Misplaced Pages

#54945

64-669: 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 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

128-474: 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,

192-495: 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

256-524: A LAN. It was thought, as a result of random initialization, the routing updates would spread out in time, but this was not true in practice. Sally Floyd and Van Jacobson showed in 1994 that, without slight randomization of the update timer, the timers synchronized over time. RIPv1 can be configured into silent mode, so that a router requests and processes neighbouring routing tables, and keeps its routing table and hop count for reachable networks up to date, but does not needlessly send its own routing table into

320-416: A RIPv1 router will in most cases only have one entry for a reachable network, the one with the lowest hop count. If a router receives information from two different neighbouring router that the same network is reachable with the same hop count but via two different routes, the network will be entered into the routing table two times with different next hop routers. The RIPv1 enabled router will then perform what

384-413: A limit on the number of hops allowed in a path from source to destination. The largest number of hops allowed for RIP is 15, which limits the size of networks that RIP can support. RIP implements the split horizon , route poisoning , and holddown mechanisms to prevent incorrect routing information from being propagated. In RIPv1 routers broadcast updates with their routing table every 30 seconds. In

448-652: 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

512-404: 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

576-517: A particular location. It has a touch screen, stylus, and handwriting recognition . Xerox designed the similar and larger PARCPad. Both devices were developed around the same time as the Apple Newton . PARC's distinguished researchers include four Turing Award winners: Butler Lampson (1992), Alan Kay (2003), Charles P. Thacker (2009), and Robert Metcalfe (2022). The Association for Computing Machinery (ACM) Software System Award recognized

640-681: 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

704-609: 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

SECTION 10

#1733085912055

768-424: 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 is required to handle them, and no mechanism

832-523: 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

896-493: 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

960-658: A wholly owned subsidiary. In late April of 2023, Xerox announced the donation of the lab to SRI International . In 1969, Goldman talked with George Pake , a physicist specializing in nuclear magnetic resonance and provost of Washington University in St. Louis , about starting a second research center for Xerox. On July 1, 1970, the Xerox Palo Alto Research Center opened. Its 3,000-mile distance from Xerox headquarters in Rochester, New York , afforded scientists at

1024-857: 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: Xerox PARC SRI Future Concepts Division (formerly Palo Alto Research Center , PARC and Xerox PARC )

1088-651: Is a research and development company in Palo Alto, California . It was founded in 1969 by Jacob E. "Jack" Goldman , chief scientist of Xerox Corporation , as a division of Xerox , tasked with creating computer technology-related products and hardware systems. Xerox PARC has been foundational to numerous revolutionary computer developments, including laser printing , Ethernet , the modern personal computer , GUI ( graphical user interface ) and desktop paradigm , object-oriented programming , ubiquitous computing , electronic paper , a-Si ( amorphous silicon ) applications,

1152-456: Is also no support for router authentication, making RIP vulnerable to various attacks. Due to the deficiencies of the original RIP specification, RIP version 2 (RIPv2) was developed in 1993, published in 1994, and declared Internet Standard 56 in 1998. It included the ability to carry subnet information, thus supporting Classless Inter-Domain Routing (CIDR). To maintain backward compatibility,

1216-500: Is an extension of RIPv2 for support of IPv6 , the next generation Internet Protocol. The main differences between RIPv2 and RIPng are: RIPng sends updates on UDP port 521 using the multicast group ff02::9 . RIP messages use the User Datagram Protocol on port 520 and all RIP messages exchanged between routers are encapsulated in a UDP datagram. RIP defined two types of messages: The routing information protocol uses

1280-461: 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

1344-607: Is easy to configure, because RIP does not require any parameters, unlike other protocols. RIP uses the User Datagram Protocol (UDP) as its transport protocol, and is assigned the reserved port number 520. Based on the Bellman–Ford algorithm and the Ford–Fulkerson algorithm , distance-vector routing protocols started to be implemented from 1969 onwards in data networks such as the ARPANET and CYCLADES . The predecessor of RIP

SECTION 20

#1733085912055

1408-441: Is known as equal-cost load balancing for IP packets. RIPv1 enabled routers not only request the routing tables of other routers every 30 seconds, they also listen to incoming requests from neighbouring routers and send their own routing table in turn. RIPv1 routing tables are therefore updated every 25 to 35 seconds. The RIPv1 protocol adds a small random time variable to the update time, to avoid routing tables synchronizing across

1472-450: 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 the low-latency LAN connections it runs on, XNS uses

1536-460: Is the router interface IP address from which the RIPv1 response was sent. As the requesting router receives updates from different neighbouring routers it will only update the reachable networks in its routing table, if it receives information about a reachable network it has not yet in its routing table or information that a network it has in its routing table is reachable with a lower hop count. Therefore,

1600-516: The computer mouse , and VLSI ( very-large-scale integration ) for semiconductors . Unlike Xerox's existing research laboratory in Rochester, New York, which focused on refining and expanding the company's copier business, Goldman's "Advanced Scientific & Systems Laboratory" aimed to pioneer new technologies in advanced physics, materials science, and computer science applications. In 2002, Xerox spun off Palo Alto Research Center Incorporated as

1664-440: The liquid-crystal display (LCD), some major innovations in optical disc technology, and laser printing were actively and successfully introduced by Xerox to the business and consumer markets. Microsoft co-founder Bill Gates has said that the Xerox graphical interface has notably influenced Microsoft and Apple. Apple Inc. co-founder Steve Jobs said that "Xerox could have owned the entire computer industry, could have been

1728-733: The Alto system in 1984, Smalltalk in 1987, InterLisp in 1992, and the remote procedure call in 1994. Lampson, Kay, Bob Taylor , and Thacker received the National Academy of Engineering 's prestigious Charles Stark Draper Prize in 2004 for their work on the Alto. Lynn Conway was recognized by the National Inventors Hall of Fame for her work on VLSI (2023). Xerox has been heavily criticized, particularly by business historians, for failing to properly commercialize and profitably exploit PARC's innovations. Xerox management failed to see

1792-603: 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

1856-530: The IBM of the nineties, could have been the Microsoft of the nineties." 37°24′10″N 122°08′55″W  /  37.40278°N 122.14861°W  / 37.40278; -122.14861 Routing Information Protocol The Routing Information Protocol ( RIP ) is one of the oldest distance-vector routing protocols which employs the hop count as a routing metric . RIP prevents routing loops by implementing

1920-529: The IP RIP. The 1982 Berkeley Software Distribution of the UNIX operating system implemented RIP in the routed daemon . The 4.2BSD release proved popular and became the basis for subsequent UNIX versions, which implemented RIP in the routed or gated daemon. Ultimately, RIP had been extensively deployed before the standard, written by Charles Hedrick, was passed as RIPv1 in 1988. The routing metric used by RIP counts

1984-482: 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

Xerox Network Systems - Misplaced Pages Continue

2048-554: 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

2112-652: 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 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

2176-531: 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 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

2240-705: 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

2304-439: 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,

2368-445: The address 224.0.0.9 , as opposed to RIPv1 which uses broadcast . Unicast addressing is still allowed for special applications. ( MD5 ) authentication for RIP was introduced in 1997. Route tags were also added in RIP version 2. This functionality allows a distinction between routes learned from the RIP protocol and routes learned from other protocols. RIPng (RIP next generation)

2432-453: 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 a checksum covering the entire packet, but it

2496-566: 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 is a five-layer system, like the later Internet protocol suite . The Physical and Data Link layers of the OSI model correspond to

2560-410: 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 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

2624-567: The computer field was under the leadership of its Computer Science Laboratory manager Bob Taylor , who guided the lab as associate manager from 1970 to 1977, and as manager from 1977 to 1983. Work at PARC since the early 1980s includes advances in ubiquitous computing , aspect-oriented programming , and IPv6 . After three decades as a division of Xerox, PARC was transformed in 2002 into an independent, wholly owned subsidiary company dedicated to developing and maturing advances in science and business concepts. Xerox announced that it would donate

Xerox Network Systems - Misplaced Pages Continue

2688-564: The computer prompted the development of the PARC Universal Packet architecture, which is structured much like the modern Internet's architecture. The PARCTab is an experimental mobile computer as an early experiment in Ubiquitous Computing or UbiComp. Its appearance resembles a PDA . Its functionality depends on the user's location, by receiving location-specific information via infrared sensors from gateway nodes installed in

2752-428: The computing industry. Many advancements made at the center were not equaled or surpassed for two decades. Xerox PARC has been the inventor and incubator of many elements of modern computing, including: Most of these developments were included in the Alto, which added the computer mouse . These developments unified into a single model most aspects of now-standard personal computers use. The integration of Ethernet into

2816-509: 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)

2880-459: The early deployments, routing tables were small enough that the traffic was not significant. As networks grew in size, however, it became evident there could be a massive traffic burst every 30 seconds, even if the routers had been initialized at random times. In most networking environments, RIP is not the preferred choice of routing protocol , as its time to converge and scalability are poor compared to EIGRP , OSPF , or IS-IS . However, it

2944-409: 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 the 1990s. XNS was used unchanged by 3Com 's 3+Share and Ungermann-Bass 's Net/One. It was also used, with modifications, as

3008-485: The following timers as part of its operation: Cisco 's proprietary Interior Gateway Routing Protocol (IGRP) was a somewhat more capable protocol than RIP. It belongs to the same basic family of distance-vector routing protocols . Cisco has ceased support and distribution of IGRP in their router software. It was replaced by the Enhanced Interior Gateway Routing Protocol (EIGRP) which is

3072-507: The global potential of many of PARC's inventions, but this was mostly a problem with its computing research, a relatively small part of PARC's operations. One notable example of this is the graphical user interface (GUI), initially developed at PARC for the Alto and then sold as the Xerox 8010 Information System workstation (with office software called Star) by the Xerox Systems Development Department. It heavily influenced future system design, but

3136-449: The hop count limit of 15 remained. RIPv2 has facilities to fully interoperate with the earlier specification if all Must Be Zero protocol fields in the RIPv1 messages are properly specified. In addition, a compatibility switch feature allows fine-grained interoperability adjustments. In an effort to avoid unnecessary load on hosts that do not participate in routing, RIPv2 multicasts the entire routing table to all adjacent routers at

3200-472: 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

3264-464: The lab and its related assets to SRI International in April 2023. As part of the deal, Xerox would keep most of the patent rights inside PARC, and benefit from a preferred research agreement with SRI/PARC. On January 18, 2024, SRI announced the research group from the PARC will become its Future Concepts division. PARC's developments in information technology served for a long time as standards for much of

SECTION 50

#1733085912055

3328-399: The network. Silent mode is commonly implemented to hosts. RIPv1 uses classful routing. The periodic routing updates do not carry subnet information, lacking support for variable length subnet masks (VLSM). This limitation makes it impossible to have different-sized subnets inside of the same network class . In other words, all subnets in a network class must have the same size. There

3392-624: The new lab great freedom in their work, but it increased the difficulty of persuading management of the promise of some of their greatest achievements. In its early years, PARC's West Coast location helped it hire many employees of the nearby SRI Augmentation Research Center (ARC) as that facility's funding began reducing from DARPA , NASA , and the U.S. Air Force . By leasing land at Stanford Research Park , it encouraged Stanford University graduate students to be involved in PARC research projects and PARC scientists to collaborate with academic seminars and projects. Much of PARC's early success in

3456-481: The number of routers that need to be passed to reach a destination IP network. The hop count 0 denotes a network that is directly connected to the router. 16 hops denote a network that is unreachable, according to the RIP hop limit. There are three standardized versions of the Routing Information Protocol: RIPv1 and RIPv2 for IPv4 , and RIPng for IPv6 . The original specification of RIP

3520-408: 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

3584-436: 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

3648-420: 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

3712-592: Was deemed a failure because Xerox only sold about 25,000 units of the computer. A small group from PARC led by David Liddle and Charles Irby formed Metaphor Computer Systems . Metaphor Computer Systems extended the Star desktop concept into an animated graphic and communicating office-automation model and sold the company to IBM . Several GUI engineers left to join Apple Computer to work on Lisa and Macintosh . Technologies pioneered by its materials scientists such as

3776-614: 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

3840-480: 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 ,

3904-467: 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, 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

SECTION 60

#1733085912055

3968-439: Was published in 1988. When starting up, and every 30 seconds thereafter, a router with RIPv1 implementation broadcasts to 255.255.255.255 a request message through every RIPv1 enabled interface. Neighbouring routers receiving the request message respond with a RIPv1 segment, containing their routing table . The requesting router updates its own routing table, with the reachable IP network address, hop count and next hop, that

4032-615: Was the Gateway Information Protocol (GWINFO) which was developed by Xerox in the mid-1970s to route its experimental network. As part of the Xerox Network Systems (XNS) protocol suite GWINFO transformed into the XNS Routing Information Protocol. This XNS RIP in turn became the basis for early routing protocols, such as Novell 's IPX RIP, AppleTalk 's Routing Table Maintenance Protocol (RTMP), and

4096-428: 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

#54945