In some examples, high speed bidirectional OTDR-based testing may include transmitting data from a first end of a device under test (DUT) towards an optical time-domain reflectometer (OTDR) that is operatively connected to a second opposite end of the DUT. Further data that is transmitted by the OTDR may be received from the second opposite end of the DUT towards the first end of the DUT. Based on an amplitude of the further data, a direction of receiving of the further data may be adjusted towards a first receiver or towards a second receiver.