(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.