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28-562: The internet layer is a group of internetworking methods, protocols, and specifications in the Internet protocol suite that are used to transport network packets from the originating host across network boundaries ; if necessary, to the destination host specified by an IP address . The internet layer derives its name from its function facilitating internetworking , which is the concept of connecting multiple networks with each other through gateways . The internet layer does not include

56-419: A reliable 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 as video streaming or voice chat. Two architectural models are commonly used to describe the protocols and methods used in internetworking. The Open System Interconnection (OSI) reference model

84-563: A common host protocol would be more reliable and efficient. The ARPANET connection to UCL later evolved into SATNET . In 1977, ARPA demonstrated a three-way internetworking experiment, which linked a mobile vehicle in PRNET with nodes in the ARPANET, and, via SATNET, to nodes at UCL. The X.25 protocol, on which public data networks were based in the 1970s and 1980s, was supplemented by the X.75 protocol which enabled internetworking. Today

112-674: A common internetwork protocol, and instead of the network being responsible for reliability, as in the ARPANET, the hosts became responsible, as demonstrated in the CYCLADES network. Researchers at Xerox PARC outlined the idea of Ethernet and the PARC Universal Packet (PUP) for internetworking. Research at the National Physical Laboratory in the United Kingdom confirmed establishing

140-611: 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 the Protocol Wars . It was unclear which of the OSI model and the Internet protocol suite would result in the best and most robust computer networks. Network layer In

168-547: A misbehaving host can deny Internet service to many other users. The internet layer has three basic functions: In Version 4 of the Internet Protocol ( IPv4 ), during both transmit and receive operations, IP is capable of automatic or intentional fragmentation or defragmentation of packets, based, for example, on the maximum transmission unit (MTU) of link elements. However, this feature has been dropped in IPv6 , as

196-577: A note circulated to the International Network Working Group , later published in a 1974 paper " A Proposal for Interconnecting Packet Switching Networks" . Pouzin was a pioneer in packet-switching technology and founder of the CYCLADES network, at a time when network meant what is now called a local area network . Catenet was the concept of linking these networks into a network of networks with specifications for compatibility of addressing and routing. The term catenet

224-483: A way to connect disparate types of networking technology, but it became widespread through the developing need to connect two or more local area networks via some sort of wide area network . The first international heterogenous resource sharing network was the 1973 interconnection of the ARPANET with early British academic networks through the computer science department at University College London (UCL). In

252-489: Is defined by a unified global addressing system , packet format, and routing methods provided by the Internet Protocol . The term internetworking is a combination of the components inter (between) and networking . An earlier term for an internetwork is catenet , a short-form of (con)catenating networks . Internetworking, a combination of the components inter (between) and networking , started as

280-425: Is designed to provide an unreliable (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 appropriate transport layer protocol, such as Transmission Control Protocol (TCP), which provides

308-422: Is equated with the OSI network layer. However, this comparison is misleading, as the allowed characteristics of protocols (e.g., whether they are connection-oriented or connection-less) placed into these layers are different in the two models. The TCP/IP Internet layer is in fact only a subset of functionality of the network layer. It describes only one type of network architecture, the Internet. The network layer

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336-527: Is responsible for fragmentation and reassembly for IPv4 packets that are larger than the smallest MTU of all the intermediate links on the packet's path to its destination. It is the function of routers to fragment packets if needed, and of hosts to reassemble them if received. Conversely, IPv6 packets are not fragmented during forwarding, but the MTU supported by a specific path must still be established, to avoid packet loss . For this, Path MTU discovery

364-479: Is sometimes incorrectly termed internetworking, but the resulting system is simply a larger, single subnetwork , and no internetworking protocol , such as Internet 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

392-507: Is the duty of higher-level protocols, such as the Transmission Control Protocol (TCP) in the transport layer . In IPv4, a checksum is used to protect the header of each datagram. The checksum ensures that the information in a received header is accurate, however, IPv4 does not attempt to detect errors that may have occurred to the data in each packet. IPv6 does not include this header checksum, instead relying on

420-547: Is used by IPv4 hosts and adjacent IP multicast routers to establish multicast group memberships. Internet Protocol Security (IPsec) is a suite of protocols for securing IP communications by authenticating and encrypting each IP packet in a data stream. IPsec also includes protocols for key exchange . IPsec was originally designed as a base specification in IPv6 in 1995, and later adapted to IPv4, with which it has found widespread use in securing virtual private networks . Because

448-426: The communication endpoints , the hosts, now have to perform path MTU discovery and ensure that end-to-end transmissions don't exceed the maximum discovered. In its operation, the internet layer is not responsible for reliable transmission . It provides only an unreliable service, and best effort delivery. This means that the network makes no guarantees about the proper arrival of packets. This in accordance with

476-508: The end-to-end principle and a change from the previous protocols used on the early ARPANET . Since packet delivery across diverse networks is an inherently unreliable and failure-prone operation, the burden of providing reliability was placed with the endpoints of a communication path, i.e., the hosts, rather than on the network. This is one of the reasons of the resiliency of the Internet against individual link failures and its proven scalability . The function of providing reliability of service

504-517: The ARPANET, the network elements used to connect individual networks were called gateways , 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

532-529: The OSI model and does not refer to it in any of the normative specifications in Request for Comments and Internet 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

560-467: The interconnecting gateways are called routers . The definition of an internetwork today includes the connection of other types of computer networks such as personal area networks . Catenet , a short-form of (con)catenating networks, is obsolete terminolgy for a system of packet-switched communication networks interconnected via gateways . The term was coined by Louis Pouzin in October 1973 in

588-535: The internet layer of the TCP/IP model is easily compared directly with the network layer (layer 3) in the Open Systems Interconnection (OSI) protocol stack, the internet layer is often improperly called network layer . Internetworking The most notable example of internetworking is the Internet , a network of networks based on many underlying hardware technologies. The Internet

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616-420: The link layer to assure data integrity for the entire packet including the checksum. The primary protocols in the internet layer are the Internet Protocol (IP). It is implemented in two versions, IPv4 and IPv6 . The Internet Control Message Protocol (ICMP) is primarily used for error and diagnostic functions. Different implementations exist for IPv4 and IPv6. The Internet Group Management Protocol (IGMP)

644-469: The network layer responds to service requests from the transport layer and issues service requests to the data link layer . Functions of the network layer include: The TCP/IP model describes the protocols used by the Internet. The TCP/IP model has a layer called the Internet layer , located above the link layer . In many textbooks and other secondary references, the TCP/IP Internet layer

672-399: The participating networks by routing packets to their destinations based on standardized addresses. Another type of interconnection of networks often occurs within enterprises at the link 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 with network bridges and network switches . This

700-427: The protocols that fulfill the purpose of maintaining link states between the local nodes and that usually use protocols that are based on the framing of packets specific to the link types. Such protocols belong to the link layer . Internet-layer protocols use IP-based packets. A common design aspect in the internet layer is the robustness principle : "Be liberal in what you accept, and conservative in what you send" as

728-452: The seven-layer OSI model of computer networking , the network layer is layer 3 . The network layer is responsible for packet forwarding including routing through intermediate routers . The network layer provides the means of transferring variable-length network packets from a source to a destination host via one or more networks. Within the service layering semantics of the OSI (Open Systems Interconnection) network architecture,

756-564: Was developed under the auspices of the International 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 the Network Layer (Layer 3) of the model. The Internet Protocol Suite , also known as the TCP/IP model, was not designed to conform to

784-436: Was gradually displaced by the short-form of the term internetwork, internet (lower-case i ), when the Internet Protocol replaced earlier protocols on the ARPANET in the early 1980s. To build an internetwork, the following are needed: A standardized scheme to address packets to any host on any participating network; a standardized protocol defining format and handling of transmitted packets; components interconnecting

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