An optical line terminal (OLT) for an optical network configured to communicate with optical network units (ONUs) in a PON-type optical network, the OLT including: a processing circuitry, for each ONUs, to manage a transmission delay time in transmission to the ONU to manage an acceptable waiting time of uplink data of the ONU; to obtain an uplink transmission start time and data amount of the optical network unit, based on uplink assignment information; and to generate uplink transmission grant information, which is made up of a time point and time length of uplink transmission to the ONU, wherein the processing circuitry determines the uplink transmission grant information on transmission to the ONU, based on a transmission delay time of the ONU, on the uplink transmission start time and data amount of the ONU, and on the acceptable waiting time of uplink data of the ONU.