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James O'Toole, Chris Torek, and Mark Weiser
USENIX Winter Conference Proceedings, Dallas, Texas, January 1985
We have implemented the Xerox Networking Systems protocol suite
in 4.2bsd UNIX1 in order to communicate with Xerox
workstations which do not implement IP/TCP. In this paper, we
discuss the problems we encountered while making the necessary
changes to the UNIX kernel. We found a multitude of IP/TCP dependencies
in the lowest level UNIX device driver and network interface code,
which were eliminated by replacing inline code with protocol specific
subroutine calls. Another problem was that 4.2bsd expects all
protocols to be connectionless or byte stream, and the XNS stream
level is neither. We generalized the socket code to satisfy the
additional requirements of the XNS stream protocol. The result
of all these changes is not just the ability to handle XNS but
a more general network system without IP/TCP dependencies, ready
for the next generation of protocols.
1UNIX is trademark of AT&T Bell Laboratories
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