Service SAP QoS Policy Command Reference
352 Quality of Service Guide
For egress Ethernet queues, the frame-encapsulation overhead is calculated by multiplying the number
of offered-packets for the queue by 20 bytes. If a queue was offered 50 packets then the frame-
encapsulation overhead would be 50 x 20 or 1,000 octets.
• Frame-based offered-load — The frame-based offered-load is calculated by adding the
offered-load to the frame-encapsulation overhead. If the offered-load is 10,000 octets and the
encapsulation overhead was 1,000 octets, the frame-based offered-load would equal 11,000
octets.
• Packet to frame factor — The packet -to-frame factor is calculated by dividing the frame-
encapsulation overhead by the queue’s offered-load (packet based). If the frame-
encapsulation overhead is 1,000 octets and the offered-load is 10,000 octets then the packet
to frame factor would be 1,000 / 10,000 or 0.1. When in use, the avg-frame-overhead will be
the same as the packet to frame factor making this calculation unnecessary.
• Frame-based CIR — The frame-based CIR is calculated by multiplying the packet to frame
factor with the queue’s configured CIR and then adding that result to that CIR. If the queue
CIR is set at 500 octets and the packet to frame factor equals 0.1, the frame-based CIR would
be 500 x 1.1 or 550 octets.
• Frame-based within-cir offered-load — The frame-based within-cir offered-load is the
portion of the frame-based offered-load considered to be within the frame-based CIR. The
frame-based within-cir offered-load is the lesser of the frame-based offered-load and the
frame-based CIR. If the frame-based offered-load equaled 11000 octets and the frame-based
CIR equaled 550 octets, the frame-based within-cir offered-load would be limited to 550
octets. If the frame-based offered-load equaled 450 octets and the frame-based CIR equaled
550 octets, the frame-based within-cir offered-load would equal 450 octets (or the entire
frame-based offered-load).
As a special case, when a queue or associated intermediate scheduler is configured with a CIR-weight
equal to 0, the system automatically sets the queue’s frame-based within-cir offered-load to 0,
preventing it from receiving bandwidth during the port scheduler’s within-cir pass.
• Frame-based PIR — The frame-based PIR is calculated by multiplying the packet to frame-
factor with the queue’s-configured PIR and then adding the result to that PIR. If the queue
PIR is set to 7500 octets and the packet to frame-factor equals 0.1, the frame-based PIR would
be 7,500 x 1.1 or 8,250 octets.
• Frame-based within-pir offered-load — The frame-based within-pir offered-load is the
portion of the frame-based offered-load considered to be within the frame-based PIR. The
frame-based within-pir offered-load is the lesser of the frame-based offered-load and the
frame-based PIR. If the frame-based offered-load equaled 11,000 octets and the frame-based
PIR equaled 8250 octets, the frame-based within-pir offered-load would be limited to 8,250
octets. If the frame-based offered-load equaled 7,000 octets and the frame-based PIR equaled
8,250 octets, the frame-based within-pir offered load would equal 7,000 octets.
Port Scheduler Operation Using Frame Transformed Rates — The port scheduler uses the frame based
rates to figure the maximum rates that each queue may receive during the within-cir and above-cir
bandwidth allocation passes. During the within-cir pass, a queue may receive up to its frame based
within-cir offered-load. The maximum it may receive during the above-cir pass is the difference
between the frame based within-pir offered load and the amount of actual bandwidth allocated during
the within-cir pass.
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