Welcome to O-RAN SC O-DU-L2 Documentation

O-DU-L2 Architecture

O-DU implements the functional blocks of L2 layer of a 5G NR protocol stacks. These layers primarily include NR MAC NR Scheduler and NR RLC layers.

O-DU modules are developed as shown in the below diagram.

ODU Arch diagram

O-DU Thread Architecture

As shown in Figure 1, there are multiple entities within O-DU. Modules sharing a given color belong to one thread. O-DU architecture can be defined at a thread level as follows:

  • Thread 1: O-DU thread
  • Thread 2: DU APP inclusive of Config Handler, DU Manager, UE Manager, EGTP Handler and ASN.1 Codecs
  • Thread 3: 5G NR RLC DL and MAC (inclusive of 5G NR SCH and Lower MAC)
  • Thread 4: 5G NR RLC UL
  • Thread 5: SCTP Handler

O-DU Modules

DU APP

This module configures and manages all the operations of O-DU. It interfaces with external entities as follows:

  • OAM: DU APP interacts with OAM on the O1 interface for configuration, alarms and performance management.
  • O-CU: DU APP interacts with O-CU for RAN functionalities over the F1 interface which is built on SCTP. Control messages are exchanged on the F1-C interface and data messages on the F1-U interface.
  • RIC: DU APP interacts with RIC on E2 interface over SCTP.

DU App submodules are as follows:

  • Config Handler manages the configurations received on O1 interfaces andstores them within DU APP context.
  • DU Manager handles all cell operations at the DU APP.
  • UE Manager handles UE contexts at the DU APP.
  • SCTP handler is responsible for establishing SCTP connections with O-CU, RIC.
  • EGTP handler is responsible for establishing EGTP connection with O-CU for data message exchange.
  • ASN.1 Codecs contain ASN.1 encode/decode functions which are used for System information, F1AP and E2AP messages.

5G NR RLC

This module provides services for transferring the control and data messages between MAC layer and O-CU (via DU App).

5G NR RLC UL and 5G NR RLC DL are the sub modules of this module that implement uplink and downlink functionality respectively.

5G NR MAC

This module uses the services of the NR physical layer to send and receive data on the various logical channels. Functions of the 5G NR MAC module are as follows:

  • 5G NR MAC is responsible for multiplexing and de-multiplexing of the data on various logical channels.
  • 5G NR SCH schedules resources on UL and DL for cell and UE based procedures.
  • Lower MAC interfaces between the MAC and the lower layers of the O-DU and implements all the messages of FAPI specification.

O-DU Utility and Common Functions

These modules help in the working of O-DU and message exchanges between the O-DU modules.

Release-Notes

This document provides the release notes for Bronze Release of O-DU-L2.

Version history

Date Ver. Author Comment
2019-10-29 0.1.0 Radisys Amber Release
2020-06-17 0.2.0 Radisys Bronze Release

Summary

Bronze

This release contains the following: - Enhancements to F1-C interface for UE attach procedure.

  • Implementation of F1-U interface.
  • Implementation of E2 interface.
  • Support for traffic steering usecase.
  • Support for single carrier.
  • Implementation of basic scheduler.
  • Implementation of Cell broadcast procedure.
  • Implementation of UE procedure till msg-4 for single UE. Complete testing of these messages is in progress.
  • Implementation of FAPI interface towards O-DU Low using WLS.
  • Partial implementation of RLC layer interfaces towards upper and lower layers conforming to AAD spec.

Release Data

Project ODUHIGH
Repo/commit-ID o-du/l2/ 27844f9c01c08472b86b1a75adaed0e450a88 907
Release designation Bronze Release
Release date 2020-06-17
Purpose of the delivery Bronze Release

Feature Additions

JIRA BACK-LOG:

JIRA REFERENCE SLOGAN
https://jira.o-ran-sc.org/browse/ODUHIGH-1 F1-C enhancement
https://jira.o-ran-sc.org/browse/ODUHIGH-5 F1-U implementation
https://jira.o-ran-sc.org/browse/ODUHIGH-11 E2 implementation
https://jira.o-ran-sc.org/browse/ODUHIGH-9 Cell broadcast procedure
https://jira.o-ran-sc.org/browse/ODUHIGH-10 UE attach procedure till msg-4
https://jira.o-ran-sc.org/browse/ODUHIGH-8 FAPI interface implementation
https://jira.o-ran-sc.org/browse/ODUHIGH-27 RLC layer interface enhancements

Bug Corrections

JIRA TICKETS:

NA

Deliverables

Software Deliverables

This release contains O-DU code, along with test code as part of CU stub, RIC stub and phy stub. Instructions to build and execute ODU, CU and RIC stub binaries are also present. All of the above can be found in the o-du/l2 repo.

Documentation Deliverables

This release contains - README with instruction to build and execute binaries.

  • overview.rst
  • release-notes.rst

Known Limitations, Issues and Workarounds

System Limitations

  • Current code contains support for below configuration:

    Duplex mode = FDD

    Freuency Range = FR 1

    numerology = 0

    bandwidth = 20 MHz

    DL/UL Modulation = QPSK

    single HARQ transmission

  • Support for single UE.

  • Cell broadcast is for SSB and SIB1 only.

  • This release implements a basic scheduler with fixed scheduling.

  • E2 interface is limited to Traffic Steering Usecase.

  • Forming of RIC event trigger definition, RIC indication header and RIC indication message is unclear in the E2AP draft spec versions. Therefore, implementation does not contain accurate values. Contents of RIC indication message are mocked and triggered just once.

  • On the F1-U interface, UE, RB and tunnel configurations are static.

  • System runs on preconfigured values due to absence of O1 interface.

  • O-DU High has not been integrated with O-DU Low and O-CU.

Known Issues

None

JIRA TICKETS:

NA

References

  1. ORAN-WG8.AAD.0-v02.05.00
  2. ORAN WG3.E2AP v01.00
  3. ORAN WG3.E2SM v01.00
  4. 3GPP 38.473-f60 v15.3
  5. 3GPP TS 38.211 v15.3
  6. 3GPP TS 38.212 v15.3
  7. 3GPP TS 38.213 v15.3
  8. 3GPP TS 38.214 v15.3
  9. 3GPP TS 38.321 v15.3
  10. 3GPP TS 38.331 v15.3
  11. 5G PHY FAPI Specification v1.0.5