impact on EPC to support the dual registration is minimized. However, in order to improve the mobility performance between LTE and 5G, it is necessary to temporarily support dual radio transmission when moving to the other network, although the UE can support dual registration solution even with single radio transmission capability. Deployments based on different 3GPP architecture options (i.e., EPC based or 5GC based) and UEs with different capabilities (EPC NAS and 5GC NAS) may coexist at the same time within one PLMN. In order to interwork with EPC, the UE that supports both 5GC and EPC NAS can operate in single- or dual-registration mode. In single-registration mode, the UE has only one active MM state (either RM state in 5GC or EMM state in EPC) and it is either in 5GC NAS mode or in EPC NAS mode (when connected to 5GC or EPC, respectively). The UE main- tains a single coordinated registration for 5GC and EPC. Accordingly, the UE maps the EPS-GUTI to 5G-GUTI during mobility between EPC and 5GC and vice versa. In dual- registration mode, the UE can handle independent registrations for 5GC and EPC. In this mode, UE maintains 5G-GUTI and EPS-GUTI independently. In this mode, the UE pro- vides native 5G-GUTI, if previously allocated by 5GC, for registration with 5GC and it pro- vides native EPS-GUTI, if previously allocated by EPC, for Attach/TAU with EPC. In this mode, the UE may be registered to 5GC only, EPC only, or to both 5GC and EPC. The sup- port of single registration mode is mandatory for UEs that support both 5GC and EPC NAS. During LTE initial attach procedure, the UE supporting both 5GC and EPC NAS indi- cates its support of 5G NAS in UE network capability [3]. The Ethernet and unstructured PDU session types are transferred to EPC as non-IP PDN type (when supported by UE and network). The UE sets the PDN type to non-IP when it moves from 5GS to EPS. After the transfer to EPS, the UE and the SMF maintain informa- tion about the PDU session type used in 5GS, that is, the information indicating that th