Reflections caused by connector interfaces "blind" OTDRs for a short period of time. The period of time it takes for an OTDR to recover from this "blindness" is commonly referred to as a "dead-zone". During this dead-zone period, OTDRs are unable to distinguish one anomaly (e.g. breaks, shatters, bends, or even another connector) from another.

The Optical Wavelength Labs FR-SM-500-FCFC Singlemode OTDR Fiber Ring, which is simply an extremely long patch cable with connectors on the ends, can be placed at the near-end patch panel to allow the OTDR detector port to recover from the OTDR port dead zone. The fiber ring also enables an OTDR to measure relative loss and reflectance through the near-end and far-end patch panels.