Cisco Systems uBR7200 Series manual Pinging Unresponsive Cable Modems, Configure Prbs Test Signals

Chapter 4 Troubleshooting the System

Pinging Unresponsive Cable Modems

Configure PRBS Test Signals

Table 4-30 Instructions to Configure PRBS Test Signals

Step Command

1.# router(config-if)#cable downstream if-output prbs

2.Router(config-if)#no cable downstream if-output

Purpose

Generates a PRBS test signal on the downstream channel. The interface is shut down.

Stops sending test signals.

Note Remember to reenable the interface to resume normal operations.

Verify Test Signal Output

To verify the output of a continuous-wave test signal or the output of a PRBS test signal, use a spectrum analyzer on the downstream channel. The downstream carrier is enabled as a default.

The standard mode of operation is modulated signal output and the interface is active. For PRBS and continuous wave output, the selected interface will be shut down.

The functioning of the no cable downstream if-outputcommand has not changed. The interface is shut down.

Pinging Unresponsive Cable Modems

Ping a Cable Modem

Ping DOCSIS is a Cisco patent-pending feature that allows a cable system administrator to quickly diagnose the health of a channel between the Cisco uBR7200 series universal broadband router and the cable modem. The technology uses 1/64—the bandwidth of IP ping—and works with cable modems that don’t have an IP address. This allows cable operators to ping cable modems that are unable to complete registration, have internal bugs, or that are unresponsive due to a crash.

Information the Ping DOCSIS feature includes a real-time view and plot of requested power adjustments, as well as a measure of optimal headend reception power. This gives the cable operator the ability to solicit a configurable number of periodic ranging requests from a cable modem.

To ping a specific cable modem to determine if it is online, use the following command in EXEC mode.

Table 4-31 Instructions to Ping a Cable Modem

Command	Purpose
CMTS01# ping docsis addr	Ping the cable modem with a specific MAC address
	or IP address to see if it is online.

Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide

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