uction and Background Ixiii networks is required to address some key design principles in order to meet the above- mentioned requirements. The following is a list of key architectural focus areas and their associated requirements that were identified by system architecture working group in 3GPP in the early stages of 5G standards development [13,21]: Support of the 3GPP NR access, evolution of LTE, legacy 3GPP access, and non-3GPP access such as Wi-Fi networks is a key requirement for the new architecture. As part of non-3GPP access types, trusted and untrusted WLAN access support is necessary for heterogeneous networks. Satellite radio access network needs to be supported in order to enable coverage of rural and remote areas using satellite access nodes. The 5G sys- tem supports most of the existing LTE evolved packet system services in addition to the new services that includes seamless handover between the NR and the legacy 3GPP radio access networks. Interworking between the new radio and LTE is required consid- ering the necessity for efficient inter-RAT mobility and aggregation/distribution of data flows via dual connectivity between LTE and the new radio in NSA scenarios. This requirement applies to both collocated and non-collocated site deployments. 2. Unified authentication framework for different access systems is required to simplify access to the next-generation networks via any of their constituent radio access net- works. The authentication protocol is responsible for the validation of the user identity that is presented to the network when a UE requests to receive service(s) from the next- generation network. 3. Support of several simultaneous connections of a UE via multiple access technologies served by a single 5GC network is another important requirement. For UEs that can be simultaneously connected to both 3GPP access and non-3GPP access, the next- generation system should be able to exploit the availability of multiple radio links in a way that improves the user experience, optimizes the tra