Docsis Qos Support; Traffic Priority - Cisco cBR 8 Configuration Manual

DOCSIS WFQ Scheduler on the Cisco CMTS Routers

DOCSIS QoS Support

DOCSIS defines a set of quality of service (QoS) parameters, including traffic priority, maximum sustained
traffic rate, minimum reserved traffic rate, maximum traffic burst, maximum downstream latency, and peak
traffic rate.
The downstream service flows use the QoS parameters to specify the desired QoS. The downstream policer
and scheduler provides services such as traffic shaping, bandwidth provisioning, traffic prioritization, and
bandwidth guarantee.
The DOCSIS service flow parameters are mapped to the packet queue parameters and provided with appropriate
QoS support for the packet queues to support the DOCSIS parameters
The following DOCSIS QoS parameters are supported:

• Traffic priority

• Maximum sustained traffic rate
• Minimum reserved traffic rate
Note The maximum traffic burst size and the peak traffic rate are supported as described in the
www.cisco.com/c/en/us/td/docs/cable/cbr/configuration/guide/b_cmts_quality_of_services/docsis_wfq_
scheduler.html#con_1085732.
Traffic Priority
The downstream channel bandwidth available to the best effort traffic, namely the channel bandwidth minus
the amount consumed by the priority traffic and the CIR traffic, is allocated to the best effort service flows
in proportion to their DOCSIS traffic priorities. For example, if there are three service flows sending packets
at a particular moment over the same downstream channel, and their DOCSIS traffic priorities are 0, 1 and
3, respectively, their share of the channel bandwidth will be 1:2:4. To achieve this bandwidth allocation, each
service flow is assigned a value known as its excess ratio which is derived from its DOCSIS priority. Table
below shows the default mappings of DOCSIS priority to excess ratio.
When traffic priority for a flow is not explicitly specified, a default priority value of 0 is used as per the
Note
DOCSIS specification.
Table 19: DOCSIS Priority to Excess Ratio Mapping
DOCSIS Traffic Priority
0
1
2
Cisco cBR Series Converged Broadband Routers Quality of Services Configuration Guide for Cisco IOS XE Fuji
Excess Ratio
4
8
12
DOCSIS QoS Support
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