Cisco Systems uBR7200 Series manual CMTS01config-if#no cable insertion-interval, Automatic

Chapter 4 Troubleshooting the System

Managing Cable Modems on the HFC Network

Although the binary exponential backoff algorithm operates in a distributed fashion at different CMs, the CMTS provides centralized control for the backoff algorithm. To achieve this, it remotely monitors traffic load—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 algorithm where 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.

Table 4-4	Instructions to Modify Dynamic Contention Algorithm Defaults
Command		Purpose
CMTS01(config-if)#[no] cable insertion-interval		Disable or enable the dynamic ranging interval
automatic		algorithm. If lower and upper bounds for varying the
		period are not specified, the system uses default values
		of 50 msecs and 2 secs respectively.
CMTS01(config-if)#cable insertion-interval automatic min		Set the lower bound on the initial ranging period for
<25-2000>		the auto ranging algorithm.
CMTS01(config-if)#cable insertion-interval max		Set the upper bound on initial ranging period for the
<500-2000>		auto ranging algorithm.
CMTS01(config-if)#no cable insertion-interval		Reset fixed initial ranging period to default value of
		500 msecs. Also invokes fixed initial ranging
		algorithm.
CMTS01(config-if)#cable insertion-interval <100-2000>		Enabled fixed initial ranging period algorithm with
		specified fixed period (msecs).

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/optimal lookahead time in MAPs significantly improves the per-modem upstream throughput.

Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide

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