Hidden overlap kills redundancy. Two “separate” circuits that share a curb cut, a bridge, or a manhole can fall at the same time and drain a budget in a single outage. This guide shows where fake diversity hides, how to get photo proof, and how to run the quick math that turns a vague risk into a clear decision to fix the route.
Different provider names and two circuit IDs can still share a curb entrance, a first handhole, a bridge, or a railroad crossing. Ask for visual proof and distance in kilometers, not just a marketing map.
| Pattern | Example | How to detect |
|---|---|---|
| Shared lateral | Both links enter at the same curb or vault | Request first handhole photos and GPS tags for each path |
| Common choke crossing | Both routes use the same bridge or rail trench | Ask for route in kilometers plus photos of each crossing |
| Single building room | Both hand off in the same MMR or closet | Require separate rooms where possible or separated risers |
| Shared conduit segment | Different carriers share a 200 m duct | Look for plan and profile sheets that show duct occupancy |
| Last mile subcontract | Both carriers rent the same local fiber | Ask if any segment is third party and demand route proof |
| Same on ramp detour | Traffic hairpins to a distant cloud on ramp | Measure site to on ramp latency and compare providers |
- Route in kilometers with primary and backup overlaid
- List of crossings with photos and coordinates
- Handhole and vault IDs for each path
- OTDR and light-level thresholds by span
- As-built files with labeled closures and trays
- Turn up method with rollback plan
- “Paths are diverse to industry standards”
- “Best effort to avoid shared facilities”
- “Credits may be applied for outages”
- “Paths enter different curbs and first handholes, photos attached”
- “No common bridge or rail crossing, crossing list attached”
- “Credits apply automatically when both circuits fail together”
| Signal | Typical threshold | What it means |
|---|---|---|
| Both links flap together | Several times per quarter | Shared segment or maintenance window |
| Same latency step on both paths | Jump at the same time | Hairpin to the same on ramp |
| Repair truck fixes both issues | One field visit, two tickets | Shared vault or conduit segment |
| Storm or parade outage | Both down on the same block | Common curb or first handhole |
| Single room handoff | One MMR for both links | Local single point of failure |
- Collect photos for entrances and crossings
- Confirm room separation for handoffs
- List third party segments
- Use the score and cost calculators above
- Compare current risk to fix cost
- Pick the least cost path that clears your threshold
- Add route proof to the contract
- Set credits that trigger automatically
- Define acceptance with maps, tests, and photos
Treat diversity as a measured control, not a slogan. Ask for route distance, entrance photos, and crossing lists in every proposal, then score overlap and compare the fix cost to expected outage impact. If one or two adjustments move the score into the healthy zone and the annual benefit is clear, make the change and keep the evidence in your acceptance file.
