As the name implies, bidirectional OTDR testing is a method of optical fiber characterization and loss testing that is performed from both ends of the fiber run. Both TIA and ISO standards use the term “Tier 1” to describe testing with an OLTS. An OTDR characterizes the loss of the link for individual splices and connectors by transmitting light pulses into a fiber and measuring the amount of light reflected from each pulse. As the components like fiber, connectors, splices, LED or laser sources, detectors and receivers are being developed, testing confirms their performance specifications and helps. For every fiber optic cable plant, you will need to test for continuity, end-to-end loss and then troubleshoot the problems.