Alterna(ve Backoff: Achieving Low Latency and High...
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Alterna(ve Backoff: Achieving Low Latency and High Throughput with ECN and AQM Naeem Khademi , Grenville Armitage, Michael Welzl, Sebas:an Zander, Gorry Fairhurst and David Ros IFIP Networking 2017, Stockholm, Sweden – June 14, 2017 naeemk@ifi.uio.no
Transcript of Alterna(ve Backoff: Achieving Low Latency and High...
Alterna(veBackoff:AchievingLowLatencyandHighThroughputwithECNandAQM
NaeemKhademi,GrenvilleArmitage,MichaelWelzl,Sebas:anZander,GorryFairhurstandDavidRos
IFIPNetworking2017,Stockholm,Sweden–June14,2017
§ Acommonphrasewehaveallheard/said:“Internetistooslowtoday!”
§ FastInternettranslatesintofeelingofcontrolandinterac:vitybytheuser
§ “fast”=>highermediumspeed(bandwidth),shorter:me(delay)andhighertransferrate(transportprotocol)
§ Internetiss:llslowontoday’sbandwidthover-provisionednetworks.Infact,delay(latency)isamajorsourceofprobleminaccesslinks
StuartCheshire(AppleInc.),“It'stheLatency,Stupid”,1996h_p://rescomp.stanford.edu/~cheshire/rants/Latency.html
Internet’sLatencyProblem
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Source: http://fc04.deviantart.net/fs71/f/2011/330/d/b/slow_internet_by_syas-d4hdtpl.jpg
m3/s t
m3/s
Awater-pipeexample
§ WithstandardTCPConges:onControl’sMul:plica:veDecreasefactor(β=0.5):morethroughputmeansmorebuffering(morelatency)o 1BDPforfullu:liza:ono TCPwillfillupanybuffer!
§ Ac(veQueueManagement(AQM)solu(ons:aimingtokeeptheaveragelatencylow:(FQ_)CoDel,PIE,ARED,…
§ AQMs’defaultthresholdstranslateintoa:nyaveragebuffer(e.g.5ms~20msfor(FQ_)CoDelandPIE)
Internet’sLatencyProblem(#2)
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7.6 7.8
8 8.2 8.4 8.6 8.8
9 9.2 9.4 9.6 9.8 10
10 20 30 40 50 60 70 80 90 100
Thro
ughp
ut (M
bps)
Buffer Size (pkts)
BDP
2/3 BDP
3/7 BDP
1/4 BDP
1/9 BDP
β=0.5β=0.6β=0.7β=0.8β=0.9
ns-2simula:onvs.modelOneNewRenoflow
@10Mbps,RTT100ms,DropTail
Standard TCP
§ Under-u:liza:onbecomesmoreproblema:casRTTfurtherincreases
TheProblemwithUsingAQMs
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20 40 80 160 240RTT (ms)
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No_ECN ECN
PIE
One CUBIC flow @ 20 Mbps (real-life tests)
§ Linkunder-u:liza:onwithAQMs’
defaultthresholdswhenRTTsheadaboveintra-countrylevels(60ms~80ms)
Problemwithlong-RTTpaths
link capacity(C.2Tp)
time
Under-utilized portion of the link capacity
buffering (b)
CWmax
β.CWmax
“CanweusealargerTCPβ?”
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150
200
250
300
350
0 10 20 30 40 50 60
cwnd
(pa
cket
s)
Time (sec)
Capacity limit
RTTmin 213ms
RTTmin 283ms
Queue length: 1/2 BDPQueue length: 1 BDP
e.g.,CUBICCC(defaultsinceLinux2.6.25)usesβ=0.7
CUBICgeneratesastandingqueue(withDropTail)(i.e.cwndconstantlyabovethecapacitylimit)
§ Packetloss:tail-loss(andothersourcesofloss)versusAQM-losso Notagoodindicatoroftheonsetofconges:on
§ AnECN-CEsignalexplicitlyindicatesanAQM’spresence(mostlikelytobe(FQ_)CoDelorPIE)withalowmarkingthreshold
Alterna(veBackoffwithECN(ABE)
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§ OnlyasimpleTCPparameterchange=>useaβhigherthan
0.5inresponsetoECN-CE(βECN)andreactwithβ=0.5inresponsetoloss
§ Fewlinesofcodeinthekernel(inthesenderonly)
Alterna(veBackoffwithECN(ABE)
§ UsedTEACUP,anexperimentautoma:onsuiteforTCPh_p://caia.swin.edu.au/tools/teacup/
§ TEACUPisdrivingaphysicaltestbedwithadumbbelltopologyusing
FreeBSDandLinuxhosts,andaLinux-basedsotwarerouter(netem)
§ UsedLinux3.17.4implementa:onsofPIEandCoDelwiththeirdefaultparameters
§ iperftogeneratetraffic,tcpdumptocapturethetraffic
§ Per-flowRTTsarecalculatedusingSPPh_p://caia.swin.edu.au/tools/spp/
NoteonExperimentalSetup
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Latencyvs.ThroughputTradeoff
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One NewReno flow, CoDel @ 10 Mbps
0 50 100 150 200 250 300
050
100
RTT=100ms
Byte
s D
epar
ted
βecn
0.60.70.750.8
0.850.90.95
Impr
ovem
ent o
ver β
ecn=
0.5
(%)
0 50 100 150 200 250 300
RTT=200ms
Time(s)0 100 200 300 400 500 600
RTT=400ms
0 2 4 6 8 10
020
4060
8010
0 RTT=100ms
CD
F (%
) βecn
0.50.60.70.750.80.850.90.95
CD
F(%
)
0 2 4 6 8 10
RTT=200ms
Queueing Delay (ms)0 2 4 6 8 10
RTT=400ms
24%improvementforβECN=0.8
Latencyvs.ThroughputTradeoff(#2)
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One NewReno flow, PIE @ 10 Mbps
0 50 100 150 200 250 300
050
100
RTT=100ms
Byte
s D
epar
ted
βecn
0.60.70.750.8
0.850.90.95
Impr
ovem
ent o
ver β
ecn=
0.5
(%)
0 50 100 150 200 250 300
RTT=200ms
Time(s)0 100 200 300 400 500 600
RTT=400ms
0 5 10 15 20 25 30 35
020
4060
8010
0 RTT=100ms
CD
F (%
) βecn
0.50.60.70.750.80.850.90.95
CD
F(%
)
0 5 10 15 20 25 30 35
RTT=200ms
Queueing Delay (ms)0 5 10 15 20 25 30 35
RTT=400ms
23%improvementforβECN=0.8
0.7≤βECN≤0.85:agoodtrade-offbetweenimprovedthroughputandincreasedlatency.
Latencyvs.ThroughputTradeoff(#3)
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400.5
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RTT (ms)βecn
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Increased βECN causes insignificant change in median RTT
Source:h_p://frenchyme.blogspot.no
§ Lowlatencyandhighu(liza(on
ABEPerformance
Latencyvs.ThroughputTradeoff(#4)
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§ We also tested for One CUBIC flow, with PIE/CoDel @ 10 Mbps
§ Evident throughput gains, although smaller than NewReno’s due to CUBIC’s already aggressive additive increase and default βECN = 0.7
§ Queuing delay distributions are similar to NewReno’s
TCPConvergenceTime
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F
Convergence time / default (βecn 0.5)
βecn 0.6βecn 0.7
βecn 0.75βecn 0.8
βecn 0.85βecn 0.9
Two NewReno flows, CoDel
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1
0 1 2 3 4 5
CD
F
Convergence time / default (βecn 0.5)
βecn 0.6βecn 0.7
βecn 0.75βecn 0.8
βecn 0.85βecn 0.9
Two NewReno flows, PIE
@ {1, 5, 10, 20, 40, 100} Mbps and RTT={10, 20, 40, 60, 80, 160, 240, 320} ms
JFI of the cumulative number of bytes transferred per flow from the time a new flow entered, (after 30 sec during a 90 sec experiment) and noting the time it took until this index reached a threshold (0.95)
FriendlinesswithStandard(Loss-based)TCP
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0.5
1
1.5
2
2.5
3
3.5
1 vs 9 3 vs 7 5 vs 5 7 vs 3 9 vs 1
Nor
mal
ized
thro
ughp
ut ra
tio(E
CN
flow
s / n
oEC
N fl
ows)
# noECN flows vs # ECN flows
βecn=0.5βecn=0.6
βecn=0.7βecn=0.75
βecn=0.8βecn=0.85
βecn=0.9
CoDel
0.5
1
1.5
2
2.5
3
3.5
1 vs 9 3 vs 7 5 vs 5 7 vs 3 9 vs 1
Nor
mal
ized
thro
ughp
ut ra
tio(E
CN
flow
s / n
oEC
N fl
ows)
# noECN flows vs # ECN flows
βecn=0.5βecn=0.6
βecn=0.7βecn=0.75
βecn=0.8βecn=0.85
βecn=0.9
PIE
Normalized throughput ratio between two groups of 10 flows (CUBIC with different βECN against standard TCP) @10 Mbps using RTTpath={20, 80, 160, 320} ms.
For βECN between 0.7 and 0.85 the average throughput ratio is between 1.25 and 2
ABEandMedium-sizedFlows
14140 2 4 6 8 10 12
010
020
030
040
0
Time (s)
cwnd
(pac
kets
)
RTT, βecn
160ms,0.5240ms,0.5160ms,0.9240ms,0.9
160ms X 20Mbps capacity
240ms X 20Mbps capacity
Theeffectofovershootattheendofslow-start@20Mbps(experiment)
- Benefitsmedium-sizeflowsi.e.flowstermina:ngrightaterSS- E.g.reduc:oninPLToflargeweb-pages- Numberofreduc:onstepsboundtologβECN (0.5)
Lucky flow Unlucky flow
§ ABEisbeingconsideredforstandardiza:onasanExperimentaldratbytheInternetEngineeringTaskForce(IETF)
drat-iev-tcpm-alterna:vebackoff-ecn§ ItisdefinedwithinthescopeofECNexperimenta:ondrat
drat-iev-tsvwg-ecn-experimenta:on
§ ItisaWorkingGroupitematTCPMaintenanceandMinorExtensions(tcpm)WorkingGroupattheIETF
§ KernelpatchesforLinuxandFreeBSD,technicalreportandthepaperareavailableath_p://heim.ifi.uio.no/naeemk/research/ABE/
ABE’sStatus
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§ ABEisaminorsender-sidemodifica:on(changesβECNonly!)
§ ComplieswiththerestofRFC3168
§ Incrementaldeploymentwithnoflag-day!
Conclusion
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a) Significantthroughputgainwithlightly-mul:plexedtraffic
b) Lowlatency(usingCoDelorPIE)
c) Nostarva:onofstandardTCP
d) Reasonableconvergenceandfairnesswithrecommendedβs
ABEPerformance
Q&A17
