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Chapter 4
Connecting the Cisco uBR7225VXR Router to the Cable Headend
Verify that your headend RF measurements meet the recommended DOCSIS parameters listed in the
Step 10
tables in
Step 11
Record your headend settings in
Cisco uBR7225VXR universal broadband router installation later in the process.
Note
Be sure not to narrow the focus of your analysis any further than approximately 3-MHz channel width.
Doing so can yield incorrect readings. For example, if you were to view an upstream RF signal with a
resolution bandwidth of only 300 kHz and a video channel bandwidth of only 100 kHz, your
measurements would register lower than the actual transmission levels.
Analyzing the Upstream RF Signal
When you have set up your spectrum analyzer to accurately read the upstream RF signal, you can verify
that a remote cable modem is operating as it should by pinging the modem via a console terminal.
Log in to your Cisco uBR7225VXR universal broadband router with a console terminal.
Step 1
Adjust the sweep time on your spectrum analyzer to 20 microseconds.
Step 2
Step 3
Ping the remote cable interface card using first a 64-byte, then a 1500-byte ping packet request, and take
note of the upstream RF signal in each case. Several hundred or thousand ping packets might be required
for a usable pattern to emerge.
Figure 4-29
or 1500-byte ping of a single remote cable interface. The more slender of the data spikes in the RF signal
(the first and third spikes in
spikes are the actual 64- or 1500-byte ping packet returns.
Figure 4-29
OL-17309-01
Appendix B, "RF Specifications."
Appendix G, "Site Log."
and
Figure 4-30
provide two examples of an ideal upstream RF signal based on a simple 64-
Figure
Analyzing the Upstream RF Signal—64-Byte Data Packets
Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
This will assist in troubleshooting the
4-29) are bandwidth request packet transmissions, while the larger
Measuring the Upstream RF Signal
4-25
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Table of Contents
Troubleshooting
