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

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Chapter 3
Configuring Queue Profiles for Buffer
Management
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
■
Configuring Queue Profiles to Manage Buffers and Thresholds on page 22
■
Monitoring Queues and Buffers on page 24
Queuing and Buffer Management Overview
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.
Queuing and Buffer Management Overview
■ 17