 of different GGSNs for sessions toward different data networks. It is worth pointing out that the Serving GPRS Support Node (SGSN), the equivalent of the MME and SGW in EPS, is selected based on serving RAN node. In other words, GPRS does not support selection of different SGSNs for different groups of subscribers. The same limitation applies to EPS as defined in 3GPP Release-8, which selects MME and SGW only based on network topology and load. 3GPP Release-13 addressed this gap by adding the notion of DECOR. The key idea of DECOR (3GPP TS 23.401, 2019) was to select the serving MME not only based on serving RAN node and MME load but also based on a new subscription parameter, namely the subscribed UE usage type. MMEs that serve different UE usage types may also have different configurations for selection of other core network nodes (SGW and PGW), which enables operators for instance to use different SGWs and PGWs for the same APN depending on the subscribed UE usage type. In summary, DECOR enabled operators to deploy and select different Dedicated Core Networks (DCNs), consisting of all CN nodes (MME, SGW, PGW, PCRF, etc.), for differ- ent groups of subscribers, e.g. DCN 1 for massive IoT subscribers and DCN 2 for mobile broadband subscribers. 3.2 5G Core Network Target S1-MME DCN 2 Redirection S1-MME Initial DCN 1 Figure 3.2.10 Release-13 DECOR enables redirection to a target MME in the right DCN based on subscribed UE usage type received from the HSS. The key drawback of Release-13 DECOR is that the RAN is not aware of the UE usage type. When a UE attaches to EPS the RAN selects an initial MME, which then retrieves the UE's subscription. As depicted in Figure 3.2.10, if the initial MME selected by the RAN does not support the subscribed UE usage type, then the initial MME redirects the UE to a different MME that supports the subscribed UE usage type. In other words, the drawback of Release-13 DECOR is that the RAN cannot directly select the right MME; the right MME can only be selected by redirection. Those r