XNS - Xerox Network Systems (1)
created in late 1970s and early 1980s; similar to TCP/IP
works across a variety of media (X.25, Ethernet, HDLC)
early adopted by Novell - evolved into IPX
implementations for PC networks became popular
5-layer protocol model
- layer 0 - corresponds roughly to OSI layers 1 and 2 (link access and bit-stream manipulation)
- layer 1 - corresponds to the portion of OSI layer 3 that refers to network traffic (logical addressing and end-to-end datagram delivery)
- layer 2 - corresponds to the portion of OSI layer 3 that refers to inter-network routing and to OSI layer 4 (for inter process communication)
- layers 3 and 4 - correspond to OSI layers 6 and 7 (data structuring, process to process interaction and application)
No protocol corresponding to OSI layer 5 (session layer)