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Masaki Hirabaru masaki@nict.go.jp NICT Koganei 3rd e-VLBI Workshop October 6, 2004 Makuhari, Japan Performance Measurement on Large Bandwidth-Delay Product Networks
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An Example How much speed can we get? Receiver Sender a-2) High- Speed Backbone L2/L3 SW GbE 100M RTT 200ms a-1) Receiver Sender High- Speed Backbone SW GbE 100M RTT 200ms GbE SW GbE 100M
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Average TCP Throughput less than 20Mbps In case we limit the sending rate at 100Mbps This is TCP’s fundamental behavior.
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An Example (2) Receiver Sender High- Speed Backbone GbE RTT 200ms b) GbE Only 900 Mbps available
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Purposes Measure, analyze and improve end-to-end performance in high bandwidth-delay product, packet-switched networks –to support for networked science applications –to help operations in finding a bottleneck –to evaluate advanced transport protocols (e.g. Tsunami, SABUL, HSTCP, FAST, XCP, [ours]) Improve TCP under easier conditions –with a signle TCP stream –memory to memory –bottleneck but no cross traffic Consume all the available bandwidth
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TCP on a path with bottleneck bottleneck overflow queue The sender may generate burst traffic. The sender recognizes the overflow after the delay > RTT/2. The bottleneck may change over time. loss
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Web100 (http://www.web100.org) A kernel patch for monitoring/modifying TCP metrics in Linux kernel We need to know TCP behavior to identify a problem. Iperf ( http://dast.nlanr.net/Projects/Iperf/) –TCP/UDP bandwidth measurement bwctl ( http://e2epi.internet2.edu/bwctl/) –Wrapper for iperf with authentication and scheduling tcpplot –visualizer for web100 data
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1 st Step: Tuning a Host with UDP Remove any bottlenecks on a host –CPU, Memory, Bus, OS (driver), … Dell PowerEdge 1650 (*not enough power) –Intel Xeon 1.4GHz x1(2), Memory 1GB –Intel Pro/1000 XT onboard PCI-X (133Mhz) Dell PowerEdge 2650 –Intel Xeon 2.8GHz x1(2), Memory 1GB –Intel Pro/1000 XT PCI-X (133Mhz) Iperf UDP throughput 957 Mbps –GbE wire rate: headers: UDP(8B)+IP(20B)+EthernetII(38B) –Linux 2.4.26 (RedHat 9) with web100 –PE1650: TxIntDelay=0
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2 nd Step: Tuning a Host with TCP Maximum socket buffer size (TCP window size) –net.core.wmem_max net.core.rmem_max (64MB) –net.ipv4.tcp_wmem net.tcp4.tcp_rmem (64MB) Driver descriptor length –e1000: TxDescriptors=1024 RxDescriptors=256 (default) Interface queue length –txqueuelen=100 (default) –net.core.netdev_max_backlog=300 (default) Interface queue descriptor –fifo (default) MTU –mtu=1500 (IP MTU) Iperf TCP throughput 941 Mbps –GbE wire rate: headers: TCP(32B)+IP(20B)+EthernetII(38B) –Linux 2.4.26 (RedHat 9) with web100 Web100 (incl. High Speed TCP) –net.ipv4.web100_no_metric_save=1 (do not store TCP metrics in the route cache) –net.ipv4.WAD_IFQ=1 (do not send a congestion signal on buffer full) –net.ipv4.web100_rbufmode=0 net.ipv4.web100_sbufmode=0 (disable auto tuning) –Net.ipv4.WAD_FloydAIMD=1 (HighSpeed TCP) –net.ipv4.web100_default_wscale=7 (default)
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TransPAC/I2 Test: High Speed TCP (60 mins) From Tokyo to Indianapolis
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Test in a Laboratory – with Bottleneck Network Emulator ReceiverSender L2SW (FES12GCF) Bandwidth 800Mbps Delay 88 ms Loss 0 GbE/SX GbE/T PE 2650PE 1650 2*BDP = 16MB BGP: Bandwidth Delay Product
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Laboratory Tests: 800Mbps Bottleneck TCP NewReno (Linux) HighSpeed TCP (Web100)
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BIC TCP buffer size 100 packets buffer size 1000 packets
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FAST TCP buffer size 100 packets buffer size 1000 packets
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Identify the Bottleneck existing tools: pathchar, pathload, pathneck, etc. –Available bandwidth along the path –How much the bottleneck (router) buffer size? pathbuff (under development) –measuring buffer size at the bottleneck –sending a packet train then detect a loss and delay
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A Method of Measuring Buffer Size Receiver Sender network with bottlenec k packet train T Capacity C n packets
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Typical cases of congestion points RouterSwitch Congestion Point with small buffer (~100 packets) Router Congestion Point with large buffer (>=1000 packets) Inexpensive, but… Poor TCP performance for high BW delay path Better TCP performance for high BW delay path
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Summary Performance measurement to get a reliable result and identify a bottleneck Bottleneck buffer size impact on the result Future Work Performance measurement platform in cooperation with applications
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Kwangju Busan 2.5G Fukuoka Korea 2.5G SONET KOREN Taegu Daejon 10G 1G (10G) 1G Seoul XP Genkai XP Kitakyushu Kashima 1G (10G) Fukuoka Japan 250km 1,000km 2.5G TransPAC / JGN II 9,000km 4,000km Los Angeles Chicago Washington DC MIT Haystack 10G 2.4G (x2) APII/JGNII Abilene Koganei 1G(10G) Indianapolis 100km bwctl server Network Diagram for e-VLBI and test servers 10G Tokyo XP *Performance Measurement Point Directory http://e2epi.internet2.edu/pipes/pmp/pmp-dir.html perf server e-vlbi server JGNII 10G GEANT SWITCH 7,000km
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