Implementation and Testing of MP-TCP ATSSS in a 5G Multi-Access Configuration

5G represents the latest currently available and the state of the art of mobile cellular networks. 5G is defined on the basis of new concepts like Software Defined Network (SDN), Network Function Virtualization (NFV) and Network Slicing, enabling a wide set of use-cases and applications. An innovative feature introduced in 5G since 3GPP Release 16 is Access Traffic Steering, Splitting and Switching (ATSSS), which gives the possibility to the user equipment (UE) connected to a 5G network using a 3GPP link (i.e., the gNB New Radio access) and a non-3GPP one (e.g., a public WLAN access point) to access 5G services using both links simultaneously. ATSSS can improve the user-experience, maximizing the throughput and improving resilience to network faults by downloading or uploading data using both channels at the same time or selecting the best link where to transmit for each data flow. In this paper, we analyze in depth the ATSSS functionality and the associated Multipath TCP (MP-TCP) mode in a Linux simulation testbed, including an Open Source 5G Core Network, with the full implementation of the User Plane and 3GPP and non-3GPP access links, using Free5GC, UERANSIM and a custom implementation of N3IWF. In this testbed setup, we run real traffic and assess the MP-TCP configuration and performance in realistic conditions, when the non-3GPP access is performed wither via terrestrial wireless or a high latency satellite link.