Cisco Systems uBR7200 Setting the Downstream Center Frequency, Verifying the Downstream Carrier

Configuring Headend Broadband Access Router Features

Configuring the Downstream Cable Interface

	Command	Purpose
Step 4
	CMTS01(config-if)#cable downstream if-output or	Default. Activates downstream digital data from the
	CMTS01(config-ikf)#no cable downstream if-output	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:	Returns to privileged EXEC mode.
	Configured from console by console
		This message is normal and does not indicate an error.

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.

Cisco IOS Multiservice Applications Configuration Guide

MC-536