CONFIG_ISDN_BOOL ISDN ("Integrated Services Digital Networks", called RNIS in France) is a special type of fully digital telephone service; it's mostly used to connect to your Internet service provider (with SLIP or PPP). The main advantage is that the speed is higher than ordinary modem/telephone connections, and that you can have voice conversations while downloading stuff. It only works if your computer is equipped with an ISDN card and both you and your service provider purchased an ISDN line from the phone company. For details, read on the WWW. Select this option if you want your kernel to support ISDN.