What is fiber optic bypass and why use it in industrial networks?

Fiber optic bypass (also called failsafe or fail-to-wire) allows fiber traffic to pass through a device even if it loses power.

The Problem

In fiber ring networks, if one switch loses power, the ring is broken and all downstream traffic stops — even if only the local switch failed.

How Bypass Works

• Passive optical relay or MEMS-based switch
• Normally routes fiber through active switch electronics
• On power loss, relay directly connects incoming to outgoing fiber
• Downstream devices continue communicating through the powered-off unit

Deployment Scenarios

• Long fiber rings where switches are unreachable for quick repair
• Remote sites (wind farms, oil rigs, mountains)
• Deployments where single-point failures cascade badly

Limitations

• Local device (attached to bypassed switch) loses access
• Optical loss increases with each bypass (typically 1-3dB)
• Adds cost and complexity
• Not all switch models support this feature

Alternatives

• Redundant power: Second PSU prevents most power-related failures
• Ring protection: ERPS reroutes around failed nodes
• Dual-homed devices: Multiple uplinks to different switches

When Bypass Makes Sense

• Very long-distance links (satellite links, undersea)
• Extremely limited maintenance access
• When even brief ring re-convergence is unacceptable

Most modern industrial deployments rely on fast ring protocols (sub-20ms) rather than fiber bypass, since they preserve local connectivity while maintaining ring integrity.