  Video conferencing applications (VCAs) have become a critical Internet
application, even more so during the COVID-19 pandemic, as users worldwide now
rely on them for work, school, and telehealth. It is thus increasingly
important to understand the resource requirements of different VCAs and how
they perform under different network conditions, including: how much speed
(upstream and downstream throughput) a VCA needs to support high quality of
experience; how VCAs perform under temporary reductions in available capacity;
how they compete with themselves, with each other, and with other applications;
and how usage modality (e.g., number of participants) affects utilization. We
study three modern VCAs: Zoom, Google Meet, and Microsoft Teams. Answers to
these questions differ substantially depending on VCA. First, the average
utilization on an unconstrained link varies between 0.8 Mbps and 1.9 Mbps.
Given temporary reduction of capacity, some VCAs can take as long as 50 seconds
to recover to steady state. Differences in proprietary congestion control
algorithms also result in unfair bandwidth allocations: in constrained
bandwidth settings, one Zoom video conference can consume more than 75% of the
available bandwidth when competing with another VCA (e.g., Meet, Teams). For
some VCAs, client utilization can decrease as the number of participants
increases, due to the reduced video resolution of each participant's video
stream given a larger number of participants. Finally, one participant's
viewing mode (e.g., pinning a speaker) can affect the upstream utilization of
other participants.
