Abstract: In a conventional art, ONUs in services are significantly affected even when just one ONU is activated, and thus a communication bandwidth fails to be effectively utilized. To address this, an OLT includes a first distance information storing unit that stores information on the distance to an ONU in association with identification information which identifies the ONU (ONUi), and by using the distance information stored in the first distance information storing unit, an activation control unit controls activation of the ONUi.

Abstract: To shorten the service downtime as a communication system and to provide improved performance in communication by only checking if a device, in which the continuation of communication has become impossible, has recovered, a station terminating device includes: a connection management unit for maintaining without stopping a bandwidth allocation to a connected subscriber terminating device even when receiving a communication inability message from the subscriber terminating device; and a signal existence detection unit for detecting existence of a signal from the subscriber terminating device after receiving the communication inability message from the subscriber terminating device.