ETSI GR NFV-IFA 046 V5.1.1 (2023-05)

Network Functions Virtualisation (NFV) Release 5; Architectural Framework; Report on NFV support for virtualisation of RAN

DGR/NFV-IFA046

General Information

• Status: Not Published
• Technical Committee: NFV IFA - Interfaces and Architecture
• Current Stage: 12 - Completion
• Due Date: 31-Mar-2023
• Completion Date: 26-May-2023

Standards Content (Sample)

GROUP REPORT
Network Functions Virtualisation (NFV) Release 5;
Architectural Framework;
Report on NFV support for virtualisation of RAN
Disclaimer
The present document has been produced and approved by the Network Functions Virtualisation (NFV) ETSI Industry
Specification Group (ISG) and represents the views of those members who participated in this ISG.
It does not necessarily represent the views of the entire ETSI membership.

2 ETSI GR NFV-IFA 046 V5.1.1 (2023-05)

Reference
DGR/NFV-IFA046
Keywords
5G, architecture, management, RAN, NFV

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ETSI
3 ETSI GR NFV-IFA 046 V5.1.1 (2023-05)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definition of terms, symbols and abbreviations . 10
3.1 Terms . 10
3.2 Symbols . 10
3.3 Abbreviations . 10
4 Introduction and overview . 11
4.1 Introduction to the virtualised RAN . 11
4.1.1 Overview . 11
4.1.2 The concept of RAN disaggregation and functional splits . 11
4.1.3 Open and virtualised RAN . 12
4.2 State of the art and other organizations landscape . 13
4.2.1 Overview of SDOs activities on vRAN . 13
4.2.1.1 Introduction . 13
4.2.1.2 ETSI NFV . 13
4.2.1.3 3GPP . 13
4.2.1.4 O-RAN Alliance (O-RAN) . 14
4.2.1.5 Small Cell Forum (SCF) . 14
4.2.1.6 CPRI Forum . 14
4.2.1.7 IEEE . 14
4.3 Characteristics of the virtualised RAN . 14
4.3.1 Reference architecture and functional splits in O-RAN. 14
4.3.2 Cloudification, management and orchestration. 15
4.4 Problem statement . 15
5 NFV support for the virtualised RAN . 16
5.1 Overview . 16
5.1.1 Introduction. 16
5.1.2 Terminology alignment . 17
5.2 Key issues and potential solutions . 18
5.2.1 Key Issue A: Architectural Mappings . 18
5.2.1.1 Introduction . 18
5.2.1.1.1 Overview . 18
5.2.1.1.2 NFV-MANO with container management and multi-site connectivity support . 18
5.2.1.1.3 O-RAN Orchestration related architecture elements . 19
5.2.1.1.4 Challenges related to architectural elements mapping . 20
5.2.1.2 Potential Solutions . 21
5.2.1.2.1 Overview . 21
5.2.1.2.2 Solutions for challenge A1: SMO and O-Cloud boundaries and mapping of interfaces . 21
5.2.1.2.3 Solutions for challenge A3: Physical Infrastructure Management . 23
5.2.1.3 Gap analysis . 26
5.2.1.4 Evaluation and concluding remark . 27
5.2.2 Key Issue B: Support for Acceleration abstraction . 30
5.2.2.1 Introduction . 30
5.2.2.1.1 Overview . 30
5.2.2.1.2 NFV-MANO support for Acceleration abstraction . 30
5.2.2.1.3 O-RAN support for Acceleration abstraction . 32
5.2.2.1.4 Challenges . 33
5.2.2.2 Potential Solutions . 34
5.2.2.2.1 Overview . 34
ETSI
4 ETSI GR NFV-IFA 046 V5.1.1 (2023-05)
5.2.2.2.2 Solutions for Challenge B.1: virtualised accelerator in NFV for both VM and containerized
environments . 35
5.2.2.2.3 Solutions for challenge B.2: Virtual and hardware acceleration resource management . 36
5.2.2.2.4 Solutions for challenge B.3: Northbound interface exposed by the virtualised accelerator to
the application (VNF). . 37
5.2.2.3 Gap analysis . 38
5.2.2.4 Evaluation and concluding remark . 38
5.2.3 Key Issue C: VNF descriptors and packaging . 39
5.2.3.1 Introduction . 39
5.2.3.1.1 Overview . 39
5.2.3.1.2 Descriptors and Packaging in NFV-MANO . 40
5.2.3.1.3 Descriptors and Packaging in O-RAN . 40
5.2.3.1.4 Challenges . 41
5.2.3.2 Potential Solutions . 42
5.2.3.2.1 Overview . 42
5.2.3.2.2 Solutions for challenge C.1: ML modelling information . 42
5.2.3.2.3 Solutions for challenge C.2: CRDs in NFV . 42
5.2.3.2.4 Solutions for challenge C.3: VNF dependencies and different LCM cycles . 43
5.2.3.3 Gap analysis . 44
5.2.3.4 Evaluation and concluding remark . 44
5.2.4 Key Issue D: Transport Network management . 48
5.2.4.1 Introduction . 48
5.2.4.1.1 Overview . 48
5.2.4.1.2 Transport Network Management in NFV-MANO . 48
5.2.4.1.3 Transport Network Management in O-RAN . 50
5.2.4.1.4 Challenges . 51
5.2.4.2 Potential Solutions . 52
5.2.4.2.1 Overview . 52
5.2.4.2.2 Solutions for challenge D.1: O-Cloud boundaries and network demarcation points . 52
5.2.4.2.3 Solutions for challenge D.2: Network management boundaries . 53
5.2.4.2.4 Solutions for challenge D.3: Time synchronization . 53
5.2.4.2.5 Solutions for challenge D.4: Transport Network Slicing . 54
5.2.4.2.6 Solutions for challenge D.5: Transport specific protocols . 54
5.2.4.3 Gap analysis . 55
5.2.4.4 Evaluation and concluding remark . 55
6 Recommendations . 57
6.1 Overview . 57
6.2 Recommendations for solutions . 57
6.3 Recommendations related to the NFV architectural framework . 59
6.4 Recommendations related to functional aspects . 59
6.5 Recommendations related to NFV descriptors and other artifacts . 60
6.6 Recommendations related to interfaces and information model. 61
6.7 Recommendations related to cross organization collaboration . 62
7 Conclusion . 62
Annex A: Virtualised RAN Use Cases . 63
A.1 Introduction . 63
A.2 Use cases from O-RAN WG1 . 63
A.3 Use cases from O-RAN WG6 . 69
Annex B: Background information on Functional Splits . 75
B.1 Introduction . 75
Annex C: Change history . 77
History . 78

ETSI
5 ETSI GR NFV-IFA 046 V5.1.1 (2023-05)
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Foreword
This Group Report (GR) has been produced by ETSI Industry Specification Group (ISG) Network Functions
Virtualisation (NFV).
Modal verbs terminology
In the present document "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be
interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.

ETSI
6 ETSI GR NFV-IFA 046 V5.1.1 (2023-05)
1 Scope
The present document analyses the NFV framework to determine how it can further support virtualised RAN (vRAN)
use cases. Several key technical challenges are identified relevant to architectural, operational and management aspects,
in case the NFV architectural framework is leveraged to support virtualisation of the RAN. For each technical challenge
a detailed analysis is provided, together with a description of potential solutions. Potential gaps in ETSI NFV
specifications are articulated and a comparison between the different potential solutions is also accommodated.
In addition, an analysis of vRAN use cases from relevant specifications from other SDOs is performed, together with a
mapping to the current NFV concepts supported by the NFV architectural framework.
The present document also provides recommendations for enhancements to the NFV architectural framework and its
functionality, aiming to provide further support for vRAN use cases.
2 References
2.1 Normative references
Normative references are not applicable in the present document.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long-term validity.
The following referenced documents are not necessary for the application of the present document, but they assist the
user with regard to a particular subject area.
[i.1] ETSI GR NFV 003: "Network Functions Virtualisation (NFV); Terminology for Main Concepts in
NFV".
[i.2] NGMN Alliance: "5G White Paper", 2015.
[i.3] Recommendation ITU-R M.2083-0: "MT Vision - Framework and overall objectives of the future
development of IMT for 2020 and beyond".
[i.4] ETSI TS 123 501 (V16.10.0): "5G; System architecture for the 5G System (5GS) (3GPP
TS 23.501 version 16.10.0 Release 16)".
[i.5] Common Public Radio Interface (CPRI).
rd
[i.6] 3GPP TR 38.801 (V14.0.0): "3 Generation Partnership Project; Technical Specification Group
Radio Access Network; Study on new radio access technology: Radio access architecture and
interfaces (Release 14)".
[i.7] ETSI TS 138 300 (V16.7.0): "5G; NR; NR and NG-RAN Overall description; Stage-2 (3GPP
TS 38.300 version 16.7.0 Release 16)".
[i.8] ETSI TS 138 401 (V16.7.0): "5G; NG-RAN; Architecture description (3GPP TS 38.401
version 16.7.0 Release 16)".
[i.9] ETSI TS 138 470 (V16.5.0): "5G; NG-RAN; F1 general aspects and principles (3GPP TS 38.470
version 16.5.0 Release 16)".
[i.10] ETSI TS 138 460 (V16.3.0): "5G; NG-RAN; E1 general aspects and principles (3GPP TS 38.460
version 16.3.0 Release 16)".
ETSI
7 ETSI GR NFV-IFA 046 V5.1.1 (2023-05)
[i.11] ETSI TS 138 410 (V16.4.0): "5G; NG-RAN; NG general aspects and principles (3GPP TS 38.410
version 16.4.0 Release 16)".
rd
Generation Partnership Project; Technical Specification Group
[i.12] 3GPP TR 32.842 (V13.1.0): "3
Services and System Aspects; Telecommunication management; Study on network management of
virtualised networks (Release 13)".
[i.13] ETSI TS 128 622 (V16.9.0): "Universal Mobile Telecommunications System (UMTS); LTE; 5G;
Telecommunication management; Generic Network Resource Model (NRM) Integration
Reference Point (IRP); Information Service (IS) (3GPP TS 28.622 version 16.9.0 Release 16)".
rd
Generation Partnership Project; Technical Specification Group
[i.14] 3GPP TR 23.742 (V16.0.0): "3
Services and System Aspects; Study on Enhancements to the Service-Based Architecture
(Release 16)".
[i.15] ETSI GR NFV-IFA 037 (V4.1.1): "Network Functions Virtualisation (NFV) Release 4;
Architectural Framework; Report on further NFV support for 5G".
[i.16] ETSI GR NFV-EVE 017 (V1.1.1): "Network Functions Virtualisation (NFV); Management and
Orchestration; Report on the support of real-time/ultra-low latency aspects in NFV related to
service and network handling".
[i.17] ETSI GS NFV-IFA 001 (V1.1.1): "Network Functions Virtualisation (NFV); Acceleration
Technologies; Report on Acceleration Technologies & Use Cases".
[i.18] ETSI GS NFV-IFA 002 (V2.4.1): "Network Functions Virtualisation (NFV) Release 2;
Acceleration Technologies; VNF Interfaces Specification".
[i.19] ETSI GS NFV-IFA 004 (V2.4.1): "Network Functions Virtualisation (NFV) Release 2;
Acceleration Technologies; Management Aspects Specification".
[i.20] ETSI GS NFV-IFA 018 (V3.1.1): "Network Functions Virtualisation (NFV); Acceleration
Technologies; Network Acceleration Interface Specification; Release 3".
[i.21] ETSI GS NFV-IFA 019 (V3.1.1): "Network Functions Virtualisation (NFV); Acceleration
Technologies; Acceleration Resource Management Interface Specification; Release 3".
[i.22] ETSI TS 128 541 (V16.10.0): "5G; Management and orchestration; 5G Network Resource Model
(NRM); Stage 2 and stage 3 (3GPP TS 28.541 version 16.10.0 Release 16)".
rd
[i.23] 3GPP TR 32.864 (V15.0.0): "3 Generation Partnership Project; Technical Specification Group
Services and System Aspects; Telecommunication management; Study on management aspects of
virtualised network functions that are part of the New Radio (NR) (Release 15)".
[i.24] SmallCellForum SCF159 (V159.07.02): "Small cell virtualisation functional splits and use cases".
[i.25] SmallCellForum SCF222 (V222.10.03): "5G FAPI: PHY API Specification".
[i.26] SmallCellForum SCF225 (V225.2.0.0): "5G nFAPI Specification".
[i.27] IEEE 1914.1™-2019: "IEEE Standard for Packet-based Fronthaul Transport Networks".
[i.28] O-RAN, ORAN-WG1-ARCH (V08.00.13): "O-RAN Architecture Description".
[i.29] O-RAN, ORAN.WG8.AAD (V04.00): "Base Station O-DU and O-CU Software Architecture and
APIs".
[i.30] O-RAN, O-RAN.WG6.CAD (V04.02): "Cloud Architecture and Deployment Scenarios for
O-RAN Virtualised RAN".
[i.31] O-RAN, O-RAN.WG6.O2-GA&P (V01.2): "O2 Interface General Aspects and Principles".
[i.32] ETSI GS NFV-IFA 010 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Functional requirements specification".
ETSI
8 ETSI GR NFV-IFA 046 V5.1.1 (2023-05)
[i.33] ETSI GR NFV-EVE 018 (V0.0.20) "Network Functions Virtualisation (NFV) Release 5;
Evolution and Ecosystem; Report on Multi-tenancy in NFV".
[i.34] ETSI GR NFV-EVE 019 (V4.1.1): "Network Functions Virtualisation (NFV) Release 4;
Architectural Framework; Report on VNF generic OAM functions".
[i.35] ETSI GS NFV-IFA 032 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Interface and Information Model Specification for Multi-Site
Connectivity Services".
[i.36] ETSI GS NFV-IFA 030 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Multiple Administrative Domain Aspect Interfaces
Specification".
[i.37] ETSI GR NFV-IFA 028 (V3.1.1): "Network Functions Virtualisation (NFV) Release 3;
Management and Orchestration;Report on architecture options to support multiple administrative
domains".
[i.38] ETSI GR NFV-REL 011 (V4.1.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Report on NFV-MANO software modification".
[i.39] ETSI GS NFV-IFA 005 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration;Or-Vi reference point - Interface and Information Model
Specification".
[i.40] ETSI GS NFV-IFA 006 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration;Vi-Vnfm reference point - Interface and Information Model
Specification".
[i.41] ETSI GR NFV-IFA 024 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Information Modeling;Report on External Touchpoints related to NFV Information Model".
[i.42] ETSI GR NFV-IFA 023 (V3.1.1): "Network Functions Virtualisation (NFV); Management and
Orchestration;Report on Policy Management in Mano; Release 3".
[i.43] ETSI GR NFV-IFA 042 (V4.1.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Report on policy information and data models for NFV-MANO".
[i.44] ETSI GS NFV-IFA 014 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Network Service Templates Specification".
[i.45] ETSI GS NFV-IFA 027 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Performance Measurements Specification".
[i.46] ETSI GS NFV-TST 008 (V3.3.1): "Network Functions Virtualisation (NFV) Release 3; Testing;
NFVI Compute and Network Metrics Specification".
[i.47] O-RAN.WG1.Use-Cases-Analysis-Report (V06.00): "O-RAN Working Group 1 Use Cases
Analysis Report".
[i.48] O-RAN.WG10.OAM-Architecture (V09.00): "O-RAN Operations and Maintenance Architecture".
[i.49] ETSI GR NFV-IFA 029 (V3.3.1): Network Functions Virtualisation (NFV) Release 3;
Architecture; Report on the Enhancements of the NFV architecture towards "Network Functions
Virtualisation (NFV) Release 3; Architecture; Report on the Enhancements of the NFV
architecture towards "Cloud-native" and "PaaS"".
[i.50] O-RAN.WG6.ORCH-USE-CASES (V02.01): "Orchestration Use Cases and Requirements for
O-RAN Virtualised RAN".
[i.51] ETSI GS NFV-IFA 031 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Requirements and interfaces specification for management of
NFV-MANO".
ETSI
9 ETSI GR NFV-IFA 046 V5.1.1 (2023-05)
[i.52] ETSI GS NFV-IFA 036 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Requirements for service interfaces and object model for
container cluster management and orchestration specification".
[i.53] ETSI GS NFV-IFA 007 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Or-Vnfm reference point - Interface and Information Model
Specification".
[i.54] ETSI GS NFV-IFA 008 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Ve-Vnfm reference point - Interface and Information Model
Specification".
[i.55] ETSI GS NFV-IFA 011 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; VNF Descriptor and Packaging Specification".
[i.56] ETSI GS NFV-REL 006 (V3.1.1): "Network Functions Virtualisation (NFV) Release 3;
Reliability; Maintaining Service Availability and Continuity Upon Software Modification".
[i.57] ETSI GR NFV-IFA 041 (V4.1.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Report on enabling autonomous management in NFV-MANO".
[i.58] ETSI GS NFV-IFA045 (V0.0.5): "Network Functions Virtualisation (NFV) Release 5;
Management and Orchestration; Faults and alarms modeling specification".
[i.59] ETSI GR NFV-EVE 022 (V5.1.1): "Network Functions Virtualisation (NFV) Release 5;
Architectural Framework; Report on VNF configuration".
[i.60] ETSI GS NFV-SOL 001 (V4.3.1) "Network Functions Virtualisation (NFV) Release 4; Protocols
and Data Models; NFV descriptors based on TOSCA specification".
[i.61] ETSI GR NFV-TST 006 (V1.1.1) "Network Functions Virtualisation (NFV); Testing; Report on
CICD and Devops".
[i.62] ETSI GS NFV 006 (V4.4.1): "Network Functions Virtualisation (NFV) Release 4; Management
and Orchestration; Architectural Framework Specification".
[i.63] IEEE 802.1Q™-2018: "IEEE Standard for Local and Metropolitan Area Network--Bridges and
Bridged Networks".
[i.64] ETSI GS NFV-IFA 013 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Os-Ma-nfvo reference point - Interface and Information Model
Specification".
[i.65] O-RAN.WG6.AAL-GAnP (V04.00): "O-RAN Acceleration Abstraction Layer General Aspects
and Principles".
[i.66] O-RAN.WG6.AAL-Common API (V03.00.05): "O-RAN Working Group 6 Acceleration
Abstraction Layer Common API".
[i.67] ETSI GS NFV-SOL 004 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4; Protocols
and Data Models; VNF Package and PNFD Archive specification".
[i.68] ETSI GS NFV-SOL 007 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4; Protocols
and Data Models; Network Service Descriptor File Structure Specification".
[i.69] ETSI GS NFV-IFA047 (V0.0.5): "Network Functions Virtualisation (NFV) Release 4;
Management and Orchestration; Management data analytics Service Interface and Information
Model specification".
[i.70] O-RAN-WG4.CUS.0 (V08.00): "O-RAN Working Group 4 (Open Fronthaul Interfaces WG)
Control, User and Synchronization Plane Specification". .
[i.71] ETSI GR NFV-IFA 044 (V0.0.4): "Network Functions Virtualisation (NFV) Release 5;
Management and Orchestration; Report on Flexible VNF Deployment".
ETSI
10 ETSI GR NFV-IFA 046 V5.1.1 (2023-05)
[i.72] ETSI GR NFV-IFA 035 (V0.14.0): "Network Functions Virtualisation (NFV) Release 5;
Architectural Framework; Report on network connectivity integration and operationalization for
NFV".
[i.73] ETSI GS NFV-SOL 005 (V4.3.1): "Network Functions Virtualisation (NFV) Release 4; Protocols
and Data Models; RESTful protocols specification for the Os-Ma-nfvo Reference Point".
[i.74] ORAN, O-RAN.WG9.XTRP-MGT.0(V04.00): "Management interfaces for Transport Network
Elements".
[i.75] ORAN, O-RAN.WG9.XPSAAS (03.00): "Xhaul Packet Switched Architectures and Solutions".
[i.76] ORAN, ORAN-WG9.XTRP-SYN.0 (03.00): "Synchronization Architecture and Solution
Specification".
[i.77] ETSI TS 128 533 (V16.8.0): "5G; Management and orchestration; Architecture framework (3GPP
TS 28.533 version 16.8.0 Release 16)".
[i.78] O-RAN.WG6.O2-O2dms-Interface-ETSI-NFV-profile (V01.00): "O-RAN Working Group 6
O-RAN, O-Cloud O2dms Interface Specification, Profile based on ETSI NFV protocol and data
models".
[i.79] ONF TR-547 (V1.1): "TAPI Reference Implementation Agreement".
[i.80] ETSI GR NFV-IFA049 (V0.0.4): "Network Functions Virtualisation (NFV) Release 4;
Architectural Framework; VNF generic OAM functions specification".
[i.81] IEEE 1914.3™-2018: "IEEE Standard for Radio over Ethernet Encapsulations and Mappings".
3 Definition of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the terms given in ETSI GR NFV 003 [i.1] apply.
3.2 Symbols
Void.
3.3 Abbreviations
For the purposes of the present document, the abbreviations given in ETSI GR NFV 003 [i.1] and the following apply:
5GCN 5G Core Network
5GS 5G System
AAL Acceleration Abstraction Layer
AALI Acceleration Abstraction Layer Interface
AMF Access and Mobility Management Function
ASIC Application-Specific Integrated Circuit
CRD Custom Resource Definition
CSE Connectivity Service Endpoint
CU Centralized Unit
DU Distributed Unit
EPD Extensible Para-virtualised Device
FPGA Field-Programmable Gate Array
GPU General Purpose Processor
LPU Logical Processing Unit
MDA Management Data Analytics
NFO Network Function Orchestration
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NSMF Network Slice Management Function
NSSMF Network Slice Subnet Management Function
PAP Policy Administration Point
PF Policy Function
RAN Radio Access Network
RIC RAN Intelligent Controller
RU Radio Unit
SMO Service Management and Orchestration
TNE Transport Network Element
UC Use Case
UPF User Plane Function
URLLC Ultra-Reliable Low Latency Communications
VF Virtual Function
VID VLAN Identifier
4 Introduction and overview
4.1 Introduction to the virtualised RAN
4.1.1 Overview
The 5G system (5GS) was designed to satisfy stringent requirements by means of several KPIs like throughput, delay,
and reliability in challenging use cases, as originally described by NGMN in "NGMN 5G White Paper" [i.2] and ITU
IMT 2020 specifications (like in [i.3]), but also beyond. It greatly evolves both the packet core and the Radio Access
Network (RAN) of the previous generation mobile network, where compared to the 4G design, several key
technological innovations were introduced. These span from control-user plane decoupling and migrating the packet
core to a Service Based Architecture (SBA), to the introduction of the 5G New Radio (NR) and the Next Generation-
RAN (NG-RAN). 5G NR develops under the 3GPP RAN TSG and mainly targets outperforming spectrum efficiency
and high frequency band utilization. It is considered as an umbrella term though, covering for example the radio
interface, radio spectrum usage and massive MIMO technology. NG-RAN is the term used to refer to RAN architectural
related aspects, as defined in ETSI TS 123 501 [i.4].
The present document investigates the advances concerning the virtualisation of the RAN and profiles the NFV
framework to determine how it can support virtualised RAN (vRAN) use cases. The basic concepts and terminology
used are introduced, based on the major SDOs' and industrial fora activities that are driving the transformation of the
RAN into an open, disaggregated, and virtualised system.
4.1.2 The concept of RAN disaggregation and functional splits
In a monolithic design, a single integrated base station (either 4G eNB, 5G ng-eNB or a gNB) provides the full set of
RAN control and user plane functionalities that enable user equipment (UE) access to the mobile network. These
functionalities span from the management of radio resources, control plan signalling (e.g. UE handover), data packet
transportation, baseband processing (e.g. channel coding, modulation), to the radio frequency (RF) part for single/multi-
antenna transmission/reception.
Following a basic disaggregation model, a monolithic base station is decomposed into two parts:
1) Remote Radio Heads (RRHs) which include the RF part, the power amplifier and the analogue-to digital or
digital-to-analogue converter being mounted externally and co-located with the antenna; and
2) Base Band Units (BBUs) located in a centralized pool being responsible for the baseband processing.
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The link connecting a BBU and a RRH is known as fronthaul, and CPRI [i.5] is the standardized interface used for the
BBU to RRH communication. This disaggregation model is also known as Cloud-RAN. Although Cloud-RAN heralds
an evolving change, its extreme need for bandwidth on the fronthaul makes the wide adoption difficult towards 5G,
especially for challenging URLLC use cases. In this regard, the functional split concept was introduced to relocate RAN
functions between BBUs and RRHs. Main SDOs working on the topic are 3GPP, O-RAN Alliance, Small Cell Forum
and CPRI [i.5]. Note that different standardization bodies are using their individual terminologies to articulate the
concept of functional splits. To avoid confusion in this study, the terminology used by 3GPP (primarily), and O-RAN
(when necessary) are followed.
In Figure 4.1.2-1, a high-level view of the NG-RAN architecture is depicted presenting the different functional
components and relevant interfaces. In 3GPP TR 38.801 [i.6] the 5G RAN functions and the functional splits concept
have been initially described. Detailed specification of the NG-RAN architecture and the different components for 5G
are in ETSI TS 138 300 [i.7] and ETSI TS 138 401 [i.8]. The idea is that a single 5G gNB can be decomposed into a
Centralized Unit (CU) and Distributed Units (DUs), to flexibly deploy RAN functionalities over different sites.
Depending on the split, different functionality is allocated to DUs and CUs. Splits 1 to 5 consider functionality
reallocation above the MAC and have been considered as High Layer Splits (HLS). Splits 6 to 8 are relevant to different
splitting options below MAC and are considered as Low Layer Splits (LLS). Split option 8 is the one that was used in
the case of "legacy" BBU - RRH decoupling followed by Cloud-RAN. In principle a DU hosts RAN functions between
LLS and HLS and aggregates multiple RUs, and a CU hosts all RAN functions above HLS and aggregates several DUs.
F1 interface is used for the communication between a CU and a DU according to ETSI TS 138 470 [i.9]. RU is
responsible for Low-PHY and RF processing, like D/A and digital beamforming (depending on the split). Background
information about the disaggregated RAN and the functional splits concept is provided in Annex B.

Figure 4.1.2-1: NG-RAN architecture according to ETSI TS 138 401 [i.8]
and 3GPP TR 38.801 [i.6]
3GPP also splits CU functionality into Control Plane (CU-CP) and User Plane (CU-UP) functions, where E1 is the
interface between them specified in ETSI TS 138 460 [i.10]. Communication between NG-RAN and 5GCN is realized
over the NG interface according to ETSI TS 138 410 [i.11]. On the user plane, GTP-U based communication is used
between NG-RAN node (CU or gNB or ng-eNB) and the UPF residing in 5GCN (N3 interface). On the control plane,
communication is over the (NG-C) interface defined between the NG-RAN node and AMF residing in the 5GCN
(N2 interface). NG interface is following the point-to-point model and is not part of SBA. Xn is the interface between
CUs or between CUs and integrated gNBs. For the transport network part, as shown in Figure 4.1.2-1 fronthaul link is
the link between a DU and a RU, midhaul the link between a DU and a CU and backhaul the link between a CU and
5GCN. In the case of Cloud-RAN (split 8), fronthaul is used to denote the link between BBU and RRH and backhaul
the link BBU to 5GCN; there is no midhaul link.
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4.1.3 Open and virtualised RAN
Besides achieving performance related KPIs, another key goal of 5G is to provide substantial deployment flexibility.
Such goal has been achieved in the core network, via decomposing the EPC
...