Local area network

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] By contrast, a wide area network (WAN) not only covers a larger geographic distance, but also generally involves leased telecommunication circuits.

Ethernet and Wi-Fi are the two most common technologies in use for local area networks. Historical technologies include ARCNET, Token ring, and AppleTalk.

Ethernet LAN
A conceptual diagram of a local area network.

History

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 between 1973 and 1974.[5][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 to share storage and printers, both of which were 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 and cable types, and a much more sophisticated operating system than most of its competitors. Netware dominated the personal computer LAN business from early after its introduction in 1983 until the mid-1990s when Microsoft introduced Windows NT.[12]

Of the competitors to NetWare, only Banyan Vines had comparable technical strengths, but Banyan never gained a secure base. 3Com produced 3+Share and Microsoft produced MS-Net. These then formed the basis for collaboration between Microsoft and 3Com to create a simple network operating system LAN Manager and its cousin, IBM's LAN Server. None of these enjoyed any lasting success.

In 1983, TCP/IP was first shown capable of supporting actual defense department applications on a Defense Communication Agency LAN test bed located at Reston, Virginia.[13] [14]The TCP/IP-based LAN successfully supported Telnet, FTP, and a Defense Department teleconferencing application.[15] This demonstrated the feasibility of employing TCP/IP LANs to interconnect Worldwide Military Command and Control System (WWMCCS) computers at command centers throughout the United States.[16] However, WWMCCS was superseded by the Global Command and Control System (GCCS) before that could happen.

During the same period, Unix workstations were using TCP/IP 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 replaced IPX, AppleTalk, NBF, and other protocols used by the early PC LANs.

Cabling

Early Ethernet (10BASE-5 and 10BASE-2) used coaxial cable. Shielded twisted pair was used in IBM's Token Ring LAN implementation. In 1984, StarLAN showed the potential of simple unshielded twisted pair by using Cat3 cable—the same 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 optical fiber cable is common for links between network switches, use of fiber to the desktop is rare.[17]

Wireless media

Many LANs use wireless technologies that are built into smartphones, tablet computers and laptops. 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.

Technical aspects

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. At the higher layers, NetBEUI, IPX/SPX, AppleTalk and others were once common, but the Internet Protocol Suite (TCP/IP) has prevailed as a standard of choice.

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 network intrusion detection.[18] Advanced 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 their ability 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).

See also

References

  1. ^ Gary A. Donahue (June 2007). Network Warrior. O'Reilly. p. 5.
  2. ^ Samuel F. Mendicino (1970-12-01). "Octopus: The Lawrence Radiation Laboratory Network". Rogerdmoore.ca. Archived from the original on 2010-10-11.
  3. ^ "THE LAWRENCE RADIATION LABORATORY OCTOPUS". Courant symposium series on networks. Osti.gov. 29 Nov 1970. OSTI 4045588.
  4. ^ "A brief informal history of the Computer Laboratory". University of Cambridge. 20 December 2001. Archived from the original on 11 October 2010.
  5. ^ The History of Ethernet. NetEvents.tv. 2006. Retrieved September 10, 2011.
  6. ^ "Ethernet Prototype Circuit Board". Smithsonian National Museum of American History. 1973. Retrieved September 2, 2007.
  7. ^ "ARCNET Timeline" (PDF). ARCNETworks magazine. Fall 1998. Archived from the original (PDF) on 2010-10-11.
  8. ^ Lamont Wood (2008-01-31). "The LAN turns 30, but will it reach 40?". Computerworld.com. Retrieved 2016-06-02.
  9. ^ "'The Year of The LAN' is a long-standing joke, and I freely admit to being the comedian that first declared it in 1982...", Robert Metcalfe, InfoWorld Dec 27, 1993
  10. ^ "...you will remember numerous computer magazines, over numerous years, announcing 'the year of the LAN.'", Quotes in 1999
  11. ^ "...a bit like the Year of the LAN which computer industry pundits predicted for the good part of a decade...", Christopher Herot
  12. ^ Wayne Spivak (2001-07-13). "Has Microsoft Ever Read the History Books?". VARBusiness. Archived from the original on 2010-10-11.
  13. ^ Scott, W. Ross (1984-05-01), "Updated Local Area Network Demonstration Plan." (U) MITRE Corporation Working Paper No. WP83W00222R1.
  14. ^ Havard (II.), Richard (17 June 1986). MITRENET: A Testbed Local Area Network at DTNSRDC. Ft. Belvoir Defense Technical Information Center: Defense Technical Information Center. pp. i.
  15. ^ Scott, W. Ross; Cavedo, Robert F. (1984-09-01), "Local Area Network Demonstration Procedures." (U) MITRE Corporation Working Paper No. WP83W00595.
  16. ^ Scott, W. Ross (1984-08-01), "Local Area Network Alternative "A" Demonstration Analysis (DRAFT). (U) MITRE Corporation Working Paper No. WP84W00281.
  17. ^ "Big pipe on campus: Ohio institutions implement a 10-Gigabit Ethernet switched-fiber backbone to enable high-speed desktop applications over UTP copper", Communications News, 2005-03-01, archived from the original on 2016-09-10, 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."
  18. ^ "A Review of the Basic Components of a Local Area Network (LAN)". NetworkBits.net. Retrieved 2008-04-08.
CXFS

The CXFS file system (Clustered XFS) is a proprietary shared disk file system designed by Silicon Graphics (SGI) specifically to be used in a storage area network (SAN) environment.

A significant difference between CXFS and other distributed file systems is that data and metadata are managed separately from each other. CXFS provides direct access to data via the SAN for all hosts which will act as clients. This means that a client is able to access file data via the fiber connection to the SAN, rather than over a local area network such as Ethernet (as is the case in most other distributed file systems, like NFS). File metadata however, is managed via a metadata broker. The metadata communication is performed via TCP/IP and Ethernet.

Another difference is that file locks are managed by the metadata broker, rather than the individual host clients. This results in the elimination of a number of problems which typically plague distributed file systems.

Though CXFS supports having a heterogeneous environment (including Solaris, Linux, Mac OS X, AIX and Windows), either SGI's IRIX Operating System or Linux is required to be installed on the host which acts as the metadata broker.

Data center bridging

Data center bridging (DCB) is a set of enhancements to the Ethernet local area network communication protocol for use in data center environments, in particular for use with clustering and storage area networks.

Data link layer

The data layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between adjacent network nodes in a wide area network (WAN) or between nodes on the same local area network (LAN) segment. The data link layer provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in the physical layer.

The data link layer is concerned with local delivery of frames between nodes on the same level of the network. Data-link frames, as these protocol data units are called, do not cross the boundaries of a local area network. Inter-network routing and global addressing are higher-layer functions, allowing data-link protocols to focus on local delivery, addressing, and media arbitration. In this way, the data link layer is analogous to a neighborhood traffic cop; it endeavors to arbitrate between parties contending for access to a medium, without concern for their ultimate destination. When devices attempt to use a medium simultaneously, frame collisions occur. Data-link protocols specify how devices detect and recover from such collisions, and may provide mechanisms to reduce or prevent them.

Examples of data link protocols are Ethernet for local area networks (multi-node), the Point-to-Point Protocol (PPP), HDLC and ADCCP for point-to-point (dual-node) connections. In the Internet Protocol Suite (TCP/IP), the data link layer functionality is contained within the link layer, the lowest layer of the descriptive model.

Fiber Distributed Data Interface

Fiber Distributed Data Interface (FDDI) is a standard for data transmission in a local area network.

It uses optical fiber as its standard underlying physical medium, although it was also later specified to use copper cable, in which case it may be called CDDI (Copper Distributed Data Interface), standardized as TP-PMD (Twisted-Pair Physical Medium-Dependent), also referred to as TP-DDI (Twisted-Pair Distributed Data Interface).

Hotspot (Wi-Fi)

A hotspot is a physical location where people may obtain Internet access, typically using Wi-Fi technology, via a wireless local area network (WLAN) using a router connected to an internet service provider.

Public hotspots may be created by a business for use by customers, such as coffee shops or hotels. Public hotspots are typically created from wireless access points configured to provide Internet access, controlled to some degree by the venue. In its simplest form, venues that have broadband Internet access can create public wireless access by configuring an access point (AP), in conjunction with a router and connecting the AP to the Internet connection. A single wireless router combining these functions may suffice.Private hotspots may be configured on a smartphone or tablet with a mobile network data plan to allow Internet access to other devices via Bluetooth pairing or if both the hotspot device and the device/s accessing it are connected to the same Wi-Fi network.

LAN messenger

A LAN Messenger is a instant messaging program for computers designed for use within a single local area network (LAN).

Many LAN Messengers offer basics functionality for sending private messages, file transfer, chatrooms and graphical smileys. The advantage of using a simple LAN messenger over a normal instant messenger is that no active Internet connection or central server is required, and only people inside the firewall will have access to the system.

Link layer

In computer networking, the link layer is the lowest layer in the Internet Protocol Suite, the networking architecture of the Internet. It is described in RFC 1122 and RFC 1123. The link layer is the group of methods and communications protocols that only operate on the link that a host is physically connected to. The link is the physical and logical network component used to interconnect hosts or nodes in the network and a link protocol is a suite of methods and standards that operate only between adjacent network nodes of a local area network segment or a wide area network connection.

Despite the different semantics of layering in TCP/IP and OSI, the link layer is sometimes described as a combination of the data link layer (layer 2) and the physical layer (layer 1) in the OSI model. However, the layers of TCP/IP are descriptions of operating scopes (application, host-to-host, network, link) and not detailed prescriptions of operating procedures, data semantics, or networking technologies.

RFC 1122 exemplifies that local area network protocols such as Ethernet and IEEE 802, and framing protocols such as Point-to-Point Protocol (PPP) belong to the link layer.

Local Peer Discovery

The Local Peer Discovery protocol, specified as BEP-14, is an extension to the BitTorrent file-distribution system. It is designed to support the discovery of local BitTorrent peers, aiming to minimize the traffic through the Internet service provider's (ISP) channel and maximize use of higher-bandwidth local area network (LAN).

Local Peer Discovery is implemented with HTTP-like messages on User Datagram Protocol (UDP) multicast group 239.192.152.143:6771 which is an administratively scoped multicast address. Since implementation is simple, Local Peer Discovery is implemented in several clients (µTorrent, BitTorrent/Mainline, MonoTorrent, libtorrent and its derivatives, Transmission 2.0, aria2 ). An alternative multicast peer discovery protocol is published as BEP 26, but is not widely adopted since it is considered too complex in comparison.

Logical link control

In the IEEE 802 reference model of computer networking, the logical link control (LLC) data communication protocol layer is the upper sublayer of the data link layer (layer 2) of the seven-layer OSI model. The LLC sublayer provides multiplexing mechanisms that make it possible for several network protocols (e.g. IP, IPX, Decnet and Appletalk) to coexist within a multipoint network and to be transported over the same network medium. It can also provide flow control and automatic repeat request (ARQ) error management mechanisms.

The LLC sublayer acts as an interface between the media access control (MAC) sublayer and the network layer.

Metropolitan area network

A metropolitan area network (MAN) is a computer network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). The term MAN is applied to the interconnection of networks in a city into a single larger network which may then also offer efficient connection to a wide area network. The term is also used to describe the interconnection of several local area networks in a metropolitan area through the use of point-to-point connections between them. It has a range of 5 to 50 kilometres.

Network operating system

The term network operating system is used to refer to two rather different concepts:

A specialized operating system for a network device such as a router, switch or firewall.

An operating system oriented to computer networking, to allow shared file and printer access among multiple computers in a network, to enable the sharing of data, users, groups, security, applications, and other networking functions, typically over a local area network (LAN), or private network. This sense is now largely historical, as common operating systems generally now have such features included.

Novell Storage Services

Novell Storage Services (NSS) is a file system used by the Novell NetWare operating system. Support for NSS was introduced in 2004 to SUSE Linux via low-level network NCPFS protocol. It has some unique features that make it especially useful for setting up shared volumes on a file server in a local area network.

NSS is a 64-bit journaling file system with a balanced tree algorithm for the directory structure. Its published specifications (as of NetWare 6.5) are:

Maximum file size: 8 TiB

Maximum partition size: 2 TiB

Maximum device size (Physical or Logical): 2 TiB

Maximum pool size: 8 TiB

Maximum volume size: 8 TiB

Maximum files per volume: 8 trillion

Maximum mounted volumes per server: unlimited if all are NSS

Maximum open files per server: 1 million

Maximum directory tree depth: limited only by client

Maximum volumes per partition: unlimited

Maximum extended attributes: no limit on number of attributes.

Maximum data streams: no limit on number of data streams.

Unicode characters supported by default

Support for different name spaces: DOS, Microsoft Windows Long names (loaded by default), Unix, Apple Macintosh

Support for restoring deleted files (salvage)

Support for transparent compression

Support for encrypted volumes

Support for data shredding

Split tunneling

Split tunneling is a computer networking concept which allows a mobile user to access dissimilar security domains like a public network (e.g., the Internet) and a local LAN or WAN at the same time, using the same or different network connections. This connection state is usually facilitated through the simultaneous use of a Local Area Network (LAN) Network Interface Card (NIC), radio NIC, Wireless Local Area Network (WLAN) NIC, and VPN client software application without the benefit of access control.

For example, suppose a user utilizes a remote access VPN software client connecting to a corporate network using a hotel wireless network. The user with split tunneling enabled is able to connect to file servers, database servers, mail

servers and other servers on the corporate network through the VPN connection. When the user connects to Internet resources (Web sites, FTP sites, etc.), the connection request goes directly out the gateway provided by the hotel network.

Split tunneling is sometimes categorized based on how it is configured. A split tunnel configured to only tunnel traffic destined to a specific set of destinations is called a split-include tunnel. When configured to accept all traffic except traffic destined to a specific set of destinations, it is called a split-exclude tunnel.

Telnet

Telnet is a protocol used on the Internet or local area network to provide a bidirectional interactive text-oriented communication facility using a virtual terminal connection. User data is interspersed in-band with Telnet control information in an 8-bit byte oriented data connection over the Transmission Control Protocol (TCP).

Telnet was developed in 1969 beginning with RFC 15, extended in RFC 855, and standardized as Internet Engineering Task Force (IETF) Internet Standard STD 8, one of the first Internet standards. The name stands for "teletype network".Historically, Telnet provided access to a command-line interface (usually, of an operating system) on a remote host, including most network equipment and operating systems with a configuration utility (including systems based on Windows NT). However, because of serious security concerns when using Telnet over an open network such as the Internet, its use for this purpose has waned significantly in favor of SSH.

The term telnet is also used to refer to the software that implements the client part of the protocol. Telnet client applications are available for virtually all computer platforms. Telnet is also used as a verb. To telnet means to establish a connection using the Telnet protocol, either with command line client or with a programmatic interface. For example, a common directive might be: "To change your password, telnet into the server, log in and run the passwd command." Most often, a user will be telnetting to a Unix-like server system or a network device (such as a router) and obtaining a login prompt to a command line text interface or a character-based full-screen manager.

Virtual Extensible LAN

Virtual Extensible LAN (VXLAN) is a network virtualization technology that attempts to address the scalability problems associated with large cloud computing deployments. It uses a VLAN-like encapsulation technique to encapsulate OSI layer 2 Ethernet frames within layer 4 UDP datagrams, using 4789 as the default IANA-assigned destination UDP port number. VXLAN endpoints, which terminate VXLAN tunnels and may be either virtual or physical switch ports, are known as VXLAN tunnel endpoints (VTEPs).VXLAN is an evolution of efforts to standardize on an overlay encapsulation protocol. It increases scalability up to 16 million logical networks and allows for layer 2 adjacency across IP networks. Multicast or unicast with head-end replication (HER) is used to flood broadcast, unknown unicast, and multicast (BUM) traffic.The VXLAN specification was originally created by VMware, Arista Networks and Cisco. Other backers of the VXLAN technology include Huawei, Broadcom, Citrix, Pica8, Big Switch Networks, Cumulus Networks, Dell EMC, Ericsson, Mellanox, FreeBSD, OpenBSD, Red Hat, Joyent, and Juniper Networks.

VXLAN was officially documented by the IETF in RFC 7348.

Open vSwitch is an example of a software-based virtual network switch that supports VXLAN overlay networks.

Virtual LAN

A virtual LAN (VLAN) is any broadcast domain that is partitioned and isolated in a computer network at the data link layer (OSI layer 2). LAN is the abbreviation for local area network and in this context virtual refers to a physical object recreated and altered by additional logic. VLANs work by applying tags to network packets and handling these tags in networking systems – creating the appearance and functionality of network traffic that is physically on a single network but acts as if it is split between separate networks. In this way, VLANs can keep network applications separate despite being connected to the same physical network, and without requiring multiple sets of cabling and networking devices to be deployed.

VLANs allow network administrators to group hosts together even if the hosts are not directly connected to the same network switch. Because VLAN membership can be configured through software, this can greatly simplify network design and deployment. Without VLANs, grouping hosts according to their resource needs necessitates the labor of relocating nodes or rewiring data links. VLANs allow networks and devices that must be kept separate to share the same physical cabling without interacting, improving simplicity, security, traffic management, or economy. For example, a VLAN could be used to separate traffic within a business due to users, and due to network administrators, or between types of traffic, so that users or low priority traffic cannot directly affect the rest of the network's functioning. Many Internet hosting services use VLANs to separate their customers' private zones from each other, allowing each customer's servers to be grouped together in a single network segment while being located anywhere in their data center. Some precautions are needed to prevent traffic "escaping" from a given VLAN, an exploit known as VLAN hopping.

To subdivide a network into VLANs, one configures network equipment. Simpler equipment can partition only per physical port (if at all), in which case each VLAN is connected with a dedicated network cable. More sophisticated devices can mark frames through VLAN tagging, so that a single interconnect (trunk) may be used to transport data for multiple VLANs. Since VLANs share bandwidth, a VLAN trunk can use link aggregation, quality-of-service prioritization, or both to route data efficiently.

Website

A website is a collection of related web resources, such as web pages, multimedia content, which are typically identified with a common domain name, and published on at least one web server. Notable examples are wikipedia.org, google.com, and amazon.com.

A website may be accessible via a public Internet Protocol (IP) network, such as the Internet, or a private local area network (LAN), by referencing a uniform resource locator (URL) that identifies the site.

Websites can have many functions and can be used in various fashions; a website can be a personal website, a corporate website for a company, a government website, an organization website, etc. Websites are typically dedicated to a particular topic or purpose, ranging from entertainment and social networking to providing news and education. All publicly accessible websites collectively constitute the World Wide Web, while private websites, such as a company's website for its employees, are typically a part of an intranet.

Web pages, which are the building blocks of websites, are documents, typically composed in plain text interspersed with formatting instructions of Hypertext Markup Language (HTML, XHTML). They may incorporate elements from other websites with suitable markup anchors. Web pages are accessed and transported with the Hypertext Transfer Protocol (HTTP), which may optionally employ encryption (HTTP Secure, HTTPS) to provide security and privacy for the user. The user's application, often a web browser, renders the page content according to its HTML markup instructions onto a display terminal.

Hyperlinking between web pages conveys to the reader the site structure and guides the navigation of the site, which often starts with a home page containing a directory of the site web content. Some websites require user registration or subscription to access content. Examples of subscription websites include many business sites, news websites, academic journal websites, gaming websites, file-sharing websites, message boards, web-based email, social networking websites, websites providing real-time stock market data, as well as sites providing various other services. End users can access websites on a range of devices, including desktop and laptop computers, tablet computers, smartphones and smart TVs.

Wireless LAN

A wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, office building etc. This gives users the ability to move around within the area and yet still be connected to the network. Through a gateway, a WLAN can also provide a connection to the wider Internet.

Most modern WLANs are based on IEEE 802.11 standards and are marketed under the Wi-Fi brand name.

Wireless LANs have become popular for use in the home, due to their ease of installation and use. They are also popular in commercial properties that offer wireless access to their employees and customers.

Wireless WAN

wireless wide area network (WWAN), is a form of wireless network.

The larger size of a wide area network compared to a local area network requires differences in technology.

Wireless networks of different sizes deliver data in the form of telephone calls, web pages, and streaming video.

A WWAN often differs from wireless local area network (WLAN) by using mobile telecommunication cellular network technologies such as LTE, WiMAX (often called a wireless metropolitan area network or WMAN), UMTS, CDMA2000, GSM, cellular digital packet data (CDPD) and Mobitex to transfer data. It can also use Local Multipoint Distribution Service (LMDS) or Wi-Fi to provide Internet access. These technologies are offered regionally, nationwide, or even globally and are provided by a wireless service provider. WWAN connectivity allows a user with a laptop and a WWAN card to surf the web, check email, or connect to a virtual private network (VPN) from anywhere within the regional boundaries of cellular service. Various computers can have integrated WWAN capabilities.

A WWAN may also be a closed network that covers a large geographic area. For example, a mesh network or MANET with nodes on buildings, towers, trucks, and planes could also be considered a WWAN.

A WWAN may also be a low-power, low-bit-rate wireless WAN, (LPWAN), intended to carry small packets of information between things, often in the form of battery operated sensors.

Since radio communications systems do not provide a physically secure connection path, WWANs typically incorporate encryption and authentication methods to make them more secure. Some of the early GSM encryption techniques were flawed, and security experts have issued warnings that cellular communication, including WWAN, is no longer secure. UMTS (3G) encryption was developed later and has yet to be broken.

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