Configuring Policy-Based Rate Shaping; Configuring Weights And Ecn For Wred - Dell S6100 Configuration Manual

Configuring Policy-Based Rate Shaping

You can configure the rate shaping for QoS output policies in packets per second (pps).
You can explicitly specify the rate shaping functionality for QoS output policies as peak rate and committed rate attributes. You can also
configure the peak burst and committed burst sizes. All of these settings can be configured in Kbps, Mbps, or pps.
To configure the peak and committed rates and burst sizes, perform the following steps:
1 Configure the peak rate and peak burst size in pps in QoS Policy Out Configuration mode.
QOS-POLICY-OUT mode
Dell(config-qos-policy-out)# rate shape pps peak-rate burst-packets
2 Alternatively, configure the peak rate and peak burst size in bytes.
QOS-POLICY-OUT mode
Dell(config-qos-policy-out)# rate shape Kbps peak-rate burst-KB
3 Configure the committed rate and committed burst size in pps.
QOS-POLICY-OUT mode
Dell(config-qos-policy-out)# rate shape pps peak-rate burst-packets committed pps committed-
rate burst-packets
4 Alternatively, configure the committed rate and committed burst size in bytes.
QOS-POLICY-OUT mode
Dell(config-qos-policy-out)# rate shape Kbps peak-rate burst-KB committed Kbps committed-rate
burst-KB

Configuring Weights and ECN for WRED

The WRED congestion avoidance functionality drops packets to prevent buffering resources from being consumed. Traffic is a mixture of
various kinds of packets. The rate at which some types of packets arrive might be greater than others. In this case, the space on the buffer
and traffic manager (BTM) (ingress or egress) can be consumed by only one or few types of traffic, leaving no space for other types. You
can apply a WRED profile to a policy-map so that the specified traffic can be prevented from consuming too much of the BTM resources.
WRED drops packets when the average queue length exceeds the configured threshold value to signify congestion. ECN is a capability that
enhances WRED by marking the packets instead of causing WRED to drop them when the threshold value is exceeded. If you configure
ECN for WRED, devices employ ECN to mark the packets and reduce the rate of sending packets in a congested network.
In a best-effort network topology, data packets are transmitted in a manner in which latency or throughput is not maintained to be at an
effective level. Packets are dropped when the network 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.
718 Quality of Service (QoS)