EXFO EXpert IPTV Test Tools (FTB-1 / 2 Pro) - Manual (Page 71)

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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