The following information is an overview of the most important modem standards, how they can be categorized into four compatibility levels, and how they pertain to RAS and RAS data compression. This information, along with the RAS online Help topic "Modifying MODEM.INF," also enables you to implement unsupported modems with RAS versions 1.x, RAS for Windows for Workgroups 3.11, and RAS for Windows NT versions 3.1, 3.5, and 3.51.
You can apply most of the information to RAS for Windows 95; however, RAS for Windows 95 does not use a Modem.inf file. Instead, it uses Telephone Application Programming Interface (TAPI), which relies on entries in the Windows 95 registry for modem initialization. To implement unsupported modems with RAS for Windows 95, it is recommended that you obtain a modem driver from the modem manufacturer.
Windows NT 4.0 RAS also includes support for TAPI as well as supporting new modems through the Universal Modem Driver (Unimodem). RAS continues to support modems for older legacy systems. To configure a previously installed unsupported modem to work with RAS, add an entry for that modem in the Modem.inf file.