Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
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Chapter 7 Troubleshooting the CMTS
Troubleshooting the Cisco uBR7246VXR
Similar to the show cable flap-list display, the * symbol in the show cable modem output indicates that
the Cisco uBR7246VXR is using the power adjustment method on this modem. The ! symbol indicates
that the cable modem has reached maximum transmit power.
The following commands pertaining to amplitude averaging, and are discussed in more detail in the
following sections:
cable upstream power-adjust noise
cable upstream frequency-adjust averaging
Enabling or Disabling Power Adjustment
To enable or disable the power adjustment capability, use the following commands:
cable upstream n power-adjust [ threshold threshold # | continue tolerable value | noise % of power
adjustment ]
no cable upstream power-adjust
Table 7-3 displays descriptions of the arguments in the cable upstream power-adjust command.
Note The threshold default is 1 dB. The tolerable value default is 2 dB. The power adjustment is 30 percent.
Caution Default settings are adequate for system operation. Amplitude averaging is an automatic procedure.
In general, Cisco does not recommend you adjust values. Cisco does recommend, however, that you
clean up your cable plant should you encounter flapping cable modems.
Note In some instances, you might adjust certain values:
If cable modems cannot complete ranging because they have reached maximum power levels, you
might try to set the tolerable value CONTINUE field to a larger value than the default of 2 dB. Values
larger than 10 dB on “C” versions of cable modem cards, or 5 dB on FPGA versions, are not
recommended.
If the flap list shows modems with a large number of power adjustments, but the cable modems are
not detected as “noisy,” you might try to decrease the percentage for “noisy”. If you think too many
modems are unnecessarily detected as “noisy,” you might try to increase it.
Table 7-3 Cable Upstream Power Adjust Syntax Descriptions
Syntax Valid Values
n Specifies the upstream port number.
threshold # Specifies the power adjustment threshold. The threshold range is from 0
through 10 dB. The default is 1 dB.
tolerable value Determines if the status of the RNG-RSP should be set to CONTINUE
or SUCCESS. The range is from 2 through 15 dB. The default is 2 dB.
% of power adjustment Specifies the percentage of power adjustment packets required to switch
from the regular power adjustment method to the noise power adjustment
method. Range is from 10 through 100 percent. The default is 30 percent.