WRED ECN

WRED algorithm:

New average = (Old_average * (1-2^n) + (Current_Q_depth * ^n)
WRED with a default of n of 9:
New average = (Old_average * .998) + (Current_Q_depth * .002)

The current queue depth only accounts for .2 percent of the new average each time it is calculated
When configuring WRED, change the value of n in this formula by setting the exponential weighting constant parameter. Smaller, average changes more quickly. Larger, average changes more slowly

Difference between RED and WRED, WRED creates a WRED profile for each precedence or DSCP value. WRED profile is a set of minimum and maximum thresholds plus a packet discard percentage, defined as number of entries in a queue. Configured as Mark Probability Denominator (MPD) percentage being 1/MPD, an MPD of 10 yields a calculated value of 1/10, meaning the maximum discard rate is 10%. Allowing a profile for each IP Precedence or DSCP value, WRED can treat packets differently.

WRED physical interface, the ONLY queuing tool!!!! And this is FIFO queue…
MQC applied for individual class queues… Cannot be used in priority queue (LLQ class)

ECN – Explicit Congestion Notification
ECN is just a feature of WRED, choose to mark with ECN bits and send to host rather than drop
COMMAND: Random-dectect ecn

SET THE mark probability per PREC or DSCP value:
policy-map test
class test
bandwidth remaining percent 50
random-detect
random-detect precedence 0 100 500 20

Service-policy output: test

Class-map: test (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: none
Queueing
Output Queue: Conversation 25
Bandwidth remaining 50 (%)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
exponential weight: 9
mean queue depth: 0

class Transmitted Random drop Tail drop Minimum Maximum Mark
pkts/bytes pkts/bytes pkts/bytes thresh thresh prob
0 0/0 0/0 0/0 100 500 1/20
1 0/0 0/0 0/0 22 40 1/10
2 0/0 0/0 0/0 24 40 1/10
3 0/0 0/0 0/0 26 40 1/10
4 0/0 0/0 0/0 28 40 1/10
5 0/0 0/0 0/0 30 40 1/10
6 0/0 0/0 0/0 32 40 1/10
7 0/0 0/0 0/0 34 40 1/10
rsvp 0/0 0/0 0/0 36 40 1/10

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