During many enterprise networking discussions, you’ll hear jargon thrown around such as “dark fiber” and “lit fiber,” but what do these terms mean anyway? What would make an enterprise want to power its network with dark fiber as opposed to lit fiber? Isn’t all fiber connectivity solid? In this post, we’ll answer all of the above so you can make an informed evaluation of dark vs. lit fiber as it pertains to your business.
How does fiber work?
Fiber optics cables are built from numerous glass fiber strands, with diameters equal to about the size of a human hair, that transmit data via light at high speed. This is great for high-speed Internet users, as with the right electronics, fiber’s speed and capacity is nearly infinite, making fiber the gold-standard for internet service delivery.
Further, fiber technology enables multiple data streams to travel in a single fiber — often done with a process called dense wavelength division multiplexing (DWDM) that transmits different data streams at different wavelengths. Therefore, it’s possible for a company to use just a fraction of a cable’s potential to transmit data in the same cable as other companies.
In the DWDM example above, an ISP “lights” the fiber with its own electronics and sells services to other companies who will utilize the ISP’s network. Often, multiple companies will ride the same fiber with the ISP, provisioning the network, and managing traffic. This model makes the most sense for enterprises who have regular, well-defined network needs and don’t have in-house network engineering capabilities.
However, the heaviest users of bandwidth who care about optimizing latency and would benefit operationally from managing the network themselves often would rather buy “dark fiber” (unused, unlit fiber strands) and “light” the fiber themselves with their own electronics and network management.
Lit fiber essentially refers to fiber optic cables that are in use, i.e., “lit” by a network provider’s electronics. Whether they be through dedicated internet circuits, point-to-point, or wave circuits, most enterprise internet access comes in the form of lit fiber products.
In most cases, users have well-defined bandwidth needs, and it would make more sense for an ISP to take on the liability of managing your network backbone and ensuring uptime meets an SLA. If a user’s bandwidth needs are high, that’s fine, as lit fiber product capacities are now topping 100Gbps.
For most businesses, lit fiber presents the most operationally convenient and flexible form of fiber optic connection. Further, with so much competition in the ISP market today, bandwidth is cheaper than ever and per megabit prices on lit products continue to trend cheaper with time.
However, if your bandwidth needs are less well defined, and you’d like to set up a private, highly customized, secure network, dark fiber may be your best bet.
In contrast to the above, dark fiber represents unused, “unlit” fiber optic cable that an enterprise leases from an ISP to manage privately. Dark fiber is not managed by a network provider. Instead, the responsibility for “lighting the fiber” (buying and maintaining the equipment and the staff required to operate it) falls on the business user. You get to become your own ISP in a way!
Because these are otherwise unused strands on fiber, you get to dictate the capabilities of the entire network’s architecture, speed, and security with no limits on bandwidth or uptime. For the most bandwidth-intensive enterprises, dark fiber is actually cost-competitive / cheaper with lit fiber and gives you complete control over how you scale your network.
Certain private network use cases can be better accomplished with dark fiber than any other connectivity option. Need to set up a trading network with extremely low latency? Need to connect a data center with real-time transmission links? Have highly specific security needs? Dark fiber is probably your best bet.
Of course, the flexibility and scalability of dark fiber comes with several big drawbacks as well. The main drawbacks can be summed up succinctly: you’re in charge of everything. From architecting the network itself to maintenance to troubleshooting, any business that deploys dark fiber better have some great internal network expertise managing the network.
Also, dark fiber requires companies to invest in expensive electronics that can be complex to maintain. Finally, dark fiber strands are often leased at lengthier terms (three to 20 years) than their lit counterparts (two to five years).
If connectivity is important to you however, dark fiber can be among the best values out there. Every connection and use case is different, and it’s not uncommon to see companies leveraging both lit and dark fiber in different instances.