NR Architecture: Understanding Variants of Option 7 (Opt. 7, 7a, 7x) in 5G
NR Architecture of Option 7 Variants in 5G
The shift from 4G LTE to 5G New Radio (NR) brings a bunch of deployment choices aimed at ensuring flexibility and interoperability. Among these, Option 7 and its variants (7, 7a, and 7x) are key for maintaining smooth coexistence between LTE and NR while making good use of the 5G Core (5GC).
The image we've included gives a clear look at how Option 7 variants manage control plane (NG-C, Xn-C) and user plane (NG-U, Xn-U) signaling. Let’s dive into these architectures.
Background: The Importance of Option 7 Variants
When 5G came on the scene, operators were faced with a big question: how can they transition from LTE to 5G without disrupting services? To tackle this, deployment options put together by 3GPP were designed to provide a flexible transition.
Option 7 represents a non-standalone (NSA) architecture where LTE (ng-eNB) serves as the master node (MN) and 5G NR (gNB) acts as the secondary node (SN).
The 5G Core (5GC) is still part of the picture, but the anchor remains with LTE, which ensures everything stays compatible.
The variants 7a and 7x differ in their approach to managing user plane connections among UE (user equipment), ng-eNB, gNB, and the 5G Core.
This setup enables operators to gradually roll out 5G coverage while still utilizing their existing LTE infrastructure.
Option 7: Basic Architecture
In Option 7, the ng-eNB (master node) acts as the anchor for both the control plane (NG-C) and the user plane (NG-U) connecting to the 5G Core.
Features of Option 7:
Master Node (MN): ng-eNB
Secondary Node (SN): gNB
Control Plane (NG-C): Handled by ng-eNB
User Plane (NG-U): Anchored at ng-eNB but supported by gNB
Data Flow in Option 7:
UE connects to ng-eNB as the main anchor.
ng-eNB links directly to the 5GC for both control and user planes.
gNB helps offload user traffic using the Xn-U interface.
Benefits:
Provides a straightforward migration route for operators heavily invested in LTE.
Keeps LTE as the anchor, which helps minimize disruptions.
Drawback:
Since ng-eNB handles both planes, it might get bogged down, especially with increasing data demand.
Option 7a: User Plane via gNB
In Option 7a, while the control plane stays with the ng-eNB, the user plane traffic can take a shortcut by going directly from the gNB to the 5G Core.
Features of Option 7a:
Control Plane (NG-C): Based at ng-eNB
User Plane (NG-U): Has two paths – either through ng-eNB or directly via gNB
Data Routing: gNB has a direct link to 5GC for handling user traffic
Data Flow in Option 7a:
Control signaling always goes through ng-eNB.
User data can go straight from gNB to 5GC, which reduces latency.
Benefits:
Offloads user traffic from ng-eNB.
Lowers latency and boosts throughput for data sessions.
Makes better use of NR spectrum.
Drawback:
Adds complexity since user plane anchoring can switch between ng-eNB and gNB.
Option 7x: More Flexibility
Option 7x is an enhanced version of Option 7a. This one offers the greatest flexibility for routing user plane traffic by allowing both ng-eNB and gNB to connect independently to the 5G Core user plane (NG-U).
Features of Option 7x:
Control Plane (NG-C): Centered at ng-eNB
User Plane (NG-U): Fully flexible – both ng-eNB and gNB can send data directly to 5GC
Routing Options: Traffic can go either from UE → gNB → 5GC, or UE → ng-eNB → 5GC
Data Flow in Option 7x:
User traffic is routed dynamically based on conditions like load, latency, or application needs.
gNB plays a more significant role compared to Options 7 and 7a.
Benefits:
Balances traffic effectively between ng-eNB and gNB for maximum efficiency.
Tailored for various use cases, such as enhanced mobile broadband (eMBB) and ultra-reliable low-latency communication (URLLC).
Drawback:
The most complex of the three options.
Requires advanced orchestration and coordination.
Key Differences Among Option 7, 7a, and 7x
Here’s a quick comparison:
Feature Option 7Option 7aOption 7xMaster Node ng-e NB ng-e NB ng-e NB Secondary Node gNB gNB gNB Control Plane ng-e NB → 5GCng-eNB → 5GCng-eNB → 5GCUser Plane ng-e NB → 5GC (with help from Xn-U)gNB → 5GC (directly bypassing ng-eNB)Flexible: gNB → 5GC or ng-eNB → 5GCLatencyHigherLower than Option 7Lowest (optimized dynamic routing)Complexity Low Medium High
Practical Considerations for Operators
Operators need to weigh these options based on their deployment objectives, LTE presence, and readiness for 5G.
Option 7: Best for those heavily reliant on LTE, making gradual NR rollouts easier.
Option 7a: Great for enhancing latency and performance while keeping LTE as the anchor.
Option 7x: Good for operators prepared for advanced 5G services and needing dynamic traffic routing.
Conclusion
The NR architecture of Option 7 and its variants (7, 7a, 7x) showcases the evolution of strategies for transitioning to 5G.
Option 7 retains LTE (ng-eNB) as the anchor, providing stability.
Option 7a boosts efficiency by letting gNB manage user plane traffic.
Option 7x delivers the most sophisticated model, allowing flexible routing for user data.
Understanding these options is key for telecom experts in crafting smooth LTE-to-5G transition strategies that balance performance, costs, and complexity.
As the adoption of 5G ramps up, these architectures will be critical in shaping how networks evolve to support low latency, high throughput, and massive IoT deployments.