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Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
OL-2239-03
Chapter3 Configuring Cable Modem Interface Features
Configuring the Upstream Cable Modem Interface
Setting Upstream Traffic Shaping
Upstream traffic shaping, available on the DOCSIS upstream channel, delays the scheduling of the
upstream packet, which in turn causes the packet to be buffered on the cable customer premises
equipment (CPE) device, instead of being dropped. This allows the user’s TCP/IP stack to pace the
application traffic appropriately and approach throughput commensurate with the subscriber’s defined
quality of service (QoS) levels.
The CMs are buffered without incurring TCP-related timeouts and retransmits. This enables the CMTS
to enforce the peak upstream rate for each CM, without degrading overall TCP performance for the
subscriber CPEs. Upstream grant shaping is per cableinterface (per service ID (SID)).
Token-bucket policing with shaping is the per-upstream default rate-limiting setting at the CMTS.
Shaping can be enabled or disabled for the token-bucket algorithm.
To enable upstream traffic shaping for an upstream port on a Cisco cable interface line card, use one of
the following commands in cable interface configuration mode.
To disable upstream traffic shaping for an upstream port, enter the following command in cable interface
configuration mode:
Router(config-if)# no cable upstream usport rate-limit
The software supports:
• Generic calendar queuing routines
• New token-bucket policing function
• Grant shaping application of the calendar queues
• Upstream rate-shaping option to the token-bucket keyword
• A default state change from 1-second burst policing to token bucket with shaping
Tip Upstream grant shaping is per CM (per service ID (SID)). Shaping can be enabled or disabled for the
token-bucket algorithm.
Note Before the introduction of this feature, the CMTS would drop bandwidth requests from a CM it 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.
Command Purpose
Step1
Router(config-if)# cable upstream
usport rate-limit
Router(config-if)# cable upstream
usport rate-limit token-bucket
Router(config-if)# cable upstream
usport rate-limit token-bucket
shaping
Enables traffic shaping for the specified upstream cable interface.
Enables traffic shaping for the upstream cable interface employing the
token-bucket policing algorithm. With this command the
CiscouBR7200series CMTS automatically drops packets in violation of
allowable upstream bandwidth.
Default. Enables traffic shaping for the upstream cable interface employing
the token-bucket policing algorithm with traffic shaping.
Step2
Router(config-if)# ^Z
Router#
Exits back to the EXEC mode so that you can verify upstream traffic shaping.