The IEC has published a new standard for the testing of fibre optic cabling. IEC 61280-4-5 provides test methods to measure the attenuation of installed multimode and single-mode optical fibre cabling plant as well as the determination of their polarity and length. Fiber optic testing of a newly installed system not only verifies that the system meets its design requirements, but also creates a performance baseline for all future testing and troubleshooting of t at system. OTDR testing requires interpretation of the data acquired, called the trace or signature, by a skilled operator. It helps find breaks, shows cable length, and checks connection quality. Using an OTDR often stops network problems.