4.4.1 Disposal control
Drop control is functionality that controls the queuing priority, which indicates how easily a frame can be dropped from a queue, and that controls whether the frame can be queued or dropped according to the number of retained frames.
If frames remain in a queue, you can implement more detailed QoS by changing the queuing priority.
The amount of frames that can be queued in a single queue is called the queue length.
The Switch uses the tail drop method for drop control.
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(1) Tail drop
The tail drop method functionality drops frames if the queue length exceeds the drop threshold. The drop threshold varies depending on the queuing priority. Frames in a queue that has a higher queuing priority are more difficult to drop. The following figure shows an overview of the tail drop method. When the drop threshold for queuing priority 2 is exceeded, the queuing priority 2 frames are all dropped.
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![[Figure Data]](./GRAPHICS/ZU202130.GIF)
The following table describes the queuing priorities and corresponding drop thresholds for the tail drop method functionality. The drop threshold indicates the percentage of frames remaining in the queue to the queue length.
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Queuing priority |
Drop threshold (%) |
|---|---|
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1 |
50 |
|
2 |
75 |
|
3 |
100 |