On the coexistence of transport protocols in data centers

The emergence of cloud data centers has led to the design of customized transport protocols such as Data Center TCP (DCTCP). These protocols improve the performance of cloud applications by explicitly accounting for the unique network and traffic characteristics in data centers. However, such protocols have only been evaluated under greenfield deployment scenarios, where the entire data center is assumed to use the same protocol, which may not always be desirable or feasible. This leads to scenarios where these protocols coexist with TCP and thus share the same network resources. This paper considers such scenarios and presents a comprehensive study of the coexistence of DCTCP and TCP. In particular, we evaluate their bandwidth sharing properties under different active queue management schemes (AQM) including RED, DCTCP AQM, and CHOKe. Our results show that under the DCTCP AQM, DCTCP can starve TCP flows. This problem is mitigated through the use of RED, however, significant unfairness remains. Interestingly, we find that CHOKe exacerbates this unfairness. We show that a modified version of CHOKe considerably improves fairness by more accurately penalizing dominating flows.