Cisco Systems uBR7200 Series manual

Chapter 4 Troubleshooting the System

Troubleshooting Using Cable Flap Lists

Tips In Cisco IOS Release 12.0(7)XR2, Cisco IOS Release 12.1(1a)T1, and higher, the system supports automatic power adjustments. The show cable flap-listand show cable modem commands now indicate when the Cisco uBR7200 series router has detected an unstable return path for a particular modem and has compensated with a power adjustment. An asterisk appears in the power adjustment field for a modem when a power adjustment has been made; an exclamation point appears when the modem has reached its maximum power transmit level and cannot increase its power level any further.

The following tips and scenarios allow you to use the flap list in the most effective way:

•If a subscriber's cable modem shows a lot of flap list activity, it is having communication problems.

•If a subscriber's cable modem shows little or no flap list activity, it is communicating reliably; the problem is probably in the subscriber's computer equipment or in the connection to the

cable modem.

•The top 10% most active cable modems in the flap list are most likely to have difficulties communicating with the headend.

•Cable modems with more than 50 power adjustments per day have a suspect upstream path.

•Cable modems with approximately the same number of hits and misses and with a lot of insertions have a suspect downstream path (for example, low level into the cable modem).

•All cable modems incrementing the insertion at the same time indicates a provisioning server failure.

•Cable modems with high CRC errors have bad upstream paths or in-home wiring problems.

•Correlating cable modems on the same physical upstream port with similar flap list statistics can quickly resolve outside plant problems to a particular node or geography.

•Monitoring the flap list cannot affect cable modem communications.

•The flap list should be saved to a database computer and cleared at least once a day.

•Important upstream performance data can be obtained by tracking flap list trend data.

•Important installation quality control and performance data is directly available from the flap list.

Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide

4-36 78-5897-01