Optical fiber technology is firmly established as an economic preference for long-haul and interoffice telephony transmission applications. For the local network, fiber optics has been less pervasive to date, primarily due to the issue of return on capital plant investment. The fiber optics market growth for telephony has been relatively flat for the past few years while the industry has pondered ways of penetrating the network for local services distribution. Having proven itself in high performance usage, such as long distance and high capacity trunk routes, fiber optic systems must now evolve to meet the "Local Loop Challenge". The migration of fiber from the local switching office or wire center toward the home has been slower than many had hoped, but according to the number of field trials (at last count 12-15 in the USA alone) there is a significant commitment by the Operating Telephone Companies to the implementation of such systems. Perhaps the state of the market for fiber optics in local applications can be compared with the evolving ISDN (integrated services digital network) environment. The core technology readily exists, yet there is debate among the industry as to the form the applications of the technology will take. Thus these local loop trials are intended to help the industry identify the most promising services and architectures for the subscriber network.