📕 5G network comprises a remote radio unit (RRU), distributed unit (DU), a centralized unit (CU), and a core network. The terms fronthaul, midhaul, and backhaul are describing the 5G transport network support for the interfaces between these nodes.
📕 A Fronthaul transport network supports the low-layer functional split point of 3GPP NG-RAN (e.g., Option 6 for MAC/PHY split or Option 7 for intra PHY split).
📕 A Midhaul transport network supports the 3GPP NG-RAN F1 interface (between a gNB-CU and a gNB-DU), or the Xn interface that provides interconnection between different NG-RAN nodes (gNB).
📕 A Backhaul transport network supports the 3GPP NG interface (between the 5GC and the NGRAN) or the Xn interface that provides interconnection between different NG-RAN nodes (gNB).
📃 Notes:
- A backhaul network always exists to connect the CUs to the core network.
- When DU and RU are integrated, there is no fronthaul network.
- When the DU and CU are integrated, there is no midhaul network.
📃 Interfaces:
- F1: Logical interface between the CU and DU.
- NG: Logical interface between the 5GC and gNB.
- Xn: Logical Interfaces internal to the RAN (“Xn” specifically refers to one connection between two gNB nodes).