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102-632: Despite the different semantics of layering between the Internet protocol suite and OSI model , the link layer is sometimes described as a combination of the OSI's data link layer (layer 2) and physical layer (layer 1). The link layer is described in RFC   1122 and RFC   1123 . RFC 1122 considers local area network protocols such as Ethernet and other IEEE 802 networks (e.g. Wi-Fi ), and framing protocols such as Point-to-Point Protocol (PPP) to belong to

204-561: 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 the public switched telephone network (PSTN). As

306-535: A reliable byte stream service to its users, not datagrams . Several versions were developed through the Internet Experiment Note series. As experience with the protocol grew, collaborators recommended division of functionality into layers of distinct protocols, allowing users direct access to datagram service. Advocates included Bob Metcalfe and Yogen Dalal at Xerox PARC; Danny Cohen , who needed it for his packet voice work; and Jonathan Postel of

408-522: A router is provided with an interface to each network. It forwards network packets back and forth between them. Originally a router was called gateway , but the term was changed to avoid confusion with other types of gateways . In March 1982, the US Department of Defense declared TCP/IP as the standard for all military computer networking. In the same year, NORSAR / NDRE and Peter Kirstein 's research group at University College London adopted

510-402: 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,

612-447: 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 a single communication. A group of protocols designed to work together is known as a protocol suite; when implemented in software they are

714-639: 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

816-599: 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

918-532: A few programmers. Jay Elinsky and Oleg Vishnepolsky of IBM Research wrote TCP/IP stacks for VM/CMS and OS/2, respectively. In 1984 Donald Gillies at MIT wrote a ntcp multi-connection TCP which runs atop the IP/PacketDriver layer maintained by John Romkey at MIT in 1983–84. Romkey leveraged this TCP in 1986 when FTP Software was founded. Starting in 1985, Phil Karn created a multi-connection TCP application for ham radio systems (KA9Q TCP). The spread of TCP/IP

1020-461: A four-layer model, with the layers having names, not numbers, as follows: The protocols of the link layer operate within the scope of the local network connection to which a host is attached. This regime is called the link in TCP/IP parlance and is the lowest component layer of the suite. The link includes all hosts accessible without traversing a router. The size of the link is therefore determined by

1122-494: A hardware layer or physical layer below the link layer, and several of them adopt the OSI term data link layer instead of link layer in a modified description of layering. In the predecessor to the TCP/IP model, the ARPAnet Reference Model (RFC 908, 1982), aspects of the link layer are referred to by several poorly defined terms, such as network-access layer , network-access protocol , as well as network layer , while

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1224-429: A host is connected to. Such protocol packets are not routed to other networks. The link layer includes the protocols that define communication between local (on-link) network nodes which fulfill the purpose of maintaining link states between the local nodes, such as the local network topology, and that usually use protocols that are based on the framing of packets specific to the link types. The core protocols specified by

1326-453: 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

1428-453: 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

1530-417: 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

1632-496: A period in the late 1980s and early 1990s, engineers, organizations and nations were 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 technical standards underlying the Internet protocol suite and its constituent protocols have been delegated to the Internet Engineering Task Force (IETF). The characteristic architecture of

1734-740: A period of time. In this process, the specifics of protocol components and their layering changed. In addition, parallel research and commercial interests from industry associations competed with design features. In particular, efforts in the International Organization for Standardization led to a similar goal, but with a wider scope of networking in general. Efforts to consolidate the two principal schools of layering, which were superficially similar, but diverged sharply in detail, led independent textbook authors to formulate abridging teaching tools. The following table shows various such networking models. The number of layers varies between three and seven. Communication protocol A communication protocol

1836-554: 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

1938-457: 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

2040-481: A reliable data-link protocol such as the High-Level Data Link Control (HDLC). The User Datagram Protocol (UDP) is a connectionless datagram protocol. Like IP, it is a best-effort, unreliable protocol. Reliability is addressed through error detection using a checksum algorithm. UDP is typically used for applications such as streaming media (audio, video, Voice over IP , etc.) where on-time arrival

2142-399: A response from a range of possible responses predetermined for that particular situation. The specified behavior 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

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2244-478: 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

2346-448: A set of protocols to send its data down the layers. The data is further encapsulated at each level. An early pair of architectural documents, RFC   1122 and 1123 , titled Requirements for Internet Hosts , emphasizes architectural principles over layering. RFC 1122/23 are structured in sections referring to layers, but the documents refer to many other architectural principles, and do not emphasize layering. They loosely defines

2448-456: 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;

2550-430: 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

2652-454: A unique protocol number : for example, Internet Control Message Protocol (ICMP) and Internet Group Management Protocol (IGMP) are protocols 1 and 2, respectively. The Internet Protocol is the principal component of the internet layer, and it defines two addressing systems to identify network hosts and to locate them on the network. The original address system of the ARPANET and its successor,

2754-505: Is a system of rules that allows two or more entities of a communications system to transmit information via any variation of 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

2856-453: 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

2958-482: Is message-stream-oriented, not byte-stream-oriented like TCP, and provides multiple streams multiplexed over a single connection. It also provides multihoming support, in which a connection end can be represented by multiple IP addresses (representing multiple physical interfaces), such that if one fails, the connection is not interrupted. It was developed initially for telephony applications (to transport SS7 over IP). Reliability can also be achieved by running IP over

3060-581: Is more important than reliability, or for simple query/response applications like DNS lookups, where the overhead of setting up a reliable connection is disproportionately large. Real-time Transport Protocol (RTP) is a datagram protocol that is used over UDP and is designed for real-time data such as streaming media . The applications at any given network address are distinguished by their TCP or UDP port. By convention, certain well-known ports are associated with specific applications. The TCP/IP model's transport or host-to-host layer corresponds roughly to

3162-452: Is organized into four abstraction layers , which classify all related protocols according to each protocol's scope of networking. An implementation of the layers for a particular application forms a protocol stack . From lowest to highest, the layers are the link layer , containing communication methods for data that remains within a single network segment (link); the internet layer , providing internetworking between independent networks;

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3264-449: 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,

3366-408: 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

3468-485: The International Network Working Group , which Cerf chaired, and researchers at Xerox PARC . By the summer of 1973, Kahn and Cerf had worked out a fundamental reformulation, in which the differences between local network protocols were hidden by using a common internetwork protocol , and, instead of the network being responsible for reliability, as in the existing ARPANET protocols, this function

3570-621: The Internet Engineering Task Force (IETF) in this layer are the Address Resolution Protocol (ARP), the Reverse Address Resolution Protocol (RARP), and the Neighbor Discovery Protocol (NDP), which is a facility delivering similar functionality as ARP for IPv6 . The link layer of the TCP/IP model is often compared directly with the combination of the data link layer and the physical layer in

3672-423: 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

3774-522: The Open Systems Interconnection (OSI) protocol stack. Although they are congruent to some degree in technical coverage of protocols, they are not identical. The link layer in TCP/IP is still wider in scope and in principle a different concept and terminology of classification. This may be observed when certain protocols, such as ARP, which is confined to the link layer in the TCP/IP model, is often said to fit between OSI's data link layer and

3876-612: 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

3978-543: 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

4080-487: The transport layer , handling host-to-host communication; and the application layer , providing process-to-process data exchange for applications. The technical standards underlying the Internet protocol suite and its constituent protocols are maintained by the Internet Engineering Task Force (IETF). The Internet protocol suite predates the OSI model , a more comprehensive reference framework for general networking systems. Early research and development: Merging

4182-534: The ARPANET that used the same principle, irrespective of other local characteristics, thereby solving Kahn's initial internetworking problem. A popular expression is that TCP/IP, the eventual product of Cerf and Kahn's work, can run over "two tin cans and a string." Years later, as a joke in 1999, the IP over Avian Carriers formal protocol specification was created and successfully tested two years later. 10 years later still, it

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4284-516: The DARPA Information Processing Technology Office , where he worked on both satellite packet networks and ground-based radio packet networks, and recognized the value of being able to communicate across both. In the spring of 1973, Vinton Cerf joined Kahn with the goal of designing the next protocol generation for the ARPANET to enable internetworking . They drew on the experience from the ARPANET research community,

4386-585: The IETF has never modified this structure. As such a model of networking, the Internet protocol suite predates the OSI model, a more comprehensive reference framework for general networking systems. The end-to-end principle has evolved over time. Its original expression put the maintenance of state and overall intelligence at the edges, and assumed the Internet that connected the edges retained no state and concentrated on speed and simplicity. Real-world needs for firewalls, network address translators, web content caches and

4488-410: The Internet protocol suite is its broad division into operating scopes for the protocols that constitute its core functionality. The defining specifications of the suite are RFC 1122 and 1123, which broadly outlines four abstraction layers (as well as related protocols); the link layer, IP layer, transport layer, and application layer, along with support protocols. These have stood the test of time, as

4590-513: The Internet, is Internet Protocol version 4 (IPv4). It uses a 32-bit IP address and is therefore capable of identifying approximately four billion hosts. This limitation was eliminated in 1998 by the standardization of Internet Protocol version 6 (IPv6) which uses 128-bit addresses. IPv6 production implementations emerged in approximately 2006. The transport layer establishes basic data channels that applications use for task-specific data exchange. The layer establishes host-to-host connectivity in

4692-573: The OSI model. Application layer protocols are often associated with particular client–server applications, and common services have well-known port numbers reserved by the Internet Assigned Numbers Authority (IANA). For example, the HyperText Transfer Protocol uses server port 80 and Telnet uses server port 23. Clients connecting to a service usually use ephemeral ports , i.e., port numbers assigned only for

4794-706: 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 the National Physical Laboratory in the United Kingdom, it

4896-406: The TCP/IP model, do not discuss hardware issues and physical data transmission and set no standards for those aspects. Some textbook authors have supported the interpretation that physical data transmission aspects are part of the link layer. Others assumed that physical data transmission standards are not considered communication protocols, and are not part of the TCP/IP model. These authors assume

4998-522: The University of Southern California's Information Sciences Institute , who edited the Request for Comments (RFCs), the technical and strategic document series that has both documented and catalyzed Internet development. Postel stated, "We are screwing up in our design of Internet protocols by violating the principle of layering." Encapsulation of different mechanisms was intended to create an environment where

5100-469: The applications are usually aware of key qualities of the transport layer connection such as the endpoint IP addresses and port numbers, application layer protocols generally treat the transport layer (and lower) protocols as black boxes which provide a stable network connection across which to communicate. The transport layer and lower-level layers are unconcerned with the specifics of application layer protocols. Routers and switches do not typically examine

5202-456: 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

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5304-448: 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

5406-442: 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

5508-474: The corporate politics to get a stream of TCP/IP products for various IBM systems, including MVS , VM , and OS/2 . At the same time, several smaller companies, such as FTP Software and the Wollongong Group , began offering TCP/IP stacks for DOS and Microsoft Windows . The first VM/CMS TCP/IP stack came from the University of Wisconsin. Some of the early TCP/IP stacks were written single-handedly by

5610-414: The duration of the transaction at random or from a specific range configured in the application. At the application layer, the TCP/IP model distinguishes between user protocols and support protocols . Support protocols provide services to a system of network infrastructure. User protocols are used for actual user applications. For example, FTP is a user protocol and DNS is a support protocol. Although

5712-509: The encapsulated traffic, rather they just provide a conduit for it. However, some firewall and bandwidth throttling applications use deep packet inspection to interpret application data. An example is the Resource Reservation Protocol (RSVP). It is also sometimes necessary for Applications affected by NAT to consider the application payload. The Internet protocol suite evolved through research and development funded over

5814-673: 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

5916-464: The first Interop conference focused on network interoperability by broader adoption of TCP/IP. The conference was founded by Dan Lynch, an early Internet activist. From the beginning, large corporations, such as IBM and DEC, attended the meeting. IBM, AT&T and DEC were the first major corporations to adopt TCP/IP, this despite having competing proprietary protocols . In IBM, from 1984, Barry Appelman 's group did TCP/IP development. They navigated

6018-589: The form of end-to-end message transfer services that are independent of the underlying network and independent of the structure of user data and the logistics of exchanging information. Connectivity at the transport layer can be categorized as either connection-oriented , implemented in TCP, or connectionless , implemented in UDP. The protocols in this layer may provide error control , segmentation , flow control , congestion control , and application addressing ( port numbers ). For

6120-424: The fourth layer in the OSI model, also called the transport layer. QUIC is rapidly emerging as an alternative transport protocol. Whilst it is technically carried via UDP packets it seeks to offer enhanced transport connectivity relative to TCP. HTTP/3 works exclusively via QUIC. The application layer includes the protocols used by most applications for providing user services or exchanging application data over

6222-426: 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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6324-643: 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

6426-410: The involvement of service discovery or directory services . Because IP provides only a best-effort delivery , some transport-layer protocols offer reliability. TCP is a connection-oriented protocol that addresses numerous reliability issues in providing a reliable byte stream : The newer Stream Control Transmission Protocol (SCTP) is also a reliable, connection-oriented transport mechanism. It

6528-476: 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

6630-427: 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

6732-407: The like have forced changes in this principle. The robustness principle states: "In general, an implementation must be conservative in its sending behavior, and liberal in its receiving behavior. That is, it must be careful to send well-formed datagrams, but must accept any datagram that it can interpret (e.g., not object to technical errors where the meaning is still clear)." "The second part of

6834-404: The link layer. Local area networking standards such as Ethernet and IEEE 802.3 specifications use terminology from the seven-layer OSI model rather than the TCP/IP model. The TCP/IP model, in general, does not consider physical specifications, rather it assumes a working network infrastructure that can deliver media-level frames on the link. Therefore, RFC 1122 and RFC 1123, the definition of

6936-402: 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

7038-511: The network addressing methods used in the Internet Protocol to link-layer addresses, such as media access control (MAC) addresses. All other aspects below that level, however, are implicitly assumed to exist and are not explicitly defined in the TCP/IP model. The link layer in the TCP/IP model has corresponding functions in Layer 2 of the OSI model. Internetworking requires sending data from

7140-935: The network connections established by the lower-level protocols. This may include some basic network support services such as routing protocols and host configuration. Examples of application layer protocols include the Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP), the Simple Mail Transfer Protocol (SMTP), and the Dynamic Host Configuration Protocol (DHCP). Data coded according to application layer protocols are encapsulated into transport layer protocol units (such as TCP streams or UDP datagrams), which in turn use lower layer protocols to effect actual data transfer. The TCP/IP model does not consider

7242-483: The network included the recognition that it should provide only the functions of efficiently transmitting and routing traffic between end nodes and that all other intelligence should be located at the edge of the network, in the end nodes. This end-to-end principle was pioneered by Louis Pouzin in the CYCLADES network, based on the ideas of Donald Davies . Using this design, it became possible to connect other networks to

7344-523: The network layer. In general, direct or strict comparisons should be avoided, because the layering in TCP/IP is not a principal design criterion and in general, is considered to be "harmful" (RFC 3439). Another term sometimes encountered, network access layer , tries to suggest the closeness of this layer to the physical network. However, this use is misleading and non-standard, since the link layer implies functions that are wider in scope than just network access. Important link layer protocols are used to probe

7446-404: The networking hardware design. In principle, TCP/IP is designed to be hardware independent and may be implemented on top of virtually any link-layer technology. This includes not only hardware implementations but also virtual link layers such as virtual private networks and networking tunnels . The link layer is used to move packets between the internet layer interfaces of two different hosts on

7548-637: The networks and creating the Internet: Commercialization, privatization, broader access leads to the modern Internet: Examples of Internet services: Initially referred to as the DOD Internet Architecture Model , the Internet protocol suite has its roots in research and development sponsored by the Defense Advanced Research Projects Agency ( DARPA ) in the late 1960s. After DARPA initiated

7650-403: The next higher layer is called internetwork layer . In some modern textbooks, network-interface layer , host-to-network layer and network-access layer occur as synonyms either to the link layer or the data link layer, often including the physical layer. The link layer in the TCP/IP model is a descriptive realm of networking protocols that operate only on the local network segment (link) that

7752-415: 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

7854-483: The pioneering ARPANET in 1969, Steve Crocker established a "Networking Working Group" which developed a host-host protocol, the Network Control Program (NCP). In the early 1970s, DARPA started work on several other data transmission technologies, including mobile packet radio, packet satellite service, local area networks, and other data networks in the public and private domains. In 1972, Bob Kahn joined

7956-457: 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

8058-409: The principle is almost as important: software on other hosts may contain deficiencies that make it unwise to exploit legal but obscure protocol features." Encapsulation is used to provide abstraction of protocols and services. Encapsulation is usually aligned with the division of the protocol suite into layers of general functionality. In general, an application (the highest level of the model) uses

8160-540: The protocol that is still in use in the Internet, alongside its current successor, Internet Protocol version 6 (IPv6). In 1975, a two-network IP communications test was performed between Stanford and University College London. In November 1977, a three-network IP test was conducted between sites in the US, the UK, and Norway . Several other IP prototypes were developed at multiple research centers between 1978 and 1983. A computer called

8262-401: 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

8364-526: 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

8466-494: The protocol. The migration of the ARPANET from NCP to TCP/IP was officially completed on flag day January 1, 1983, when the new protocols were permanently activated. In 1985, the Internet Advisory Board (later Internet Architecture Board ) held a three-day TCP/IP workshop for the computer industry, attended by 250 vendor representatives, promoting the protocol and leading to its increasing commercial use. In 1985,

8568-415: The purpose of providing process-specific transmission channels for applications, the layer establishes the concept of the network port . This is a numbered logical construct allocated specifically for each of the communication channels an application needs. For many types of services, these port numbers have been standardized so that client computers may address specific services of a server computer without

8670-435: The responsibility of sending packets across potentially multiple networks. With this functionality, the internet layer makes possible internetworking, the interworking of different IP networks, and it essentially establishes the Internet. The internet layer does not distinguish between the various transport layer protocols. IP carries data for a variety of different upper layer protocols . These protocols are each identified by

8772-443: The same link. The processes of transmitting and receiving packets on the link can be controlled in the device driver for the network card , as well as in firmware or by specialized chipsets . These perform functions, such as framing, to prepare the internet layer packets for transmission, and finally transmit the frames to the physical layer and over a transmission medium . The TCP/IP model includes specifications for translating

8874-435: The source network to the destination network. This process is called routing and is supported by host addressing and identification using the hierarchical IP addressing system. The internet layer provides an unreliable datagram transmission facility between hosts located on potentially different IP networks by forwarding datagrams to an appropriate next-hop router for further relaying to its destination. The internet layer has

8976-461: The specifics of formatting and presenting data and does not define additional layers between the application and transport layers as in the OSI model (presentation and session layers). According to the TCP/IP model, such functions are the realm of libraries and application programming interfaces . The application layer in the TCP/IP model is often compared to a combination of the fifth (session), sixth (presentation), and seventh (application) layers of

9078-697: The suite are the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Internet Protocol (IP). Early versions of this networking model were known as the Department of Defense ( DoD ) model because the research and development were funded by the United States Department of Defense through DARPA . The Internet protocol suite provides end-to-end data communication specifying how data should be packetized, addressed, transmitted, routed , and received. This functionality

9180-461: 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

9282-413: The topology of the local network, and discover routers and neighboring hosts, i.e. functions that go well beyond network access. Internet protocol suite The Internet protocol suite , commonly known as TCP/IP , is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in

9384-506: 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

9486-406: 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

9588-477: The upper layers could access only what was needed from the lower layers. A monolithic design would be inflexible and lead to scalability issues. In version 4 , written in 1978, Postel split the Transmission Control Program into two distinct protocols, the Internet Protocol as connectionless layer and the Transmission Control Protocol as a reliable connection-oriented service . The design of

9690-513: Was adapted for IPv6. DARPA contracted with BBN Technologies , Stanford University , and the University College London to develop operational versions of the protocol on several hardware platforms. During development of the protocol the version number of the packet routing layer progressed from version 1 to version 4, the latter of which was installed in the ARPANET in 1983. It became known as Internet Protocol version 4 (IPv4) as

9792-461: Was delegated to the hosts. Cerf credits Louis Pouzin and Hubert Zimmermann , designers of the CYCLADES network, with important influences on this design. The new protocol was implemented as the Transmission Control Program in 1974 by Cerf, Yogen Dalal and Carl Sunshine. Initially, the Transmission Control Program (the Internet Protocol did not then exist as a separate protocol) provided only

9894-415: 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

9996-582: Was fueled further in June 1989, when the University of California, Berkeley agreed to place the TCP/IP code developed for BSD UNIX into the public domain. Various corporate vendors, including IBM, included this code in commercial TCP/IP software releases. For Windows 3.1, the dominant PC operating system among consumers in the first half of the 1990s, Peter Tattam's release of the Trumpet Winsock TCP/IP stack

10098-800: Was key to bringing the Internet to home users. Trumpet Winsock allowed TCP/IP operations over a serial connection ( SLIP or PPP ). The typical home PC of the time had an external Hayes-compatible modem connected via an RS-232 port with an 8250 or 16550 UART which required this type of stack. Later, Microsoft would release their own TCP/IP add-on stack for Windows for Workgroups 3.11 and a native stack in Windows 95. These events helped cement TCP/IP's dominance over other protocols on Microsoft-based networks, which included IBM's Systems Network Architecture (SNA), and on other platforms such as Digital Equipment Corporation 's DECnet , Open Systems Interconnection (OSI), and Xerox Network Systems (XNS). Nonetheless, for

10200-580: 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

10302-516: 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

10404-457: 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 ,

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