Exfo EXpert IPTV Test Tools (FTB-200v2) Uživatelský manuál stáhnout pdf (Strana 65)

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bearerchanneltosupportreliablevideo.Thisvideoservicequalitymetricisexpressed

intherangeof0.0to50.0,asdefinedin[14].

VSTQcanbecalculatedbyamappingfunctionfromPeakSignal‐to‐NoiseRatioPSNR

valuesasfollows:

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VSTQ=max(0,min(50,(PSNR‐12)*1.8))

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Ofcourse,VQmon/HDusesamoresophisticatedalgorithmtocalculatetheresulting

VSTQ

score,whichtakestime‐varyingdistributionsofnetworkimpairmentsandrecency

intoaccount.

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Note:TheVSTQscorethatVQmon/HD’sAPIfunctionproducesactuallyrangesfrom0

to100.Thisvalueisscaledby2togethalf‐pointaccuracyforthescore.

A.2.3.3 DegradationFactors

Tofacilitatetroubleshooting,VQmon/HDhastheabilitytoobtainabreakdownof

factorscontributingtoqualitydegradation.VQmon/HDreportstheseverityofquality

degradation(onascaleof0‐10,with0indicatingnodegradationand10indicatingthe

mostseverelevelofdegradation)attributabletoeachofthefollowingfactors:

 Packetloss

 Audio‐videosync

 Codecquantization

 GOPlength

 Codecbandwidthrestriction

 Frameresolution

 Packetdiscardsduetojitter

 Framerate

 (One‐way)delay

 Recency

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*Note:Information in this document is proprietary to Telchemy, Incorporated and was

published with its permission.

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Exfo EXpert IPTV Test Tools (FTB-200v2) Uživatelský manuál Strana 65