Installation guide

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Cisco uBR7100 Series Universal Broadband Router Software Configuration Guide
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Chapter 5 Troubleshooting the System
Troubleshooting Cable Flap Lists
Troubleshooting with the Flap List
This section includes suggestions on how to interpret different network conditions based on the flap list
statistics:
• Condition 1: Low miss/hit ratio (< 2% for MC16 card), low insertion, low P-adj, low flap counter
and old timestamp.
Analysis: This exhibits an optimal network situation.
• Condition 2: High ratio of misses over hits (> 10%).
Analysis: 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, the upstream can be experiencing
noise. If the miss count is greater, then the modem is probably dropping out frequently and not
Power Adjustments
(P-Adj)
The station maintenance poll in the CMTS constantly adjusts the modem
transmit power, frequency, and timing. The P-Adj column indicates the
number of times the modem’s power adjustment exceeded the threshold
value. The power adjustment threshold may be set using the <cable flap
power threshold > parameter with a value range of 0 to 10 dB and a default
value of 2 dB. Tuning this threshold is recommended to decrease irrelevant
entries in the flap list. Power Adjustment values of 2 dB and below will
continuously increment the P-Adj counter. The modem transmitter step size
is 1.5 dB, whereas the headend may command 0.25 dB step sizes. Power
adjustment flap strongly suggests upstream plant problems such as:
• Amplifier degradation
• Poor connections
• Thermal sensitivity
• Attenuation problem
Flap The Flap counter indicates the number of times the modem has flapped.
This counter is incremented when one of the following events is detected:
• Unusual modem insertion or reregistration attempts. The Flap and the
Ins counters are incremented when the modem tries to reestablish the
RF link with the CMTS within a period of time that is less than the
user-configurable insertion interval value.
• Abnormal Miss/Hit ratio. The Flap counter is incremented when N
consecutive Misses are detected after a Hit where N can be
user-configurable with a default value of 6.
• Unusual power adjustment. The Flap and P-adj counters are
incremented when the modem’s upstream power is adjusted beyond a
user-configurable power level.
Time Time is the timestamp indicating the last time the modem flapped. The
value is based on the clock configured on the local Cisco uBR7100 series
CMTS. If no time is configured, this value is based on the current uptime of
the Cisco uBR7100 series CMTS. When a cable modem meets one of the
three flap list criteria, the Flap counter is incremental and Time is set to the
current time.
Table 5-8 Flap List Statistics Description (continued)
Statistic Description