Fiber to the x or fiber in the loop is a generic term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last-mile telecommunications. As fiber optic cables are able to carry much more data than copper cables, especially over long distances, copper telephone networks built in the 20th century are being replaced by fiber.

FTTX is a generalization for several configurations of fiber deployment, arranged into two groups: FTTPFTTHFTTB (Fiber laid all the way to the premiseshomebuilding) and FTTCN (fiber laid to the cabinetnode, with copper wires completing the connection).

Residential areas already served by a balanced pair distribution plant call for a trade-off between cost and capacity. The closer the fiber head, the higher the cost of construction and the higher the channel capacity. In places not served by metallic facilities, the little cost is saved by not running fiber to the home.

Fiber to the x is the key method used to drive next-generation access (NGA), which describes a significant upgrade to the broadband available by making a step change in the speed and quality of the service. This is typically thought of as asymmetrical with a download speed of 24 Mbits plus and a fast upload speed. Ofcom has defined super-fast broadband as “broadband products that provide a maximum download speed that is greater than 24 Mbits - this threshold is commonly considered to be the maximum speed that can be supported on current generation (copper-based) networks.”

A similar network called a hybrid fiber-coaxial (HFC) network is used by cable television operators but is usually not synonymous with “fiber In the loop”, although similar advanced services are provided by the HFC networks. Fixed wireless and mobile wireless technologies such as Wi-Fi, WiMAX and 3GPP Long Term Evolution (LTE) are an alternative for providing Internet access.