Editing Xerox Network Systems (section)

==History==

===Origins in Ethernet and PUP===
In his final year at [[Harvard University]], [[Robert Metcalfe|Bob Metcalfe]] began interviewing at a number of companies and was given a warm welcome by [[Jerome I. Elkind|Jerry Elkind]] and [[Robert Taylor (computer scientist)|Bob Taylor]] at [[Xerox PARC]], who were beginning to work on the networked computer workstations that would become the [[Xerox Alto]]. He agreed to join PARC in July, after defending his thesis. In 1970, while [[couch surfing]] at [[Steve Crocker]]'s home while attending a conference, Metcalfe picked up a copy [[Joint Computer Conference|Proceedings of the Fall Joint Computer Conference]] off the table with the aim of falling asleep while reading it. Instead, he became fascinated by an article on [[ALOHAnet]], an earlier wide-area networking system. By June he had developed his own theories on networking and presented them to his professors, who rejected it and he was "thrown out on my ass."{{sfn|Pelkey|2007|loc=6.7}}

Metcalfe was welcomed at PARC in spite of his unsuccessful thesis, and soon started development of what was then referred to as "ALOHAnet in a wire". He teamed up with [[David Boggs]] to help with the electronic implementation, and by the end of 1973 they were building working hardware at 3&nbsp;Mbit/s. The pair then began working on a simple protocol that would run on the system. This led to the development of the [[PARC Universal Packet]] (Pup) system, and by late 1974 the two had Pup successfully running on Ethernet. They filed a patent on the concepts, with Metcalfe adding several other names because he believed they deserved mention, and then submitted a paper on the concept to [[Communications of the ACM]] on "Ethernet: Distributed Packet Switching for Local Computer Networks", published in July 1976.{{sfn|Pelkey|2007|loc=6.7}}

===PUP to XNS===
By 1975, long before PUP was complete, Metcalfe was already chafing under the stiff Xerox management. He believed the company should immediately put Ethernet into production, but found little interest among upper management. A seminal event took place when professors from [[MIT]]'s famed [[MIT Computer Science and Artificial Intelligence Laboratory|Artificial Intelligence Laboratory]] approached Xerox in 1974 with the intention of buying Ethernet for use in their lab. Xerox management declined, believing Ethernet was better used to help sell their own equipment. The AI Lab would then go on to make their own version of Ethernet, [[Chaosnet]].{{sfn|Pelkey|2007|loc=6.8}}

Metcalfe eventually left Xerox November 1975 for Transaction Technology, a division of [[Citibank]] tasked with advanced product development. However, he was lured back to Xerox seven months later by [[David Liddle]], who had recently organized the Systems Development Division within Xerox specifically to bring PARCs concepts to market. Metcalfe immediately began re-designing Ethernet to work at 20&nbsp;Mbit/s and started an effort to re-write Pup in a production quality version. Looking for help on Pup, Metcalfe approached [[Yogen Dalal]], who was at that time completing his PhD thesis under [[Vint Cerf]] at [[Stanford University]]. Dalal was also being heavily recruited by [[Bob Kahn]]'s [[ARPANET]] team (working on TCP/IP), but when Cerf left to join [[DARPA]], Dalal agreed to move to PARC and started there in 1977.{{sfn|Pelkey|2007|loc=6.9}}

Dalal built a team including [[William Crowther (programmer)|William Crowther]] and Hal Murray, and started with a complete review of Pup. Dalal also attempted to remain involved in the TCP efforts underway at DARPA, but eventually gave up and focussed fully on Pup. Dalal combined his experience with ARPANET with the concepts from Pup and by the end of 1977 they had published the first draft of the Xerox Network System specification. This was essentially a version of Pup with absolute 48-bit host IDs, and TCP's 3-Way handshake in the Sequenced Packet Protocol.{{sfn|Pelkey|2007|loc=6.10}}

By early 1978 the new system was working, but management was still not making any move to commercialize it. As Metcalfe put it:

<blockquote>When I came back to Xerox in 1976, we were about two and a half years from product shipment and in 1978 we were about two and a half years from product shipment.{{sfn|Pelkey|2007|loc=6.9}}</blockquote>

When no further action was forthcoming, Metcalfe left the company at the end of 1978.{{sfn|Pelkey|2007|loc=6.9}}

===Impact===
Last used by Xerox for communication with the [[DocuTech]] 135 Publishing System, XNS is no longer in use, due to the ubiquity of IP. However, it played an important role in the development of networking technology in the 1980s, by influencing software and hardware vendors to seriously consider the need for computing platforms to support more than one network protocol stack simultaneously.

A wide variety of proprietary networking systems were directly based on XNS or offered minor variations on the theme. Among these were Net/One, 3+,{{sfn|Stephens|1989|p=15}} [[Banyan VINES]]<ref>[http://docwiki.cisco.com/wiki/Banyan_VINES Banyan VINES], cisco</ref> and Novell's [[IPX/SPX]].<ref>[http://www.cisco.com/cpress/cc/td/cpress/fund/ith2nd/it2431.htm NetWare Protocols], cisco</ref> These systems added their own concepts on top of the XNS addressing and routing system; VINES added a [[directory service]] among other services, while [[Novell NetWare]] added a number of user-facing services like printing and file sharing. [[AppleTalk]] used XNS-like routing, but had incompatible addresses using shorter numbers.

XNS also helped to validate the design of the [[BSD|4.2BSD]] network subsystem by providing a second protocol suite, one which was significantly different from the Internet protocols; by implementing both stacks in the same kernel, [[UC Berkeley College of Engineering#Research units|Berkeley researchers]] demonstrated that the design was suitable for more than just IP.<ref>{{cite web
| title = On the performance of Courier Remote Procedure Calls under 4.1c BSD
| first=James
| last=Larus
| publisher=UC Berkeley ECE Department
| url = http://www.eecs.berkeley.edu/Pubs/TechRpts/1983/CSD-83-123.pdf
| year = 1983
| access-date = 2013-07-05}}</ref>  Additional BSD modifications were eventually necessary to support the full range of [[Open Systems Interconnection]] (OSI) protocols.