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

experiences a large traffic load. This best-effort network deployment is not suitable for applications that
are time-sensitive, such as video on demand (VoD) or voice over IP (VoIP) applications. In such cases, you
can use ECN in conjunction with WRED to resolve the dropping of packets under congested conditions.
Using ECN, the packets are marked for transmission at a later time after the network recovers from the
heavy traffic state to an optimal load. In this manner, enhanced performance and throughput are
achieved. Also, the devices can respond to congestion before a queue overflows and packets are
dropped, enabling improved queue management.
When a packet reaches the device with ECN enabled for WRED, the average queue size is computed. To
measure the average queue size, a weight factor is used. This weight factor is user-configurable. You can
use the wred weight number command to configure the weight for the WRED average queue size. The
mark probability value is the number of packets dropped when the average queue size reaches the
maximum threshold value.
The weight factor is set to zero by default, which causes the same behavior as dropping of packets by
WRED during network loads or also called instantaneous ECN marking. In a topology in which congestion
of the network varies over time, you can specify a weight to enable a smooth, seamless averaging of
packets to handle the sudden overload of packets based on the previous time sampling performed. You
can specify the weight parameter for front-end and backplane ports separately in the range of 0 through
15.
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

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.
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Quality of Service (QoS)