Library /sys$common/syshlp/nclhelp.hlb set, modem_connect, line, alternate_speed  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Default: 0

    Alternate (low) speed (in bits per second) to operate the
    line. You can modify this characteristic only when the entity
    is disabled. This characteristic is supported only when the
    characteristic communications mode is asynchronous, the
    characteristic modem control is full, the characteristic modem
    options includes rateselect, the characteristic clock is internal,
    and when the alternate line speed is needed.