Why is average rate sometimes higher than peak rate?

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Article ID: 167581

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PacketShaper

Issue/Introduction

I've noticed that if I fetch the data (Statistics/Data) on a class, sometimes the avg-bps is higher than the peak-bps.

For example, during a certain minute interval the average rate is 13 bps and the peak rate is 0.

I thought the peak rate should always be higher than the average rate.

Resolution

Peak-bps is calculated after avg-bps. It takes a little while for calculating the average, before the peak is calculated.

The window for both values is one minute. But the one-minute interval starts at the time PacketWise starts calculating the variable. Since there is a slight difference in the one minute used to calculate the average and the one minute used to calculate the peak, it is possible that a few bytes are taken into account for calculating the average, that are not taken into account for calculating the peak.

In your case, some bytes are taken into account for calculating the average of 13, but are not taken into account for calculating the peak. An average of 13 bytes in 1 minute results in 13 x 60 = 780 bytes in 1 minute.

On a small link (let's assume a 128 kbps ISDN-link = 131072 bps), it takes 780 / 131072 = 6 msec to transfer. If the time difference between calculating the average and peak takes 6 msec or more, these 780 bytes are not taken into account for calculating peak-bps. That's why peak-bps shows up as 0.

This sliding window calculation is only visible with classes with little to no traffic. Classes with high traffic load will not show this behavior.

See alsoHow does PacketWise calculate peak rate and average rate?