In Open RAN network deployments, interface between DU and RU is known as Fronthaul. As shown in below picture, the fronthaul carrier, the fronthaul carries Control and User Plane (C/U) data, Sync and Management using eCPRI standard defined format.
- C-Plane (Control Plane): Control plane messages define the scheduling, coordination required for data transfer, beam-forming etc.
- U-Plane (User Plane): User plane messages for efficient data transfer within the strict time limits of 5G numerologies.
- S-Plane (Synchronization Plane) : Synchronization plane is responsible for the timing and sync aspects between the O-DU and O-RU.
- M-plane (Management Plane) : Management plane messages are used to manage the radio unit.
In the C-Plane, messages are encapsulated using a two-layered header approach.
- First layer header is an eCPRI header to indicate the message type
- Second layer is an Application Common header including necessary fields for control and synchronization
A “section” defines the characteristics of U-plane data to be transferred or received from a beam with one pattern id within the application common header. Section is 8 bit and can have possible 2^8=256 types called section type, but at present only 6 section types are in use.
- Control Plane has following 6 section types in use :
- Section Type 0 – used for indicating idle or guard periods from O-DU and O-RU
- Section Type 1 – used for most DL and UL radio channels
- Section Type 3 – used for PRACH and mixed-numerology channels
- Section Type 5 – used for UE scheduling information
- Section Type 6 – used for sending channel information for a specific UE ID
- Section Type 7 – used to support LAA
- User-plane has following 4 section types in use:
- Section Type 1
- Section Type 3
- Section Type 5
- Section Type 6
The structure of a “section” is consist of transport header (shown in yellow color), radio application head (pink color) and other others are repeated sections.
- Section Types#0 Structure
- Section Types#1 Structure
- Section Types#3 Structure
- Section Types#5 Structure
- Section Types#6 Structure
- O-RAN Fronthaul C/U, Synchronization and Management Planes
- Open RAN Management Plane (M-plane)
- O-RAN Fronthaul Protocols Stack
- O-RAN Fronthaul Delay Management
- O-RAN Fronthaul Synchronization Configuration
- IEEE 1588: Precision Time Protocol (PTP) for Telecom Networks