True diversity must be evidenced from the building entry to the relevant network or destination. Check ducts, chambers, road and bridge crossings, splice points, exchanges, POPs, wholesale carriers, power and internal routes. Two contracts, two colours on a diagram or two supplier names do not prove that a single incident cannot affect both services.
What true route diversity means
Diversity means that the services do not share a material single point of failure within the scope being assessed. The required scope may be local access only, the metro network, the full route between sites or the end-to-end service including equipment and power.
Define the required diversity boundary before asking carriers to prove it. “Diverse to the exchange” is different from “diverse to the remote data centre.”
Where hidden shared risks occur
- Both services entering through the same duct or chamber
- Separate street routes merging at a bridge, railway or river crossing
- Different retail carriers using the same wholesale access provider
- Shared Openreach PIA duct or pole infrastructure
- Common splice closures, aggregation nodes or exchanges
- Separate fibre routes terminating on the same chassis or power feed
- Two building entries joining in one internal tray or riser
- “Resilient” logical paths carried over one physical cable
- Maintenance or change processes capable of affecting both services
Evidence to request from carriers
Ask for enough information to support a reasoned conclusion without requiring the carrier to disclose sensitive network detail publicly.
- Route drawings with the diversity scope and confidence level stated
- Building entry points, chambers and internal demarcations
- Known shared sections and critical crossings
- Underlying wholesale networks and access products
- Serving POPs, exchanges or aggregation nodes
- Confirmation of whether routes are surveyed, planned or indicative
- Any dependencies on new civils, wayleaves or third-party infrastructure
- A statement of exceptions to the requested diversity standard
Do not stop at the site boundary
External diversity can be defeated by the building design. Check:
- Two physically separated entry points where justified
- Separate ducts, containment and fire compartments
- Different meet-me rooms or protected internal paths
- Independent carrier equipment and power
- Clear labelling and change control
- Safe access for repair without disturbing the other path
Testing and acceptance
Before acceptance, confirm that each path is correctly identified and that the service behaves as designed when one component is removed.
- Validate documentationRoute, demarcation, port, equipment and service identifiers.
- Test each service independentlyCapacity, latency, packet loss and operational monitoring.
- Test failoverRemove or isolate one path in a controlled way and confirm traffic recovers.
- Record restorationConfirm the service returns without instability or asymmetric routing problems.
- Update the operational packEscalation, fault references, route evidence and maintenance contacts.
A practical decision standard
Classify the result rather than forcing a binary “diverse/not diverse” conclusion:
| Status | Meaning |
|---|---|
| Verified | Sufficient current evidence supports the required diversity boundary |
| Partially verified | Most of the route is evidenced, with stated residual shared risks |
| Indicative | The design appears diverse but relies on unverified records or future construction |
| Not diverse | A material shared point of failure is known |
Frequently asked questions
Common questions
Do two different carriers guarantee diversity?
No. Different carriers can use the same wholesale access network, duct, chamber, crossing, exchange or building entry.
Can route diversity be guaranteed permanently?
No route is immune from future change or emergency repair. The objective is to obtain proportionate evidence, record limitations and manage change.
Does BGP provide physical diversity?
BGP can provide logical routing resilience, but it does not prove that the underlying circuits use independent physical paths.
Can CROSS review a carrier diversity proposal?
Yes. CROSS can review route evidence, identify shared risks, challenge supplier claims and define practical acceptance criteria.
Apply this to a live site
You do not need to know the product before speaking to us.
Send us the site, project or carrier quotation and we will identify the most useful next step.