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

 Applies only to X.25 PVCs and X.25 DLM circuits. Specifies the
 maximum  window size allowed for the X.25 circuit--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 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.