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Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
78-5897-01
Chapter4 Troubleshooting the System Managing Cable Modems on the HFC Network
Although the binary exponential backoff algorithm operates in a distributed fashion at different CMs,
theCMTS provides centralized control for the backoff algorithm. To achieve this, it remotely monitors
trafficload—the backlog developing on the contention channel—and then varies the backoff start and
end specified in the MAPs for that upstream channel. This ensures colliding CMs are properly
randomized in time.
The following cable interface commands are available to configure the dynamic contention algorithms:
[no]cable insertion-interval [
automatic
[<
Imin
[
Imax
]>]] | [<
msecs
>]
[no]cable upstream <
port num
> range-backoff [
automatic
] | [<
start
> <
end
>]
[no]cable upstream <
port num
> data-backoff [
automatic
] | [<
start
> <
end
>]
Tips System defaults are to have dynamic ranging interval enabled, dynamic ranging backoff
enabled, and fixed data backoffs for each upstream of a cable interface.
The default automatic insertion interval setting enables the Cisco automatic initial ranging period
algorithmwhere lower and upper default values of 50 msecs and 2 secs are used. The default automatic
range-backoff enables the dynamic backoff algorithm.
To deviate from system defaults, use one of the following commands in cable interface configuration
mode.
Configure the Dynamic Map Advance Algorithm
A CMTS administrator can enhance the upstream throughput from a cable modem connected to the
Cisco uBR7200 series. The system employs a new algorithm that auto tunes the lookahead time in
MAPs based on several input parameters for the corresponding upstream channel. The use of
dynamic/optimallookahead time in MAPs significantly improves the per-modem upstream throughput.
Table4-4 Instructions to Modify Dynamic Contention Algorithm Defaults
Command Purpose
CMTS01(config-if)#
[no]
cable insertion-interval
automatic
CMTS01(config-if)# cable insertion-interval automatic min
<25-2000>
CMTS01(config-if)# cable insertion-interval max
<500-2000>
CMTS01(config-if)# no cable insertion-interval
CMTS01(config-if)# cable insertion-interval
<100-2000>
Disable or enable the dynamic ranging interval
algorithm. If lower and upper bounds for varying the
periodare not specified, the system uses default values
of 50 msecs and 2 secs respectively.
Set the lower bound on the initial ranging period for
the auto ranging algorithm.
Set the upper bound on initial ranging period for the
auto ranging algorithm.
Reset fixed initial ranging period to default value of
500 msecs. Also invokes fixed initial ranging
algorithm.
Enabled fixed initial ranging period algorithm with
specified fixed period (msecs).