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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.
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
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. 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.
•
When WRED is configured on the global service-pool (regardless of whether ECN on global service-pool is configured), and one
or more queues are enabled with both WRED and ECN, ECN marking takes effect. The packets are ECN marked up to shared-
buffer limits as determined by the shared-ratio for that global service-pool.
WRED/ECN configurations for the queues that belong to backplane ports are common to all the backplane ports and cannot be
specified separately for each backplane port granularity. This behavior occurs to prevent system-level complexities in enabling this
support for backplane ports. Also, WRED/ECN is not supported for multicast packets.
Quality of Service (QoS)
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Содержание S4048-ON
Страница 1: ...Dell Configuration Guide for the S4048 ON System 9 9 0 0 ...
Страница 146: ...Figure 14 BFD Three Way Handshake State Changes 146 Bidirectional Forwarding Detection BFD ...
Страница 477: ...Figure 68 Inspecting Configuration of LAG 10 on ALPHA Link Aggregation Control Protocol LACP 477 ...
Страница 480: ...Figure 70 Inspecting a LAG Port on BRAVO Using the show interface Command 480 Link Aggregation Control Protocol LACP ...
Страница 481: ...Figure 71 Inspecting LAG 10 Using the show interfaces port channel Command Link Aggregation Control Protocol LACP 481 ...
Страница 522: ...Figure 87 Configuring Interfaces for MSDP 522 Multicast Source Discovery Protocol MSDP ...
Страница 523: ...Figure 88 Configuring OSPF and BGP for MSDP Multicast Source Discovery Protocol MSDP 523 ...
Страница 524: ...Figure 89 Configuring PIM in Multiple Routing Domains 524 Multicast Source Discovery Protocol MSDP ...
Страница 528: ...Figure 91 MSDP Default Peer Scenario 1 528 Multicast Source Discovery Protocol MSDP ...
Страница 529: ...Figure 92 MSDP Default Peer Scenario 2 Multicast Source Discovery Protocol MSDP 529 ...
Страница 530: ...Figure 93 MSDP Default Peer Scenario 3 530 Multicast Source Discovery Protocol MSDP ...
Страница 633: ...Policy based Routing PBR 633 ...
Страница 777: ...Figure 119 Single and Double Tag TPID Match Service Provider Bridging 777 ...
Страница 778: ...Figure 120 Single and Double Tag First byte TPID Match 778 Service Provider Bridging ...