PM73487 Datasheet, PDF (42/251 Pages) PMC-Sierra, Inc – 622 Mbps ATM Traffic Management Device

Released
Datasheet
PMC-Sierra, Inc.
PM73487 QRT
PMC-980618
Issue 3
622 Mbps ATM Traffic Management Device
A congestion hysteresis bit is kept for each threshold. This bit is set whenever the queue depth
exceeds the congestion limit for that threshold. This bit remains asserted until the queue depth
falls below one-half of the congestion threshold.
Figure 35 illustrates the operation of EPD/PTD.
Maximum Threshold
Queue
Depth
Congested Threshold
Congested Queue Depth ÷ 2
Drop these frames
Tail drop this frame
•
•
•
•
•
•
•
Always send the last cell of each
Time
Cells are arriving at a rate greater than the
rate at which they are being played out.
• = End-Of-Frame (EOF) cell
Figure 35. EPD/PTD Operation
Figure 36 shows the operation of EPD in combination with CLP-based dropping.
Maximum Threshold
Queue
Depth
Congested Threshold
Congested Queue Depth ÷ 2
Tail drop this frame
Drop these frames
•
•
•
•
•
•
•
Always send the last cell of each
Time
Cells are arriving at a rate greater than the
rate at which they are being played out.
• = End-Of-Frame (EOF) cell
= Cell Loss Priority (CLP)
Figure 36. EPD/PTD with CLP Operation
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