Cisco Systems uBR7200 Series Performing Amplitude Averaging, Enable or Disable Power Adjustment

Chapter 4 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 router averages 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.

The show cable flap-listand 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 the show cable flap-listcommand:

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

Similar to the show cable flap-listdisplay, 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 n power-adjust {threshold [threshold #] continue [tolerable value] noise [% of power adjustment]}

no cable upstream power-adjust

Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide

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