All the optical fiber that is laid, but not yet illuminated by data transmission equipment. Operators always install more cables than they intend to use at the time of installation to anticipate future demand for this type of networkNetwork In computer language, the term network defines a set of hardware and software devices which, when linked together, enable the exchange and sharing of resources, data or information. In a computer network, the devices that generate, route and terminate data are called network nodes.. This is primarily possible because the cost of fiber optics is a fraction of the total cost of building infrastructure (excavation, work sites, etc.). Dark fiberDark fiber All the optical fiber that is laid, but not yet illuminated by data transmission equipment. Operators always install more cables than they intend to use at the time of installation to anticipate future demand for this type of network. This is primarily possible because the cost of fiber optics is a fraction of the total cost of building infrastructure (excavation, work sites, etc.). Dark fiber can then be rented and bought by entities that then connect their own transmission equipment to it. can then be rented and bought by entities that then connect their own transmission equipment to it.