Specifications

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Cisco Cable Modem Termination System Feature Guide
0L-1467-02
Chapter 3 Spectrum Management for the Cisco Cable Modem Termination System
Configuration Examples
Step 1 Configure a low-peak upstream rate limit for the cable modem in its QoS profile. Either use the
command-line interface (CLI) to modify the modem’s QoS profile, or edit the modem’s TFTP
configuration file.
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 2 Enable grant shaping on the upstream channel by using the new shaping keyword extension to the
token-bucket algorithm CLI command.
Step 3 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 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 nonshaping 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:
• Ensure that the cable connections are not loose or disconnected.
• Ensure that the cable interface line card is firmly seated in its chassis slot.
• Ensure that the captive installation screws are tight.
• Verify that you have entered the correct slot and port numbers.
• Verify that you selected a valid frequency for your router.
Configuring the Low-Peak-Rate Limit Example
Router# show cable modem
Interface SID Online Timing Receive QoS IP address MAC address
State Offset Power
Cable3/0/U0 1 online 3564 0.00 6 1.11.53.102 0010.7b6b.7235
Router# show cable qos profile 6
Service Prio Max Guarantee Max Max tx TOS TOS Create B
class upstream upstream downstream burst mask value by priv
bandwidth bandwidth bandwidth enab
6 7 128000 100000 4000000 0 0x0 0x0 management yes