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{{short description|Framework for communication protocols used in IP networking}}
{{About|the protocols that make up the Internet architecture|the IP network protocol only|Internet Protocol}}
{{Use American English|date=October 2020}}
{{Use mdy dates|date=October 2020}}

{{IPstack}}

The '''Internet protocol suite''', commonly known as '''TCP/IP''', is a framework for organizing the [[communication protocol]]s used in the [[Internet]] and similar [[computer network]]s according to functional criteria. The foundational protocols in 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 principle|end-to-end data communication]] specifying how data should be packetized, addressed, transmitted, [[routed]], and received. This functionality is organized into four [[abstraction layer]]s, which classify all related protocols according to each protocol's scope of networking.{{Ref RFC|1122}}{{Ref RFC|1123}} 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; the [[transport layer]], handling host-to-host communication; and the [[application layer]], providing process-to-process data exchange for applications.

The [[technical standard]]s 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.

==History==
{{Further|History of the Internet}}
{{Internet history timeline}}

===Early research===
[[File:SRI First Internetworked Connection diagram.jpg|thumb|right|Diagram of the first internetworked connection]]
[[File:SRI Packet Radio Van.jpg|thumb|right|An [[SRI International]] [[Packet Radio Van]], used for the first three-way [[internetworked]] transmission]]
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.<ref name="Cerf DoD">{{cite journal|title=The DoD Internet Architecture Model|first1=Vinton G.|last1=Cerf|first2=Edward|last2=Cain|name-list-style=amp|journal=Computer Networks|volume=7|issue=5|date=October 1983|publisher=North-Holland|doi=10.1016/0376-5075(83)90042-9|pages=307–318}}</ref> After DARPA initiated the pioneering [[ARPANET]] in 1969, [[Steve Crocker]] established a "Networking Working Group" which developed a host-host protocol, the [[Network Control Program (ARPANET)|Network Control Program]] (NCP).{{Ref RFC|1000}} 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 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]].<ref>{{Cite book |last1=Hafner |first1=Katie |url=http://archive.org/details/wherewizardsstay00haf_vgj |title=Where wizards stay up late : the origins of the Internet |last2=Lyon |first2=Matthew |date=1996 |publisher=New York : Simon & Schuster |others=Internet Archive |isbn=978-0-684-81201-4 |page=263}}</ref><ref name=":0">{{cite book |last1=Russell |first1=Andrew L. |url=https://books.google.com/books?id=jqroAgAAQBAJ&pg=PA196 |title=Open standards and the digital age: history, ideology, and networks |date=2014 |publisher=Cambridge Univ Press |isbn=978-1107039193 |location=New York |page=196 |access-date=December 20, 2022 |archive-date=December 28, 2022 |archive-url=https://web.archive.org/web/20221228072845/https://books.google.com/books?id=jqroAgAAQBAJ&pg=PA196 |url-status=live }}</ref> They drew on the experience from the ARPANET research community, the [[International Network Working Group]], which Cerf chaired, and researchers at [[Xerox PARC]].<ref name="ZVVpe">{{Cite book|last=Abbate|first=Janet|author-link=Janet Abbate|url=https://books.google.com/books?id=E2BdY6WQo4AC&pg=PA123|title=Inventing the Internet|date=2000|publisher=MIT Press|isbn=978-0-262-51115-5|pages=123–4|language=en|access-date=May 15, 2020|archive-date=January 17, 2023|archive-url=https://web.archive.org/web/20230117175132/https://books.google.com/books?id=E2BdY6WQo4AC&pg=PA123|url-status=live}}</ref><ref>{{Citation |last=Taylor |first=Bob |title=Oral History of Robert (Bob) W. Taylor |date=October 11, 2008 |url=http://archive.computerhistory.org/resources/access/text/2013/05/102702015-05-01-acc.pdf |journal=Computer History Museum Archive |volume=CHM Reference number: X5059.2009 |page=28}}</ref><ref>{{Cite book |last=Isaacson |first=Walter |url=http://archive.org/details/innovatorshowgro0000isaa_p2p3 |title=The innovators : how a group of hackers, geniuses, and geeks created the digital revolution |date=2014 |publisher=New York : Simon & Schuster |others=Internet Archive |isbn=978-1-4767-0869-0}}</ref>

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 was delegated to the hosts. Cerf credits [[Louis Pouzin]] and [[Hubert Zimmermann]], designers of the [[CYCLADES]] network, with important influences on this design.<ref name="YSZAX">{{Cite journal|last1=Cerf|first1=V.|last2=Kahn|first2=R.|date=1974|title=A Protocol for Packet Network Intercommunication|url=https://www.cs.princeton.edu/courses/archive/fall06/cos561/papers/cerf74.pdf|journal=IEEE Transactions on Communications|volume=22|issue=5|pages=637–648|doi=10.1109/TCOM.1974.1092259|issn=1558-0857|quote=The authors wish to thank a number of colleagues for helpful comments during early discussions of international network protocols, especially R. Metcalfe, R. Scantlebury, D. Walden, and H. Zimmerman; D. Davies and L. Pouzin who constructively commented on the fragmentation and accounting issues; and S. Crocker who commented on the creation and destruction of associations.|access-date=October 18, 2015|archive-date=October 10, 2022|archive-url=https://ghostarchive.org/archive/20221010/https://www.cs.princeton.edu/courses/archive/fall06/cos561/papers/cerf74.pdf|url-status=live}}</ref><ref name="MevuR">{{cite news|date=13 December 2013|title=The internet's fifth man|work=Economist|url=https://www.economist.com/news/technology-quarterly/21590765-louis-pouzin-helped-create-internet-now-he-campaigning-ensure-its|access-date=11 September 2017|quote=In the early 1970s Mr Pouzin created an innovative data network that linked locations in France, Italy and Britain. Its simplicity and efficiency pointed the way to a network that could connect not just dozens of machines, but millions of them. It captured the imagination of Dr Cerf and Dr Kahn, who included aspects of its design in the protocols that now power the internet.|archive-date=April 19, 2020|archive-url=https://web.archive.org/web/20200419230318/https://www.economist.com/news/technology-quarterly/21590765-louis-pouzin-helped-create-internet-now-he-campaigning-ensure-its|url-status=live}}</ref> The new protocol was implemented as the [[Transmission Control Program]] in 1974 by Cerf, [[Yogen Dalal]] and Carl Sunshine.{{Ref RFC|675}}

Initially, the Transmission Control Program, the precursor to the later protocol suite, provided only a [[reliable byte stream]] service, not [[datagram]]s.<ref name="TCP2">{{Cite web|url=https://www.rfc-editor.org/ien/ien5.pdf|title=Specification of Internet Transmission Control Protocol TCP (Version 2)|first=Vinton|last=Cerf|author-link=Vint Cerf|date=March 1977|access-date=2022-08-04|archive-date=May 25, 2022|archive-url=https://web.archive.org/web/20220525061950/https://www.rfc-editor.org/ien/ien5.pdf|url-status=live}}</ref> Several versions were developed by communication via the [[Internet Experiment Note]] series.<ref name=":30" /> As experience with the protocol grew, collaborators recommended division of functionality into layers of distinct protocols, providing direct access to datagram service. Advocates included [[Bob Metcalfe]] and Yogen Dalal at Xerox PARC;<ref name="BpyJd">{{cite book |last1=Panzaris |first1=Georgios |url=https://books.google.com/books?id=9yMhAQAAIAAJ |title=Machines and romances: the technical and narrative construction of networked computing as a general-purpose platform, 1960–1995 |date=2008 |publisher=[[Stanford University]] |page=128 |access-date=September 5, 2019 |archive-url=https://web.archive.org/web/20230117175134/https://books.google.com/books?id=9yMhAQAAIAAJ |archive-date=January 17, 2023 |url-status=live}}</ref><ref name="2J9cz">{{cite book |last1=Pelkey |first1=James L. |url=https://historyofcomputercommunications.info/ |title=Entrepreneurial Capitalism and Innovation: A History of Computer Communications, 1968–1988 |date=2007 |chapter=Yogen Dalal |access-date=8 October 2020 |chapter-url=https://historyofcomputercommunications.info/interviews/yogen-dalal/ |archive-url=https://web.archive.org/web/20221008232443/https://historyofcomputercommunications.info/ |archive-date=October 8, 2022 |url-status=live}}</ref> [[Danny Cohen (computer scientist)|Danny Cohen]], who needed it for his [[packet voice]] work; and [[Jonathan Postel]] of 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.<ref name="i1TtW">Internet Hall of Fame</ref> Postel stated, "We are screwing up in our design of Internet protocols by violating the principle of layering."<ref name="xgruR">{{citation|url=https://www.rfc-editor.org/ien/ien2.txt|first=Jon|last=Postel|author-link=Jon Postel|title=2.3.3.2 Comments on Internet Protocol and TCP|id=IEN 2|date=15 August 1977|access-date=June 11, 2016|archive-date=May 16, 2019|archive-url=https://web.archive.org/web/20190516055704/http://www.rfc-editor.org/ien/ien2.txt|url-status=live}}</ref> Encapsulation of different mechanisms was intended to create an environment where 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 [[IPv4|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]].<ref>Abbate, ''Inventing the Internet'', 129–30.</ref><ref>{{cite journal |author=Vinton G. Cerf |date=October 1980 |title=Protocols for Interconnected Packet Networks |journal=ACM SIGCOMM Computer Communication Review |volume=10 |issue=4 |pages=10–11 |authorlink=Vint Cerf}}</ref><ref>{{Cite thesis |last=Russell |first=Andrew L. |title="Industrial Legislatures": Consensus Standardization in the Second and Third Industrial Revolutions |date=2007 |degree=PhD |publisher=Johns Hopkins University |url=https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/32576/alr-diss-08012007-CBO-opt.pdf |access-date=December 28, 2022 |archive-date=December 28, 2022 |archive-url=https://web.archive.org/web/20221228000055/https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/32576/alr-diss-08012007-CBO-opt.pdf |url-status=live }}</ref><ref group ="nb">For records of discussions leading up to the TCP/IP split, see the series of [[Internet Experiment Notes]] at [https://www.rfc-editor.org/ien/ien-index.html the Internet Experiment Notes Index].</ref>

The design of 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,<ref name="Bennett2009">{{cite web |last1=Bennett |first1=Richard |date=September 2009 |title=Designed for Change: End-to-End Arguments, Internet Innovation, and the Net Neutrality Debate |url=https://www.itif.org/files/2009-designed-for-change.pdf |access-date=11 September 2017 |publisher=Information Technology and Innovation Foundation |pages=7, 11}}</ref> based on the ideas of [[Donald Davies]].<ref name="Pelkey2">{{cite book |last=Pelkey |first=James |url=https://www.historyofcomputercommunications.info/section/8.3/cyclades-network-and-louis-pouzin-1971-1972/ |title=Entrepreneurial Capitalism and Innovation: A History of Computer Communications 1968-1988 |chapter=8.3 CYCLADES Network and Louis Pouzin 1971-1972 |quote=The inspiration for datagrams had two sources. One was Donald Davies’ studies. He had done some simulation of datagram networks, although he had not built any, and it looked technically viable. The second inspiration was I like things simple. I didn’t see any real technical motivation to overlay two levels of end-to-end protocols. I thought one was enough. |access-date=2021-11-21 |archive-url=https://web.archive.org/web/20210617093154/https://www.historyofcomputercommunications.info/section/8.3/cyclades-network-and-louis-pouzin-1971-1972/ |archive-date=2021-06-17 |url-status=dead}}</ref><ref name=":5">{{cite conference |last1=Davies |first1=Donald |last2=Bartlett |first2=Keith |last3=Scantlebury |first3=Roger |last4=Wilkinson |first4=Peter |date=October 1967 |title=A Digital Communication Network for Computers Giving Rapid Response at remote Terminals |url=https://people.mpi-sws.org/~gummadi/teaching/sp07/sys_seminar/how_did_erope_blow_this_vision.pdf |conference=ACM Symposium on Operating Systems Principles |archive-url=https://ghostarchive.org/archive/20221010/https://people.mpi-sws.org/~gummadi/teaching/sp07/sys_seminar/how_did_erope_blow_this_vision.pdf |archive-date=2022-10-10 |access-date=2020-09-15 |url-status=live |quote=all users of the network will provide themselves with some kind of error control}}</ref> Using this design, it became possible to connect other networks to 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."{{citation needed|reason=I can only find possibly circular references for this phrase.|date=November 2017}} Years later, as a [[April Fools' Day|joke]] in 1999, the [[IP over Avian Carriers]] formal protocol specification was created{{Ref RFC|1149}} and successfully tested two years later. 10 years later still, it was adapted for IPv6.{{Ref RFC|6214}}

DARPA contracted with [[BBN Technologies]], [[Stanford University]], and the [[University College London]] to develop operational versions of the protocol on several hardware platforms.<ref name="IjTdeF">{{cite web |author1=by Vinton Cerf, as told to Bernard Aboba |date=1993 |title=How the Internet Came to Be |url=http://elk.informatik.hs-augsburg.de/tmp/cdrom-oss/CerfHowInternetCame2B.html |url-status=dead |archive-url=https://web.archive.org/web/20170926042220/http://elk.informatik.hs-augsburg.de/tmp/cdrom-oss/CerfHowInternetCame2B.html |archive-date=26 September 2017 |access-date=25 September 2017 |quote=We began doing concurrent implementations at Stanford, BBN, and University College London. So effort at developing the Internet protocols was international from the beginning.}}</ref> 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 the protocol that is still in use in the Internet, alongside its current successor, [[Internet Protocol version 6]] (IPv6).

===Early implementation===
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.<ref name=":30">{{Cite web |last=Cerf |first=Vinton G. |date=1 April 1980 |title=Final Report of the Stanford University TCP Project |url=https://www.rfc-editor.org/ien/ien151.txt}}</ref>

A computer called a [[Router (computing)|router]] is provided with an interface to each network. It forwards [[network packet]]s back and forth between them.{{Ref RFC|1812}} Originally a router was called ''gateway'', but the term was changed to avoid confusion with other types of [[Gateway (telecommunications)|gateways]].<ref name="DXqFd">{{cite book |last1=Crowell |first1=William |last2=Contos |first2=Brian |last3=DeRodeff |first3=Colby |title=Physical and Logical Security Convergence: Powered By Enterprise Security Management |date=2011 |publisher=Syngress |isbn=9780080558783 |page=99}}</ref>

===Adoption===
In March 1982, the US Department of Defense declared TCP/IP as the standard for all military computer networking.<ref name="EMuq6">{{cite web |author=Ronda Hauben |title=From the ARPANET to the Internet |url=http://www.columbia.edu/~rh120/other/tcpdigest_paper.txt |url-status=live |archive-url=https://web.archive.org/web/20090721093920/http://www.columbia.edu/~rh120/other/tcpdigest_paper.txt |archive-date=July 21, 2009 |access-date=2007-07-05 |publisher=TCP Digest (UUCP)}}</ref><ref>{{Cite IETF|ien=207}}</ref><ref>{{Cite IETF|ien=152}}</ref> In the same year, [[NORSAR]]/[[Norwegian Defence Research Establishment|NDRE]] and [[Peter T. Kirstein|Peter Kirstein]]'s research group at [[University College London]] adopted the protocol.<ref>{{cite journal |last=Hauben |first=Ronda |year=2004 |title=The Internet: On its International Origins and Collaborative Vision |url=http://www.ais.org/~jrh/acn/ACn12-2.a03.txt |journal=Amateur Computerist |volume=12 |issue=2 |access-date=May 29, 2009 |quote=Mar '82 – Norway leaves the ARPANET and become an Internet connection via TCP/IP over SATNET. Nov '82 – UCL leaves the ARPANET and becomes an Internet connection.}}</ref> The migration of the ARPANET from [[Network Control Protocol (ARPANET)|NCP]] to TCP/IP was officially completed on [[Flag day (software)|flag day]] January 1, 1983, when the new protocols were permanently activated.<ref name="EMuq6" /><ref name="LuqX7">{{cite web|url=https://www.livinginternet.com/i/ii_tcpip.htm|title=TCP/IP Internet Protocol|access-date=2017-12-31|archive-url=https://web.archive.org/web/20180101082256/https://www.livinginternet.com/i/ii_tcpip.htm|archive-date=1 January 2018}}</ref>

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, 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.<ref name="HPAsn">{{citation |url=https://www.internetsociety.org/wp-content/uploads/2017/09/ISOC-History-of-the-Internet_1997.pdf |title=Brief History of the Internet |date=1997 |first=Barry M. |last=Leiner |display-authors=et al. |publisher=[[Internet Society]] |page=15 |access-date=January 17, 2018 |archive-date=January 18, 2018 |archive-url=https://web.archive.org/web/20180118011131/https://www.internetsociety.org/wp-content/uploads/2017/09/ISOC-History-of-the-Internet_1997.pdf |url-status=live }}</ref><ref>{{Cite web |date=2020 |title=Vinton G. Cerf : An Oral History |url=https://exhibits.stanford.edu/oral-history/catalog/pj259nj7501 |access-date=2024-06-29 |website=Stanford Oral History Collections - Spotlight at Stanford |page=113, 129, 145 |language=en}}</ref>

IBM, AT&T and DEC were the first major corporations to adopt TCP/IP, this despite having competing [[proprietary protocol]]s. In IBM, from 1984, [[Barry Appelman]]'s group did TCP/IP development. They navigated the corporate politics to get a stream of TCP/IP products for various IBM systems, including [[MVS]], [[VM (operating system)|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]].<ref name="TtEPm">{{cite web| url = http://support.microsoft.com/kb/108007| title = Using Wollongong TCP/IP with Windows for Workgroups 3.11| website=Microsoft Support| archive-url=https://web.archive.org/web/20120112105314/http://support.microsoft.com/kb/108007| archive-date = 12 January 2012| url-status=dead}}</ref> The first [[VM/CMS]] TCP/IP stack came from the University of Wisconsin.<ref name="BZHnU">{{cite web|url=http://www.weblab.isti.cnr.it/education/ssfs/lezioni/slides/archives/cern.htm|title=A Short History of Internet Protocols at CERN|access-date=12 September 2016|archive-url=https://web.archive.org/web/20161110200124/http://www.weblab.isti.cnr.it/education/ssfs/lezioni/slides/archives/cern.htm|archive-date=10 November 2016|url-status=dead}}</ref>

Some programmers are notable for early TCP/IP stack implementations. Jay Elinsky and Oleg Vishnepolsky of IBM Research wrote software for VM/CMS and OS/2, respectively.<ref>''An Introduction to Computer Networks''. Stanford University, CS144, Fall 2012, pp. 21–22. Available at: <nowiki>https://kirils.org/skype/stuff/pdf/2012/An_Introduction_to_Computer_Networksweek_one.pdf</nowiki></ref> 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.<ref name="j7VeG">{{cite web |title= Desktop TCP/IP at middle age |last1= Baker |first1= Steven |last2= Gillies |first2= Donald W |url= http://www.ece.ubc.ca/~gillies/9802net.html |access-date= September 9, 2016 |archive-date= August 21, 2015 |archive-url= https://web.archive.org/web/20150821010509/http://www.ece.ubc.ca/~gillies/9802net.html |url-status= dead }}</ref><ref name="vss61">{{cite web|url=http://www.romkey.com/about/|title=About|last=Romkey|first=John|date=17 February 2011|access-date=12 September 2016|archive-date=November 5, 2011|archive-url=https://web.archive.org/web/20111105074443/http://www.romkey.com/about/|url-status=live}}</ref> Starting in 1985, Phil Karn created a multi-connection TCP application for ham radio systems (KA9Q TCP).<ref name="vCamZ">Phil Karn, ''KA9Q TCP Download Website''</ref>

The spread of TCP/IP 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 was key to bringing the Internet to home users. Trumpet Winsock allowed TCP/IP operations over a serial connection ([[Serial_Line_Internet Protocol|SLIP]] or [[Point-to-Point Protocol|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 a period in the late 1980s and early 1990s, engineers, organizations and nations were [[Protocol Wars|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.<ref name="I2M49">{{cite magazine|author=Andrew L. Russell|date=30 July 2013|title=OSI: The Internet That Wasn't|url=https://spectrum.ieee.org/osi-the-internet-that-wasnt|magazine=[[IEEE Spectrum]]|volume=50|issue=8|access-date=February 6, 2020|archive-date=August 1, 2017|archive-url=https://web.archive.org/web/20170801171503/http://spectrum.ieee.org/computing/networks/osi-the-internet-that-wasnt|url-status=live}}</ref><ref name="vfIkT">{{Cite web|url=https://www2.cs.duke.edu/courses/common/compsci092/papers/govern/consensus.pdf|title=Rough Consensus and Running Code' and the Internet-OSI Standards War|last=Russell|first=Andrew L.|publisher=IEEE Annals of the History of Computing|url-status=dead|archive-url=https://web.archive.org/web/20191117080112/https://www2.cs.duke.edu/courses/common/compsci092/papers/govern/consensus.pdf|archive-date=2019-11-17}}</ref><ref name="IuDfGrr">{{Cite book|last1=Davies|first1=Howard|url=https://books.google.com/books?id=DN-t8MpZ0-wC&q=%22protocol+wars%22&pg=PA106|title=A History of International Research Networking: The People who Made it Happen|last2=Bressan|first2=Beatrice|date=2010-04-26|publisher=John Wiley & Sons|isbn=978-3-527-32710-2|language=en|access-date=November 7, 2020|archive-date=January 17, 2023|archive-url=https://web.archive.org/web/20230117175133/https://books.google.com/books?id=DN-t8MpZ0-wC&q=%22protocol+wars%22&pg=PA106|url-status=live}}</ref>

===Formal specification and standards===
The [[technical standard]]s underlying the Internet protocol suite and its constituent protocols have been delegated to the [[Internet Engineering Task Force]] (IETF).<ref name="introduction-to-the-ietf">{{Cite web |title=Introduction to the IETF |url=https://www.ietf.org/about/introduction/ |access-date=2024-02-27 |website=IETF |language=en}}</ref><ref>{{Cite journal |last1=Morabito |first1=Roberto |last2=Jimenez |first2=Jaime |date=June 2020 |title=IETF Protocol Suite for the Internet of Things: Overview and Recent Advancements |url=http://dx.doi.org/10.1109/mcomstd.001.1900014 |journal=IEEE Communications Standards Magazine |volume=4 |issue=2 |pages=41–49 |doi=10.1109/mcomstd.001.1900014 |issn=2471-2825|arxiv=2003.10279 }}</ref>

The characteristic architecture of 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 layer]]s (as well as related protocols); the link layer, IP layer, transport layer, and application layer, along with support protocols.<ref name="rfc1122" /><ref name="rfc1123" /> These have stood the test of time, as 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.<ref name="IuDfGrr" />

==Key architectural principles==
{{see also|Communication protocol#Software layering}}
[[Image:IP stack connections.svg|thumb|350px|Conceptual data flow in a simple network topology of two hosts (''A'' and ''B'') connected by a link between their respective routers. The application on each host executes read and write operations as if the processes were directly connected to each other by some kind of data pipe. After establishment of this pipe, most details of the communication are hidden from each process, as the underlying principles of communication are implemented in the lower protocol layers. In analogy, at the transport layer the communication appears as host-to-host, without knowledge of the application data structures and the connecting routers, while at the internetworking layer, individual network boundaries are traversed at each router.]]
[[Image:UDP encapsulation.svg|thumb|350px|Encapsulation of application data descending through the layers described in RFC 1122]]

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 the like have forced changes in this principle.<ref name="pTfJe">{{cite web|url=https://www.csd.uoc.gr/~hy558/papers/Rethinking_2001.pdf|title=Rethinking the design of the Internet: The end-to-end arguments vs. the brave new world|first1=Marjory S.|last1=Blumenthal|first2=David D.|last2=Clark|author-link2=David D. Clark|date=August 2001|access-date=October 8, 2022|archive-date=October 8, 2022|archive-url=https://web.archive.org/web/20221008213500/https://www.csd.uoc.gr/~hy558/papers/Rethinking_2001.pdf|url-status=live}}</ref>

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)."{{Ref RFC|791|rp=23}} "The second part of the principle is almost as important: software on other hosts may contain deficiencies that make it unwise to exploit legal but obscure protocol features."{{Ref RFC|1122|rp=13}}

[[Encapsulation (networking)|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 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, {{IETF RFC|1122}} and {{IETF RFC|1123|plainlink=yes}}, titled ''Requirements for Internet Hosts'', emphasizes architectural principles over layering.{{Ref RFC|1958}} 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 a four-layer model, with the layers having names, not numbers, as follows:{{ref RFC|1122}}{{ref RFC|1123}}
* The [[application layer]] is the scope within which applications, or [[Process (computing)|processes]], create user data and communicate this data to other applications on another or the same host. The applications make use of the services provided by the underlying lower layers, especially the transport layer which provides [[Reliability (computer networking)|reliable or unreliable]] ''pipes'' to other processes. The communications partners are characterized by the application architecture, such as the [[client–server model]] and [[peer-to-peer]] networking. This is the layer in which all application protocols, such as SMTP, FTP, SSH, and HTTP, operate. Processes are addressed via ports which essentially represent [[Service (systems architecture)|services]].
* The [[transport layer]] performs host-to-host communications on either the local network or remote networks separated by routers.<ref name="AoJD3">{{cite book |last=Hunt |first=Craig |date=2002 |title=TCP/IP Network Administration |edition=3rd |publisher=O'Reilly |pages=9–10 |isbn=9781449390785}}</ref> It provides a channel for the communication needs of applications. The [[User Datagram Protocol]] (UDP) is the most basic{{Citation needed|date=June 2025|reason=Which source states UDP is the most basic transport layer protocol ? I refer to Jim Kurose (2012), Computer Networking: A Top-Down Approach, 7th Edition, Chapter 3: Transport layer, Section 3.1 Introduction and Transport-layer services), which states that both TCP and UDP are two best known transport layer protocols, which made up many application layer protocols like HTTP, IMAP, POP3, and SMTP. So what makes UDP is the "most basic", compared to TCP ?}} transport layer protocol, providing an unreliable [[connectionless]] datagram service. The [[Transmission Control Protocol]] (TCP) provides flow-control, connection establishment, and reliable transmission of data.
* The [[internet layer]] exchanges datagrams across network boundaries. It provides a uniform networking interface that hides the actual topology (layout) of the underlying network connections.  It is therefore also the layer that establishes internetworking. Indeed, it defines and establishes the Internet. This layer defines the addressing and routing structures used for the TCP/IP protocol suite. The primary protocol in this scope is the Internet Protocol, which defines [[IP address]]es.<ref>{{Cite journal |last=Guttman |first=E. |date=1999 |title=Service location protocol: automatic discovery of IP network services |url=http://dx.doi.org/10.1109/4236.780963 |journal=IEEE Internet Computing |volume=3 |issue=4 |pages=71–80 |doi=10.1109/4236.780963 |issn=1089-7801|url-access=subscription }}</ref>{{failed verification|date=April 2024}}<ref name=kz>{{Cite journal |last=Zheng |first=Kai |date=July 2017 |title=Enabling "Protocol Routing": Revisiting Transport Layer Protocol Design in Internet Communications |url=http://dx.doi.org/10.1109/mic.2017.4180845 |journal=IEEE Internet Computing |volume=21 |issue=6 |pages=52–57 |doi=10.1109/mic.2017.4180845 |issn=1089-7801|url-access=subscription }}</ref> Its function in routing is to transport datagrams to the next host, functioning as an IP router, that has the connectivity to a network closer to the final data destination.<ref name=kz/>{{failed verification|date=April 2024}}
* The [[link layer]] defines the networking methods within the scope of the local network link on which hosts communicate without intervening routers. This layer includes the protocols used to describe the local network topology and the interfaces needed to effect the transmission of internet layer datagrams to next-neighbor hosts.<ref>{{Cite journal |last=Huang |first=Jing-lian |date=2009-04-07 |title=Cross layer link adaptation scheme in wireless local area network |url=http://dx.doi.org/10.3724/sp.j.1087.2009.00518 |journal=Journal of Computer Applications |volume=29 |issue=2 |pages=518–520 |doi=10.3724/sp.j.1087.2009.00518 |doi-broken-date=June 25, 2025 |issn=1001-9081|url-access=subscription }}</ref>

==Link layer==
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 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 network]]s and [[tunneling protocol|networking tunnels]].

The link layer is used to move packets between the internet layer interfaces of two different hosts on 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 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.

==Internet layer==
[[Internetworking]] requires sending data from the source network to the destination network. This process is called [[routing]] and is supported by host addressing and identification using the hierarchical [[IP address]]ing 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 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 protocol]]s. These protocols are each identified by a unique [[List of IP protocol numbers|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, 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.

==Transport layer==
The transport layer establishes data channels that applications use for task-specific data exchange. The layer establishes host-to-host connectivity in 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]], [[Network segmentation|segmentation]], [[Flow control (data)|flow control]], [[Network congestion|congestion control]], and application addressing ([[port numbers]]).

For 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 the involvement of [[service discovery]] or [[directory service]]s.

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]]:
* data arrives in-order
* data has minimal error (i.e., correctness)
* duplicate data is discarded
* lost or discarded packets are resent
* includes traffic congestion control

The newer [[Stream Control Transmission Protocol]] (SCTP) is also a reliable, connection-oriented transport mechanism. It 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 [[Signaling System 7|SS7]] over IP).

Reliability can also be achieved by running IP over 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 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 [[List of TCP and UDP port numbers|'' well-known ports'']] are associated with specific applications.

The TCP/IP model's transport or host-to-host layer corresponds roughly to 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.

==Application layer==
The application layer includes the protocols used by most applications for providing user services or exchanging application data over the network connections established by the lower-level protocols. This may include some basic network support services such as [[routing protocol]]s 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).<ref name="RxqD0">{{cite book|url=http://www.kohala.com/start/tcpipiv1.html|title=TCP/IP Illustrated: the protocols|isbn=0-201-63346-9|first=W. Richard|last=Stevens|author-link=W. Richard Stevens|date=February 1994|publisher=Addison-Wesley |access-date=April 25, 2012|archive-date=April 22, 2012|archive-url=https://web.archive.org/web/20120422024917/http://www.kohala.com/start/tcpipiv1.html|url-status=live}}</ref> Data coded according to application layer protocols are  [[encapsulation (networking)|encapsulated]] into transport layer protocol units (such as TCP streams or UDP datagrams), which in turn use [[lower layer protocol]]s to effect actual data transfer.

The TCP/IP model does not consider 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 [[Library (computing)|libraries]] and [[application programming interface]]s. 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 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. [[client (computing)|Clients]] connecting to a service usually use [[ephemeral port]]s, i.e., port numbers assigned only for 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''.{{Ref RFC|1122|rsection=1.1.3}} 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 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 box]]es 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 [[network switch|switches]] do not typically examine the encapsulated traffic, rather they just provide a conduit for it. However, some [[Firewall (computing)|firewall]] and [[bandwidth throttling]] applications use [[deep packet inspection]] to interpret application data. An example is the [[Resource Reservation Protocol]] (RSVP).{{citation needed|date=May 2021}} It is also sometimes necessary for [[Network address translation#Applications affected by NAT|Applications affected by NAT]] to consider the application payload.

==Layering evolution and representations in the literature==
The Internet protocol suite evolved through research and development funded over 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.

{| class="wikitable"
|-

! style="background:#adb" | Arpanet Reference Model<br/><small>(RFC 871)</small>
! style="background:#adb" | Internet Standard<br/><small>(RFC 1122)</small>
! style="background:#adb" | Internet model<br/><small>(Cisco Academy<ref name="5VTuU">{{cite book |last1=Dye |first1=Mark |url=https://books.google.com/books?id=JVAk7r6jHF4C |title=Network Fundamentals, CCNA Exploration Companion Guide |last2=McDonald |first2=Rick |last3=Rufi |first3=Antoon |date=29 October 2007 |publisher=Cisco Press |isbn=9780132877435 |access-date=12 September 2016 |via=Google Books}}</ref>)</small>
! style="background:#adb" | TCP/IP 5-layer reference model<br/><small>(Kozierok,<ref name="6zcxM">{{cite book |last=Kozierok |first=Charles M. |url=https://books.google.com/books?id=Pm4RgYV2w4YC |title=The TCP/IP Guide: A Comprehensive, Illustrated Internet Protocols Reference |date=1 January 2005 |publisher=No Starch Press |isbn=9781593270476 |access-date=12 September 2016 |via=Google Books}}</ref> Comer<ref name="lkPs4">{{cite book |last=Comer |first=Douglas |url=https://books.google.com/books?id=jonyuTASbWAC |title=Internetworking with TCP/IP: Principles, protocols, and architecture |date=1 January 2006 |publisher=Prentice Hall |isbn=0-13-187671-6 |access-date=12 September 2016 |via=Google Books}}</ref>)</small>
! style="background:#adb" | TCP/IP 5-layer reference model<br/><small>(Tanenbaum<ref name="1Hpdo">{{cite book |last=Tanenbaum |first=Andrew S. |url=https://archive.org/details/computernetworks00tane_2 |title=Computer Networks |date=1 January 2003 |publisher=Prentice Hall PTR |isbn=0-13-066102-3 |page=[https://archive.org/details/computernetworks00tane_2/page/42 42] |quote=networks. |access-date=12 September 2016 |url-access=registration |via=Internet Archive}}</ref>)</small>
! style="background:#adb" | TCP/IP protocol suite or Five-layer Internet model<br/><small>(Forouzan,<ref name="bOyR7">{{cite book |last1=Forouzan |first1=Behrouz A. |url=https://books.google.com/books?id=U3Gcf65Pu9IC |title=Data Communications and Networking |last2=Fegan |first2=Sophia Chung |date=1 August 2003 |publisher=McGraw-Hill Higher Education |isbn=9780072923544 |access-date=12 September 2016 |via=Google Books}}</ref> Kurose<ref name="aCpZD">{{cite book|url=http://www.pearsonhighered.com/educator/academic/product/0,,0321497708,00%2ben-USS_01DBC.html|first1=James F.|last1=Kurose|first2=Keith W.|last2=Ross|title=Computer Networking: A Top-Down Approach|date=2008|publisher=Pearson/Addison Wesley |isbn=978-0-321-49770-3|access-date=July 16, 2008|archive-date=January 23, 2016|archive-url=https://web.archive.org/web/20160123195916/http://www.pearsonhighered.com/educator/academic/product/0,,0321497708,00%2ben-USS_01DBC.html|url-status=live}}</ref>)</small>
! style="background:#adb" | TCP/IP model<br/><small>(Stallings<ref name="IRA2X">{{cite book |last=Stallings |first=William |url=https://books.google.com/books?id=c_AWmhkovR0C |title=Data and Computer Communications |date=1 January 2007 |publisher=Prentice Hall |isbn=978-0-13-243310-5 |access-date=12 September 2016 |via=Google Books}}</ref>)</small>
! style="background:#adb" | OSI model<br/><small>(ISO/IEC 7498-1:1994<ref>{{cite ISO standard|csnumber=20269|title=ISO/IEC 7498-1:1994 Information technology — Open Systems Interconnection — Basic Reference Model: The Basic Model}}</ref>)</small>
|-

| style="background:#cfc" | ''Three layers''
| style="background:#cfc" | ''Four layers''
| style="background:#cfc" | ''Four layers''
| style="background:#cfc" | ''Four+one layers''
| style="background:#cfc" | ''Five layers''
| style="background:#cfc" | ''Five layers''
| style="background:#cfc" | ''Five layers''
| style="background:#cfc" | ''Seven layers''
|-

| rowspan="3" | Application/ Process
| rowspan="3" | Application
| rowspan="3" | Application
| rowspan="3" | Application
| rowspan="3" | Application
| rowspan="3" | Application
| rowspan="3" | Application
| Application
|-
| Presentation
|-
| Session
|-
| rowspan="2" | Host-to-host
| Transport
| Transport
| Transport
| Transport
| Transport
| Host-to-host or transport
| Transport
|-

| Internet
| Internetwork
| Internet
| Internet
| Network
| Internet
| Network
|-

|| Network interface
|| Link
|| Network interface
| Data link (Network interface)
|| Data link
| Data link
| Network access
| Data link
|-

|{{n/a}}
|{{n/a}}
|{{n/a}}
| (Hardware)
| Physical
| Physical
| Physical
| Physical
|}

Some of the networking models are from textbooks, which are secondary sources that may conflict with the intent of RFC 1122 and other [[IETF]] primary sources.{{Ref RFC|3439}}

==Comparison of TCP/IP and OSI layering==
{{See also|OSI model#Comparison with TCP/IP model}}
The three top layers in the OSI model, i.e. the application layer, the presentation layer and the session layer, are not distinguished separately in the TCP/IP model which only has an application layer above the transport layer. While some pure OSI protocol applications, such as [[X.400]], also combined them, there is no requirement that a TCP/IP protocol stack must impose monolithic architecture above the transport layer. For example, the NFS application protocol runs over the [[External Data Representation]] (XDR) presentation protocol, which, in turn, runs over a protocol called [[Remote Procedure Call]] (RPC). RPC provides reliable record transmission, so it can safely use the best-effort UDP transport.

Different authors have interpreted the TCP/IP model differently, and disagree whether the link layer, or any aspect of the TCP/IP model, covers OSI layer 1 ([[physical layer]]) issues, or whether TCP/IP assumes a hardware layer exists below the link layer. Several authors have attempted to incorporate the OSI model's layers 1 and 2 into the TCP/IP model since these are commonly referred to in modern standards (for example, by [[IEEE]] and [[ITU]]). This often results in a model with five layers, where the link layer or network access layer is split into the OSI model's layers 1 and 2.{{cn|date=September 2024}}

The IETF protocol development effort is not concerned with strict layering. Some of its protocols may not fit cleanly into the OSI model, although RFCs sometimes refer to it and often use the old OSI layer numbers. The IETF has repeatedly stated<ref name="introduction-to-the-ietf" />{{failed verification|date=April 2024}} that Internet Protocol and architecture development is not intended to be OSI-compliant. RFC 3439, referring to the internet architecture, contains a section entitled: "Layering Considered Harmful".{{ref RFC|3439}}

For example, the session and presentation layers of the OSI suite are considered to be included in the application layer of the TCP/IP suite. The functionality of the session layer can be found in protocols like [[HTTP]] and [[SMTP]] and is more evident in protocols like [[Telnet]] and the [[Session Initiation Protocol]] (SIP). Session-layer functionality is also realized with the port numbering of the TCP and UDP protocols, which are included in the transport layer of the TCP/IP suite. Functions of the presentation layer are realized in the TCP/IP applications with the [[MIME]] standard in data exchange.

Another difference is in the treatment of [[routing protocol]]s. The OSI routing protocol [[IS-IS]] belongs to the network layer, and does not depend on [[CLNS]] for delivering packets from one router to another, but defines its own layer-3 encapsulation. In contrast, [[OSPF]], [[Routing Information Protocol|RIP]], [[BGP]] and other routing protocols defined by the IETF are transported over IP, and, for the purpose of sending and receiving routing protocol packets, routers act as hosts. As a consequence, routing protocols are included in the application layer.{{Ref RFC|1812}} Some authors, such as Tanenbaum in ''Computer Networks'', describe routing protocols in the same layer as IP, reasoning that routing protocols inform decisions made by the forwarding process of routers.

IETF protocols can be encapsulated recursively, as demonstrated by tunnelling protocols such as [[Generic Routing Encapsulation]] (GRE). GRE uses the same mechanism that OSI uses for tunnelling at the network layer.

==Implementations==
{{unreferenced section|date=March 2014}}
The Internet protocol suite is generally independent of a specific hardware or software environment. It only requires the hardware and a software layer to exist, capable of sending and receiving packets on a computer network. As a result, the suite has been implemented on essentially every computing platform. A minimal implementation of TCP/IP includes the following: [[Internet Protocol]] (IP), [[Address Resolution Protocol]] (ARP), [[Internet Control Message Protocol]] (ICMP), [[Transmission Control Protocol]] (TCP), [[User Datagram Protocol]] (UDP), and [[Internet Group Management Protocol]] (IGMP).<ref>{{Citation| publisher = IETF| doi = 10.17487/RFC1122| last = Braden| first = Robert T.| editor-first1 = R.| editor-last1 = Braden| title = RFC 1122: Requirements for internet hosts - communication layers| year = 1989}}</ref> In addition to IP, ICMP, TCP, UDP, Internet Protocol version 6 requires [[Neighbor Discovery Protocol]] (NDP), [[ICMPv6]], and [[Multicast Listener Discovery]] (MLD) and is often accompanied by an integrated [[IPSec]] security layer.

==See also==
* [[BBN Report 1822]], an early layered network model
* [[Internetwork Packet Exchange]]
* [[Fast Local Internet Protocol]]
* [[List of automation protocols]]
* [[List of information technology initialisms]]
* [[List of IP protocol numbers]]
* [[Lists of network protocols]]
* [[List of TCP and UDP port numbers]]

==Notes==
{{reflist|group=nb}}

==References==
{{reflist}}

==Bibliography==
* {{cite book |author=Douglas E. Comer |author-link=Douglas E. Comer |title=Internetworking with TCP/IP – Principles, Protocols and Architecture |year=2001 |publisher=CET [i. e.] Computer Equipment and Trade |isbn=86-7991-142-9}}
* {{cite book |author1=Joseph G. Davies |author2=Thomas F. Lee |title=Microsoft Windows Server 2003 TCP/IP Protocols and Services |year=2003 |publisher=Microsoft Press |isbn=0-7356-1291-9}}
* {{cite book| last=Forouzan| first=Behrouz A.| year=2003| title=TCP/IP Protocol Suite| edition=2nd| publisher=McGraw-Hill| isbn=978-0-07-246060-5 }}
* {{cite book |author=Craig Hunt |title=TCP/IP Network Administration |publisher=O'Reilly |date=1998 |isbn=1-56592-322-7}}
* {{cite book| last=Maufer| first=Thomas A.| year=1999| title=IP Fundamentals| publisher=Prentice Hall | isbn=978-0-13-975483-8 }}
* {{cite book |author=Ian McLean |title=Windows 2000 TCP/IP Black Book |year=2000 |publisher=Coriolis Group Books |isbn=1-57610-687-X}}
* {{cite book |author=Ajit Mungale |title=Pro .NET 1.1 Network Programming |date=September 29, 2004 |publisher=Apress |isbn=1-59059-345-6}}
* {{cite book |author=W. Richard Stevens |author-link=W. Richard Stevens |title=TCP/IP Illustrated, Volume 1: The Protocols |date=April 24, 1994 |publisher=Addison-Wesley |isbn=0-201-63346-9}}
* {{cite book |author1=W. Richard Stevens |author1-link=W. Richard Stevens |author2=Gary R. Wright |title=TCP/IP Illustrated, Volume 2: The Implementation |year=1994 |publisher=Addison-Wesley |isbn=0-201-63354-X}}
* {{cite book |author=W. Richard Stevens |author-link=W. Richard Stevens |title=TCP/IP Illustrated, Volume 3: TCP for Transactions, HTTP, NNTP, and the UNIX Domain Protocols |year=1996 |publisher=Addison-Wesley |isbn=0-201-63495-3}}
* {{cite book |author=Andrew S. Tanenbaum |author-link=Andrew S. Tanenbaum |title=Computer Networks |year=2003 |publisher=Prentice Hall PTR |isbn=0-13-066102-3}}
* {{cite conference |last=Clark |first=D. |author-link=David D. Clark|year=1988|title=The Design Philosophy of the DARPA Internet Protocols |book-title=Proceedings of the Sigcomm '88 Symposium on Communications Architectures and Protocols |publisher=[[Association for Computing Machinery|ACM]] |pages=106–114 |doi=10.1145/52324.52336 |url=https://www.cs.princeton.edu/~jrex/teaching/spring2005/reading/clark88.pdf |access-date=2011-10-16 |isbn=978-0897912792 |s2cid=6156615}}
* {{cite journal |url=https://www.cs.princeton.edu/courses/archive/fall06/cos561/papers/cerf74.pdf |title=A Protocol for Packet Network Intercommunication |last1=Cerf |first1=Vinton G. |author-link1=Vint Cerf |last2=Kahn |first2=Robert E. |author-link2=Bob Kahn |journal=[[IEEE Transactions on Communications]] |volume=22 |issue=5 |date=May 1974|pages=637–648 |doi=10.1109/TCOM.1974.1092259 }}

==External links==
{{Wikiversity | Internet protocol suite}}
* [https://www.livinginternet.com/i/ii.htm Internet History] – Pages on Robert Kahn, Vinton Cerf, and TCP/IP (reviewed by Cerf and Kahn).
* {{Ref RFC|1180|ref=no}}
* [https://www.itprc.com/tcpipfaq/ The Ultimate Guide to TCP/IP]
* [http://www.tcpipguide.com/free/ The TCP/IP Guide] – A comprehensive look at the protocols and the procedure and processes involved
* {{citation |url=http://www.columbia.edu/~rh120/other/tcpdigest_paper.txt |archive-url=https://web.archive.org/web/20211204202600/http://www.columbia.edu/~rh120/other/tcpdigest_paper.txt |archive-date=2021-12-04 |title=A Study of the ARPANET TCP/IP Digest}}

[[Category:Internet protocols| ]]
[[Category:History of the Internet]]
[[Category:Network architecture]]
[[Category:Reference models]]