Cisco Systems UBR10012 Configuring CM Registration Timeout, Configuring Dynamic Contention Algorithms (Cable Insertion Interval, Range, and Data Backoff)

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Cisco uBR10012 Universal Broadband Router Software Configuration Guide

OL-1520-05

Chapter4 Managing Cable Modems on the Hybrid Fiber-Coaxial Network Configuring CM Registration Timeout

Configuring CM Registration Timeout

By default, registered CMs that have no upstream activity for three minutes are timed out and

disconnected from the CiscouBR10012router. This timeout interval can be decreased to 2 minutes or

increased up to 60 minutes.

To specify the registration timeout interval for CMs connected to the CiscouBR10012router, use the

following command in cable interface configuration mode.

Configuring Dynamic Contention Algorithms (Cable Insertion Interval, Range, and Data Backoff)

The CiscouBR10000series software includes the following algorithms that control the capacity of the

contention subchannel and control the efficient use of a given contention subchannel capacity:

•Algorithm that dynamically controls the rate of upstream contention slots—initial ranging and

bandwidth requests.

•Algorithm that varies the backoff parameters that CMs use. Backoff variation falls within each of

the initial ranging and bandwidth request upstream contention subchannels.

In high contention mode, the CiscouBR10000series MAC scheduler uses collision statistics and

sustains a high frequency of initial ranging slots until it detects a steady ranging state. The CMTS

dynamically varies the frequency of initial ranging slots using the data grant utilization on the upstream

channels. The CMTS trades upstream bandwidth between data grants and initial ranging slots. The

CMTS autodetects a high collision state and switches to low insertion interval mode after a steady state

is achieved where few collisions occur.

The CMTS is careful when monitoring the ranging channel health to revert to a steady state. In steady

state mode, data grants—grant utilization—receive preference over initial ranging slots.

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 that 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]

To deviate from system defaults when modifying the dynamic contention algorithm, use one of the

following commands in cable interface configuration mode.

Command Purpose

cable registration-timeout nSpecifies the maximum number of minutes allowed to elapse with

no upstream activity before terminating the connection. Valid

range is from 2 to 60 minutes. Default = 3 minutes.