Editing Latency (engineering) (section)

===Fiber optics===
Latency in [[optical fiber]] is largely a function of the [[speed of light]].  This would equate to a latency of 3.33&nbsp;[[μs]] for every kilometer of path length.  The [[index of refraction]] of most fiber optic cables is about 1.5, meaning that light travels about 1.5 times as fast in a vacuum as it does in the cable.  This works out to about 5.0&nbsp;μs of latency for every kilometer.  In shorter metro networks, higher latency can be experienced due to extra distance in building risers and cross-connects. To calculate the latency of a connection, one has to know the distance traveled by the fiber, which is rarely a straight line, since it has to traverse geographic contours and obstacles, such as roads and railway tracks, as well as other rights-of-way.

Due to imperfections in the fiber, light degrades as it is transmitted through it. For distances of greater than 100 kilometers, [[Optical amplifier|amplifiers]] or [[Regenerator (telecommunication)|regenerators]] are deployed. Latency introduced by these components needs to be taken into account.