Cisco Systems UBR10012 Setting Upstream Backoff Values

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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

To return the upstream time-adjustment ranging value to the default of 2 seconds, enter the following

command in cable interface configuration mode:

Router(config-if)# no cable upstream usport time-adjust continue

To return the upstream time adjustment threshold value to the default of 1 second, enter the following

command in cable interface configuration mode:

Router(config-if)# no cable upstream usport time-adjust threshold

To determine if upstream timing adjustment is configured and activated, enter the showrunning-config

command and look for the cable interface configuration information. If upstream timing adjustment is

enabled, either or both of the continue and threshold timing-adjustment entries appear in the show

running-config command output. If both the continue and threshold upstream timing adjustments are

disabled, no timing adjustment entry appears in the showrunning-config command output.

Tip Perform the following steps if you are having difficulty with verification:

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

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

Step3 Verify that the captive installation screws are tight.

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

Setting Upstream Backoff Values

The DOCSIS-specified method of contention resolution for CMs wanting to transmit data or requests on

the upstream channel is a truncated binary exponential backoff value, with the initial backoff window

and the maximum backoff window controlled by the CMTS. The CiscouBR10000series CMTS

specifies backoff window values for both data and initial ranging, and sends these values downstream as

part of the Bandwidth Allocation Map (MAP) MAC message.

The values are configurable on the CiscouBR10000series software and are power-of-two values. For

example, a value of 4 indicates a window between 0 and 15; a value of 10 indicates a window between

0 and 1023. You can set fixed start and end values for data backoff on the upstream ports, or you can set

the upstream ports for automatic data backoff. You have the same options for ranging backoff. For both

backoff windows, the default start value is 0; the default end value is 4. Valid values are from 0 to 15.

Note Cisco does not recommend that you adjust default values, but that you enable the automatic dynamic

backoff algorithm. Refer to the “Configuring Dynamic Contention Algorithms (Cable Insertion

Interval, Range, and Data Backoff)” section on page7.

To set data or ranging backoff values for an upstream port, use one or more of the following commands,

in cable interface configuration mode.