A first optical path and a second optical path have a common path branching point. An OTDR sampling optical signal is emitted into the first optical path and into the second optical path through the common path branching point. At least one predefined optical property of the OTDR sampling optical signal emitted into the second optical path is altered and/or of a reflection of the OTDR sampling optical signal received from the second optical path is altered. An OTDR reflected optical signal resulting from a reflection of the OTDR sampling optical signal on the first optical path and/or from a reflection on the second optical path is detected. The OTDR reflected optical signal is analyzed to determine, based on the at least one predefined optical property, whether the OTDR reflected optical signal resulted from a reflection on the first optical path and/or on the second optical path.