CU

As outlined in the Knowledge Base section discussing the CU, the CU is split into the control plane (CU-CP) and the user plane (CU-UP). The srsRAN Project CU follows the architecture seen in the Knowledge Base.

CU-CP

As multiple DUs can be connected to the CU-CP, the F1AP, PDCP, and RRC are bundled into the so called DU processor that is created for each connected DU. Likewise multiple CU-UPs can be connected to the CU-CP, so the E1AP is created inside the CU-UP processor for each connected CU-UP.

Components:

  • E1AP-CU-CP: The CU-CP specific implementation of the E1AP

  • F1AP-CU: The CU specific implementation of the F1AP

  • PDCP: Packet Data Convergence Protocol

  • RRC: Radio Resource Control

  • NGAP: The CU specific implementation of the NGAP

Interfaces:

  • E1: Interface with the CU-UP

  • F1-C: Control plane interface with the DU

  • NG-C: Control plane interface with the Core (AMF)

CU-UP

Components:

  • E1AP-CU-UP: The CU-UP specific implementation of the E1AP

  • F1-U: The CU-UP specific implementation of the F1-U

  • PDCP: Packet Data Convergence Protocol

  • SDAP: Service Data Adaption Protocol

  • NG-U: The CU specific implementation of the NG-U

Interfaces:

  • E1: Interface with the CU-CP

  • F1-U User plane interface with the DU

  • NG-U User plane interface with the Core (AMF)