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ally referred to as the dod internet architecture model 35 together with the transmission control protocol it became commonly known as tcp ip early implementation edit 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 19 a computer called a router is provided with an interface to each network it forwards network packets back and forth between them 36 originally a router was called gateway but the term was changed to avoid confusion with other types of gateways 37 adoption edit in march 1982 the us department of defense declared tcp ip as the standard for all military computer networking 38 39 40 in the same year norway norsar and ndre and peter kirstein s research group at university college london adopted the protocol 41 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 38 42 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 43 44 ibm at t and dec were the first major corporations to adopt tcp ip this despite having competing proprietary protocols at 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 and os 2 several smaller companies such as ftp software and the wollongong group began offering tcp ip stacks for ms dos and windows 45 the first vm cms tcp ip stack came from the university of wisconsin 46 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 47 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 48 49 starting in 1985 phil karn created a multi connection tcp application for ham radio systems ka9q tcp 50 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 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 its 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 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 51 52 53 formal specification and standards edit the technical standards underlying the internet protocol suite and its constituent protocols have been delegated to the internet engineering task force ietf 54 55 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 outline four abstraction layers as well as related protocols the link layer ip layer transport layer and application layer along with support protocols 1 2 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 53 a successor internet protocol version 6 ipv6 was developed to address issues such as ipv4 address exhaustion 56 key architectural principles edit see also communication protocol software layering 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 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 57 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 58 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 1 13 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 rfc 1122 and 1123 titled requirements for internet hosts emphasizes architectural principles over layering 59 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 define a four layer model with the layers having names not numbers as follows 1 2 the application layer is the scope within which applications or 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 reliable or unreliable pipes to other processes the communication 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 services the transport layer performs host to host communications on either the local network or remote networks separated by routers 60 it provides a channel for the communication needs of applications the user datagram protocol udp is the most basic citation needed 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 addresses 61 failed verification 62 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 62 failed verification 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 63 link layer edit 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 networks and 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 edit 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 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 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 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 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 edit 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 segmentation flow control 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 services because ip provides only 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 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...
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