Put the muscle where the data is.
CUPS decouples the UPF (user plane) from the SMF (control plane) over N4/PFCP. Once decoupled, the UPF can live central, at the edge, or — for a regenerative payload — onboard the satellite. Where you put it decides how many times a packet crosses the feeder link.
One split, three places to stand.
The SMF stays central — signalling tolerates the long round-trip. The UPF is latency-sensitive, so you move it toward the data. Below, each option and what it costs on a satellite link.
UPF deep in the core, beside the internet peering. Simplest to operate; every user packet traverses the full backhaul — and, over NTN, the feeder link twice.
UPF at the NTN gateway or a regional edge site. Local breakout to nearby content; the feeder is still crossed, but backhaul to a distant core is avoided.
UPF on the satellite with the gNB (regenerative). Traffic can break out through an onboard/edge DN without ever crossing the feeder — only N2 signalling does.
Fly the edge onto the satellite.
Switch the payload type and watch what physically moves into space. In a transparent payload the satellite only relays RF; go regenerative and the gNB — then the UPF — fly up, and the feeder link stops carrying raw radio and starts carrying only what has to reach the ground. Click any node for detail.
When the feeder link comes and goes.
A LEO satellite is not always in sight of a gateway. Rel-19 turns that from a failure into a mode of operation.
Store-and-forward Rel-19
With the UPF (and gNB) onboard, the satellite can accept a UE\u2019s delay-tolerant traffic, buffer it in space, and forward it to the ground the next time a feeder link is available — ideal for IoT-NTN telemetry that does not need a live path.
Local breakout
An onboard or edge UPF anchors N6 to a local/edge Data Network, so traffic never has to descend to a central core and climb back. Only the control-plane N2 signalling crosses the feeder — the user plane stays at the edge.
CUPS for EPC
SGW/PGW split into -C / -U over the Sx interface (PFCP). The user plane first became relocatable.
Native SMF / UPF
5G is CUPS by design — SMF (control) and UPF (user) over N4. Placement becomes a first-class choice.
Onboard & store-and-forward
The UPF can ride the satellite; the user plane is served even without a live feeder link.
Sources & specifications
- TS 23.501 — 5G System architecture · SMF/UPF
- TS 29.244 — PFCP · N4 · PDR/FAR/QER/URR
- TS 23.214 — CUPS for EPC (Rel-14)
- TR 38.821 — NTN architecture · UPF placement
- Rel-19 — regenerative payload & store-and-forward
- TS 23.502 — session-management procedures