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

Xerox Network System

    (XNS) A proprietary network architecture
   developed by the Xerox Office Systems Division of Xerox
   corporation at Xerox PARC in the late 1970s/early 1980s to
   run on LAN (Ethernet) and WAN networks.  The XNS
   protocol stack provided routing and packet delivery.

   Implementations exist for 4.3BSD derived systems and the
   Xerox Star computers.  Novell based much of the lower layers
   of their protocol suite IPX/SPX on XNS.

   The main components are: Internet datagram protocol (IDP),
   Routing information protocol (RIP), Packet Exchange protocol
   (PEP), and Sequences packet protocol (SPP).

   XNS has strong parellels to TCP/IP in that the network
   layer, IDP, is roughly equivalent to IP.  RIP has the same
   functions (and obviously name) as the routing information
   protocol, RIP.  SPP, a connectionless transport layer
   protocol, is similar to UDP.  PEP is also in the transport
   layer but is connection-oriented and similar to TCP.

   XNS specifically is no longer in use due to the all
   pervasiveness of IP.

   XNS denotes not only the protocol stack, but also an
   architecture of standard programming interfaces, conventions,
   and service functions for authentication, directory, filing,
   e-mail, and remote procedure call.  XNS is also the name
   of Xerox's implementation.

   Many PC networking companies, such as 3Com, Banyan,
   Novell, and Ungermann-Bass Networks used or use a
   variation of XNS as their primary transport protocol.  XNS was
   desigined to be used across a variety of communication media,
   processors, and office applications.  UB, (now a part of
   Tandem Computers) adopted XNS in developing its Net/One
   XNS routing protocol.

   [Or is it "Service(s)"?  Date?]

   (2003-11-10)