CU-UP

The CU-UP (Central Unit - User Plane) terminates the user plane at the CU layer. It implements PDCP for header compression, ciphering, and integrity protection of user data, and SDAP for mapping QoS flows to data radio bearers. User plane traffic is routed between the UPF via GTP-U tunnels on the N3 interface and the DU-high via the F1-u interface. Bearer configuration is managed by the CU-CP via the E1 interface, and optionally the near-RT RIC via the E2 interface.

Components

• UE Manager: Manages connected UEs in the CU-UP. Responsible for adding and removing UEs and providing relevant UE information to other processes. Communicates UE information to and from the CU-CP, DU, and Core.
• GTP-U: The GPRS Tunneling Protocol User Plane (GTP-U) is responsible for transporting user plane traffic to and from the UPF via the N3 interface.
• SDAP: The Service Data Adaptation Protocol (SDAP) is responsible for adapting and mapping Quality of Service (QoS) requirements onto user plane traffic.
• PDCP: The Packet Data Convergence Protocol (PDCP) is responsible for handling user plane data before and after it passes through the DU-high.

Interfaces

Interface	Connects to
E2	Near-RT RIC
E1	CU-CP
F1-u	DU (user plane)
N3	UPF