Control and User Plane Separation (CUPS) in 5G - Tech.in | 5G, SDN/NFV & MEC

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Saturday, March 9, 2019

Control and User Plane Separation (CUPS) in 5G

What is CUPS?

CUPS stands for Control and User Plane Separation. It was introduced by 3GPP, for Evolved Packet Core (EPC) as part of their Release 14 specifications. 



Why do we need CUPS?

Service providers across the globe are seeing a jump in the mobile data growth, year-after-year, due to the growth in the consumption of video, online gaming and social media services. 5G is not only facing the challenge of supporting higher data speeds, but also has to reduce the network latency for customers. Network latency has a direct impact on the customer experience and almost a non-negotiable thing for the new 5G use-cases.

The architects of 5G are looking at multiple ways of bringing down the network latency for customers, to meet the requirements of emerging 5G use cases such as Smart Cars, AR/VR and Holograms. 5G architecture tries to reduce the network latency through multiple mechanisms such as Network Slicing, Massive MIMO, Small Cells and Multi-access Edge Computing (MEC). MEC infrastructure, being closer to the user, plays a critical role in bringing down the network latency by providing a compute infrastructure for Over-The-Top (OTT) and Internet of Things (IOT) services. CUPS is another ammunition in 5G kitty, which helps in bringing down the network latency.

When was CUPS introduced in the wireless network architecture?

CUPS was originally introduced in the 4G Evolved Packet Core (EPC) architecture. EPC with CUPS support separates the control plane function from the user plane function in the network. Network functions within 4G EPC such as Packet Gateway (PGW), Serving Gateway (SGW) and Traffic Detection Function (TDF), were split into control plane and user plane functions. EPC with CUPS support had PGW-U/PGW-C, SGW-U/SGW-C and TDF-U/TDF-C. 

When EPC supports CUPS, service providers would have the option of 

  • deploying the control plane functions co-located with the user plane functions (i.e., in the same data center)
  • deploying the control plane functions and user-plane functions in a distributed fashion, across multiple locations
  • deploying the control plane function in a centralized location and deploy the user-plane functions in multiple locations
How does CUPS helps in reducing network latency?


The multiple deployment options supported by CUPS, provide great flexibility to the service providers, to deploy user-plane functions in one or more locations to meet the bandwidth and latency requirements of customer services. For example, a service provider may have to deploy more instances of the user plane function near a college, where several 100s of students are watching video and playing online games. However, in a shopping district, there will be several 1000s of mobile users who would be browsing Internet for checking information about stores and shopping deals. In such locations, the control plane has to scale to support several 1000s of customer sessions. So, the service provider may have to deploy more control plane functions in such geographies to support the 1000s of mobile users. 

How does 5G support CUPS?

5G adopts CUPS based architecture for the 5G Core. 5G Core has a distinct User Plane Function (UPF) that handles all of the user-plane functions performed by SGW-U and PGW-U in 4G EPC. 5G's control plane functions are distributed across different network functions such as Authentication Server Function (AUSF), User Data Management (UDM), Policy and Charging Function (PCF) and Session Management Function (SMF). This gives a lot of flexibility for the service providers to decide the network functions which have to be deployed at the edge of the network vs. core of the network. 

Since 5G supports cloud-native network services, it becomes easy for the vendors and service providers to implement CUPS in the 5G network architecture (when compared to the 4G network). 

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