All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 1 Transport-layer optimization for thin-client systems Yukio OGAWA Systems Development Laboratory, Hitachi, Ltd. Go HASEGAWA, Masayuki MURATA Osaka University 2007 International CQR Workshop May 15-17, 2007

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 2 Overview of thin-client systems office Internet data center thin client intranet VPN gateway server satellite office, home, desktop service without data, apps thin client user event screen updates Isolating computer resources from users resource management, user mobility System performance depends on network performance VPN: Virtual Private Network TCP proxy

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 3 Research objective and our approach System performance (usability) depends on network performance. - intranet performance – designed in advance, controllable - Internet performance – uncontrollable Improve performance of thin-client traffic - especially of flows traversing Internet - thin-client traffic = long-lived interactive TCP data flows - affected by TCP's Nagle algorithm and delayed ACK - affected by buffering of TCP segments and SSR Transport layer optimization on basis of actual traffic observations - observation of Hitachi SDL's prototype system - Dec. 20, 2006 to Jan. 25, pairs of a server and a thin-client - number of co-existing sessions during office hours: several dozen research objective drawback our approach

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 4 Characteristics of thin-client traffic - traffic patterns clientserver time request response large interval interactive data flow (character information) clientserver time bulk data flow (screen update information) request response distinguished by interarrival time of response packets size of data segment time MSS m ( n MSS + a ) MSS: Maximum Segment Size ~10 2 packets short interval

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 5 Characteristics of thin-client traffic - interarrival time distribution of request packets data segment size (log10 bytes) access from Internet interarrival time of request packets (log10 sec)

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 6 Characteristics of thin-client traffic - interarrival time distribution of response packets data segment size (log10 bytes) access from Internet interarrival time of response packets (log10 sec) m sec interactive bulk (head) bulk (inside of 'nMSS+a') bulk (head of 'nMSS+a') data segment size time MSS head inside head of 'nMSS+a'inside of 'nMSS+a' bulk interactive

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 7 Proposed methods for improving performance - interactive data flow clientserver time request response gateway (TCP proxy) × TiTi titi sending copy of data packet sending interval t i = min( RTT – RTT min, T i / 2 ) 1h1h

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 8 Proposed methods for improving performance - bulk data flow clientserver time gateway (TCP proxy) request response no SSR data segment size time MSS m ( n MSS + a ) data segment size time MSS n MSS + a MSS: Maximum Segment Size SSR: Slow-Start Restart paused for buffering resegmenting TCP data segments

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 9 Simulation model - system model R R R router 20 Mbps, 5 msec sender host (server) gateway (TCP proxy) receiver host (client) 20 Mbps, 0.1 msec 1 Mbps, 30 – 300 msec 100 Mbps, 0.1 msec intranet Internet receiver hosts sender hosts thin-client traffic background traffic (UDP: 64 bytes, 128 Kbps) x n packet drop ratio: 0, 3% tail-drop router (buffer size 50, 1024 packets) bottleneck link

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 10 Simulation model - thin-client traffic for evaluation interactive bulk (-0.6, -1.3) : -1.3 = mean - 2 std (-0.6, -0.6) access from Internet average interarrival time of response packets (log10 sec ) evaluation traffic number 30 duration 60 sec -6-5 average interarrival time of response data flows (contiguous packets) (log10 sec)

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 11 Simulation results - interactive data flow – packet drop average number of packet drops (log10) transmission delay of bottleneck link (log10 msec) (UDP 1024 Kbps)(UDP 1152 Kbps)(UDP 1280 Kbps) bottleneck link - 1 Mbps - 3% drop ratio router buffer - 50 packets send a copy with pause send a copy without pause send no copies bg: background drop from tail-drop router random drop from bottleneck link

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 12 Simulation results - bulk data flow – transfer time median transfer time (log10 sec) number of packets in bulk data flow (log10) buffer size = 1024 packets bottleneck link - 1 Mbps - 80 msec - 0% drop ratio background - 3 UDP flows (= 384 Kbps) no-SSR, resegmentation no-SSR buffer size = 50 packets SSR, resegmentation SSR

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 13 transmission delay of bottleneck link (log10 msec) Simulation results - bulk data flow – drop from tail-drop router (UDP 384 Kbps) no-SSR, resegmentation no-SSR SSR, resegmentation SSR bottleneck link - 1 Mbps - 0% drop ratio router buffer - 50 packets (UDP 768 Kbps) bg: background average number of packet drops (log10)

All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd. 14 Conclusion for interactive data flows (transferring character information) - send a packet copy with pause increases tolerance for packets drops for bulk data flows (transferring screen update information) - disable TCP slow-start restart increases packet sending rate increases burstiness of traffic - resegment TCP data segments reducees burstiness of traffic TCP optimization for improving performance of thin-client traffic