PARC Universal Packet

PARC Universal Packet
Name	PARC Universal Packet
Developer	Xerox PARC
Introduced	1970s
Type	Internetworking protocol suite
Platform	Ethernet, ARPANET, DECnet, Xerox Alto
Influenced	Internet Protocol, TCP/IP, Open Systems Interconnection, ISO/OSI model, Ethernet II

Contents

PARC Universal Packet is an early internetworking protocol suite developed at Xerox PARC during the 1970s to interconnect heterogeneous Ethernet networks, research systems such as the Xerox Alto, and external networks including ARPANET and DECnet. It provided packet forwarding, addressing, and routing mechanisms that influenced later standards like Internet Protocol and the Open Systems Interconnection efforts at International Organization for Standardization. The design emerged amid concurrent work at institutions including Stanford Research Institute, RAND Corporation, Bolt Beranek and Newman, and Massachusetts Institute of Technology.

Overview

PARC Universal Packet (PUP) was conceived at Xerox PARC to enable transparent communication among workstations from vendors such as Digital Equipment Corporation, Hewlett-Packard, and Intel Corporation across media including Ethernet and X.25. The suite defined network, transport, and application conventions to support services like remote file access on the Xerox Alto, terminal sessions with DECsystem-10, and printer spooling for Hewlett-Packard devices. PUP’s architecture paralleled contemporaneous efforts at University of California, Berkeley and Massachusetts Institute of Technology while influencing projects at Stanford University, Carnegie Mellon University, Bell Labs, and NASA Ames Research Center.

Work on PUP at Xerox PARC overlapped with seminal projects such as the Xerox Alto workstation, the Xerox Star office system, and research by figures affiliated with Alan Kay, Bob Taylor, and D. Richard Bohm. Development drew on packet switching research from ARPANET and concepts from Alohanet and NPL Network. Funding and collaboration involved industrial and academic partners including Digital Equipment Corporation, Hewlett-Packard, Bell Labs, Stanford Research Institute, and University College London. PUP was demonstrated in environments that included connections to ARPANET gateways, university campuses such as Stanford University and University of California, Berkeley, and corporate networks at Xerox Corporation research sites.

PUP employed an addressing scheme combining 8-bit host identifiers and 16-bit network numbers to route packets across interconnected segments including Ethernet and X.25 links. Hosts such as the Xerox Alto, DECsystem-10, VAX-11 systems, and IBM 370 mainframes could run PUP stacks implemented in systems developed by Digital Equipment Corporation and Intel Corporation. The architecture featured packet forwarding via gateways implemented on machines from Bell Labs and Sun Microsystems, and provided transport capabilities resembling later Transmission Control Protocol concepts used at University of California, Berkeley. PUP’s modular design informed the layering approach later formalized by International Organization for Standardization in the Open Systems Interconnection model.

The PUP protocol suite specified packet header formats, checksum methods, and service multiplexer fields to support datagram and connection-oriented semantics for applications like file transfer on the Xerox Alto and remote login sessions for DECsystem-10. Protocol elements mapped to hardware interfaces found on Ethernet adapters from 3Com and Intel Corporation and accommodated reliable delivery features similar to those in TCP/IP research at University of California, Berkeley. PUP defined naming and addressing conventions that paralleled work on the Domain Name System at University of Southern California and routing strategies that would later influence protocols at Stanford Research Institute and Carnegie Mellon University.

Implementations of PUP ran on platforms such as the Xerox Alto, Xerox Star, DEC VAX-11, DECsystem-10, and various IBM systems using network interfaces from vendors like Intel Corporation, 3Com, and Hewlett-Packard. Gateways connected PUP networks to ARPANET nodes, DECnet clusters, and commercial services based on X.25 provided by telecommunication carriers including AT&T and British Telecom. PUP influenced software projects at Carnegie Mellon University, MIT Project MAC, and Stanford University where researchers integrated PUP concepts into distributed file systems, remote procedure mechanisms, and early email systems developed at BBN Technologies and Bolt Beranek and Newman.

Although eventually superseded by Internet Protocol and the TCP/IP suite standardized through efforts at Defense Advanced Research Projects Agency and Internet Engineering Task Force, PUP’s layering, addressing, and internetworking concepts influenced standards work at International Organization for Standardization, the Open Systems Interconnection model, and implementations produced by Sun Microsystems, Cisco Systems, and 3Com. PUP’s integration with the Xerox Alto and Xerox Star contributed to design paradigms adopted by projects at Apple Inc. and Microsoft Corporation for networking personal computers. Historical study of PUP appears alongside archival material from Xerox PARC, analyses by researchers at Stanford University and University of California, Berkeley, and retrospectives in texts associated with Alan Kay, Bob Taylor, and other computing pioneers.

Category:Computer networking protocols