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

    Default:  0            Value:  0-255

    When operating over CLNS, indicates network priority encoded in
    NPDU header for all transmitted packets.  It may only be used by
    intermediate systems to assign the packets to queues of appropriate
    priority.