Functional Split Between NG-RAN and 5G Core: Architecture and Key Roles
Distribution of Responsibilities Between NG-RAN and 5G Core
The 5G network architecture has been designed to be flexible, scalable, and have low latency. One of the important distinctions of the 5G architecture is the functional split between the Next Generation Radio Access Network (NG-RAN) and the 5G Core (5GC).
This functional split allows the radio access network and core subsystems to evolve independently and enables operators to optimize their performance for different use cases (eMBB, URLLC, and mMTC).
NG-RAN: The 5G Radio Access Network
In 5G, radio access is usually identified as using gNodeB (gNB) or gNS in this diagram.
Highlights of NG-RAN Functions includes:
RRM (Radio Resource Management) - Efficient management of spectrum and scheduling.
Slice Support - Multiple network slices with separate performance profiles.
QoS Management - Basic QoS enforcement prior to traffic hitting the core.
U/C Plane Routing - Routing user/control plane traffic for the core.
Connection Setup - Establishing links between the user equipment (UE) and the network.
5G Core: Cloud-Native and Service-Based
The 5G Core is a service-based architecture (SBA) that is service-based architecture (SBA) that runs on virtualized cloud infrastructure supporting a highly modular architecture allowing functions to be scaled independently.
Key Core Network Functions
AMF (Access and Mobility Management Function)
Security
Authentication
Mobility management (handover, roaming)
SMF selection
SMF (Session Management Function)
Session initiation and management
Traffic steering to appropriate UPF
Policy control based on subscriber profile
Manage QoS
UPF (User Plane Function)
Packet routing and forwarding
Deep packet inspection
Usage reporting for billing/analytics functions
User plane QoS handling
Functional Split Overview Table
Network Part Function Type Primary Responsibilities
NG-RAN (gNS) RRM, Slice Support, QoS, Routing, Connection Setup Radio resource management, initiate connection, basic QoS
AMF Control Plane Security, authentication, mobility management, SMF selection
SMF Control Plane Session management, traffic steering, policy/QoS control
UPF User Plane Packet routing, inspection, usage reporting, QoS handling
Advantages of the Functional Split
Scalability – Scale radio and core resources autonomously.
Flexibility – Push control or user plane functions required for a solution to the edge or cloud central.
Lower Latency – Place UPF closer to end user for latency sensitive applications.
Support for Better Network Slicing – Allocate dedicated resources for various use cases.
Conclusion
The functional split between NG-RAN and 5G Core is a dramatic difference over prior generations. With the decoupling of the radio access function from the core network functions, 5G provides unlimited flexibility, operational efficiency, and service agility in the deployment of various services.
This separation plays the critical role in low-latency (URLLC) applications, massive IoT applications, and high speed eMBB applications.
Deeper Technical Context: The Functional Split Perspective
In LTE/EPC, much of the control and user-plane processes were embedded with the eNB and centralized core, limiting flexibility and increasing the difficulty of scaling new services.
5G's functional split between NG-RAN and 5G Core introduces:
Service-Based Core - Core functions are independent network services (AMF, SMF, UPF) that can run in containers or virtual machines in a cloud-native environment.
Edge Computing Enablement - UPFs can be deployed in close proximity to the radio network, which is beneficial for latency-sensitive applications (e.g., industrial automation, AR/VR).
Network Slicing Enablement - The NG-RAN has the ability to differentiate traffic in the RAN layer and forward it to dedicated slices in the core.
Discrete Scaling - Operators are able to increase RAN capacity without reengineering core capacity, and vice versa.
Use case Deployment Scenarios
- Smart Factory (Low Latency URLLC)
UPF deployed at the edge inside of the factory.
NG-RAN adds slicing and forwards URLLC traffic to a dedicated low-latency slice.
AMF and SMF remain in a centralized model for control efficiency. - Video Streaming Service (High Bandwidth eMBB)
Multiple gNBs connect to centralized UPF to support bulk data throughput.
SMF enforces QoS for premium subscribers.
AMF manages mobility for users that are moving. - IoT Sensor Network (mMTC)
RAN completes the enormous task of connecting all data object instances to a 5G mobile platform says RSP. - Control and User Plane Separation (CUPS) in EPC
Prior to 3GPP Release 14, nodes in the EPC such as SGW, PGW, and TDF implemented both control signalling and user data forwarding in the same entity.
CUPS functionality, each node is split into a control function and a user function:
SGW → SGW-C and SGW-U
PGW → PGW-C and PGW-U
TDF → TDF-C and TDF-U
The interfaces introduced are:
Sxa – SGW-C ↔ SGW-U
Sxb – PGW-C ↔ PGW-U
Sxc – TDF-C ↔ TDF-U
The main features include:
Control and user planes can independently scale
Reduced latency by deploying user plane functions to the edge
Path for seamless migration to 5G's UPF model
- LTE vs 5G QoS Architecture
In LTE (4G):
QoS is implemented through EPS bearers identified as S1 bearers then MQoS configurations are applied at the radio bearers
Static QoS parameters.
In 5G:
QoS is implemented via QoS flows. A Qos Flow Identifier (QFI) identifies a QoS flow
The UPF uses SDF rules to classify packets into QoS flows.
Final Thought
The functional splits between NG-RAN and the 5G Core create a new baseline for next generation mobile networking. Specific functions that can be offloaded to a specialized cloud-native function allow the provisioning of:
Lower latency to end device with UPFs at the edge of the network
Flexible service delivery is possible simply because of slicing across the network
Efficient operations due to independent scaling
Future capabilities for application cases, e.g., immersive AR/VR, autonomous vehicles, mIoT
This allows us to be design 5G and not just make it an upgrade from LTE but as a normalized design for our next fully programmable, software driven network to be able to support the needs of the next decades of the need to connect.
4G to 5G Network Architecture Evolution
The mobile network has changed from 4G LTE's EPC (Evolved Packet Core) to 5G service-based architecture (SBA). The changes are:
Control and User Plane Separation (CUPS) in the EPC (3GPP Release 14)
Evolution of QoS from EPS bearers to 5G QoS flows
Functional split between NG-RAN and the 5G Core