Learn how OTDR testing works and compare ZION OTDR models to choose the best tester for FTTH, PON, ODN, and backbone networks. VIAVI provides the widest range of OTDR testing tools delivering everything from basic fiber certification to fully automated bidirectional OTDR testing that scales for multi-fiber cable certification. The lightweight and compact SmartOTDR speeds and optimizes field testing of metro and access. This is why OTDR (Optical Time Domain Reflectometer) testing has become essential for construction acceptance, maintenance, and troubleshooting. Automatic, bidirectional IL, ORL.