Ease the queue oscillation: analysis and enhancement of DCTCP

Because of the terrible performance of TCP protocol
in data center environment, DCTCP has been proposed as
a TCP replacement, which uses a simple marking mechanism
at switches and a few amendments at end hosts to adjust
congestion window based on the extent of the congestion in
networks. Thus, DCTCP can make a proper tradeoff between
high throughput and low latency. However, through our observation,
we discover that DCTCP causes severe oscillation of
queue under some parameters and network configuration. Our
perceptual analysis concludes that the rough single-threshold
marking mechanism may be the essential reason. Therefore,
we propose Double-Threshold DCTCP as an improvement of
DCTCP. Then, by applying describing function method in nonlinear
control theory, we analyze the stability of both DCTCP
and Double-Threshold DCTCP, and theoretically explain why
Double-Threshold DCTCP is more stable than DCTCP. At last,
we validate theoretical analysis and conclude that the Double-
Threshold DCTCP can achieve smaller queue, and the queue
length of Double-Threshold DCTCP is less sensitive to the
growing number of flows. Further, Double-Threshold DCTCP
can postpone the throughput collapse caused by Incast traffic
and reduce the tail latency in completion time experiment.