A dark-fiber connection consists of fiber-optic pairs that are already installed underground but remain unused until a company rents or leases them. Unlike standard internet connections, the provider only supplies the physical fiber without active hardware (such as routers or switches).
The user is responsible for “lighting” the endpoints using their own hardware. This is often done with DWDM technology (Dense Wavelength Division Multiplexing) to transmit multiple data streams simultaneously over different wavelengths on a single fiber. At the same time, the customer must consider route length and characteristics, including attenuation, optical power margins, and dispersion.
This setup maximizes capacity and minimizes latency, since there are no intermediary provider nodes delaying signal processing.
To fully answer the question “What is Dark Fiber?”, it is important to distinguish it from conventional “lit” connections (Lit Fiber). For dark fibers not provided by firstcolo as the provider, no guarantees can be made regarding route separation from external dark fibers.Um die Frage „was ist Dark Fiber“ vollständig zu beantworten, ist die Unterscheidung zu herkömmlichen, „beleuchteten“ Leitungen (Lit Fiber) entscheidend. Bei Darkfibern, die nicht durch firstcolo als Provider bereitgestellt werden, können keine Garantien hinsichtlich der Kreuzungsfreiheit zu externen Darkfibern übernommen werden.
User provides own optics & routers
Provider supplies hardware
Virtually unlimited (hardware-dependent)
Limited by service plan
Provider handles end-to-end maintenance
Fixed rental costs per route
Costs usually depend on bandwidth
In practice, companies use dark fiber for Data Center Interconnect (DCI). For example, a financial institution may connect two sites in Frankfurt via a dark-fiber line to perform real-time data replication. Because the institution controls encryption and routing itself, it achieves a level of security and speed that would not be possible over public networks.
A key advantage of dark fiber is independence from the provider’s innovation cycle. Customers using standard connections must wait for their provider to upgrade to new standards (e.g., 400G or 800G). A dark-fiber user, however, can increase capacity at any time simply by replacing the SFP modules at the endpoints.
This reduces long-term costs and provides strategic flexibility in network design.
