Make an easy link to your modem device:
ln -s /dev/ttyS1 /dev/modem
Now change to the /usr/sbin directory and look for ppp files. Look for either a
pppsetup or a pppconfig script. You may directly start this script to
set up PPP on your system. On my Slackware system I typed pppsetup and started
the script. This script asks for various parameters for connecting via the ISP.
It first asks for the phone number to dial -- enter “atdt#777”, where 777 is replaced by the number that you need to dial.
It then asks for the modem -- select /dev/ttyS1
Baud Rate -- select “115200”
Callback -- Answer “NO”
Modem INIT String -- “ATZ OK "at+crm=1" OK”
ISP Domain Name -- Leave blank
DNS Server Address -- Enter a valid DNS Server IP, for instance “202.41.97.3” or “202.41.97.132”, or leave blank
Authentication -- “PAP”
Username
Password
Refer to Section 3, “Activating Internet Services on your Handset” for Username and Password.
Finally it shows you your configuration.
Some more work needs to be done. We need to edit the options file present in
the /etc/ppp folder. We need to check if the following entries are present in
the file:
lock defaultroute noipdefault modem /dev/ttyS1 115200 crtscts noauth passive asyncmap 0
Remember that noauth is by default commented; you need to uncomment it.
You can use egrep -v '#|^ *$' /etc/ppp/options to list only the options present
in this file so as to quickly judge which ones are missing or incorrect.