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50-490: XNS or xns may refer to: Computing [ edit ] Xerox Network Systems , an early computer networking protocol suite Extensible Name Service , an XML-based digital identity architecture Other uses [ edit ] Kanashi language (ISO 639:xns), a Sino-Tibetan language Navtech System Support (IATA code: XNS), in the List of airline codes Christians (XNS), in

100-419: A reliable stream . Some applications use a simpler, connection-less transport protocol, User Datagram Protocol (UDP), for tasks which do not require reliable delivery of data or that require real-time service, such as video streaming or voice chat. Two architectural models are commonly used to describe the protocols and methods used in internetworking. The Open System Interconnection (OSI) reference model

150-474: A remote procedure call protocol named Courier . Courier contained primitives to implement most of the features of Xerox's Mesa programming language function calls. Applications had to manually serialize and de-serialize function calls in Courier; there was no automatic facility to translate a function activation frame into an RPC (i.e. no "RPC compiler" was available). Because Courier was used by all applications,

200-496: A C-series or D-series machine, anywhere on earth, and then restart the machine. Also, there was a remote debug protocol for the world-swap debugger. This protocol could, via the debugger "nub", freeze a workstation and then peek and poke various parts of memory, change variables, and continue execution. If debugging symbols were available, a crashed machine could be remote debugged from anywhere on earth. In his final year at Harvard University , Bob Metcalfe began interviewing at

250-490: A checksum covering the entire packet, but it is optional, not mandatory. This reflects the fact that LANs generally have low-error rates, so XNS removed error correction from the lower-level protocols in order to improve performance. Error correction could be optionally added at higher levels in the protocol stack, for instance, in XNS's own SPP protocol. XNS was widely regarded as faster than IP due to this design note. In keeping with

300-554: A common host protocol would be more reliable and efficient. The ARPANET connection to UCL later evolved into SATNET . In 1977, ARPA demonstrated a three-way internetworking experiment, which linked a mobile vehicle in PRNET with nodes in the ARPANET, and, via SATNET, to nodes at UCL. The X.25 protocol, on which public data networks were based in the 1970s and 1980s, was supplemented by the X.75 protocol which enabled internetworking. Today

350-641: A common internetwork protocol, and instead of the network being responsible for reliability, as in the ARPANET, the hosts became responsible, as demonstrated in the CYCLADES network. Researchers at Xerox PARC outlined the idea of Ethernet and the PARC Universal Packet (PUP) for internetworking. Research at the National Physical Laboratory in the United Kingdom confirmed establishing

400-563: A note circulated to the International Network Working Group , later published in a 1974 paper " A Proposal for Interconnecting Packet Switching Networks" . Pouzin was a pioneer in packet-switching technology and founder of the CYCLADES network, at a time when network meant what is now called a local area network . Catenet was the concept of linking these networks into a network of networks with specifications for compatibility of addressing and routing. The term catenet

450-652: A number of companies and was given a warm welcome by Jerry Elkind and 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 Proceedings of the Fall Joint Computer Conference off

500-405: A packet level, there was little or no capability to call each other's application services. This led to complete fragmentation of the XNS market, and has been cited as one of the reasons that IP easily displaced it. The XNS protocols also included an Authentication Protocol and an Authentication Service to support it. Its "Strong credentials" were based on the same Needham–Schroeder protocol that

550-682: 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. 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 Artificial Intelligence Laboratory approached Xerox in 1974 with

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600-609: A programmable and easily debug-able print job in ASCII, Warnock and Geschke created the Postscript language as one of their first products at Adobe. Because all 8000+ machines in the Xerox corporate Intranet ran the Wildflower architecture (designed by Butler Lampson), there was a remote-debug protocol for microcode. Basically, a peek and poke function could halt and manipulate the microcode state of

650-523: A team including 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

700-495: A version of Pup with absolute 48-bit host IDs, and TCP's 3-Way handshake in the Sequenced Packet Protocol. By early 1978 the new system was working, but management was still not making any move to commercialize it. As Metcalfe put it: 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. When no further action

750-478: A way to connect disparate types of networking technology, but it became widespread through the developing need to connect two or more local area networks via some sort of wide area network . The first international heterogenous resource sharing network was the 1973 interconnection of the ARPANET with early British academic networks through the computer science department at University College London (UCL). In

800-781: Is "a general discussion meant for those who want to know how office people can become more effective and productive by using the Xerox Network Systems." The components of Xerox Network Systems Architecture are briefly described in Xerox Network Systems Architecture General Information Manual (XNSG 068504). A series of sixteen individual protocol descriptions are listed in the Xerox Systems Institute Literature Catalog . Possibly more recent versions of these standards are: Internetwork Internetworking

850-554: Is a close descendant of Pup's internetwork protocol , and roughly corresponds to the Internet Protocol (IP) layer in the Internet protocol suite. IDP uses Ethernet's 48-bit address as the basis for its own network addressing , generally using the machine's MAC address as the primary unique identifier. To this is added another 48-bit address section provided by the networking equipment; 32 bits are provided by routers to identify

900-552: Is a five-layer system, like the later Internet protocol suite . The Physical and Data Link layers of the OSI model correspond to the Physical layer (layer 0) in XNS, which was designed to use the transport mechanism of the underlying hardware and did not separate the data link. Specifically, XNS's Physical layer is really the Ethernet local area network system, also being developed by Xerox at

950-422: Is defined by a unified global addressing system , packet format, and routing methods provided by the Internet Protocol . The term internetworking is a combination of the components inter (between) and networking . An earlier term for an internetwork is catenet , a short-form of (con)catenating networks . Internetworking, a combination of the components inter (between) and networking , started as

1000-526: Is defined. XNS combined the OSI's Session and Transport layers into the single Interprocess Communications layer (layer 2). Layer 3 was Resource Control, similar to the OSI's Presentation. Finally, on top of both models, is the Application layer, although these layers were not defined in the XNS standard. The main internetwork layer protocol is the Internet Datagram Protocol ( IDP ). IDP

1050-425: Is designed to provide an unreliable (not guaranteed) packet service across the network. The architecture avoids intermediate network elements maintaining any state of the network. Instead, this function is assigned to the endpoints of each communication session. To transfer data reliably, applications must utilize an appropriate transport layer protocol, such as Transmission Control Protocol (TCP), which provides

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1100-479: Is different from Wikidata All article disambiguation pages All disambiguation pages Xerox Network Systems XNS was developed by the Xerox Systems Development Department in the early 1980s, who were charged with bringing Xerox PARC 's research to market. XNS was based on the earlier (and equally influential) PARC Universal Packet (PUP) suite from the late 1970s. Some of

1150-506: Is required to handle them, and no mechanism is defined to discover if the intervening routers support larger packets. Also, packets can not be fragmented, as they can in IP. The Routing Information Protocol (RIP), a descendant of Pup's Gateway Information Protocol , is used as the router information-exchange system, and (slightly modified to match the syntax of addresses of other protocol suites), remains in use today in other protocol suites, such as

1200-479: Is sometimes incorrectly termed internetworking, but the resulting system is simply a larger, single subnetwork , and no internetworking protocol , such as Internet Protocol , is required to traverse these devices. However, a single computer network may be converted into an internetwork by dividing the network into segments and logically dividing the segment traffic with routers and having an internetworking software layer that applications employ. The Internet Protocol

1250-504: Is the practice of interconnecting multiple computer networks , such that any pair of hosts in the connected networks can exchange messages irrespective of their hardware-level networking technology. The resulting system of interconnected networks is called an internetwork , or simply an internet . The most notable example of internetworking is the Internet , a network of networks based on many underlying hardware technologies. The Internet

1300-453: The List of acronyms: X Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title XNS . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=XNS&oldid=1180244174 " Category : Disambiguation pages Hidden categories: Short description

1350-562: The 1990s. XNS was used unchanged by 3Com 's 3+Share and Ungermann-Bass 's Net/One. It was also used, with modifications, as the basis for Novell NetWare , and Banyan VINES . XNS was used as the basis for the AppleNet system, but this was never commercialized; a number of XNS's solutions to common problems were used in AppleNet's replacement, AppleTalk . In comparison to the OSI model 's 7 layers, XNS

1400-506: The ARPANET, the network elements used to connect individual networks were called gateways , but the term has been deprecated in this context, because of possible confusion with functionally different devices. By 1973-4, researchers in France, the United States, and the United Kingdom had worked out an approach to internetworking where the differences between network protocols were hidden by using

1450-604: The Clearinghouse Protocol 3-level directory service was created to perform service location, and the expanding-ring broadcasts were used only to locate an initial Clearinghouse. Due to its tight integration with Mesa as an underlying technology, many of the traditional higher-level protocols were not part of the XNS system itself. This meant that vendors using the XNS protocols all created their own solutions for file sharing and printer support. While many of these 3rd party products theoretically could talk to each other at

1500-483: The IP header. There are two primary transport layer protocols, both very different from their Pup predecessor: XNS, like Pup, also uses EP , the Error Protocol , as a reporting system for problems such as dropped packets. This provided a unique set of packets which can be filtered to look for problems. In the original Xerox concept, application protocols such as remote printing, filing, and mailing, etc., employed

1550-505: The Internet protocol suite. XNS also implements a simple echo protocol at the internetwork layer, similar to IP's ping , but operating at a lower level in the networking stack. Instead of adding the ICMP data as payload in an IP packet, as in ping, XNS's echo placed the command directly within the underlying IDP packet. The same might be achieved in IP by expanding the ICMP Protocol field of

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1600-524: The OSI model and does not refer to it in any of the normative specifications in Request for Comments and Internet standards . Despite similar appearance as a layered model, it has a much less rigorous, loosely defined architecture that concerns itself only with the aspects of the style of networking in its own historical provenance. It assumes the availability of any suitable hardware infrastructure, without discussing hardware-specific low-level interfaces, and that

1650-706: The Systems Development Division within Xerox specifically to bring PARCs concepts to market. Metcalfe immediately began re-designing Ethernet to work at 20 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. Dalal built

1700-440: The XNS application protocol documents specified only courier function-call interfaces, and module+function binding tuples. There was a special facility in Courier to allow a function call to send or receive bulk data. Initially, XNS service location was performed via broadcasting remote procedure-calls using a series of expanding ring broadcasts (in consultation with the local router, to get networks at increasing distances.) Later,

1750-510: The design of the 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, Berkeley researchers demonstrated that the design was suitable for more than just IP. Additional BSD modifications were eventually necessary to support the full range of Open Systems Interconnection (OSI) protocols. Xerox Network Systems Architecture Introduction to Xerox Network Systems (XNSG 058504)

1800-473: 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 . 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

1850-462: The interconnecting gateways are called routers . The definition of an internetwork today includes the connection of other types of computer networks such as personal area networks . Catenet , a short-form of (con)catenating networks, is obsolete terminolgy for a system of packet-switched communication networks interconnected via gateways . The term was coined by Louis Pouzin in October 1973 in

1900-433: The low-latency LAN connections it runs on, XNS uses a short packet size, which improves performance in the case of low error rates and short turnaround times. IDP packets are up to 576 bytes long, including the 30 byte IDP header . In comparison, IP requires all hosts to support at least 576, but supports packets of up to 65K bytes. Individual XNS host pairs on a particular network might use larger packets, but no XNS router

1950-565: The network number in the internetwork, and another 16 bits define a socket number for service selection within a single host. The network number portion of the address also includes a special value which meant "this network", for use by hosts which did not (yet) know their network number. Unlike TCP/IP, socket numbers are part of the full network address in the IDP header, so that upper-layer protocols do not need to implement demultiplexing; IDP also supplies packet types (again, unlike IP). IDP also contains

2000-448: The participating networks by routing packets to their destinations based on standardized addresses. Another type of interconnection of networks often occurs within enterprises at the link layer of the networking model, i.e. at the hardware-centric layer below the level of the TCP/IP logical interfaces. Such interconnection is accomplished with network bridges and network switches . This

2050-557: The protocols in the XNS suite were lightly modified versions of the ones in the Pup suite. XNS added the concept of a network number, allowing larger networks to be constructed from multiple smaller ones, with routers controlling the flow of information between the networks. The protocol suite specifications for XNS were placed in the public domain in 1977. This helped XNS become the canonical local area networking protocol, copied to various degrees by practically all networking systems in use into

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2100-461: The same time, and a number of its design decisions reflect that fact. The system was designed to allow Ethernet to be replaced by some other system, but that was not defined by the protocol (nor had to be). The primary part of XNS is its definition of the Internal Transport layer (layer 1), which corresponds to OSI's Network layer, and it is here that the primary internetworking protocol, IDP,

2150-409: 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." Metcalfe was welcomed at PARC in spite of his unsuccessful thesis, and soon started development of what

2200-439: The theme. Among these were Net/One, 3+, Banyan VINES and Novell's IPX/SPX . 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

2250-420: Was a binary-formatted standard for controlling laser printers. The designers of this language, John Warnock and Chuck Geschke, later left Xerox PARC to start Adobe Systems . Before leaving, they realized the difficulty of specifying a binary print language, where functions to serialize the print job were cumbersome and which made it difficult to debug errant printing jobs. To realize the value of specifying both

2300-546: Was developed under the auspices of the International Organization for Standardization (ISO) and provides a rigorous description for layering protocol functions from the underlying hardware to the software interface concepts in user applications. Internetworking is implemented in the Network Layer (Layer 3) of the model. The Internet Protocol Suite , also known as the TCP/IP model, was not designed to conform to

2350-615: Was forthcoming, Metcalfe left the company at the end of 1978. 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

2400-436: Was gradually displaced by the short-form of the term internetwork, internet (lower-case i ), when the Internet Protocol replaced earlier protocols on the ARPANET in the early 1980s. To build an internetwork, the following are needed: A standardized scheme to address packets to any host on any participating network; a standardized protocol defining format and handling of transmitted packets; components interconnecting

2450-481: Was later used by Kerberos . After contacting the authentication service for credentials, this protocol provided a lightweight way to digitally sign Courier procedure calls, so that receivers could verify the signature and authenticate senders over the XNS internet, without having to contact the Authentication service again for the length of the protocol communication session. Xerox's printing language, Interpress ,

2500-428: 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 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

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