Problem with dial-in of PPP

["=?gb2312?B?WWFuZyBKaXpoYW5nIFwo0e68zNXFXCk=?=" <jzyang@cernet.edu.cn>]

After I had set an OpenBSD machine as an dial-in server according to the
man page of ppp(8), the following vague message displayed when running
command "/usr/sbin/ppp -direct incoming" directly:
~ÿ}#?}!}!} }8}(}"}'}"}"}&} } } } }!}$}%Ü}%}&YI«äˆ™~~ÿ}#?}!}!} }8}(}"}'}"}"}&} } } } }!}$}%Ü}%}&YI«äˆ™~~ÿ}#?}!}!} }8}(}"}'}"}"}&} } } } }!}$}%Ü}%}&YI«äˆ™~~ÿ}#?}!}!} }8}(}"}'}"}"}&} } } } }!}$}%Ü}%}&YI«äˆ™~~ÿ}#?}!}!} }8}(}"}'}"}"}&} } } } }!}$}%Ü}%}&YI«äˆ™~

My ppp.conf is as follows:
default:
 set device /dev/cua00
 set speed 38400
incoming:
 allow users ppp

I can use other modes of PPP on the machine without problem. Is the above
phenomenon abnormal or normal for direct mode? When I tried dialing into
the machine from another OpenBSD machine, vague message was displayed too:
asus2# ppp
Working in interactive mode
Using interface: tun0
ppp ON asus2> term
deflink: Entering terminal mode on /dev/cua00
Type `~?' for help
atz
OK
atdt201
CONNECT 14400/LAPM
àÀüà~üàŽàŽ~ÇààpàŽàþŽ€üþŽ~~ÇþŽþüŽàà8pÿàààÇàŽàÀàÀŽüŽàà~üÇàà

A getty process was running on the server machine, but it could not
be changed into login process by entering username. How can I make
my dial-in server machine work normally?