  The choice of feedback mechanism between delay and packet loss has long been
a point of contention in TCP congestion control. This has partly been resolved,
as it has become increasingly evident that delay based methods are needed to
facilitate modern interactive web applications. However, what has not been
resolved is what control should be used, with the two candidates being the
congestion window and the pacing rate. BBR is a new delay based congestion
control algorithm that uses a pacing rate as its primary control and the
congestion window as a secondary control. We propose that a congestion window
first algorithm might give more desirable performance characteristics in
situations where latency must be minimized even at the expense of some loss in
throughput. To evaluate this hypothesis we introduce a new congestion control
algorithm called TCP D*, which is a congestion window first algorithm that
adopts BBR's approach of maximizing delivery rate while minimizing latency. In
this paper, we discuss the key features of this algorithm, discuss the
differences and similarity to BBR, and present some preliminary results based
on a real implementation.
