Cisco SR2016T-NA Reference Manual page 62

cable downstream frequency
Release
12.2(15)CX
12.2(15)BC2
Usage Guidelines This command is either optional or required, depending on the cable interface line card being used.
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We recommend configuring this command on all cable interfaces, even those that are using external
Tip
upconverters. This is because this command is required to enable the downstream frequency override
feature and for N+1 line card redundant operation when using SNMP-capable external upconverters.
The downstream frequency of your RF output must be set to match the expected input frequency of your
upconverter. To do this, you enter the fixed center frequency of the downstream channel 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 858,000,000 Hz. The center frequency is also used to
configure an IF-to-RF upconverter that must be installed in your downstream path.
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.
In Cisco IOS software releases before Cisco IOS Release 12.2(15)BC2, the cable downstream
frequency command allowed the center frequency to be specified in 125 KHz increments. In Cisco IOS
Release 12.2(15)BC2 and later releases, this was changed to allow only 250 KHz increments, because
of the requirements of the Broadband Processing Engine cable interface line cards that use an internal
upconverter (Cisco uBR-MC16U, Cisco uBR-MC28U, and Cisco uBR-MC5X20S/U).
Note DOCSIS allows downstreams to use any center frequency within 88,000,000 to 855,000,000 MHz.
However, when most cable modems first come online, they initially start scanning the downstream for
the frequencies that are in the NTSC channel plan. If a valid downstream is not found among those
frequencies, the cable modems then beginning scanning the remaining frequencies. For the fastest and
most efficient registration times, we recommend configuring downstreams for the frequencies that are
specified in the NTSC channel plan.
Cisco Broadband Cable Command Reference Guide
2-50
Modification
Support was added for the Cisco uBR-MC16U/X and Cisco uBR-MC28U/X
cable interface line cards.
Support was added for the extended frequency range and for the
Cisco uBR-MC5X20U cable interface line card. In addition, the command
was changed to accept only center frequencies in 250 KHz increments
(previously, the command allowed 125 KHz increments).
On the Cisco uBR7100 series routers using the integrated upconverter (the DS0 RF output), and on
cable interfaces that support integrated upconverters (such as the Cisco uBR-MC16U,
Cisco uBR-MC28U, and Cisco uBR-MC5X20U), this command configures the frequency for the
integrated upconverter. The no form of this command unsets the frequency and disables the output
from the integrated upconverter.
For cable interfaces that use an external upconverter (such as the Cisco uBR-MC16S and the DS0
(IF) output on Cisco uBR7100 series routers), this command is informational-only, because it does
not affect the external upconverter. The external upconverter must be programmed separately with
the appropriate center frequency.
Chapter 2 Cisco CMTS Configuration Commands
OL-1581-08