I have 4 of these modems running on my dial-in server, to support up to 4 simultaneous dial-up modem logins.

• V.92 56k hardware modem
• RS232 serial interface
• 56k upstream requires a special originate/data center type modem, and digital lines on the answering side, so in my purposes these are only able to handle 38.4kbps, but most of the modems I dial in with are only 14.4kbps or slower anyways, so this is not a real hindrance.