Docsis 1.0+ Feature Support - Cisco 7246VXR - uBR Router Software Configuration Manual

Supported Software Features for the Cisco uBR7200 Series
To change these settings, two or more traffic profiles are defined, with differing downstream QoS
settings as desired.
Table 11
QoS Profile Setting
Maximum Downstream Transmit Burst (bytes) max-burst 4000
Maximum Downstream Burst (bps)
Maximum Downstream Bandwidth
In this scenario, both QoS profiles are identical except for the max-ds-burst size, which is set to 5000 in
QoS profile 101 and 5000 in QoS profile 102.
Optimal Settings for DOCSIS 1.0 Downstream Powerburst
DOCSIS allows the setting different token bucket parameters for each service flow, including the token
bucket burst size. When burst sizes are closer to 0, QoS is enforced in a stricter manner, allowing a more
predictable sharing of network resources, and as a result easier network planning.
When burst sizes are larger, individual flows can transmit information faster (lower latency), although
the latency variance can be larger as well.
For individual flows, a larger burst size is likely to be better. As long as the system is not congested, a large
burst size reduces the chances of two flows transmitting at the same time, because each burst is likely to take
less time to transmit. However, as channel bandwidth consumption increases, it is probably that large burst
traffic would exceed the thresholds of buffer depths, and latency is longer than with well shaped traffic.
For additional information about the cable qos profile command and configuring QoS profiles, refer to
the following documents on Cisco.com:
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DOCSIS 1.0+ Feature Support

In response to the limitations of DOCSIS 1.0 in handling real-time traffic, such as voice calls,
Cisco created the DOCSIS 1.0+ extensions to provide the more important QoS enhancements that were
expected in DOCSIS 1.1. The main enhancements provide basic Voice-over IP (VoIP) service over the
DOCSIS link, support for dynamic creation and teardown of flows during voice calls, support for one
new unsolicited grant service (UGS) slot scheduling mechanism for voice slots, and per IP-precedence
rate shaping on the downstream. In particular, the Cisco DOCSIS 1.0+ extensions include the
DOCSIS 1.1 features described in this section:
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Refer to the following online document for additional information about DOCSIS 1.0+ support on the
Cisco uBR7200 Series:
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Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
1-56
Table 11 provides two examples of such QoS profiles for illustration:
Sample QoS Profiles with Differing ERBA (Maximum Downstream) Settings
Cisco IOS CMTS Cable Command Reference Guide
http://www.cisco.com/en/US/docs/ios/cable/command/reference/cbl_book.html
DOCSIS 1.1 for the Cisco CMTS
http://www.cisco.com/en/US/docs/cable/cmts/feature/guide/ufg_docs.html
Concatenation for DOCSIS 1.0+, page 1-57
Dynamic MAC messages, page 1-57
Multiple SIDs per Cable Modem, page 1-57
Separate Downstream Rates, page 1-57
Unsolicited Grant Service (CBR-scheduling) on the Upstream, page 1-57
Frequently Asked Questions on DOCSIS 1.0+
Chapter 1 Overview of Cisco uBR7200 Series Software
QoS Profile 101
max-ds-burst 20000
max-downstream 100
QoS Profile 102
max-burst 4000
max-ds-burst 5000
max-downstream 100
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