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

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Figure 12: True Strict-Priority Configuration
This configuration provides low latency for the strict-priority queues, irrespective of
the state of the nonstrict queues. The worst-case latency for a strict packet caused
by a nonstrict packet is the propagation delay of a single large packet at the port
rate. For a 1500 byte frame at OC3 rate, that latency is less than 100 microseconds.
Because the strict and nonstrict packets for a VC are scheduled in separate round
robins, the scheduler cannot enforce an aggregate rate for both of them.
Schedulers and Relative Strict Priority
In the relative strict-priority configuration in Figure 13 on page 63, the scheduler
provides relative strict-priority scheduling relative to the VC. If the port is not
oversubscribed, the VC round robin does not cause significant latency.
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Comparison of True Strict Priority with Relative Strict Priority Scheduling
JUNOSe 11.1.x Quality of Service Configuration Guide