出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2016/09/13 21:01:50」(JST)
「LAN」はこの項目へ転送されています。Light At Nightについては「常夜灯」を、その他の用法については「ラン」をご覧ください。 |
Local Area Network(ローカル・エリア・ネットワーク)とは、
LANの標準化組織である米国電気電子技術者協会(IEEE)や国際標準化機構(ISO)での定義によると
といった特徴をもっている。
かつては様々な方式のLANが使用されていたが、現在ではイーサネットと、インターネットの(レイヤ4以下の)プロトコルであるTCP/IPを組み合わせるタイプ(イントラネット)が一般的である。
最初に発明されたLANがイーサネットであることから[要出典]、イーサネットとLANがほぼ同義の意味で使用される場合も多い。
近年は無線方式による、無線LAN(IEEE 802.11シリーズ)も普及している。
HomePNAは家庭内の既設電話線を利用するLANである。
既設の電灯線・配電線を利用するPLCも家庭内LANの新技術として注目されている。
1970年、大阪万博で提唱・試験的に運用される。
この節の加筆が望まれています。 |
レイヤについてはOSI参照モデルを参照の事。
ネットワーク形態による分類では、Peer to Peer型LANとクライアント・サーバ型LANに分けられる。
トポロジー(形状)による分類では、スター型、バス型、リング型の3つに分類される。
スター型
バス型
リング型
変調方式による分類では、ベースバンド方式とブロードバンド方式に分けられる。
この項目は、コンピュータに関連した書きかけの項目です。この項目を加筆・訂正などしてくださる協力者を求めています(PJ:コンピュータ/P:コンピュータ)。 |
Computer network types by spatial scope |
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A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building[1] and has its network equipment and interconnects locally managed. By contrast, a wide area network (WAN), not only covers a larger geographic distance, but also generally involves leased telecommunication circuits or Internet links.
Ethernet and Wi-Fi are the two most common transmission technologies in use for local area networks. Historical technologies include ARCNET, Token ring, and AppleTalk.
The increasing demand and use of computers in universities and research labs in the late 1960s generated the need to provide high-speed interconnections between computer systems. A 1970 report from the Lawrence Radiation Laboratory detailing the growth of their "Octopus" network gave a good indication of the situation.[2][3]
A number of experimental and early commercial LAN technologies were developed in the 1970s. Cambridge Ring was developed at Cambridge University starting in 1974.[4] Ethernet was developed at Xerox PARC in 1973–1975,[5] and filed as U.S. Patent 4,063,220. In 1976, after the system was deployed at PARC, Robert Metcalfe and David Boggs published a seminal paper, "Ethernet: Distributed Packet-Switching for Local Computer Networks".[6] ARCNET was developed by Datapoint Corporation in 1976 and announced in 1977.[7] It had the first commercial installation in December 1977 at Chase Manhattan Bank in New York.[8]
The development and proliferation of personal computers using the CP/M operating system in the late 1970s, and later DOS-based systems starting in 1981, meant that many sites grew to dozens or even hundreds of computers. The initial driving force for networking was generally to share storage and printers, which were both expensive at the time. There was much enthusiasm for the concept and for several years, from about 1983 onward, computer industry pundits would regularly declare the coming year to be, “The year of the LAN”.[9][10][11]
In practice, the concept was marred by proliferation of incompatible physical layer and network protocol implementations, and a plethora of methods of sharing resources. Typically, each vendor would have its own type of network card, cabling, protocol, and network operating system. A solution appeared with the advent of Novell NetWare which provided even-handed support for dozens of competing card/cable types, and a much more sophisticated operating system than most of its competitors. Netware dominated[12] the personal computer LAN business from early after its introduction in 1983 until the mid-1990s when Microsoft introduced Windows NT Advanced Server and Windows for Workgroups.
Of the competitors to NetWare, only Banyan Vines had comparable technical strengths, but Banyan never gained a secure base. Microsoft and 3Com worked together to create a simple network operating system which formed the base of 3Com's 3+Share, Microsoft's LAN Manager and IBM's LAN Server - but none of these was particularly successful.
During the same period, Unix workstations were using TCP/IP based networking. Although this market segment is now much reduced, the technologies developed in this area continue to be influential on the Internet and in both Linux and Apple Mac OS X networking—and the TCP/IP protocol has now almost completely replaced IPX, AppleTalk, NBF, and other protocols used by the early PC LANs.
Early LAN cabling had generally been based on various grades of coaxial cable. Shielded twisted pair was used in IBM's Token Ring LAN implementation, but in 1984, StarLAN showed the potential of simple unshielded twisted pair by using Cat3 cable—the same simple cable used for telephone systems. This led to the development of 10BASE-T (and its successors) and structured cabling which is still the basis of most commercial LANs today.
While fiber-optic cabling is common for links between switches, use of fiber to the desktop is rare.[13]
Many LANs are now based partly or wholly on wireless technologies. Smartphones, tablet computers and laptops typically have wireless networking support built-in. In a wireless local area network, users may move unrestricted in the coverage area. Wireless networks have become popular in residences and small businesses, because of their ease of installation. Guests are often offered Internet access via a hotspot service.
Network topology describes the layout of interconnections between devices and network segments. At the Data Link Layer and Physical Layer, a wide variety of LAN topologies have been used, including ring, bus, mesh and star, but the most common LAN topology in use today is switched Ethernet. At the higher layers, NetBEUI, IPX/SPX, AppleTalk and others were once common, but the Internet Protocol Suite (TCP/IP) is now the standard.
Simple LANs generally consist of cabling and one or more switches. A switch can be connected to a router, cable modem, or ADSL modem for Internet access. A LAN can include a wide variety of other network devices such as firewalls, load balancers, and sensors;[14] and more complex LANs are characterized by their use of redundant links with switches using the spanning tree protocol to prevent loops, their ability to manage differing traffic types via quality of service (QoS), and to segregate traffic with VLANs.
LANs can maintain connections with other LANs via leased lines, leased services, or across the Internet using virtual private network technologies. Depending on how the connections are established and secured, and the distance involved, such linked LANs may also be classified as a metropolitan area network (MAN) or a wide area network (WAN).
As alternatives were considered, fiber to the desk was evaluated, yet only briefly due to the added costs for fiber switches, cables and NICs. "Copper is still going to be a driving force to the desktop for the future, especially as long as the price for fiber components remains higher than for copper."
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