User & Control Plane Essentials

{{  :user_control_planes_essentials.png?400  }}

User Plane (Data Plane)

Purpose: Transports user-generated data (e.g., internet traffic, voice packets via VoNR).

Protocols: Uses protocols like GTP-U (GPRS Tunneling Protocol for User Plane) for tunneling data between nodes (e.g., between UPF and gNodeB).

No APIs: These connections are not RESTful APIs - they are optimized for high-speed, low-latency data transfer.

Control Plane

Purpose: Manages signaling between network functions (e.g., AMF, SMF, NRF) for tasks like authentication, session setup, or service discovery.

Interfaces: These are called Service-Based Interfaces (SBIs) and are RESTful APIs (HTTP/2 + JSON).

Examples:

  * Namf: API exposed by AMF for communication with other functions.
  * Nsmf: API exposed by SMF for session management.
  * Nnrf: API exposed by NRF for service discovery.

How it works?: Functions like AMF or SMF act as HTTP clients/servers, invoking or exposing RESTful endpoints to exchange control messages (e.g. AMF queries NRF via Nnrf_NFDiscovery to find suitable SMF).

When a device connects to 5G:

  - Control Plane: AMF (Access and Mobility Management Function) uses RESTful SBIs to communicate with NRF (Network Repository Function) to discover SMF (Session Management Function).
  - User Plane: SMF selects a UPF (User Plane Function), and GTP-U tunnels are established to route user data.

Bibliography:

  - [[https://www.sharetechnote.com/html/db/html/FAQ_4G_Architecture_Cplane_Uplane.html|https://www.sharetechnote.com/html/db/html/FAQ_4G_Architecture_Cplane_Uplane.html]] (semi-AI generated)
  - [[https://www.telecomgurukul.com/post/understanding-control-and-user-plane-separation-in-5g-networks-updated-in-2024|https://www.telecomgurukul.com/post/understanding-control-and-user-plane-separation-in-5g-networks-updated-in-2024]]
  - [[https://devopedia.org/control-and-user-plane-separation|https://devopedia.org/control-and-user-plane-separation]]