An Evaluation of Fairness Among Heterogeneous TCP Variants Over 10Gbps High-speed Networks Lin Xue*, Suman Kumar', Cheng Cui* and Seung-Jong Park* *School of Electrical Engineering and Computer Science, Center for Computation & Technology, Louisiana State University, USA 'Department of Computer Science, Troy University, USA CRON (  Cyber-infrastructure of Reconfigurable Optical Networks  Experimental networking testbed for 10Gbps high-speed networks 10Gbps Testbed Setup References  [1] P. Yang, W. Luo, L. Xu, J. Deogun, and Y. Lu, “Tcp congestion avoidance algorithm identification,” in Distributed Computing Systems (ICDCS), st International Conference on. IEEE, 2011, pp. 310–321.  [2] Ao Tang; Xiaoliang Wei; Low, S.H.; Mung Chiang;, "Equilibrium of Heterogeneous Congestion Control: Optimality and Stability," Networking, IEEE/ACM Transactions on, vol.18, no.3, pp , June 2010 Introduction and Background Components  Hardware Cisco N5000 switch with 48 X 10Gbps ports High-end servers with 10GE NICs 10Gbps hardware emulators  Software Emulab-based interface & controller 10Gbps software emulators (optimized 10Gbps Dummynet ) Experimental Design  Dumbbell Topology 2 10Gbps Linux Router (4X10Gbps NICs) 3 X 10Gbps links (120ms delay) 3 senders and 3 receivers running heterogeneous TCP flows Evaluation of Fairness Among Heterogeneous TCP Variants Heterogeneous TCP variants  Traditional network is rapidly evolving into a heterogeneous one.  According to a recent study on 5000 most popular web servers[1]: Fairness Problem for heterogeneous TCP flows  Every TCP employs its own congestion control mechanism.  Fairness among heterogeneous TCP variants depends on router parameters such as queue management schemes and buffer size[2]  Software OS: Optimized Ubuntu 64bit & FreeBSD 64bit Measurement S/W : Zero- copy Iperf TCP variants: TCP-SACK, HSTCP, CUBIC, etc. Patched Queue Management schemes: Drop-tail, RED, CHOKe, etc. High-speed TCP congestion control variants Queue Management Schemes Homogeneous TCP vs. Heterogeneous TCP  Fairness index for buffer size = 20% BDP, RTT = 120ms 1 TCP-SACK, 1 CUBIC, and 1 HSTCP flow 10 TCP-SACK, 10 CUBIC, and 10 HSTCP flow10 TCP-SACK, 10 CUBIC, and 10 HSTCP flow with short-lived TCP flows Fairness for Heterogeneous TCP flows  Three scenarios 1 TCP-SACK, 1 CUBIC, and 1 HSTCP flow 10 TCP-SACK, 10 CUBIC, and 10 HSTCP flow 10 TCP-SACK, 10 CUBIC, and 10 HSTCP flow with short-lived TCP flows  Active queue management schemes (e.g. RED, CHOKe) perform better fairness than Drop-tail for large buffer sizes  All three queue management schemes show same fairness behavior for small buffer sizes  Short-lived TCP flows improve fairness in heterogeneous TCP networks Throughput for Heterogeneous TCP flows  Tradeoff between fairness and throughput  Drop-tail performs the best among three queue management schemes Loss Synchronization Effect  AQM schemes make de-synchronization of TCP flows  Very small buffer sizes (e.g. 1% BDP) create TCP loss synchronization Buffer Size = 20% de-synchronization Buffer Size = 1% synchronization