Logical Interface Traffic Carried In Other Queues; Traffic Starvation And Shared Shaping; Figure 17: Implicit Constituent Selection For Compound Shared Shaper: Mixed Interface Types - Juniper JUNOSE 11.1.X - QUALITY OF SERVICE CONFIGURATION GUIDE 3-21-2010 Configuration Manual

JUNOSe 11.1.x Quality of Service Configuration Guide
For more information about configuring low-CDV mode, see "ATM Integrated
Scheduler Overview" on page 159.

Logical Interface Traffic Carried in Other Queues

A shared shaper affects only the queues and nodes for a single interface. Queues
associated with other interfaces are not constrained by the shared shaper. This
behavior should cause no problems if you configure all queues for a single logical
interface type. However, if you configure queues for multiple interface types, you
may have problems with shared shaping.
For example, a shared shaper for VC 1 does not directly constrain the rate for a queue
for IP 1 unless that queue is stacked above a node for VC 1 in the scheduler hierarchy.
If the IP queue is stacked above a node for VC 1, then the shared shaper indirectly
controls the queue bandwidth through the VC 1 node. But if the IP 1 queue is not
stacked above a VC 1 node, it is immune to the shared shaper, and the total
bandwidth for VC 1 can exceed the shared rate.
As another example, if a shared queue exists for VP 1 where VC 1 is contained within
VP 1, the shared shaper for VC 1 does not constrain the bandwidth of a VP queue.
The total bandwidth for VC 1 can again exceed the shared rate.
Figure 17 on page 76 illustrates an example of mixed interface shaping and its
implications for implicit constituent selection for compound shared shaping.

Figure 17: Implicit Constituent Selection for Compound Shared Shaper: Mixed Interface Types

Traffic Starvation and Shared Shaping

Traffic in the strict-priority traffic-class group can starve out other traffic competing
within the shared shaper. You might want to configure an individual shaping rate
76
Guidelines for Configuring Simple and Compound Shared Shaping