Nonlinear Instabilities in D2TCP-II

Abstract: In the era of heavy-duty transmission control protocols (TCP), adapted for extremely hi-bandwidth datacenters, the fundamental question of stable interaction with either proposed active queue management(AQM) or popularly discussed Random Early Detection (RED) remains a hotly debated issue. While there are claims of "oscillation" only dynamical behavior, there are equally large number of claims which demonstrate the chaotic nature of different flavors of TCP and their AQM interaction. In this work, we provide a sound and analytical mathematical model of DTCP/D2TCP and study their interaction with threshold based packet marking policy. Our work shows that for a simple scenario this interaction is chaotic in nature and has large variability in dynamical behavior over orders of magnitude changes in parameter range as demonstrated by bifurcation diagrams. We conclude with numerical simulation evidence that chaotic behavior of protocols is inherent in their design which they inherit from their early vanilla TCP days, and it has serious implications for data-center throughput, load batching and collapse in Incast kind of scenario.