Understanding TIA-568 can lead to more consistent loss
measurements: TIA standards for structured cabling include many
details on the installation and testing of fiber optic cabling,
but some of the requirements are unusual and not well-explained,
although they can be very important to the installer. One in
particular, the use of a “mandrel wrap” on a multimode launch
reference cable to create a standardized test condition, has
always been a source of confusion. Why do you need to wind the
launch cable around a mandrel anyway? How does it work? What
effect does it have on the measurement? To comprehend the effect
of a mandrel wrap, you must first understand how light is
transmitted in multimode fiber. This fiber is called multimode
because it transmits light in many modes or rays of light, which
travel in curving (sine wave) paths (see Figure 1). Notice the
light in some modes stays close to the center of the fiber core
(called lower-order modes), while others (called higher-order
modes) go close to the edge