Using "delay" to emulate a satellite link

[Dave Raven]

Hi all,
	I've been looking at the ipfw (dummynet) ability to do delay and
have a few questions - I hope this is the right list. I want to simulate a
1000ms RTT on a satellite link. To do that I've created an inbound and
outbound pipe and given each 1mb and 500ms of delay.

However, I'm unable to get anywhere near 1mb of throughput on it until I
drop the delay. I believe I understand the slowdown due to the latency, but
my question is this - an http download through a 500ms "emulated" link
that's running 1 mb can't get 1mb, yet if I download over the internet on a
site that's pinging 500ms, it goes 1mb 

Whats the difference between dummynet delay and real life distance delay?

Thanks
Dave