Administrator Guide

Global Service-Pools for WRED with ECN
You can enable WRED with ECN to work with global service-pools. Global service pools that function as shared buers are accessed by
multiple queues when the minimum guaranteed buers for a queue are consumed. The switch supports four global service-pools in the
egress direction.
Two types of service-pools are used: one for lossy queues and the other for lossless (priority-based ow control (PFC)) queues.
NOTE: Service pool 1 for lossless queues is not supported in software releases that do not support PFC.
You can dene WRED proles and a weight on global service-pools for both lossy and lossless (PFC) service-pools. The following events
occur when you congure WRED with ECN on a global service-pool:
• 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
eective based on global service-pool WRED thresholds. The queue on which trac is scheduled must have WRED/ECN settings
enabled for WRED to be valid for its trac.
• When WRED is congured on a global service-pool (regardless of whether ECN is congured on the global service-pool), and one or
more queues have WRED enabled and ECN disabled, WRED is eective for the minimum threshold between the queue threshold and
the service-pool threshold.
• When WRED is congured on the global service-pool (regardless of whether ECN is congured on the global service-pool), and one or
more queues are enabled with both WRED and ECN, ECN marking takes eect. The packets are ECN marked to the shared-buer
limits as determined by the shared-ratio for the global service-pool.
WRED/ECN congurations for backplane port queues are applied to all backplane ports and cannot be specied separately on each
backplane port. Also, WRED/ECN is not supported for multicast packets.
The following table describes the WRED and ECN operations performed on a queue and service pool for various WRED with ECN
scenarios. (N/A indicates that a conguration is not applicable. )
Table 86. Scenarios for WRED and ECN
Conguration
Queue Conguration Service-Pool Conguration WRED Threshold
Relationship
Q threshold = Q-T
Service-pool
threshold = SP-T
Expected
Functionality
WRED ECN WRED ECN
Disabled Disabled N/A N/A N/A WRED/ECN not
applicable
Enabled Disabled Disabled N/A N/A Queue-based WRED;
No ECN marking
Enabled N/A Q-T < SP-T
SP-T < Q-T Service-pool-based
WRED;
No ECN marking
Enabled Enabled Disabled N/A N/A Queue-based ECN
marking above queue
threshold.
Enabled N/A Q-T < SP-T
866 Quality of Service (QoS)