67-455: DIXIE is an obsolete protocol for accessing X.500 directory services. DIXIE was intended to provide a lightweight means for clients to access X.500 directory services. DIXIE allowed TCP/IP clients to connect a DIXIE-to-DAP gateway which would provide access to the X.500 Directory Service. This design allows the client to access the directory without requiring it to support the cumbersome Open Systems Interconnection protocol stack. DIXIE
134-489: A physical quantity . The protocol defines the rules, syntax , semantics , and synchronization of communication and possible error recovery methods . Protocols may be implemented by hardware , software , or a combination of both. Communicating systems use well-defined formats for exchanging various messages. Each message has an exact meaning intended to elicit a response from a range of possible responses predetermined for that particular situation. The specified behavior
201-402: A tunneling arrangement to accommodate the connection of dissimilar networks. For example, IP may be tunneled across an Asynchronous Transfer Mode (ATM) network. Protocol layering forms the basis of protocol design. It allows the decomposition of single, complex protocols into simpler, cooperating protocols. The protocol layers each solve a distinct class of communication problems. Together,
268-639: A coarse hierarchy of functional layers defined in the Internet Protocol Suite . The first two cooperating protocols, the Transmission Control Protocol (TCP) and the Internet Protocol (IP) resulted from the decomposition of the original Transmission Control Program, a monolithic communication protocol, into this layered communication suite. The OSI model was developed internationally based on experience with networks that predated
335-599: A computer environment (such as ease of mechanical parsing and improved bandwidth utilization ). Network applications have various methods of encapsulating data. One method very common with Internet protocols is a text oriented representation that transmits requests and responses as lines of ASCII text, terminated by a newline character (and usually a carriage return character). Examples of protocols that use plain, human-readable text for its commands are FTP ( File Transfer Protocol ), SMTP ( Simple Mail Transfer Protocol ), early versions of HTTP ( Hypertext Transfer Protocol ), and
402-551: A de facto standard operating system like Linux does not have this negative grip on its market, because the sources are published and maintained in an open way, thus inviting competition. NPL network Early research and development: Merging the networks and creating the Internet: Commercialization, privatization, broader access leads to the modern Internet: Examples of Internet services: The NPL network , or NPL Data Communications Network ,
469-453: A machine rather than a human being. Binary protocols have the advantage of terseness, which translates into speed of transmission and interpretation. Binary have been used in the normative documents describing modern standards like EbXML , HTTP/2 , HTTP/3 and EDOC . An interface in UML may also be considered a binary protocol. Getting the data across a network is only part of the problem for
536-453: A networking protocol, the protocol software modules are interfaced with a framework implemented on the machine's operating system. This framework implements the networking functionality of the operating system. When protocol algorithms are expressed in a portable programming language the protocol software may be made operating system independent. The best-known frameworks are the TCP/IP model and
603-487: A number of user systems ( time-sharing computers and other users ) and for communicating with "high level network". The latter would be constructed with "switching nodes" connected together with megabit rate circuits ( T1 links, which run with a 1.544 Mbit/s line rate). In Scantlebury's report following the conference, he noted "It would appear that the ideas in the NPL paper at the moment are more advanced than any proposed in
670-417: A packet-switched network, rather than this being a service of the network itself. His team was the first to tackle the highly complex problem of providing user applications with a reliable virtual circuit service while using a best-effort service , an early contribution to what will be the Transmission Control Protocol (TCP). Bob Metcalfe and others at Xerox PARC outlined the idea of Ethernet and
737-554: A protocol. The data received has to be evaluated in the context of the progress of the conversation, so a protocol must include rules describing the context. These kinds of rules are said to express the syntax of the communication. Other rules determine whether the data is meaningful for the context in which the exchange takes place. These kinds of rules are said to express the semantics of the communication. Messages are sent and received on communicating systems to establish communication. Protocols should therefore specify rules governing
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#1732854783287804-554: A reference model for communication standards led to the OSI model , published in 1984. For a period in the late 1980s and early 1990s, engineers, organizations and nations became polarized over the issue of which standard , the OSI model or the Internet protocol suite, would result in the best and most robust computer networks. The information exchanged between devices through a network or other media
871-478: A set of cooperating processes that manipulate shared data to communicate with each other. This communication is governed by well-understood protocols, which can be embedded in the process code itself. In contrast, because there is no shared memory , communicating systems have to communicate with each other using a shared transmission medium . Transmission is not necessarily reliable, and individual systems may use different hardware or operating systems. To implement
938-649: A single communication. A group of protocols designed to work together is known as a protocol suite; when implemented in software they are a protocol stack . Internet communication protocols are published by the Internet Engineering Task Force (IETF). The IEEE (Institute of Electrical and Electronics Engineers) handles wired and wireless networking and the International Organization for Standardization (ISO) handles other types. The ITU-T handles telecommunications protocols and formats for
1005-456: A standardization process. Such protocols are referred to as de facto standards . De facto standards are common in emerging markets, niche markets, or markets that are monopolized (or oligopolized ). They can hold a market in a very negative grip, especially when used to scare away competition. From a historical perspective, standardization should be seen as a measure to counteract the ill-effects of de facto standards. Positive exceptions exist;
1072-430: A transfer mechanism of a protocol is comparable to a central processing unit (CPU). The framework introduces rules that allow the programmer to design cooperating protocols independently of one another. In modern protocol design, protocols are layered to form a protocol stack. Layering is a design principle that divides the protocol design task into smaller steps, each of which accomplishes a specific part, interacting with
1139-453: Is governed by rules and conventions that can be set out in communication protocol specifications. The nature of communication, the actual data exchanged and any state -dependent behaviors, is defined by these specifications. In digital computing systems, the rules can be expressed by algorithms and data structures . Protocols are to communication what algorithms or programming languages are to computations. Operating systems usually contain
1206-449: Is referred to as communicating sequential processes (CSP). Concurrency can also be modeled using finite state machines , such as Mealy and Moore machines . Mealy and Moore machines are in use as design tools in digital electronics systems encountered in the form of hardware used in telecommunication or electronic devices in general. The literature presents numerous analogies between computer communication and programming. In analogy,
1273-408: Is the synchronization of software for receiving and transmitting messages of communication in proper sequencing. Concurrent programming has traditionally been a topic in operating systems theory texts. Formal verification seems indispensable because concurrent programs are notorious for the hidden and sophisticated bugs they contain. A mathematical approach to the study of concurrency and communication
1340-594: Is typically independent of how it is to be implemented . Communication protocols have to be agreed upon by the parties involved. To reach an agreement, a protocol may be developed into a technical standard . A programming language describes the same for computations, so there is a close analogy between protocols and programming languages: protocols are to communication what programming languages are to computations . An alternate formulation states that protocols are to communication what algorithms are to computation . Multiple protocols often describe different aspects of
1407-665: The European Informatics Network (EIN) in 1976. In 1976, 12 computers and 75 terminal devices were attached, and more were added. The network remained in operation until 1986. The first use of the term protocol in a modern data-commutations context occurs in a memorandum entitled A Protocol for Use in the NPL Data Communications Network written by Roger Scantlebury and Keith Bartlett in April 1967. A further publication by Bartlett in 1968 introduced
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#17328547832871474-590: The IMP team working for Bolt Beranek & Newman . The CYCLADES network designed by Louis Pouzin at the IRIA in France built on the work of Donald Davies and pioneered important improvements to the ARPANET design. Moreover, in the view of some, the research and development of internetworking , and TCP/IP in particular (which was sponsored by DARPA), marks the true beginnings of
1541-507: The Lightweight Directory Access Protocol . LDAP replaced DIXIE. When created, the acronym DIXIE did not stand for anything, however later it became known to stand for D irectory I nterface to X .500 I mplemented E fficiently. Communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any variation of
1608-694: The National Physical Laboratory in the United Kingdom, it was written by Roger Scantlebury and Keith Bartlett for the NPL network . On the ARPANET , the starting point for host-to-host communication in 1969 was the 1822 protocol , written by Bob Kahn , which defined the transmission of messages to an IMP. The Network Control Program (NCP) for the ARPANET, developed by Steve Crocker and other graduate students including Jon Postel and Vint Cerf ,
1675-423: The OSI model . At the time the Internet was developed, abstraction layering had proven to be a successful design approach for both compiler and operating system design and, given the similarities between programming languages and communication protocols, the originally monolithic networking programs were decomposed into cooperating protocols. This gave rise to the concept of layered protocols which nowadays forms
1742-612: The PARC Universal Packet (PUP) for internetworking. Research in the early 1970s by Bob Kahn and Vint Cerf led to the formulation of the Transmission Control Program (TCP). Its RFC 675 specification was written by Cerf with Yogen Dalal and Carl Sunshine in December 1974, still a monolithic design at this time. The International Network Working Group agreed on a connectionless datagram standard which
1809-543: The finger protocol . Text-based protocols are typically optimized for human parsing and interpretation and are therefore suitable whenever human inspection of protocol contents is required, such as during debugging and during early protocol development design phases. A binary protocol utilizes all values of a byte , as opposed to a text-based protocol which only uses values corresponding to human-readable characters in ASCII encoding. Binary protocols are intended to be read by
1876-447: The public switched telephone network (PSTN). As the PSTN and Internet converge , the standards are also being driven towards convergence. The first use of the term protocol in a modern data-commutation context occurs in April 1967 in a memorandum entitled A Protocol for Use in the NPL Data Communications Network. Under the direction of Donald Davies , who pioneered packet switching at
1943-609: The "lack of standard access interfaces for emerging public packet-switched communication networks is creating 'some kind of monster' for users". For a long period of time, the network engineering community was polarized over the implementation of competing protocol suites, commonly known as the Protocol Wars . It was unclear which type of protocol would result in the best and most robust computer networks. Derek Barber proposed an electronic mail protocol in 1979 in INWG 192 and implemented it on
2010-531: The EIN. This was referenced by Jon Postel in his early work on Internet email, published in the Internet Experiment Note series. Davies' later research at NPL focused on data security for computer networks. The concepts of packet switching, high-speed routers, layered communication protocols, hierarchical computer networks, and the essence of the end-to-end principle that were researched and developed at
2077-512: The NPL became fundamental to data communication in modern computer networks including the Internet . Beyond NPL, and the designs of Paul Baran at RAND, DARPA was the most important institutional force, creating the ARPANET, the first wide-area packet-switched network, to which many other network designs at the time were compared or replicated. The ARPANET's routing, flow control, software design and network control were developed independently by
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2144-650: The Post Office Experimental Packet Switched Service used a common host protocol in both networks. This work confirmed establishing a common host protocol would be more reliable and efficient. Davies and Barber published Communication networks for computers in 1973 and Computer networks and their protocols in 1979. They spoke at the Data Communications Symposium in 1975 about the "battle for access standards" between datagrams and virtual circuits , with Barber saying
2211-488: The USA". The first theoretical foundation of packet switching was the work of Paul Baran , at RAND , in which data was transmitted in small chunks and routed independently by a method similar to store-and-forward techniques between intermediate networking nodes. Davies independently arrived at the same model in 1965 and named it packet switching . He chose the term "packet" after consulting with an NPL linguist because it
2278-520: The United Kingdom based on packet switching in Proposal for the Development of a National Communications Service for On-line Data Processing . The following year, he refined his ideas in Proposal for the Development of a National Communications Service for OnLine Data Processing . The design was the first to describe the concept of an "interface computer", today known as a router . A written version of
2345-456: The approval or support of a standards organization , which initiates the standardization process. The members of the standards organization agree to adhere to the work result on a voluntary basis. Often the members are in control of large market shares relevant to the protocol and in many cases, standards are enforced by law or the government because they are thought to serve an important public interest, so getting approval can be very important for
2412-448: The basis of protocol design. Systems typically do not use a single protocol to handle a transmission. Instead they use a set of cooperating protocols, sometimes called a protocol suite . Some of the best-known protocol suites are TCP/IP , IPX/SPX , X.25 , AX.25 and AppleTalk . The protocols can be arranged based on functionality in groups, for instance, there is a group of transport protocols . The functionalities are mapped onto
2479-483: The chair of INWG in 1976. He proposed and implemented a mail protocol for EIN. NPL investigated the "basic dilemma" involved in internetworking; that is, a common host protocol would require restructuring existing networks if they were not designed to use the same protocol. NPL connected with the European Informatics Network by translating between two different host protocols while the NPL connection to
2546-488: The concept of an alternating bit protocol (later used by the ARPANET and the EIN) and described the need for three levels of data transmission, roughly corresponding to the lower levels of the seven-layer OSI model that emerged a decade later. The Mark II version, which operated from 1973, used such a "layered" protocol architecture. The NPL team also introduced the idea of protocol verification . Protocol verification
2613-442: The content being carried: text-based and binary. A text-based protocol or plain text protocol represents its content in human-readable format , often in plain text encoded in a machine-readable encoding such as ASCII or UTF-8 , or in structured text-based formats such as Intel hex format , XML or JSON . The immediate human readability stands in contrast to native binary protocols which have inherent benefits for use in
2680-673: The field of computer networking, it has been historically criticized by many researchers as abstracting the protocol stack in this way may cause a higher layer to duplicate the functionality of a lower layer, a prime example being error recovery on both a per-link basis and an end-to-end basis. Commonly recurring problems in the design and implementation of communication protocols can be addressed by software design patterns . Popular formal methods of describing communication syntax are Abstract Syntax Notation One (an ISO standard) and augmented Backus–Naur form (an IETF standard). Finite-state machine models are used to formally describe
2747-426: The horizontal message flows (and protocols) are between systems. The message flows are governed by rules, and data formats specified by protocols. The blue lines mark the boundaries of the (horizontal) protocol layers. The software supporting protocols has a layered organization and its relationship with protocol layering is shown in figure 5. To send a message on system A, the top-layer software module interacts with
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2814-643: The internet as a reference model for general communication with much stricter rules of protocol interaction and rigorous layering. Typically, application software is built upon a robust data transport layer. Underlying this transport layer is a datagram delivery and routing mechanism that is typically connectionless in the Internet. Packet relaying across networks happens over another layer that involves only network link technologies, which are often specific to certain physical layer technologies, such as Ethernet . Layering provides opportunities to exchange technologies when needed, for example, protocols are often stacked in
2881-476: The layers make up a layering scheme or model. Computations deal with algorithms and data; Communication involves protocols and messages; So the analog of a data flow diagram is some kind of message flow diagram. To visualize protocol layering and protocol suites, a diagram of the message flows in and between two systems, A and B, is shown in figure 3. The systems, A and B, both make use of the same protocol suite. The vertical flows (and protocols) are in-system and
2948-427: The layers, each layer solving a distinct class of problems relating to, for instance: application-, transport-, internet- and network interface-functions. To transmit a message, a protocol has to be selected from each layer. The selection of the next protocol is accomplished by extending the message with a protocol selector for each layer. There are two types of communication protocols, based on their representation of
3015-491: The local-area network began in 1968 using a Honeywell 516 node. The NPL team liaised with Honeywell in the adaptation of the DDP516 input/output controller, and, the following year, the ARPANET chose the same computer to serve as Interface Message Processors (IMPs). Elements of the first version of the network, Mark I NPL Network, became operational in early 1969 (before the ARPANET installed its first node). The network
3082-402: The module directly below it and hands over the message to be encapsulated. The lower module fills in the header data in accordance with the protocol it implements and interacts with the bottom module which sends the message over the communications channel to the bottom module of system B. On the receiving system B the reverse happens, so ultimately the message gets delivered in its original form to
3149-415: The other parts of the protocol only in a small number of well-defined ways. Layering allows the parts of a protocol to be designed and tested without a combinatorial explosion of cases, keeping each design relatively simple. The communication protocols in use on the Internet are designed to function in diverse and complex settings. Internet protocols are designed for simplicity and modularity and fit into
3216-457: The possible interactions of the protocol. and communicating finite-state machines For communication to occur, protocols have to be selected. The rules can be expressed by algorithms and data structures. Hardware and operating system independence is enhanced by expressing the algorithms in a portable programming language. Source independence of the specification provides wider interoperability. Protocol standards are commonly created by obtaining
3283-493: The proposal entitled A digital communications network for computers giving rapid response at remote terminals was presented by Roger Scantlebury at the Symposium on Operating Systems Principles in 1967. The design involved transmitting signals ( packets ) across a network with a hierarchical structure. It was proposed that "local networks" be constructed with interface computers which had responsibility for multiplexing among
3350-401: The protocol, creating incompatible versions on their networks. In some cases, this was deliberately done to discourage users from using equipment from other manufacturers. There are more than 50 variants of the original bi-sync protocol. One can assume, that a standard would have prevented at least some of this from happening. In some cases, protocols gain market dominance without going through
3417-526: The protocol. The need for protocol standards can be shown by looking at what happened to the Binary Synchronous Communications (BSC) protocol invented by IBM . BSC is an early link-level protocol used to connect two separate nodes. It was originally not intended to be used in a multinode network, but doing so revealed several deficiencies of the protocol. In the absence of standardization, manufacturers and organizations felt free to enhance
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#17328547832873484-427: The technical foundations of the modern Internet . Beginning in late 1966, Davies' tasked Derek Barber, his deputy, to establish a team to build a local-area network to serve the needs of NPL and prove the feasibility of packet switching. The team consisted of: The team worked through 1967 to produce design concepts for a wide-area network and a local-area network to demonstrate the technology. Construction of
3551-510: The top module of system B. Program translation is divided into subproblems. As a result, the translation software is layered as well, allowing the software layers to be designed independently. The same approach can be seen in the TCP/IP layering. The modules below the application layer are generally considered part of the operating system. Passing data between these modules is much less expensive than passing data between an application program and
3618-506: The transmission. In general, much of the following should be addressed: Systems engineering principles have been applied to create a set of common network protocol design principles. The design of complex protocols often involves decomposition into simpler, cooperating protocols. Such a set of cooperating protocols is sometimes called a protocol family or a protocol suite, within a conceptual framework. Communicating systems operate concurrently. An important aspect of concurrent programming
3685-406: The transport layer. The boundary between the application layer and the transport layer is called the operating system boundary. Strictly adhering to a layered model, a practice known as strict layering, is not always the best approach to networking. Strict layering can have a negative impact on the performance of an implementation. Although the use of protocol layering is today ubiquitous across
3752-416: The world. Larry Roberts incorporated these concepts into the design for the ARPANET . The NPL network initially proposed a line speed of 768 kbit/s . Influenced by this, the planned line speed for ARPANET was upgraded from 2.4 kbit/s to 50 kbit/s and a similar packet format adopted. Louis Pouzin's CYCLADES project in France was also influenced by Davies' work. These networks laid down
3819-630: Was a local area computer network operated by a team from the National Physical Laboratory (NPL) in London that pioneered the concept of packet switching . Based on designs first conceived by Donald Davies in 1965, development work began in 1966. Construction began in 1968 and elements of the first version of the network, the Mark I, became operational in early 1969 then fully operational in January 1970. The Mark II version operated from 1973 until 1986. The NPL network
3886-500: Was a testbed for internetworking research throughout the 1970s. Davies, Scantlebury and Barber were active members of the International Network Working Group (INWG) formed in 1972. Vint Cerf and Bob Kahn acknowledged Davies and Scantlebury in their 1974 paper A Protocol for Packet Network Intercommunication, which DARPA developed into the Internet protocol suite used in the modern Internet . Barber
3953-502: Was appointed director of the European COST 11 project and played a leading part in the European Informatics Network (EIN). Scantlebury led the UK technical contribution, reporting directly to Donald Davies. The EIN protocol helped to launch the INWG and X.25 protocols. INWG proposed an international end to end protocol in 1975/6, although this was not widely adopted. Barber became
4020-644: Was capable of being translated into languages other than English without compromise. In July 1968, NPL put on a demonstration of real and simulated networks at an event organised by the Real Time Club at the Royal Festival Hall in London. Davies gave the first public presentation of packet switching on 5 August 1968 at the IFIP Congress in Edinburgh. Davies' original ideas influenced other research around
4087-515: Was created in 1990 at the University of Michigan by Tim Howes , Mark Smith, and Bryan Beecher . DIXIE was formally specified in RFC 1249, published in 1991. The university offered a completed UNIX implementation of the protocol, including a DIXIE server, an application development library, and DIXIE clients. A DIXIE client for Apple Macintosh was also provided. These efforts led to the development of
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#17328547832874154-652: Was discussed in the November 1978 special edition of the Proceedings of the IEEE on packet switching. The NPL team also carried out simulation work on the performance of wide-area packet networks, studying datagrams and network congestion . This work was carried out to investigate networks of a size capable of providing data communications facilities to most of the U.K. Davies proposed an adaptive method of congestion control that he called isarithmic . The NPL network
4221-415: Was first implemented in 1970. The NCP interface allowed application software to connect across the ARPANET by implementing higher-level communication protocols, an early example of the protocol layering concept. The CYCLADES network, designed by Louis Pouzin in the early 1970s was the first to implement the end-to-end principle , and make the hosts responsible for the reliable delivery of data on
4288-468: Was fully operational in January 1970. The local-area NPL network followed by the wide-area ARPANET in the United States were the first two computer networks that implemented packet switching. The network used high-speed links, the first computer network to do so. The NPL network was later interconnected with other networks, including the Post Office Experimental Packet Switched Service (EPSS) and
4355-580: Was presented to the CCITT in 1975 but was not adopted by the CCITT nor by the ARPANET. Separate international research, particularly the work of Rémi Després , contributed to the development of the X.25 standard, based on virtual circuits , which was adopted by the CCITT in 1976. Computer manufacturers developed proprietary protocols such as IBM's Systems Network Architecture (SNA), Digital Equipment Corporation's DECnet and Xerox Network Systems . TCP software
4422-466: Was redesigned as a modular protocol stack, referred to as TCP/IP. This was installed on SATNET in 1982 and on the ARPANET in January 1983. The development of a complete Internet protocol suite by 1989, as outlined in RFC 1122 and RFC 1123 , laid the foundation for the growth of TCP/IP as a comprehensive protocol suite as the core component of the emerging Internet . International work on
4489-527: Was the first computer network to implement packet switching and NPL was the first to use high-speed links. Its original design, along with the innovations implemented in the ARPANET and the CYCLADES network, laid down the technical foundations of the modern Internet . In 1965, Donald Davies , who was later appointed to head of the NPL Division of Computer Science, proposed a commercial national data network in
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