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

    Default: 0             Value: 1-60000

    Maximum time to wait before sending an acknowledgment supervisory
    frame if no other frames carry the acknowledgment. A value of
    zero means that the frame will be sent immediately if no I-frame
    can be sent. You can modify this characteristic only when the
    entity is disabled.