Troubleshooting guide

BSR Troubleshooting Guide
4-60
5. View the show cable interface signal-quality statistics for the specific
upstream interface. If there is a high number of unerroreds (uncorrupted
packets), the upstream signal-quality is good.
Table 4-4 describes the show cable interface signal-quality statistics:
6. If there is a large number of correctables there is a physical problem with the
upstream signal. Use a spectrum analyzer to measure the signal to noise ratio
for the upstream path. For 16 QAM and QPSK, the optimum signal-to-noise
ratio is 33 dB or greater.
The signal-to noise ratio learned from the spectrum analyzer may indicate the
following conditions:
• If the loss in signal quality is less than 10dB, the cable interface can
compensate by correcting packets.
• If the loss in signal quality is greater than 10 dB, the signal is degraded to
the point where it can no longer carry data, and you must troubleshoot and
correct the noise problem.
• A high number of correctables (corrected packets) and uncorrectables
(uncorrected, dropped packets) occurs when the signal-to-noise ratio is
approximately 25 dB for QAM 16 and QPSK. You must manually
troubleshoot and correct the problem. See if errors increment at a specific
time at a higher than expected rate.
• The number of micro reflections (expressed in dB) can signify a high
number of corrupted packets (erroreds) and fixed packets (correcteds).
Follow these steps to manually resolve an upstream signal-to-noise ratio problem:
Table 4-5 show cable interface signal-quality Command Output Statistics
Field Identification
correctables Number of corrected error packets received through this upstream
interface
ifIndex Cable interface number
unerroreds Number of unerrored packets on cable interface