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

    Default:  none               Value:  Local entity name

    A local entity name specifying the physical layer line entity on
    which the link entity is to operate.  A non-null value must be
    set before the link can be enabled.  Can only be set when the
    link is off.