  Middleboxes such as web proxies, firewalls, etc. are widely deployed in
today's network infrastructure. As a result, most protocols need to adapt their
behavior to co-exist. One of the most commonly used transport protocols, QUIC,
adapts to such middleboxes by falling back to TCP, where they block it. In this
paper, we argue that the blind fallback behavior of QUIC, i.e., not
distinguishing between failures caused by middleboxes and that caused by
network congestion, hugely impacts the performance of QUIC. For this, we focus
on YouTube video streaming and conduct a measurement study by utilizing
production endpoints of YouTube by enabling TCP and QUIC at a time. In total,
we collect over 2600 streaming hours of data over various bandwidth patterns,
from 5 different geographical locations and various video genres. To our
surprise, we observe that the legacy setup (TCP) either outperforms or performs
the same as the QUIC-enabled browser for more than 60% of cases. We see that
our observation is consistent across individual QoE parameters, bandwidth
patterns, locations, and videos. Next, we conduct a deep-dive analysis to
discover the root cause behind such behavior. We find a good correlation
(0.3-0.7) between fallback and QoE drop events, i.e., quality drop and
re-buffering or stalling. We further perform Granger causal analysis and find
that fallback Granger causes either quality drop or stalling for 70% of the
QUIC-enabled sessions. We believe our study will help designers revisit the
decision to enable fallback in QUIC and distinguish between the packet drops
caused by middleboxes and network congestion.

Networking and Internet Architecture;Systems and Control;Systems and Control