Whilst fiber optic cables can carry data at high speeds over long distances, copper cables used in traditions telephone lines and ADSL cannot. Fiber to the x (FTTX) 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.