Understanding Cos Tail Drop Profiles - Juniper JUNOS OS 10.3 - SOFTWARE Manual

Understanding CoS Tail Drop Profiles

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Copyright © 2010, Juniper Networks, Inc.
Tail drop profile is a congestion management mechanism that allows switch to drop
arriving packets when queue buffers become full or begin to overflow.
Tail drop profiles define the meanings of the loss priorities. When you configure tail drop
profiles you are essentially setting the value for queue fullness. The queue fullness
represents a percentage of the memory used to store packets in relation to the total
amount that has been allocated for that specific queue.
The queue fullness defines the delay-buffer bandwidth, which provides packet buffer
space to absorb burst traffic up to the specified duration of delay. Once the specified
delay buffer becomes full, packets with 100 percent drop probability are dropped from
the tail of the buffer.
On Juniper Networks EX Series Ethernet Switches, drop probability is implicitly set to
percent and it cannot be modified.
You specify drop probabilities in the drop profile section of the CoS configuration hierarchy
and reference them in each scheduler configuration.
By default, if you do not configure any drop profile, tail drop profile is in effect and functions
as the primary mechanism for managing congestion. In the default tail drop profile, when
the fill level is 0 percent, the drop probability is 0 percent. When the fill level is 100 percent,
the drop probability is 100 percent.
NOTE: The default drop profile associated with the packets whose loss
priority is low cannot be modified. You can configure custom drop profile only
for those packets whose loss priority is high.
Understanding Junos OS CoS Components for EX Series Switches on page 3148
Example: Configuring CoS on EX Series Switches on page 3173
Configuring CoS Tail Drop Profiles (CLI Procedure) on page 3215
Chapter 107: Class of Service (CoS)—Overview
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