Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - QUALITY OF SERVICE CONFIGURATION GUIDE 2010-09-22 Configuration Manual page 138

JunosE 11.3.x Quality of Service Configuration Guide
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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:
Strict constituents in the auto-strict-priority traffic-class group
1.
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
2.
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
3.
Weighted constituents in the auto-strict-priority traffic class group
4.
Weighted constituents in extended traffic class groups
5.
Weighted constituents in the default group
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
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