Fiber Bypass Power-Off Protection vs ERPS Ring Protection

Understanding the Differences, Use Cases, and Why Industrial Networks Need Both

In industrial Ethernet networks, high availability is not an optional feature but a fundamental design requirement.

Power instability, harsh environments, and long-term unattended operation make network resilience a top priority in sectors such as power utilities, rail transit, oil & gas, manufacturing, and intelligent transportation systems (ITS).

Two protection mechanisms are often mentioned together in industrial network designs: Fiber Bypass power-off protection and ERPS (Ethernet Ring Protection Switching, ITU-T G.8032).

Although both aim to improve network reliability, they operate at completely different layers, solve different problems, and are frequently misunderstood as interchangeable.

This article explains what Fiber Bypass and ERPS actually do, how they differ, and why a truly industrial-grade network design often requires both.

1. What Is Fiber Bypass Power-Off Protection?

Fiber Bypass Switch protection is a hardware-level mechanism designed to ensure optical link continuity when a network device loses power or becomes non-operational.

1.1 The Problem It Solves

In many industrial deployments, devices such as:

• Industrial Ethernet switches
• Firewalls or security gateways
• Intrusion detection systems (IDS)

are installed inline on fiber links. 

Under normal conditions, optical signals pass through the device’s optical transceivers.

However, if the device:

• Loses power
• Experiences hardware failure
• Crashes or hangs at the CPU level

the optical path is physically broken, causing a complete link outage.

Fiber Bypass addresses this exact scenario: a device failure should not break the physical fiber link.

1.2 How Fiber Bypass Works

Fiber Optic Bypass operates at Layer 0 / Layer 1 (physical layer), independent of any software or protocol.

When the device is powered on:

Optical signals pass through the device normally.

When power is lost:

A mechanical optical switch or relay (usually passive)

Automatically connects the incoming and outgoing fiber pairs directly.

This creates a physical optical loop-through, allowing light to pass even though the device is completely offline.

Key characteristics:

• No CPU involvement
• No configuration required
• No protocol dependency
• Immediate activation upon power loss (milliseconds)

Fiber Bypass is often described as a “last-line hardware safeguard.”

1.3 Key Characteristics of Fiber Bypass

Operates at physical layer (L0/L1)

Works even when the device is fully powered off

Protects against device-level failures

Does not perform path selection or topology management

Does not prevent Ethernet loops

2. What Is ERPS (Ethernet Ring Protection Switching)?

ERPS is a Layer 2 protocol defined by ITU-T G.8032, designed to protect Ethernet ring topologies against link failures while preventing broadcast storms.

2.1 The Problem It Solves

Ethernet rings provide natural redundancy, but they also create loops. Without protection, loops cause:

• Broadcast storms
• MAC table instability
• Network collapse
• ERPS allows Ethernet networks to use ring topologies safely by:
• Blocking one link under normal conditions
• Rapidly switching paths when a failure occurs

2.2 How ERPS Works

In an ERPS ring: one link is logically blocked to prevent loops, control messages monitor link health

When a link failure is detected: the blocked port is unblocked, traffic is redirected through the alternate path

Typical convergence time: less than 50 ms, depending on implementation and ring size

ERPS relies on:

• Active switching hardware
• Operational CPU and firmware
• Correct protocol configuration

2.3 Key Characteristics of ERPS

Operates at Layer 2

Requires powered-on, functioning devices

Protects against link failures, not device power loss

Provides fast path re-convergence

Prevents Ethernet loops and broadcast storms

3. Core Differences at a Glance

4. A Critical Misconception

A common misconception in industrial networking is: “ERPS can handle device power failures.”

This is incorrect.

If a fiber switch in an ERPS ring loses power: its optical ports go dark

The physical fiber ring is broken, ERPS cannot exchange control messages

In this case, ERPS alone cannot restore connectivity because the physical link no longer exists.

5. Why Fiber Bypass and ERPS Are Complementary?

A robust industrial network design treats Fiber Bypass and ERPS as complementary, not competing technologies.

Fiber Bypass ensures that the physical fiber ring remains intact during device power loss.

ERPS ensures that logical topology convergence and loop-free forwarding.

When used together:

A device loses power, fiber bypass module maintains optical continuity

ERPS detects topology change and traffic is rerouted correctly

This layered protection approach ensures both physical continuity and logical stability.

6. Typical Industrial Use Cases

Fiber Bypass is essential when:

Devices are deployed inline on critical fiber paths

Power instability is expected

Security appliances must not become single points of failure

ERPS is essential when:

Ethernet rings are used for redundancy

Fast recovery from fiber cuts is required

Layer-2 stability is critical

Best Practice: Industrial-grade networks use Fiber Bypass for hardware-level fail-safe protection and ERPS for protocol-level self-healing.

7. Engineering-Level Conclusion

Fiber Bypass power-off protection and ERPS ring protection serve fundamentally different roles:

Fiber Bypass protects the network from dead devices

ERPS protects the network from broken links

One ensures light keeps flowing when hardware fails; the other ensures traffic flows correctly when topology changes.

For mission-critical industrial Ethernet networks, choosing between them is not a design decision.

Using both is.

8. What Olycom Can Offer

As an OEM manufacturer, Olycom has been delivering good-quality optical fiber bypass and ERPS solutions.

We integrate an optic bypass unit in a manageable LAN switch to fully fulfill the protection tasks.

Please contact us if you have any projects available, we are here to help.