AN OTDR TEST SYSTEM AND OTDR TEST METHOD FOR A TWDM PON

An optical time domain reflectometry (OTDR) test system detects a physical impairment in a TWDM PON in operational use by a service provider, and thereto comprises a processor (107; 207; 307; 407) configured to: - assess the status of the TWDM PON; - select a test channel amongst the available TWDM channels for an OTDR test through an optimization criterion minimizing impact for one or more users; - move optical network terminations or ONTs (171, 175; 271, 275; 371, 275; 471, 475) that are using the test channel to alternate TWDM channels; - instruct injection of an OTDR test signal by the respective laser (121; 221; 321; 421) in the optical line termination or OLT (101; 201; 301; 401) into the test channel; - capture reflections of the OTDR test signal at the OLT (101; 201; 301; 401); - move the ONTs (171, 175; 271, 275; 371, 275; 471, 475) back to the test channel or a more optimal channel configuration; and - process the reflections of the OTDR test signal to detect the physical impairment.