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You can define WRED profiles and weight on each of the global service-pools for both loss-based and
lossless (PFC) service- pools. The following events occur when you configure WRED and ECN on global
service-pools:
• If WRED/ECN is enabled on the global service-pool with threshold values and if it is not enabled on
the queues, WRED/ECN are not effective based on global service-pool WRED thresholds. The queue
on which the traffic is scheduled must contain WRED/ECN settings, which are enabled for WRED, to
be valid for that traffic.
• When WRED is configured on the global service-pool (regardless of whether ECN on global service-
pool is configured), and one or more queues have WRED enabled and ECN disabled, WRED is
effective for the minimum of the thresholds between the queue threshold and the service-pool
threshold.
• When WRED is configured on the global service-pool (regardless of whether ECN on global service-
pool is configured), and one or more queues are enabled with both WRED and ECN, ECN marking
takes effect. The packets are ECN marked up to shared- buffer limits as determined by the shared-
ratio for that global service-pool.
WRED/ECN configurations for the queues that belong to backplane ports are common to all the
backplane ports and cannot be specified separately for each backplane port granularity. This behavior
occurs to prevent system-level complexities in enabling this support for backplane ports. Also,
WRED/ECN is not supported for multicast packets.
The following table describes the WRED and ECN operations that occur for various scenarios of WRED
and ECN configuration on the queue and service pool. (X denotes not-applicable in the table, 1 indicates
that the setting is enabled, 0 represents a disabled setting. )
Table 63. Scenarios of WRED and ECN Configuration
Queue
Configuration
Service-Pool
Configuration
WRED Threshold
Relationship
Q threshold = Q-
T,
Service pool
threshold = SP-T
Expected Functionality
WRED ECN WRED ECN
0 0 X X X WRED/ECN not applicable
1 0 0 X X Queue based WRED,
No ECN marking
1 X Q-T < SP-T
SP-T < Q-T SP based WRED,
No ECN marking
1 1 0 X X Queue-based ECN marking above queue
threshold.
ECN marking to shared buffer limits of the
service-pool and then packets are tail dropped.
1 X Q-T < SP-T
Quality of Service (QoS)
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