using dummynet to simulate modem, dsl, etc

[Mark Hannon]

Hello,

I am trying to use dummynet to simulate different network links and 
demonstrate
application level performance for a variety of scenarios.  The first 
test is three
ftp file transfers over a simulated 56k modem as per below:

    iifconfig lo0 mtu 1500
    fconfig lo0 alias 127.0.0.100
    ipfw -q add 1 pipe 1 ip from any to 127.0.0.100
    ipfw -q add 2 pipe 2 ip from 127.0.0.100 to any
    ipfw -q pipe 1 config bw 33kbit/s queue 0 delay 40ms
    ipfw -q pipe 2 config bw 56kbit/s queue 0 delay 112ms


The results seem strange ... larger file sizes seem to have a slower 
transfer rate,
where I would have thought that steady-state transfers would have been 
reached
for the larger files.  Are these results logical?  Have I done something 
silly with the
pipe configs?

    Receiving test_large (1937201 bytes): 100% (ETA 00:00)
    1937201 bytes transferred in 551.1 seconds (3.43 kBps)
    Receiving test_medium (248476 bytes): 100% (ETA 00:00)
    248476 bytes transferred in 66.7 seconds (3.64 kBps)
    Receiving test_small (40960 bytes): 100%
    40960 bytes transferred in 7.3 seconds (5.52 kBps)


Regards/mark