Latency and proximity: “close to the exchange” no longer means close to Paris
Many companies look for a data centre “close to the Paris Bourse”, thinking about latency. The instinct is right, the geography no longer is: since June 2022, the engine that matches Euronext orders sits neither in Paris nor near London. This guide says what a kilometre costs, and where the machines actually are.
Estimate my cost →A kilometre of fibre costs ten microseconds #
Light does not travel through glass at its vacuum speed: the refractive index brings it down to roughly 200,000 kilometres per second. One kilometre therefore costs about 5 microseconds one way, and 10 microseconds for the round trip that matters when you send an order and wait for its acknowledgement. A hundred kilometres cost one millisecond. No equipment and no software optimisation gets around this floor.
The Paris exchange no longer keeps its servers near London #
Until 6 June 2022, the Euronext matching engine ran in Basildon, Essex, some forty kilometres east of London, inside an ICE facility. On that date Euronext completed its migration to the Aruba IT3 data centre in Bergamo, Italy, a campus rated Rating 4 under ANSI/TIA-942-B. The reasons Euronext published were the regulatory uncertainty created by Brexit, which made an EU location preferable, and a move to green energy.
Paris, Amsterdam, Brussels, Lisbon, Milan, Dublin and Oslo share one engine #
Euronext's Optiq platform powers the Paris, Amsterdam, Brussels, Dublin, Lisbon, Milan and Oslo markets. “The Paris Bourse” is therefore not a place but a market, whose orders are matched by a single engine, today hosted in Bergamo. Choosing a Paris data centre to be close to that engine means moving about 655 kilometres away as the crow flies.
The engine answers in 15 microseconds, the distance costs 6,500 #
Euronext publishes an average processing latency as low as 15 microseconds for an order round trip. Over the same 655 straight-line kilometres between Paris and Bergamo, the travel of light alone costs about 6,500 microseconds round trip, and a real fibre route is always longer than a straight line. For anyone sitting in Paris, distance therefore weighs hundreds of times more than the engine itself. That ratio is worth holding in mind before comparing offers down to the microsecond.
Three ways to get closer, in order of proximity #
- Colocation inside the market's data centre. Euronext offers cabinets in Aruba IT3 at 4, 9 or 18 kW, with dedicated fibre to the exchange up to 10 Gbps and MiFID II-compliant time synchronisation over PTP with redundant GNSS sources. It is the only option that removes distance.
- Proximity hosting, in a neighbouring data centre linked to the market campus. Distance becomes a cost again, but a small one, and the colocation offer is often broader and less constrained.
- Remote access through a carrier, from any data centre, over a link into the campus Meet-Me Room (MMR). Latency is then the route's, not the straight line's: this is where the carrier and its path matter more than the building.
Distance is only one line of the latency budget #
- The optical path: incompressible, 10 microseconds per kilometre round trip, and always longer than the straight line because fibre follows roads and railways.
- The equipment crossed: every switch, router and regeneration unit adds its own processing time.
- The cross-connect and in-building cabling: a few dozen metres, negligible in distance, but they decide the path and the number of hops.
- The software stack and the protocol: queuing and application processing often weigh more than the building, and they are what you control.
Who actually needs the microsecond #
High-frequency trading and market making are decided in microseconds and justify colocation inside the market's data centre. Asset management and back offices live comfortably with a few milliseconds. For an online shop, a business API or an ERP, the latency a user perceives is measured in tens of milliseconds and depends far more on the access network and the code than on the building. Paying for proximity colocation in those cases buys precision nobody will ever notice.
What DataColoc computes, and what it does not measure #
The comparator can tell which data centres lie within a given radius of a point, and therefore what the physical latency floor is between two sites: that is a calculation, from a distance and a physical constant. DataColoc measures no latency. A figure shown on a listing comes from that listing, not from a measurement made here, and it says nothing about the path between you and it. Real latency depends on a route, a carrier and a moment; announcing it without measuring it would be inventing a figure. The floor, on the other hand, rules out: if physics already forbids your target threshold, no offer will meet it.
FAQ #
No. The Paris market is matched by Euronext's Optiq platform, whose data centre has been in Bergamo, Italy, since 6 June 2022. Before that it sat in Basildon, Essex, near London. A Paris data centre is therefore not “close to the exchange” in latency terms.
About one millisecond round trip, as a physical floor. Light travels at some 200,000 kilometres per second in fibre, meaning 5 microseconds per kilometre one way. Since a real route is longer than a straight line, the observed value is always higher.
Colocation inside the market's data centre removes distance and gives access to the market's time synchronisation services; it is constrained and expensive. Proximity hosting adds back a few microseconds but opens up the choice of operator, cabinet formats and pricing. The right trade-off depends on what one extra microsecond costs your business.
Unless you run high-frequency trading or market making, almost never. Check where your time goes first: if your application processing takes milliseconds, shaving microseconds off the path will change nothing you can measure.
Written on 6 September 2026.
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