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

 Specifies in bytes the maximum number of transmit buffers, thereby
 controlling the maximum size NSP message segment that can be
 transmitted.  (This value is the maximum size message the End
 Communication layer can transmit; it does not include Routing layer or
 Data Link layer overhead.)  The default value is equal to the value of
 the BUFFER SIZE if specified; otherwise the default is 576.

 The value of the SEGMENT BUFFER SIZE parameter must be less than or
 equal to the value of the BUFFER SIZE parameter.  The two values are
 normally equal but may differ to permit the network manager to alter
 buffer size on all nodes without interruption of service.  Refer to
 the DECnet for OpenVMS Networking Manual for information about how to
 modify buffer sizes.