PPP and ftp slow on UDB

[martonak prr mpi-stuttgart mpg de (Roman Martonak)]

I tried to run PPP on my UDB with a 33.6 modem under RH 4.2 and 5.0,
and observed under both versions a strange behaviour. I used the network 
configuration tool to configure PPP, and when I specified the speed to 115200, 
the modem does not even dial up. In /var/log/messages I found the following:

May  1 17:34:12 roman ifup-ppp: pppd started for ppp0 on /dev/modem at 115200
May  1 17:34:12 roman pppd[410]: pppd 2.3.3 started by root, uid 0
May  1 17:34:14 roman chat[413]: abort on (BUSY)
May  1 17:34:14 roman chat[413]: abort on (ERROR)
May  1 17:34:14 roman chat[413]: abort on (NO CARRIER)
May  1 17:34:14 roman chat[413]: abort on (NO DIALTONE)
May  1 17:34:14 roman chat[413]: abort on (Invalid Login)
May  1 17:34:14 roman chat[413]: abort on (Login incorrect)
May  1 17:34:14 roman chat[413]: send (ATZ^M)
May  1 17:34:14 roman chat[413]: expect (OK)
May  1 17:34:59 roman chat[413]: alarm
May  1 17:34:59 roman pppd[410]: Connect script failed
May  1 17:34:59 roman chat[413]: Failed
May  1 17:35:00 roman pppd[410]: Exit.

When I lowered the speed to 57600, everything worked, but when I used ftp
to get a file, it transfered at a rate of about 800 bytes/s, which seems to
me rather slow. Actually, when the same computer and modem is running under 
Windows NT, it can PPP connect at 115200 without any problem and ftp from the 
same computer at a rate of about 3700 bytes/s, therefore factor of 4.5 faster
than RH Linux. Does anybody know what can be the origin of this behaviour and
how to improve on the speed of PPP and ftp connection under RH Linux ?

	Thanks a lot in advance,

				Roman Martonak.
----------------------------------------------------------------------------	
	Roman Martonak
	Max-Planck-Institute for Solid State Research
	Heisenbergstr.1
 70569	Stuttgart
	Germany