envelope-ofacebook2linkedinsearchtriangle-downTwitter_Logo_White-on-Bluetwitter

What Is Dark Fiber?

Dark fiber is typically leased from the company that installed it, or from companies that manage and market dark fiber. As dark fiber requires customers to “light” the fiber with their own equipment, there is an additional step where the fiber needs to be terminated (connected) directly to the district’s network. In many cases, the small piece of terminating equipment used to light fiber (called a Small Form-Factor Pluggable or SFP) can be plugged into an empty port on existing network switches. Many districts have an empty SFP interface on an existing switch at both endpoints. If not, please consult with your vendor about which SFP to buy.

Today, there are markets around the country where an oversupply of fiber assets have made leased dark fiber more widely available and more affordable than lit circuits. As a result, K-12 schools with high‐bandwidth needs look to leased dark fiber as a means to find economies of scale by owning and operating their own network as opposed to purchasing lit circuits.

EducationSuperHighway encourages districts to consider leased dark fiber as an option for their WAN given the many benefits.


Lease or IRU?

Traditional dark fiber leases are for shorter annual terms (usually up to 5 years) and paid with a monthly recurring cost that may include maintenance cost of the leased dark fiber by the lessor. The lessor may be responsible for maintenance and/or maintenance costs on the fiber depending on the terms of the contract. The contract of a traditional dark fiber lease will usually have stricter terms dictating what the customer can and cannot do with the dark fiber.

Indefeasible Right of Use (IRU) is a lease vehicle whereby the term is usually longer (5-20 years) and the entire lease fee is paid in two installments (one-half upon agreement to lease and one-half upon acceptance of the fiber (post testing). The lease has attributes of ownership like survivability in case of the sale or bankruptcy/insolvency of the fiber owner. IRU contracts usually have more flexible terms, though this does not usually include maintenance and repair of the fiber. Typically the provider will charge an extra recurring fee for this or a 3rd party contractor must be hired to perform these services.


Benefits of dark fiber

  • Bandwidth scalability – A single strand of fiber is capable of transmitting at over 100 Gbps. However, the transmission speed is determined by the electronics at either end of the fiber, and higher speed electronics are considerably more expensive. A district currently utilizing a 1 Gbps leased dark fiber circuit can upgrade to 10 Gbps by simply replacing the electronics at either end. The fiber itself remains untouched.
  • Flexibility – Districts that obtain leased dark fiber provide their own electronics (called transceivers) to light the fiber, giving them direct operational control of their network and ability to upgrade bandwidth without coordinating with a carrier.
  • Security – Dark fiber networking creates a fully dedicated, private physical network infrastructure for school districts.
  • Cost – A long-term dark fiber lease can cut costs in the short- and long-term.
    • Many districts find that in forecasting their 10-year bandwidth needs, it is cheaper to invest in a dark fiber backbone now rather than to pay for 10 more years of managed lit service.
    • As a district’s bandwidth grows, leased dark fiber provides consistent monthly costs and very low incremental costs per Mbps.
    • Costs associated with leased dark fiber are eligible for E-rate.

Considerations with Leased Dark Fiber

Despite the many benefits, leased dark fiber may not be the best solution for all school networks.

  • Providers of dark fiber do not provide network support for the fiber network termination. This includes configuration of switches and routers and technical support for electronics on the leased dark fiber. It is the responsibility of the school district to either perform these functions with in-house technology staff or outsource these duties to a 3rd party.
  • Similarly, when a connection isn’t functioning properly the district will be required to do more troubleshooting to determine if the problem is with the dark fiber or with the district equipment connected to it. This requires more expertise than troubleshooting a managed lit fiber connection.
  • Not all school districts are in areas where dark fiber is commercially available or it may not be the most cost-effective solution.