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Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
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Chapter4 Troubleshooting the System Performing Amplitude Averaging
Performing Amplitude Averaging
The Cisco uBR7200 series uses an averaging algorithm to determine the optimum power level for a
cable modem with low carrier-to-noise ratio that is making excessive power adjustments—known as
flapping. To avoid dropping flapping cable modems, the Cisco uBR7200 series universal broadband
routeraverages a configurable number of RNG-REQ messages before it makes power adjustments. By
compensating for a potentially unstable return path, the Cisco uBR7200 series router maintains
connectivity with affected cable modems. You can interpret these power adjustments, however, as
indicating unstable return path connections.
Theshow cable flap-list and show cable modem commands are expanded to indicate which paths the
Cisco uBR7200 series is making power adjustments and which modems have reached maximum
transmit power settings. These conditions indicate unstable paths that should be serviced.
The following example shows the output of theshow cable flap-list command:
router# show cable flap-list
MAC Address Upstream Ins Hit Miss CRC P-Adj Flap Time
0010.7bb3.fd19 Cable5/0/U1 0 2792 281 0 *45 58 Jul 27 16:54:50
0010.7bb3.fcfc Cable5/0/U1 0 19 4 0 !43 43 Jul 27 16:55:01
0010.7bb3.fcdd Cable5/0/U1 0 19 4 0 *3 3 Jul 27 16:55:01
The * symbol indicates that the CMTS is using the power adjustment method on this modem. The !
symbol indicates that the modem has reached maximum transmit power.
Output of the show cable modem command appears below:
router# show cable modem
Interface Prim Online Timing Rec QoS CPE IP address MAC address
Sid State Offset Power
Cable3/0/U0 1 online 2257 0.00 3 0 10.30.128.142 0090.8330.0217
Cable3/0/U0 2 online 2262 *-0.50 3 0 10.30.128.145 0090.8330.020f
Cable3/0/U0 3 online 2260 0.25 3 0 10.30.128.146 0090.8330.0211
Cable3/0/U0 4 online 2256 *0.75 3 0 10.30.128.143 0090.8330.0216
Cable3/0/U0 5 online 2265 *0.50 3 0 10.30.128.140 0090.8330.0214
Cable3/0/U0 6 online 2256 0.00 3 0 10.30.128.141 0090.8330.0215
Cable3/0/U0 7 online 4138 !-1.00 3 1 10.30.128.182 0050.7366.124d
Cable3/0/U0 8 online 4142 !-3.25 3 1 10.30.128.164 0050.7366.1245
Cable3/0/U0 9 online 4141 !-3.00 3 1 10.30.128.185 0050.7366.17e3
Cable3/0/U0 10 online 4142 !-2.75 3 0 10.30.128.181 0050.7366.17ab
Cable3/0/U0 11 online 4142 !-3.25 3 1 10.30.128.169 0050.7366.17ef
Similarto the show cable flap-list display, the * symbol in the show cable modem output indicates that
the CMTS is using the power adjustment method on this CM. The ! symbol indicates that the CM has
reached maximum transmit power.
This section documents the commands pertaining to amplitude averaging:
•cable upstream power-adjust noise
•cable upstream frequency-adjust averaging

Enable or Disable Power Adjustment

To enable or disable the power adjustment capability, use the following commands:
cable upstream npower-adjust {threshold [threshold #] | continue [tolerable value] | noise [%
of power adjustment]}
no cable upstream power-adjust