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Chapter 2
Cisco CMTS Configuration Commands
cable upstream data-backoff
To specify automatic or fixed start and stop values for data backoff, use the cable upstream data-
backoff command in cable interface configuration mode. To use the default data backoff values, use the
no form of this command.
Syntax Description
n
automatic
start
end
Defaults
Automatic
Command Modes
Interface configuration (cable interface only)
Command History
Release
12.1 T
12.1(5)EC1
12.2(4)BC1
Usage Guidelines
The DOCSIS-specified method of contention resolution for CMs used to send data or requests on the
upstream channel is a truncated binary exponential backoff with the initial backoff window and the
maximum backoff window controlled by the CMTS. The Cisco CMTS router 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 specified in this command are exponential 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.
Cisco recommends that you use the automatic settings for data backoff. If you decide to manually specify
the data-backoff values, use the following formula as a guideline for the start and end binary exponents:
where n is the number of CMs on the upstream. Choose start and stop values that come closest to the
value of 0.33 (which is the optimal probability to transmit on a contention-based system).
OL-1581-08
cable upstream n data-backoff {automatic | start end}
no cable upstream n data-backoff
Modification
This command was introduced.
Support was added for the Cisco uBR7100 series router.
Support was added for the Cisco uBR10012 router.
0.33 = (2**stop - 2**start)/n
Specifies the upstream port number. Valid values start with 0 for the
first upstream port on the cable interface line card.
Specifies automatic data backoff start and stop values. It enables
dynamic variation in the start and end values.
Binary exponential algorithm. Sets the start value for data backoff.
Valid values are from 0 to 15.
Binary exponential algorithm. Sets the end value for data backoff.
Valid values are from 0 to 15.
Cisco Broadband Cable Command Reference Guide
cable upstream data-backoff
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