Internetworking is the practice ofinterconnecting multiplecomputer networks.[1]: 169 Typically, this enables any pair ofhosts in the connected networks to exchange messages irrespective of their hardware-level networking technology. The resulting system of interconnected networks is called aninternetwork, or simply aninternet.
The most notable example of internetworking is theInternet, a network of networks based on many underlying hardware technologies. The Internet is defined by a unifiedglobal addressing system,packet format, androuting methods provided by theInternet Protocol.[2]: 103
The terminternetworking is a combination of the componentsinter (between) andnetworking. An earlier term for an internetwork iscatenet,[3] a short-form of(con)catenating networks.
The first international heterogenousresource sharing network was developed by the computer science department atUniversity College London (UCL) who interconnected theARPANET with earlyBritish academic networks beginning in 1973.[4][5][6] In the ARPANET, the network elements used to connect individual networks were calledgateways, but the term has been deprecated in this context, because of possible confusion with functionally different devices. By 1973-4, researchers in France, the United States, and the United Kingdom had worked out an approach to internetworking where the differences between network protocols were hidden by using a common internetwork protocol, and instead of the network being responsible for reliability, as in the ARPANET, the hosts became responsible, as demonstrated in theCYCLADES network.[7][8][9] Researchers atXerox PARC outlined the idea ofEthernet and thePARC Universal Packet (PUP) for internetworking.[10][11] Research at theNational Physical Laboratory in the United Kingdom found that establishing a common host protocol would be more reliable and efficient.[12] The ARPANET connection to UCL later evolved intoSATNET. In 1977, ARPA demonstrated a three-way internetworking experiment, which linked a mobile vehicle inPRNET with nodes in the ARPANET, and, via SATNET, to nodes at UCL. TheX.25 protocol, on whichpublic data networks were based in the 1970s and 1980s, was supplemented by theX.75 protocol which enabled internetworking.
Today the interconnecting gateways are calledrouters. The definition of an internetwork today includes the connection of other types of computer networks such aspersonal area networks.
Catenet, a short-form of(con)catenating networks, is obsolete terminology for a system ofpacket-switched communication networks interconnected viagateways.[3]
The term was coined byLouis Pouzin, who designed theCYCLADES network, in an October 1973 note circulated to theInternational Network Working Group,[13][14] which was published in a 1974 paper "A Proposal for Interconnecting Packet Switching Networks".[15] Pouzin was a pioneer of internetworking at a time whennetwork meant what is now called alocal area network. Catenet was the concept of linking these networks into anetwork of networks with specifications for compatibility of addressing and routing. The term was used in technical writing in the late 1970s and early 1980s,[16] including inRFCs andIENs.[17] Catenet was gradually displaced by the short-form of the term internetwork,internet (lower-casei), when theInternet Protocol spread more widely from the mid 1980s and the use of the term internet took on a broader sense and became well known in the 1990s.[18][19][20][21][22][23][24][25][excessive citations]
Internetworking, a combination of the componentsinter (between) andnetworking, started as a way to connect disparate types of networking technology, but it became widespread through the developing need to connect two or morelocal area networks via some sort ofwide area network.
To build an internetwork, the following are needed:[2]: 103 A standardized scheme toaddress packets to any host on any participating network; a standardizedprotocol defining format and handling of transmitted packets; components interconnecting the participating networks byrouting packets to their destinations based on standardized addresses.
Another type of interconnection of networks often occurs within enterprises at thelink layer of the networking model, i.e. at the hardware-centric layer below the level of the TCP/IP logical interfaces. Such interconnection is accomplished withnetwork bridges andnetwork switches. This is sometimes incorrectly termed internetworking, but the resulting system is simply a larger, singlesubnetwork, and no internetworkingprotocol, such asInternet Protocol, is required to traverse these devices. However, a single computer network may be converted into an internetwork by dividing the network into segments and logically dividing the segment traffic with routers and having an internetworking software layer that applications employ.
The Internet Protocol is designed to provide anunreliable (not guaranteed)packet service across the network. The architecture avoids intermediate network elements maintaining any state of the network. Instead, this function is assigned to the endpoints of each communication session. To transfer data reliably, applications must utilize an appropriatetransport layer protocol, such asTransmission Control Protocol (TCP), which provides areliable stream. Some applications use a simpler, connection-less transport protocol,User Datagram Protocol (UDP), for tasks which do not require reliable delivery of data or that require real-time service, such asvideo streaming[26] or voice chat.
Two architectural models are commonly used to describe the protocols and methods used in internetworking. TheOpen System Interconnection (OSI) reference model was developed under the auspices of theInternational Organization for Standardization (ISO) and provides a rigorous description for layering protocol functions from the underlying hardware to the software interface concepts in user applications. Internetworking is implemented in theNetwork Layer (Layer 3) of the model.
TheInternet Protocol Suite, also known as the TCP/IP model, was not designed to conform to the OSI model and does not refer to it in any of the normative specifications inRequest for Comments andInternet standards. Despite similar appearance as a layered model, it has a much less rigorous, loosely defined architecture that concerns itself only with the aspects of the style of networking in its own historical provenance. It assumes the availability of any suitable hardware infrastructure, without discussing hardware-specific low-level interfaces, and that a host has access to this local network to which it is connected via a link layer interface.
For a period in the late 1980s and early 1990s, the network engineering community was polarized over the implementation of competing protocol suites, commonly known as theProtocol Wars. It was unclear which of the OSI model and the Internet protocol suite would result in the best and most robust computer networks.[27][28][29]
The term "catenet" was introduced by L. Pouzin in 1974.
From the outset of the project, we aimed not only to carry out innovative research, but also to provide network services to UK and U.S. groups that wished to cooperate.
But the ARPANET itself had now become an island, with no links to the other networks that had sprung up. By the early 1970s, researchers in France, the UK, and the U.S. began developing ways of connecting networks to each other, a process known as internetworking.
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.
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.
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