Exfo EXpert IPTV Test Tools (FTB-1 / 2 Pro) Manuale Utente Scaricare il pdf (Pagina 71)

A.5 IGMP Latency vs. Zap time

The zap time is the total duration from the time viewer presses the channel change button, to

the point the picture of the new channel is displayed, along with corresponding audio. These

kind of delays exist in all television systems, but they are greater in digital television

and

systems that use the Internet like IPTV. Human interaction with the system is completely

ignored in these measurements, so zap time is not the same as channel surfing.

Key Factors affecting Zap Time

• Encoding

• Network

• Set top Box (leave and joins)

Examples:

In this section some typical values of zap time are shown. Actually, in IPTV television these

delays are greater than in other technologies:

• Analog (Cable

) ~ 1s

• Analog (off-air) ~ 1 – 3s

• MPEG2 over QAM ~ 1.2 – 3s

• MPEG2 over QPSK ~ 2 – 4s

• MPEG2 over IPTV Multicast ~ 1.5 – 3.5s

• H.264 over IPTV Multicast ~ 1.7 – 4s

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Exfo EXpert IPTV Test Tools (FTB-1 / 2 Pro) Manuale Utente Pagina 71