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Configure the Downstream Cable Interface
VC-142
Voice, Video, and Home Applications Configuration Guide
To set the downstream modulation, use the following command in cable interface configuration
mode:
Validation Tips
To verify the downstream modulation setting, enter the show controllers cable command for the
downstream port that you have just configured:
router# show controllers cable 6/0 downstream
Cable6/0 Downstream is up
Frequency=96000000, Channel Width 6 MHz, 64-QAM, Symbol Rate 5.056941 Msps
FEC ITU-T J.83 Annex B, R/S Interleave I=32, J=4
Troubleshooting Tips
If you are having trouble:
• Make sure the cable connections are not loose or disconnected.
• Make sure the cable modem card is firmly seated in its Cisco uBR7246 chassis slot.
• Make sure that you have entered the correct slot and port numbers when you typed the command.
• Make sure you have selected the default if you are not certain about the modulation rate needed.
• Make sure the downstream carrier is active by entering the cable downstream if-output
command.
Set the Downstream Interleave Depth
The next step is to set the interleave depth for a downstream port on a cable modem card. A higher
interleave depth provides more protection from bursts of noise on the HFC network; however, it will
increase downstream latency. The valid values are 8, 16, 32 (default), 64, and 128.
To set the downstream interleave depth, use the following command in cable interface configuration
mode:
Validation Tips
To verify the downstream interleave depth setting, enter the show controllers cable command for
the downstream port that you have just configured:
router# show controllers cable 6/0 downstream
Cable6/0 Downstream is up
Frequency=96000000, Channel Width 6 MHz, 64-QAM, Symbol Rate 5.056941 Msps
FEC ITU-T J.83 Annex B, R/S Interleave I=32, J=
Command Purpose
cable downstream modulation 64qam Set the standard MCNS rate.
Command Purpose
cable downstream interleave-depth
{8 | 16 | 32 | 64 | 128} Set the downstream interleave depth.