Dell Networking S6000 Uživatelský manuál stáhnout pdf (Strana 719)

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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 feature to configure a weight factor for weighted random early detection (WRED) and Explicit

Congestion Notification (ECN) functionality for backplane ports is supported on the Additionally, the

feature to configure a weight for WRED and ECN functionality for front-end ports is supported on the

S6000 platform.

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.

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.

Quality of Service (QoS)

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