This procedure can be used to measure the optical loss between any two passively-connected points, including end terminations, of a single-mode optical fiber cable piant. The optical fiber cable plant, as the term is used here, may consist of optical fiber cables, connectors, mounting panels, jumper cables, and other passive components, but may not include active components.

Two methods for measuring the installed cable plant loss are described. Method A uses optical power measurement equipment. Method B uses an Optical Time Domain Reflectometer (OTDR). Method B provides an indirect estimate of the loss of the cable plant, and although calibration is possible, generally, more accurate or reliable values may be obtained by using Method A. If the values obtained by Method A and Method B differ from each other, the results of Method A shall be accepted as correct. Method B is not recommended for cable plants containing branching devices and/or isolators.