Comparison Of True Strict Priority With Relative Strict Priority Scheduling; Schedulers And True Strict Priority; Figure 12: True Strict-Priority Configuration - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - QUALITY OF SERVICE CONFIGURATION GUIDE 2010-09-22 Configuration Manual

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Comparison of True Strict Priority with Relative Strict Priority Scheduling

Schedulers and True Strict Priority

Figure 12: True Strict-Priority Configuration

Copyright © 2010, Juniper Networks, Inc.
port will not become congested, and the latency caused by the round-robin behavior of
both the HRR and cell schedulers is nominal. In these undersubscribed conditions, the
latency of a strict-priority queue within each VC is calculated as if the VC were draining
onto a wire with bandwidth equal to the shaped rate.
Relative strict priority is carried out in the HRR scheduler on E Series ASIC line modules.
Comparison of True Strict Priority with Relative Strict Priority Scheduling on page 59
Configuring Strict-Priority Scheduling on page 63
Configuring Relative Strict-Priority Scheduling for Aggregate Shaping Rates on page 65
This section explains how the HRR and SAR schedulers handle true strict-priority and
relative strict-priority configurations.
In the strict-priority configuration in Figure 12 on page 59, the queues stacked above the
single strict priority scheduler node make up a round-robin separate from the nonstrict
queues. All strict queues are drained to completion first, and any residual bandwidth is
allocated to the nonstrict round-robin.
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
Chapter 8: Configuring Strict-Priority Scheduling
59