DU-high
The DU-high (Distributed Unit - High) implements the MAC and RLC layers of the protocol stack. The MAC layer schedules radio resources for connected UEs, manages HARQ retransmissions, handles the Random Access procedure, and broadcasts System Information. The RLC layer provides segmentation, concatenation, and, in acknowledged mode, retransmission of data between PDCP in the CU and MAC. The DU-high communicates with the CU-CP and CU-UP via the F1-c and F1-u interfaces, with the DU-low via the FAPI interface, and optionally with the near-RT RIC via the E2 interface.
Components
- DU Manager: Manages the DU, specifically the connected UEs and RAN resources.
- RLC: The Radio Link Control (RLC) layer sits between the MAC in the DU-high and the F1AP/PDCP in the CU. It provides transport services for SRBs and DRBs and operates in three modes: transparent (TM), unacknowledged (UM), and acknowledged (AM).
- MAC: The Medium Access Control (MAC) layer is responsible for encoding and decoding MAC PDUs, scheduling uplink and downlink grants, and other control services including System Information, Paging, UE data scheduling, and Random Access handling.
Interfaces
| Interface | Connects to |
|---|---|
| E2 | Near-RT RIC |
| F1-c | CU-CP |
| F1-u | CU-UP |
| FAPI | DU-low |