EXFO EXpert IPTV Test Tools (FTB-200v2) - Manual (Page 70)

70
 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.
A.4 PCR Jitter
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 variations 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.