Dark Fiber: Embracing The Dark Side

Leveraging unused fiber optic cables is becoming practical for more than large corporations.

Marcia Savage

February 2, 2016

4 Min Read
Network Computing logo

Organizations’ ever-increasing demand for faster bandwidth is driving fresh thinking about the options available. While the common choice has been Ethernet broadband services from telecommunication providers, dark fiber is becoming a viable option.

Dark fiber is the term used for unused fiber optic cables, and today it’s become increasingly common to lay more fiber lines than currently needed for future use. Historically, only large organizations could take the dark fiber route, but now it's becoming affordable for smaller companies. With dark fiber no longer the sole domain of multinational corporations, maybe it's time to finally embrace the “dark side.”

Location, location, location

A distinguishing feature of fiber services is that they are location sensitive. Carriers may have an accessible fiber running on one side of a road but not on the other and some larger buildings will have already been “lit” by a particular carrier while others have not. These buildings may or may not warrant the cost of constructing new fiber connections.

Organizations running bandwidth-intensive applications are therefore faced with a choice: Order a fiber-based service from a carrier that is available in their area or buy/rent dark fiber to create their own wide-area network. Each option has pros and cons when comparing performance, cost and installation time, and cost is not always the top criteria. The wait time for service availability can often be a top factor. It can sometimes be weeks or even months, depending upon the application, before a provider can complete an installation. This can be a good option for those planning ahead, but if the need is more immediate, then availability often trumps cost. 

Speed choices

Fiber-based services are categorized into several major groups, each with their own application. The traditional telecom service is SONET/SDH with OC-3 as the lowest bandwidth of 156 Mbps. An OC-3 circuit can also carry three multiplexed DS3/E3 lines at 45 Mbps each. Commonly, the service provider will deliver DS3/E3 by fiber optic cables. Other SONET levels are available with speeds up to 100 Gbps. In other words, fiber-based services carry vastly more data than Ethernet.

According to Butter’s Law of Photonics, the amount of data travelling through fiber optic cables doubles every nine months. This increase is not due to upgraded optics, but new techniques used at either end, such as dense wavelength division multiplexing (DWDM). Using wavelengths, DWDM can turn a fiber into several virtual fibers, usually referred to as channels -- colors of laser light -- and each color or virtual fiber can be dedicated to a customer or a service thanks to its protocol independence. 

dark fiber

Dark Fiber illustration.png

With this, a large amount of data can be sent down the same fiber optic cable -- hundreds of gigabits and even terabits per second. Techniques such as these slow the demand for new fiber installations, instead driving better performance from existing fibers. This in turn has helped drive the price of fiber down. 


Today, traditional Ethernet service tends to be both more scalable and lower cost than SDH/SONET. But bandwidth options are 100 Mbps Fast Ethernet, 250 Mbps, 500 Mbps, 1 Gbps Gigabit Ethernet  and 10GbE.

While 100 GbE can now be ordered in some areas, this high level of bandwidth remains expensive compared to dark fiber solutions. When an organization’s demand is more like 10 gigabits, they need alternatives.

Dark fiber can carry multiple wavelengths, increasing bandwidth significantly, plus it starts making more economic sense when the organization owns and manages the equipment itself. When ordering a wavelength, customers receive a virtual fiber all to themselves with the added advantage of low latency and high security. It can also be fortified with AES-strength encryption, meaning even with a break the data cannot be intercepted.

With an entire wavelength dedicated to a customer’s use, there's the added flexibility of being able to use a different protocol for other customers on the fiber -- for example, running Ethernet while others are running SONET. If running multiple lower speed legacy services, customers can also multiplex these into one higher capacity wavelength.

By leasing or installing dark fiber, businesses have all the wavelengths at their disposal. It requires buying the termination equipment for each end, but once that equipment is in place, the customer has the option to light up as few or as many wavelengths as necessary. Wavelengths can be configured based on current business needs, and easily reconfigured as needs change.

Phil Bartlett is director of product management at Sorrento Networks, part of the Comtek Group. He has nearly 20 years’ experience focused on the issues of fiber-optic cabling and broadband deployment, and how telecom providers are able to maximize their network infrastructure.

About the Author(s)

Marcia Savage

Executive Editor, Network Computing

Stay informed! Sign up to get expert advice and insight delivered direct to your inbox
More Insights