Demystify Undesired Handoff in Cellular Networks · Demystify Undesired Handoff in Cellular...
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Demystify Undesired Handoff in Cellular Networks Chunyi Peng The Ohio State University Yuanjie Li University of California, Los Angeles
Transcript of Demystify Undesired Handoff in Cellular Networks · Demystify Undesired Handoff in Cellular...
DemystifyUndesiredHandoffinCellularNetworks
Chunyi PengTheOhioStateUniversity
Yuanjie LiUniversityofCalifornia,LosAngeles
MobileEra:“AlwaysConnected”
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In-building Outdoor Walking
Driving On the subway On the high-speed train
“AlwaysConnected”viaCellularNetworks
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cellular networks
cellular networks
“AlwaysConnected”viaMobilitySupport(Handoff)
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DesiredHandoffs:“AlwaysWellConnected”
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cellular networks
2G
3G
4G-2
4G-1
§ Multiplechoices¨ RAT:4G,3G,2G¨ Freq bands:700MHz,
1900MHz,etc.
§ Desiredhandoff:¨ BetterRAT(4G>3G)¨ Strongersignal
coverage¨ …
UndesiredHandoffs:“NotWellConnected”§ Notaniceorwisehandoffchoice
¨ Ex1:in2Gwhen4G/3Gisavailable¨ Ex2:evenoutofservicewhen4G/3Gisavailable
§ Questionsinthiswork¨ Q1:Dotheyhappeninreality?(Yes)¨ Q2:Howtodetectthem?¨ Q3:Whydotheyoccur?¨ Q4:Whatlessonslearnt?
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Fromtheorytopractice
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Q2: HowtoDetect?
Background:HandoffProcedure§ 3steps:trigger-decision-execution
§ Configurable¨ Versatilehandoffgoals
- Idle-state- active-stateE.g.seamlessconnectivity,loadbalancingviaoffloading
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Cell 1
2
decisionrulesparas
meas
Cell 2
3
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Handoff decision@C1
Background:HandoffProcedure§ 3steps:trigger-decision-execution
§ Configurable¨ Versatilehandoffgoals
§ Distributed¨ Localdecision&configurations
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Cell 1
2
decisionrulesparas
meas
Cell 2
3
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Handoff decision@C1
……5
decisionrules’paras’
meas’
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Handoff decision@C2
OurMethodology:Formulation§ Step1:Buildahandoffmodel
¨ Eachiteration:oneatomichandoffdecision:
- s, t:serving/target cell- C:setofcandidatecells- Ω:decisionlogic- G:configuration(tunableparameters)- O:measurement(runtimeobservation)
¨ Handoffsequences:sàc1à…à ci à [ci+1 =Ωci (ci)]à …10
s→ t =Ωs (Gs,Os ), t ∈Cs
OurMethodology:Analysis§ Step2:Undesiredreachabilityanalysis
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S
C1
Ci
t
……
Possible path
Handoff path
OurMethodology:Twocases§ Step2:Undesiredreachabilityanalysis
¨ ClassI:convergencesplit
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Possible path
Handoff path
S
C1
Ci
t
……Cj
topt…
OurMethodology:Twocases§ Step2:Undesiredreachabilityanalysis
¨ ClassI:convergencesplit¨ ClassII:prematureconvergence
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Possible path
Handoff path
S
C1
Ci
t
Cjtopt………
FromTheorytoPractice§ Step3:Buildanin-devicedetectorviaMMDIAG++
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ConfigurationCollector111
ConvergenceAnalyzer2
Scenario Emulator
ReachabilityAnalyzer
Counterexamples
Empirical Validation
MM Automata
1MobileInsight (Mobicom’16): http://metro.cs.ucla.edu/mobile_insight
Static
Dynamic
2MMDIAG (SIGMetrics’16)
Reality-checkandroot-causeanalysis
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Q1:Dotheyexistinreality?Q3:Andwhy?
RealityCheck§ Experimentsettings
¨ TwoUScarriers¨ Intwocities(LosAngeles,CAandColumbus,OH)¨ 50 outdoor locations,63 indoor locations,¨ Macrocells plusfemtocells (self-deployed)¨ Collectedhandoffprofiles(logic,config.,meas.)
§ Fourinstancesidentified¨ Inbothcategories¨ Threecauses
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CategoryI.A:Unaccessible intermedite cells(1/5)
§ Instance#1:Failtoreach4Gfrom2G
§ Cause:missingconfigurationfor2Gà 4G¨ Likelynoupdatein2G
§ Morerealcasesinthepaper17
Prefs,c > Prefs,sradioc>-108dBm
s (2G) c (3G) t (4G)
Prefc,t > Prefc,cradiot>-108dBmx
CategoryI.A:Unaccessible intermedite cells(2/5)
§ Realitycheck:¨ US-I:missing2Gà4Gconfigurationduringidleandactive¨ US-II:missing2Gà4Gconfigurationduringactive¨ 5out63locations:3Gisnotaccessible(<-105dBm)
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Prefs,c > Prefs,sradioc>-108dBm
s (2G) c (3G) t (4G)
Prefc,t > Prefc,cradiot>-108dBmx
CategoryI.A:Unaccessible intermedite cells(3/5)
§ Performanceimpact:muchsmaller¨ Webbrowsing(cnn.com):every1min
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2G
4G
0 600 1200 1800 2400 3000 36Time (s)
US-IUS-II
0
30
60
90
0 10 20 30 40 50 6CD
F (%
)Page loading time (s)
US-IUS-II
CategoryI.A:Unaccessible intermedite cells(4/5)
§ Instance#2:OutofservicefromFemto to4G
§ Cause:missingconfigurationfromFemtoà 4G¨ Improperconfigurationsin3GFemtocells
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Prefs,c = Prefs,sradioc> radios
s (Femto) c (3G)(No/weak relay)
t (4G)
Prefc,t > Prefc,cradiot>-108dBm
CategoryI.A:Unaccessible intermedite cells(5/5)
§ Realitycheck¨ US-I(only):allfemtocells (Nofemtocells inUS-II)
¨ 5outof63locations:4Gbutno/weak3G
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CategoryI.A:Unaccessible intermedite cells(5/5)
§ Realitycheck§ Performanceimpact:
¨ Exp:out-of-servicedurationw/wo 3G
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W 3G
W/o 3G
0 30 60 90 120 150Out-of-service Duration (s)
0
30
60
90
0 20 40 60 80 100CD
F (%
)Out-of-service duration (s)
W/o 3GW 3G
CategoryII.B:BlockedDecision(1/2)§ Instance#3:3Gblockedby2G
¨ Scenario:both3Gand2Gavailablewhenleaving4G;¨ Duringactive
§ Causes:¨ Device:2Gmeas.comesfirst¨ Servingcell:first-come-first-serve¨ improperdevice-networkcoordination
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CategoryII.B:BlockedDecision(2/2)§ Realitycheckonmeasurementcriteriasatisfied
¨ OP-I:60outof63locations(95.2%)¨ OP-II:100%locations
§ Realitycheckonactualhandoffresults¨ OP-I:100%to2G(allservingcellsuseFCFS)¨ OP-II:5.7%to2G(notallservingcellsuseFCFS)
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CategoryII.B:BlockedDecision(2/2)§ Realitycheckonmeasurementcriteriasatisfied§ Realitycheckonactualhandoffresults§ Performanceimpact:handofflatency
¨ 10.8%calldropinUS-II(when2G+3Gavailable)
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0 20 40 60 80
100
0 5 10 15 20 25 30
CDF
(%)
Handoff latency (s)
2G+3G3G
0 20 40 60 80
100
0 5 10 15 20 25 30CD
F (%
)
Handover latency (s)
2G+3G3G
US-I US-II
CategoryII.C:ProblematicDevice-Networkcoordination
§ Instance#4:Outofservicewhen3Gbandunsupported¨ Scenario:movinginto3GareaafterleavingFemtocells
§ Cause:¨ Servingcell:measuringall3Gbands¨ Device’s3Gcapabilitynotcompatible¨ Devicerejection(halt)
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CategoryII.C:ProblematicDevice-Networkcoordination
§ Reality-check¨ Whenmovingoutof3Gfemtocells (US-Ionly)¨ Alltestphones:100%failure
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Q4: LessonsLearnt
BlameWhom?§ Operator:Practicalchallenges
¨ Manyreasonsfortoday’schoices
§ Device(chipsetvendors):Freedom¨ Nothingwrongfromitsperspective
§ Lessons:¨ Verificationrequired(@operator,@device-operator)¨ Easyfixshouldbemadepossible(NFV,easyconfigurationupdates)
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BlameWhom?§ Operator:Practicalchallenges
¨ 2Gcells:expensiveupgrade(Nodirect2Gà4Gpath)¨ Full3Gdeploymentnotguaranteed¨ Seeminglyreasonablestrategies
- FCFS(handoffuponfirstmeas):reducelatencybutmissbetterchoices- Measureall3Gbands:don’tmisshandoffwithoutpriorknowledge
§ Device(chipsetvendors):Freedom¨ Freedom:conductmeas inanyorder;rejectoncefailure
§ Lessons:¨ Verificationrequired(@operator,@device-operator)¨ Easyfixshouldbepossible(NFV,configurationupdatesmadeeasy)
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PossibleFixes§ Device-side:Beamoreproactivelocalcontroller
¨ Self-checkandcorrectifimproperhandoffs¨ Lesson:devicesshouldnotsimplyfollow
§ Network-side:acentralizedcontroller¨ Self-checkandcoordinatehandoffconfigurationsamongcells¨ Makeconfigurationupdateseasy(NFV,ongoing5G)
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Summary§ Firstworktostudyundesiredhandoffreachability
¨ Overlookedinthepast¨ Real-worldcasesreported¨ Rootcausesinmobilitymanagementmisconfigurationsexplored
¨ Makeacallforattentionfromresearchandindustrycommunity
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