4-7
Cisco uBR10012 Universal Broadband Router Software Configuration Guide
OL-1520-05
Chapter 4 Managing Cable Modems on the Hybrid Fiber-Coaxial Network
Configuring CM Registration Timeout
Tip
Be sure that you entered the correct CM IP address or
MAC address
when you typed the
clear cable modem reset
command. It might take up to 30 seconds for the CM to start the reset
sequence.
Note
The
clear cable modem reset
command is useful if a Simple Network Management Protocol (SNMP)
manager is not available, or if the CM is unable to obtain an IP address or respond to SNMP messages.
Configuring CM Registration Timeout
By default, registered CMs that have no upstream activity for three minutes are timed out and
disconnected from the Cisco uBR10012 router. 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 Cisco uBR10012 router, use the
following command in cable interface configuration mode.
Configuring Dynamic Contention Algorithms (Cable Insertion
Interval, Range, and Data Backoff)
The Cisco uBR10000 series 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 Cisco uBR10000 series 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.
Command
Purpose
cable registration-timeout
n
Specifies 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.
