se industries. Therefore, one of the key themes of 5GS is to enable private network deployments where parts or even the entire network (RAN and core network) is deployed on site, e.g. in a factory. The remainder of this section illustrates each of these paradigms in greater detail. 3.2.2 Service-Based Architecture 3.2.2.1 Fostering Functional Reuse Comparing the EPS architecture (Figure 3.2.1) and the 5GS architecture (Figure 3.2.2) reveals a significant architectural difference. As depicted in Figure 3.2.1, EPS is based on point-to-point interfaces between network functions3 such as Mobility Management Entity (MME), Serving Gateway, and Packet Data Network (PDN) Gateway. Consequently, functionality supported on an interface between an EPS network function A and a network function B can only be used by those two net- work functions. If yet another network function (e.g. network function C) needs to use 3 Sometimes referred to as network nodes. 3 5G System Overview UTRAN GERAN S1-MME LTE-Uu Operator's IP E-UTRAN Serving Gateway Services Gateway (e.g. IMS, PSS etc.) Figure 3.2.1 EPS non-roaming architecture. (Source: reproduced with permission from © 3GPP). Nnssf Nausf (R)AN Figure 3.2.2 5GS non-roaming architecture. (Source: reproduced with permission from © 3GPP). similar functionality from network function A, then a new interface needs to be introduced between A and C and the functionality in question needs to be replicated on this new inter- face. This not only slows down standardization projects in 3GPP, but more importantly poses an obstacle for operators to extend and customize the core network to their needs. To illustrate this, it is worth looking at an example. The S11 interface supports reporting of UE location changes (e.g. to report when the UE changes Tracking Areas or changes cells) from MME to Serving Gateway (SGW). As knowledge of user location is useful for many services, it would be interesting to make this information available for use by other network functions. However, the S11 location report