Installation guide

CHAPTER
5-1
Cisco uBR7100 Series Universal Broadband Router Software Configuration Guide
OL-2238-03
5
Troubleshooting the System
This chapter contains troubleshooting information for various functions of your Cisco uBR7100 series
CMTS, and includes the following sections:
• “Using a Cable Modem at the Headend to Verify Downstream Signals” section on page 5-1
• “Managing Cable Modems on the HFC Network” section on page 5-2
• “Polling Cable Modems” section on page 5-15
• “Understanding Show Command Responses” section on page 5-17
• “Troubleshooting Cable Flap Lists” section on page 5-31
• “Performing Amplitude Averaging” section on page 5-42
• “Setting Downstream Test Signals” section on page 5-44
• “Pinging Unresponsive Cable Modems” section on page 5-46
• “Using the Cable Monitor Feature” section on page 5-46
• “Using Cable Interface debug Commands” section on page 5-48
Using a Cable Modem at the Headend to Verify Downstream
Signals
You can use a Cisco uBR924 cable access router to verify the downstream signal originating from a
Cisco uBR7100 series universal broadband router. Be sure you configure the Cisco uBR924 according
to DOCSIS cable modem practices. To verify the downstream signal from a Cisco uBR7100 series
universal broadband router using a Cisco uBR924, follow the procedure below:
Step 1 After the Cisco uBR924 is operational and you have an input signal between 0 and +5 dBmV, enter the
show controller c0 tuner command.
Step 2 Scan the output for the value corresponding to the signal to noise (SNR) estimate variable. If this value
is at least 35 dB, you have an optimized signal. If the value is less than 34 dB, adjust the upconverter at
the cable headend.
Tip The SNR estimate for a cable modem installed at a headend should be between 35 and 39 dB. Although
the exact value displayed will vary from cable modem to cable modem, values collected on the same
cable modem from measurement to measurement will be consistent. Maximizing SNR optimizes cable
modem reliability and service quality.