96-485: The access stratum (AS) in computer networking and telecommunications is a functional layer in the UMTS and LTE wireless telecom protocol stacks between radio network and user equipment . While the definition of the access stratum is very different between UMTS and LTE , in both cases the access stratum is responsible for transporting data over the wireless connection and managing radio resources. The radio network
192-615: A best-effort service , an early contribution to what will be the Transmission Control Protocol (TCP). Bob Metcalfe and others at Xerox PARC outlined the idea of Ethernet and the PARC Universal Packet (PUP) for internetworking. In May 1974, Vint Cerf and Bob Kahn described the Transmission Control Program , an internetworking protocol for sharing resources using packet-switching among
288-400: A header and a payload . Data in the header is used by networking hardware to direct the packet to its destination, where the payload is extracted and used by an operating system , application software , or higher layer protocols . Packet switching is the primary basis for data communications in computer networks worldwide. During the early 1960s, American engineer Paul Baran developed
384-784: A patent application in the United Kingdom for time-sharing in February 1959. In June that year, he gave a paper "Time Sharing in Large Fast Computers" at the UNESCO Information Processing Conference in Paris where he passed the concept on to J. C. R. Licklider . Licklider (along with John McCarthy ) was instrumental in the development of time-sharing. After conversations with Licklider about time-sharing with remote computers in 1965, Davies independently invented
480-737: A protocol stack , often constructed per the OSI model, communications functions are divided up into protocol layers, where each layer leverages the services of the layer below it until the lowest layer controls the hardware that sends information across the media. The use of protocol layering is ubiquitous across the field of computer networking. An important example of a protocol stack is HTTP (the World Wide Web protocol) running over TCP over IP (the Internet protocols) over IEEE 802.11 (the Wi-Fi protocol). This stack
576-555: A concept he called distributed adaptive message block switching , with the goal of providing a fault-tolerant , efficient routing method for telecommunication messages as part of a research program at the RAND Corporation , funded by the United States Department of Defense . His ideas contradicted then-established principles of pre- allocation of network bandwidth , exemplified by the development of telecommunications in
672-404: A connection identifier rather than address information and the packet header can be smaller, as it only needs to contain this code and any information, such as length, timestamp, or sequence number, which is different for different packets. In this case, address information is only transferred to each node during the connection setup phase, when the route to the destination is discovered and an entry
768-499: A diverse set of networking capabilities. The protocols have a flat addressing scheme. They operate mostly at layers 1 and 2 of the OSI model. For example, MAC bridging ( IEEE 802.1D ) deals with the routing of Ethernet packets using a Spanning Tree Protocol . IEEE 802.1Q describes VLANs , and IEEE 802.1X defines a port-based network access control protocol, which forms the basis for the authentication mechanisms used in VLANs (but it
864-552: A general architecture for a large-scale, distributed, survivable communications network. The proposal was composed of three key ideas: use of a decentralized network with multiple paths between any two points; dividing user messages into message blocks; and delivery of these messages by store and forward switching. Baran's network design was focused on digital communication of voice messages using switches that were low-cost electronics. Christopher Strachey , who became Oxford University's first Professor of Computation, filed
960-727: A human user. This addressed a key question about the viability of computer networking. Larry Roberts brought Kleinrock into the ARPANET project informally in early 1967. Roberts and Taylor recognized the issue of response time was important, but did not apply Kleinrock's methods to assess this and based their design on a store-and-forward system that was not intended for real-time computing . After SOSP, and after Roberts' direction to use packet switching, Kleinrock sought input from Baran and proposed to retain Baran and RAND as advisors. The ARPANET working group assigned Kleinrock responsibility to prepare
1056-440: A large, congested network into an aggregation of smaller, more efficient networks. A router is an internetworking device that forwards packets between networks by processing the addressing or routing information included in the packet. The routing information is often processed in conjunction with the routing table . A router uses its routing table to determine where to forward packets and does not require broadcasting packets which
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#17328581416041152-440: A multi-port bridge. Switches normally have numerous ports, facilitating a star topology for devices, and for cascading additional switches. Bridges and switches operate at the data link layer (layer 2) of the OSI model and bridge traffic between two or more network segments to form a single local network. Both are devices that forward frames of data between ports based on the destination MAC address in each frame. They learn
1248-584: A proposal for packet switching". Davies' paper reignited a previous dispute over who deserves credit for getting the ARPANET online between engineers at Bolt, Beranek, and Newman (BBN) who had been involved in building and designing the ARPANET IMP on the one side, and ARPA-related researchers on the other. This earlier dispute is exemplified by BBN's Will Crowther , who in a 1990 oral history described Paul Baran's packet switching design (which he called hot-potato routing ), as "crazy" and non-sensical, despite
1344-453: A repeater hub assists with collision detection and fault isolation for the network. Hubs and repeaters in LANs have been largely obsoleted by modern network switches. Network bridges and network switches are distinct from a hub in that they only forward frames to the ports involved in the communication whereas a hub forwards to all ports. Bridges only have two ports but a switch can be thought of as
1440-516: A report on software for the IMP. In 1968, Roberts awarded Kleinrock a contract to establish a Network Measurement Center (NMC) at UCLA to measure and model the performance of packet switching in the ARPANET. Bolt Beranek & Newman (BBN) won the contract to build the network. Designed principally by Bob Kahn , it was the first wide-area packet-switched network with distributed control. The BBN "IMP Guys" independently developed significant aspects of
1536-516: A response, thus diminishing the attractiveness of the first strike advantage by enemies (see Mutual assured destruction ). In the early 1960s, Baran invented the concept of distributed adaptive message block switching in support of the Air Force initiative. The concept was first presented to the Air Force in the summer of 1961 as briefing B-265, later published as RAND report P-2626 in 1962, and finally in report RM 3420 in 1964. The reports describe
1632-634: A scale to provide data communication across the United Kingdom. Larry Roberts made the key decisions in the request for proposal to build the ARPANET . Roberts met Baran in February 1967, but did not discuss networks. He asked Frank Westervelt to explore the questions of message size and contents for the network, and to write a position paper on the intercomputer communication protocol including “conventions for character and block transmission, error checking and re transmission, and computer and user identification." Roberts revised his initial design, which
1728-471: A shared physical medium (such as radio or 10BASE5 ), the packets may be delivered according to a multiple access scheme. Packet switching contrasts with another principal networking paradigm, circuit switching , a method which pre-allocates dedicated network bandwidth specifically for each communication session, each having a constant bit rate and latency between nodes. In cases of billable services, such as cellular communication services, circuit switching
1824-406: A similar data communication concept, using short messages in fixed format with high data transmission rates to achieve rapid communications. He went on to develop a more advanced design for a hierarchical, high-speed computer network including interface computers and communication protocols . He coined the term packet switching , and proposed building a commercial nationwide data network in
1920-418: A single failure can cause the network to fail entirely. In general, the more interconnections there are, the more robust the network is; but the more expensive it is to install. Therefore, most network diagrams are arranged by their network topology which is the map of logical interconnections of network hosts. Common topologies are: The physical layout of the nodes in a network may not necessarily reflect
2016-403: A standard voice telephone line. Modems are still commonly used for telephone lines, using a digital subscriber line technology and cable television systems using DOCSIS technology. A firewall is a network device or software for controlling network security and access rules. Firewalls are inserted in connections between secure internal networks and potentially insecure external networks such as
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#17328581416042112-877: A transmission medium. Power line communication uses a building's power cabling to transmit data. The following classes of wired technologies are used in computer networking. Network connections can be established wirelessly using radio or other electromagnetic means of communication. The last two cases have a large round-trip delay time , which gives slow two-way communication but does not prevent sending large amounts of information (they can have high throughput). Apart from any physical transmission media, networks are built from additional basic system building blocks, such as network interface controllers , repeaters , hubs , bridges , switches , routers , modems, and firewalls . Any particular piece of equipment will frequently contain multiple building blocks and so may perform multiple functions. A network interface controller (NIC)
2208-406: A variety of network topologies . The nodes of a computer network can include personal computers , servers , networking hardware , or other specialized or general-purpose hosts . They are identified by network addresses and may have hostnames . Hostnames serve as memorable labels for the nodes and are rarely changed after initial assignment. Network addresses serve for locating and identifying
2304-495: A variety of different sources, primarily to support circuit-switched digital telephony . However, due to its protocol neutrality and transport-oriented features, SONET/SDH also was the obvious choice for transporting Asynchronous Transfer Mode (ATM) frames. Asynchronous Transfer Mode (ATM) is a switching technique for telecommunication networks. It uses asynchronous time-division multiplexing and encodes data into small, fixed-sized cells . This differs from other protocols such as
2400-652: A virtual system of links that run on top of the Internet . Overlay networks have been used since the early days of networking, back when computers were connected via telephone lines using modems, even before data networks were developed. The most striking example of an overlay network is the Internet itself. The Internet itself was initially built as an overlay on the telephone network . Even today, each Internet node can communicate with virtually any other through an underlying mesh of sub-networks of wildly different topologies and technologies. Address resolution and routing are
2496-519: Is computer hardware that connects the computer to the network media and has the ability to process low-level network information. For example, the NIC may have a connector for plugging in a cable, or an aerial for wireless transmission and reception, and the associated circuitry. In Ethernet networks, each NIC has a unique Media Access Control (MAC) address —usually stored in the controller's permanent memory. To avoid address conflicts between network devices,
2592-400: Is a proprietary suite of networking protocols developed by Apple in 1985 for Apple Macintosh computers. It was the primary protocol used by Apple devices through the 1980s and 1990s. AppleTalk included features that allowed local area networks to be established ad hoc without the requirement for a centralized router or server. The AppleTalk system automatically assigned addresses, updated
2688-422: Is a virtual network that is built on top of another network. Nodes in the overlay network are connected by virtual or logical links. Each link corresponds to a path, perhaps through many physical links, in the underlying network. The topology of the overlay network may (and often does) differ from that of the underlying one. For example, many peer-to-peer networks are overlay networks. They are organized as nodes of
2784-410: Is added to the switching table in each network node through which the connection passes. When a connection identifier is used, routing a packet requires the node to look up the connection identifier in a table. Connection-oriented transport layer protocols such as TCP provide a connection-oriented service by using an underlying connectionless network. In this case, the end-to-end principle dictates that
2880-562: Is also called access network. This article about wireless technology is a stub . You can help Misplaced Pages by expanding it . Computer network A computer network is a set of computers sharing resources located on or provided by network nodes . Computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are made up of telecommunication network technologies based on physically wired, optical , and wireless radio-frequency methods that may be arranged in
2976-553: Is also found in WLANs ) – it is what the home user sees when the user has to enter a "wireless access key". Ethernet is a family of technologies used in wired LANs. It is described by a set of standards together called IEEE 802.3 published by the Institute of Electrical and Electronics Engineers. Wireless LAN based on the IEEE 802.11 standards, also widely known as WLAN or WiFi, is probably
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3072-478: Is an electronic device that receives a network signal , cleans it of unnecessary noise and regenerates it. The signal is retransmitted at a higher power level, or to the other side of obstruction so that the signal can cover longer distances without degradation. In most twisted-pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. With fiber optics, repeaters can be tens or even hundreds of kilometers apart. Repeaters work on
3168-428: Is characterized by a fee per unit of connection time, even when no data is transferred, while packet switching may be characterized by a fee per unit of information transmitted, such as characters, packets, or messages. A packet switch has four components: input ports, output ports, routing processor, and switching fabric. The concept of switching small blocks of data was first explored independently by Paul Baran at
3264-493: Is implemented by the Internet Protocol Suite using a variety of link layer technologies. For example, Ethernet and Frame Relay are common. Newer mobile phone technologies (e.g., GSM , LTE ) also use packet switching. Packet switching is associated with connectionless networking because, in these systems, no connection agreement needs to be established between communicating parties prior to exchanging data. X.25 ,
3360-412: Is inefficient for very big networks. Modems (modulator-demodulator) are used to connect network nodes via wire not originally designed for digital network traffic, or for wireless. To do this one or more carrier signals are modulated by the digital signal to produce an analog signal that can be tailored to give the required properties for transmission. Early modems modulated audio signals sent over
3456-409: Is needed in the packet header, which is therefore larger. The packets are routed individually, sometimes taking different paths resulting in out-of-order delivery . At the destination, the original message may be reassembled in the correct order, based on the packet sequence numbers. Thus a virtual circuit carrying a byte stream is provided to the application by a transport layer protocol, although
3552-404: Is not sending packets, the link can be filled with packets from other users, and so the cost can be shared, with relatively little interference, provided the link is not overused. Often the route a packet needs to take through a network is not immediately available. In that case, the packet is queued and waits until a link is free. The physical link technologies of packet networks typically limit
3648-415: Is the process of selecting network paths to carry network traffic. Routing is performed for many kinds of networks, including circuit switching networks and packet switched networks. Packet-switched network In telecommunications , packet switching is a method of grouping data into short messages in fixed format, i.e. packets , that are transmitted over a digital network . Packets are made of
3744-459: Is used between the wireless router and the home user's personal computer when the user is surfing the web. There are many communication protocols, a few of which are described below. The Internet protocol suite , also called TCP/IP, is the foundation of all modern networking. It offers connection-less and connection-oriented services over an inherently unreliable network traversed by datagram transmission using Internet protocol (IP). At its core,
3840-526: The Bell System . The new concept found little resonance among network implementers until the independent work of Welsh computer scientist Donald Davies at the National Physical Laboratory in 1965. Davies coined the modern term packet switching and inspired numerous packet switching networks in the decade following, including the incorporation of the concept into the design of the ARPANET in
3936-457: The Institute of Electrical and Electronics Engineers (IEEE) maintains and administers MAC address uniqueness. The size of an Ethernet MAC address is six octets . The three most significant octets are reserved to identify NIC manufacturers. These manufacturers, using only their assigned prefixes, uniquely assign the three least-significant octets of every Ethernet interface they produce. A repeater
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4032-462: The Internet era which initially competed with the OSI model . Research into packet switching at the National Physical Laboratory (NPL) began with a proposal for a wide-area network in 1965, and a local-area network in 1966. ARPANET funding was secured in 1966 by Bob Taylor , and planning began in 1967 when he hired Larry Roberts . The NPL network followed by the ARPANET became operational in 1969,
4128-537: The Internet protocol suite and the associated Internet architecture and governance that emerged in the 1980s. For a period in the 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 Internet protocol suite and the OSI model would result in the best and most robust computer networks. Leonard Kleinrock's research work during
4224-631: The RAND Corporation during the early 1960s in the US and Donald Davies at the National Physical Laboratory (NPL) in the UK in 1965. In the late 1950s, the US Air Force established a wide area network for the Semi-Automatic Ground Environment (SAGE) radar defense system. Recognizing vulnerabilities in this network, the Air Force sought a system that might survive a nuclear attack to enable
4320-526: The User Datagram Protocol (UDP). Connection-oriented systems include X.25, Frame Relay , Multiprotocol Label Switching (MPLS), and TCP. In connectionless mode each packet is labeled with a destination address, source address, and port numbers. It may also be labeled with the sequence number of the packet. This information eliminates the need for a pre-established path to help the packet find its way to its destination, but means that more information
4416-470: The World Wide Web , digital video and audio , shared use of application and storage servers , printers and fax machines , and use of email and instant messaging applications. Computer networking may be considered a branch of computer science , computer engineering , and telecommunications , since it relies on the theoretical and practical application of the related disciplines. Computer networking
4512-524: The end-to-end principle . Davies proposed that a local-area network should be built at the laboratory to serve the needs of NPL and prove the feasibility of packet switching. After a pilot experiment in early 1969, the NPL Data Communications Network began service in 1970. Davies was invited to Japan to give a series of lectures on packet switching. The NPL team carried out simulation work on datagrams and congestion in networks on
4608-419: The 1970s addressed packet switching networks, packet radio networks, local area networks, broadband networks, nomadic computing, peer-to-peer networks, and intelligent software agents. His theoretical work on hierarchical routing with student Farouk Kamoun became critical to the operation of the Internet. Kleinrock published hundreds of research papers, which ultimately launched a new field of research on
4704-413: The 1970s, which was an extension of his pioneering work in the early 1960s on the optimization of message delays in communication networks. However, Kleinrock's claims that his work in the early 1960s originated the concept of packet switching and that his work was a source of the packet switching concepts used in the ARPANET have affected sources on the topic, which has created methodological challenges in
4800-456: The ARPA team having advocated for it. The reignited debate caused other former BBN employees to make their concerns known, including Alex McKenzie, who followed Davies in disputing that Kleinrock's work was related to packet switching, stating "... there is nothing in the entire 1964 book that suggests, analyzes, or alludes to the idea of packetization". Former IPTO director Bob Taylor also joined
4896-589: The ARPANET. His work influenced the development of the ARPANET and packet-switched networks generally. The ARPANET was demonstrated at the International Conference on Computer Communication (ICCC) in Washington in October 1972. However, fundamental questions about the design of packet-switched networks remained. Roberts presented the idea of packet switching to communication industry professionals in
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#17328581416044992-440: The Internet protocol suite or Ethernet that use variable-sized packets or frames . ATM has similarities with both circuit and packet switched networking. This makes it a good choice for a network that must handle both traditional high-throughput data traffic, and real-time, low-latency content such as voice and video. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before
5088-574: The Internet. Firewalls are typically configured to reject access requests from unrecognized sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in cyber attacks . A communication protocol is a set of rules for exchanging information over a network. Communication protocols have various characteristics. They may be connection-oriented or connectionless , they may use circuit mode or packet switching, and they may use hierarchical addressing or flat addressing. In
5184-477: The UK. He gave a talk on the proposal in 1966, after which a person from the Ministry of Defence (MoD) told him about Baran's work. Roger Scantlebury , a member of Davies' team, presented their work (and referenced that of Baran) at the October 1967 Symposium on Operating Systems Principles (SOSP). At the conference, Scantlebury proposed packet switching for use in the ARPANET and persuaded Larry Roberts
5280-566: The United States and the CYCLADES network in France. The ARPANET and CYCLADES were the primary precursor networks of the modern Internet . A simple definition of packet switching is: The routing and transferring of data by means of addressed packets so that a channel is occupied during the transmission of the packet only, and upon completion of the transmission the channel is made available for
5376-410: The United States, Europe and Japan and was the "cornerstone" that inspired numerous packet switching networks in the decade following. The history of packet-switched networks can be divided into three overlapping eras: early networks before the introduction of X.25; the X.25 era when many postal, telephone, and telegraph (PTT) companies provided public data networks with X.25 interfaces; and
5472-567: The above claim made on Kleinrock's profile on the UCLA Computer Science department website sometime in the 1990s. Here, he was referred to as the "Inventor of the Internet Technology". The webpage's depictions of Kleinrock's achievements provoked anger among some early Internet pioneers. The dispute over priority became a public issue after Donald Davies posthumously published a paper in 2001 in which he denied that Kleinrock's work
5568-627: The actual data exchange begins. ATM still plays a role in the last mile , which is the connection between an Internet service provider and the home user. There are a number of different digital cellular standards, including: Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), cdmaOne , CDMA2000 , Evolution-Data Optimized (EV-DO), Enhanced Data Rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Digital Enhanced Cordless Telecommunications (DECT), Digital AMPS (IS-136/TDMA), and Integrated Digital Enhanced Network (iDEN). Routing
5664-409: The application of queueing theory in the field of message switching for his doctoral dissertation in 1961–62 and published it as a book in 1964. Davies, in his 1966 paper on packet switching, applied Kleinorck's techniques to show that "there is an ample margin between the estimated performance of the [packet-switched] system and the stated requirement" in terms of a satisfactory response time for
5760-468: The association of physical ports to MAC addresses by examining the source addresses of received frames and only forward the frame when necessary. If an unknown destination MAC is targeted, the device broadcasts the request to all ports except the source, and discovers the location from the reply. Bridges and switches divide the network's collision domain but maintain a single broadcast domain. Network segmentation through bridging and switching helps break down
5856-460: The conference, which a number of sources describe as "vague"), and that this originated with his old colleague, Kleinrock, who had written about such concepts in his Ph.D. research in 1961-2. In 1997, along with seven other Internet pioneers , Roberts and Kleinrock co-wrote "Brief History of the Internet" published by the Internet Society . In it, Kleinrock is described as having "published
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#17328581416045952-491: The cost of removing bandwidth guarantees. In practice, congestion control is generally used in IP networks to dynamically negotiate capacity between connections. Packet switching may also increase the robustness of networks in the face of failures. If a node fails, connections do not need to be interrupted, as packets may be routed around the failure. Packet switching is used in the Internet and most local area networks . The Internet
6048-565: The debate, stating that "authors who have interviewed dozens of Arpanet pioneers know very well that the Kleinrock-Roberts claims are not believed". Walter Isaacson notes that "until the mid-1990s Kleinrock had credited [Baran and Davies] with coming up with the idea of packet switching". A subsequent version of Kleinrock's biography webpage was copyrighted in 2009 by Kleinrock. He was called on to defend his position over subsequent decades. In 2023, he acknowledged that his published work in
6144-672: The distributed namespace, and configured any required inter-network routing . It was a plug-n-play system. AppleTalk implementations were also released for the IBM PC and compatibles, and the Apple IIGS . AppleTalk support was available in most networked printers, especially laser printers , some file servers and routers . The protocol was designed to be simple, autoconfiguring, and not require servers or other specialized services to work. These benefits also created drawbacks, as Appletalk tended not to use bandwidth efficiently. AppleTalk support
6240-431: The early 1960s was about message switching and claimed he was thinking about packet switching. Primary sources and historians recognize Baran and Davies for independently inventing the concept of digital packet switching used in modern computer networking including the ARPANET and the Internet. Kleinrock has received many awards for his ground-breaking applied mathematical research on packet switching, carried out in
6336-418: The early 1970s to study internetworking . It was the first to implement the end-to-end principle of Davies, and make the host computers responsible for the reliable delivery of data on a packet-switched network, rather than this being a service of the network itself. His team was thus first to tackle the highly-complex problem of providing user applications with a reliable virtual circuit service while using
6432-418: The early 1970s. Before ARPANET was operating, they argued that the router buffers would quickly run out. After the ARPANET was operating, they argued packet switching would never be economic without the government subsidy. Baran had faced the same rejection and thus failed to convince the military into constructing a packet switching network in the 1960s. The CYCLADES network was designed by Louis Pouzin in
6528-490: The economics were favorable to message switching . Davies had chosen some of the same parameters for his original network design as did Baran, such as a packet size of 1024 bits. To deal with packet permutations (due to dynamically updated route preferences) and datagram losses (unavoidable when fast sources send to a slow destinations), he assumed that "all users of the network will provide themselves with some kind of error control", thus inventing what came to be known as
6624-415: The edge of the network and the network core. In the datagram system, operating according to the end-to-end principle, the hosts have the responsibility to ensure orderly delivery of packets. In the virtual call system, the network guarantees sequenced delivery of data to the host. This results in a simpler host interface but complicates the network. The X.25 protocol suite uses this network type. AppleTalk
6720-440: The end nodes, not the network itself, are responsible for the connection-oriented behavior. In telecommunication networks, packet switching is used to optimize the usage of channel capacity and increase robustness . Compared to circuit switching , packet switching is highly dynamic, allocating channel capacity based on usage instead of explicit reservations. This can reduce wasted capacity caused by underutilized reservations at
6816-515: The first paper on packet switching theory in July 1961 and the first book on the subject in 1964". Many sources about the history of the Internet began to reflect these claims as uncontroversial facts. This became the subject of what Katie Hafner called a "paternity dispute" in The New York Times in 2001. The disagreement about Kleinrock's contribution to packet switching dates back to a version of
6912-406: The first two networks to use packet switching. Larry Roberts said many of the packet switching networks built in the 1970s were similar "in nearly all respects" to Donald Davies' original 1965 design. Before the introduction of X.25 in 1976, about twenty different network technologies had been developed. Two fundamental differences involved the division of functions and tasks between the hosts at
7008-660: The historiography of the Internet. Historian Andrew L. Russell said "'Internet history' also suffers from a third, methodological, problem: it tends to be too close to its sources. Many Internet pioneers are alive, active, and eager to shape the histories that describe their accomplishments. Many museums and historians are equally eager to interview the pioneers and to publicize their stories". Packet switching may be classified into connectionless packet switching, also known as datagram switching, and connection-oriented packet switching, also known as virtual circuit switching. Examples of connectionless systems are Ethernet, IP, and
7104-562: The international CCITT standard of 1976, is a notable use of packet switching in that it provides to users a service of flow-controlled virtual circuits . These virtual circuits reliably carry variable-length packets with data order preservation. DATAPAC in Canada was the first public network to support X.25, followed by TRANSPAC in France. Asynchronous Transfer Mode (ATM) is another virtual circuit technology. It differs from X.25 in that it uses small fixed-length packets ( cells ), and that
7200-505: The link capacity and the traffic load on the network. Packets are normally forwarded by intermediate network nodes asynchronously using first-in, first-out buffering, but may be forwarded according to some scheduling discipline for fair queuing , traffic shaping , or for differentiated or guaranteed quality of service , such as weighted fair queuing or leaky bucket . Packet-based communication may be implemented with or without intermediate forwarding nodes (switches and routers). In case of
7296-620: The literature as the physical medium ) used to link devices to form a computer network include electrical cable , optical fiber , and free space. In the OSI model , the software to handle the media is defined at layers 1 and 2 — the physical layer and the data link layer. A widely adopted family that uses copper and fiber media in local area network (LAN) technology are collectively known as Ethernet. The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 802.3 . Wireless LAN standards use radio waves , others use infrared signals as
7392-665: The means that allow mapping of a fully connected IP overlay network to its underlying network. Another example of an overlay network is a distributed hash table , which maps keys to nodes in the network. In this case, the underlying network is an IP network, and the overlay network is a table (actually a map ) indexed by keys. Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service guarantees achieve higher-quality streaming media . Previous proposals such as IntServ , DiffServ , and IP multicast have not seen wide acceptance largely because they require modification of all routers in
7488-415: The most well-known member of the IEEE 802 protocol family for home users today. IEEE 802.11 shares many properties with wired Ethernet. Synchronous optical networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers. They were originally designed to transport circuit mode communications from
7584-617: The network imposes no flow control to users. Technologies such as MPLS and the Resource Reservation Protocol (RSVP) create virtual circuits on top of datagram networks. MPLS and its predecessors, as well as ATM, have been called "fast packet" technologies. MPLS, indeed, has been called "ATM without cells". Virtual circuits are especially useful in building robust failover mechanisms and allocating bandwidth for delay-sensitive applications. Donald Davies' work on data communications and computer network design became well known in
7680-412: The network needs to deliver the user data, for example, source and destination network addresses , error detection codes, and sequencing information. Typically, control information is found in packet headers and trailers , with payload data in between. With packets, the bandwidth of the transmission medium can be better shared among users than if the network were circuit switched . When one user
7776-421: The network only provides a connectionless network layer service. Connection-oriented transmission requires a setup phase to establish the parameters of communication before any packet is transferred. The signaling protocols used for setup allow the application to specify its requirements and discover link parameters. Acceptable values for service parameters may be negotiated. The packets transferred may include
7872-420: The network topology. As an example, with FDDI , the network topology is a ring, but the physical topology is often a star, because all neighboring connections can be routed via a central physical location. Physical layout is not completely irrelevant, however, as common ducting and equipment locations can represent single points of failure due to issues like fires, power failures and flooding. An overlay network
7968-672: The network's internal operation, including the routing algorithm, flow control, software design, and network control. The UCLA NMC and the BBN team also investigated network congestion. The Network Working Group, led by Steve Crocker , a graduate student of Kleinrock's at UCLA, developed the host-to-host protocol, the Network Control Program , which was approved by Barry Wessler for ARPA, after he ordered certain more exotic elements to be dropped. In 1970, Kleinrock extended his earlier analytic work on message switching to packet switching in
8064-729: The network. On the other hand, an overlay network can be incrementally deployed on end-hosts running the overlay protocol software, without cooperation from Internet service providers . The overlay network has no control over how packets are routed in the underlying network between two overlay nodes, but it can control, for example, the sequence of overlay nodes that a message traverses before it reaches its destination . For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast ). Academic research includes end system multicast, resilient routing and quality of service studies, among others. The transmission media (often referred to in
8160-486: The nodes by communication protocols such as the Internet Protocol . Computer networks may be classified by many criteria, including the transmission medium used to carry signals, bandwidth , communications protocols to organize network traffic , the network size, the topology, traffic control mechanisms, and organizational intent. Computer networks support many applications and services , such as access to
8256-582: The nodes. The specifications of the TCP were then published in RFC 675 ( Specification of Internet Transmission Control Program ), written by Vint Cerf, Yogen Dalal and Carl Sunshine in December 1974. The X.25 protocol , developed by Rémi Després and others, was built on the concept of virtual circuits . In the mid-late 1970s and early 1980s, national and international public data networks emerged using X.25 which
8352-515: The physical layer of the OSI model but still require a small amount of time to regenerate the signal. This can cause a propagation delay that affects network performance and may affect proper function. As a result, many network architectures limit the number of repeaters used in a network, e.g., the Ethernet 5-4-3 rule . An Ethernet repeater with multiple ports is known as an Ethernet hub . In addition to reconditioning and distributing network signals,
8448-456: The protocol suite defines the addressing, identification, and routing specifications for Internet Protocol Version 4 (IPv4) and for IPv6 , the next generation of the protocol with a much enlarged addressing capability. The Internet protocol suite is the defining set of protocols for the Internet. IEEE 802 is a family of IEEE standards dealing with local area networks and metropolitan area networks. The complete IEEE 802 protocol suite provides
8544-515: The sharing of files and information, giving authorized users access to data stored on other computers. Distributed computing leverages resources from multiple computers across a network to perform tasks collaboratively. Most modern computer networks use protocols based on packet-mode transmission. A network packet is a formatted unit of data carried by a packet-switched network . Packets consist of two types of data: control information and user data (payload). The control information provides data
8640-493: The size of packets to a certain maximum transmission unit (MTU). A longer message may be fragmented before it is transferred and once the packets arrive, they are reassembled to construct the original message. The physical or geographic locations of network nodes and links generally have relatively little effect on a network, but the topology of interconnections of a network can significantly affect its throughput and reliability. With many technologies, such as bus or star networks,
8736-468: The theory and application of queuing theory to computer networks. Complementary metal–oxide–semiconductor ( CMOS ) VLSI (very- large-scale integration ) technology led to the development of high-speed broadband packet switching during the 1980s–1990s. Roberts claimed in later years that, by the time of the October 1967 SOSP, he already had the concept of packet switching in mind (although not yet named and not written down in his paper published at
8832-550: The transfer of other traffic . Packet switching allows delivery of variable bit rate data streams, realized as sequences of short messages in fixed format, i.e. packets , over a computer network which allocates transmission resources as needed using statistical multiplexing or dynamic bandwidth allocation techniques. As they traverse networking hardware , such as switches and routers , packets are received, buffered, queued, and retransmitted ( stored and forwarded ), resulting in variable latency and throughput depending on
8928-545: Was developed with participation from France, the UK, Japan, USA and Canada. It was complemented with X.75 to enable internetworking. Packet switching was shown to be optimal in the Huffman coding sense in 1978. In the late 1970s, the monolithic Transmission Control Program was layered as the Transmission Control Protocol (TCP), atop the Internet Protocol (IP). Many Internet pioneers developed this into
9024-462: Was influenced by a wide array of technological developments and historical milestones. Computer networks enhance how users communicate with each other by using various electronic methods like email, instant messaging, online chat, voice and video calls, and video conferencing. Networks also enable the sharing of computing resources. For example, a user can print a document on a shared printer or use shared storage devices. Additionally, networks allow for
9120-460: Was related to packet switching. Davies also described ARPANET project manager Larry Roberts as supporting Kleinrock, referring to Roberts' writings online and Kleinrock's UCLA webpage profile as "very misleading". Walter Isaacson wrote that Kleinrock's claims "led to an outcry among many of the other Internet pioneers, who publicly attacked Kleinrock and said that his brief mention of breaking messages into smaller pieces did not come close to being
9216-481: Was to connect the host computers directly, to incorporate Wesley Clark's idea to use Interface Message Processors (IMPs) to create a message switching network, which he presented at SOSP. Roberts was known for making decisions quickly. Immediately after SOSP, he incorporated Davies' and Baran's concepts and designs for packet switching to enable the data communications on the network. A contemporary of Roberts' from MIT , Leonard Kleinrock had researched
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