Date: Tue, 12 Nov 2013 20:50:10 -0800 From: Julian Elischer <julian@freebsd.org> To: Ahmed Hamza <ahmed.hmz@gmail.com>, freebsd-ipfw@freebsd.org Subject: Re: Bursty data transfer with Dummynet Message-ID: <52830502.30809@freebsd.org> In-Reply-To: <CAL_s3F5Hx0XJ8Nct=urWGN72hrGQ2LT2nJfG3OxgWT5oxtjW9Q@mail.gmail.com> References: <CAL_s3F5Hx0XJ8Nct=urWGN72hrGQ2LT2nJfG3OxgWT5oxtjW9Q@mail.gmail.com>
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On 11/12/13, 6:35 PM, Ahmed Hamza wrote: > Hi All, > > I'm trying to use Dummynet to test the behaviour of my video streaming > application in various network conditions. Dummynet was compiled and > installed on an Ubuntu 12.04 box with a 2.6 Linux kernel. I'm > experiencing a strange behaviour when I reduce the bandwidth of the > link/path. > > For some reason, instead of having a slow download speed. It seems as > if the download is happening in bursts! A portion of the data is > downloaded at a high speed, then the data transfer stops for a period > of time and then resumes again (and so on). Does anyone have an idea > what could be the cause? Or is this even an expected behaviour? If so, > why? I can't really speak for dummynet on Linux but the granularity of the queues is dependent on the timer granularity of the kernel you have and to some extent will rely on the correct integration of dummynet into the timer facility of the kernel you are running it in. On freeBSD with a 1kHz 'tick' I'd' expect to see packets being release from the queue each mSec or so. if you are getting second sized chunks then it probably is a bug. Either dummynet is not compatible with that kind of kernel, something else has gone wrong. It COULD also be that you are catching the wrong packets.. I've seen similar behaviour when I was accidentally queuing all the acks instead of all the data going in the other direction, but I presume you have already checked to see what you are queuing. > > Thanks, > -Ahmed > _______________________________________________ > freebsd-ipfw@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-ipfw > To unsubscribe, send any mail to "freebsd-ipfw-unsubscribe@freebsd.org" >
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