In this post we will learn what is 5G CUPS.
CUPS refers to "control plane and user plane separation".
5G CUPS means that the 5G network is separated into "control plane" and "user plane".
In order to understand CUPS, first we should know that in order for the UE to be able to exchange user plane data between the UE and the data network.
First, the UE should register to the 5G network. As a result of registration procedure, the network will know about the existence of the UE, the location of the UE, and other information about the UE.
Then, the UE should establish a data tunnel between the UE and a network function in the 5G core network named the UPF, through the gNB. This data tunnel is named the "PDU session".
The user plane data between the UE and the data network, will move inside this established PDU session between the UE and the UPF.
Now , we are ready to learn the meaning of CUPS.
CUPS means control plane and user plane separation.
This means to separate between the control plane and the user plane in 5G network.
In the following graph, the user plane is marked in Green, while the control plane is marked in Yellow.
The user plane is used to exchange user plane data between the UE and the data network.
So the user plane contains the UE, the gNB, and the UPF. Which are marked in green color in this graph.
While the control plane contains the network functions that control all aspects of the network. Like authenticating the UE, registering the UE to the network, establishing, modifying or terminating the PDU sessions, determine the QoS used in the PDU session, saving all data related to the UEs and the PDU sessions.
The control plane network functions are marked in Yellow in this graph, and they contain the AMF, the SMF, the AUSF, the PCF.
The control plane is not only limited to those network functions. There are additional network functions that work in the control plane that we will discuss later .
As you can see in this graph, the only network function from the 5G core network working in the user plane is the UPF, while the other network functions in the 5G core network are working in the control plane.