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

Page: 78 / 398

Figure 8: QoS Scheduler Hierarchy
Shaping Rates, Assured Rates, and Relative Weights in a Scheduler Hierarchy
The scheduler supports hierarchical and static assured rates, relative weights, and
shaping rates on all three levels of the hierarchy: first-level node, second-level node,
and queue. The bandwidth delivered from a given node or queue is a function of the
shaping rate and either the assured rate or relative weight:
■
When the scheduler is not congested, the shaping rates determine which node
or queue can claim the bandwidth. The shaping rate specifies the maximum
bandwidth to the node or queue.
■
When the scheduler is congested, either the hierarchical or static assured rate
or the weight specifies the minimum bandwidth.
■
If the scheduler is configured to use a static assured rate and the assured
rate is other than none (the default), it is used to determine the allocated
bandwidth, and the weight setting is ignored. If the assured rate is zero, the
weight setting is used to determine the bandwidth.
The static assured rate specifies the desired bandwidth. This rate is
guaranteed until the bandwidth becomes oversubscribed.
■
If the scheduler is configured to use hierarchical assured rate, the scheduler
dynamically adjusts the amount of allocated bandwidth for service delivery
based on the sum of the assured rates of all child nodes and queues.
■
The assured rate also specifies that if bandwidth is over- or undersubscribed,
all adjustments are made in proportion to the original assured-rate
specification.
For example, if Node A is configured to receive 40 Mbps and Node B receives
20 Mbps, any available bandwidth above the subscribed total of 60 Mbps
would be allocated to the two nodes at the same 2-to-1 ratio. Similarly, if
the bandwidth were oversubscribed and only 30 Mbps were available, this
amount would also be allocated to the two nodes at the 2-to-1 ratio, with
Node A getting 20 Mbps and Node B getting 10 Mbps.
46 ■
Scheduler Hierarchy Overview
JUNOSe 11.1.x Quality of Service Configuration Guide