Data dissemination

mobile computing

1. Data Dissemination
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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2. •Datadisseminationentailsdistributingand
pushingdatageneratedbyasetofcomputing
systemsorbroadcastingdatafromaudio,
video,anddataservices.
•Theoutputdataissenttothemobiledevices.
•Amobiledevicecanselect,tuneandcache
therequireddataitems,whichcanbeusedfor
applicationprograms.
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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3. Classification of Data-Delivery
Mechanisms
•Therearetwofundamentalinformationdelivery
methodsforwirelessdataapplications:
1.Point-to-Pointaccess
2.Broadcast
•Therearethreekindsofbroadcastmodels:
1.push-basedbroadcast
2.On-demand(orpull-based)broadcast
3.hybridbroadcast
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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4. Push-based Mechanisms
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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5. Push-basedmechanismsfunctioninthefollowingmanner:
1.Astructureofdatarecordstobepushedisselected.An
algorithmprovidesanadaptablemulti-levelmechanismthat
permitsdataitemstobepusheduniformlyornon-uniformly
afterstructuringthemaccordingtotheirrelativeimportance.
2.Dataispushedatselectedtimeintervalsusinganadaptive
algorithm.Pushingonlyoncesavesbandwidth.However,
pushingatperiodicintervalsisimportantbecauseitprovides
thedevicesthatweredisconnectedatthetimeof
previouspushwithachancetocachethedatawhenitispushed
again.
3.Bandwidthsareadaptedfordownlink(forpushes)usingan
algorithm.Usuallyhigherbandwidthisallocatedtorecords
havinghighernumberofsubscribersortothosewith
higheraccessprobabilities.
4.Amechanismisalsoadoptedtostoppusheswhenadeviceis
handedovertoanothercell.
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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6. Advantages
•Push-basedmechanismsenablebroadcastofdata
servicestomultipledevices.
•Theserverisnotinterruptedfrequentlybyrequests
frommobiledevices.
•Thesemechanismsalsopreventserveroverload,
whichmightbecausedbyfloodingofdevice
requests
•Also,theuserevengetsthedatahewouldhave
otherwiseignoredsuchastrafficcongestion,
forthcomingweatherreportsetc
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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7. Disadvantages
•Push-basedmechanismsdisseminateof
unsolicited,irrelevant,orout-of-contextdata,
whichmaycauseinconveniencetotheuser.
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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8. Pull based Mechanisms
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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9. Pull-basedmechanismsfunctioninthefollowingmanner:
1.Thebandwidthusedfortheuplinkchanneldepends
uponthenumberofpullrequests.
2.Apullthresholdisselected.Thisthresholdlimitsthe
numberofpullrequestsinagivenperiodoftime.This
controlsthenumberofserverinterruptions.
3.Amechanismisadoptedtopreventthedevice
frompullingfromacell,whichhashanded
overtheconcerneddevicetoanothercell.On
devicehandoff,thesubscriptioniscancelledor
passedontothenewserviceprovidercell
4.Inpull-basedmechanismstheuser-devicereceives
datarecordssentbyserverondemandonly.
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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10. AdvantagesofPullbasedmechanisms:
•Withpull-basedmechanisms,nounsolicitedor
irrelevantdataarrivesatthedeviceandtherelevant
dataisdisseminatedonlywhentheuserasksforit.
•Pull-basedmechanismsarethebestoptionwhenthe
serverhasverylittlecontentionandisabletorespond
tomanydevicerequestswithinexpectedtime
intervals.
Disadvantages:
•Theserverfacesfrequentinterruptionsandqueuesof
requestsattheservermaycausecongestionincasesof
suddenriseindemandforcertaindatarecord.
•Inon-demandmode,anotherdisadvantageisthe
energyandbandwidthrequiredforsendingthe
requestsforhotitemsandtemporalrecords
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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11. Hybrid Mechanisms
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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12. Hybrid mechanisms function in the following manner:
1.Therearetwochannels,oneforpushesbyfrontchannel
andtheotherforpullsbybackchannel.
2.Bandwidthissharedandadaptedbetweenthetwo
channelsdependinguponthenumberofactivedevices
receivingdatafromtheserverandthenumberofdevices
requestingdatapullsfromtheserver.
3.Analgorithmcanadaptivelychoptheslowestlevelofthe
scheduledpushessuccessivelyThedatarecordsatlower
levelwheretherecordsareassignedlowerprioritiescan
havelongpushintervalsinabroadcastingmodel.
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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13. AdvantagesofHybridmechanisms:
•Thenumberofserverinterruptionsandqueued
requestsaresignificantlyreduced.
Disadvantages:
•PPdoesnoteliminatethetypicalserverproblemsof
toomanyinterruptionsandqueuedrequests.
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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14. Selective Tuning and Indexing
Technique
•Selectivetuningisaprocessbywhichclientdeviceselectsonlythe
requiredpushedbucketsorrecords,tunestothem,andcaches
them.
•Tuningmeansgettingreadyforcachingatthoseinstantsand
intervalswhenaselectedrecordofinterestbroadcasts.
•Broadcastdatahasastructureandoverhead.
•Databroadcastfromserver,whichisorganizedintobuckets,is
interleaved.
•Theserverprefixesadirectory,hashparameter(fromwhichthe
devicefindsthekey),orindextothebuckets.
•Theseprefixesformthebasisofdifferentmethodsofselective
tuning.
•Accesstime(t
access)isthetimeintervalbetweenpullrequestfrom
deviceandreceptionofresponsefrombroadcastingordata
pushingorrespondingserver.
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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15. •Indexingisanothermethodforselectivetuning.Indexestemporarilymap
thelocationofthebuckets.
•Ateachlocation,besidesthebitsforthebucketinrecordofinterestdata,
anoffsetvaluemayalsobespecifiedthere.
•Whileanindexmapstotheabsolutelocationfromthebeginningofa
broadcastcycle,anoffsetindexisanumberwhichmapstotherelative
locationaftertheendofpresentbucketofinterest.
•Offsetmeansavaluetobeusedbythedevicealongwiththepresent
locationandcalculatethewaitperiodfortuningtothenextbucket.
•Allbucketshaveanoffsettothebeginningofthenextindexedbucketor
item.
•Indexingisatechniqueinwhicheachdatabucket,record,orrecordblock
ofinterestisassignedanindexatthepreviousdatabucket,record,or
recordblockofinteresttoenablethedevicetotuneandcachethebucket
afterthewaitaspertheoffsetvalue.
•Theservertransmitsthisindexatthebeginningofabroadcastcycleas
wellaswitheachbucketcorrespondingtodataofinteresttothedevice.
•Adisadvantageofusingindexisthatitextendsthebroadcastcycleand
henceincreasest
access.
10/10/2019
Vikram Neerugatti, SVCET, Chittoor, Andhra
Pradesh.
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