4G to 5G Migration Plan Explained: NSA, SA, and Common Core Evolution
4G to 5G Migration Plan: From EPC to Common Core and Beyond
Transitioning from 4G LTE to 5G isn’t just a straightforward swap; it’s a thoughtfully crafted evolution with several phases. Operators need to maintain compatibility with older systems while gearing up for next-gen 5G networks. The 4G to 5G Migration Plan outlines this transformation, addressing 5G Ready EPC, 5G NSA, 5G SA, and ultimately a unified core that integrates Wi-Fi.
In this blog, we’re going to break this down into clear stages, explaining how operators can move from today’s LTE networks to a fully integrated 5G Standalone (SA) core.
Why Migration Matters
Telecom operators have to juggle keeping legacy LTE users happy while also bringing in new 5G subscribers. Migration is crucial for:
Smooth user experience across both 4G and 5G.
Cost-effective investments by making the most of existing infrastructure.
Scalability to handle a massive IoT, super-low latency, and enhanced mobile broadband (eMBB).
Future readiness with a flexible common core.
Stage 1: 5G Ready EPC
We kick things off with the Evolved Packet Core (EPC) that powers LTE.
Components:
MME (Mobility Management Entity)
GW-C (Gateway Control Plane)
GW-U (Gateway User Plane)
HSS (Home Subscriber Server)
PCRF (Policy and Charging Rules Function)
Key Features:
Works exclusively with 4G UEs.
Partners with 4G DU (Distributed Unit) for LTE access.
Basically, this is a 4G-only network—no 5G capabilities here.
Stage 2: 5G NSA Core
The first step into 5G is adopting Non-Standalone (NSA) mode, where 5G radios (gNB/DU) depend on the existing 4G EPC for control signaling.
New Addition:
5G DU for New Radio (NR).
vUC (Virtualized User Control) to handle dual connectivity.
Functionality:
4G EPC takes care of signaling (control plane).
5G NR boosts data rates (user plane).
Supports both 4G UEs and 5G NSA UEs.
This path to 5G keeps costs down since it leverages the EPC.
Stage 3: Intermediate Stage (NSA + SA Common Core)
Next up is a 5G common core that can handle both NSA and SA setups.
Supported Users: 4G UEs, 5G NSA UEs, and 5G SA UEs.
Core Functions:
UDM (Unified Data Management)
PCF (Policy Control Function)
NRF (Network Repository Function)
NSSF (Network Slice Selection Function)
NEF (Network Exposure Function)
UDSF (Unstructured Data Storage Function)
Key Gateway Enhancements:
GW-C + SMF (Session Management Function)
GW-U + UPF (User Plane Function)
Advantage: Operators can gradually transition traffic from EPC to the 5G core, allowing them to adapt as needed.
This stage is super important since it ensures dual support, letting operators cater to both NSA and SA users without forcing an immediate upgrade for customers.
Stage 4: Target Stage (5G NSA + SA + Wi-Fi Convergence)
The last stage sees a fully converged core that supports LTE, 5G NSA, 5G SA, and even Wi-Fi.
Common Core Includes:
HSS + UDM integration for unified management of subscribers.
PCF + PCRF collaborating for policy enforcement.
AUSF (Authentication Server Function) for 5G security.
N3IWF (Non-3GPP Interworking Function) for Wi-Fi integration.
AMF (Access and Mobility Management Function) for 5G control.
Capabilities:
Supports 4G, 5G NSA, and 5G SA UEs all at once.
Wi-Fi integration for a seamless user experience.
Network slicing to cater to different use cases.
This is the end goal of migration: a service-based 5G core that supports a variety of connectivity scenarios.
Migration Path Summary
Here’s a quick look at each stage:
Stage Access Supported Core Type Key Features5G Ready EPC4GEPCLegacy LTE only5G NSA Core4G + 5G NSAEPC + NSA Uses EPC signaling, 5G NR for data Intermediate (NSA + SA)4G + 5G NSA + 5G SA Common Core Dual support, new 5G core functions Target Stage (NSA + SA + Wi-Fi)4G + 5G NSA + 5G SA + Wi-Fi Unified Common Core Full convergence, network slicing, Wi-Fi interworking
Benefits of a Common Core Approach
The common core is vital for a successful migration. The advantages include:
Simplified Operations – A single core that serves multiple access technologies.
Cost Efficiency – Cuts down on infrastructure duplication.
Service Flexibility – Allows for network slicing tailored to IoT, eMBB, and URLLC.
Improved Security – Cohesive authentication and policy enforcement.
Future-Proofing – Brings together 4G, 5G, and Wi-Fi within one framework.
Challenges in 4G to 5G Migration
Even with the perks, migration comes with its own set of challenges:
Interoperability issues between the old EPC and the new 5G core.
Upgrade costs for hardware and software.
Spectrum allocation for NSA and SA modes.
Subscriber migration without disrupting services.
Security management across different networks.
To handle this, operators often go for a phased rollout to minimize risks.
Real-World Use Cases
Smart Cities: Utilizing a common core for managing LTE sensors, 5G cameras, and Wi-Fi hotspots together.
Enterprise 5G: Implementing private 5G networks with network slicing and seamless Wi-Fi transitions.
Industry 4.0: Supporting both old LTE devices and cutting-edge 5G machinery.
Consumer Services: Enhancing gaming, AR/VR, and streaming with NSA today, leading to SA in the future.
Conclusion
The 4G to 5G Migration Plan goes beyond just boosting speeds—it’s about creating a flexible, integrated, and intelligent network. Starting from EPC and moving through NSA, SA, and ultimately reaching a unified core with Wi-Fi, operators can facilitate a smooth transition while safeguarding their previous investments.
For telecom professionals, this guide underscores the need for strategic planning, phased implementation, and the importance of a common core architecture. Tech enthusiasts can appreciate how networks evolve to meet the increasing demand for connectivity, automation, and ultra-low latency services.
The journey from 4G to 5G is truly evolutionary rather than revolutionary—but the goal is a cohesive core that fuels the digital future.