Library /sys$common/syshlp/ncphelp.hlb SET, MODULE, X25-PROTOCOL, KNOWN_DTES, DEFAULT WINDOW number  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Specifies the default window size for X.25 virtual circuits, that
 is, the maximum number of packets for which outstanding
 acknowledgments  are allowed. Specify a value in the range 1
 to 127.  By default, window size takes the network value
 specified by the  PROFILE parameter.  See the Public Network
 Information manual for the network  value of this parameter.