Manage congestion

Finally, define a QoS policy for each traffic class, which involves these activities:

■ Set a minimum bandwidth guarantee

■ Set a maximum bandwidth limit

■ Assign priorities to each class

■ Use QoS technologies, such as advanced queuing, to manage congestion

Example: Defining QoS Policies

Using the traffic classes previously defined, you can determine QoS policies as follows:

■ Voice: Minimum bandwidth 1 Mbps. Use QoS marking to mark voice packets as priority 5; use LLQ to always give voice priority.

■ Mission-critical: Minimum bandwidth 1 Mbps. Use QoS marking to mark critical data packets as priority 4; use class-based weighted fair queuing (CBWFQ) to prioritize critical class traffic flows.

■ Best-effort: Maximum bandwidth 500 kbps. Use QoS marking to mark these data packets as priority 2; use CBWFQ to prioritize best-effort traffic flows that are below mission-critical and voice.

■ Scavenger: Maximum bandwidth 100 kbps. Use QoS marking to mark less-than-best-effort (scavenger) data packets as priority 0; use weighted random early detection (WRED) to drop these packets whenever the network has a propensity for congestion.

A QoS policy is a network-wide definition of the specific levels of QoS assigned to different classes of network traffic.

Having a QoS policy is just as important in a converged network as a security policy. A written and public QoS policy allows users to understand and negotiate for QoS in the network.

QoS Policy (Cont.)

Align Network Resources with Business Priorities

The graphic illustrates how a QoS policy could be defined for a network.

Enterprise resource planning (ERP) applications have a high QoS priority and must be available all the time.

Video applications are guaranteed 100 KB/s of bandwidth, but can operate only between the hours of 9:00 a.m. to 5:00 p.m. (0900 to 1700) on weekdays.

Voice traffic is guaranteed less than 150 ms delay in each direction but limited to the hours of 9:00 a.m. to 5:00 p.m. (0900 to 1700) on weekdays; toll calls are completely restricted to avoid personal long-distance calls.


This topic summarizes the key points discussed in this lesson.

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