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Comment by iso947 | Hacker News Reader

Latency to where? One of the promises of starlink is reducing latency over mid distance - say transatlantic or even across the states, due to using vacuum rather than fibres. Will be interesting how HFT use it.

Starlink network is nowhere near complete so I’d expect things to only get better (until customers start piling on)

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If I understood it correctly Starlink doesn't send between satellites yet, only sat<->ground. Sat<->sat is a big point of starlink and when they roll that out the latency should go down, especially for starlink<->starlink comms I imagine.

Yes that’s a few more years before then, and the more sats the more capacity and the lower the latency.

What is the lifetime of a SpaceX satellite?

Judging from their high launch cadence, it seems satellite-satellite communication was just a means to excite the fanboys and motivate their employees, the same way the peddle the Mars stuff.

I don't understand how this is meant to lower the latency. Currently:

    ground <--> satellite <--> ground

With satellite links:

    ground <--> satellite <--> satellite <--> ground

How can the latter possibly be faster?

Edit: Thanks for all the responses. I'd been assuming it was a test of Starlink latency only, but if it's Starlink -> ground station -> open internet -> ISP then it would make sense how that would be slower than a pure Starlink connection.

Current satellites are in a much higher orbit

This is a good question, I see three main reasons but I may miss something:

1. Hop count is not one on the ground to go same distance.

2. Speed of light is significantly faster in vacuum.

3. The path is potentially straighter for longer distances.

Currently:

ground <--> satellite <--> ground <------------> ground

With satellite links:

ground <--> satellite <--> satellite <--> ground

i.e. the sat-to-sat link should be faster than the ground-to-ground link, on the basis that light transmitted in vacuum goes faster than light transmitted in glass. That's the theory at least.

Plus they're transmitting in a straight line without a lot of switches in between.

More like this:

Currently:

  ground <--> satellite <--> ground <--> ground farther away via legacy infrastructure

With satellite links:

  ground <--> satellite <--> satellite <--> ground farther away directly

Light travels through glass (fiber optics) at 2/3 of the speed in vacuum. So as long as you are skipping some ground links by doing similar length links in space it is faster.

Low altitude orbits mean that the hops up and down can be compensated by faster hops across.

That all of course is not there yet and depends on Starlink implementing the cross sattelite links.

There are some places where there is no ground, say the middle of the Atlantic. Satellite to satellite is important for that.

Why would HFT even consider using it? They are located as close as possible to the exchange they operate on, not across states or halfway across the world.

arbitrage

Geographically distributed arbitrage?

Arbitrage between multiple exchanges requires data to go from exchange A to exchange B as fast as possible.

Light in vacuum is faster than light in fiber.

Light in vacuum is only faster if it goes in a straight line from point A to B, not if it zig-zags across 50 satellites.

How could zigzagging through fiber be faster thaz zigzagging through vacuum? You still need to cross nearly the same distance with fiber.

The fiber is a fixed geometry.

The satellite mesh is not, a straight line from point A to point B is not possible most of the time, given the number of satellites available and range of laser communication in space.

https://www.youtube.com/watch?v=QEIUdMiColU is an animation of how it's supposed to work, including latencies

There are enough satelites and low enough routing on the lasers to mean packets will arrive from London to NY faster than even a great-circle fibre.

In reality how much bandwidth is available is a function of money, and HFTs tend to have a lot of money.

But if you can access to information from an exchange halfway across the world faster than others, you can definitely trade on that.

And if you can break the speed of light, you don't need a second exchange.

It’s quite easy to “break” the speed of light in fiberoptic glass.

But it's not that useful even if you pour a glass cube over the whole exchange to slow it down.

> It’s quite easy to “break” the speed of light in fiberoptic glass.

I don’t understand this, why? Does light travel faster than the speed of light in fibre optic glass?

"the speed of light in fiberoptic glass" is the thing being broken.

Same stock is listed in more than one place, and also e.g. stock movements in NY affect stocks in London. There are undersea cables built for this purpose: https://www.popularmechanics.com/technology/infrastructure/a...

What a waste of human ingenuity. And I thought ad-tech was bad enough

That is true for much of the finance field.

Actually it's not. There are objective benefits to society that you simply ignore.

As there are objective downsides that we, collectively, are ignoring right now.

Financial capitalism shouldn't be praised, at the very best it's a lesson, we got useful tools out of it and that is all.

I am not praising anything, I am correcting your statement that much of the financial industry is a waste of human ingenuity. That "waste of human ingenuity" enabled us to build the modern world.

It wasn't my statement.

I think you can argue on the whole is a waste, but I do believe it does have some advantages. EG efficient HFTs can reduce bid ask spreads which does save a lot of money for retail traders.

I think the premise was that such investments are wasteful if it's only for a trading arms race.

But being able to do that 50 milliseconds faster really doesn't.

> EG efficient HFTs can reduce bid ask spreads which does save a lot of money for retail traders.

Berkshire Hathway has $1000+ spreads yet you dont see a lot of people complaining.

Stock price is probably a pretty big factor in that along with volume.

Exactly, that is the point.

Don't forget using the equivalent of the entire power consumption of Austria to mine bitcoin?

They make trades at one exchange based of prices at another. For that reason there has been a lot of microwave relays set up between New York and Chicago, for example. Starlink could reduce latency from New York to London, another important center of trade.

Light travels 47% slower in a fiber optic cable than it does in the vacuum of space. [1]

[1] https://youtu.be/giQ8xEWjnBs?t=288 (the whole video is worth watching, but that timestamp answers your specific question.

Too lazy to watch it -- does it take into account the multiple criss-crossing satellite hops?

I watched it -- no it doesn't :) It is comparing fiberoptics latency with straight line light propagation. So the worst case scenario of non-existing inter-satellite communication could easily be worse than fiberoptics.

But I guess if the hedgefunds knew exactly which packet travels in a straight line, they could send one packet via Starlink and others via fiberoptics.

yes

Too lazy to answer

HFT have installed microwave relays between Chicago and New York and between London and Berlin to arbitrage on the 47% fiber optic delay between the exchanges. A LEO satellite relay serves the same purpose. I can see London to New York, New York to Tokyo fiber connections being superceded by LEO satellite.

Quite surprised why LEO for cross exchange arbitrage was not already done. Microwaves were not super with weather conditions the last time taking an arbitrary interest.

LEO sat constellations that are low enough to beat existing solutions need to be almost global to provide reliable communication anywhere.

If you mean Deutsche Börse AG, than that would be Frankfurt am Main and not Berlin which is a slight difference of about 400 km. Frankfurt to London is actually a shorter distance. https://en.wikipedia.org/wiki/List_of_stock_exchanges

They need sat-sat links for that, I think the current generation of starlink doesn't have that so initial customers will not see that kind of benefit, their data will be bounced back to a ground station from the same satellite.

I'd assume latency from endpoint to satellite back to terrestrial base station.

I can get satellite Internet right now with 40Mbps down / 5 up, but the latency is 800 to 1000 ms, so it's slow.

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