Installation guide

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Cisco uBR7100 Series Universal Broadband Router Software Configuration Guide
OL-2238-03
Chapter 3 Configuring the Cisco Cable Interface
Configuring the Upstream Cable Interface
Step 2 Use a regular rate-limiting algorithm on the upstream without rate shaping and note the drops of the
excess bandwidth requests from this cable modem when it exceeds its peak upstream rate.
Use the show interface cx/y sid counters command to see the bandwidth request drops. Verify that the
upstream rate received by that modem is less than its configured peak rate due to the timeouts and
backoffs produced by the drop in bandwidth requests. Enter the show interface cx/y sid command to see
the input rate at CMTS in bps.
Step 3 Enable grant shaping on the upstream channel by using the new shaping keyword extension to the
token-bucket algorithm CLI command.
Step 4 Make the cable modem exceed its peak upstream rate by generating upstream traffic, and note the effect
of grant buffering (shaping) at the CMTS. If you use cable modem-to-CMTS pings, you will see a
perceivable slowing down of the pings.
Let the pings run for a period to let averages at the CMTS settle; then view the upstream rate received
by this single modem. Use the show interface cx/y command and see the input rate in bps. This value
should be close to the modem’s peak upstream rate. Also note the drop counts for the modem’s SID by
using the show interface sid counters command and verify that the CMTS no longer drops the
bandwidth requests from the cable modem.
The bandwidth request drop count (from previous non-shaping test) remains unchanged when upstream
rate shaping is used, indicating that the CMTS is actually shaping (buffering) the grants for the modem.
Verify that the input rate at the CMTS (from the single rate-exceeded CM) stabilizes close to the
configured peak rate of 128 Kbps.
Perform these steps if you are having difficulty with verification:
1. Ensure the cable connections are not loose or disconnected.
2. Ensure the cable modem card is firmly seated in its chassis slot.
3. Ensure the captive installation screws are tight.
4. Verify that you have entered the correct slot and port numbers.
5. Verify that you selected a valid frequency for your router.
Activating Upstream Frequency Adjustment
To enable automatic upstream frequency adjustment for a specified cable interface, use the following
commands in cable interface configuration mode.
To return the automatic upstream frequency adjustment percentage to the default value of 30 percent,
enter the following command in cable interface configuration mode:
CMTS01(config-if)# no cable upstream usport frequency-adjust averaging
Command Purpose
CMTS01(config-if)# cable upstream
usport frequency-adjust averaging
percentage
Set the minimum number of frequency adjustment
packets required to justify changing the upstream
frequency adjustment method as a percentage.
Acceptable range is 10 to 100 percent.
Default = 30 percent.
CMTS01(config-if)# end
CMTS01#
Return to enable (privileged EXEC) mode.