SD-WAN Network Transformation: Migrating 192 Sites from MPLS to SD-WAN

This programme involved the complete migration of a rail operator's wide-area network from legacy MPLS to a modern SD-WAN architecture across 192 sites. The transformation required careful supplier coordination, a phased rollout strategy, and full operational transition to ensure internal teams could support the new infrastructure from day one. Here's how the programme was structured and delivered.

1. Assessing the Legacy MPLS Environment

The existing MPLS network had served the organisation well but was increasingly costly to maintain and lacked the flexibility needed for modern operational demands. With 192 geographically dispersed sites — including stations, depots, and administrative offices — the network complexity was significant. I led a comprehensive assessment of the existing infrastructure, documenting circuit types, bandwidth requirements, and dependencies at every location to build a clear picture of the migration challenge.

2. Designing the SD-WAN Target Architecture

Working closely with network architects and the selected SD-WAN supplier, I helped define the target architecture that would deliver improved resilience, centralised management, and cost efficiency. Key design decisions included:

1. Dual-circuit resilience: Critical sites were provisioned with dual WAN links to ensure failover capability and continuous operations.
2. Centralised orchestration: The SD-WAN platform enabled centralised policy management, reducing the need for site-by-site configuration and accelerating future changes.
3. Security integration: Embedded security features replaced standalone firewall appliances at many sites, simplifying the architecture and reducing hardware costs.

3. Supplier Coordination and Procurement

A programme of this scale required coordination across multiple suppliers — the SD-WAN platform vendor, circuit providers, hardware logistics partners, and installation teams. I established a structured supplier governance model with regular checkpoints, escalation paths, and shared tracking of site readiness. This ensured that circuit installations, hardware deliveries, and engineering visits were aligned and that dependencies between suppliers were actively managed.

4. Phased Rollout Strategy

Migrating 192 sites required a carefully staged approach to manage risk and minimise operational disruption. I designed a phased rollout plan that grouped sites by type, criticality, and geographic region. Early phases focused on lower-risk administrative sites, allowing the team to refine installation processes and identify common issues before tackling high-criticality operational locations. Each phase included defined entry and exit criteria, rollback procedures, and stakeholder communications.

5. Managing Operational Risk During Migration

Network migrations in a transportation environment carry inherent operational risk — any loss of connectivity at a critical site could impact passenger services, safety systems, or revenue operations. I implemented rigorous change management processes, including out-of-hours migration windows for high-risk sites, real-time monitoring during cutover, and on-site engineering support for the most critical transitions. A dedicated war room was established during major migration waves to provide rapid response to any issues.

6. Knowledge Transfer and Operational Transition

A key programme objective was ensuring that internal teams could fully support the new SD-WAN environment without ongoing reliance on external resources. I established a structured knowledge transfer programme that included hands-on training, documentation of operational procedures, and a period of shadowed support where internal engineers worked alongside the implementation team. By the end of the programme, the internal network operations team was fully capable of managing the SD-WAN platform independently.

7. Delivering Measurable Outcomes

The programme delivered significant improvements across multiple dimensions. Annual network operating costs were reduced through the elimination of expensive MPLS circuits and consolidation of hardware. Network performance improved with better bandwidth utilisation and application-aware routing. Centralised management reduced the time required for network changes from days to hours, and the improved resilience architecture reduced the frequency and impact of network outages across the estate.

Conclusion

This SD-WAN transformation programme demonstrated the value of thorough planning, disciplined supplier management, and a phased delivery approach when undertaking large-scale network migrations. By maintaining focus on operational risk management and investing in knowledge transfer, the programme not only delivered a modern, cost-effective network infrastructure but also ensured the organisation was fully equipped to manage and evolve it for the future.