Enterprise / Networking

What Is Dark Fiber?

Dennis Thankachan

What is Dark Fiber?

You may have heard the term and wondered: what is dark fiber? Though it might sound ominous, it represents a big opportunity for many enterprise networks.

In the 1980s and 1990s, when communications companies installed miles of fiber optic cable underground, their strategy was often to dig down and bury more fiber than they needed at the time. The rationale was that if the lion’s share of the cost associated with underground fiber installation was due to the labor, equipment and operations necessary to bury cable – not the cable itself – it made sense to install extra cable to save money in the future when more communications and data transfer capacity would be required. Since cable was first installed underground, the thousands of miles of unused optical fiber, aka “dark fiber,” has reserved great potential for telecom companies and internet service providers (ISPs). It also represents, however, a viable option for businesses and enterprises that are looking for the best ways to expand their networks.

Fiber Optics 101

To understand how your business can leverage dark fiber, you need to understand how fiber optics work. Fiber optics cables are constructed of numerous strands of glass fibers, drawn to the diameter equal to about the size of a human hair, that transmit data via light at high speed.

Fiber optics technology enables multiple data streams to travel in one fiber — often done with a process called dense wavelength division multiplexing (DWDM) that can transmit different data streams at different wavelengths. Therefore, it’s possible for a smaller company to use just a fraction of a cable’s potential to transmit data in the same cable that a larger company uses for its needs. This is distinctly different, however, from how dark fiber is used, as we’ll outline below.

Making Use of Dark Fiber

Reliable, high-capacity connectivity is more important than ever before, and with ISPs handling more bandwidth than ever, companies in need of greater volumes are often finding themselves paying more and more for premium access or services, such as very high bandwidth point-to-point or Wave circuits (what you’d call “lit fiber” products).

Dark fiber represents an alternative. Also called “unlit” or simply “black” fiber, a dark fiber optic cable is, quite literally, one that is dark -- there are no light pulses being transmitted through it. For the most part, these cables are reserved by and leased out by large telecoms and ISPs, but businesses can take advantage of them as well by leasing the fibers and “lighting” them with their own electronics and network gear, dictating the network’s architecture, speed, and security.

The providers of dark fiber are the “usual suspects” of enterprise telecom - the same ones who provide standard enterprise ISP services - such as Zayo, CenturyLink and Crown Castle. When leasing dark fiber from one of these providers, rather than buying a certain amount of bandwidth over a term, you’ll lease a certain number of strands of fiber from them over a longer term than a regular ISP contract (normally 3-20 years).

Dark Fiber use cases

Your bandwidth needs are high and continue to grow

If your bandwidth needs are topping 1 Gbps currently, dark fiber should be cost competitive with traditional ISP connectivity options for your needs. Given that bandwidth needs continue to grow a double digit annual rate for most companies, if you’re at cost parity with dark fiber now, the economics of dark fiber should get better for you over time.

You want to set up a private, highly customized / secure network

There are certain private network use cases that dark fiber can accomplish better than any other connectivity option. For example, do you need to set up a trading network with extremely low latency, or a data center link that needs near real-time transmission capabilities? Have highly specific security needs? With dark fiber, you can architect such networks with complete control over speed, latency, jitter, and security. Standard ISP options offer far less flexibility.

Standard WAN use cases

Need to connect two buildings with a high bandwidth connection? Need a high bandwidth data center link? If you’re in a major metro area with lots of fiber, dark fiber may be an attractive, futureproof option to replace what you’d typically use a wave circuit or other point-to-point fiber option for. Dark fiber pricing can vary dramatically depending on regional competition.

What are the Benefits of a Dark Fiber Network?

One of the main selling points of using dark fiber for your business is that it allows you almost complete control of your network infrastructure. Universities and other government institutions often prefer setting up their own network because of the increased security and ability to directly manage their networks. Individual users of dark fiber can set and control the speed and latency of their network, providing fine-tuned control not always available from an ISP.

Another benefit of using dark fiber is business continuity. Relying on commercial internet or telecom services alone to access infrastructure and applications in the cloud can create risks; if service is interrupted, teams can’t access the systems and data they need. Forward-thinking organizations will often have a backup communications system and internet access, but are still reliant on their ISP for connectivity. Opting to use dark fiber minimizes the risk of outages and increases uptime.

Moreover, when problems with the network arise outside of the physical cable itself, your business can handle it internally, rather than relying on an ISP to get you on their list to restore service or make repairs. If the issue does lie with the physical cable, you can negotiate very specific SLA’s with the carrier that will address the issue within a predetermined period of time. With dark fiber, you control your network rather than ceding control to a provider. You also won’t have to be concerned with hidden fees or new taxes levied against ISPs or telecom providers.

What are the Potential Pitfalls of a Dark Fiber Network?

Savvy readers will probably have already guessed the main limitations of a dark fiber network, which is that you’re in charge of everything. From architecting the network itself, to maintenance and troubleshooting, any business that elects to go with dark fiber will want to have a high level of technical expertise and be certain that it’s worth the expense and effort. Additionally, companies must invest in premise equipment to light the fiber and make it usable, this equipment can be costly and complex to maintain.

It’s also worth remembering that even being able to connect to a dark fiber strand requires there to be unused cable in your area — this may not be an option, depending on where you are.

Another main concern, of course, is cost — most strand leases are for infinite capacity over a long period, which can require a hefty investment. Using dark fiber can be cost-effective for many businesses, but it is especially beneficial when businesses with larger networks compare costs to their monthly ISP bill. Large organizations can reach a tipping point where they are transmitting so much data that charges for purchasing bandwidth from an ISP grows higher than a flat rate for leasing or buying dark fiber. Sometimes the other advantages make dark fiber worth the investment, but at a certain point, it’s a dollars game.

The Network Potential Under Your Feet

Investing in dark fiber is not something to be taken lightly, but for sophisticated users with high bandwidth needs, it’s a viable and attractive option. Everyone from local municipalities to e-commerce enterprises are exploring how dark fiber can help them expand their networks and keep their team securely connected to the systems, data, and people necessary to operate successfully.

If you’re interested in seeing what dark fiber options might be available to connect two points within your own network, fill out our questionnaire to receive a quote.

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