
Description
6418771XGX-5B 3
Description
GPONtechnologyprovidesaconsistentandcommonapproachtoadvancingthepublic
communicationsnetworkusing:
• Traditionaltelephoneservices(PlainOldTelephoneService(POTS))
•Highspeeddataservices
•Videoservices
TheGPONnetworkconsistsofanOpticalLineTerminal(OLT)locatedatthecentraloffice
andasetofOpticalNetworkTerminals(ONTs)locatedatthecustomer’spremises.Between
themliestheOpticalDistributionNetwork(ODN)consistingoffibersandpassivesplittersor
couplers.Asplitterisadevicethatdividesanopticalsignalintotwoormoresignals.Itcan
alsoreassemblesignalsfrommultiplesignalsourcesintoonesignal.TheGPONtechnologyis
basedonPassiveOpticalNetwork(PON)technology.
Traditionally,telecommunicationnetworksusedevicesthatrequirepowertotransmitdata
fromonepointtoanotherincludingprocessors,memorychips,repeaters,andrelays.With
passiveopticalnetworks,componentsthatneedpowertotransmitdatabetweenthecentral
officeandthecustomerpremisesarereplacedbypassivecomponentsthatguidetrafficbased
onsplittingopticalwavelengthstoendpointsalongtheway.Thesepassivecomponents,such
assplittersandcouplerdevices,workbypassingorrestrictinglightanddonotrequirepower
totransmitdata.
InaPON,asinglepieceoffibercanberunfromtheservingexchangeouttoasubdivisionor
officepark.Then,individualfiberstrandscanberuntoeachbuilding.Also,serving
equipmentcanbesplitfromthemainfiberusingpassivesplitters/couplers.Thisallowsone
pieceoffibercablefromtheexchangetothecustomertobesharedbymanycustomers.This
dramaticallylowerstheoverallcostsofdeploymentforFiberToThePremises(FTTP)applica‐
tions.
Inthistypeofnetwork,subscriber’svoice,video,anddatadevicesareconnectedtotheGPON
viatheONT.TheONTtranslatesIPdataandanalogvoiceintoGPONEncapsulatedMethod
(GEM)framesandcombines/splitsthesignalwithanalogand/ordigitalvideotoandfromthe
OLT.Thesignalissplit/combinedattheOLTsimilartotheONT.
GEMisbasedontheSONET/SDHGenericFramingProcedure(GFP)forhandlingtime
divisionmultipleaccess(TDMA),ATMandEthernetbasedtrafficwithoutadditionalencap‐
sulationprotocols.
SignaltransmissionfromONTstoOLTusesatypeofTDMA.TDMAisatechniqueusedto
framechannelsofdata.Inthistechnique,datacommunicationsessionsoriginatingfrom
multiplepointsaretransmittedinturn.Eachdatacommunicationsessionisassignedatime
slotintheTDMAframeandtransmits(oraccessesthattimeslot)onlyatthattime.
Inordertoallowforthetransmissionofdownstreamandupstreamtrafficonasinglefiber,
differentwavelengthsareusedforbothdirections.Downstreamtrafficuses1490nmwhile
upstreamtrafficuses1310nm.ForoverlayRFTVdistribution,aseconddownstream
wavelengthof1550nmisused.
DownstreamdataisbroadcastfromtheOLTtoallONTs.EachONTprocessesthedata
destinedtoitbymatchingtheaddressattheprotocoltransmissionunitheader.The
downstreamPONsignalisbroadcasttoupto32ONTswithadatarateof2.5Gbpsforvoice
anddata,plustheadditionalvideooverlaywavelengthdivisionmultiplexing(WDM)signal.
IntheupstreamdirectiontransmissionofdatamustbecoordinatedbetweeneachONTto
avoidcollisionsduetothesharedmediaoftheopticaldistributionnetwork(ODN).Datais
transmittedaccordingtocontrolmechanismsconfiguredintheOLT.Theaggregateupstream
rateis1.25Gbps.Figure1illustratesthefrontoftheONThousing.