Cisco uBR10-SRP-OC12SML Specifications download pdf (Page 154)

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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

When considering whether to adjust backoff values, keep the following considerations in mind:

• The cableinterface reconnection time after a power outage is related to the following factors:

–

DHCP, ToD, and TFTP servers often operate well below 1 percent load under normal situations,

but can jump to over 100 percent after an outage.

–

Adjusting the backoffs to larger numbers slows cableinterface reconnection and reduces server

load.

–

Backoffs that are too small result in cableinterfaces failing to range the upstream RF levels

correctly and cycling to maximum power, thus increasing connection time and reducing

network performance.

–

Backoffs that are too large result in increased recovery time after a large service outage.

–

There is significant variation in cableinterface performance (brand to brand) in cableinterface

restart time.

• All cableinterfaces should recover in 0 to 10 minutes after all services are restored

(CiscouBR10012router, RF transport, DHCP, TFTP, and ToD servers). A CM that takes longer than

10minutes could be experiencing a problem with the modem itself, a problem with CMTS settings,

or a problem in the DOCSIS provisioning servers.

Note Upstream segments serving a relatively large number of cableinterfaces (for example,

more than 1600) might suffer recovery times greater than 10minutes.

Verifying Upstream Data Backoff

To verify backoff window settings, 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 1.600 MHz, QPSK Symbol Rate 1.280 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)

Command Purpose

Step1

Router(config-if)# cable upstream

usport data-backoff start end

Router(config-if)# cable upstream

usport data-backoff automatic

Optimizes the automatic setting for as many as 250 cableinterfaces per

upstream port. Sets manual values for data backoff windows only when

operating with more than 250 cableinterfaces per upstream port.

Configures the default backoff window values of 0 and 4.

Step2

Router(config-if)# cable upstream

usport range start end

Router(config-if)# cable upstream

usport range automatic

Optimizes the automatic setting for as many as 250 cableinterfaces per

upstream port. Sets manual values for data backoff windows only when

operating with more than 250 cableinterfaces per upstream port.

Configures the default backoff window values of 0 and 4.

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