Cisco uBR10-SRP-OC12SML Specifications download pdf (Page 144)

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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 Downstream Cable Interface

Verifying the Downstream Interleave Depth

To verify the downstream interleave depth setting, enter the show controllers cable command for the

downstream port you have just configured:

Router# show controllers cable5/0/0 downstream

Cable5/0/0 Downstream is up

Frequency=96000000, Channel Width 6 MHz, 64-QAM, Symbol Rate 5.056941 Msps

FEC ITU-T J.83 Annex B, R/S Interleave I=32, J=

Perform these steps if you are having difficulty with verification:

Step1 Ensure that the cable connections are not loose or disconnected.

Step2 Ensure that the cable interface line card is firmly seated in its chassis slot.

Step3 Ensure that the captive installation screws are tight.

Step4 Verify that you have entered the correct slot and port numbers.

Step5 Verify that the downstream carrier is active, using the cable downstream if-output command.

Setting the Downstream Modulation

To set the downstream modulation, define the speed in symbols per second at which data travels

downstream to the subscriber’s CM. Asymbol is the basic unit of modulation. Quadrature Phase Shift

Key (QPSK) encodes 2 bits per symbol, Quadrature Amplitude Modulation (QAM) -16 encodes 4 bits

per symbol, QAM-64 encodes 6 bits per symbol, and QAM-256 encodes 8 bits per symbol.

Note Setting a downstream modulation rate of QAM-256 requires approximately a 6dB higher

signal-to-noise ratio (SNR) than QAM-64 at the subscriber’s cableinterface. If your network is

marginal or unreliable at QAM-256, use the QAM-64 format instead. Also, consider the significance

of your data.

To set the downstream modulation, use the following command in cable interface configuration mode.

The standard DOCSIS modulation rate (and the Cisco default) is QAM-64.

Router(config-if)# cable downstream modulation 64qam

Verifying the Downstream Modulation

To verify the downstream modulation setting, enter the show controllers cable command for the

downstream port you have just configured. See the following example:

Router# show controllers cable5/0/0 downstream

Cable5/0/0 Downstream is up

Frequency=96000000, Channel Width 6 MHz, 64-QAM, Symbol Rate 5.056941 Msps

FEC ITU-T J.83 Annex B, R/S Interleave I=32, J=4

Perform these steps if you are having difficulty with verification:

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Cisco uBR10-SRP-OC12SML Specifications Page 144