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Configuring Spectrum Management on an Upstream Cable Interface

Cisco uBR7200 Series MC16S Cable Modem Card Spectrum Management 29

cable upstream power-level

Enter the nominal input power level for the upstream RF carrier in decibels per millivolt (dBmV).

You can also select the default of 0 dBmV, which is the optimal setting for the upstream power level.

The valid range for the input power level depends on the data rate. At 1.6 MHz, the valid range is

–10 dBmV to 25 dBmV. If your power levels operate at greater than the maximum valid level, you

must use an inline attenuator to bring the power level to within the valid range.

Caution If you increase the input power level, the cable modems on your HFC network increase

their transmit power level. This increases the C/N ratio on the network, but also increases distortion

products. CSO and CTB/CX0 values worsen by 2 dB for every 1 dB-increased C/N. The return path

laser immediately enters a non-linear mode called clipping and all communication is no longer

reliable. Many return lasers send “short” bursts well above the clipping thresholds and fail on longer

or successive bursts.

It is almost impossible to see CSO and CTB/CX0 products on a lightly loaded HFC network.

Approximately 70-90% upstream trafﬁc utilization is required if you directly measure these products

using a spectrum analyzer. Be careful if you adjust this parameter.

You should not adjust your input power level by more than 5 dB in a 30-second interval. If you

increase the power level by more than 5 dB within 30 seconds, cable modem service on your

network will be disrupted. If you decrease the power level by more than 5 dB within 30 seconds,

cable modems on your network will be forced ofﬂine.

Note When you run cable upstream 0 power-level, Cisco recommends that the adjacent channel

not have a large variation. The recommended maximum input power variance is 5 to 6 dBmV.

cable upstream interface number power-level power

no cable upstream interface number power-level

Syntax Description

Default

0 dBmV

Command Mode

Cable interface conﬁguration

interface number Speciﬁes the upstream cable interface for which you are

assigning the given power level

power Speciﬁes the power level for the given upstream interface

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Cisco MC16S Manual de usuario Pagina 29