  The practical realization of beam steering mechanisms in millimeter wave
communications has a large impact on performance. The key challenge is to find
a pragmatic trade-off between throughput performance and the overhead of
periodic beam sweeping required to improve link quality in case of transient
link blockage. This is particularly critical in commercial off-the-shelf
devices, which require simple yet efficient solutions. First, we analyze the
operation of such a commercial device to understand the impact of link blockage
in practice. To this end, we measure TCP throughput for different traffic loads
while blocking the link at regular intervals. Second, we derive a Markov model
based on our practical insights to compute throughput for the case of transient
blockage. We use this model to evaluate the trade-off between throughput and
periodic beam sweeping. Finally, we validate our results using throughput
traces collected using the aforementioned commercial device. Both our model and
our practical measurements show that transient blockage causes significant
signal fluctuation due to suboptimal beam realignment. In particular,
fluctuations increase with traffic load, limiting the achievable throughput. We
show that choosing lower traffic loads allows us to reduce fluctuations by 41%
while achieving the same net throughput than with higher traffic loads.
