Juniper JUNOSE 11.1.X - QUALITY OF SERVICE CONFIGURATION GUIDE 3-21-2010 Configuration Manual page 144

JUNOSe 11.1.x Quality of Service Configuration Guide
For compound implicit shared shaping, the shared shaper assigns the voice queue
all the 2 MB, the video queue the next priority, and the best-effort node the last
priority. The voice queue is unlikely to drop because it has highest priority in the
hierarchical scheduler as well as highest priority within its shared shaper. The video
queue is less likely to drop, but you must still take care that the hierarchical scheduler
is provisioned to allocate the proper assured bandwidth to video. The shared shaper
can shape, or deny, bandwidth to its constituents, but it cannot allocate assured
bandwidth in the hierarchical scheduler.
The compound shared-shaper mechanism also works as follows. In the legacy
scheduler, weight and shaping rate are independent attributes that together determine
bandwidth allocation. The scheduler allocates bandwidth based on relative weights,
and the shaper can deny that bandwidth when the shaping rate is reached. With the
shared shaper in effect, two independent shaping rates must be satisfied for the
queue or node to dequeue. A deficit in either type of shaping bounds the bandwidth.
As a general way of predicting the scheduler behavior, if the physical port is congested
because many queues and nodes are competing in the hierarchical scheduler, the
legacy weights and shaping rates dominate the scheduler outcome. If the hierarchical
scheduler is not congested, a shared shaper configured for a logical interface
dominates the outcome for the traffic scheduled through that logical interface.
The compound shared shaper orders constituents, and allocates shared bandwidth
to them, according to the following rules:
1.
2.
3.
4.
5.
6.
By default, strict constituents transmit traffic at a rate up to the lesser of their
shared-shaping rate or the legacy shaping rate. Individual strict constituents can be
allocated any bandwidth value less than the shared rate. The sum of all constituent
rate credits does not have to be less than the shared rate. Individual constituent rates
are not capped, because a particular traffic class often does not exceed a limit because
of admission control, or because the class is policed at some point in the path.
Unlike strict constituents, which can consume bandwidth up to the legacy shaping
rate or the shared-shaping rate, weighted constituents share bandwidth with their
peers solely in proportion to their shared-shaping-weight. A higher weight value
grants the constituent a greater proportion of the available bandwidth.
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Implicit Constituent Selection Overview
Strict constituents in the auto-strict-priority traffic-class group
For multiple strict-priority traffic-class groups, bandwidth allocation order is the
same order in which the additional strict traffic class groups were configured.
You can issue the show traffic-class-groups command to view this order.
Strict constituents in extended traffic-class groups
For multiple extended traffic class groups, bandwidth allocation order is the
same order in which the traffic class groups were configured. You can issue the
show traffic-class-groups command to view this order.
Strict constituents in the default group
Weighted constituents in the auto-strict-priority traffic class group
Weighted constituents in extended traffic class groups
Weighted constituents in the default group