The Free On-line Dictionary of Computing (30 December 2018):

Sequenced Packet Exchange

    (SPX) A transport layer protocol
   built on top of IPX.  SPX is used in Novell NetWare
   systems for communications in client/server application
   programs, e.g. BTRIEVE (ISAM manager).

   SPX is not used for connections to the file server itself;
   this uses NCP.  It has been extended as SPX-II.  SPX/IPX
   perform equivalent functions to TCP/IP.


(http://developer.novell.com/research/appnotes/1995/december/03/04.htm).

   [Better reference?]

   (1999-05-27)