About Verifying The Downstream Signal - Cisco 7246 - uBR Router Hardware Installation Manual

About Verifying the Downstream Signal

About Verifying the Downstream Signal
If the Cable Modem Termination System (CMTS) has not been properly set up to support digital data,
the Cisco uBR7200 series router might start up, but fail to support data transmission. You can use a
router with diagnostic capabilities, such as the Cisco uBR900 series cable access routers, to verify the
downstream signal originating from a Cisco uBR7200 series router. The Cisco uBR900 series cable
access routers are equipped with 64- and 256-QAM receivers that require only minimal setup. Configure
the Cisco uBR900 series routers according to DOCSIS practices.
A maximized signal-to-noise ratio (SNR) estimate optimizes cable interface reliability and service
Tip
quality.
The SNR estimate for a cable interface installed at the headend should be between 35 and 39 dB.
Note
Before starting this procedure,
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To verify the downstream signal originating from the Cisco uBR7200 series router:
When the Cisco uBR900 series cable access router is operating and you have established an input signal
Step 1
of between –10 and +10 dBmV on the modem, enter the show controllers cable-modem 0 command.
This command displays:
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Example:
Router# show controllers cable-modem 0
Tuner:status=0x00
Rx:tuner_freq 555000000, symbol_rate 5055926, local_freq 11520000
This shows a downstream frequency of 555 MHz, 64-QAM downstream, and an SNR estimate of
35.2dB.
Use the debug cable mac log verbose and show controllers cable 0 mac state commands when
Note
troubleshooting the cable interface's initialization sequence and locking on the downstream signal.
Cisco uBR7200 Series Universal Broadband Router Hardware Installation Guide
6-10
Connect the Cisco uBR7200 series router to the console. See the
Connection Equipment" section on page
Set up the console. See the Cisco uBR7200 Series Software Configuration Guide at the following
URL:
http://www.cisco.com/en/US/docs/cable/cmts/ubr7200/configuration/guide/cr72scg.html
Signal-to-noise ratio (SNR)
Downstream signal frequency
Downstream signal modulation scheme (64 QAM or 256 QAM)
snr_estimate 352(TenthdB), ber_estimate 0, lock_threshold 26000
QAM in lock, FEC in lock, qam_mode QAM_64
"Console and Auxiliary Port
3-16.
Chapter 6 Troubleshooting
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