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Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
OL-2239-03
Chapter3 Configuring Cable Modem Interface Features
Configuring the Upstream Cable Modem Interface
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:
Step1 Use a valid combination of modulation format (QPSK and QAM-16), minislot size, frequency, and the
noshutdown command.
Step2 Use a recommended or previously tested modulation profile. It is not uncommon to create a modulation
profile that does not allow cableinterface-to-headend communication. Because each message type is
individually specified, some messages might not work.
Step3 Verify using IP ping packets of varying lengths (64 to 1500 bytes). Ping from the headend to the
cableinterface.
Step4 Verify with your cableinterface vendor that your CM software is fully certified or compatible with
DOCSIS1.0 and extensions, as appropriate.
Setting the Upstream Frequency
The upstream channel frequency of your RF output must be set to comply with the expected input
frequency of your Cisco cable interface line card. To configure upstream channel frequencies, perform
one of the following tasks:
• Configure a fixed frequency from 5 to 42MHz for NTSC operations, then enable the upstream port.
• Create a global spectrum group, assign the interface to it, and enable the upstream port.
Note You can also select a default that does not set a specific fixed value.
Note The upstream port is frequency agile. If you define spectrum groups, the frequency can change while the
interface is up and carrying traffic.
A modulation profile consists of a table of physical layer characteristics for the different types of
upstream bursts; for example, initial maintenance, long grant, request/data, request, short grant, and
station maintenance.
Note The upstream cable interface does not operate until you either set a fixed upstream frequency or create
and configure a spectrum group.
If you are setting a fixed upstream frequency, make sure that the frequency selected does not interfere
with the frequencies used for any other upstream applications running on the cable plant.
To set a fixed upstream frequency, use the following commands in cable interface configuration mode.