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SZ-DOC-W5-1.pdf LTU/NTU
Version: 1.5 Operating Manual
31 Revision: 2002-09-10
4 Performance Monitoring
The transmission performance of a DSL link can be monitored in two different ways. The DSL
signal quality is typically used during installation and maintenance procedures, whereas the
G.826 error performance parameters are intended to be used for long term evaluation of an
operating DSL link. Refer also to the “SQ” and “G826” monitor commands described in the
“Monitor Operation” chapter.
4.1 Noise Margin SNR
The Noise Margin (NM) provides qualitativeperformance of a specific loop and is an effective
maintenance tool to determine inadequate or bad cable pairs.
A NM of 0dB, in presence of Gaussian noise would yield an expected Bit-Error-Ratio of 10
-7
.
4.2 G.826 Performance Monitoring
The G.826 error performance parameters provide quantitative performance information of a
specific loop. They are intended to be used for long-term evaluation of operating DSL links.
The evaluation of the G.826 error performance parameters is based on CRC (Cyclic Redundancy
Check) error detection: The estimation of a bit-error rate is not within the scope of the G.826
calculations.
4.2.1 DSL Interface
On the DSL side, six CRC6 check bits are generated per DSL frame for each channel and
direction.
The software counting block errors and evaluating the error performance according to ITU-T
G.826 of the respective DSL channel is using these CRC6 bits.
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