Juniper JUNOSE 11.1.X - QUALITY OF SERVICE CONFIGURATION GUIDE 3-21-2010 Configuration Manual page 199

You can configure queues in default integrated mode in the HRR that are immune
to VC backpressure so that you can run voice and video applications. Queues and
nodes in any named traffic class group are not subject to VC backpressure.
In addition, ATM VP and ATM (port level) queues are not stacked above ATM VC
nodes, so queues are not subject to backpressure, regardless of the traffic class group.
Take care not to saturate SAR queues with too much traffic from the HRR, especially
when shaping VP tunnels or VCs in the SAR. You can accomplish this in several ways:
NOTE: These rules apply only to the default integrated mode. VC backpressure is
disabled in low-latency or low-cdv modes. You must account for cell tax; to do this,
use the qos-shaping-mode cell command for the line module.
Use external admission control to guarantee that the sum of non-backpressured
traffic into the VC is less than the SAR shaping rate for the VC.
Shape the non-backpressured queues or nodes in the HRR, making the aggregate
of the non-backpressured traffic for a VC less than the VC rate.
In JUNOSe Release 6.0 and later, you can configure a shared shaper on the ATM
VC node in the default traffic class group. Configure the shared-shaping rate to
be less than or equal to the VC shaping rate in the SAR.
Special rules apply for VP tunnels shaped in the SAR. When shaping in the SAR,
configure ATM VP nodes in the HRR, and arrange that the aggregate traffic
dequeued from the HRR for that vp-tunnel is less than or equal to the VP tunnel
shaping rate in the SAR.
Use one of the following two techniques for VP tunnels shaped in the SAR:
Partition the SAR VP tunnel bandwidth across the ATM VP nodes in the
different traffic class groups in the HRR. For example, using a 4 Mbps VP
tunnel, allocate 1 Mbps for the ATM VP node in the default traffic class group,
2 Mbps for the ATM VP node in the video traffic class group, and 1 Mbps for
the ATM VP node in the voice traffic class group.
When using this technique, keep in mind that the different traffic classes
cannot share bandwidth.
In JUNOSe Release 6.1 and later, using the EFA2 ASIC, you can configure
shared shaping on the ATM VP nodes in the HRR to perform bandwidth
sharing.
Integrating the HRR Scheduler and SAR Scheduler on page 161
Related Topics
Shared Shaping and Low-CDV Mode on page 75
Configuring Default Integrated Mode for ATM Interface on page 168
Configuring Low-Latency Mode for Per-Port Queuing on ATM Interfaces on
page 169
Configuring Low-CDV Mode for Per-Port Queuing on ATM Interfaces on page 171
Configuring the QoS Shaping Mode for ATM Interfaces on page 174
Chapter 19: Configuring an Integrated Scheduler to Provide QoS for ATM
Guidelines for Configuring QoS over ATM
167