The Path Is Clear: Mission-Critical Networks Deserve Segment Routing

Mission-critical networks, such as power utilities, transportation grids and public safety systems, form the connective backbone of society. Their traffic isn't just data – it's public trust.

Yet many of these networks remain anchored in the legacy architectures they originally developed in. For decades, SONET delivered the deterministic timing and rapid failover that made it an exceptional choice for critical communications. Unfortunately, SONET is now well past its end-of-life, and vendor support for it is essentially extinct.

As SONET has aged, IP over Ethernet has come to dominate the transport landscape as a more cost-effective alternative, leading many mission-critical operators to migrate toward IP/MPLS infrastructures. But the protocols that historically made MPLS powerful—LDP and RSVP-TE—also added complexity. These protocols have worked great for predictability and resiliency, but they are difficult to manage and scale.

That's where Segment Routing (SR) comes in. It's not just an MPLS enhancement — it's the natural evolution of IP/MPLS architecture. By reducing complexity, improving scalability and enabling deterministic control, Segment Routing gives mission-critical operators a clear, incremental path to modernization.

Segment routing: Simplifying scale and resiliency

Segment Routing replaces distributed signaling with a stateless model. Instead of routers negotiating per-tunnel state, SR encodes a list of forwarding instructions—called segments—directly into the packet header. Each segment tells the network exactly how to forward traffic: "go to node X," "take link Y" or "follow this computed path."

This innovation collapses two stateful protocols (LDP and RSVP) into a single stateless IGP extension. The result is a simpler, more deterministic network fabric that scales naturally and converges faster.

This isn't theoretical. Segment Routing is already running in thousands of production networks across virtually every industry. The IETF standards are mature and every major vendor—including Cisco, Nokia and Juniper—supports them natively.

Figure 1: Typical evolution of mission-critical network architectures

A practical roadmap: Phased, measurable adoption

One of the best things about Segment Routing is that it is never an all-or-nothing venture. It doesn't require you to go from 0 to 100 in order to add value, because it's not an overnight migration. It's a journey that can co-exist with existing MPLS protocols such as LDP and RSVP. You don't have to rip and replace – Segment Routing lets you modernize at your own pace.

Our WWT Segment Routing Maturity Model describes this journey:

Level 0: Absent: Segment Routing is not present. The network relies on legacy IP/MPLS or RSVP-TE mechanisms for forwarding and route protection.
Level 1: Enabled: Segment Routing is activated within the IGP, unlocking TI-LFA for immediate Fast Reroute benefits with minimal effort.
Level 2: Engineered: Traffic Engineering policies are introduced using SR-TE, allowing for controlled, constraint-based forwarding.
Level 3: Diversified: Advanced services like disjoint path protection, BGP EPE and Flexible Algorithms are used to differentiate service classes and enhance resiliency.
Level 4: Orchestrated: A centralized controller or SR-PCE manages policies programmatically, enabling dynamic, intent-based routing and automation.

This approach minimizes risk, delivers measurable gains at each step, allowing operators to modernize without disrupting service—a crucial consideration for critical sectors where every millisecond and every budget cycle matters.

You don't have to rip and replace – Segment Routing lets you modernize at your own pace.

Real-world use case: Energy and the need for deterministic transport

Very few mission-critical applications are as high-stakes as the teleprotection relays used in energy utilities. These relays are responsible for detecting electrical faults and isolating them — often across hundreds of miles — within 10-20 milliseconds. Failure to do so means expensive damage to infrastructure and widespread power outages.

Historically, SONET's ring topologies have successfully provided that level of performance. More recently, many energy utilities have successfully achieved the same level of deterministic guarantees with RSVP-TE over an IP/MPLS network. RSVP-TE creates stateful "tunnels" throughout the network that the relay traffic can pass through. These tunnels are capable of detecting failure and switching traffic over to a new tunnel within 50 milliseconds.

The issue lies in the stateful and chatty characteristics of RSVP-TE tunnels. Many energy utilities have several hundred of these relays, with some even having thousands. At that scale, the network becomes heavily burdened with control plane traffic while operators struggle to keep up with the underlying complexity.

With Segment Routing, energy utilities can implement basic TI-LFA (which really just means enabling Segment Routing within their routing protocol) to gain Fast Reroute functionality for all OT traffic. They can continue to use explicit RSVP-TE tunnels to carry teleprotection traffic while they migrate towards Segment Routing policies that enforce the same type of explicit, low-latency routing. There is no requirement to immediately migrate all teleprotection traffic to Segment Routing — it can be done gradually and intentionally.

Meanwhile, less critical applications, such as SCADA and corporate IT, can begin to share the same SR-enabled backbone. This capability supports the broader push in the energy industry for IT/OT integration. With SR, operational control systems maintain deterministic transport, while enterprise IT gains visibility, telemetry, and automation across the same infrastructure. The outcome is a unified, secure fabric aligned with NERC-CIP, PUC modernization and digital transformation goals—not a compromise between them.

The same pattern extends to transportation, oil and gas, and industrial manufacturing, where deterministic control and rapid failover remain paramount in OT, but the need to modernize is becoming unavoidable.

The broader impact: Security, compliance and mission continuity

Modernization is more than just a technical upgrade. It's a matter of governance and trust. Mission-critical networks are subject to stringent compliance frameworks, including NERC-CIP, NIST, DOT and DHS. Segment Routing is designed to meet these standards.

Reduced attack surface: Removing RSVP and LDP daemons simplifies the control plane and limits protocol exposure.
Explicit path control: Defined SR Policies allow operators to isolate sensitive traffic and verify compliance with deterministic routing.
Integrated telemetry: SR supports built-in path visibility and performance reporting for audit readiness.
Simplified change management: Centralized, topology-aware path definition minimizes configuration drift and human error.

These capabilities of Segment Routing provide a solid framework for secure, auditable, and predictable network operations—key for industries where reliability is tied to regulation.

Conclusion

At the end of the day, Segment Routing brings significant operational value:

Simplified control plane reduces OPEX
Increased automation ability minimizes configuration effort
Pre-computed repair paths (TI-LFA) reduce the mean time to recovery
Centralized path computation eases capacity management

Through these advantages and others, Segment Routing provides mission-critical operators with both modern agility and old-school deterministic reliability. Each step of adoption, from enabling SR all the way to automating traffic engineering policies, yields discrete improvements in resiliency, efficiency and visibility.

The path forward for mission-critical networks is clear—and it leads through Segment Routing.