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Dark fiber (unused fiberoptic cables) is a confusing term for me. Why would any company build so much excess capacity? Such a business decision seems unwise. There are even companies that brand themselves as 'dark fiber providers' which is even more confusing.

https://www.ufinet.com/services/dark-fiber/

Was the expectation of utilization massively overestimated? Or is switching and multiplexing tech rendering it cheaper to use few fibers?

I realize this is not technically an EE question but am hoping that some real EEs have insight into why this has happened. If the mods feel a different forum is more appropriate I can move this post there.

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    \$\begingroup\$ Are they just burying more cable than needed when digging? Because re-digging is a pain in the ass. \$\endgroup\$ – DKNguyen Jul 28 at 2:23
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    \$\begingroup\$ I’m voting to close this question because it is a business question and not a technical question \$\endgroup\$ – Chris Stratton Jul 28 at 2:36
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    \$\begingroup\$ Nobody will ever need more than 640KB RAM, IPV4 addresses will never run out, etc ... \$\endgroup\$ – Alan B Jul 28 at 12:51
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    \$\begingroup\$ When a company "provides dark fiber" to a customer, it probably won't be dark for much longer... The customer takes an unused fiber and can do whatever they like with it (including leaving it dark, if they so wish...). The provider is only facilitating the fiber link, no equipment at either end, no internet connectivity, etc... \$\endgroup\$ – Attie Jul 28 at 15:01
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Dark fiber (unused fiberoptic cables) is a confusing term for me. Why would any company build so much excess capacity?

The marginal cost of adding one more fiber when digging up a street is very, very small relative to the cost of digging up the street in the first place. So when you decide to dig a trench across the country, string a fiber across the ocean, etc you typically put more than one in place so that in the future you don't have to do it all over again when you need more capacity.

In addition, much of the cost of the fiber link is actually the equipment at the ends of links (WDMs, receivers, pump lasers for amplifiers, etc). Burying a lot of dark fiber therefore allows you the option of paying to install more lines sometime later in the future (by buying more receivers) for a relatively small up front cost (just whatever it costs to put one more fiber in the trench).

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    \$\begingroup\$ Some areas have laws (or guidelines) stating that you must install fiber every time you dig a trench for another purpose. This is much better than digging up and patching the same roads over and over again every time you need to add something like a wire or pipe. \$\endgroup\$ – mkeith Jul 28 at 3:19
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    \$\begingroup\$ Yes, fibre itself is dirt cheap; further they're not pulling single cores through but may not need to use all cores in a bundle at least at first. Per metre, 24 core cable is only around 7x the price of single-core, and far cheaper than digging again \$\endgroup\$ – Chris H Jul 28 at 11:39
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    \$\begingroup\$ I suppose if they run out of 24-core cable, their next upgrade will be to more like 240 cores. And for reference, last time I checked (ages ago), single-core fibre cable was something like $0.30/metre. \$\endgroup\$ – user253751 Jul 28 at 12:58
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In addition to the previous answer just a comment on terminology, If industry speaks about Dark Fibre, especially renting them, this typically means you buy the fibre capacity and have to take yourself care for transmitting/receiving and multiplexing.

It does not mean the Connection is not used or in excess, it means you are not bound to the provider equippment. Of course before you can rent those lines they do have to exist and be unused. The lines are digged into the ground in expectation of beeing sold (managed or unmanaged).

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