In a preceding paragraph we explained how you can make the configuration files needed by the script isdn in an easy way by using conf-isdn-account to realize an ISDN PPP link in Linux.

If you find it necessary,  you can modify these configuration files yourself,  by using a texteditor,  like vi or emacs.

Here they are:

/etc/isdn/isdncard
/etc/isdn/activeisdn
/etc/isdn/accounts/conf-<name>
/etc/ppp/pap-secrets
/etc/ppp/chap-secrets

Warning !  Only do this,  when you know what you are doing.