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QoS Basics

The mission statement of QoS could read something like “to categorize traffic and apply a policy to those traffic categories, in accordance with a QoS policy.” Specifically, QoS configuration involves the following three basic steps:

Step 1 Determine network performance requirements for various traffic types. For example, consider the following design rules of thumb for voice, video, and data traffic:

Voice:

  • No more than 150 ms of one-way delay

  • No more than 30 ms of jitter

  • No more than 1 percent packet loss

Video:

  • No more than 150 ms of one-way delay for interactive voice applications (for example, video conferencing)

  • No more than 30 ms of jitter

  • No more than 1 percent packet loss

Data:

  • Applications have varying delay and loss characteristics. Therefore, data applications should be categorized into predefined “classes” of traffic, where each class is configured with specific delay and loss characteristics.

Step 2 Categorize traffic into specific categories. For example, you can have a category named “Low Delay,” and you decide to place voice and video packets in that category. You can also have a “Low Priority” class, where you place traffic such as music downloads from the Internet. As a rule of thumb, Cisco recommends that you create no more that ten classes of traffic.

Step 3 Document your QoS policy, and make it available to your users. Then, for example, if a user complains that his network gaming applications are running slowly, you can point him to your corporate QoS policy, which describes how applications such as network gaming have “best-effort” treatment.

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