Lit fiber is fiber-optic service where the provider supplies, operates and maintains the equipment that sends light over the fiber, and sells you a connection at a defined speed. You plug into a port the provider hands off; the provider runs everything between that port and the other end. Most business fiber services, including dedicated internet access, Ethernet private lines, MPLS ports and wavelengths, are lit services. The term is mostly used to contrast with dark fiber, where you lease the strands and light them yourself.
At a glance
- With lit fiber, the provider runs the optical equipment; you buy a service with a set speed and hand-off.
- Common lit services include dedicated internet access, Ethernet private lines, MPLS and wavelengths.
- It sits at one end of a spectrum: dark fiber (you light it), dim fiber or wavelengths (dedicated optical capacity the provider manages), and fully lit services.
- Capacity may be dedicated or shared, depending on the service; ask which applies.
- Upgrades usually depend on the provider’s equipment and available capacity, not your own hardware.
What problem it solves
Fiber can carry enormous capacity, but using it takes optical equipment, network engineering and around-the-clock operations. Many organizations do not want to buy transceivers and multiplexers, plan optical power budgets, or monitor and repair long-haul links.
Lit fiber hands that work to the provider. You choose a speed, such as 1, 10 or 100 Gbps, and a service type, and the provider designs, installs and operates the path. You get a defined hand-off, an SLA and one provider accountable for faults under the contract. For most businesses connecting offices, data centers and the internet, lit services are the practical way to use fiber.
How it works
Physical path. The provider uses fiber it owns or leases between your sites and its network, often including a last-mile segment into each building.
Provider equipment. At each end and in its network, the provider installs the optical and switching gear that lights the fiber: transceivers, multiplexers such as DWDM systems, routers or switches. That equipment determines the speeds and services available.
Service layer. On top of the optical layer, the provider delivers a specific service:
- A wavelength gives a dedicated optical channel between two points at a fixed rate.
- An Ethernet private line gives a point-to-point layer 2 connection.
- Dedicated internet access gives a committed-rate internet connection.
- MPLS or other private WAN services connect many sites.
Hand-off. The provider presents a port, copper or optical, at your demarcation point. You connect your router, switch or firewall to it.
Operations. The provider monitors the service, handles faults and manages capacity. SLAs typically cover availability and repair time, and sometimes latency between endpoints.
To compare lit services with dark fiber and wavelengths for your sites, see our Wavelength solution page.
When it matters for buyers
- Connecting data centers or large offices. Choose between lit services, wavelengths and dark fiber based on capacity, distance, cost and in-house skills.
- Limited network staff. Lit services keep optical operations with the provider.
- Growth planning. Ask how far you can upgrade before the provider must change equipment or build new fiber.
- Comparing quotes. Lit services from different providers can differ in what is dedicated, how diversity is engineered and what the SLA covers.
- Renewals. Lit service prices tend to fall over time in competitive markets, so older contracts may be above current rates.
Questions to ask vendors
- Which service type do you propose, and why that one rather than a wavelength or dark fiber?
- What capacity is dedicated to us, and where is it shared with other customers?
- What is the physical route, and can you provide a diverse second path?
- What hand-off port and optics will you provide at each end?
- What availability, repair time and latency commitments are in the SLA?
- How quickly can we upgrade speed, and what changes are needed?
How it differs from dark fiber
Dark fiber is fiber leased without provider equipment attached. You supply the optics, decide how much capacity to run, and take responsibility for operating and repairing the optical layer, often with the provider still maintaining the cable itself. Lit fiber is the opposite: the provider operates everything and sells you a service at a defined speed. Dim fiber and wavelengths sit between the two, giving you dedicated optical capacity that the provider still manages. Dark fiber gives the most control and capacity headroom; lit fiber needs the least in-house expertise.