Iden%fyingandMeasuringPointsofConges%on
GeorgiosSmaragdakis
ATeamEffort
DavidClark,SteveBauer,WilliamLehr
2
KimberlyClaffy,Ma>hewLuckie,AmoghDhamdhere,BradleyHuffaker
ArthurBerger,KCNg,BalaChandrasekaran(internfromDuke)
WhyStudyConges%on?- TheInternetisnotanymorea“nicetohave”service;networkdelaysaffectproducOvity
- RevenuecanbesensiOvetomillisecondsdelay(seereferencesin[1])- Amazonfoundthat100msecoflatencycost1%ofsales.- GooglefoundthatdelaysindisplayingwebpagesleadtorevenuereducOon(upto
20%fora500msecdelay).
- EngagementofusersisalsosensiOvetodelay[2]- Usersstarttoabandonavideostreamingisstart-upOme>2seconds.- Usersexperiencere-bufferingfor1%ofvideoduraOonplay5%lessvideo(and
watchfewerads).
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[1]“PracOcalGuidetoControlledExperimentsontheWeb:ListentoYourCustomersnottotheHiPPO”KDD’07[2]“VideoStreamQualityImpactsViewerBehavior:InferringCausalityUsingQuasi-ExperimentalDesigns”IMC’12
WhyStudyConges%on?- Unintendedconsequences,e.g.,congesOoncancauseerrorstoNTPaccuracy
- LocaOonwherecongesOonoccursma>ers:- CongesOoninaccesslinksaffectsusersinaregion- CongesOonintransit/interconnecOonsaffectsthousandsofusers!
- ShedlightontherootcausesofcongesOon(economic,technical,architectural)towardsbuildingabe>erInternet/informpolicymakers.
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Conges%on:AnecdoteorEvidence?
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WhyYouTubebuffers:Thesecretdealsthatmake—andbreak—onlinevideo
Nejlix’sDisputesWithVerizon,ComcastUnderInvesOgaOon
Nejlixwarisover,butmoneydisputessOllharmInternetusers.
NejlixtoPayComcastforSmootherStreaming
Europe'scompeOOonwatchdogisinvesOgaOngsomeoftheregion'sbiggesttelecomscompaniesoverwhethertheyabusedtheirmarketposiOon
BuildingaConges%onMeasurementPlaBorm
ObjecOves:- CollectandanalyzedatatoprovideunbiasedevidenceofcongesOon.
- Developtoolstoconstructadetailed“heatmap”ofcongesOonpercity,peeringlocaOon,theinterconnecOonbetweentwonetworks.
Focuson:- PersistentcongesOon;cleardailypa>ernsthatspanmulOpledays
Requirements:- Large-scalebutlightweightmeasurements
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Iden%fyingandMeasuringPointsofConges%on
PartI:TargetedInterconnecOonsorInternalLinks
-“ChallengesinInferringInternetInterdomainCongesOon”,Luckieetal.,IMC2014-“MeasurementandAnalysisofInternetInterconnecOonandCongesOon”Clarkatal.,TPRC2014
Methodology:TimeSequenceLatencyProbes(TSLP)
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VantagePoint
BorderRouter#A
BorderRouter#B
AccessRouter DesOnaOon:
VideoServer
Methodology:TimeSequenceLatencyProbes(TSLP)
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VantagePoint
BorderRouter#A
BorderRouter#B
AccessRouter DesOnaOon:
VideoServer
“Near” “Far”
Methodology:TimeSequenceLatencyProbes(TSLP)
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VantagePoint
BorderRouter#A
BorderRouter#B
AccessRouter DesOnaOon:
VideoServer
“Near” “Far”
SendTTL-limitedpacketsthatexpireinthe“Near”and“Far”router
Methodology:TimeSequenceLatencyProbes(TSLP)
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VantagePoint
BorderRouter#A
BorderRouter#B
AccessRouter DesOnaOon:
VideoServer
“Near” “Far”
SendTTL-limitedpacketsthatexpireinthe“Near”and“Far”router
Frequentlymeasure:
RTT#A
RTT#B
TTL=2
TTL=3
AnExample(November2013)
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AnExample(November2013)
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ToinferdiurnalpaWern:FFTanalysisof%meserieswithfrequency1/day.
Limita%ons- AsymmetricRouOng
- ReverseTraceroute[1]mayunveilthereversepath(usingIPopOons)
- Bothforwardandbackwardpathshouldbemonitored;vantagepointsareneededatbothends
- RouterQueuingManagement
- Measuringpackets(ICMPpackets)maybeassignedtolowpriorityqueues
- RandomEarlyDetecOon(RED)beforequeuebecomesfull
- RouterOwnership- Itisnottrivialtomapaninterface/routertoanetwork;itrequiresanalysisofmassiveamountofmeasurements(aliasing)
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[1]“ReverseTraceroute”NSDI’10
Iden%fyingandMeasuringPointsofConges%on
PartII:AtInternet-wideScale-“AServer-to-ServerViewoftheInternet”,Chandrasekaranetal.,CoNEXT2015
U%lizingaHighlyDistributedPlaBorm
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-Large-scalemeasurementsu%lizing5,000+serverclusters(oneserverpercluster)-2,000+loca%ons:coloca%onfacili%es,IXPs,datacenters,residen%alnetworks,enterprisenetworks.-1,200+networks
U%lizingaHighlyDistributedPlaBorm
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Measurementtools(opera%onalversions):- ping- traceroute(Paris)
Methodology
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FrequentServer-to-Server
pingMeasurements
ApplyFFTtoselectcandidatepairswith
“conges%on”
Performtraceroutecampaigns
Infertheloca%onofconges%on
BootstrapPhase:Server-to-ServerPingMeasurements
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late
ncy
[ms]
1 if
any
pack
et lo
ss
d-trip time and Packet Loss between regions 19247__23336 (SH-SJC3__TWC-DF95th minus 5th percentile = 29 ms. Power Ratio = 0.845
latencyany packet loss
Mon Tue Wed Thu Fri Sat Sun Mon
BootstrapPhase:Server-to-ServerPingMeasurements
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- Wecollectedandanalyzedaround2MillionOmeseriesofpings
- Frequency:1sampleper15minutesfor1week
- TheFFTanalysisshowedthataround6%arepotenOalcandidatepairsforcongesOon- NoOcethatrouOngmayplayarole- NoOcethattheincreaseofdelaymaynotbealwayssignificant
Server-to-ServerTracerouteMeasurements
- UnfortunatelywithpingmeasurementsisnotpossibletolocatewherethecongesOonoccurs.
- Weperformserver-to-servertraceroutemeasurementsinbothdirecOons,foraround100Kpairs
- Measurementsspantwoweekswithfrequency1tracerouteevery30mins.
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Loca%ngConges%onPoints
%me
hops
hop1 hop2 hop3 hop4 Lasthop
Loca%ngConges%onPoints
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%me
hops
hop1 hop2 hop3 hop4 Lasthop
Loca%ngConges%onPoints
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%me
hops
hop1 hop2 hop3 hop4 Lasthop
Tolocatethecongestedlink:ComputethePearsoncorrela%oncoefficientρin(-1,1).
Loca%ngConges%onPoints
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%me
hops
hop1 hop2
Tolocatethecongestedlink:ComputethePearsoncorrela%oncoefficientρin(-1,1).
ρ=0.004 ρ=0.005 ρ=0.60 ρ=0.60
hop3 hop4 Lasthop
Loca%ngConges%onPoints
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%me
hops
hop1 hop2
Tolocatethecongestedlink:ComputethePearsoncorrela%oncoefficientρin(-1,1).
ρ=0.004 ρ=0.005 ρ=0.60 ρ=0.60
hop3 hop4 Lasthop
Loca%ngConges%onPoints
-SymmetricRouOng:Forwardandreverseinferthesamerouter
-AsymmetricRouOng:Wecanonlyargueinternal/interconnecOonlink
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SomeObserva%ons
- WeinvesOgated310Klinks;weinferredaround3,000linkswithpersistentcongesOon
- BothinternalandinterconnecOonlinkswerecongested
- But,interconnecOonlinkswereinferredfromalargenumberoftraceroutes,insomecasesby>300probes.
- Bothcustomer-providerandpeer-peerinterconnecOonswerecongested
- Publicpeeringlinks(atIXPs)werelesscongestedthanprivateinterconnects.
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WhatistheOverheadofConges%on?
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“uniform”overheadinUS-USlinks;around25+msec
Bestprac%cesinrouterconfigura%ons?
WhatistheOverheadofConges%on?
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less“uniform”overheadinlinksaroundtheglobe
Bestlocalprac%ces?Longer/transcon%nentaldistances?
WhatistheOverheadofConges%on?
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No%cethatrou%ngchangesmayincreasethedelayby50+milliseconds.
Summary
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- AswerelyonasmoothoperaOonoftheInternet,anydisrupOonsuchascongesOon,hasanegaOveimpactonuserexperienceandproducOvity
- WepresentedtechniquestomeasurecongesOonandlocalizeittoalinkoranetwork
- Ourlarge-scalestudyshowsthatcongesOonisnotthenorm,butinsomepathsitcontributestotheend-to-enddelay
NextSteps
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- ConOnuetomeasuretheInternetandseekforpointsofcongesOon
- Improveourtechniquesanddealwith“blackbox”behavior;wewelcomeyourhelp!
- Scaleupouranalysis
- MakeanInternet“heatmap”ofcongesOonpubliclyavailable
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Thank you!
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