The first section of the preceding Figure E.3 shows that modem error control (MNP4, V.42 [LAPM], MNP10) standards take effect only between modems (DCE-to-DCE link). For RAS versions 1.0 and 1.1, these standards are not supported; however, in RAS version 1.1a and later these standards are activated.
MNP4 is the oldest and least efficient of the three error control standards; V.42 is newer and more efficient than MNP4; and MNP10 is the newest (nonstandard) protocol, although it is not available in many modems. MNP10 is designed to enable change of modulation modes during connections and to operate under extremely adverse environments where V.42 fails. Error control between computer and modem (DTE and DCE) is handled automatically by the RAS protocol by encompassing the entirety of the connection¾not only the connection between DTE and DCE, but the connection between RAS client and RAS server (DTE-to-DTE).