>"For those unaware, dark fiber refers to fiber in the ground that was overbuilt by the owning company, in this case Level3."
Overbuilding is not the differentiator though. During the original dot com boom of the 90's yes there was a lot of excess capacity due to overbuilding but dark fiber is really any fiber that is currently unlit that is available for lease.
Building capacity can be and often is the business model itself. For example you pull fiber through an urban area and then sell IRUs(indefeasible right of use) on a cable pair, usually for a period of 20 years. As a fiber provider I may not have ever intended to light that fiber myself so it was never overbuilt.
Overbuilding is not the differentiator though. During the original dot com boom of the 90's yes there was a lot of excess capacity due to overbuilding but dark fiber is really any fiber that is currently unlit that is available for lease.
Building capacity can be and often is the business model itself. For example you pull fiber through an urban area and then sell IRUs(indefeasible right of use) on a cable pair, usually for a period of 20 years. As a fiber provider I may not have ever intended to light that fiber myself so it was never overbuilt.