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xStack
®
DES-3528/DES-3552 Series Layer 2 Stackable Fast Ethernet Managed Switch User Manual
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SRED
Simple random early detection (sRED) is a simplified RED mechanism based on ASIC capability. Random Early
Detection (RED) is a congestion avoidance mechanism at the gateway in packet switched networks. RED gateways
keep the average queue size low while allowing occasional bursts of packets in the queue. The switch provides
support for sRED through active queue management by probabilistic dropping of incoming colored packets.
Active queue management is a class of algorithms that attempt to proactively drop or mark frames before congestion
becomes excessive. The goal is to detect the onset of persistent congestion and take proactive action so that TCP
sources contributing to the congestion back off gracefully, insuring good network utilization while minimizing frame
loss.
This proactive approach starts discarding specific colored packets before the packet buffer becomes full. If this queue
depth is less than the threshold, there is minimal (or no) congestion and the packet is enqueued. If congestion is
detected the packet is dropped or queued based on the DSCP.
SRED Settings
To view this window click
QoS > SRED > SRED Settings
Figure 5 - 10 SRED Settings window
The following parameters may be set:
Parameter Description
From port/To port
A consecutive group of ports may be configured starting with the selected port.
Class ID
Select the Class ID, from 0-7 , to configure for the SRED parameters. Selecting all will set the
parameters configured here for all CoS queues.
Drop Green
Enabled: probabilistic drop yellow and red colored packets if the queue depth is above the lower
threshold, and probabilistic drop green colored packets if the queue depth is above the upper
threshold.
Disabled : probabilistic drop red colored packets if the queue depth is above the lower threshold,