Global Service Pools With Wred And Ecn Settings - Dell Force10 Z9000 Configuration Manual

Global Service Pools With WRED and ECN Settings

A global buffer pool, whichis a shared buffer pool accessed by multiple queues when the minimum guaranteed buffers for the queue
are consumed, can be configured on the Z9000 platform.
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. Z9000 platform support four global service-
pools in the egress direction. 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 44. Scenarios of WRED and ECN Configuration
Queue Service-Pool
Configuration Configuration
WRED ECN WRED
0 0 X
1 0 0
1
1 1 0
1
596
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.