Exfo EXpert IPTV Test Tools (FTB-200v2) Manuale Utente Pagina 51

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A.1.1.2 ImpactofPacketLossonSpecificVideoCodecs
AsshowninFigure23,asimplenonrobustvideostreamcanbeseverelydegraded
withevenlowlevelsofpacketlossduetotheerrorpropagationeffectsdescribedabove.
PeakSignaltoNoiseRatio(PSNR)isanobjectivemeasurementofvideoservice
quality
comparingthemaximumpowerofthevideosignaltothepowerofcorruptingnoiseaffecting
thesignal.Generally,aPSNRofunder20dBisregardedasunwatchable,andthislevelis
reachedforMPEGvideowithalossrateunder1percent.
Figure23.
EstimatedPSNR
forThree
CommonCodecs
Errormi
tigationalgorithmsarebeingincreasinglyappliedtohelptocompensateforpacket
loss[11][12].Methodsinclude:
ForwardErrorCorrection(FEC)‐redundancyisappliedtothedatastreamtoallowsome
proportionoflostorerroredpacketstobereplaced
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