Virtualisation and Soft RNCs: Can Legacy Networks Modernise?

The transition from physical infrastructure to software-defined networks is well underway in most telecoms. But when it comes to legacy systems like the Radio Network Controller (RNC)—a core component of 3G UMTS architecture—many operators are still running ageing hardware in far-flung data centres or field locations.

Virtualisation of the RNC—often referred to as the soft RNC (sRNC) or virtual RNC (vRNC)—offers a middle path: modernising the control layer without tearing down the entire legacy radio access network. This blog explores what soft RNCs are, how they work, and what benefits (and limitations) they offer operators trying to extract long-term value from 3G networks.

What Is a Virtual RNC (vRNC)?

A virtual RNC replicates the software functions of a traditional hardware-based RNC in a virtualised environment—typically running on standard x86 server infrastructure in a private or public cloud.

It retains full support for:

• 3G UTRAN control functions

• Node B management

• Handover, power, and admission control

• Interfaces: Iub, Iur, Iu-CS, and Iu-PS

What changes is the deployment model: instead of residing on bespoke vendor equipment, the vRNC runs as a set of virtual network functions (VNFs) within a Network Function Virtualisation (NFV) framework.

Why Operators Are Moving Toward vRNCs

The decision to virtualise the RNC is often driven by five primary forces:

1. Hardware Obsolescence

Many original RNC platforms from Ericsson, Nokia, Huawei or ZTE are reaching end-of-life. Replacing them with more of the same is not financially or operationally viable.

2. Data Centre Consolidation

Operators are consolidating legacy infrastructure into centralised, cloud-native environments, enabling unified control, orchestration, and lifecycle management.

3. Cost Reduction

Removing proprietary hardware eliminates:

• Maintenance contracts

• Spare parts inventory

• Field engineering site visits

• Power and cooling overhead

4. Agility and Flexibility

vRNCs can be:

• Scaled elastically based on user load

• Relocated across regions as needed

• Patched or upgraded centrally with minimal disruption

5. Vendor Interoperability

By virtualising the RNC layer, operators can manage multi-vendor Node B estates with improved flexibility—particularly when working across Huawei, Ericsson, and Nokia radio networks.

How a vRNC Is Architected

A vRNC typically runs as a VNF within a larger NFV Infrastructure (NFVI). The architecture includes:

• VNF Manager – Controls lifecycle events (instantiation, scaling, healing)

• Virtual Infrastructure Manager (VIM) – Manages compute, storage, and networking resources (e.g. OpenStack)

• Element Management System (EMS) – Provides GUI and scripting for config and fault management

• Service Orchestrator – Coordinates multiple VNFs across the network (often part of MANO stack)

The interfaces (Iub, Iu, Iur) are maintained over IP/MPLS transport, often supported by IPsec tunnels, VLAN tagging, and QoS policies to maintain service integrity.

Key Benefits of a Virtualised RNC

Operational Agility

Operators can spin up or down vRNC instances based on demand (e.g. seasonal traffic, events, regional growth).

Improved Uptime and Disaster Recovery

Redundancy and failover become software-defined. Failures in one data centre can trigger automated restart in another.

Centralised Management

Configuration, patching, and monitoring are managed centrally, reducing human error and improving consistency.

Hybrid Coexistence

vRNCs can coexist with physical RNCs or with virtualised EPC components, enabling phased migration strategies.

Reduced Physical Footprint

Fewer racks, less cooling, and reduced energy bills—all important for sustainability and site consolidation.

Challenges and Limitations

Virtualisation brings complexity. A poorly planned vRNC project can backfire.

1. Performance Tuning

Running real-time RNC functions on virtual machines requires careful tuning of latency, jitter, and scheduling.

2. Integration Overhead

vRNCs must integrate with:

• Legacy Node Bs over IP

• Hybrid OSS/BSS platforms

• Multi-vendor backhaul transport

• Regulatory compliance systems (e.g. lawful interception)

3. Vendor Licensing Models

Some traditional vendors offer vRNC as licensed software only—removing hardware but not reducing TCO significantly.

4. Engineering Skills Gap

Operators need cloud-native network engineers who understand both 3G protocols and virtualised environments.

Case Example: A Phased Transition Strategy

Operators pursuing virtualisation often follow a phased strategy:

1. Assess RNC Inventory – Hardware age, traffic loads, Node B density

2. Identify vRNC Targets – Start with regions with limited 3G growth or stable usage

3. Create a vRNC Pilot – Deploy in a lab or controlled metro area

4. Integrate with OSS/NMS – Align alarms, KPIs, and dashboards

5. Migrate Node Bs in Batches – Test handover, fallback, and KPI integrity

6. Expand Gradually – Based on results and operational readiness

This minimises risk, especially in markets where 3G shutdown is still years away.

Is Virtualisation a Bridge to 4G/5G?

In many cases, yes. A virtualised control layer:

• Eases integration with multi-RAT (Radio Access Technology) nodes

• Prepares the ground for Cloud-RAN architectures

• Enables more unified network slicing across legacy and next-gen domains

For operators looking to move toward single-RAN architectures, the vRNC can be an intermediate but valuable step.

Strategic Considerations for Boards

Virtualising legacy assets might not sound glamorous, but it has real financial and operational implications. Boards should evaluate:

• Cost vs. lifecycle of legacy RNCs

• Impact on sustainability targets

• Staffing model changes (cloud vs. field)

• Vendor lock-in mitigation

• Regulatory obligations for service continuity

vRNC deployment may be part of de-risking the 3G sunset, while extracting the last phase of value from past investments.

Conclusion: Modernising Without Disruption

The virtual RNC may never win headlines, but it offers practical, cost-effective, and operationally sound modernisation for operators managing the long tail of 3G.

In a sector often driven by innovation hype, soft RNCs represent a grounded, risk-managed approach to keeping legacy infrastructure aligned with next-generation operational models.