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JunosE 11.3.x Quality of Service Configuration Guide
Integrating the HRR Scheduler and SAR Scheduler
154
The proper integration of the two schedulers is an important element of the router's ATM
QoS support. Three QoS port modes control integration of the two schedulers:
Default integrated QoS port mode—ATM application controls the scheduling facilities
of the SAR scheduler.
Low-latency QoS port mode—HRR scheduler controls the traffic rate.
Low-CDV QoS port mode—HRR scheduler and the SAR scheduler work together to
schedule traffic.
Improper configuration of the two schedulers might create an inefficient scenario in which
extra latency is introduced, or might cause the scheduler to underuse the link.
To configure integration of the schedulers, use the qos-mode-port commands listed in
Table 16 on page 154.
Table 16: qos-mode-port Commands
Command
no qos-mode-port (default integrated mode)
qos-mode-port low-cdv
qos-mode-port low-latency
qos-mode-port
NOTE: For ERX7xx models, ERX14xx models, and the ERX310 router, the
qos-mode-port commands are valid only for the major interface on port 0.
To properly integrate the schedulers, make sure that the HRR and the SAR schedulers
shape packets at the same rate. If the HRR scheduler sends packets at a higher rate than
the SAR scheduler shapes them, the SAR scheduler can become congested and block
the entire port.
To manage the integration of the HRR and the SAR schedulers:
Specify the cell-based shaping mode.
1.
See "Configuring the QoS Shaping Mode for ATM Interfaces" on page 166.
Configure low-CDV QoS port mode to ensure that the HRR and SAR schedulers are
2.
configured at the same rate.
See "Configuring Low-CDV Mode for Per-Port Queuing on ATM Interfaces" on page 163.
Backpressure
SAR Buffering
VC and port
significant
port
normal
port
minimal
port
minimal
Copyright © 2010, Juniper Networks, Inc.
Scheduling
SAR
SAR and HRR
HRR
HRR
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