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CHAPTER 3
Configuring Queue Profiles for Buffer
Management
Queuing and Buffer Management Overview
Copyright © 2010, Juniper Networks, Inc.
This chapter provides information for configuring queue profiles for buffer management
on the E Series router.
QoS topics are discussed in the following sections:
Queuing and Buffer Management Overview on page 17
Memory Requirements for Queue and Buffers on page 19
Guidelines for Managing Queue Thresholds on page 19
Guidelines for Managing Buffers on page 20
Monitoring Queues and Buffers on page 24
A queue is a set of first-in, first-out (FIFO) buffers that buffer packets on the data path.
QoS associates queues with a traffic class/interface pair. For example, if you create 4000
IP interfaces and configure each interface with four traffic classes, then 16,000 queues
are created. For specific information about the maximum number of QoS queues
supported, see JunosE Release Notes, Appendix A, System Maximums.
The E Series router dynamically manages the shared memory on egress line modules to
provide a good balance between sharing the memory among queues and protecting an
individual queue's claim on its fair share of the egress memory.
When egress packet memory is in high demand and aggregate utilization of the packet
memory is high, queue lengths are set to lengths that strictly partition egress memory
into per-queue memory sections. This conservative buffer-management strategy reserves
a fair share of buffers for each queue, so that high bandwidth consumers cannot starve
out moderate traffic consumers by allocating all the shared memory resource for
themselves.
When egress packet memory is in low demand, a more liberal buffer management strategy
is used to provide active queues with more access to the shared memory resource.
17
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Troubleshooting
