Dummynet and simulating random delay

[Andresen, Jason R.]

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.

My first thought was to create three or four different queues with
different delays and use the probability rule to dump them into the
queue, but that gets packets out of order and doesn't work.  

My next thought is to write a script that reconfigures the pipe
randomly every few hundred milliseconds or so during the test, but I'm
not sure what that means for packets that are already in it.  Does it
mean bursts of data when the delay is turned down (which would actually
be realistic in this scenario), or is there a danger of out of order
packets?  Are there any dummynet experts out there that can tell me
exactly how it will behave when delays are changed while there are
still packets in the buckets?  Thanks.