When a whole country’s internet slows at once, the cause is usually one of a small number of things. Telling them apart matters, because the fix and the timescale differ enormously.
Submarine cables carry almost everything
International internet traffic travels through undersea fibre-optic cables. Satellite capacity, however visible, carries a tiny fraction by comparison. A country is typically served by a handful of these cables, and a single cut can remove a large share of its international capacity in an instant.
Cuts happen most often in shallow water, from ship anchors and fishing gear, and occasionally from seabed landslides and earthquakes. Repair means locating the fault, sending a specialised cable ship, lifting the cable and splicing it, which typically takes weeks rather than hours, and longer if a repair ship is already committed elsewhere.
The signature of each cause
- Cable fault. International sites slow or fail while local sites stay fast. Onset is abrupt and recovery is gradual as traffic reroutes.
- Congestion. Everything slows at predictable times of day and recovers overnight.
- Routing or peering problem. Some destinations are unreachable while others are perfectly fine, often with no pattern a user can see.
- Deliberate throttling or shutdown. Specific services degrade while others are unaffected, frequently around scheduled events, and often without announcement.
- Power or equipment failure. Sharply geographic, affecting one city or region while the rest of the country is normal.
How to work out which one you are seeing
Test a local site and an international one separately: if local is fast and international is not, the problem is almost certainly upstream capacity rather than your connection. Test a second network, such as mobile data against fixed line, since a fault affecting one operator narrows the cause considerably. Check whether the problem is service-specific: if one platform fails while everything else works, that is not a cable.
Independent network observatories publish country-level reachability data, which is more reliable than social media reports and distinguishes a genuine national event from a local one.
Why recovery is uneven
When capacity is lost, operators reroute traffic through remaining paths, which are then oversubscribed. The result is a period where the internet works but badly, and where performance varies by destination and time of day. Full restoration usually waits for the physical repair.
Common questions
Why does mobile data sometimes still work? Mobile and fixed networks may use different international routes, so a fault can affect one and not the other.
Does a VPN help during a slowdown? Occasionally, if it routes around a congested path, but it adds overhead and often makes things worse during a capacity shortage.
How long do cable repairs take? Commonly one to several weeks, driven by ship availability, weather and permits rather than the splice itself.
Can a country protect itself against this? Partly, by connecting to more cables on diverse routes and by hosting content locally so less traffic needs to leave the country at all.
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