  For data communications over long distances, optical wireless satellite
networks (OWSNs) can offer lower latency than optical fiber terrestrial
networks (OFTNs). However, when is it beneficial to switch or crossover from an
OFTN to an OWSN for lower latency data communications? In this work, we
introduce a crossover function that enables to find the crossover distance,
i.e., a distance between two points on the surface of the Earth beyond which
switching or crossing over from an OFTN to an OWSN for data communications
between these points is useful in terms of latency. Numerical results reveal
that a higher refractive index of optical fiber (or $i$) in an OFTN and a lower
altitude of satellites (or $h$) in an OWSN result in a shorter crossover
distance. To account for the variation in the end-to-end propagation distance
that occurs over the OWSN, we examine the crossover function in four different
scenarios. Numerical results indicate that the crossover distance varies with
the end-to-end propagation distance over an OWSN and is different for different
scenarios. We calculate the average crossover distance over all scenarios for
different $h$ and $i$ and use it to evaluate the simulation results.
Furthermore, for a comparative analysis of OFTNs and OWSNs in terms of latency,
we study three different OFTNs having different refractive indices and three
different OWSNs having different satellite altitudes in three different
scenarios for long-distance inter-continental data communications, including
connections between New York and Dublin, Sao Paulo and London, and Toronto and
Sydney.
