  Single-mode optical fiber is a highly efficient connecting medium, used not
only for optical telecommunications but also for the dissemination of
ultra-stable frequencies or timing signals. In 1994, Ma, Jungner, Ye and Hall
described a measurement and control system to deliver the same optical
frequency at two places, namely the two ends of a fiber, by eliminating the
"fiber-induced phase-noise modulation, which corrupts high-precision
frequency-based applications". We present a simple detection and control scheme
to deliver the same optical frequency at many places anywhere along a
transmission path, or in its vicinity, with a relative instability of 1 part in
$10^{19}$. The same idea applies to radio frequency and timing signals. This
considerably simplifies future efforts to make precise timing/frequency signals
available to many users, as required in some large scale science experiments.
