Installation guide

5-6
Cisco uBR7100 Series Universal Broadband Router Software Configuration Guide
OL-2238-03
Chapter 5 Troubleshooting the System
Managing Cable Modems on the HFC Network
Caution Cisco recommends if you are adjusting the dynamic map advance algorithm that you 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.
Configuring Per Modem Filters
You can configure the Cisco uBR7100 series router to filter incoming packets from individual hosts or
cable modems based on the source Media Access Controller (MAC) or Internet Protocol (IP) address.
Definition of filters follows standard Cisco IOS configuration practices for access lists and groups.
To configure per modem filters, use the following commands in cable interface configuration mode.
Command Purpose
CMTS01(config-if)# cable
map-advance dynamic [n]|static
Specify a value to enhance the upstream throughput from a
cable modem connected to the Cisco uBR7100 series router.
The
n parameter provides the safety factor for the dynamic
map advance algorithm. This parameter 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 between 500 to 1500 usecs. This parameter
is a delta value added to the dynamic map-advance 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 map advance command. The
Cisco uBR7100 series router will use a fixed lookahead time
in MAPs, regardless of the real propagation delay of the
farthest cable modem on the network. This fixed lookahead
time is computed based on the worst case parameters such as
farthest DOCSIS propagation delay for the CMs.