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Cisco uBR10012 Universal Broadband Router Software Configuration Guide
OL-1520-05
Chapter3 Configuring Cable Interface Features for the CiscouBR10012Router
Configuring the Upstream Cable Interface
Setting the Upstream Input Power Level
The CiscouBR10012router controls the output power levels of CMs to meet the desired upstream input
power level. The nominal input power level for the upstream RF carrier is specified in decibels per
millivolt (dBmV). The default setting of 0dBmV is the optimal setting for the upstream power level.
The valid range for the input power level depends on the data rate. At 1.6MHz, the valid range is
–10to25dBmV. If your power levels operate at greater than the maximum valid level, use an inline
attenuator to bring the power level to within the valid range.
Caution If you increase the input power level, CMs on your HFC network increase their transmit power level.
This increases the carrier-to-noise ratio (C/N) on the network, but also increases distortion products.
Composite Second Order Beat (CSO) and Composite Triple Beat (CTB) values worsen by 2dB for
every 1dB-increased C/N. The return path laser immediately enters a nonlinear mode called
clipping, and all communication becomes unreliable. Many return lasers send short bursts above the
clipping thresholds and fail on longer or successive bursts.
You should not adjust your input power level by more than 5dB in a 30-second interval. If you
increase the power level by more than 5dB within 30seconds, cableinterface service on your
network is disrupted. If you decrease the power level by more than 5dB within 30seconds,
cableinterfaces on your network are forced offline.
Note When you run the cable upstream 0 power-level command, Cisco recommends that the adjacent
channel not have a large variation. The recommended maximum input power variance is 5to
6dBmV.
To set the upstream input power level in dBmV, use the following command in cable interface
configuration mode. The default is 0 dBmV.
Router(config-if)# cable upstream usport power-level dbmv

Verifying the Upstream Input Power Level

To verify the current value of the upstream input power level, enter the show controllers cable command
for the upstream port you have just configured:
Router# show controllers cable5/0/0 u0
Cable5/0/0 Upstream 0 is up
Frequency 24.016 MHz, Channel Width 0.800 MHz, QPSK Symbol Rate 0.640 Msps
Spectrum Group is overridden
SNR 33.2560 dB
Nominal Input Power Level 0 dBmV, Tx Timing Offset 2288
Ranging Backoff automatic (Start 0, End 3)
Ranging Insertion Interval automatic (60 ms)
Tx Backoff Start 0, Tx Backoff End 4
Modulation Profile Group 1
Perform these steps if you are having difficulty with verification:
1. Verify that the upstream amplitude of an optimal RF carrier (injected at the fiber node reference
input point) reaches the cable interface line card input point at a consistent level (node-to-node and
port-to-port).
2. Verify that this absolute level, as installed, matches both the design and software settings on the
CiscouBR10000series CMTS.