Tektronix MTD200, Руководство пользователя

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Measurement Functions
2–12
MTD200 MPEG Test Decoder User Manual
CRC_error (2nd priority)
If program-specific information (PSI tables), such as PAT, CAT, PMT, NIT, EIT,
SDT, BAT and TOT, is transmitted, a value for checking the check sum of this
section is inserted at the end of each table section. The so-called CRC (Cyclic
Redundancy Check) is used for calculating the check sum at the transmitter and
receiver end. Combined with the additionally transmitted CRC value, the check
sum for each table section must be zero.
If the resulting check sum does not equal zero, the MPEG-2 decoder must reject
the information contained in this table.
If a CRC_error is detected, it cannot be predicted which part of the information
contained in the table is not correct. In this case, the MPEG test decoder signals
the CRC_error, but the transport stream is not checked for further errors which
are derived from the faulty content of this table (for example, a search for PMT
PIDs from a PAT or ES PIDs from a PMT).
In the DVB Measurement Guidelines (ETR 290), the preconditions for a
CRC_Error message are set as follows:
CRC ERROR is signaled if
a packet with PAT, CAT, PMT, NIT, EIT, BAT, SDT or TOT and CR check of a section does
not equal zero
An error of this type (cumulative message) is indicated by the LED labeled CRC
lighting (line of LEDs at front panel). As additional information, the PID of the
packet containing the error can be obtained from the monitoring report.