Exfo EXpert IPTV Test Tools (FTB-200v2) Uživatelský manuál stáhnout pdf (Strana 70)

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 ErrorsinPMT,PAT,PID/PSI(PacketIdentifier/ProgramSpecificInformation)Errors

willcausethesettopboxlosecontactwiththestream.Theseerrorsmayoriginateat

anyoftheMPEGtransportmultiplexerswhennewstreamsareinserted.

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A.4 PCRJitter

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PCR(programcounterreference)timestampsisgeneratedbytheMPEG‐2encoder

andreceivedthroughoutthesubsequentlinksinthenetworkatleast100millisecondsapart.

ThedecoderusesthePCRtolockitsown27MHzclocktotheencodersystemtimeclock(STC).

This27Mhzclockisverysensitivetovaria

tionscausedprimarilybypackettransmissions

delays.Therefore,measurementofthePCRtimestamparrivaltimevariationcalledcommonly

“PCRjitter”isessential.The27Mhzoscillatoritselfmaynotexceed500nsecofinternaljitter

perTR101290.

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Exfo EXpert IPTV Test Tools (FTB-200v2) Uživatelský manuál Strana 70