  As global cellular networks converge to 5G, one question lingers: Are we
ready for the 5G challenge? A growing concern surrounds how well do existing
congestion control algorithms perform in diverse 5G networks. Given that 5G
networks are not yet widely deployed, assessing the performance of existing
congestion control algorithms in realistic 5G settings presents several
challenges. Moreover, existing network simulation and emulation environments
are also not ideally suited to address the unique challenges of 5G network
environments. Therefore, building a simple and easily accessible platform
becomes crucial to allow testing and comparison of congestion control
algorithms under different testing conditions. This paper makes two main
contributions. First, we present Zeus, an open-source testbed that emulates 5G
channels to evaluate congestion control algorithms in a repeatable and
reproducible manner. Second, we assess and characterize ten of today's
state-of-the-art congestion control algorithms under different 5G environments
and show the difficulties of these solutions to achieve high performance under
highly varying 5G channel conditions. In addition, we also utilize the recently
proposed harm metric to characterize the detriment done by such algorithms to
TCP Cubic cross traffic in 5G environments.
