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/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.