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LINKNAME LINKSPEED 1SECTRAFFIC SECSOFTRAFFIC INA10GBCACHE OC24 12Gbps 015GBs 64secs OC48 24Gbps 031GBs 32secs OC192 99Gbps 125GBs 4secs OC768 398Gbps 5GBs 2secs OC1536 796Gbps 1 ID: 479988
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networktrafcredundancy[5]andcachingredundancy[13],[9].Cachinghasbeentraditionallyusedtoreducetrafcredundancy[4],[6].Assumingasetofavailablecaches,asopposedtoasingleproxycache,redundancycanstillexistbetweencachedcontentsindifferentlocations,somethingthathasalsobeeninvestigatedinthepastforoverlaycachingschemes[13],[9].However,andasmentionedearlier,overlayschemesrequiresomeformofco-operationbetweenthecachesthemselvesand/orbetweenthecachesandacentralmanagemententity.Incontrast,inthecaseofin-networkcaching,managementhastohappeninanuncoordinated,uncooperativefashion.Inthispaper,weconsidereachpathofcachingentitiesasapoolofcachingresources;wetrytondoptimalwaysofdistributingcontentinthesecachesinordertoeliminatecachingredundancyandinturn,reducetrafcredundancy.Ourresultsshowthatcarefulcontentowmultiplexingincachescanachieveupto20%morecachehits.Surprisingly,thistranslatestooneorderofmagnitudereductionintermsoftrafcredundancy.II.SYSTEMMODELANDASSUMPTIONSWearguethatin-networkcachemanagementhastotakeintoaccounttheapproximatecachecapacityofthepathofcachesandtheestimatedamountoftrafcthatthesecachesserveperunittime,inordertomakedecisionsonwhethertocacheincomingcontentsornot.InSectionII-A,wemakeassumptionsthathelpusapproximatethecachecapacityofagivenpathandinSectionII-B,wepresentourdesignprinciples.A.AssumptionsonCachingTechnologiesBydenition,cachingisdifferenttostorage,bothinnet-worksandincomputersystems,inthatcachingkeepscontentsstoredforaspecicamountoftimeandnotindenitely,asinstorage.Therefore,thesizeofacacheisarelativefactor,whichcannotstandonitsown,butinsteadhastobelinkedtotheamountoftimethatagivencontentiscachedfor.We,therefore,associatethecachesizewiththetrafcthatthecorrespondingrouterservespersecond.Ourcachesizeunitisthenumberofsecondsworthoftrafccachedinagivenrouteranddependsonthespeedoftheoutgoinglinksoftherouterinquestion.Oneimportantquestionthenis:“Forhowlongcanweaffordtocachecontentsinagivenrouter?”.Furthermore,giventhatinthisstudyweareconcernedwithpathsofcachesandnotwithsingle-cachesonly,anotherimportantquestionis:“Forhowlongdoweneedtocachecontentsinagivenpathinordertominimiseredundanttrafcandmaximisegain?”.Ourreasoningforansweringthesequestionsisasfollows:Today'smemoryaccesstechnologiesguaranteeline-speedaccesstoDRAMchipsofupto10GBytesatareasonableprice[16].Thismeansthata5GByte-long LINKNAME LINKSPEED 1-SECTRAFFIC SECSOFTRAFFIC INA10GBCACHE OC-24 1,2Gbps 0.15GBs 64secs OC-48 2,4Gbps 0.31GBs 32secs OC-192 9,9Gbps 1.25GBs 4secs OC-768 39,8Gbps 5GBs 2secs OC-1536 79,6Gbps 10GBs 1sec OC-3072 159,2Gbps 20GBs 0.5secs TABLEILINKSPEEDSANDRELATEDCACHINGPROPERTIEScachebehinda40Gbpslink1cansafelybeassumedtoholdcontentsforonesecond(seealsoTableI).Withoutlossofgenerality,weassumethateachcachealongapathhassufcientmemorytocachecontentsinaDRAMchipforatleastonesecond(seethirdcolumninTableI).Authorsin[5]showupto60%bandwidthsavingsbyredundanttrafceliminationwithintherst10secondsaftertheoriginaltransmission,insomeenterprisenet-works.Weassociateredundanttrafc,i.e.,subsequentrequestsforthesamecontent,withtheaforementionedresult.Thatis,weconsider,withoutlossofgenerality,thatanycontentshouldbekeptinanyoneofthepath'scachesforatargettimewindow,Ttw,of10seconds.Boththeabovesettingsarerelativelyarbitraryandcanchangeinthefuture,butthesevaluesareagoodstartingpointbasedontoday'stechnology.Inaddition,ourconceptsandalgorithmspresentednextarestillapplicableshouldthesevalueschange.B.SystemModelWeassumethetopologyofFig.1.Thepathfromsourcetodestinationcomprisesnrouters,whererouterrihasNicacheslots,eachabletoholdoneaddressablecontentchunk;basedonthediscussionabove,weassumethatNislotscanholdonesecondworthoftrafc.OurmodelnotationisgiveninTableII.PathCacheCapacity.ThecachingcapacityofourpathofcachesisPni=1Ni,intermsofmemory,whichamountstonsecondsworthoftrafccachedalongthepath.PathCacheCapability.GiventhatourtargettimewindowisTtwsecondsworthoftrafccachedalongagivenpath,thecachingcapabilityofann-longpath,asafractionoftherequiredcapacityforTtwseconds,isPni=1Ni TtwN,whereNistheaveragecachesizealongthepath.Werevisittheissueofaveragecachesizeinthenextsection.SymmetricPaths.RequestandContentmessagesfollowthesameroute,accordingtorecentproposals[1],[19],[2],[21].PathLengthMonitoring.SimilartotheTTLeldincludedinIPpackets,ourdesignrequiresthatICNrequestmessage1Tothebestofourknowledge,operatorstodateuselinksofupto40Gbps,whilesomeoperatorsplantoupdatealimitednumberoftheirlinksto100Gbps:http://www.prnewswire.com/news-releases/verizon-rst-service-provider-to-announce-100g-deployment-on-us-network-118891754.html