The present disclosure relates to an optical line terminal, OLT, which is enabled to range optical network units, ONUs, in a point-to-multipoint optical network by detecting interference burst sequences transmitted by one or more joining ONUs during transmission of upstream data traffic from transmitting ONUs. The present disclosure further relates to an optical network unit, ONU, which is enabled to transmit, at a selected transmission time, an interference burst sequence including a sequence of pulses allowing the OLT to identify the ONU as a joining ONU.