A Tutorial on Trusted and Untrusted Non-3GPP Accesses in 5G Systems—First Steps Toward a Unified Communications Infrastructure

fifth-generation (5G) systems are designed to enable convergent access-agnostic service availability. This means that 5G services will be available over 5G New Radio air interface and also through other non-Third Generation Partnership Project (3GPP) access networks, e.g., IEEE 802.11 (Wi-Fi). 3GPP has recently published the Release 16 that includes trusted non-3GPP access network concept and wireless wireline convergence. The main goal of this tutorial is to present an overview of access to 5G core via non-3GPP access networks specified by 3GPP until Release 16 (i.e., untrusted, trusted, and wireline access). The tutorial describes convergence aspects of a 5G system and these non-3GPP access networks, such as the authentication and authorization procedures and the data session establishment from the point of view of the protocol stack and exchanged messages among the network functions. In order to illustrate several concepts and part of 3GPP specification, we present a basic but fully operational implementation of untrusted non-3GPP access using WLAN. We perform experiments illustrating how a Wi-Fi user is authorized in a 5G core, establishing user plane connectivity to a data network. Moreover, we evaluate the performance of this access in terms of time consumed, the number of messages, and protocol overhead to established data sessions.