what is network latency and why does it matter? · pdf filewhat is network latency and why...
TRANSCRIPT
www.o3bnetworks.com 1
Contents
ThispaperispresentedbyO3bNetworkstoprovideclarityandunderstandingofacommonlymisunderstoodfacetofdatacommunicationsknownaslatency.ItisourgoalthatthereadertakesawayaclearunderstandingoflatencyandgainsinsightintothesignificantadvantagethatO3bNetworksbringstothesatellitecommunicationsmarketforthedevelopingworld.
Executive Summary 2
What Causes Latency? 2
Transmission Rate and Bandwidth 4
Latency and TCP/IP 6
Satellite Link Latencies 7
Applications 10
Summary 10
Appendix 11
What is latency? 11
Networking 101 11
What is Network Latencyand Why Does It Matter? by O3b Networks
www.o3bnetworks.com 2
Executive Summary
Internetdataispackagedandtransportedinsmallpiecesofdata.Theflowofthesesmallpiecesofdatadirectlyaffectsauser’sinternetexperience.Whendatapacketsarriveinasmoothandtimelymannertheuserseesacontinuousflowofdata;ifdatapacketsarrivewithlargeandvariabledelaysbetweenpacketstheuser’sexperienceisdegraded.
Latencyandoverallthroughputisdominatedbytwofactors,thelengthoftheroutethatthepacketshavetotakebetweensenderandreceiverandtheinteractionbetweentheTCPreliabilityandcongestioncontrolprotocols.
ThispaperwilladdressthesourcesofdelaystointernetdataanddescribewhyO3bNetworkssatelliteconstellationhaslowerpathlengthandlatencythantraditionalgeosynchronoussatellitesandinsomecasesfiberbasednetworks.
What Causes Latency?
Regardlessofthespeedoftheprocessorortheefficiencyofthesoftware,ittakesafiniteamountoftimetomanipulateandpresentdata.Whethertheapplicationisawebpageshowingthelatestnewsoralivecamerashotshowingatrafficjam,therearemanywaysinwhichanapplicationcanbeaffectedbylatency.Fourkeycausesoflatencyare:propagationdelay,serialization,dataprotocols,routingandswitching,andqueuingandbuffing.
Propagation Delay
Propagationdelayistheprimarysourceoflatency.Itisafunctionofhowlongittakesinformationtotravelatthespeedoflightinthecommunicationsmediafromsourcetodestination.Infreespace,thespeedoflightisapproximately3x105km/sec.Thespeedoflightislowerinothermediasuchascopperwireorfiberopticcable.Theamountofslowingcausedbythistypeoftransmissioniscalledthevelocityfactor(VF).
Mostpeoplearesurprisedtolearnthatcopperwireandfiber-opticcableshavesimilarvelocityfactors.Fiberopticcablestypicallymeasurearound70%ofthespeedoflightwhereascoppercablevariesfrom40%to80%dependingontheconstruct.CoaxialcableiscommonlyusedandmanytypeshaveaVFof66%.
Satellitecommunicationlinksuseelectromagneticwavestopropagateinformationthroughtheatmosphereandspace.Theinformationisconvertedfromelectricalsignalstoradiosignalsbythetransmitterandtheantenna.Oncetheseradiosignalsleavetheantenna,theytravelapproximatelyatthespeedoflightforfreespace.
Let’scalculatehowlongitwilltakeanemailtotravelfromNewYorktoLondonassumingthatwearetheonlyuseronaprivatecommunicationschannel.
What is Network Latency and Why Does It Matter?
www.o3bnetworks.com 3
Ignoringtheactualroutestakenbyunderseacablesduetotheocean’sfloor,let’sassumethepathfromNewYorktoLondonisthegreatcircledistanceof5458km.
Propagation delay = distance/speed:
The email sent using a copper link: 5458 / 197863.022 = 23.58 msThe email sent using a fiber-optic link: 5458 / 209854.720 = 26.01 msThe email sent using a radio link: 5458 / 299792.458 = 18.21 ms
Thesearethelatenciescausedonlybypropagationdelaysinthetransmissionmedium.Ifyouweretheonlyonesendingonesingledatabitandyouhadunlimitedbandwidthavailable,thespeedofthepacketwouldstillbedelayedbythepropagationdelay.
Thisdelayhappenswithoutregardfortheamountofdatabeingtransmitted,thetransmissionrate,theprotocolbeingusedoranylinkimpairment.
Serialization Delay
Serializationistheconversionofbytes(8bits)ofdatastoredinacomputer’smemoryintoaserialbitstreamtobetransmittedoverthecommunicationsmedia.Serializationtakesafiniteamountoftimeandiscalculatedasfollows:
Serializationdelay=packetsizeinbits/transmissionrateinbitspersecond
For example:
- Serialization of a 1500 byte packet used on a 56K modem link will take 214 milliseconds
- Serialization of the same 1500 byte packet on a 100 Mbps LAN will take 120 microseconds
Serializationcanrepresentasignificantdelayonlinksthatoperatealowertransmissionrates,butformostlinksthisdelayisatinyfractionoftheoveralllatencywhencomparedtotheothercontributors.
Voiceandvideodatastreamsgenerallyusesmallpacketsizes(~20msofdata)tominimizetheimpactofserializationdelay.
Data Protocols and Latency
Datacommunicationsprotocolsatvariouslayersintheprotocolstackusehandshakessynchronizethetransmitterandreceiver,forthetransmitterandreceivertoupdateeachotheronlinkstatusandtocorrectforerrosintransmission.Thesehandshakestaketimetopropagateacrossthelinkandcanaddtothelatencyofthetransmissionofinformationfromsourcetodestination.
What is Network Latency and Why Does It Matter?
www.o3bnetworks.com 4
Routing and Switching Latencies
InIPnetworkssuchastheInternet,IPpacketsareforwardedfromsourcetodestinationthroughaseriesofIProutersorswitchesthatcontinuouslyupdatetheirdecisionaboutwhichnextrouteristhebestonetogetthepackettoitsdestination.Arouterorcircuitoutageorcongestiononalinkalongthepathcanchangetheroutingpathwhichinturncanaffectthelatency.
HighperformanceIProutersandswitchesaddapproximately200microsecondsoflatencytothelinkduetopacketprocessing.IfweassumethattheaverageIPbackbonerouterspacingis800km,the200microsecondsofrouting/switchingdelayisequivalenttotheamountoflatencyinducedby40kmoffiber;routing/switchinglatencycontributestoonly5%oftheendtoenddelayfortheaverageinternetlink.
Queuing and Buffer Management
Anotherissuewhichoccurswithinthetransportlayersiscalled“queuinglatency”.ThisreferstotheamountoftimeanIPpacketspendssittinginaqueueawaitingtransmissionduetoover-utilizationoftheoutgoinglinkaftertherouting/switchingdelayhasbeenaccountedfor.Thiscanadduptoanadditional20msoflatency.
Transmission Rate and Bandwidth
TransmissionRateisatermusedtodescribethenumberofbitswhichcanbeextractedfromthemedium.Transmissionrateiscommonlymeasuredasthenumberofbitsmeasuredoveraperiodofonesecond.
The“maximumtransmissionrate”describesthefundamentallimitationofanetworkmedium:
IfthemediumisacopperLocalAreaNetwork,maximumtransmissionratesarecommonly10,100,or1000Megabitspersecond.Theseratesareprimarilylimitedbythepropertiesofthecopperwiresandthecapabilitiesofthenetworkinterfacecardarealsoafactor.
Fiber-opticthetransmissionratesrangefromaround50Mbpsupto100Gbps.Unlikecoppernetworks,theprimaryfactorlimitingfiber-optictransmissionratesistheelectronicswhichoperatesateachendofthefiber.
Wirelesslocalareanetworks(LANs)andsatellitelinksusemodems(modulator/demodulator)toconvertdigitalbitsintoananalogmodulatedwaveformatthetransmitterendofalink,andthenatthereceiveendademodulatorwillthenconverttheanalogsignalbackintodigitalbits.Thelimitingfactorintransmittinginformationoverradio-basedchannelsisthebandwidthofthechannelthatisavailabletoaparticularsignalandthenoisethatispresentthatwillcorruptthesignalwaveform.
What is Network Latency and Why Does It Matter?
www.o3bnetworks.com 5
Radio Channel Bandwidth and Noise
Signalstransmittedusingradiowavesoccupyradiospectrum.Radiospectrumisnotanunlimitedresourceandmustbeshared.Topreventradiointerferencebetweenuserstheuseofradiospectrumiscontrolledbynearlyeverygovernmentontheplanet.Theamountofradiospectrumoccupiedbyanygivenradiosignaliscalleditsbandwidth.
Thenatureofradiospectrumuseisbeyondthispaperbutit’simportanttounderstandthatgenerallytheoccupiedradiospectrumofamodemsignalwillincreasewiththedatarate:
- Higher modem data rates cause the modem to occupy more radio bandwidth
- Lower modem data rates will let the modem occupy less radio bandwidth
Sinceradiospectrumisalimitedresource,theoccupiedradiobandwidthisanimportantlimitingfactorinwirelessandsatellitelinks.
Noiseintheradiochannelwillperturbtheanalogsignalwaveformandcancausethedemodulatoratthereceivertochangeadigitaloneintoazeroorviceversus.Theeffectofnoisecanbeovercomebyincreasingthepowerlevelofthetransmittedsignal,orbyaddingafewextraerrorcorrectingbitstothedatathatisbeingtransmitted.Theseerrorcorrectingbitshelpthereceivercorrectbiterrors.However,theerrorcorrectionbitsincreasethebandwidththatisrequired.
Data Bandwidth
Indatatransmission,thedatabandwidthissynonymoustothetransmissionratebeingused.Bandwidthisimportantbecauseitdefinesthemaximumcapacityofadatalink.
- A 10 Mbps copper LAN cannot sustain traffic flowing at a higher rate than 10 megabits every second.
- A satellite link using modems operating at a 600 Mbps rate cannot flow any more than 600 megabits every second.
It’sveryimportanttounderstandthatdatabandwidthisamaximumdataflowobtainableoveragiventransportationsegmentoveragivenperiodoftime.
What is Network Latency and Why Does It Matter?
www.o3bnetworks.com 6
Latency and TCP/IP
ThefinaldetailrequiredforunderstandingwhylatencyisimportantisanunderstandingofwhatisgoingonattheTransportprotocollayer.TheTransportlayersitsbetweentheapplication-specificApplicationlayerandtheIPlayerthatisusedforpacketrouting.TheTransportlayerperformsanumberoffunctionsincludingsequencingthepacketsintotheirproperorder.
There are two types of Transport layer protocols:
- connectionless - connection-oriented
Connectionlessdataprotocolssimplypushthedatapacketstotheenddestinationwithoutregardforpacketlossorpacketorder.Connectionlessprotocolsareoftenusedforreal-timecommunicationssuchasvoiceorinteractivevideowhereretransmissionoflostpacketsisnotusefulbecausetheywillarrivetoolatetobeplayedout.IntheInternet,themostcommonconnectionlessTransportlayerprotocolistheUserDatagramProtocol(UDP).
Connection-orientedprotocolsaremorecomplex.Theseprotocolsrelyontheestablishmentofa“connection”whichrequireshandshakesandinteractionbetweenthesourceanddestinationcomputers.Connection-orientedTransportprotocolsprovideerrorfreesequenceddeliveryofpackets.Themostcommonconnection-orientedTransportprotocolusedintheInternetistheTransmissionControlProtocol(TCP).IfpacketsarriveoutofordertheTCPlayerputsthembackinorder.Ifpacketsaremissingorcorruptedintransmission,TCPusesanacknowledgement(destinationbacktosourcefeedback)mechanismtoaskforthemissingorcorruptedpackettoberetransmitted.TheTCPprotocolalsomeasurestheperformanceofthelinkintermsofavailablebandwidth,delayanderrorrate.Usingawindowingtechnique,itadjuststhetransmissionrateofdatapacketstomatchtheabilityofthechannelbetweensourceanddestinationtoacceptthemanddeliverthemcorrectly.AstheTCPprotocolatthesourceanddestinationdeterminethatthechannelisoperatingefficientlywithlowdelay,itwillopenthewindowtoallowmorepacketstobeoutstanding(inflightbetweenthesourceanddestinationandnotyetacknowledged).Thishastheeffectofincreasingthetransmissionrate.Aserrors,congestion,ordelayincreases,theTCPprotocolwillclosedownthewindowtoslowdownthetransmissionrate.Becauseofthehighdelaysingeosynchronoussatellitelinks,theTCPprotocolactstoreducetheoverallthroughputofthelink.Tocompensateforthis,satellitelinkequipmentvendorshavedevelopedTCPspoofingmechanismsthatfaketheTCPhandshakebyterminatingtheTCPlinklocallytothetransmittingsiteandtrytoconvincethetransmittingsitethatthelinkhaslowerdelaythanitreallyhas.Thisspoofingworksifthelinkisrelativelyuncongestedandhasaverylowerrorrate,whichisnotnecessarilythecaseforsatellitelinks.
What is Network Latency and Why Does It Matter?
www.o3bnetworks.com 7
Satellite Link Latencies
Satellitelinkscanintroducelargerlatenciesthanmostterrestrialnetworkingsegmentsduetolongdistancesfromthegroundstationstothesatellite.Thefollowingtableshowsthelatencycausedbypropagationdelaysfromtwotypesofsatelliteconfigurations,1)theO3bNetworksMEOorbitconstellationatanaltitudeof8063Kilometers,2)ageosynchronoussatelliteat35,786Kilometers.
Altitudeiskeydeterminateinlatencybecausethehigherthesatellitethegreaterthelatency.
Forsatelliteswhichoperateasabent-pipe,thepropagationdelaysaredoubledsincethesignalhastotravelbothuptothesatelliteandbackdowntotheearthbeforeitreachesthenextsegmentofthenetwork.
ThefollowingtablecomparestwotypesofsatellitesusingagroundstationinLagos,Nigeria.
What is Network Latency and Why Does It Matter?
Latency Calculations – London Internet Exchange (LINX) to Lagos
Gateway to Satellite km
Customer to Satellite km
Gateway to Satellite msec
Customer to Satellite msec
Total Sat RTT msec
Fiber to LINX km
Fibre RTT msec
Total Sat RTT msec
O3b w/8 SatellitesSpain GWY Lagos
10126 8135 33.8 27.1 121.7 2144 10.7 132.5
GeosyndchronousSatUK Teleport Lagos
38,469 35,847 128.2 119.5 495.4 135 0.7 496.1
Fiber
London Lagos km
Total Fiber RTT
8,000 80.0
Satellite Latency Calculations
TheO3bNetworksMEOsatelliteusingtoateleportinSpainwillexperienceroundtriptime(RTT)ofapproximately122msec.IfweaddintheaverageInternetlatencyfromtheSpainteleporttotheLondonInternetExchange(LINX)(~10msec.),weendupwithanoveralllatencyfromLagostoaEuropeaninternetsiteof132.5msec.O3b’s132.5msec.roundtriplatencyisclosetofiber’s80msec.RTT
Bycomparison,thesameLagoscustomersiteusingageosynchronoussatellitetoaUKTeleportandthenontoLINXwillhavelatenciesof496msec.
ToactuallyretrieveawebpagefromanInternetserveratLINX,willtakesomeadditionaltimeforthedatarequestpacketsandtheiracknowledgments:
www.o3bnetworks.com 8
What is Network Latency and Why Does It Matter?
This data request time includes:
- Therequestpacketfromtheusertothewebserver- Thewebserveracknowledgingtherequest- Thewebserverpushingtorequesteddatatotheuser- Thedataarrivingattheuser’scomputer
Geosynchronoussatelliteusersmustwaitalmost750msec.beforetheystartgettingdata,whereasthelowerlatencyO3bsatellitelinkwillreceiveitnearly4xsooner.
Anotherproblemwithhighlatencylinksistheintroductionofalargeamountofinter-packetjitterduetotheTCPprotocolflowcontroloperatinglessefficientlyoverlongerdelaypaths.ThefollowingplotsweremadeusingaTCP/IPpacketcaptureutility.Theseplotsshowthepacketbitrateonthey-axisandtimeofdayonthex-axis.Thedatabeingtransmittedwastheun-cachedweb-pagere-loadofthecontentfromtheCNNwebpage(http://www.cnn.com).
Theonlyconditionchangedduringwasthedelaybetweenpackets–thetransmissionrateremainedthesame.
www.o3bnetworks.com 9
TheaddednetworklatencyanditaffectontheflowofTCPdataspreadthewebpageloadovertime.
• The 50 ms latency link took 3 seconds• The 150 ms latency link took 5 seconds• The 300 ms latency link took 11 seconds• The 600 ms latency link tool 17 seconds
Thespreadingofnetworkdataovertimereduceswhat’scalledthe“EffectiveBandwidth”ofalink.Packetsarestillbeingtransportedatthesamebitratebutduetolatencyitistakingmuchmoretimeforalloftheweb-pagepacketstoarrive.
It’sthis“spreadingovertime”behaviorofhighlatencynetworkswhichbecomesnoticeabletotheuserandcreatestheimpressionthatalinkisnotoperatingatahighspeed.
O3brecentlyconductedanotherdemonstrationofreal-worldeffectsoflatencyusingthetimetoloadawebpage.Thisisaverycommonactivityandclearlyshowsusersthatlatencydirectlyaffectsthewayauserobtainsdatafromtheinternet.
ThefollowingplotsshowtheeffectsoflatencyonthetimetoloadtheWallStreetJournalwebpage(http://www.wsj.com):
Web Page Load Time: wsj.com to Florida
Itisclearthatwebpageloadtimesdramaticallyincreasewhenlatencyincreases.Inthiscasedoublingthelatencynearlydoubledthewebpageloadtimes
Whenlookingatthebasiclatencynumbers,it’seasytoseethattheO3bSatelliteconstellationwillofferusersanoticeablybetterinternetexperiencewithmoreimmediatefeedbackandquickeraccesstodata.
What is Network Latency and Why Does It Matter?
www.o3bnetworks.com 10
Applications
Whatapplicationscannowberunoverlowerorbitsatellitesthatwerepossibleafewyearsago?
Manyapplications,suchasbasicwebsitedownloads,Internetvideostreamingthatoperatedsluggishly(orwereveryslowtostartup)overgeosynchronoussatellitelinksnowhavemuchfasterresponseandworkmuchbetteroverO3b’slowlatencyconnections.Videoconferencingandregularvoicecallsovergeosynchronoussatelliteswereverystiltedandnon-interactive.Conversationswere“half-duplex”andonepartyhadtowaitfortheotherpartytofinishtalkingbeforetheycouldstartup.Youcouldnotbreakintoaconversationandinterrupt.VoicecallsandvideoconferencingaremuchmorenaturalandinteractiveoverO3b’slinks.Interactivegamingplayerswhowereontheendofageosynchronoussatellitelinkwereoftenkilledbeforetheycouldgetashotoff.Nowtheycanbefullparticipantsintheaction.
Manybusinessapplicationssuchasremotedatabaseaccessandinteractivetransactionprocessingcontainsoftwaretimersthatdonotadjustforlongdelaysovergeosynchronoussatellites.Examplesincludemanybankingapplicationsandairlinereservationandschedulingapplications.Nowtheseapplicationswillworkforusersthatareinremoteunderservedlocations.
Summary
WehavedescribedthestructureofIP-basedpacketswitchednetworks,thefunctionsofthevariousprotocollayers,andthecausesoflatencyinpacketswitcheddatanetworks,suchastheInternet.Latencyandoverallthroughputisdominatedbytwofactors,thelengthoftheroutethatthepacketshavetotakebetweensenderandreceiverandtheinteractionbetweentheTCPreliabilityandcongestioncontrolprotocolsandthispathlength.O3bNetworkssatelliteconstellationinamuchlowerMEOorbithassignificantlylowerpathlengthandthereforesignificantlylowerlatencythantraditionalgeosynchronoussatellites.O3b’snetworklatencyandthroughputapproximatethatoffiber-basedterrestrialnetworksandpermitusersinremotelocationsthatarenotservedbyfibertorunmanyapplicationsthatonlyworkoverfiber.
What is Network Latency and Why Does It Matter?
www.o3bnetworks.com 11
Appendix:
What is latency?
Definition of Latency from Wikipedia:
Latencyisatimedelaybetweenthemomentsomethingisinitiated,andthemomentoneofitseffectsbeginsorbecomesdetectable.Thewordderivesfromthefactthatduringtheperiodoflatencytheeffectsofanactionarelatent,meaning“potential”or“notyetobserved”.
Mostpeopleunderstandthatittakestimeforwebpagestoloadandforemailstogetfromyouroutboxtothedestinationinboxandyes,thisisaformoflatency.Butinordertounderstandwhythishappensweneedtothinkaboutlatencyatalowerlevel:
Latencyisatimedelayimpartedbyeachelementinvolvedinthetransmissionofdata.
Theremainderofthispaperwilldiscussthespecificmechanismsinvolvedandhowlatencylimitstheperformanceofadatacommunicationslink.
Networking 101
It’simportantforthereadertounderstandtheverybasicelementsofnetworkingtoproperlygraspthelatencyissue.
Earlynetworkingengineersanticipatedtheneedbeabletohandlethousandstomillionsofusersononecohesivenetwork,andthustheTCP/IPnetworkingmodelwasdeveloped.
ThekeydesignfeatureoftheTCP/IPnetworkingmodelistheconceptofencapsulationwhichistheideaoftakingdataandwrappingitinacommoncontainerforshipping.ThecontainerthatwasdevelopediscalledtheIPDatagram,alsoknownasan“IPPacket”.
TheIPPacketisaverysimplething:aheader,followedbydata.
TheHeadercontainsinformationusedforroutingthepackettothedestination.Thedatacanbeanyinformationwhichneedstobetransportedsuchasasnippetofstreamingmusicoraportionofemailtraffic.TheexactconstructofthedataportionofanIPPacketisdefinedbythedataprotocolthatisbeingcarried.Dataprotocolswillbediscussedlater.
Tounderstandexactlywherelatencyoccurs,it’svaluabletoknowhowthismostbasicunitofnetworkingdataisbuiltandtransported.ForthisweturntotheOSIModel:
What is Network Latency and Why Does It Matter?
www.o3bnetworks.com 12
The OSI Model
TheOSImodelwascreatedtodescribetheprocessofturningyourapplicationdataintosomethingthatcanbetransportedontheinternet.
TheupperlayersoftheOSImodeldescribethingsthathappenwithintheapplicationsthatarerunningonthecomputer.Theseapplicationsarewebbrowsers,emailprograms,etc.
Thelowerlayersarewhereinformationtoandfromapplicationsareturnedintodatafortransportonanetwork.Thisiswheredataencapsulationoccursandourbasicnetworkingdataelement–theIPDatagramor“packet”isbuilt.
Thefollowingdiagramshowstheencapsulationprocessinwhat’sknownastheTCP/IPStack.ThepreciseworkingsoftheTCP/IPstackcanbedifferentbetweenvariouscomputeroperatingsystems.Thesedifferencesmayseemtrivialaslongastheprotocolsareimplementedproperlybutwhenseekingtheabsolutehighestlevelsofperformanceit’simportanttoknowthatthenetworkstackimplementationcanbeasignificantcauseofnetworkingperformancevariability.
What is Network Latency and Why Does It Matter?
Application LayerMessageformat,Human-MachineInterfaces
Presentation LayerCodinginto1sand0s;encryption,compression
Session LayerAuthentication,permissions,sessionrestoration
Transport LayerEnd-to-enderrorcontrol
Network LayerNetworkaddressing;routingorswitching
Data Link LayerErrordetection,flowcontrolonphysicallink
Physical LayerBitstream:physicalmedium,methodofrepresentingbits
Tran
spor
t se
rvic
eU
pper
Lay
ers 7
6
5
4
3
2
1
www.o3bnetworks.com 13
Upper Layers
Upper Layers
Upper Layer Message
Upper Layer
Headers
Upper Layer
Headers
TCP /UDPHeader
Upper Layer(Application) Data
Upper Layer(Application) Data
TCP/UDP Message
Upper Layer
Headers
TCP /UDPHeader
IPHeader
Upper Layer(Application) Data
IP Datagram
Upper Layer
Headers
TCP/UDPHeader
IPHeader
Layer 2Header
Layer 2Header
Upper Layer(Application) Data
Layer 2 Frame
1 0 0 1 0 1 1 0 1 1 0 0 1 0 1 1
TCP /UDP
IP
Layer 2
Layer 1
TCP /UDP
IP
Layer 2
Layer 1
The TCP/IP Stack
Thetransportofnetworkdataisathreestepprocess:
1. Data from a source application is passed down through the stack. During this process the application data is wrapped into IP Datagrams which are commonly called “packets”. Packets are then transmitted by the sending computer in the network
2. Packets are passed along the network (purple line) until they reach the destination computer
3. Packets are received from the network by the destination computer and are passed up through the stack. During this process the application data is extracted and the passed along to the destination application.
TheadditionalencapsulationatLayer2iscalledframing.ThisisthestagewheretheIPDatagramisturnedintobitswhichareappropriateforaparticulartypeofnetwork.
Layer1isthephysicalnetworkmediumconnection.Thislayerhandlestheconversionofthelayer2bitsintoelectrical,optical,orradiosignalsthatcanbetransported.Thenetworkinterface,oftencalledtheNICorNetworkInterfaceCard,canbefiber-optic,copperwire,orawirelessradiointerface.
What is Network Latency and Why Does It Matter?