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4.8 QoS
4.8.1 Understand QOS
Quality of Service (QoS) is an advanced traffic prioritization feature that allows you to establish control
over network traffic. QoS enables you to assign various grades of network service to different types of
traffic, such as multi-media, video, protocol-specific, time critical, and file-backup traffic.
QoS reduces bandwidth limitations, delay, loss, and jitter. It also provides increased reliability for delivery
of your data and allows you to prioritize certain applications across your network. You can define exactly
how you want the switch to treat selected applications and types of traffic.
You can use QoS on your system to:
Control a wide variety of network traffic by:
。
Classifying traffic based on packet attributes.
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Assigning priorities to traffic (for example, to set higher priorities to time-critical or business-critical
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applications).
Applying security policy through traffic filtering.
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Provide predictable throughput for multimedia applications such as video conferencing or voice
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over IP by minimizing delay and jitter.
Improve performance for specific types of traffic and preserve performance as the amount of traffic
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grows.
Reduce the need to constantly add bandwidth to the network.
。
Manage network congestion.
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QoS Terminology
Classifier－classifies the traffic on the network. Traffic classifications are determined by protocol,
application, source, destination, and so on. You can create and modify classifications. The Switch then
groups classified traffic in order to schedule them with the appropriate service level.
DiffServ Code Point (DSCP) － is the traffic prioritization bits within an IP header that are encoded by
certain applications and/or devices to indicate the level of service required by the packet across a
network.
Service Level－defines the priority that will be given to a set of classified traffic. You can create and
modify service levels.
Policy－comprises a set of "rules" that are applied to a network so that a network meets the needs of the
business. That is, traffic can be prioritized across a network according to its importance to that particular
business type.
QoS Profile－consists of multiple sets of rules (classifier plus service level combinations). The QoS
profile is assigned to a port(s).
Rules－comprises a service level and a classifier to define how theSwitch will treat certain types of traffic.
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