Two conduits, one entry point. If both of your "diverse" services come in this way, one event at the wall takes out both. Illustrative photo, not the incident site.
One cut fibre cable grounded five major US airports for eight hours. The backup existed on paper. Two exchanges, two routes, two entry points: if your carrier can't name all three, you're buying two circuits, not diversity.
Two conduits, one entry point. If both of your "diverse" services come in this way, one event at the wall takes out both. Illustrative photo, not the incident site.
Redundancy is something you buy. Diversity is something you prove. Plenty of organisations pay for the first and assume the second, and only find out otherwise when one cable goes and the other turns out to be no help at all.
What happened
On Sunday 20 September 2026, the US Federal Aviation Administration moved its Philadelphia air traffic control facility onto its backup telecommunications line after error messages appeared on the primary circuit. Then a construction crew working on a rail project in New Jersey cut a Verizon fibre cable. It was carrying the backup.
With the primary already out of service, there was nothing left. Ground stops hit five airports: Newark, Philadelphia, JFK, LaGuardia and Teterboro. Thousands of flights were delayed or cancelled, and the repair took around eight hours. The crew reported they were digging roughly 10 feet from the utility markings.
Two paths existed. But once the primary was down, every flight in that airspace depended on a single cable running beside a rail line where construction work was under way.
"Two communications links means that if anything happens to one of them, you're operating on zero redundancy."
The legal view
Telecom law firm CommLawGroup reviewed the incident and landed somewhere most network teams never look: the agreement. Cable strikes are not rare events either. The Common Ground Alliance, a US damage prevention body, puts the cost of buried utility damage at about US$83 billion a year.
Make sure primary and backup facilities don't share vulnerabilities such as location, conduit systems or construction zones. Define responsibility for notice, facility marking, contractor oversight, insurance and damage liability before work begins.
Put simply, physical diversity shouldn't be something your network team assumes. It should be something a contract makes someone prove.
Where it gets lost
When we discussed the incident on LinkedIn, the most telling stories weren't about cables. They were about budgets.
A developer with nearly 40 years in the industry recalled IT requisitioning two T1 lines for redundancy. By the time the order reached purchasing, it had become a single T3, because it delivered the same bandwidth for less.
Same bandwidth. Same SLA on paper. Zero resilience left. The requirement survived engineering and died on a spreadsheet that didn't know what it was cutting.
An outside plant veteran in the same discussion described the other half of the problem. Challenge a design on whether it's truly redundant and the pushback is usually commercial, not technical. Once "fully redundant" has been written into a scope of work, admitting the paths aren't diverse means reopening a conversation nobody wants to have. So the diagram stays as it is.
Before you sign
Before you sign for a redundant or "diverse" link, get three things from the carrier in writing: the two exchanges serving your primary and backup, the route each path takes to your building, and where each one enters the building. If they can't provide all three, you're buying two circuits, not diversity.
A requirement that isn't written into the agreement is only a preference. Get the three answers into the order or contract so someone is accountable for them.
The honest limit
Some buildings have a single incoming lead-in, and no amount of paperwork changes that. Physical separation at the front door isn't always possible, particularly in existing and multi-tenant sites.
That doesn't make diversity pointless. Serving your primary and backup from two distinct exchanges still removes the largest shared risks out in the network. What matters is that the remaining shared section is known, documented and accepted as a risk, rather than discovered during an outage.
Then the question changes from "what should we buy?" to "what did we actually get?" That's a physical verification job, covered in Route diversity: when both paths share the same trench.
What the thread confirmed
The original post drew 5,142 impressions and a discussion that went further than the post did. Telecommunications made up 42% of the audience. These are the insights, not the quotes.
Above Layer 1
The documentation specialist in the thread made a point worth repeating: physical diversity reduces physical risk, but the logical design has to match it, at the network, system and authentication levels. Static routes and manual failover don't help if the paths still converge somewhere else.
Two diverse fibres landing on one device is still a single point of failure. Test failover the way it will actually happen, not the way the diagram suggests. We cover that in Your redundant network has never actually failed over.
Our position
On new carriage requests, we specify diverse carriage from two distinct exchanges. Before the circuit goes live, you receive a written route statement naming both exchanges and both paths, checked at handover.
Two distinct exchanges, specified in writing. Both routes and both building entry points named. A route statement checked at handover, before the circuit goes live. One accountable partner, nationwide, on live business-critical networks, as a Telstra Partner since 1992.
Diversity you can't produce on paper is diversity you're hoping for. The time to find out is before you sign, not when the excavator does.
Common questions
Sources
CommLawGroup: When a fiber cut grounds airports
Cabling Installation & Maintenance: Fiber cut causes air traffic control outage
US News / Reuters: FAA says error messages prompted shift to backup
ABC News: US flights disrupted as cable is cut
Send us the site address and the services you're ordering. We specify two distinct exchanges and hand you a written route statement naming both paths before the circuit goes live.
Talk to AAA About Diverse Carriage