GIT-CERCS-04-09
Hao Jiang, Constantine Dovrolis,
The origin of TCP traffic burstiness in short time scales
Internet traffic exhibits multifaceted burstiness and correlation structure
over a wide span of time scales. Previous work analyzed this structure in terms
of heavy-tailed session characteristics, as well as TCP timeouts and congestion
avoidance, in relatively long time scales. We focus on shorter scales,
typically less than 100-1000 milliseconds. Our objective is to identify the
actual mechanisms that are mostly responsible for creating bursty traffic in
those scales. We show that TCP self-clocking, joint with queueing in the
network,
can shape the packet interarrivals of a TCP connection in a two-level ON-OFF
pattern. This structure creates strong correlations and burstiness in time
scales that extend up to the Round-Trip Time (RTT) of the connection,
especially for bulk transfers that have a large bandwidth-delay product
relative to their window size. Also, the aggregation of many flows, without
rescaling their packet interarrivals, does not converge to a Poisson stream, as
one might expect from classical superposition results. Instead, the burstiness
in those scales can be significantly reduced by TCP pacing, depending however
on the minimum pacing timer. Finally, we show that sub-RTT burstiness is
important in queueing performance not only in moderate load conditions, as
previously shown, but also in high loads when the bottleneck buffer size is
relatively small.