
Network Latencies and Speed of Light - zerokernel
https://fgiesen.wordpress.com/2018/01/20/network-latencies-and-speed-of-light/
======
ericjang
Money is no object to HFT firms when it comes to reducing latency. A recent
technique involves laying optic fiber cables with hollow interiors, so that
the internal refraction of light spends more time in a vacuum and less time
slowed down by the pesky glass medium.

~~~
sgt101
Which is why the regulators really need to get sharper with them vs. what they
are doing to the economy. They are front running, destroying value and
spending the money on a whole load of tat - a massive case of misallocation of
capital. They need to be shuttered.

~~~
paulddraper
HFT, or Bitcoin?

~~~
andrepd
Stop shoehorning and derailing the conversation please.

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mirimir
There's another key issue: peering. Minimum rtt between nearby ISPs can be
huge, when nearest shared peer is a few hundred km away. That's so for parts
of Hong Kong vs mainland China. Also Salt Lake City and Zurich.

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wmf
Here's some academic work that goes into much more detail about this topic:
[https://arxiv.org/abs/1505.03449](https://arxiv.org/abs/1505.03449)

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ksec
Very Naive Questions.

There are now fibre that has hollow core instead of light travelling through
glass. Assuming we could do that in long distance, that is close to 0.98c, we
should have +40% latency improvement right?

i.e Someday if we needed more capacity and this tech is available, we could
lay this new fibre along side the same router as the current fibre. And enjoy
some improved latency?

How much latency does each network hoop adds? 0.05ms?

How much latency does our own machine add? Are the 70ms actually all spent
within the Network? Or would there be 0.5ms just coming from the Ethernet
Controller, buffer or what ever?

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bpchaps
Serious question: for a transatlantic network, would it ever make sense to do
something along the lines of buoy + helium balloons + laser or microwave? Or
in a similar vain, would it make sense to attach microwave 'towers' to
shipping vessels?

I could see something like that work really well for the HFT world, where some
clever hacks could make use of an unstable, but extremely low latency
connections.

~~~
itcmcgrath
I doubt that would be lower latency. Even forgetting the physics and curvature
issues, you'll end up with many more hops which is going slow it down due to
processing and retransmission delays.

~~~
wmf
Microwave is faster even though it requires more hops.

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sova
Depending on how your Bond-villain vacuum tunnels and repeaters are set up,
it's possible, i surmise, to create a tunnel way that can repeat without
adding an interminable delay node or nodes. Imagine the One Way Valve Nikola
Tesla patented, except with microwave repeaters shelled and pocketed into the
sides of the tunnel passage instead of water-holding empty pockets.

Although I think that this is very nice, I always like to go to the "ultimate
level" and consider what we would do if there was a way to send informative
electrical signals using the earth as a resonator, and that idea chiefly
brings me back to Wardenclyffe.

Did you know that the magnetic field of mars is weirdly shaped? It is only
magnetic on the "Southern Half" of the ball that is Mars and has a slight
gradient. So, assuming we can create some sort of information share that could
function on the dynamic magnetic shielding of the earth, we'd have to rethink
it for Mars, and any planet with a non uniform magnetic field from pole to
pole.

Thanks a lot for your creativity. Keep writing, together we got this!

~~~
wmf
Don't forget neutrinos. They pass right through the earth, no tunnel needed.

~~~
sova
Hmmmm can we encode information in neutrinos? I thought they were so few and
far between it's difficult to reliably harness them.

~~~
wmf
But you can produce them artificially.
[https://arxiv.org/abs/1203.2847](https://arxiv.org/abs/1203.2847)

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mkj
Why aren't HFT firms using short wave radio (DXing)?

I suppose low-orbit satellite-to-satellite would probably beat fibre for
anything over ~4000km too.

~~~
bostik
> _Why aren 't HFT firms using short wave radio (DXing)?_

They are. See mshook's response, with nice reference links downthread:
[https://news.ycombinator.com/item?id=16196339](https://news.ycombinator.com/item?id=16196339)

~~~
mkj
Those are microwave which basically need line of sight? I was thinking of
lower frequencies which can sometimes go hundreds of kilometers without
repeaters.

~~~
jlgaddis
Bandiwdth, mostly.

The lower you go in frequency, the less bandwidth is available.

The entire "HF" spectrum is ~30 MHz. My Wi-Fi at home uses a wider channel
than that.

The lower frequencies -- that will travel across the ocean, unaided -- don't
have anywhere near the bandwidth necessary (to support the throughput that
they need).

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RyanShook
What about all the hops your signal has to take to make the round trip?
Couldn’t those be optimized or sped up? Is copper latency really equivalent to
fiber?

~~~
0xcde4c3db
> Is copper latency really equivalent to fiber?

Notwithstanding differences between specific types of cables and transceivers,
yes, the rule of thumb is that they're roughly equivalent. The big advantages
with fiber mostly come with being physically smaller for a given bandwidth
(e.g. more bandwidth per square inch of conduit cross-section, more bandwidth
per cable weight for vertical or suspended runs) and needing less active
equipment between any two points in the network (e.g. PON, long-haul single-
mode runs).

~~~
mhurd
An old style copper ladder line is ~0.95c and optical fibre is ~0.66c:

Old style, pre-coaxial, undersea cables may have been ~0.45. Newer coax is
sometimes ~0.87c.

YMMV: [https://meanderful.blogspot.com/2017/05/lines-radios-and-
cab...](https://meanderful.blogspot.com/2017/05/lines-radios-and-cables-oh-
my.html)

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microcolonel
Seems like directional radio/laser-in-tube would get you back that 1/3 by
avoiding the internal reflection problem altogether.

~~~
mshook
That's why companies doing HFT or stock exchanges often use microwave links...
Just to crank it to eleven err to gain that 30% back.

Information Transmission Between Financial Markets in Chicago and New York:
[https://arxiv.org/pdf/1302.5966v1.pdf](https://arxiv.org/pdf/1302.5966v1.pdf)

Time is money when it comes to microwaves:
[https://www.ft.com/content/2bf37898-b775-11e2-841e-00144feab...](https://www.ft.com/content/2bf37898-b775-11e2-841e-00144feabdc0)

Trading Fortunes Depend on a Mysterious Antenna in an Empty Field:
[https://www.bloomberg.com/news/articles/2017-05-12/mysteriou...](https://www.bloomberg.com/news/articles/2017-05-12/mysterious-
antennas-outside-cme-reveal-traders-furious-land-war)

[https://arstechnica.com/information-
technology/2016/11/priva...](https://arstechnica.com/information-
technology/2016/11/private-microwave-networks-financial-hft/)

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6d6b73
Well, we already have tech that can provide us with virtually lowest latency
physically possible without having to dig any tunnels - high frequency radio
waves :) Of course bandwidth could be a problem but for pings it should be
enough.

~~~
dgoldstein0
The point isn't to optimize for pings. It's to optimize for real use cases -
video chat, web browsing, music and video streaming, etc. Most of these
applications need at least a moderate amount of bandwidth.

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js2
Obligatory link to "The case of the 500-mile email":

[https://www.ibiblio.org/harris/500milemail.html](https://www.ibiblio.org/harris/500milemail.html)

~~~
dfee
My favorite part: “I diffed it against the sendmail.cf in my home directory.
It hadn't been altered--it was a sendmail.cf I had written. And I was fairly
certain I hadn't enabled the "FAIL_MAIL_OVER_500_MILES" option.”

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bawana
going through the earth is a shorter distance but unfortunately light speed is
slower that way

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ec109685
Why is light slower that way?

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Simon_says
I'm not sure if this is what he's referring to, but light (and the passage of
time) is slower in a gravity well. A geodesic in spacetime will minimize the
time it takes for light to travel between two points. In the case of going
through the Earth, the geodesic will be only slightly deflected from what you
would consider the straight-line path through a sphere in a flat spacetime.

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mozumder
He mentions an overhead of about 11ms in a cross-country network, which may be
insignificant in the 35ms overall latency.

But, much of the infrastructure is communicated to regional servers or local
CDNs, not cross country. A game server might split loads across east-coast
servers and west-coast servers to improve responsiveness. In those cases, it's
not unfeasible to see a 2ms-5ms speed-of-light latency. And that's where those
11ms really starts to affect user experience, since now you're looking at
latencies that can cut into your 60fps frame rates. (or local video-chat
services or even websites)

~~~
ec109685
FPS won’t be reduced by latency increases, responsiveness will though.

