Re: Reason to drop packets

To: iperf-users --at-- dast.nlanr.net
Subject: Re: Reason to drop packets
From: Jon Dugan <jdugan --at-- ncsa.uiuc.edu>
Date: Mon, 23 Feb 2004 15:01:11 -0600
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On Mon, Feb 23, 2004 at 06:46:30PM +0100, onorati_m --at-- virgilio.it wrote:
> Hi all!
> 
> Could someone explain why Iperf really starts dropping packets?
> 
> I mean, selecting the UDP mode, setting a UDP bandwidth value and the
> number of bytes to be transmitted, why does Iperf show losses for higher
> values of the UDP bandwdith rate?
> 
> Is it a matter of CPU load or something related with the buffer sizes?

  Iperf using UDP doesn't drop packets per se, rather it will blindly transmit
  at the specified rate and if there is contention for resources somewhere in
  the system the data will be lost.  Often it is CPU utilization that is the
  culprit.  What is the CPU utilization you see during the test?  Using larger
  buffers may help this since there will be less overhead.

  The other common cause of lost data with a UDP test is loss somewhere in the
  network.  How are the two systems interconnected?

Jon
-- 
Jon Dugan             |  Senior Network Engineer, NCSA Network Research
jdugan --at-- ncsa.uiuc.edu  |  269 CAB, 605 E Springfield, Champaign, IL 61820
217-244-7715          |  http://www.ncsa.uiuc.edu/~jdugan/

Follow-Ups:
- Re: Reason to drop packets
  - From: Laurence Kirchmeier
- Re: Reason to drop packets
  - From: "Massimo Onorati"

References:
- Reason to drop packets
  - From: onorati_m --at-- virgilio.it

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