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

 Applies only to X.25 lines.  Specifies the maximum number of frames
 for which outstanding acknowledgments are allowed.  Specify a value up
 to a maximum  of 127.  By default window size takes the value
 specified by the PROFILE  parameter of the SET or DEFINE MODULE
 X25-PROTOCOL command.  See the Public Network Information manual for
 the network value of this parameter.