Abstract: An OLT includes a topology map holder that holds a topology map of a PON system, a link interruption detector that detects a link interruption of an ONU, a warning collector that collects warnings from an ONU, a filter that extracts a warning resulting from an ONU from the warnings collected by the warning collector, a fault part estimator that, when a link interruption of an ONU is detected by the link interruption detector and there is no warning which is extracted by the filter, estimates in which of optical fiber cables a fault has occurred on the basis of the topology map held by the topology map holder, and a fault part notifier that notifies information showing the fault part estimated by the fault part estimator to outside the OLT.

Abstract: A base station assigns a most appropriate carrier from wide frequency bands in response to a re-request for channel establishment received from a mobile station, even if a same slot as a slot last assigned is assigned. Furthermore, a frequency management table is managed in which carriers that form a radio channel and are grouped by a specific number thereof so as to be distributed over wide frequency bands. Priorities used to search groups are individually provided for base stations that form a system. This allows neighboring base stations to distribute carriers over the wide frequency bands.

Abstract: A base station assigns a most appropriate carrier from wide frequency bands in response to a re-request for channel establishment received from a mobile station, even if a same slot as a slot last assigned is assigned. Furthermore, a frequency management table is managed in which carriers that form a radio channel and are grouped by a specific number thereof so as to be distributed over wide frequency bands. Priorities used to search groups are individually provided for base stations that form a system. This allows neighboring base stations to distribute carriers over the wide frequency bands.