For a modem to be compatible with any communication software running on the local computer, the software must be compatible with the modem command language, also referred to as the modem command set. The command set configures the other three compatibility levels of the modem according to the needs of the local software (RAS), the supported modem standards of the modem being called, and the users' preferences. For certain modems, the modem command set works between the local and remote modems as well as between the local communications software and the local modem.
Command set compatibility between RAS modem drivers and the local modem is advantageous, but not a requirement. Many manufacturers advertise that their modem is 100 percent compatible with the popular Hayes AT command set, or that it is compatible with another popular modem's command set. This generally means that the modem uses the same commands as Hayes modems for basic operations such as dial, hang up, reset, and answer. It does not imply that the modem uses the same commands for configuration of modulation, error control, or data compression. However, if your modem is not compatible with any supported modem's command set, you can customize the RAS modem driver by modifying the Modem.inf file (or Modems.inf file in RAS versions 1.x) to make it compatible with virtually any modem's command set. For additional information on modifying the Modem.inf file, see the RAS Help topic "Modifying Modem.inf."
Command set compatibility between the local modem and the remote modem is not a requirement for RAS. Command set compatibility between the local and remote modem is only important if both modems are designed to be configurable by a command received from the other modem. For example, an administrator may call from home and issue a command to change the default settings during the next power up of the modem in the office; however, this specialized feature is not important during RAS communication.