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JunosE 11.3.x Quality of Service Configuration Guide
Guidelines for Configuring a Minimum Threshold
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Guidelines for Managing Buffers
20
You might want to limit latency of your multicast traffic by bounding the queue length
using a maximum committed threshold. The following example configures the multicast
queues so that the committed threshold never exceeds 20 KB, even when the egress
memory is lightly loaded. The forfeited buffers are allocated to other queues.
host1(config)#queue-profile multicast
host1(config-queue)#committed-length 0 20000
host1(config-queue)#exit
Be sure to include 0 in the syntax, or you will configure a minimum threshold.
Configuring a minimum threshold does not guarantee that a queue always obtains the
minimum buffer allocation. You can configure 1000 queues with a minimum of 1 MB
each, but the buffer memory is 32 MB or 128 MB, not 1 GB. In this case, the system moves
into higher operating regions (global utilization) if all these queues buffer traffic, until it
reaches 90 percent utilization. At that point, the thresholds must reduce to the reserved
percentages, and the queue thresholds drop from a high threshold to a very low one.
Queues are not guaranteed to obtain any buffering, and are buffered in the order in which
they are received.
You can configure a minimum committed threshold by specifying a value such as 1000
with the committed-length command:
host1(config)#queue-profile multicast
host1(config-queue)#committed-length 1000 20000
host1(config-queue)#exit
Memory Requirements for Queue and Buffers on page 19
Configuring Queue Profiles to Manage Buffers and Thresholds on page 22
Queue profiles enable you to manage queue thresholds and buffers to manage the
following common problems:
Queues that back up and consume too many buffers
Queues that cannot obtain buffers when they need them (called buffer starvation)
You can set the buffer weight to ensure that some sets of queues get higher thresholds
than others. Buffer weight is analogous to weight in a scheduler profile. It directs the
router to set the queue thresholds proportionately.
This feature provides graceful buffer allocation as the global utilization goes higher;
queues with more buffer weight always obtain more buffers, but they do not undergo a
dramatic drop in threshold when the system moves from region to region.
JunosE Software uses 128-byte buffers. When setting very small queue thresholds, keep
the following guidelines in mind:
Copyright © 2010, Juniper Networks, Inc.
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