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

    Default: 2000              Value: 1-5000

    Maximum time, in milliseconds, between the assertion of the
    request to send signal and receiving the assertion of the clear
    to send signal. This characteristic is not supported if the
    characteristic modem control is none.