Users Guide

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 62. 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
Quality of Service (QoS) 771