QoS Queue Dropped Packets

Any QoS queue that is dropping packets is identified. The relative priority of the queue determines the severity level of the issue that is generated in the Issue List. The table below shows the severity generated for each queue's Per-Hop Behavior (PHB) and DSCP value that are commonly associated with applications. Drops in high priority queues will generate Error issues, while medium priority queues generate Warning issues. The lowest priority queues, including the scavenger queue, generate Info issues.

When a high priority queue drops packets, it indicates that insufficient bandwidth may be allocated to that queue. Sometimes this occurs because the queue definition is based on network traffic volume assumptions that no longer apply. For example, a queue configured to handle four simultaneous voice calls may be dropping packets because more than four simultaneous calls are being handled.

Conversely, when many (or all) queues are dropping packets, the entire link may be oversubscribed and the only valid remediation is to add more bandwidth. In this scenario, the high priority queues use nearly all the bandwidth and will still drop packets because the offered load is greater than the available bandwidth. Because there is little remaining bandwidth, low priority queues will also drop packets.

When a QoS queue drop is detected during the analysis of the collected data, an issue appears on the issue list. Clicking on the issue hyperlink opens the issue in the Issue Viewer, where information is displayed about each queue that experienced the drops. The Issue Viewer provides several hyperlinks to access related information.

• To open the Device Viewer, click a hyperlink in the IP Address column.

• To open the Interface Viewer, click a hyperlink in the Interface column.

• To open the Quality of Service Viewer, click a hyperlink in the Policy Name column.

The Quality of Service Viewer provides charts showing dropped packets (quantity and percentage) versus time.