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O-RAN WG4 Open Fronthaul Specifications (CUS and M-Plane) v2.0 to v17.01

  • Writer: Venkateshu
    Venkateshu
  • Apr 29
  • 7 min read

Introduction

The O-RAN Alliance Workgroup 4 (WG4) focuses on defining open fronthaul interfaces between the O-DU (Distributed Unit) and O-RU (Radio Unit), enabling multi-vendor interoperability and modular deployments in 5G and beyond. This article summarizes the evolution of functionalities introduced in WG4's CUS-plane (Control, User, Synchronization) and M-plane (Management Plane) specifications from Version 2 through Version 17.


Version 2:

  • Foundation of O-RAN CUS and M-plane interface definitions.

  • Basic transport, timing, and control plane setup.

  • Initial NETCONF/YANG modeling for O-RU management.


ORAN-WG4.CUS.0-v02.00

ORAN-WG4.MP.0-v02.00.00

  • antenna calibration of the O-RU

  • configuration of beam tilts

  • support for longer-latency front haul transport such as GPON

  • various monitoring and logging capabilities

  • antenna calibration of the O-RU,

  • configuration of beam tilts,

  • support for longer-latency front haul transport such as GPON,

  • various monitoring and logging capabilities,




Version 3:

  • Enhanced signal and slot definitions.

  • Expanded M-plane capabilities for remote management.

  • Initial alignment with 3GPP Release 15 features. 

ORAN-WG4.CUS.0-v03.00

O-RAN.WG4.MP.0-v03.00

·       Shared Cell capability,

·       Dynamic Spectrum Sharing parameters, The ability to convey multiple beamforming weight sets at once,

·       The ability to describe multiple antenna ports with a single C-Plane command,

·       O-DU synchronization requirements, Selective RE sending on the U-Plane, Little-endian data formats,

·       Several fronthaul performance measurement counters.

Existing functionality is enhanced, with capabilities such as

·       dying gasp

·       configuration notification,

·       dynamic spectrum sharing,

·       new energy,

·       power and environmental measurements as well as the ability to group eAxC-IDs together.

Version 4:

  • Defined periodic channel configurations (e.g., PRACH, SRS).

  • Introduced support for TDD pattern exchange.

  • Improved M-plane interface efficiency


O-RAN.WG4.CUS.0-v04.00

O-RAN.WG4.MP.0-v04.00

·       M-Plane definition of periodic channels such as PRACH and SRS, as well as the TDD pattern.

·       Synchronization enhancements were made to better align to ITU-T specifications

·       M-Plane definition of periodic channels such as PRACH and SRS, as well as the TDD pattern. 

·       Synchronization enhancements were made to better align to ITU-T specifications

 

Version 5:

  • First implementation of energy-saving features.

  • Extended fault and performance management objects in M-plane.

  • Initial support for shared cell configuration.


O-RAN.WG4.CUS.0-v05.00

O-RAN.WG4.MP.0-v05.00

Enhanced C-Plane/U-Plane to increase fronthaul efficiency:

·       Includes enhancements for non-contiguous frequency allocations and frequency hopping

·       Enhancements to support CoMP CB

·       Support of ueID-based beamforming in mixed-numerology systems

·       Enhancements for Channel information based uplink beamforming

·       Support for generating advanced beamforming weights based on UE channel at O-RU.

·       PRACH support using section Type 1 (when PARCH is using same SCS as PUSCH)

 

·       Updating mandatory cipher to AES128-CTR

·       Bandwidth management to avoid over-subscription of O-RU resources

·       Shared cell updates - selective Tx/Rx using Beam ID and cascaded FHM Operation

·       New capability to support coordinated (self) antenna calibration

·       New NACM permissions for SMO and hybrid O-DU

·       New optional feature for performing pnfRegistration

·       New optional feature for configured YANG subscriptions sent over JSON/REST

 

 

Version 6:

  • Introduced Netconf/TLS and IPv6-only support for O-RUs.

  • Alarm enhancements in M-plane.

  • Synchronization accuracy improvements.


O-RAN.WG4.CUS.0-v06.00

O-RAN.WG4.MP.0-v06.00

Special provisions for sending SRS from O-RU to O-DU in an efficient manner.

Support for Netconf/TLS and IPv6-only O-RUs.


Version 7:

  • External antenna delay handling.

  • 2-step RAN delay measurement.

  • Section type extensions 19 and 20 for efficient transport.

  • FTPES support and TD-RSSI measurement via M-plane.

 

O-RAN-WG4.CUS.0-v07.00

O-RAN.WG4.MP.0-v07.00

·       External Antenna Delay handling,

·       2-step delay measurement,

·       3GPP R16 PRRACH formats and

·       New section extensions 19 & 20 for improved efficiency.

·       External antenna delay handling,

·       TD-RSSI measurement capability & FTPES based file transfer


Version 8:

  • Support for boundary clock configuration.

  • Capability for multi-cell operation.

  • Compression support for Section Type 6.

  • Mandatory support for TLS, PKIX, FTPES.

O-RAN-WG4.CUS.0-v08.00

O-RAN.WG4.MP.0-v08.00

New features for C-Plane/U-Plane or enhancements for fronthaul efficiency

·       -Introduction of alarm-type and -alignment with 3GPP 28.532

·       -Enable IANA Private Enterprise Number to be used as Vendor Code in software management

·       -Boundary Clock function

·       -Capability for supporting multi cell operation

·       -Compression support for Section Type 6 -Mandatory support of TLS, PKIX, and FTPES

·       -Supporting multiple transport session types simultaneously

·       -Shared cell enhancements introducing t-combine-net and tx-duration


Version 9:

  • Section Type 6: 4-byte alignment handling.

  • Historical alarm list capability.

  • Improved configuration validation logic.

  • Enhanced loopback testing and S-plane interactions.

O-RAN.WG4.CUS.0-v09.00

O-RAN-WG4.MP.0-v09.00

  • Added security related enhancements for fronthaul

  • Additional capabilities and formatting for Section Type 6

 

·       Handling 4 byte alignment for section type 6

·       New build-content-download option for software management

·       New historical alarm list capability

·       Defining loopback messages to group destination addresses

 

Version 10:

  • Addition of remote file path capability.

  • Improved NETCONF monitoring.

  • Alarm correlation logic updated.

O-RAN.WG4.CUS.0-v10.00

O-RAN.WG4.MP.0-v10.00

  • Acknowledgement / Negative Acknowledgement (ACK/NACK) for C-Plane messages

  • Support for Shared O-RU

  • Added FFT/iFFT size 3072 to the definition of the frameStructure field Clarifications, including:

  • Uplink frame timing to Downlink frame

  • Aligned S-plane limits with ITU-T

  • Handling of precoding schemes with Transmit Diversity and Spatial Multiplexing with Large Delay DDD

  • Downlink C-Plane and U-Plane timing

  • Byte order for U-Plane data in Section Extension 11 and19

  • extended Antenna-Carrier ID (eAxC_ID) assignment

  • Timing error requirements for LLS-C3 configuration Corrections to: n-ta-offset value per 3GPP specification Citation of IEEE 1588

 

  • Shared O-RU functionality for single and multi-operator deployments

  • IEEE 802.1X Port Based Access Control

  • Introduction of O-RU Connector concepts

  • Support of DUID/IAID when using DHCPv4

  • Updated SFP compliance does

  • Mapping certificates to NETCONF accounts

 


Version 11:

  • Inclusion of IQ imbalance calibration procedures.

  • Enhanced beamforming state control.

  • Security log monitoring via M-plane.

O-RAN.WG4.CUS.0-R003-v11.00

O-RAN.WG4.MP.0-R003-v11.00

  • Support of Section Type 4 for slot level configuration

  • U-plane only DL mode (without C-plane) for cat A O-RUs

  • Section Extension 23 for support of Modulation Compression

  • Limit on the maximum number of frequency ranges in C-Plane message to address O-RU capabilities

  • The minimum gain capability of an O-RU

  • Limit on the number of frequency hops using Section Extension 13

  • Changes to usage of ‘rb’ bit in Section Extension 6

  • Section Extension 10 support in the Shared Cell

 

  • U-Plane-only DL mode

  • SW build level file integrity check

  • Session supervision with session-id

  • Network energy savings

 


Version 12:

  • Certificate lifecycle management improvements.

  • Alarm event stream filtering.

  • Support for simultaneous multi-session transport.

O-RAN.WG4.CUS.0-R003-v12.00

O-RAN.WG4.MP.0-R003-v12.00

• Support of in-band and guard-band NB-IoT

• IEEE 802.1X supplicant functionality mandatory for O-RU

• U-Plane message processing limits

• Indication of non-scheduled Info in channel information-based beamforming • Flag in Section Extension 11 to indicate PRB region continuity

• IEEE 802.1X as MandatoryAdd supported SCSes of FHM

• Allow all NETCONF clients to change their own password

• Advanced endpoint capability reporting for NB-IoT & other scenarios

• Allow CA/RA server on non-production VLAN

• Introduce ietf-truststore YANG model

• Introduce SE11-WITH-CONTINUITY-BIT-SUPPORT

• Addition of feature non-scheduled-ueid • Continuity Check Message support

• U-plane message processing limits Bug fixes


Version 13:

  • Configuration abstraction layer enhancements.

  • Support for shared-spectrum coordination.

  • Introduction of network slicing attributes in M-plane.

O-RAN.WG4.CUS.0-R003-v13.00

O-RAN.WG4.MP.0-R003-v13.00

Introduction of new functionalities:

• Added support of Network Energy Saving functionality: Advanced Sleep Mode and TRX Control

• New compression methods: selective RE sending with RE mask in the section header for block floating point and modulation compression

• Optional function to disable message sequence number checking 

Addition of new functionality, including

• Add optional Major severity for alarm 1

• Call home re-activation

• Add optional Power Amplifier critical severity to alarm #27

• New availability status for [tr]x-array-carriers

• O-RU connectors for ALD ports and External IO ports

• Combine delays per SCS

• Disabling sequence number handling

• Enhanced Network Energy Savings functionality Bug fixes


Version 14:

  • Calibration feature extension for TSSI.

  • Enhancements to multi-cell synchronization.

  • MACsec support added.

O-RAN.WG4.CUS.0-R003-v14.00

O-RAN.WG4.MP.0-R003-v14.00

Introduction of new functionalities:

• Addition of PRB block mode in Section Extension 23

• Addition of bundleOffset in Section Extension 11

• Updates to address new network limits of ITU-T G.8271.1 for LLS-C3 topology

• Mapping of ueId to a set of channel information and number of ueId values

• Performance counters for Shared Cell

 

Addition of new functionality, including:

• New alarm for Rx signal quality

• New feature SE23-PRB-BLOCK-MODE-SUPPORT

• Performance Counter for Shared Cell

• Energy saving by Data Layer Control

• bundleOffset in SE 11

 

Version 15:

  • Vendor certificate and trust anchor mechanisms clarified.

  • Support for 3GPP Release 16 PRACH formats.

  • Improved scheduler feedback signaling.

O-RAN.WG4.CUS.0-R003-v15.00

O-RAN.WG4.MP.0-R003-v15.00

Introduction of new functionalities:

• Optimization using Section Type 5 with Section Extension 10 for sending user group scheduling information

• New filter index for mixed numerology

• Sending PRG size information in Section Extension 21 for channel-information based beamforming

• New fronthaul network time error limits based on ITU-T G.8271.1 (2022) Amendment 2 (01/24)

• Support for multiple beamId tables 

Addition of new functionality, including:

• Per-port S-plane configuration of a multi-port O-RU

• O-RU payload frame size per ethernet interface

• Extended QL TLV Support

• O-RU TCP MSS Configuration

• Multiple beamId table support

• M-Plane TRX Control energy savings • Deep hibernate energy savings

• PRG size feature

• Adding frequency-table support with EPE-Statistics

• VSWR performance management reporting

• MU-MIMO user group optimization feature

• Delay profile per beamforming method • bundleOffset in SE 11 Bug fixes


Version 16:

  • Addition of Section Extension 27 for O-DU-controlled dimensionality reduction.

  • In-service beamforming update support.

  • IEEE 802.1X MAC address configuration support.

  • Alarm Types (e.g., High IQ, VSWR) formally introduced.

  • Enhanced TSSI and RSSI measurement logic.

  • Certificate lifecycle extensions and PKI interoperability.


O-RAN.WG4.CUS.0-R004-v16.01

O-RAN.WG4.MP.0-R004-v16.01

• A new beamforming method in uplink: “DMRS-BF” for uplink performance improvement which entails:

o   New Section Types for reporting PUSCH SINR, RRM measurements and a Section Type for requesting RRM measurement.

o   New Section Extensions to convey PUSCH DMRS configuration, symbol reordering on the fronthaul interface, frequency-offset feedback and O-DU controlled dimensionality reduction.

• Introduction of new functionalities, including:

o Delay management per beamforming method.

o Expand Section Extension 20 puncturing pattern scope to cover multiple section descriptions.

o Frequency error budget in terms of MTIE for LLS-C3.

 

• Addition of new functionality, including:

o PAE credential definition

o High IQ Alarm

o VSWR Alarm

o DMRS-BF

o SE-10 feature SE10-MEMBER-CANDIDATE-LIST

o Target value configuration and used-value retrieval

o Configuring IEEE 802.1X addressing

o RSSI measurements when operating in shared spectrum.

o Simple Public Key Method for SSH Client Authentication

o TSSI Measurements

o RSSI Measurements

o Section Extension 27 for O-DU controlled dimensionality reduction

o In service beamforming configuration update

o MACsec

o Certificate lifecycle management

 


Version 17:

  • Introduction of AI/ML-based configuration parameters.

  • RAN sharing support for virtual O-RUs.

  • Section Type 30 introduced for low-latency transport.

  • Enhanced support for mMIMO calibration and trace logging.

  • Improved compatibility with 3GPP Release 17.


O-RAN.WG4.TS.CUS.0-R004-v17.01

O-RAN.WG4.TS.MP.0-R004-v17.01

  • O-RU controlled dynamic time resolution of SINR reporting when DMRS-based beamforming is used

  • O-DU controlled dynamic frequency resolution of SINR reporting when DMRS-based beamforming is used

 

  • Add a generic hardware failure alarm to M-Plane

  • Add TX output power statistics to M-Plane

  • O-RAN defined security logging

  • Dynamic SINR reporting resolution

  • Switched to importing RFC 9640, 9641, 9642 instead of Internet-Drafts

  • New transceiver measurement for thermoelectric cooler (TEC) current

  • New Ethernet statistics counters



Conclusion

The O-RAN WG4 specifications have matured significantly from Version 2 through Version 17. With each release, functionalities have expanded from basic interface definitions to advanced synchronization, security, beamforming, and performance monitoring. These enhancements ensure that open fronthaul standards keep pace with 5G evolution and support scalable, secure, and intelligent RAN deployments.


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