Understanding MR-DC in 5G: Dual Connectivity Options Explained
Understanding MR-DC in 5G: Breaking Down Dual Connectivity Options
As mobile networks are moving into 5G and beyond, operators are tasked with managing a smooth transition from LTE (4G) to NR (New Radio). One of the key ways to facilitate this shift is through MR-DC (Multi-RAT Dual Connectivity).
MR-DC allows devices to connect to two different radio access technologies (RATs) simultaneously—like LTE and 5G NR—or even a pair of 5G nodes. This approach enhances performance, reliability, and coverage by taking advantage of both the existing 4G infrastructure and the rollout of next-gen 5G.
The image above outlines the MR-DC Lists as per the 3GPP standards. Let’s dive into it.
What is MR-DC (Multi-RAT Dual Connectivity)?
MR-DC lets a UE (User Equipment) connect to two nodes at once:
A Master Node (MN): This one manages signaling, controls, and sometimes user-plane traffic.
A Secondary Node (SN): This node provides extra radio resources to improve throughput and coverage.
This setup is essential for:
📶 Extending coverage in spots where standalone 5G isn’t cutting it.
🚀 Enhancing data rates by pooling resources from different RATs.
🔄 Facilitating a smooth transition from LTE EPC-based systems to 5G Core (5GC).
MR-DC Lists Unpacked
The table in the image showcases four main MR-DC types and how they can be deployed:
MR-DC Type
Core Network Option
Master Node (MN)
Secondary Node (SN)
MR-DC Type Core Network Option Master Node (MN)Secondary Node (SN)EN-DC (E-UTRA NR Dual Connectivity)EPC Option 3eNBen-gNBEN-DC (NR-EUTRA Dual Connectivity)5GCOption 4gNBng-eNBNGEN-DC (NG-RAN E-UTRA-NR Dual Connectivity)5GCOption 7ng-eNBgNBNR-DC (NR-NR Dual Connectivity)5GCOption 2gNBgNB
Let’s break down each one in more detail.
- E-UTRA-NR Dual Connectivity (EN-DC) – Option 3
Core Network: EPC (Evolved Packet Core)
Master Node: LTE eNB
Secondary Node: en-gNB (5G node tied to EPC)
This is the most widely used dual connectivity option during early 5G rollouts. Many operators already have EPC in place, so they can easily add 5G NR as a secondary node while keeping LTE as the control signaling anchor.
🔑 Key Advantage: Quick 5G deployment without needing to wait for 5GC.
⚠️ Limitation: Limited by the capabilities of EPC (in terms of latency and flexibility).
- NR-E-UTRA Dual Connectivity (EN-DC) – Option 4
Core Network: 5GC (5G Core)
Master Node: gNB (5G node)
Secondary Node: ng-eNB (LTE node linked to 5GC)
In this case, the 5G gNB steps up as the Master Node, with LTE functioning as a backup. This is the opposite of Option 3 and works best when the operator has already set up the 5G Core.
🔑 Key Advantage: Fully utilizes the features of 5GC (like network slicing and low latency).
⚠️ Limitation: Needs migration from EPC to 5GC.
- NG-RAN E-UTRA-NR Dual Connectivity (NGEN-DC) – Option 7
Core Network: 5GC
Master Node: ng-eNB
Secondary Node: gNB
Here, an ng-eNB (upgraded LTE eNB connected to 5GC) serves as the Master Node, while the 5G gNB acts as the secondary one.
This model lets operators continue to rely on LTE while benefiting from the capabilities of the 5G Core.
🔑 Key Advantage: Allows for a gradual upgrade while keeping LTE robust.
⚠️ Limitation: Not as future-ready as a fully 5G-centric setup.
- NR-NR Dual Connectivity (NR-DC) – Option 2
Core Network: 5GC
Master Node: gNB
Secondary Node: gNB
This is the most advanced MR-DC setup, where both nodes are 5G gNBs connected to the 5G Core. It maximizes the use of 5G features like:
Massive MIMO
URLLC (Ultra-Reliable Low Latency Communications)
eMBB (Enhanced Mobile Broadband)
Network slicing
🔑 Key Advantage: Provides a complete 5G experience with top throughput, flexibility, and reliability.
⚠️ Limitation: Requires a substantial investment in 5G infrastructure.
Why MR-DC is Important for 5G Rollouts
MR-DC isn’t just a technical detail — it’s a strategic tool for operators.
Benefits:
✅ Smooth transition from LTE to 5G
✅ Better coverage and reliability
✅ Higher data rates via aggregation
✅ Flexible deployment models based on network readiness
Deployment Strategy Insights:
Operators using Option 3 EN-DC can bring 5G to market quickly.
Moving to Option 4 or Option 7 allows them to tap into 5GC advantages.
Option 2 NR-DC represents the ultimate goal for a mature 5G network.
MR-DC in Real-World Scenarios
📱 Urban Cities: EN-DC Option 3 is common in early deployments due to existing LTE coverage.
🌍 Rural Areas: NGEN-DC is handy where LTE is strong but 5G is still rolling out.
🏙 Mature 5G Markets: NR-DC is the future standard for speedy, ultra-low latency services.
Extended Blog Post
MR-DC Deployment Roadmap: From EN-DC to NR-DC
Rolling out 5G isn’t a quick process. Operators take it slow, moving gradually from LTE-based dual connectivity to complete 5G. Here’s a typical roadmap:
Option 3 (EN-DC with EPC) – Starting point
This is a fast way to introduce 5G without needing a full 5G Core.
LTE stays as the main focus.
It’s great for early rollouts and pilot projects.
Option 7 (NGEN-DC with 5GC) – Bridge stage
Here, LTE (ng-eNB) is still the main player, but it’s now linked to the 5G Core.
This lets operators bring in 5GC features like network slicing and edge computing without ditching LTE completely.
Option 4 (NR-E-UTRA DC with 5GC) – 5G-first model
In this stage, 5G gNB takes the lead, while LTE takes a backseat.
It works best in areas where 5G is well-established and LTE isn’t as prominent.
Option 2 (NR-DC with 5GC) – End goal
This is all about pure 5G deployment, using dual gNBs.
It maximizes speed and cuts down latency.
Perfect for things like self-driving cars, smart cities, and Industry 4.0.
📊 In simpler terms:
Option 3 → Early adoption
Option 7 → Transition stage
Option 4 → 5G-led evolution
Option 2 → Fully mature 5G network
Conclusion
The MR-DC framework is foundational for migrating to 5G and coexisting with LTE. Whether it’s EN-DC with EPC, dual connectivity using 5GC, or pure NR-DC, each option serves as a stepping stone toward unlocking 5G’s full potential.
For telecom professionals, getting a solid grasp of these MR-DC options is vital for effectively planning, deploying, and optimizing networks that balance speed, coverage, and cost efficiency.