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.)  Use a value in the range 1 to 65,535.
 The default value is equal to the value of the BUFFER SIZE if
 specified; otherwise the default is 576.