VMS Help DECnet-Plus, DCL Commands, SET, HOST, /X29, Qualifiers, /WINDOW_SIZE=number  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /NOWINDOW_SIZE

    (Default=/NOWINDOW_SIZE)

    Use this qualifier to request the  specified  windowsize  in  the
    range  of  1-127  in  the  call  packet.   Otherwise, the network
    default is used.  If you request a windowsize larger than the one
    configured, X.25 will use the largest size configured.