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\section{Existing Work}   To ~~To  address the problem of congestion in datacenter, there are mainly two types of work. The ~~The  first one is implicit congestion control by using ECN to forecast buffer overflow in switch/router, e.g. DCTCP \cite{bhakar_Sengupta_Sridharan_2010} and D2TCP \cite{Vamanan_Hasan_Vijaykumar_2012}. These works are well-compatible with current devices. However modifying the size of slide windows smoothly needs more than a several RTTs of time. This seemly short period of time is actually to the small flows. Another ~~Another  type of approaches are explicit flow control in switch/router, e.g. D3\cite{llani_Karagiannis_Rowtron_2011}, PDQ\cite{Hong_Caesar_Godfrey_2012}, pFabric \cite{McKeown_Prabhakar_Shenker_2013}. Though the design can be much easier, and simulation results seem great, it is hard to implement into real world, because they need hardware changes such as special-designed switch/router. The table below shows the comparison of 5 approaches in five metrics. \begin{table}  \begin{tabular}{lccccc}