The traffic through PacketShaper never reaches the link size

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Article ID: 169419

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Products

PacketShaper

Issue/Introduction

The purpose of this article is to provide an explanation as to why the traffic through PacketShaper never reaches the link size and what can be done when this occurs.

An example of this would be as follows:

  • The link size is configured to 950 Mbps.
  • There are one or more partitions burstable up to 100% of the link size.
  • The real throughput never reaches 950 Mbps (around 20% less than the link size)

Cause

The device is not allowing any flow to burst above the partition limit even for a fraction of a second, which may slow down applications in response to this control.

The “gPtnBurstLimitMsecs” sys set controls the buffer size used for the partition bandwidth utilization. By default it is set to 0 on versions older than 9.2.5 and 8.7.8. On later versions, the default value is 5. The maximum value is 125 and is measured in milliseconds.

Resolution

The immediate solution is to set the gPtnBurstLimitMsecs to a value greater than 0. 125 is the value we recommend. This can be done by using the following command: 

sys set gPtnBurstLimitMsecs 125

Also, as usual, an upgrade to the latest software version is always advisable.