Traffic Shaping - Cisco uBR10012 Software Configuration Manual

Configuring the Upstream Cable Interface
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Upstream grant shaping is per CM (per service ID (SID)). Shaping can be enabled or disabled for the
Tip
token-bucket algorithm.
Before the introduction of this feature, the CMTS would drop bandwidth requests from a CM it
Note
detected as exceeding its configured peak upstream rate. Such request dropping affects the
throughput performance of IP-based protocols such as FTP, TCP, and Simple Network Management
Protocol (SNMP). With this feature, the CMTS can shape (buffer) the grants for a CM that is
exceeding its upstream rate, rather than dropping the bandwidth requests.
Router# show interface c5/0/0 sid 1 counters
00:02:23: %ENVM-3-LASTENV: Cannot save environmental data
Sid
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Verifying Upstream Traffic Shaping
To determine if upstream traffic shaping is configured and activated, enter the show running-config
command and look for the cable interface configuration information. If upstream traffic shaping is
configured and enabled, a traffic shaping entry appears in the show running-config output. If upstream
traffic shaping is disabled, no cable upstream rate-limit appears in the output.
You can also perform the following tasks to verify that traffic shaping is enabled on the upstream channel:
Configure a low-peak upstream rate limit for the CM in its QoS profile. Either use the command-line
Step 1
interface (CLI) to modify the modem's QoS profile, or edit the modem's TFTP configuration file. refer
to the DOCSIS 1.1 for the Cisco uBR7200 Series Universal Broadband Routers feature module at
http://www.cisco.com/en/US/docs/cable/cmts/feature/DOCSIS11.html.
Use a regular rate-limiting algorithm on the upstream without rate shaping, and note the drops of the
Step 2
excess bandwidth requests from this CM when it exceeds its peak upstream rate.
Use the show interface cx/y sid counters verbose 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 service flow qos 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.
Make the CM exceed its peak upstream rate by generating upstream traffic, and note the effect of grant
Step 4
buffering (shaping) at the CMTS. If you use CM-to-CMTS pings, there is a perceivable decrease in the
frequency of the pings.
Let the pings run long enough to allow the averages at the CMTS to 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 CM.
Cisco uBR10012 Universal Broadband Router Software Configuration Guide
3-26
Upstream rate-shaping option to the token-bucket keyword
A default state change from 1-second burst policing to token bucket with shaping
Req-polls BW-reqs
issued received
0 22
0 3
0 0
Chapter 3 Configuring Cable Interface Features for the Cisco uBR10012 Router
Grants Packets Frag
issued received complete
22 22 0
3 2 0
0 0 0
Concatpkts
received
0
0
0
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