Early research and development:
45-482: Merging the networks and creating the Internet: Commercialization, privatization, broader access leads to the modern Internet: Examples of Internet services: The PARC Universal Packet ( PUP or PuP , although the original documents usually use Pup ) was one of the two earliest internetworking protocol suites ; it was created by researchers at Xerox PARC in the mid-1970s. (Technically,
90-471: A 16-bit socket number. The network number has a particular special value which means 'this network', for use by hosts which do not (yet) know their network number. Unlike TCP/IP, socket fields are part of the full network address in the PUP header, so that upper-layer protocols did not need to implement their own demultiplexing; PUP also supplies packet types (again, unlike IP). Also, an optional 2-byte checksum covers
135-424: 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 is designed to provide an unreliable (not guaranteed) packet service across the network. The architecture avoids intermediate network elements maintaining any state of
180-643: A successor, the Xerox Networking System (XNS), was developed by the Xerox Office Systems Division using many of the ideas of PUP and a globally-unique, 48-bit host identifier (which became the MAC address in DIX v2 and later IEEE 802.3 ) to solve these problems: Internetworking Internetworking is the practice of interconnecting multiple computer networks , such that any pair of hosts in
225-560: A telegram congratulating the company for being contracted to build the "Interfaith Message Processor". The team working on the IMP called themselves the "IMP Guys": BBN began programming work in February 1969 on modified Honeywell DDP-516s. The completed code was six thousand words long, and was written in the Honeywell 516 assembly language. The IMP software was produced primarily on a PDP-1, where
270-506: 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 the interconnecting gateways are called routers . The definition of an internetwork today includes
315-604: The Gateway Information Protocol (an ancestor of RIP ) is used as both the routing protocol , and for hosts to discover routers. PUP also includes a simple echo protocol at the internetwork layer, similar to IP's ping , but operating at a lower level. To establish a transport connection, two protocols came into play. The first, the Rendezvous and Termination Protocol (RTP) , which was used to initiate communication between two entities, as well as manage and terminate
360-569: The Internet ) and a data field, and transmits the message across the 1822 interface to the IMP. The IMP routes the message to the destination host using protocols that were eventually adopted by Internet routers. Messages could store a total length of 8159 bits, of which the first 96 were reserved for the header ("leader"). While packets transmitted across the Internet are assumed to be unreliable, 1822 messages were guaranteed to be transmitted reliably to
405-626: 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 the participating networks by routing packets to their destinations based on standardized addresses. Another type of interconnection of networks often occurs within enterprises at
450-411: 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 a way to connect disparate types of networking technology, but it became widespread through
495-491: 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 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,
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#1732848803973540-727: The ARPA network communications protocol running on the IMPs was discussed in RFC 1 , the first of a series of standardization documents published by what later became the Internet Engineering Task Force (IETF). The concept of an interface computer for computer networking was first proposed in 1966 by Donald Davies for the NPL network in England and implemented there in 1968-9. The same idea
585-464: The ARPANET was the one at the University of Maryland. BBN Report 1822 specifies the method for connecting a host computer to an IMP. This connection and protocol is generally referred to as 1822 , the report number. The specification was written by Bob Kahn . To transmit data, the host constructs a message containing the numeric address of another host on the network (similar to an IP address on
630-689: 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 a common host protocol would be more reliable and efficient. The ARPANET connection to UCL later evolved into SATNET . In 1977, ARPA demonstrated
675-481: The Honeywell 316, a later version of the 516. Later, some Honeywell-based IMPs were replaced with multiprocessing BBN Pluribus IMPs, but ultimately BBN developed a microprogrammed clone of the Honeywell machine. IMPs were at the heart of the ARPANET until DARPA decommissioned the ARPANET in 1989. Most IMPs were either taken apart, junked or transferred to MILNET . Some became artifacts in museums; Kleinrock placed IMP Number One on public view at UCLA. The last IMP on
720-529: The IMP a separate computer. The IMPs were built by the Massachusetts-based company Bolt Beranek and Newman (BBN) in 1969. BBN was contracted to build four IMPs, the first being due at UCLA by Labor Day; the remaining three were to be delivered in one-month intervals thereafter, completing the entire network in a total of twelve months. When Massachusetts Senator Edward Kennedy learned of BBN's accomplishment in signing this million-dollar agreement, he sent
765-559: The IMP code was written and edited, then run on the Honeywell. There was considerable technical interchange with the British team building the NPL network and Paul Baran at RAND but the BBN team independently developed significant aspects of the network's internal operation, such as routing, flow control, software design, and network control. BBN designed the IMP simply as "a messenger" that would only "store-and-forward". BBN designed only
810-491: The IMP hardware calculate the checksum, because it was a faster option than using a software calculation. The IMP was initially conceived as being connected to one host computer per site, but at the insistence of researchers and students from the host sites, each IMP was ultimately designed to connect to multiple host computers. The first IMP was delivered to Leonard Kleinrock 's group at UCLA on August 30, 1969. It used an SDS Sigma 7 host computer. Douglas Engelbart 's group at
855-581: The Stanford Research Institute (SRI) received the second IMP on October 1, 1969. It was attached to an SDS 940 host. The third IMP was installed in University of California, Santa Barbara on November 1, 1969. The fourth IMP was installed in the University of Utah in December 1969. The first communication test between two systems (UCLA and SRI) took place on October 29, 1969, when a login to the SRI machine
900-497: The UCSB-SRI line found "approximately one packet per 20,000 in error;" subsequent tests "uncovered a 100% variation in this number - apparently due to many unusually long periods of time (on the order of hours) with no detected errors." A variant of the IMP existed, called the TIP (Terminal IMP), which connected terminals (i.e., teletypes ) as well as computers to the network; it was based on
945-423: The addressed destination. If the message could not be delivered, the IMP sent to the originating host a message indicating that the delivery failed. In practice, however, there were (rare) conditions under which the host could miss a report of a message being lost, or under which the IMP could report a message as lost when it had in fact been received. The specification incorporated an alternating bit protocol , of
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#1732848803973990-467: The availability of any suitable hardware infrastructure, without discussing hardware-specific low-level interfaces, and that a host has access to this local network to which it is connected via a link layer interface. For a period in the late 1980s and early 1990s, the network engineering community was polarized over the implementation of competing protocol suites, commonly known as the Protocol Wars . It
1035-688: The base for the Xerox Network Systems (XNS) protocol suite; some of the protocols in the XNS suite (such as the Internetwork Datagram Protocol ) were lightly modified versions of the ones in the PUP suite, but others are quite different, reflecting the experience gained with PUP and IP. The main internetwork layer protocol is PUP, which roughly corresponds to the Internet Protocol (IP) layer in TCP/IP. A full PUP network address consists of an 8-bit network number, an 8-bit host number, and
1080-457: 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 is defined by a unified global addressing system , packet format, and routing methods provided by
1125-607: 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 a note circulated to the International Network Working Group , later published in a 1974 paper " A Proposal for Interconnecting Packet Switching Networks" . Pouzin
1170-505: The connection. The second was the primary transport layer protocol, Byte Stream Protocol (BSP) , which was analogous to TCP . Once RTP had started the connection, BSP took over and managed the data transfer. Like TCP, BSP's semantics and operation were in terms of bytes; this was discarded in favour of packets for the equivalent protocol in XNS, Sequenced Packet Protocol . PUP supported a large number of applications. Some of them, such as Telnet and File Transfer Protocol , were basically
1215-451: The design work on TCP/IP, and laid a foundation for the later XNS protocols. In June and July 1973, Vint Cerf and Bob Kahn organized INWG meetings at Stanford , and Xerox Researchers Bob Metcalfe and John Shoch attended. However, the Xerox attendees were told by a Xerox lawyer that they could not talk about PUP. During design discussions, the Xerox attendees kept pointing out flaws in
1260-435: 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 the ARPANET, the network elements used to connect individual networks were called gateways , but
1305-456: The entire packet . PUP packets are up to 554 bytes long (including the 20 byte PUP header ), and the checksum. This is a smaller packet size than IP, which requires all hosts to support a minimum of 576 bytes (but allows packets of up to 65K bytes, if the hosts support them); individual PUP host pairs on a particular network might use larger packets, but no PUP router is required to handle them. Larger packets can be fragmented. A protocol named
1350-440: The host-to-IMP specification, leaving host sites to build individual host-to-host interfaces. The IMP had an error-control mechanism that discarded packets with errors without acknowledging receipt; the source IMP, upon not receiving an acknowledging receipt, would subsequently re-send a duplicate packet. Based on the requirements of ARPA's request for proposal , the IMP used a 24-bit checksum for error correction. BBN chose to make
1395-504: The ideas that were suggested, until one of the Stanford researchers blurted out, "You guys have already done this, haven’t you?" John Shoch continued to be involved in the development of TCP/IP . Ed Taft was involved in early discussions about email. The biggest impact of PUP was probably as a key component of the office of the future model first demonstrated at Xerox PARC; that demonstration would not have been anything like as powerful as it
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1440-551: The model. The Internet Protocol Suite , also known as the TCP/IP model, was not designed to conform to 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
1485-517: The more modern OSPF and IS-IS . It is still in use as an interior gateway protocol, in small sites with simple requirements. In terms of flaws, the PUP protocol family was not device independent, in modern terminology the IP and MAC layers were combined into a single layer, which made wide-scale adoption difficult. PUP's 8-bit network and 8-bit host could scale to at most 64k machines, before an inter-network bridge or gateway would be needed. For this reason,
1530-417: The name PUP only refers to the internetwork-level protocol, but it is also applied to the whole protocol suite.) The entire suite provided routing and packet delivery, as well as higher-level functions such as a reliable byte stream , along with numerous applications. The PUP protocol was created in roughly the same time frame as the earliest parts of the development of TCP/IP for the Internet and also
1575-566: 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 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
1620-546: The protocols and methods used in internetworking. The Open System Interconnection (OSI) reference model 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
1665-580: The same protocols as used on the ARPANET (much as occurred with the TCP/IP suite). Others were novel, including protocols for printer spooling, copying disk packs, page-level remote access to file servers, name lookup, remote management, etc. (although some of these capabilities had been seen before, e.g. the ARPANET already made heavy use of remote management for controlling the Interface Message Processors (IMPs) which made it up). PUP showed that internetworking ideas were feasible, influenced
1710-471: The same time period as the early Ethernet local area network at PARC. The fundamental design of the PUP suite was substantially complete by 1974. PUP was designed to connect the Ethernet to the ARPANET , which was a forerunner to TCP/IP and the Internet . It was primarily designed by Robert Metcalfe , David Boggs , Charles P. Thacker , Butler Lampson and John Shoch . In the 1980s Xerox used PUP as
1755-508: 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 a common internetwork protocol, and instead of the network being responsible for reliability, as in
1800-465: Was a ruggedized Honeywell DDP-516 minicomputer with special-purpose interfaces and software. In later years the IMPs were made from the non-ruggedized Honeywell 316 which could handle two-thirds of the communication traffic at approximately one-half the cost. An IMP requires the connection to a host computer via a special bit- serial interface, defined in BBN Report 1822 . The IMP software and
1845-420: 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 was gradually displaced by the short-form of the term internetwork, internet (lower-case i ), when
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1890-410: Was attempted, but only the first two letters could be transmitted. The SRI machine crashed upon reception of the 'g' character. A few minutes later, the bug was fixed and the login attempt was successfully completed. BBN developed a program to test the performance of the communication circuits. According to a report filed by Heart, a preliminary test in late 1969 based on a 27-hour period of activity on
1935-498: Was independently developed in early 1967 at a meeting of principal investigators for the Department of Defense's Advanced Research Projects Agency (ARPA) to discuss interconnecting machines across the country. Larry Roberts , who led the ARPANET implementation, initially proposed a network of host computers . Wes Clark suggested inserting "a small computer between each host computer and the network of transmission lines", i.e. making
1980-423: Was unclear which of the OSI model and the Internet protocol suite would result in the best and most robust computer networks. Interface Message Processors The Interface Message Processor ( IMP ) was the packet switching node used to interconnect participant networks to the ARPANET from the late 1960s to 1989. It was the first generation of gateways , which are known today as routers . An IMP
2025-401: Was without all the capabilities that a working internetwork provided. The Gateway Information Protocol's descendant, RIP (with minor modifications to carry the addresses of any protocol family), remains in use today in other protocol suites, including TCP/IP. One version of RIP served as one of the initial so-called interior gateway protocols for the growing Internet , before the arrival of
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