Quanta Cloud Technology QuantaMesh QNOS5, Configuration Manual

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10. Set the exponential-weighting-constant. The exponential weighting constant smooths the result of the
average queue depth calculation by the function:
average depth = (previous queue depth * (1-1/2^n)) + (current queue depth * 1/2^n).
The average depth is used in calculating the amount of congestion on a queue. Because the instantaneous
queue depth fluctuates rapidly, larger values of the weighting constant cause the average queue depth value
to respond to changes more slowly than smaller values.
(QCT) (Config)#random-detect exponential-weighting-constant 4
11. Configure the queue parameters for traffic class 0 and 1. We set the minimum threshold and maximum
thresholds to 80–100% for green traffic, 70–100% for yellow traffic, and 50–100% for red traffic. Non-TCP
traffic drops in the 50–100% congestion range. Green traffic is dropped at a very low rate to slowly close the
TCP window. Yellow and red traffic are dropped more aggressively.
(QCT) (Config)#random-detect queue-parms 0 1 min-thresh 80 70 50 50 max-thresh 100 100 100
100 drop-prob 3 5 10 15
12. Assign the color policies to ports. The metering policies are applied on ingress ports.
(QCT) (Config)#interface 0/22
(QCT) (Interface 0/22)#service-policy in simple-policy
(QCT) (Interface 0/22)#exit
(QCT) (Config)#interface 0/23
(QCT) (Interface 0/23)#service-policy in two-rate-policy
(QCT) (Interface 0/23)#exit
3.16.3. Example 2: Data Cetner TCP (DCTCP) Configuration
This example globally configures an QNOS switch to utilize ECN marking of green packets queued for egress on
CoS queues 0 and 1, using the DCTCP threshold as it appears in “DCTCP: Efficient Packet Transport for the
Commoditized Data Center” (Alizadeh, Greenberg, Maltz, Padhye, Patel, Prabhakar, Sengupta, and Sridharan,
2010.)
In the first line of the following configuration, the first integer after the minthresh keyword configures
green- colored Congestion Enabled TCP packets in CoS queues 0 and 1 that exceed the WRED threshold
(13% or
~38 Kbytes) to mark packets as Congestion Experienced. The first integer after the max-thresh parameter
configures the upper threshold for green-colored TCP packets to the same value as the min-thresh threshold.
This causes the switch to mark all ECN-capable queued packets as Congestion Experienced when the
threshold is reached or exceeded. TCP packets without ECN capability bits set are dropped according to the
normal WRED processing when the threshold is exceeded. Packets on other CoS queues are handled in the
standard manner (i.e., are tail-dropped) when insufficient buffer is available.