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Transport aspects 2
NOTE – This value is taken from [b-BBF TR-126], corresponding to high definition television (HDTV) quality,
quantified as an average of one error event in four hours.
9.8.3.1.2 Accelerated testing of MTBE
In order to facilitate testing, a special test mode is defined. This test mode shall be selected by enabling
RTX_TESTMODE for the PMS-TC (see Table 9-18) at the transmitter and receiver, and enabling
TPS_TESTMODE for the TPS-TC (see clause 8.1.3) at the transmitter. The remote FTU shall be forced into
this test mode by sending a diagnostic command through the eoc (see clause 11.2.2.6).
When RTX_TESTMODE is enabled, retransmissions shall not be requested by the receiver (i.e., all DTUs shall
be ACKed and all uncorrected DTUs shall be discarded) nor sent autonomously by the transmitter. In this
mode, the receiver shall count uncorrected DTUs as during the normal operation.
NOTE 1 – This test provides valid results only if performed in the presence of stationary noise only.
The remote side shall enter the test mode upon eoc request (see Table 11-21 and clause 11.2.2.6.3).
NOTE 2 – In this test mode, the DRA function is configured in the DRA test mode. In the DRA test mode, the DRA sets
TTR = M and TBUDGET to the maximum value allowed within the bounds set by the ME and PCE, for upstream and
downstream.
PDTU is defined as the probability that a DTU is corrupted, i.e., a DTU is not received correctly in a single
transmission. In this test mode, it can be calculated for downstream and upstream separately from the DTU
counters as:
_ _ _
= ( _ / )
where:
Measurement_Time is expressed in seconds.
TDTU is the time duration of a DTU expressed in seconds.
Number_of_uncorrected DTUs is the number of rtx-uc anomalies (see clause 11.3.1.1) over the
measurement time.
In this accelerated test, the requirement for PDTU is:
. 8 3333 10 3 1
P T 2
DTU f DTU _in _ DMT
DMT
where fDMT is the symbol rate in Hz (see clause 10.4.4) and TDTU_in_DMT is the average duration of a DTU
expressed in symbol periods, which shall be computed as the average value of (NDTU+Q×RFEC)/BD during the
measurement period (see clause 8.2).
NOTE 1 – Appendix III provides the calculations motivating this requirement.
NOTE 2 – The value of TDTU_in_DMT for downstream and upstream, and the value of fDMT are reported in the DPU-MIB.
9.8.3.2 Definition of signal-to-noise ratio margin (SNRM)
The SNRM is equal to 1 dB plus the maximum increase (scalar gain, in dB) of the reference noise PSD (at all
relevant frequencies and assuming only stationary noise is applied at the U reference point), for which the
MTBE of the TPS-TC stream (see Figure 8-3) is not lower than the minimum MTBE (MTBE_min, see
clause 10.3) specified for this TPS-TC stream, assuming only one retransmission of each DTU is allowed,
without any change of PMD parameters (e.g., bits and gains) and PMS-TC parameters (e.g., FEC
parameters) and with error-free throughput (EFTR) (see clause 11.2.2) ≥ ETR.
NOTE 1 – At 1 dB signal-to-noise ratio margin (SNRM) working point, the transceiver operates at MTBE equal to or
better than the MTBE_min.
NOTE 2 – During testing of the SNRM, only stationary noise is applied to the U-O or U-R reference point (i.e., no
impulse noise is present), and delay_max is configured to correspond to allowing only one retransmission of each
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