System information

Configuring the CMTS
6-103
High ratio of misses over hits (> 10%) Hit/miss analysis should be done after the
"Ins" count stops incrementing. In general, if
the hit and miss counts are about the same
order of magnitude, then the upstream may
be experiencing noise. If the miss count is
greater, then the CM is probably dropping out
frequently and not completing registration.
The upstream or downstream is perhaps not
stable enough for reliable link establishment.
Very low hits and miss counters and high
insertion counters indicate provisioning
problems.
High power adjustment counter. Indicates the power adjustment threshold is
probably set at default value of 2 dB
adjustment. The CM transmitter step size is
1.5 dB, whereas the headend may command
0.25 dB step sizes. Tuning the power
threshold to 6 dB is recommended to
decrease irrelevant entries in the flap list. The
power adjustment threshold may be set using
<cable flap power threshold <0-10 dB> from
Global Configuration mode. A properly
operating HFC network with short amplifier
cascades can use a 2-3 dB threshold.
High P-Adj (power adjustment) This condition can indicate that the fiber node
is clipping the upstream return laser. Evaluate
the CMs with the highest number of
correcteds and uncorrecteds first. If the CMs
are not going offline (Ins = 0), this will not be
noticed by the subscriber. However, they
could receive slower service due to dropped
IP packets in the upstream. This condition will
also result in input errors on the cable
interface.
High insertion rate. If link re-establishment happens too
frequently, then the CM is usually having a
registration problem.This is indicated by a
high ‘Ins’ counter which tracks the ‘Flap’
counter.
Table 6-9 Troubleshooting CM Problems
Cause or Symptom Problem