ing functionality cannot easily be used by network func- tions other than the SGW for the following reasons: S11 location reporting is piggybacked on top of session management-related signaling, e.g. Modify Bearer Request (3GPP TS 29.274, 2019). In other words, S11 location reporting assumes a common session context between MME and the other termination point of the S11 interface (typically the SGW). Only a single SGW (i.e. single S11 interface between MME and SGW) is allowed per reg- istered UE. 3.2 5G Core Network For the same reasons, existing system functionality also cannot be extended easily, for example, to support location reporting for groups of UEs. As a result, as part of the Release-13 work aiming at exposing network information to third parties via the Service Capability and Exposure Function (SCEF), location reporting from MME for individual UEs and groups of UEs was therefore specified via yet another interface (the T6a interface between MME and SCEF) instead of extending the existing loca- tion reporting mechanism. To avoid such issues, 5GC follows software engineering paradigms such as modularity and self-containment for 5GC network functions to foster reuse and extensibility of system functionality (see the "Design guidelines for NF services" documented in Annex A.6 in 3GPP TS 23.502). Practically speaking, this means that whenever possible 3GPP should define procedures (i.e. interactions between network functions) as services, SO that they can be reused by other network functions and can also be extended more easily in the future. To illustrate the difference to EPC it is worth looking at the same example for 5GC, that is, how UE location information is provided by the Access and Mobility Management Function (AMF), the 5GC equivalent of the MME. AMF supports the Namf_EventExposure service, which enables any other network function to subscribe for and subsequently get notified about various events including UE reachability status changes, time zone changes, and loca- tion changes (3GPP TS 23.502