using dummynet to simulate modem, dsl, etc

[Luigi Rizzo]

On Fri, Jul 25, 2003 at 11:48:22AM -0700, Yuchung Cheng wrote:
> On 07-25-2003, Luigi Rizzo wrote:
> > I would expect you to get around 3.5KBytes/s in the steady state,
> > but with a packet transmission time of 200ms and the 600ms RTT of
> > your setting, the first few rounds might achieve somewhere between
> > that and twice the bandwidth because of less interference.
> > 
> > This is exactly what you are seeing.
> > 
> > Try this:
> >      ipfw -q add 1 pipe 1 ip from any to 127.0.0.100 in
> >      ipfw -q add 2 pipe 2 ip from 127.0.0.100 to any in
> >      ipfw -q pipe 1 config bw 33kbit/s queue 0 delay 40ms
> >      ipfw -q pipe 2 config bw 56kbit/s queue 0 delay 112ms
> >
> why set queue to 0? aren't modem banks usually 4K bytes? the reverse link
> has 3 times delay (c->s), is this for simulating ack spacing and busy
> server to client pipe?

i just copied those parameters from the original posters. I have
no idea on what system he had in mind.
In terms of delay, i typically used to see some 120-150mss RTT
for short pings (including everything).
Just the transmission time is in the order of 5-10ms at each step,
and there are many instances of it (serial->modem; modem->modem;
modem->serial on the remote side; and another 3 on the way back)
so i think this eats almost half ot the total delay.

In terms of buffering, again i have no idea, but at least on
the client side you have as much as the local OS gives you.

	cheers
	luigi

> I am doing similar experiments. Anybody can share parameters for ADSL, cable 
> modems too? Searching the web does not give any good information.
> 
> Yu-chung
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