Editing Xerox Network Systems (section)

===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}}