Dark Fiber: Questions and Answers
What is fiber?
Fiber optic cable is a bundle of strands of glass that can carry internet traffic.
Data is sent through the strands from one location to another
in the form of pulses of light.
How much data can fiber carry?
A typical fiber cable contains 72 to 144 strands.
Two of these strands can support the internet needs of 10,000 students.
This means that two strands of fiber, when connected to standard equipment,
can carry 10,000 megabits of data per second,
which is 1 megabit each for 10,000 students.
What is dark fiber?
Dark fiber is fiber that has not been lit.
It cannot carry internet traffic until it has been lit.
In the same way that newly installed electrical wiring
cannot carry electricity until it’s been connected to a power source.
How does fiber get lit?
Fiber is lit when specialized network equipment is attached to it at both ends.
This equipment lights the fiber by passing pulses of light through it
and distributes internet traffic from the fiber to devices throughout the building.
Specialized network equipment that lights fiber has two parts.
A module that the fiber plugs into and
a switch connected to your network that the module plugs into.
The module receives light pulses from the fiber and converts them
into electrical signals that it passes into the switch.
The switch then distributes the signals, which are internet traffic,
to other switches and end devices on your network.
What is the difference between dark and lit fiber?
The key difference is who owns the fiber.
Lit service providers own the fiber that comes into your building
and the equipment that lights it.
They can use the equipment to, quote, throttle down the bandwidth
in your building similar to the way that a faucet
can be tightened to reduce the amount of water that can come out.
If you own the fiber, you can light it yourself.
Because you also own the equipment that lights it, you can, quote,
leave the faucet open, using the full capacity of the fiber.
This is also true if you lease the fiber.
Why does a lit service provider throttle down the amount of traffic
coming into the building?
This is done so that the amount of bandwidth that you are receiving
matches the amount that you have agreed to pay for in your contract.
If you own or lease dark fiber, you can un-throttle the internet traffic coming
into your building because you control the equipment that lights the fiber.
If I have dark fiber, I can open up the faucet without paying anything extra?
Yes, but ...
dark fiber is not free.
There are major expenses, including installing the fiber,
networking equipment,
configuration of network equipment,
Digger’s Hotline expenses,
maintenance if the fiber is cut and needs to be repaired,
and relocates if the fiber cable needs to be moved.
All of these expenses are taken care of by a lit service provider.
How can I decide whether it be worth it for my district to consider dark fiber?
See the upcoming DPI slideshow, “Comparing Dark vs. Lit Fiber Bids.”
[ Silence ]