ATSSS Access Traffic Steering, Switching and Splitting
ATSSS (Access Traffic Steering, Switching and Splitting) is a 5G capability, introduced in 3GPP Release 16, that allows user-plane traffic to be steered, switched or split across a 3GPP access (cellular) and a non-3GPP access (typically Wi-Fi) used simultaneously, built on the MA PDU (Multi-Access Protocol Data Unit) Session anchored on a common UPF (User Plane Function) to deliver higher aggregate throughput, improved resilience and better performance than either access alone; steering selects the access for a new flow, switching moves an ongoing flow between accesses without breaking it, and splitting distributes a single flow across both accesses to aggregate capacity. Traffic handling depends on the negotiated steering functionality, MPTCP (Multi-Path TCP) for TCP flows, ATSSS-LL (Low-Layer) for non-TCP traffic such as UDP (User Datagram Protocol), and MPQUIC (Multi-Path QUIC), added in Release 17, for QUIC flows, with decisions policy-driven by the SMF (Session Management Function), which supplies ATSSS rules to the UE and N4 rules to the UPF, while the PMF (Performance Measurement Function) measures per-access metrics such as round-trip time and packet loss.
