Dummynet and simulating random delay

[Andresen, Jason R.]

>From: Luigi Rizzo [mailto:rizzo at icir.org] 
>
>On Wed, Jan 24, 2007 at 06:10:21PM +1100, Peter Jeremy wrote:
>> On Tue, 2007-Jan-23 14:22:54 -0500, Andresen, Jason R. wrote:
>> >I have a project that requires me to simulate a link with 
>varying but
>> >well defined delay.  The link is guarenteed to deliver packets in
>> >order, so I wish to maintain that behavior with Dummynet.
>> 
>> I don't think dummynet can do this in its current form.  Based on
>
>actually dummynet never does reordering within a single pipe, even
>if you change the delay on the fly.
>
>But this said, you should explain "varying but well defined delay",
>because if you use TCP or similar as the source, then you
>have no control on when the userland write->tcp transmission delay
>anyways so the concept is a bit vague and probably not a meaningful
>experiment. And even in any common network (from switched
>ethernet to wireless to dsl...) you have some variance on the delay,
>ranging from a fraction of a millisecond to much larger values,
>due to queueing and/or protocol issues (e.g. MAC channel allocation)
>and/or switch/router/operating system issues.

I'm trying to simulate a satellite link that has a normal delay of 1
second, but every 20-30 seconds or so the delay shoots up to 3.5
seconds for about 4 seconds and then settles back down to 1 second.
>From what you said, I'm thinking that just twiddling the pipe on the
fly will probably work.