Global Service Pools With Wred And Ecn Settings - Dell S4048–ON Configuration Manual

You can enable WRED and ECN capabilities per queue for granularity. You can disable these functionality per queue, and you can also
specify the minimum and maximum buffer thresholds for each color-coding of the packets. You can configure maximum drop rate
percentage of yellow and green profiles. You can set up these parameters for both front-end and backplane ports.

Global Service Pools With WRED and ECN Settings

Support for global service pools is now available. You can configure global service pools that are shared buffer pools accessed by multiple
queues when the minimum guaranteed buffers for the queue are consumed. Two service pools are used– one for loss-based queues and
the other for lossless (priority-based flow control (PFC)) queues. You can enable WRED and ECN configuration on the global service-pools.
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 79. Scenarios of WRED and ECN Configuration
Queue Configuration Service-Pool
Configuration
WRED ECN WRED
0 0 X
1 0 0
1
1 1 0
1
752 Quality of Service (QoS)
WRED Threshold
Relationship
Q threshold = Q-T,
Service pool threshold =
SP-T
ECN
X X
X X
X Q-T < SP-T
SP-T < Q-T
X X
X Q-T < SP-T
SP-T < Q-T
Expected Functionality
WRED/ECN not applicable
Queue based WRED,
No ECN marking
SP based WRED,
No ECN marking
Queue-based ECN marking above queue threshold.
ECN marking to shared buffer limits of the service-pool and
then packets are tail dropped.
Same as above but ECN marking starts above SP-T.