Installation guide

5-42
Cisco uBR7100 Series Universal Broadband Router Software Configuration Guide
OL-2238-03
Chapter 5 Troubleshooting the System
Performing Amplitude Averaging
The following displays the current allocation table and frequency assignments:
show cable spectrum-group [spectrum group number]
The following displays maximum, average, and minimum% online time and offline times for a given SID
on a given Cisco uBR7100 series router interface:
show int slot/port sid connectivity
The following command displays input and output rates, input errors, CRC, frames, overruns, underruns,
collisions, interface resets. High input errors in the CMTS retrieved from this query suggests noisy
upstream. In older versions of the chassis, loose midplane and line card screws caused a similar problem:
show interface slot/downstream-port
Performing Amplitude Averaging
The Cisco uBR7100 series CMTS 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 uBR7100 series CMTS averages a
configurable number of RNG-REQ messages before it makes power adjustments. By compensating for
a potentially unstable return path, the Cisco uBR7100 series CMTS maintains connectivity with affected
cable modems. You can interpret these power adjustments, however, as indicating unstable return path
connections.
The show cable flap-list and show cable modem commands are expanded to indicate which paths the
Cisco uBR7100 series CMTS 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 the show cable flap-list command:
Router# show cable flap-list
MAC Address Upstream Ins Hit Miss CRC P-Adj Flap Time
0010.7bb3.fd19 Cable1/0/U1 0 2792 281 0 *45 58 Jul 27 16:54:50
0010.7bb3.fcfc Cable1/0/U1 0 19 4 0 !43 43 Jul 27 16:55:01
0010.7bb3.fcdd Cable1/0/U1 0 19 4 0 *3 3 Jul 27 16:55:01
The asterisk (*) indicates that the CMTS is using the power adjustment method on this modem. An
exclamation point (!) 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
Cable1/0/U0 1 online 2257 0.00 3 0 10.30.128.142 0090.8330.0217
Cable1/0/U0 2 online 2262 *-0.50 3 0 10.30.128.145 0090.8330.020f
Cable1/0/U0 3 online 2260 0.25 3 0 10.30.128.146 0090.8330.0211
Cable1/0/U0 4 online 2256 *0.75 3 0 10.30.128.143 0090.8330.0216
Cable1/0/U0 5 online 2265 *0.50 3 0 10.30.128.140 0090.8330.0214
Cable1/0/U0 6 online 2256 0.00 3 0 10.30.128.141 0090.8330.0215
Cable1/0/U0 7 online 4138 !-1.00 3 1 10.30.128.182 0050.7366.124d
Cable1/0/U0 8 online 4142 !-3.25 3 1 10.30.128.164 0050.7366.1245
Cable1/0/U0 9 online 4141 !-3.00 3 1 10.30.128.185 0050.7366.17e3
Cable1/0/U0 10 online 4142 !-2.75 3 0 10.30.128.181 0050.7366.17ab
Cable1/0/U0 11 online 4142 !-3.25 3 1 10.30.128.169 0050.7366.17ef