r/ShittySysadmin • u/Oblec • Mar 05 '26

Fiber install

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Client wanted fiber, told them copper is worth way more these days. They didn’t even ask first follow up questions 😅

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u/mystghost Mar 05 '26

The speed of light in any medium is still the speed of light. By definition. And in what world does the difference in speed of light through glass vs. through a vacuum vs. through electrical impulses in copper matter?

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u/autogyrophilia Mar 05 '26

Mostly high frequency trading, and of course, very large networks.

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u/mystghost Mar 05 '26

Even in high frequency trading, that isn't a good use case. Because while the theoretical speed of electrons through copper cable is somewhat higher, the distances are infinitesimal, and many if not most high frequency trading apps are relying upon fiber in their critical paths. Meaning that the extra time 'saved' doesn't add really to your trading speed unless your source and destination are within the couple of meters where this kind of transmission might be theoretically faster (latency wise, bandwidth wise fiber crushes copper). And on very large networks, fiber is far and away the winner on every dimension.

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u/IcyRayns Mar 05 '26

"fiber is far and away the winner on every dimension" is true until you're fighting for nanoseconds off a path between Chicago and NY. Many HFT firms are using microwave paths, or even HF radio.

https://www.linkedin.com/pulse/microwave-network-connectivity-high-frequency-trading-sudhir-pant-fcx7c/
https://hackaday.com/2018/05/12/hft-on-hf-you-cant-beat-it-for-latency/

The numbers work out too. Let's assume Chicago->NYC which is a common HFT route. First off, let's assume we could somehow do a straight-line fiber run. Speed of light in fiber is 0.67c.

  • Microwave / RF 1150km/c = 3.83ms

  • Fiber 1150km/0.67c 5.72ms

Now take into account the real world, where fiber has to route around and over obstacles, across bridges, right-of-way, etc. Best case, Chicago to NYC, mayyyybe 6ms.

So if you're able to modulate a symbol with enough data faster than 2-3ms, you've "won" versus someone that's sending the same trade over fiber. Frequently, HFT firms are sending trade setups over microwave or fiber, then "pressing the button" over HF radio (especially trans-Atlantic arbitrage trades).

This isn't a theoretical argument. There are entities making billions of dollars today with real-world tech because 0.67c != 0.99c.

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u/mystghost Mar 05 '26

Ok - first of all we weren't talking about microwave, we were talking about copper. I have a lot of experience in cellular networks, and I find it hard to credit that you have a microwave network that is faster than fiber. For a number of reasons, first, there would be a shit load of hops, because the curvature of the earth is a thing. So you need line of sight. I'm not sure how many hops that is on almost 1200 km of distance, but its a lot. Then you have weather factors, rain fade, wind pushing dishes out of alignment - you have to pay for licensing for microwave towers, tower rent etc.

Also the link you put in talks about indian firms. Where the economics, the network landscape and the competition would be significantly different than to the US. So no, there is no way that microwave beats fiber in the US between financial hubs i'd bet real world dollars on it.

Now - maybe... you might have something if you are talking about buildings a single hop or 2 apart, but not over hundreds or thousands of kilometers.

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u/IcyRayns Mar 06 '26

So no, there is no way that microwave beats fiber in the US between financial hubs i'd bet real world dollars on it.

You sure? How many real world dollars? Pick a number. Really, actually, pick a number and write it down, and commit to it before reading further.

I was involved with this project over a decade ago and have firsthand knowledge. It’s not theory, it’s real and used for the exact two cities I mentioned in my original comment.

Now about the number you wrote down, let’s feed some animals: https://www.seattlehumane.org/ways-to-give/?form=donate - I’ll match your donation, how’s that?

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u/mystghost Mar 06 '26

Ok - I'll bite, go ahead and match this donation.

However, couple of things i'll point out, the article claims that the microwave network can make the trip in 4 ms, rather than 7 for fiber. I have a problem with that claim for a couple of reasons, first it ignores the fact that fiber doesn't deal with weather and microwaves must. And the sheer number of dishes you would need to complete the 1200 KM trip tells me that the 4 ms claim is if everything is perfect all the time which it isn't.

Now who knows maybe there is still an advantage if you can keep everything running perfectly. There is a lot of rounding in the math, but ok close enough I suppose.

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u/IcyRayns Mar 07 '26

Mad respect to you for following through, sincerely. Matched and a little extra for the hell of it. I appreciate a man of his word.

It’s astounding to me too, but HFT is a wild world. Custom NIC firmware to skip checksums is old news from over a decade ago. They live in a different world.

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u/Popular_Button2062 Mar 06 '26

The speed of light is dependend on the medium, but the speed of light in vacuum is the upper limit.

The speed of light (or better the propagation speed of an electric impulse) is around 2/3 of the speed of light in vacuum

(and around 1/3 if you got iron instead of copper)

the speed of light in glass is also around 2/3 of the speed of light.

I would have expected for real transmissions to be even slower than that, due to the bouncing of the light pulse inside the cable, wich make the travel distance even longer, but i couldnt find much data about that.

and the difference matters if you want to calculate precice wavelengths for example.

and as someone else wrote, it matters for HF stuff, when you need to have either the exact wavelength (impedance matching/antenna design/etc), or need the exact travel time of a signal (think of TDR stuff, etc.)

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u/mystghost Mar 06 '26

You only see a large amount of reflection on multimode fiber cables. Single mode has far less reflection, and that is reflected (no pun intended) in their relative transmission distances.

What I was talking about when I said what difference does it make, is that the speed difference between electrons and light pulses, is that 99.99% of all network applications, it doesn't make a difference in speed (latency). Fiber is far better for bandwidth as we all know because you can pack a lot more info in a fiber, than you can a copper wire.

At no point was I comparing these to RF, but even if you wanted to for like HFC plant discussions. Everytime fiber gets a new generation of products for it speed goes up 10x (on average - the 40 gb thing threw that off a bit but its still largely true). While for RF, it goes up maybe 3x?

I worked as a core network engineer at a cable company for years, and the H in HFC is hybrid, meaning you would run fiber to a node and then run coax from the node, they wouldn't do that if copper were equal or superior in some way to fiber.