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

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To use implicit constituent selection, you specify only the shared-shaping rate and
the logical interface. The router identifies the constituents associated with the logical
interface type and their allocated bandwidth. This method is appropriate for the
typical case where the intent is to shape all subscriber queues to the shared rate.
If you want instead to shape a subset of the queues for a subscriber to the shared
rate, the explicit selection process is appropriate. Explicit selection is also useful
when you want queues as the active constituents instead of the node below them.
By choosing queues you can assign appropriate priority or weights.
Types of Shared Shaper Constituents
The shared-shaping-constituent command in a scheduler profile specifies
constituents and their attributes. The command has two aspects. For explicit
constituent selection, this command specifies the constituents. For the compound
shared shaper only, this command specifies scheduling attributes of shared shaping:
the shared priority and the shared weight.
A shared shaper can be one of the following four types:
■
Simple implicit—Constituents are best-effort node or queues, and all nodes and
queues in named traffic-class groups.
■
Simple explicit—The software selects constituents based on the
shared-shaping-constituent command. The weight and priority attributes of
the shared-shaping-constituent command are ignored, because the simple
shared shaper does not allocate bandwidth among constituents; instead it controls
just the best-effort queue or node.
■
Compound implicit—Constituents are selected automatically by the software. If
a node exists in a given traffic-class group, the node is active and the queues
stacked above it are inactive constituents. The
shared-shaping-constituent
command does not affect constituent selection. However, if the command is
present for a constituent that was implicitly selected, the software configures
that constituent with the shared priority and shared weight as indicated.
■
Compound explicit—The software selects constituents based on the shared
priority and shared weight configured with the
shared-shaping-constituent
command. If no attributes are specified, the software supplies a shared priority
consistent with the legacy scheduler configuration.
Table 11 on page 108 compares implicit and explicit shared shaping.
Table 11: Comparison of Implicit and Explicit Shared Shaping
Explicit Shared Shaping Implicit Shared Shaping
■
To specify the logical interface for shared
shaping, associate a scheduler profile that
includes the
shared-shaping-rate rate
explicit-constituents command or the
shared-shaping-rate rate simple
explicit-constituents command with a
best-effort node or queue.
■
To specify the logical interface for shared
shaping, associate a scheduler profile that
includes the
shared-shaping-rate
command or the shared-shaping-rate
simple command with a best-effort node
or queue.
108 ■
Constituent Selection for Shared Shaping Overview
JUNOSe 11.1.x Quality of Service Configuration Guide