  Data centers traffic is composed by numerous latency-sensitive "mice" flows,
which is consisted of only several packets, and a few throughput-sensitive
"elephant" flows, which occupy more than 80% of overall load. Generally, the
short-lived "mice" flows induce transient congestion and the long-lived
"elephant" flows cause persistent congestion. The network congestion is a major
performance inhibitor. Conventionally, the hop-by-hop and end-to-end flow
control mechanisms are employed to relief transient and persistent congestion,
respectively. However, in face of the mixture of elephants and mice, we find
the hybrid congestion control scheme including hop-by-hop and end-to-end flow
control mechanisms suffers from serious performance impairments. As a step
further, our in-depth analysis reveals that the hybrid scheme performs poor at
latency of mice and throughput of elephant. Motivated by this understanding, we
argue for isolating mice and elephants in different queues, such that the
hop-by-hop and end-to-end flow control mechanisms are independently imposed to
short-lived and long-lived flows, respectively. Our solution is
readily-deployable and compatible with current commodity network devices and
can leverage various congestion control mechanisms. Extensive simulations show
that our proposal of isolation can simultaneously improve the latency of mice
by at least 30% and the link utilization to almost 100%.
