  Multi-node optical clock networks will enable future studies of fundamental
physics and enable applications in quantum and classical communications as well
as navigation and geodesy. We implement the first ever multi-node optical clock
network with real-time, relative synchronization over free-space communication
channels and precision on the order of 10 fs, realized as a three-node system
in a hub-and-spoke topology. In this paper we describe the system and its
performance, including a new, independent, out-of-loop verification of two-way
optical time synchronization.
