Per-Packet Queuing On The Sar Scheduler Overview - Juniper JUNOSE 11.1.X - QUALITY OF SERVICE CONFIGURATION GUIDE 3-21-2010 Configuration Manual

NOTE: You can also use the QoS cell mode application with QoS parameters to
manage the integration of HRR and SAR schedulers.
Specifying the QoS cell mode application with the qos-parameter-define command
enables you to configure a port with either frame or cell shaping mode and then
configure the port for low-CDV port mode.
Related Topics

Per-Packet Queuing on the SAR Scheduler Overview

You can configure port queuing on the SAR scheduler, enabling per-packet rather
than per-circuit scheduling. Port queuing mode allows you to use more of the facilities
of the HRR scheduler, which are effectively disabled in default integrated mode,
while at the same time making the SAR scheduler more transparent. In port queuing
mode, you use the QoS application to configure the three levels of the HRR scheduler,
including weighted round robin, traffic shaping, and strict priority scheduling.
You can configure the following modes:
Chapter 19: Configuring an Integrated Scheduler to Provide QoS for ATM
For more information about scheduler profiles, see Scheduler Hierarchy Overview
on page 45
For more information about configuring QoS profiles, see QoS Profile Overview
on page 127
For more information about configuring QoS parameters, see QoS Parameter
Overview on page 225
Default integrated mode The ATM SAR scheduler does the scheduling. Both VC
and port backpressure are enabled, and the HRR scheduler does minimal
scheduling. The SAR scheduler performs significant buffering.
Low-latency mode The HRR scheduler does the scheduling. All QoS
configurations are supported. VC backpressure is disabled, port backpressure is
set as aggressive, and the SAR scheduler does minimal buffering. This mode
enables the lowest latency for packets scheduled in the HRR scheduler with strict
priority. Because the SAR scheduler is running with minimal buffering, there is
no head-of-line blocking.
Low-CDV mode The HRR and SAR schedulers both perform scheduling; QoS
synchronizes the rates of the two schedulers. All QoS configurations are
supported. VC backpressure is disabled, and port backpressure is set to the
default thresholds of 6 MB per OC3 port and 24 MB per OC12 port. In this mode,
you can configure shaping in both the SAR scheduler and the HRR scheduler;
low-cdv mode works with cell shaping mode only and enables relative weighted
VCs and hierarchical shaping in the HRR scheduler. The SAR scheduler performs
normal buffering and can shape either the VC or VP, but not both.
Per-Packet Queuing on the SAR Scheduler Overview
163