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Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
OL-2239-03
Chapter8 Troubleshooting the System
Pinging Unresponsive Cable Modems
Configuring PRBS Test Signals
Verifying 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 is shut down.
The functioning of the no cable downstream if-output command has not changed. The interface is shut
down.
Pinging Unresponsive Cable Modems
Pinging 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 CiscouBR7200series routers and the cableinterface. The
technology uses 1/64—the bandwidth of IP ping—and works with CMs that do not have an IP address.
This allows cable operators to ping CMs that are unable to complete registration, that have internal bugs,
or that are unresponsive due to a crash.
The Ping DOCSIS feature includes a real-time view and plot of requested power adjustments, and 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 cableinterface.
To ping a specific cableinterface to determine if it is online, use the following command in EXEC mode.
Verifying the Ping
The pingdocsis command returns a verification from a CM that is pinged:
Queuing 5 MAC-layer station maintenance intervals, timeout is 25 msec:
!!!!!
Success rate is 100 percent (5/5)
Command Purpose
Step1
Router(config-if)# cable downstream
if-output prbs
Generates a PRBS test signal on the downstream channel. The
interface is shut down.
Step2
Router(config-if)# no cable downstream
if-output
Stops sending test signals.
Note Remember to reenable the interface to resume normal
operations.
Command Purpose
Step1
Router# ping docsis addr
Pings the CM with a specific MAC address or IP address to see if it is online.