Administrator Guide

class-map match-any class_dscp_50
match ip access-group dscp_50_non_ecn set-color yellow
match ip access-group dscp_50
policy-map-input pmap_dscp_40_50
service-queue 2 class-map class_dscp_40
service-queue 3 class-map class_dscp_50
The second example shows how to achieve the desired configuration by specifying ECN match criteria to classify ECN-capable packets:
ip access-list standard dscp_50_ecn
seq 5 permit any dscp 50 ecn 1
seq 10 permit any dscp 50 ecn 2
seq 15 permit any dscp 50 ecn 3
ip access-list standard dscp_40_ecn
seq 5 permit any dscp 40 ecn 1
seq 10 permit any dscp 40 ecn 2
seq 15 permit any dscp 40 ecn 3
ip access-list standard dscp_50_non_ecn
seq 5 permit any dscp 50 ecn 0
ip access-list standard dscp_40_non_ecn
seq 5 permit any dscp 40 ecn 0
class-map match-any class_dscp_40
match ip access-group dscp_40_non_ecn set-color yellow
match ip access-group dscp_40_ecn
class-map match-any class_dscp_50
match ip access-group dscp_50_non_ecn set-color yellow
match ip access-group dscp_50_ecn
policy-map-input pmap_dscp_40_50
service-queue 2 class-map class_dscp_40
service-queue 3 class-map class_dscp_50
Using A Configurable Weight for WRED and ECN
The switch supports a user-configurable weight that determines the average queue size used in WRED and Explicit Congestion
Notification (ECN) operation on front-end I/O and backplane interfaces.
By default, the switch uses a weight factor of 0 (instantaneous ECN marking), which results in packet dropping during times of network
congestion based on the configured minimum and maximum WRED thresholds. You can configure different weights for WRED and ECN
operation to finely tune how different types of traffic are handled when a WRED threshold is exceeded.
Benefits of Using a Configurable Weight for WRED with
ECN
Using a configurable weight for WRED and ECN allows you to specify how the average queue size is calculated. In WRED, the average
queue size determines when a threshold is exceeded and packets are dropped; in WRED with ECN, the average queue size determines
when packets are marked for later transmission and when the transmission rate is reduced on an interface during times of network
congestion.
For example, in a best-effort network topology that uses WRED with instantaneous ECN, data packets may be transmitted at a rate in
which latency or throughput are not maintained at an effective, optimal level. Packets are dropped when the network experiences a large
traffic load according to the configured WRED thresholds. This best-effort network deployment is not suitable for applications that are
time-sensitive, such as video on demand (VoD) or voice over IP (VoIP) applications.
To resolve the problem of packet loss at times of network congestion, you may need to apply WRED with ECN and more finely tune
packet transmission for certain traffic types. To do so, you can configure the weight used to calculate the average queue size; the average
queue size is used to determine when to drop packets with WRED and when to mark packets with ECN when WRED thresholds are
exceeded.
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Quality of Service (QoS)