Control-User Plane Separation (CUPS)

CUPS allows the Session Management Function (SMF) in the control plane and the User Plane Function (UPF) in the user plane to scale independently based on demand.

• Control Plane: Scales with signaling load (session creation, mobility events)
• User Plane: Scales with data throughput (packet forwarding volume)

This prevents over-provisioning of one plane to accommodate the other, directly reducing idle power consumption during low-traffic periods.

The UPF can be deployed at the network edge, close to the user, while the SMF remains in a centralized data center. This minimizes backhaul latency and reduces the energy required to transport user data across long distances.

• Centralized control plane for global policy management
• Distributed user plane for local breakout and edge computing
• Enables Edge Slice architectures for latency-sensitive applications

Decoupling enables the UPF to be implemented on specialized, energy-efficient hardware optimized solely for high-speed packet forwarding.

• Accelerator Offloading: UPF functions like GTP-U encapsulation can run on FPGAs or SmartNICs
• Dynamic Voltage and Frequency Scaling (DVFS): Applied independently to UPF workloads based on traffic load
• Eliminates the overhead of running control plane logic on packet processing nodes

CUPS enables precise Sleep Mode Coordination by allowing the control plane to orchestrate power states across distributed user plane instances.

• The SMF can signal idle UPFs to enter deep sleep states
• Wake-Up Signal (WUS) mechanisms can reactivate specific UPFs only when sessions require them
• Enables Cell Discontinuous Transmission (Cell DTX) alignment with core network power states for end-to-end energy savings

CUPS is foundational for Energy-Efficient Network Slicing. Each network slice instance can have its own dedicated or shared UPF instances, managed independently.

• Slice-Level Energy Models can quantify per-slice power consumption
• Energy-Aware Slice Selection can steer users to slices with the lowest carbon footprint
• Enables Slice Remapping to consolidate traffic onto fewer UPFs during low load, allowing others to power down

A failure in a UPF instance does not necessarily disrupt control plane functions, and vice versa. This isolation improves overall network resilience.

• Control plane can rapidly reassign sessions to healthy UPFs
• Slice Isolation is strengthened by separating control and user plane fault domains
• Enables hitless software upgrades of the SMF without impacting active user data flows

The control plane function responsible for session establishment, modification, and release. It manages UE IP address allocation, selects and controls the UPF, and enforces policy rules. In a CUPS architecture, the SMF can scale independently from data plane throughput, allowing operators to handle massive signaling loads without over-provisioning packet processing resources.

The data plane workhorse that performs packet routing, forwarding, inspection, and QoS enforcement. Key capabilities include:

• Packet detection rules for classifying traffic into flows
• Usage reporting for charging and policy control
• Buffering downlink packets during UE idle mode CUPS allows UPFs to be placed at the network edge for ultra-low latency while the SMF remains centralized.

The Packet Forwarding Control Protocol (PFCP) operating over the Sx interface between SMF and UPF. It establishes and maintains the packet detection rules (PDRs) and forwarding action rules (FARs) that govern how the UPF handles traffic. This standardized interface, defined in 3GPP TS 29.244, is what makes multi-vendor CUPS deployments possible, decoupling control logic from forwarding hardware.

A direct benefit of CUPS where the UPF is deployed at Multi-access Edge Computing (MEC) sites close to the radio network. This minimizes latency for applications like:

• Autonomous vehicle V2X communication
• Industrial AR/VR overlays
• Real-time video analytics The SMF remains in a central data center, maintaining session continuity even as the UE moves between edge UPFs.

CUPS enables operators to scale the control plane and user plane independently based on distinct demand patterns. A surge in signaling events—such as massive IoT device registrations—requires more SMF instances without affecting UPF capacity. Conversely, a spike in data throughput from video streaming scales UPFs without wasting control plane resources. This granular elasticity directly reduces infrastructure power consumption.

The 5G Core equivalent of the Sx interface, connecting the SMF to the UPF. It uses PFCP with extensions for 5G features including:

• QoS flow binding for granular per-flow treatment
• Ethernet PDU session support for industrial protocols
• Redundant transmission for URLLC reliability The N4 interface is the critical control channel that programs the distributed UPF fabric from a logically centralized SMF.