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Cisco uBR10012 Universal Broadband Router Software Configuration Guide
OL-1520-05
Chapter 3 Configuring Cable Interface Features for the Cisco uBR10012 Router
Configuring the Upstream Cable Interface
Step 1
Ensure that the cable connections are not loose or disconnected
Step 2
Ensure that the cable interface line card is firmly seated in its chassis slot.
Step 3
Ensure that the captive installation screws are tight.
Step 4
Verify that you have entered the correct slot and port numbers.
Step 5
Verify that you have selected a valid frequency for your router.
Setting the Upstream Input Power Level
The Cisco uBR10012 router 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 0 dBmV 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 to 25 dBmV. 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 2 dB for
every 1 dB-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 5 dB in a 30-second interval. If you
increase the power level by more than 5 dB within 30 seconds, cable interface service on your
network is disrupted. If you decrease the power level by more than 5 dB within 30 seconds,
cable interfaces 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 5 to
6 dBmV.
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)