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Lit fiber vs. dark fiber services explained for enterprise WANs
Lit fiber and dark fiber each offer enterprises a distinct set of advantages and challenges. It's important that IT leaders carefully assess which deployment makes the most sense.
In the past, copper-based cables underpinned WANs worldwide. Fiber optics have largely replaced these lines. Fiber, composed of thin strands of glass or plastic, delivers data as light pulses at speeds much faster than electrons in copper.
Today, fiber links corporate headquarters, branch offices, extended offices, remote locations, partners, vendors, employees and data centers. The enterprise network infrastructure now operates on a decoupled layer of fiber and software-defined virtual networks.
Fiber comes in two forms: lit and dark. The choice between the two depends on whether enterprises would rather buy a service or invest in existing infrastructure.
Lit fiber vs. dark fiber
Lit fiber is activated, ready to use and managed by the vendor. It's a finished product that an enterprise pays for. Dark fiber, on the other hand, is fiber that hasn't been activated by optical networking equipment. With dark fiber, enterprises must build everything from scratch to make it operational. Think of lit fiber as a furnished apartment, while dark fiber is an unfinished space.
Lit fiber
With lit fiber, the service provider delivers both the fiber and the associated optical equipment necessary to get it started. Maintenance, monitoring and replacement are all part of the provider's service. The bandwidth capacity is well-defined and guaranteed under the service-level agreements between the vendor and the enterprise.
Lit fiber is a quick way to initiate network operations for medium- and large-sized companies with geographically dispersed offices. Lit fiber is also a viable option for new greenfield businesses and startups that need to prioritize convenience and ease of use.
Dark fiber
Dark fiber can be a long-term leased service or a purchased infrastructure. IT leaders can rent or purchase non-functional fiber from manufacturers or service providers. Once a company has acquired fiber, it must activate it to make it operational. Dark fiber is feasible for compliance-heavy and critical industries that want to control and safeguard information flow.
Choose fiber infrastructure services
Most enterprises use lit fiber services. Hyperscalers rely on dark fiber infrastructure. IT leaders must carefully consider the financial effects of fiber: Lit fiber drives higher recurring OpEx; dark fiber involves higher upfront CapEx.
Other factors of fiber infrastructure include the following:
- Cost cycle. As lit fiber is a managed service, enterprises need to pay for installation, configuration, subscription, upgrades and maintenance costs. Even with higher CapEx, dark fiber tends to provide a lower cost-per-gigabit than lit fiber in the long run.
- Technical expertise. In addition to the one-time cost of equipment, developing and deploying dark fiber and associated hardware requires extra staffing. Some enterprises commission new job positions or contract roles that integrate optical engineering with networking expertise. Service provider teams are fully responsible for managing the lit fiber lifecycle.
- Deployment cycle. Dark fiber could take months to become fully operational. Lit fiber might take days or weeks, depending on the vendor.
- Scalability goals. Lit fiber offers bandwidth in a pre-defined range. Dark fiber can, in theory, offer high bandwidth and ultra-low latency to scale enterprise AI and machine learning workloads. Lit services are suitable for moderate bandwidth usage and latency limits.
- Customization. If an enterprise needs to increase lit fiber bandwidth, it might need to migrate to a more expensive plan and wait for the changes to be implemented. Dark fiber is flexible and faster to customize.
- Fault management. In dark fiber, engineering teams are responsible for fault management. In-house teams can fix issues more quickly than service provider technicians.
- Security and control. Dark fiber provides end-to-end security control and routing. Fiber routes aren't shared with other enterprises or nearby public areas, which gives enterprises more control. Third-party data access is often limited. Enterprises can add advanced encryption. The level of security -- for both dark and lit fiber -- depends on the cybersecurity team's expertise and the software deployed.
Private fiber
Private fiber is a physically isolated conduit that doesn't traverse the public internet, usually fully owned by the enterprise or government. Planning and laying fiber is typically the responsibility of a civil engineering team -- unless it's undersea, in which case it's the responsibility of a maritime team -- followed by the networking team to handle the technical work.
Multiple offices, hundreds of miles apart, can be connected by private fiber. Because ownership can cost billions of dollars, hyperscalers typically own and operate subsea cables. With private fiber, enterprises can gain total control and full capacity, achieve the lowest long-term costs and ensure end-to-end security.
Because deploying fiber is an expensive proposition, IT leaders must carefully plan their lit fiber or dark fiber implementation strategies. Lit services are better suited to geographically distributed offices and use cases that prioritize shorter deployment cycles and moderate network efficiency requirements. Dark fiber is better for enterprises that transmit high volumes of data and for companies that need to secure and fully control the information they manage.
Venus Kohli is an engineer turned technical content writer, having completed a degree in electronics and telecommunication at Mumbai University in 2019. Kohli writes for various tech and media companies on topics related to semiconductors, electronics, networking, programming, quantum physics and more.
