What is CUPS in mobile networks?

CUPS stands for Control and User Plane Separation. Introduced for the EPC in 3GPP Release 14 (TS 23.214), it splits the SGW and PGW into a control part (SGW-C, PGW-C) and a user part (SGW-U, PGW-U) so the data plane can be scaled and placed independently from the signalling. The 5G core is built on the same idea from the start, with the SMF as control plane and the UPF as user plane.

What is the PFCP protocol and where is it used?

PFCP (Packet Forwarding Control Protocol, TS 29.244) is how a control-plane node programs a user-plane node. It runs over UDP on port 8805 and installs PDRs, FARs, QERs and URRs — the rules that tell the user plane how to detect, forward, police and meter packets. In EPC with CUPS it runs on Sxa, Sxb and Sxc; in the 5G core it runs on the N4 interface between SMF and UPF.

How does the SMF/UPF split compare to the EPC SGW/PGW split?

They are the same pattern applied at different times. CUPS retrofitted the split onto the EPC, so an operator could keep S5/S11 reference points and add Sx interfaces for the new control-to-user link. The 5G core has no combined gateway at all: the SMF is always the control plane, the UPF always the user plane, and N4 is simply PFCP again. Because both use PFCP, a vendor’s UPF can often serve 4G and 5G traffic.

CUPS Architecture

Side-by-side comparison of Control / User Plane Separation in the evolved EPC (3GPP TS 23.214) and the fully service-based 5G Core (TS 23.501). Dashed lines are control-plane signalling, solid lines are user-plane traffic.

Left

EPC with CUPS

3GPP TS 23.214

Control plane User plane

MME — S11 → SGW-C — Sxa → SGW-U

SGW-C — S5-C → PGW-C — Sxb → PGW-U

User plane: UE → eNB → S1-U → SGW-U → S5-U → PGW-U → SGi → Internet

Right

5G Core (SBA)

3GPP TS 23.501

Control plane User plane

User plane: UE → gNB → N3 → UPF → N6 → DN

AMF — N11 → SMF — N4 → UPF

SMF ↔ SBI ↔ PCF, UDM, NRF, CHF

PFCP — Packet Forwarding Control Protocol

PFCP (3GPP TS 29.244) is the single protocol that lets a control-plane node program a user-plane node. In EPC with CUPS it runs on Sxa (SGW-C↔SGW-U), Sxb (PGW-C↔PGW-U) and Sxc (TDF-C↔TDF-U). In 5GC it runs on N4 (SMF↔UPF). Messages are UDP on port 8805 and carry PDRs (Packet Detection Rules), FARs (Forwarding Action Rules), QERs (QoS Enforcement Rules) and URRs (Usage Reporting Rules). The same machinery powers both architectures — which is why multi-vendor UPFs can be re-used across 4G and 5G deployments.

Comparison

Feature	Pre-CUPS EPC	EPC with CUPS	5GC
Control / User split	Combined in SGW & PGW	Separated (Sx)	Separated (N4)
Protocol	GTP-U + Diameter / GTP-C	PFCP (Sxa / Sxb / Sxc)	PFCP over N4
User-plane NF	SGW / PGW	SGW-U / PGW-U	UPF
Service framework	Reference points	Reference points	Service-Based (SBI, HTTP/2)
Scalability	Monolithic	CP/UP scale independently	CP fully stateless micro-services
Typical deployment	3G/4G legacy	4G + fixed-mobile conv.	5G SA, MEC, slicing

About CUPS

Before Release 14 the SGW and PGW in LTE bundled control-plane signalling with user-plane packet forwarding on the same box. Operators that wanted to scale throughput (say, for a sudden video streaming spike) had to scale the control plane too, and had to place the heavy data-plane hardware exactly where the signalling needed to sit. CUPS — introduced in TS 23.214 — broke that coupling. The control plane (SGW-C, PGW-C, TDF-C) stays centralised while the user plane (SGW-U, PGW-U, TDF-U) can be pushed to the network edge, closer to RAN aggregation sites and MEC platforms. The glue between them is PFCP.

5G Core takes the same idea and bakes it in from day one. There is no such thing as a combined SMF/UPF — the SMF is always control plane, the UPF always user plane, and the N4 interface between them is just PFCP again. The payoff is low-latency URLLC and edge-local breakout: the same SMF in a central data centre can steer a UE onto a UPF running inside a factory, stadium or base of a cell tower.

Related tools

How to use the CUPS Architecture diagram

Compare the two sides. View the EPC-with-CUPS diagram on the left and the 5G core on the right at the same time.
Tell the planes apart. Read dashed lines as control-plane signalling and solid lines as user-plane traffic in both diagrams.
Follow the user plane. Trace a packet end to end — eNB → SGW-U → PGW-U → SGi in EPC, or gNB → UPF → N6 → DN in 5G.
Map the control interfaces. Note where PFCP runs — Sxa/Sxb in EPC, N4 in 5G — using the PFCP callout.
Check the comparison table. Use the side-by-side table to contrast pre-CUPS EPC, EPC with CUPS and the 5G core on protocol, scalability and deployment.

Frequently asked questions

What is CUPS in mobile networks?: CUPS stands for Control and User Plane Separation. Introduced for the EPC in 3GPP Release 14 (TS 23.214), it splits the SGW and PGW into a control part (SGW-C, PGW-C) and a user part (SGW-U, PGW-U) so the data plane can be scaled and placed independently from the signalling. The 5G core is built on the same idea from the start, with the SMF as control plane and the UPF as user plane.
What is the PFCP protocol and where is it used?: PFCP (Packet Forwarding Control Protocol, TS 29.244) is how a control-plane node programs a user-plane node. It runs over UDP on port 8805 and installs PDRs, FARs, QERs and URRs — the rules that tell the user plane how to detect, forward, police and meter packets. In EPC with CUPS it runs on Sxa, Sxb and Sxc; in the 5G core it runs on the N4 interface between SMF and UPF.
How does the SMF/UPF split compare to the EPC SGW/PGW split?: They are the same pattern applied at different times. CUPS retrofitted the split onto the EPC, so an operator could keep S5/S11 reference points and add Sx interfaces for the new control-to-user link. The 5G core has no combined gateway at all: the SMF is always the control plane, the UPF always the user plane, and N4 is simply PFCP again. Because both use PFCP, a vendor’s UPF can often serve 4G and 5G traffic.

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