Restrictions for Fairness Across DOCSIS Interfaces
•
The CIR flows cannot reserve all the RF bandwidth. The CIR flows can only reserve 90 percent
1
of the
RF bandwidth that is not statically reserved by the “bandwidth-percent”, in addition to the legacy CIR
bandwidth.
•
It is recommended that the CIR reservation be cleared before disabling Fairness Across DOCSIS Interfaces
feature to ensure that the CIR reservation is not more than the static reservable bandwidth specified by
the “bandwidth-percent” in legacy configuration. This is to prevent CIR over-subscription after disabling
Fairness Across DOCSIS Interfaces feature.
•
The effect of Fairness Across DOCSIS Interfaces feature depends on topology and flow distribution. In
certain cases, Fairness Across DOCSIS Interfaces feature may not achieve BE fairness or maximum
CIR utilization.
•
Fairness Across DOCSIS Interfaces feature applies only to dynamic bandwidth sharing (DBS) enabled
IC and WB interfaces.
Information About Fairness Across DOCSIS Interfaces
The Fairness Across DOCSIS Interfaces feature is an enhancement over the DOCSIS WFQ scheduler. It
enables downstream CIR service flows to be admitted on the interfaces over the thresholds defined in the
legacy configuration (that is, “bandwidth-percent” or “max-reserved-bandwidth”). For example, the feature
enables large CIR flows (like multicast service flows) to be admitted when the current parameters cannot
guarantee enough bandwidth. However, its success rate depends on the allocation and reservation of the
bandwidth for cable interfaces within common RF channels.
This feature also ensures fair bandwidth for downstream BE service flows across cable interfaces with common
RF channels. The per-flow bandwidth of all active service flows on the adjacent BGs are balanced periodically.
The weights (DOCSIS traffic priority (traffic priority + 1)) of all the BGs are equal for downstream BE service
flows. The bandwidth, available for BE traffic, can be used to admit additional CIR flows.
For information about DOCSIS traffic priority, see DOCSIS WFQ Scheduler on the Cisco CMTS Routers
guide.
Note
On-demand CIR Acquisition
When multiple bonding groups sharing the RF-channel bandwidth and the current bonding group's guaranteed
bandwidth is insufficient, this feature can "borrow" neighbor bonding group's non-reserved guaranteed
bandwidth for current bonding group's CIR.
This feature is only used by multicast service flow.
1
The reservable bandwidth for CIR flows consists of static and dynamic portions. By default, the static portion of bandwidth is assigned from the legacy
configuration. The dynamic portion of bandwidth comes from the headroom left on each RF channel for BE traffic.
Cisco cBR Series Converged Broadband Routers Quality of Services Configuration Guide for Cisco IOS XE Fuji
16.7.x
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Fairness Across DOCSIS Interfaces
Restrictions for Fairness Across DOCSIS Interfaces
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