Dial-Up Modem with ethernet interface

Hi

We have a remote lan we want to remotely access -dial-in- to monitor some equippements.

All of them are connected to a TCPIP Lan; however none of them has the ability to connect a modem through serial and use it as bridge or entry point tomonitor the rest of the equippements.

Is there a modem that can be connected directlty to a TCPIP LAN? ie that has an ethernet interface and when dial-in it will connect you to the TCP LAN?

The only soluton -expensive- I found to date is to put a router and connect a modem onto the console port.

Regards

Alvaro