Monday,February29,2016

Caffeine

CaffeinereducesnetworklatencyinnativeiOSapplications.

Thisdocumentempiricallydiscussesthefollowingtwospecificitems:

• Theamountoflatencyreduced• Whatcharacteristicsaffectlatencyreduction

Abstract

We collocate a server in Switzerland and repeatedlydownload images from it using an iOS Simulator. Inconducting downloads of a series of images, we find thatfully encrypted Caffeine has 4.5x-8.5x greater throughputthanHTTPS showing a just as great decrease in perceivednetwork latency. We find Caffeine’s improvements overHTTPS to be consistent despite network congestion orotherwiseadverseconditions(packetloss,lotofdevicesonthenetwork,etc).

AHistoricalExperiment:ConsumerTechnologyoverTime

AnOSXserverinZurichSwitzerlandcontainstwenty-fourimagesofgreat

achievement—fromEdison’s1877cylinderphonographtoMusk’sSpaceX.Theseimagestotal1.615506MB.Smallerversionsoftheseimagesarebelow.

1 2 34

5 67

8

9 1011

12

13

14

1516

17

18

19

20

21

22 23

24

Thesetwenty-fourimagesaredownloadedfromtheserverinSwitzerlandto

aniOSsimulatorinCambridge,Massachusettsconsecutivelyfromoldesttonewest(1to24).Thesizesinbytesofeachindividualimagearebelow.

1 1069412 944823 52574 956555 514686 52407 1661998 150919 15400910 3877211 1293212 6551513 6548614 7848015 1470316 7345117 5560518 5575019 1672220 1335821 30949722 4266923 7125924 6965TotestHTTP/Sdownloads,weusethetraditionalNSURLSessionprovidedbyApple’sFoundationLibrary.Totestouralternativeapproachtomobilenetworking,weuseCaffeine’sprovidedAPIs.

Methodology

InattempttoscientificallyevaluatethedifferencebetweenCaffeineandHTTPSasitpertainstoimages,wetookthefollowingsteps.Note:Alldatawascollectedfromwithinthesame100-meterradiusincludingnoothersmartphones/laptops.AlltestswererunontheHarvardUniversitysecureWiFi.Theresultsinthisstudymaybemoredramaticthaniftheclientandserverwereinthesamecountry(U.S.toU.S.connection,e.g.).Weplantotestthisvariableintheimmediatefuture.

1. InCambridge,MA,starttheclientonaniPhone6simulatorrunningiOS9.2fromXcodev7.2

2. InZurich,Switzlerlandstartbothbackendservers(CaffeineandApache)onOSXElCapitan10.11.3with2.48GHzprocessingpowerand2GBDRAM.

3. PingserverinSwitzerland(usingICMP)100timesandrecordthefollowing:a. Averageping,b. Standarddeviationofpingc. Packetloss.

4. MakeaninitialrequestforimagesfromtheclientusingCaffeinetoremoveTCPSlowstart.

5. InitiateCaffeineclientrequesting24imagesfromCaffeineserver12timeswithnogreaterthan1secondinbetweeneachofthe12times.

6. MakeaninitialrequestforimagesfromclientusingHTTPStoremoveTCPSlowstart

7. InitiateNSURLSessionrequesting24imagesfromApacheserver12timeswithnogreaterthan1secondinbetweeneachofthe12times.

8. Repeatsteps3-7foratotalof10timeswherethenumberofimagesrequestedissomedifferentmultipleofthree(3,6,9,…27,30–after24images,wereuseimagesfromthebeginning)

Results

Forevery10sets(eachwithanadditional3images)oftrials(12forCaffeine,12forHTTPS),wehavethefollowingresults.

0.398 0.413 0.434 0.399 0.385 0.386 0.388 0.386 0.397 0.422 0.389 0.397

2.603 2.486 2.6532.271

2.649 2.603 2.486 2.404 2.4

3.317

2.4072.818

0

0.5

1

1.5

2

2.5

3

3.5

1 2 3 4 5 6 7 8 9 10 11 12

SecondsElapsed

TrialsfromCambridge,Mass.Meanping117ms(+-1.3ms)3.3%pl

PostTCPSlowstart:DownloadDurationsfor3images(0.20668mb)

Caffeine

HTTPS

0.619 0.6011.082 0.898 0.645 0.613 0.597 0.61 0.649 0.648 0.645 0.62

4.757 4.516 4.705 4.7445.331

4.759 4.5985.022

4.696 4.5114.866 5.01

0

1

2

3

4

5

6

1 2 3 4 5 6 7 8 9 10 11 12

SecondsElapsed

TrialsfromCambridge,Mass.Meanping118ms(+-1.1ms)

PostTCPSlowstart:DownloadDurationsfor6images(0.359043mb)

Caffeine

HTTPS

1.234

3.619

2.319

1.262 1.15 1.1482.067

1.146 1.183 1.1491.934

1.263

7.688 7.877.257 7.491 7.319 7.487 7.483 7.518 7.518 7.32

8.1577.233

0

1

2

3

4

5

6

7

8

9

1 2 3 4 5 6 7 8 9 10 11 12

SecondsElapsed

TrialsfromCambridge,Mass.Meanping120ms(+-11.7ms)0.0%pl

PostTCPSlowstart:DownloadDurationsfor9images(0.694342mb)

Caffeine

HTTPS

1.529 1.255 1.244 1.249 1.244 1.212 1.248 1.246 1.213 1.214 1.214 1.28

10.38411.08411.5310.751

10.1099.66510.32710.941

11.426

10

11.15610.985

0

2

4

6

8

10

12

14

1 2 3 4 5 6 7 8 9 10 11 12

SecondsElapsed

TrialsfromCambridge,Mass.Meanping(117ms(+-1.4ms)

PostTCPSlowstart:DownloadDurationsfor12images(0.811561mb)

Caffeine

HTTPS

1.92 1.867

3.4042.67

3.4562.67 2.099 2.201

3.655 3.122.419

3.035

12.454

14.776

13.10313.25312.83513.581

12.08313.003

12.16513.51

12.301

14.993

0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8 9 10 11 12

SecondsElapsed

TrialsfromCambridge,Mass.Meanping134ms(+-35.2ms)0.0%pl

PostTCPSlowstart:DownloadDurationsfor15images(0.970230mb)

Caffeine

HTTPS

1.835 2.502 1.837 1.834 1.8123.07

2.017 1.8682.999 2.958 2.752 2.581

15.34515.99916.164

14.90815.78315.60315.49716.083

14.6815.444

18.333

15.483

0

2

4

6

8

10

12

14

16

18

20

1 2 3 4 5 6 7 8 9 10 11 12

SecondsElapsed

TrialsfromCambridge,Mass.Meanping137ms(+-42.0ms)6.7%pl

PostTCPSlowstart:DownloadDurationsfor18images(1.176910mb)

Caffeine

HTTPS

3.411 3.4874.663

3.528 2.7493.839 3.956

2.619 2.67 2.953 2.7484.492

19.74317.78316.96516.80216.748

17.63216.4516.935

17.35116.46817.252

18.542

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10 11 12

SecondsElapsed

TrialsfromCambridge,Mass.Meanping131ms(+-33.5ms)1.0%pl

PostTCPSlowstart:DownloadDurationsfor21images(1.329273mb)

Caffeine

HTTPS

3.756 2.991 3.009 3.0363.843

3 3 3.407 2.952 3.032 2.955 2.986

19.95618.96119.42119.67419.15719.61218.956

20.27720.32621.334

22.282

19.254

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10 11 12

SecondsElapsed

TrialsfromCambridge,Mass.Meanping113ms(+-36.4ms)

PostTCPSlowstart:DownloadDurationsfor24images(1.615506mb)

Caffeine

HTTPS

3.672 2.9924.108

2.772 2.988 2.754 2.737 2.686 2.855 3.254 2.7414.663

20.82921.0521.33221.43321.83121.83

23.49121.12921.784

22.70220.82921.116

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10 11 12

SecondsElapsed

TrialsfromCambridge,Mass.Meanping126ms(+-56.0)0.0%pl

PostTCPSlowstart:DownloadDurationsfor27images(1.822186mb)

Caffeine

HTTPS

3.823 3.835 3.839 3.837 3.545.777

4.493 4.025 3.793 3.989 3.991 3.821

26.07624.60624.52624.52324.82524.69525.663

25.96227.55127.40327.325

24.578

0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10 11 12

SecondsElapsed

TrialsfromCambridge,Mass.Meanping119ms(+-5.3ms)0.0%pl

PostTCPSlowstart:DownloadDurationsfor30images(2.028866mb)

Caffeine

HTTPS

Across-sectionallookattheaverageresults:

0.39950.685581.262331.62283

2.709672.338753.42625

3.96953.18517

4.06358

2.59142

4.79292

10.65733

7.52842

13.17142

15.77683

17.38925

19.98867

21.613

25.64442

-5

0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10

SecondsElapsed

Imagesets(eachperiodrepresentsanadditional3images)

AverageDownloaddurationsforsetsofimages(3,6,9,...,27,30)

Caffeine

HTTPS

Across-sectionallookatthemedianresults:

Onaverage,Caffeineisanywherefrom400%-850%fasterthanHTTPS.Therearesomeanomaliesinthedatasuchasthe4thperiodinthemediangraph(above).Thiscanbeexplainedbywavesofcongestiononthenetwork,orlatencyoverseas.Acrosstheboard,theimprovementgainsofCaffeineoverHTTPSremainrelativelyconsistent.Becauseeachperiodreceivesanadditional3images,theirtotaldatasizedoesnotincreaselinearlylikethetotalnumberofrequests.Forexample,anadditional3

0.397 0.6325 1.245 1.248

2.67 2.25953.449 3.477 2.9215

3.838

2.5445

4.7505

10.846

7.489

13.053

15.55

17.1085

19.979521.3825

25.244

0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10

SecondsElapsed

Imagesets(eachperiodrepresentsanadditional3images)

MedianDownloadDurationsforsetsofimages

Caffeine

HTTPS

imagesfetchedfromtheserveralwaysresultsin3additionalrequests,buttheamountoftotaldataforeachofthoserequestsisvariable.Tonormalizethisvariation,wedeterminetheaveragethroughput(bytes/second).

ThisgraphmuchmoreclearlydisplaysthedifferenceofCaffeine.Itdescribeshowmuchdatacan“fitthroughthepipe”persecond.OntheX-axis,thetotalnumberofrequestsincreasesby3periodically.Intimesofnetworkstressorcongestion,suchasinthe3rdperiodabove(9requests),theperformanceofHTTPSprorateswiththeperformanceofCaffeine.ThissuggeststhatCaffeine’sperformancerelativetoHTTPSremainsconsistentdespiteunpredictablenetworksphenomena(severeweather,congestion,miscellaneouslatency).

0

100000

200000

300000

400000

500000

600000

700000

800000

1 2 3 4 5 6 7 8 9 10

Averagebytestransm

ittedpersecond

Trials(eachperiodrepresentsamultipleof3requests)

AverageThroughputforaseriesofimagerequests

Caffeine

HTTPS

ThepercentagegainofCaffeineversusHTTPSisshownbythegraphbelow.

TheminimumaveragemultiplierimprovementofCaffeineoverHTTPSshownbythisgraphis~450%,whilethemaximumis~850%.

ClosingRemarks WhendevelopingCaffeine,wecontinuallyaskedwhatisactuallynecessaryforiOSapplicationnetworkingenvironments.Thisapproachhasresultedinthereductionofalotof(whatturnouttobe)unnecessaryfeatures/datainHTTP.TheamountofbloatandlatencyincipienttoHTTPsurprisedusquitealot. Forthcomingresearchincludequantitativeanalysesofresourceusage—determininghowmuchbandwidth,CPU,battery-lifewouldbesavedinaCaffeinatedenvironment. Caffeine,asfarasweknow(andwe’velooked),isthefastestwaytosenddatainiOSrequest-responsearchitectures.Weknowthisisthefutureofnetworking,andwearelookingforthoseintrepidearlyadopters.Emailusbeyondjava@caffei.net

Thefutureisalreadyhere—it’sjustnotevenlydistributed.—WilliamGibson

0x1x2x3x4x5x6x7x8x9x

1 2 3 4 5 6 7 8 9 10Caffeinethru/HTTPSthru

Numberofimagerequests(multiplesof3)

AveragePerformanceGainsMultiplesofCaffeineComparedto

HTTPS