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Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
OL-2239-03
Chapter 5 Managing Cable Modems on the Hybrid Fiber-Coaxial Network
Configuring the Dynamic Map Advance Algorithm
Tip
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
algorithm, where lower and upper default values of 60 msecs and 480 msecs are used. The default
automatic range-backoff
setting
enables the dynamic backoff algorithm.
Configuring the Dynamic Map Advance Algorithm
A CMTS administrator can enhance the upstream throughput from a CM connected to the
Cisco uBR7200 series CMTS. The system employs a new algorithm that automatically tunes the
lookahead time in MAPs, based on several input parameters for the corresponding upstream channel.
The use of dynamic and optimal lookahead time in MAPs significantly improves the per-modem
upstream throughput.
Caution
Only a trained CMTS administrator should adjust these values.
To configure the dynamic map advance algorithm, use the
cable map-advance dynamic
[
n
]|
static
command in cable interface configuration mode.
This command specifies a value to enhance the upstream throughput from a CM connected to the
Cisco uBR7200 series router. The
n
argument provides the safety factor for the dynamic map advance
algorithm. This argument is specified in usecs and controls the amount of extra lookahead time in MAPs to
account for inaccuracies of the measurement system and software latencies. The default value is 1000 usecs.
You can vary this value from 500 to 1500 usecs. This argument is a delta value added to the dynamic
map-advance
setting that the algorithm computes. Using larger safety factors increases the run-time
lookahead in MAPs, but reduces the upstream performance.
Use the
static
keyword for the
cable map-advance
command. The Cisco uBR7200 series router uses a
fixed lookahead time in MAPs, regardless of the real propagation delay of the farthest CM on the
network. This fixed lookahead time is computed based on the worst-case parameters, such as farthest
DOCSIS propagation delay for the CMs.
Caution
If you are adjusting the dynamic map-advance algorithm, do not reduce the safety factor below the
default value of 1000 usecs in a production network, until you are confident that the reduced safety factor
suffices for your deployment. The default value is chosen to be a safe operating point for the algorithm.
Command
Purpose
[
no
]
cable insertion-interval
[
automatic
[
Imin
[
Imax
]]] |
[
msecs
]
cable insertion-interval
automatic
min 25-2000
cable insertion-interval max
500-2000
no cable insertion-interval
cable insertion-interval
100-2000
Enables or disables the dynamic ranging interval algorithm. If
lower and upper bounds for varying the period are not specified,
the system uses default frequency values of initial ranging
upstream slots between 60 milliseconds to 480 milliseconds,
respectively.
Sets the lower bound on the initial ranging period for the
automatic ranging algorithm.
Sets the upper bound on initial ranging period for the automatic
ranging algorithm.
Resets fixed initial ranging period to default value of 500 msecs.
Also invokes fixed initial ranging algorithm.
Enables fixed initial ranging period algorithm with specified fixed
period (msecs).