using dummynet to simulate modem, dsl, etc

[Yuchung Cheng]

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

Yu-chung