Service Manual

QOS-POLICY-OUT mode
Dell(config-qos-policy-out)# rate shape pps peak-rate burst-packets
2. Alternatively, congure 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. Congure 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, congure 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
Conguring Weights and ECN for WRED
The WRED congestion avoidance functionality drops packets to prevent buering resources from being consumed. Trac 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 buer and trac manager (BTM) (ingress or egress) can be consumed by only one or few types of trac, leaving no
space for other types. You can apply a WRED prole to a policy-map so that the specied trac can be prevented from consuming
too much of the BTM resources.
WRED drops packets when the average queue length exceeds the congured 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 congure ECN for WRED, devices employ ECN to mark the packets and reduce the rate of sending packets in a
congested network.
In a best-eort network topology, data packets are transmitted in a manner in which latency or throughput is not maintained to be at
an eective level. Packets are dropped when the network experiences a large trac load. This best-eort 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 trac state to an
optimal load. In this manner, enhanced performance and throughput are achieved. Also, the devices can respond to congestion
before a queue overows 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-congurable. You can use the wred weight number command to
congure 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 buer thresholds for each color-coding of the packets. You can congure maximum drop rate
percentage of yellow and green proles. You can set up these parameters for both front-end and backplane ports.
Quality of Service (QoS)
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