VMS Help Sys Parameters, TTY_DIALTYPE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    TTY_DIALTYPE provides flag bits for dialups. Bit 0 is 1 for
    United Kingdom dialups and 0 for all others. Bit 1 controls the
    modem protocol used. Bit 2 controls whether a modem line hangs
    up 30 seconds after seeing CARRIER if a channel is not assigned
    to the device. The remaining bits are reserved for future use.
    See the OpenVMS I/O User's Reference Manual for more information
    about flag bits.