What are the differences between the Control Plane and the User Plane in the 5G Core network?

In a 5G Core network, the Control Plane and User Plane are two essential components that perform distinct functions. These planes are part of the Service-Based Architecture (SBA) defined in the 3rd Generation Partnership Project (3GPP) specifications for 5G networks. Let's delve into the technical details of each plane:

  1. Control Plane (CP):
    • Functionality:
      • The Control Plane is responsible for managing and controlling the establishment, modification, and termination of communication sessions between user devices (UEs) and the network.
      • It handles signaling, policy enforcement, session management, and mobility management.
      • Control Plane functions are crucial for maintaining the overall network state and ensuring that user data is routed correctly.
    • Protocols and Interfaces:
      • The Control Plane uses various protocols and interfaces to carry out its functions. Some of the key protocols include:
        • NGAP (Next Generation Application Part): Used for communication between the Access and Mobility Management Function (AMF) and the User Plane Function (UPF) during session establishment and modification.
        • N1/N2/N3 interfaces: These are reference points between different network functions within the 5G Core network, facilitating communication for control plane functions.
    • Network Functions:
      • Key network functions involved in the Control Plane include the Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), and Policy Control Function (PCF).
    • Mobility Management:
      • The Control Plane manages the mobility of user devices within the network, ensuring seamless handovers between different cells and enabling continuous communication.
  2. User Plane (UP):
    • Functionality:
      • The User Plane is responsible for the actual transmission of user data. It is involved in forwarding data packets between the user device (UE) and external networks or services.
      • The UPF (User Plane Function) plays a central role in the User Plane, handling tasks such as packet routing, forwarding, and encapsulation/decapsulation.
    • Protocols and Interfaces:
      • The User Plane uses various protocols and interfaces to efficiently transport user data. Some of the key protocols include:
        • GTP-U (GPRS Tunnelling Protocol - User Plane): Used for the encapsulation and transport of user data between the UPF and the Radio Access Network (RAN).
        • N4/N6 interfaces: These interfaces connect the UPF with the SMF and the Data Network (DN) for efficient user data transfer.
    • Network Functions:
      • The UPF is the primary network function associated with the User Plane. It performs tasks like packet inspection, filtering, and forwarding based on policies defined by the Control Plane.
    • Data Forwarding:
      • The User Plane forwards user data packets based on the information provided by the Control Plane. It ensures the efficient and timely delivery of data between the user device and the external networks or services.

The Control Plane is responsible for managing and controlling the signaling and overall state of the network, while the User Plane focuses on the efficient forwarding and delivery of user data. The separation of these planes allows for better scalability, flexibility, and optimization of 5G networks.