What is Section Type in Open RAN Fronthaul?

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

Section Definition

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 :

1. 1. Section Type 0 – used for indicating idle or guard periods from O-DU and O-RU
   2. Section Type 1 – used for most DL and UL radio channels
   3. Section Type 3 – used for PRACH and mixed-numerology channels
   4. Section Type 5 – used for UE scheduling information
   5. Section Type 6 – used for sending channel information for a specific UE ID
   6. Section Type 7 – used to support LAA

• User-plane has following 4 section types in use:

1. 1. Section Type 1
   2. Section Type 3
   3. Section Type 5
   4. Section Type 6

Sections Structure

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

Related Posts

• 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

Reference

• ORAN Specification