rtt matters - enog · rtt matters matsuzaki‘maz’ yoshinobu [email protected] -iij/as2497 1. round...
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![Page 3: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/3.jpg)
RTT
• Thelower,thebetter– FasterTCPhandshake– BetterTCPthroughput– FasterTCPrecoveryfromapacketloss
• TherearevariouseffortstoimproveTCPperformanceeveninahighlatencysituation
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![Page 5: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/5.jpg)
Ifacedatrouble
wirelesswired• RTTwasnotstablefromawirelessclienttotheserver2.L
64bytestime=398.122ms64bytestime=316.330ms64bytestime=337.251ms64bytestime=358.155ms64bytestime=299.480ms64bytestime=387.789ms
server2
server1
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![Page 6: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/6.jpg)
let’strytoisolatetheproblem
wireless
64bytestime=169.588ms64bytestime=170.666ms64bytestime=169.793ms64bytestime=168.185ms64bytestime=169.783ms64bytestime=169.957ms
server164bytestime=3.757ms64bytestime=3.789ms64bytestime=3.768ms64bytestime=3.718ms64bytestime=3.644ms64bytestime=3.762ms
1) ThelocalWiFi networklooksprettystable
2) RTTtoserver1looksalsostable
server2
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![Page 7: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/7.jpg)
hmmm...
wirelesswired
server2
server1
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64bytestime=296.040ms64bytestime=296.105ms64bytestime=296.442ms64bytestime=296.186ms64bytestime=296.103ms64bytestime=296.070ms
3) Fromthewiredhostinthesamenetwork,RTTtotheserver2looksstable
![Page 8: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/8.jpg)
so...
wireless
server1
server2
wired
• ThisstrangebehaviorhappensonlyforthiscombinationL
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![Page 9: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/9.jpg)
RTTdistributiontoserver1
fromwiredhosttoserver1 fromwifi hosttoserver1
wired wifi
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![Page 10: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/10.jpg)
RTTdistributiontoserver2
fromwiredhosttoserver2 fromwifi hosttoserver2
wired wifi
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![Page 11: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/11.jpg)
WiFi APwasbufferingpackets
wirelesswired
Internet
server2
server1
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• ThiscausedtheunstableRTTL
![Page 12: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/12.jpg)
MyWiFi adapterdoessleep
• Toreducebatteryusage• Beforesleeping,theclientsendanotificationtothewifi AP,andtheAPkeepspacketsuntiltheclientwakeup
• MyPCwasaskingthebuffering!
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![Page 13: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/13.jpg)
WiFi APsendsbeacon
• Beaconinterval– timeintervalbetweenbeacontransmissions– usually100msec,butit’sconfigurable
• TIM(TrafficIndicationMap)– totellanysleepingclientsiftheAPhasanybufferedframespresentforit
• WiFi adaptercansleepbetweenbeacons,andwakeuptocheckabeacon(TIMcanindicateiftheadapterneedtoreceivedataornot)
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Thescenario
• Mywifi adapterwenttosleepafter200msecofnotraffic– that’swhytheunstableRTThappensonlywhenIwascommunicatingwithserver2(averageRTTis300msec)
• Basedonthebeaconintervalinformation(whichwas100msecinmycase),itwokeupandreceivedaresponse– that’swhymostRTTdistributioniswithin100msec
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![Page 15: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/15.jpg)
Sleepingandbuffering
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200msecnotraffic
goestosleepuntilthenextbeacon buffered
![Page 16: RTT matters - ENOG · RTT matters Matsuzaki‘maz’ Yoshinobu maz@iij.ad.jp -IIJ/AS2497 1. Round Trip Time (RTT) RTT t0 t1 maz@iij.ad.jp -IIJ/AS2497 2. RTT](https://reader034.vdocuments.mx/reader034/viewer/2022042414/5f2f09343e1b124fa87c7b3b/html5/thumbnails/16.jpg)
Summary• StrangeRTTbehaviorhappensifyourcommunicationis
between:– ahostconnectedtoawifi networkand– afar endhost(RTT>200msec)
• AWiFi adaptergoestosleep– “200msecofnotraffic”seemsacommontrigger
• ThesleepdurationismanageablebysettingbeaconintervalonyourWiFi AP– 100msecwouldbereasonable– Youmightbeabletoreducebatteryusagebysettingitas
1000msec,butthiscouldintroducemoreRTTpenalty– YoucanenableU-APSDifyourAPsupportsitsothatclientscan
actuallyschedulethedurationbyitself.
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