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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