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

    Default: 5000

    Maximum time, in milliseconds, the entity will wait for data set
    ready to be deasserted after it has deasserted data terminal
    ready. If this timer expires, the entity assumes it can assert
    data terminal ready once again. This characteristic is not
    supported if the characteristic modem control is none.