it must co-exist with the existing LTE-A network and then evolve over time. When an operator chooses how to deploy their radio networks, they select technology for the mobility bands and capacity bands, which could result in them having different core networks. The 5GCN architecture needs to take account of this. The 5GCN architecture captures two main deployment options, as illustrated in Figure 10-22: Non-standalone (NSA) Architecture: This architecture allows early adopters of the 5G RAN to utilize the existing LTE radios and the 4G EPC network. This option supports only 4G ser- vices, but characteristics of 5G NR can be leveraged (for example, low-latency applications). In brief, NSA allows dual connectivity between the 4G and 5G access networks and is best ap- plied when the goal is to improve eMBB services. The deployment of NR can provide capacity enhancements to the existing 4G LTE network without major network investments. Standalone (SA) Architecture: In this architecture, the NR-capable device connects to a 5GCN. This allows the full set of 5G services, SO it can be considered a fully mature 5G NR deployment. Various NSA and SA deployment options are outlined as part of the 3GPP TR 38.8xx and TS 38.xxx series of recommendations. Figure 10-22 illustrates several of the possible options and shows the flow of control and user plane traffic in both the SA and NSA cases. In a later update, 3GPP dropped the option 6 and option 8 specifications, as it did not consider these 5G options to be viable. Option 1 Option 2 Option 3 Option 4 (((2))) EPC-connected 5GCN-connected LTE-assisted NR-assisted EPC-connected 5GCN-connected Option 5 Option 6 Option 7 Option 8 (((p))) (((p))) LTE-assisted NR-assisted 5GCN-connected EPC-connected 5GCN-connected EPC-connected Figure 10-22 NSA Versus SA Deployment Options The 5GCN builds upon the 4G EPC with t