Configuring Headend Broadband Access Router Features
Configuring the Downstream Cable Interface
MC-536
Cisco IOS Multiservice Applications Configuration Guide
Verifying the Downstream Carrier
To verify whether the downstream carrier is active (up), enter the show controllers cable command for
the downstream port that you just configured:
CMTS01# 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
To troubleshoot the configuration, perform the following tasks:
• Make sure the cable connections are not loose or disconnected.
• Make sure the Cisco cable modem line card is firmly seated in its chassis slot and the captive
installation screws are tight.
• Make sure you entered the correct slot and port numbers when you typed the command.
Setting the Downstream Center Frequency
Downstream frequency is an information-only parameter that must match the digital carrier frequency,
which is the center frequency of the downstream RF carrier (the channel) for a particular downstream
port. The configuration controlling the digital carrier frequency is performed in the IF-to-RF upconverter
that must be installed in the downstream path from the Cisco uBR7200 series. Refer to the
documentation for your upconverter for information about configuring the upconverter.
Enter the fixed center frequency of the downstream RF carrier for the downstream port. You can also
select a default that does not set a specific fixed value. The valid range for a fixed center frequency is
54,000,000 to 1,020,000,000 Hz.
The digital carrier frequency is specified to be the center of a 6.0 MHz channel. For example, EIA
channel 95 spans 90.000 to 96.000 MHz. The center frequency is 93.000 MHz, which is the digital
carrier frequency that should be configured as the downstream frequency. The typical range for current
CATV headends is 88,000,000 to 860,000,000 Hz. The DOCSIS specification is 91,000,000 to
857,000,000 Hz:
• The channels must be centered on a National Television Systems Committee (NTSC) EIA channel
plan for most DOCSIS cable modems to rapidly acquire the downstream frequency.
Step 4
CMTS01(config-if)# cable downstream if-output or
CMTS01(config-ikf)# no cable downstream if-output
Default. Activates downstream digital data from the
Cisco uBR7200 series.
Deactivates downstream digital data. This command
mutes the IF output of the cable modem line card and
shuts down the interfaces.
Step 5
CMTS01(config-if)# no shutdown
Places the downstream port in the “admin up” state.
Step 6
CMTS01(config-if)# end CMTS01# %SYS-5-CONFIG_I:
Configured from console by console
Returns to privileged EXEC mode.
This message is normal and does not indicate an error.
Command Purpose
