Since it is not easy to find a usb modem for linux.(Most are winmodem). I decide to use usb-serial and serial modem. After usb-serial is plugged in, /dev/ttyUSB0 can be used as a serial device. I though it is the same as /dev/ttyS0. I create a dialin server with PPPD. When a client software dail in, the dailin negotiation is going well and pppd is started. If I use /dev/ttyS0, the remote PC connect to this dialin server with PPP connection with out problems. But if I use /dev/ttyUSB0, the dialin server side alway report "Serial line is loop back" error and connection is terminated. Does any one do use usb-serial and serial modem before? Could you point out where is the problem? How to fix it?
Thank in advance.