Docsis Quality Of Service Enhancements Prior To Docsis 1.1 - Cisco 7246VXR - uBR Router Software Configuration Manual

Supported Software Features for the Cisco uBR7200 Series

DOCSIS Quality of Service Enhancements Prior to DOCSIS 1.1

A number of DOCSIS quality of service (QoS) enhancements were added to Cisco IOS Release
12.1(1a)T1 and continue with later releases; these features paralleled some of those that were expected
in the DOCSIS 1.1 specification prior to finalization.
For supported DOCSIS 1.1 QoS features, refer to the
on page
These QoS enhancements are in addition to the currently existing QoS traffic shaping and tiered best
Note
effort features.
Concatenation Support Prior to DOCSIS 1.1
DOCSIS Concatenation combines multiple upstream packets into one packet to reduce packet overhead
and overall latency, as well as increase transmission efficiency. Using concatenation, a DOCSIS cable
modem needs to make only one bandwidth request for a concatenated packet, as opposed to making a
different bandwidth request for each individual packet; this technique is especially effective for
burst-intensive real-time traffic, such as voice calls.
Concatenation is enabled by default for current cable modem cards (see the "Cable Modem Cards"
section), but can be disabled with the Cisco IOS command no cable upstream number concatenation
interface. The show controller command displays whether concatenation is enabled on an interface.
Note
Embedded Client Signaling (dynamic SIDs)
Supports the dynamic creation, configuration, and deletion of Service Identifiers (SIDs) to accommodate
different classes of service. This allows cable modems to request high-priority or high-bandwidth data
streams as needed, such as when a VoIP call is made.
Note Dynamic SIDs can be used only with cable modems that also support this feature. Otherwise, cable
modems must use the static SIDs supported in previous releases.
IP Precedence-Based Rate Limiting
In addition to the currently supported traffic shaping techniques, Cisco IOS Release 12.1(1a)T1 supports
a new configuration field that associates a maximum bandwidth (in kbps) with a particular setting of the
IP type of service (ToS) bits. This can be used to ensure that certain traffic, such as data, does not exceed
a preset rate limit and thereby interfere with higher-priority real-time traffic, such as VoIP calls.
Support for Unsolicited Grants
New fields in the DOCSIS configuration file can be used so that when a cable modem requests a voice
or fax SID, the MAC scheduler on the Cisco uBR7200 series router schedules fixed periodic slots on the
upstream for that traffic flow. The cable modem does not have to contend for these slots, and because
the Cisco uBR7200 series router controls the timing of the slots, it has a very precise control over
potential delay and jitter. This provides a Constant Bit Rate (CBR) traffic flow for real-time traffic such
as voice and fax calls.
Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
1-52
1-60.
Concatenation is supported only with cable modems that support DOCSIS concatenation.
Chapter 1 Overview of Cisco uBR7200 Series Software
"DOCSIS 1.1 Quality of Service Features" section
OL-2239-05