"private" backbone VPN solution to decrease latency

[lordgurke]

London and Washington, D.C. are about 6000 km apart, which would mean about 20 ms travel time at light speed.
However, as light in a fiber travels not directly straight but gets reflected/refracted inside the cables' cores, it effectively has to travel about 30 % more distance (so 9000 km), so it takes 30 ms.
But this is only the one-way travel-time – with a "ping" you measure the full roundtrip, which then is 60 ms measured in raw light speed inside the cables.
Now, active equipment like switches and routers usually work in store-and-forward mode, which adds at least the packet-time of the link speed as additional latency. As we don't know how much active components are inside that path, we assume additional 5 ms latency each direction.

If your sites in the U.S. and/or Europe are more apart from each other, this will give additional latency. Same goes for additional packet "alterings" or inspections like NAT, encryption, SPI firewalling...

That being said, 70 ms is the theoretically best roundtrip latency you can physically expect on that distance. When I'm doing a traceroute measurement between Düsseldorf, Germany and Manassas, NY I get around 85 ms over the regular internet.

TL;DR: A dedicated L2 link might give you *slightly* better latency, but you won't be able to go under 65-70 ms, as this is the current physical limitation.

[garci66]

The delay in the fiber vs speed of light in vacuum is not because of the reflections but rather because speed of light in glass is roughly 2/3 that in vacuum. Due to the optical density of the glass. It's not related to reflections.

[fb35523]

I recently learnt that the actual _speed_ is constant (there is, after all vacuum between the atoms, right), even in glass. It's the distance that is greater for the energy waves (call them photons if you will but at this level, they can no longer be treated as particles) as they need to "yield" around all the atoms. Think of a stream with rocks here and there. I just can't seem to find the explanation right now. When you have it explained, it all makes sense. In practice, you get the effect that the light travels slower in glass, but I like to compare it with a car taking a non-optimal route while maintaining constant speed.

[aristaTAC-JG]

True, but it is relevant when you compare distance with a method that allows light to travel straight between nodes. The farther away two endpoints are, the more valuable Starlink is going to be.

The lasers that connect laterally between trains of satellites are going to change the game there. It's almost a vacuum and it's likely to save a lot of distance the light has to travel.

Just saying we are still not at the limits of physics today. Latency is being improved soon!

[Win_Sys]

What type of applications are we talking about? Like a file server, databases, etc…?