Specifications

3-13
Cisco Cable Modem Termination System Feature Guide
0L-1467-02
Chapter 3 Spectrum Management for the Cisco Cable Modem Termination System
Feature Overview
The criteria for modulation profile 1 to switch to modulation profile 2 (more robust modulation scheme)
includes one of the following:
• The upstream SNR goes below 25dB (SNR < 25dB)
OR
• The number of correctable FEC errors is more than 3 percent of the packets received in a 15-second
time period
OR
• The number of uncorrectable FEC errors is more than 1 percent of the packets received in a
15-second time period.
The criteria for modulation profile 2 to switch to modulation profile 1 includes all of the following:
• The upstream SNR is above 28dB (SNR > 28dB)
AND
• The number of correctable FEC errors is less than 3 percent of the packets received in a 15-second
time period
AND
• The number of uncorrectable FEC errors is less than 1 percent of the packets received in a 15-second
time period.
In the previous example, modulation profile 1 switches to modulation profile 2 based on OR conditions.
Modulation profile 2 switches to modulation profile 1 based on AND conditions.
Input Power Levels
Upstream input power level modifications were made in Cisco IOS Releases 12.0(6)SC, 12.1(1),
12.1(1)T, 12.1(2)EC1, and 12.2(4)BC1b. The input power level, power-level-dBmV, is an option in the
cable spectrum-group command. The option allows you to specify the expected U.S. input power levels
on the upstream receivers on the CMTS when the cable modems are hopping from one fixed frequency
to another or from one band to another. Each upstream frequency has an associated upstream input power
level in dBmV. The power level is the modem transmit power that each spectrum group can use when an
upstream frequency change is necessary. The input power level may be set at the time of the frequency
hop.
Specifying an input power level is done so that the cable modems do not have to increase or decrease
their transmit power with every hop. The cable operator can perform minor power equalizations as a
function of frequency. The valid range is –10 to +10dBmV. The power level value should be changed
only if you want to change the power level as part of spectrum management. Some cable plants may want
to change only the input power level and not the frequency on a daily time schedule.
For information on how to configure input power levels, see the “Setting Input Power Level” section on
page 3-34.