Using A Configurable Weight For Wred And Ecn; Benefits Of Using A Configurable Weight For Wred With Ecn; Setting Average Queue Size Using A Weight - Dell C9000 Series Networking Configuration Manual

match ip access-group dscp_50_ecn
policy-map-input pmap_dscp_40_50
service-queue 2 class-map class_dscp_40
service-queue 3 class-map class_dscp_50
Using A Configurable Weight for WRED
and ECN
The switch supports a user-configurable weight that determines the average queue size used in WRED and
Explicit Congestion Notification (ECN) operation on front-end I/O and backplane interfaces.
By default, the switch uses a weight factor of 0 (instantaneous ECN marking), which results in packet
dropping during times of network congestion based on the configured minimum and maximum WRED
thresholds. You can configure different weights for WRED and ECN operation to finely tune how different
types of traffic are handled when a WRED threshold is exceeded.
Benefits of Using a Configurable Weight for
WRED with ECN
Using a configurable weight for WRED and ECN allows you to specify how the average queue size is
calculated. In WRED, the average queue size determines when a threshold is exceeded and packets are
dropped; in WRED with ECN, the average queue size determines when packets are marked for later
transmission and when the transmission rate is reduced on an interface during times of network congestion.
For example, in a best-effort network topology that uses WRED with instantaneous ECN, data packets may be
transmitted at a rate in which latency or throughput are not maintained at an effective, optimal level. Packets
are dropped when the network experiences a large traffic load according to the configured WRED thresholds.
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.
To resolve the problem of packet loss at times of network congestion, you may need to apply WRED with
ECN and more finely tune packet transmission for certain traffic types. To do so, you can configure the
weight used to calculate the average queue size; the average queue size is used to determine when to drop
packets with WRED and when to mark packets with ECN when WRED thresholds are exceeded.
The user-configurable weight in WRED and ECN provides better control in how the switch responds to
congestion before a queue overflows and packets are dropped or delayed. Using a configurable weight for
WRED and ECN allows you to customize network performance and throughput.

Setting Average Queue Size using a Weight

You can configure the weight factor that determines the average queue size for WRED and ECN packet
handling by using the wred weight command.
Quality of Service (QoS) 933