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:

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, videoconferencing)

• 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.

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.

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.