internet:internet (disambiguation)

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Internet:-

Internet (disambiguation).

Visualization of the various routes through a portion of the Internet.

The Internet is a global network of interconnected computers, enabling users to share

information along multiple channels. Typically, a computer that connects to the Internetcan access information from a vast array of available servers and other computers by

moving information from them to the computer's local memory. The same connection

allows that computer to send information to servers on the network; that information is inturn accessed and potentially modified by a variety of other interconnected computers. A

majority of widely accessible information on the Internet consists of inter-linked

hypertext documents and other resources of the World Wide Web (WWW). Computerusers typically manage sent and received information with web browsers; other software
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for users' interface with computer networks includes specialized programs for electronic

mail,online chat,file transferandfile sharing.

The movement of information in the Internet is acheived via a system of interconnectedcomputer networks that share data by packet switching using the standardized Internet

Protocol Suite (TCP/IP). It is a "network of networks" that consists of millions of private

and public, academic, business, and government networks of local to global scope thatare linked by copper wires, fiber-optic cables, wireless connections, and other

technologies.

Computer network:-

Computer networking is the engineering discipline concerned with communicationbetween computer systems or devices. Networking, routers, routing protocols, and

networking over the public Internet have their specifications defined in documents called

RFCs.[1] Computer networking is sometimes considered a sub-discipline oftelecommunications, computer science, information technology and/or computer

engineering. Computer networks rely heavily upon the theoretical and practical

application of these scientific and engineering disciplines.

A computer network is any set of computers or devices connected to each other with theability to exchange data. Examples of different networks are:LAN,MAN,WAN

Advantages of computer network:-

Connectivity and Communication:Networks connect computers and the users of those

computers. Individuals within a building or work group can be connected into local area

networks (LANs); LANs in distant locations can be interconnected into larger wide areanetworks (WANs). Once connected, it is possible for network users to communicate with

each other using technologies such as electronic mail. This makes the transmission ofbusiness (or non-business) information easier, more efficient and less expensive than it

would be without the network.

Data Sharing: One of the most important uses of networking is to allow thesharing of data. Before networking was common, an accounting employee who

wanted to prepare a report for her manager would have to produce it on his PC,

put it on a floppy disk, and then walk it over to the manager, who would transferthe data to her PC's hard disk. (This sort of shoe-based network was sometimes

sarcastically
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Hardware Sharing: Networks facilitate the sharing of hardware devices. For

example, instead of giving each of 10 employees in a department an expensivecolor printer (or resorting to the sneakernet again), one printer can be placed on

the network for everyone to share. Internet Access: The Internet is itself an enormous network, so whenever you

access the Internet, you are using a network. The significance of the Internet onmodern society is hard to exaggerate, especially for those of us in technical fields.

Internet Access Sharing: Smallcomputer networks allow multiple users to share

a single Internet connection. Special hardware devices allow the bandwidth of the

connection to be easily allocated to various individuals as they need it, and permitan organization to purchase one high-speed connection instead of many slower

ones.

Data Security and Management: In a business environment, a network allowsthe administrators to much better manage the company's critical data. Instead of

having this data spread over dozens or even hundreds of small computers in ahaphazard fashion as their users create it, data can be centralized on shared

servers. This makes it easy for everyone to find the data, makes it possible for the

administrators to ensure that the data is regularly backed up, and also allows forthe implementation of security measures to control who can read or change

various pieces of critical information.

Performance Enhancement and Balancing: Under some circumstances, a

network can be used to enhance the overall performance of some applications by

distributing the computation tasks to various computers on the network.

Entertainment:Networks facilitate many types of games and entertainment. TheInternet itself offers many sources of entertainment, of course. In addition, many

multi-player games exist that operate over a local area network. Many home

networks are set up for this reason, and gaming across wide area networks(including the Internet) has also become quite popular. Of course, if you are

running a business and have easily-amused employees, you might insist that this

is really a disadvantage of networking and not an advantage.
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Type of computer network:-

Below is a list of the most common types of computer networks in order of scale.

Personal area network:-

A personal area network (PAN) is a computer network used for communication amongcomputer devices close to one person. Some examples of devices that are used in a PAN

are printers, fax machines, telephones, PDAs and scanners. The reach of a PAN is

typically about 20-30 feet (approximately 6-9 meters), but this is expected to increasewith technology improvements.

Local area network :-

A local area network (LAN) is a computer network covering a small physical area, like

a home, office, or small group of buildings, such as a school, or an airport. Current LANsare most likely to be based on Ethernet technology. For example, a library may have a

wired or wireless LAN for users to interconnect local devices (e.g., printers and servers)

and to connect to the internet. On a wired LAN, PCs in the library are typically connectedby category 5 (Cat5) cable, running the IEEE 802.3 protocol through a system of

interconnected devices and eventually connect to the Internet. The cables to the servers

are typically on Cat 5e enhanced cable, which will support IEEE 802.3 at 1 Gbit/s. A

wireless LAN may exist using a different IEEE protocol, 802.11b, 802.11g or possibly802.11n. The staff computers (bright green in the figure) can get to the color printer,

checkout records, and the academic networkandthe Internet. All user computers can get

to the Internet and the card catalog. Each workgroup can get to its local printer. Note thatthe printers are not accessible from outside their workgroup.

Typical library network, in a branching tree topology and controlled access to resources

All interconnected devices must understand the network layer (layer 3), because they are

handling multiple subnets (the different colors). Those inside the library, which have only

10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection

to the central router, could be called "layer 3 switches" because they only have Ethernetinterfaces and must understandIP. It would be more correct to call them access routers,

where the router at the top is a distribution router that connects to the Internet andacademic networks' customer access routers.

The defining characteristics of LANs, in contrast to WANs (wide area networks), include

their higher data transfer rates, smaller geographic range, and lack of a need for leased

telecommunication lines. Current Ethernet or otherIEEE 802.3 LAN technologies
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Campus area network :-

A campus area network(CAN) is a computer network made up of an interconnection of

local area networks (LANs) within a limited geographical area. It can be considered oneform of a metropolitan area network, specific to an academic setting.

In the case of a university campus-based campus area network, the network is likely to

link a variety of campus buildings including; academic departments, the university library

and student residence halls. A campus area network is larger than a local area network

but smaller than a wide area network (WAN) (in some cases).

The main aim of a campus area network is to facilitate students accessing internet and

university resources. This is a network that connects two or more LANs but that is

limited to a specific and contiguous geographical area such as a college campus,

industrial complex, office building, or a military base. A CAN may be considered a typeof MAN (metropolitan area network), but is generally limited to a smaller area than a

typical MAN. This term is most often used to discuss the implementation of networks for

a contiguous area. This should not be confused with a Controller Area Network. A LANconnects network devices over a relatively short distance. A networked office building,

school, or home usually contains a single LAN, though sometimes one building will

contain a few small LANs (perhaps one per room), and occasionally a LAN will span agroup of nearby buildings. In TCP/IP networking, a LAN is often but not always

implemented as a single IP subnet.

Metropolitan area network :-

A metropolitan area network(MAN) is a network that connects two or more local area

networks or campus area networks together but does not extend beyond the boundaries of

the immediate town/city. Routers, switches and hubs are connected to create ametropolitan area network.

Wide area network :-

A wide area network(WAN) is a computer network that covers a broad area (i.e., any

network whose communications links cross metropolitan, regional, or national boundaries [1]). Less formally, a WAN is a network that uses routers and public

communications links [1]. Contrast with personal area networks (PANs), local area

networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs)are usually limited to a room, building, campus or specific metropolitan area (e.g., a city)

respectively. The largest and most well-known example of a WAN is the Internet. A

WAN is a data communications network that covers a relatively broad geographic area(i.e. one city to another and one country to another country) and that often uses
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transmission facilities provided by common carriers, such as telephone companies. WAN

technologies generally function at the lower three layers of the OSI reference model: thephysical layer, thedata link layer, and the network layer.

Global area network :-

A global area networks (GAN) specification is in development by several groups, and

there is no common definition. In general, however, a GAN is a model for supporting

mobile communications across an arbitrary number of wireless LANs, satellite coverageareas, etc. The key challenge in mobile communications is "handing off" the user

communications from one local coverage area to the next. In IEEE Project 802, this

involves a succession of terrestrial WIRELESS local area networks (WLAN).[1]

Virtual private network :-

A virtual private network (VPN) is a computer network in which some of the links

between nodes are carried by open connections or virtual circuits in some larger network

(e.g., the Internet) instead of by physical wires. The link-layer protocols of the virtualnetwork are said to be tunneled through the larger network when this is the case. One

common application is secure communications through the public Internet, but a VPN

need not have explicit security features, such as authentication or content encryption.

VPNs, for example, can be used to separate the traffic of different user communities overan underlying network with strong security features.

A VPN may have best-effort performance, or may have a defined service level agreement(SLA) between the VPN customer and the VPN service provider. Generally, a VPN has a

topology more complex than point-to-point.

A VPN allows computer users to appear to be editing from an IP address location other

than the one which connects the actual computer to the Internet.

Internetwork :-

A Internetworking involves connecting two or more distinct computer networks ornetwork segments via a common routing technology. The result is called an internetwork(often shortened to internet). Two or more networks or network segments connected

using devices that operate at layer 3 (the 'network' layer) of the OSI Basic Reference

Model, such as a router. Any interconnection among or between public, private,commercial, industrial, or governmental networks may also be defined as an

internetwork.
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In modern practice, the interconnected networks use the Internet Protocol. There are at

least three variants of internetwork, depending on who administers and who participatesin them:

Intranet

Extranet

Internet

Intranets and extranets may or may not have connections to the Internet. If connected to

the Internet, the intranet or extranet is normally protected from being accessed from the

Internet without proper authorization. The Internet is not considered to be a part of the

intranet or extranet, although it may serve as a portal for access to portions of an extranet.

Intranet :-

An intranet is a set of networks, using the Internet Protocol and IP-based tools such as

web browsers and file transfer applications, that is under the control of a single

administrative entity. That administrative entity closes the intranet to all but specific,authorized users. Most commonly, an intranet is the internal network of an organization.

A large intranet will typically have at least one web server to provide users with

organizational information.

Extranet :-

An extranet is a network or internetwork that is limited in scope to a single organizationor entity but which also has limited connections to the networks of one or more other

usually, but not necessarily, trusted organizations or entities (e.g. a company's customers

may be given access to some part of its intranet creating in this way an extranet, while atthe same time the customers may not be considered 'trusted' from a security standpoint).

Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type

of network, although, by definition, an extranet cannot consist of a single LAN; it musthave at least one connection with an external network.

Internet :-

The Internet is a specific internetwork. It consists of a worldwide interconnection of

governmental, academic, public, and private networks based upon the networking

technologies of the Internet Protocol Suite. It is the successor of the Advanced ResearchProjects Agency Network(ARPANET) developed by DARPA of theU.S. Department of

Defense. The Internet is also the communications backbone underlying the (WWW). The
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'Internet' is most commonly spelled with a capital 'I' as a proper noun, for historical

reasons and to distinguish it from other generic internetworks.

Participants in the Internet use a diverse array of methods of several hundreddocumented, and often standardized, protocols compatible with the Internet Protocol

Suite and an addressing system (IP Addresses) administered by the Internet Assigned

Numbers Authority and address registries. Service providers and large enterprisesexchange information about the reachabilityof their address spaces through the Border

Gateway Protocol(BGP), forming a redundant worldwide mesh of transmission paths.

Distributed system:-

It is an application that executes a collection of protocols to coordinate the actions ofmultiple processes on a network, such that all components cooperate together to perform

a single or small set of related tasks.

Thus, a distributed system can be much larger and more powerful given the combined

capabilities of the distributed components, than combinations of stand-alone systems. But

it's not easy - for a distributed system to be useful, it must be reliable. This is a difficult

goal to achieve because of the complexity of the interactions between simultaneously

running components.

Characteristics:-

To be truly reliable, a distributed system must have the following characteristics:

Fault-Tolerant: It can recover from component failures without performing

incorrect actions.

Highly Available: It can restore operations, permitting it to resume providing

services even when some components have failed.

Recoverable: Failed components can restart themselves and rejoin the system,

after the cause of failure has been repaired.

Consistent: The system can coordinate actions by multiple components often in

the presence of concurrency and failure. This underlies the ability of a distributed

system to act like a non-distributed system.
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Scalable: It can operate correctly even as some aspect of the system is scaled to a

larger size. For example, we might increase the size of the network on which the

system is running. This increases the frequency of network outages and could

degrade a "non-scalable" system. Similarly, we might increase the number of

users or servers, or overall load on the system. In a scalable system, this should

not have a significant effect.

Predictable Performance: The ability to provide desired responsiveness in a timely

manner.

Secure: The system authenticates access to data and services [1]

World wide web:-

The World Wide Web (commonly abbreviated as "the Web") is a system of interlinked

hypertextdocuments accessed via theInternet. With a Web browser, one can view Web

pagesthat may contain text,images, videos, and othermultimedia and navigate between

them using hyperlinks. Using concepts from earlier hypertext systems, the World Wide

Web was begun in 1992 by the English physicist Tim Berners-Lee, now the Director of

the World Wide Web Consortium, and Robert Cailliau, a Belgian computer scientist,

while both working at CERN in Geneva,Switzerland. In 1990, they proposed building a

"web of nodes" storing "hypertext pages" viewed by "browsers" on a network,[1] and

released that web in 1992. Connected by the existing Internet, other websites were

created, around the world, adding international standards fordomain names & the HTML

language. Since then, Berners-Lee has played an active role in guiding the development

of Web standards (such as the markup languages in which Web pages are composed), and

in recent years has advocated his vision of a Semantic Web. Cailliau went on early

retirement in January 2005 and left CERN in January 2007.

The World Wide Web enabled the spread of information over the Internet through aneasy-to-use and flexible format. It thus played an important role in popularising use of the

Internet, to the extent that the World Wide Web has become a synonym for Internet, with

the two being conflated in popular u.
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Working :-

The terms Internet and World Wide Web are often used in every-day speech without

much distinction. However, the Internet and the World Wide Web are not one and the

same. The Internet is a global data communications system. It is a hardware and software

infrastructure that provides connectivity between computers. In contrast, the Web is one

of the services communicated via the Internet. It is a collection of interconnected

documents and other resources, linked by hyperlinks and URLs.

Viewing aWeb page on the World Wide Web normally begins either by typing the URL

of the page into a Web browser, or by following a hyperlinkto that page or resource. TheWeb browser then initiates a series of communication messages, behind the scenes, in

order to fetch and display it.

First, the server-name portion of the URL is resolved into an IP addressusing the global,

distributedInternet database known as the domain name system, or DNS. This IP addressis necessary to contact and send datapackets to the Web server.

The browser then requests the resource by sending an HTTP request to the Web server at

that particular address. In the case of a typical Web page, the HTML text of the page is

requested first and parsed immediately by the Web browser, which will then makeadditional requests for images and any other files that form a part of the page. Statistics

measuring a website's popularity are usually based on the number of 'page views' or

associated server 'hits', or file requests, which take place.

Having received the required files from the Web server, the browser then renders thepage onto the screen as specified by its HTML, CSS, and other Web languages. Any

images and other resources are incorporated to produce the on-screen Web page that the

user sees.

Most Web pages will themselves contain hyperlinks to other related pages and perhaps to

downloads, source documents, definitions and other Web resources. Such a collection of

useful, related resources, interconnected via hypertext links, is what was dubbed a "web"

of information. Making it available on the Internet created what Tim Berners-Lee firstcalled the WorldWideWeb (in its original CamelCase, which was subsequently

discarded) in November 1990.
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History:-

This NeXT Computer used by Sir Tim Berners-Lee at CERN became the first Web

server.

The underlying ideas of the Web can be traced as far back as 1980, when, at CERN inSwitzerland,Sir Tim Berners-Leebuilt ENQUIRE (a reference to Enquire Within Upon

Everything, a book he recalled from his youth). While it was rather different from the

system in use today, it contained many of the same core ideas (and even some of the

ideas of Berners-Lee's next project after the World Wide Web, theSemantic Web).

In March 1989, Berners-Lee wrote a proposal[4] which referenced ENQUIRE and

described a more elaborate information management system. With help from Robert

Cailliau, he published a more formal proposal (on November 12, 1990) to build a

"Hypertext project" called "WorldWideWeb" (one word, also "W3")[1] as a "web ofnodes" with "hypertext documents" to store data. That data would be viewed in

"hypertext pages" (webpages) by various "browsers" (line-mode or full-screen) on the

computer network, using an "access protocol" connecting the "Internet and DECnetprotocol worlds".

Browser :-

WorldWideWeb forNeXTcomputer was the first browser (1991)
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A Web browser is a software application which enables a user to display and interact

with text, images, videos, music, games and other information typically located on a Web

page at a Web site on theWorld Wide Web or a local area network. Text and images on a

Web page can contain hyperlinks to other Web pages at the same or different Web site.

Web browsers allow a user to quickly and easily access information provided on manyWeb pages at many Web sites by traversing these links. Web browsers format HTML

information for display, so the appearance of a Web page may differ between browsers.

Web browsers are the most-commonly-used type ofHTTPuser agent. Although browsers

are typically used to access the World Wide Web, they can also be used to accessinformation provided by Web servers inprivate networks or content in file systems.

Web page:-

A web page or webpage is a resource of information that is suitable for the World WideWeb and can be accessed through a web browser. This information is usually in HTML

orXHTML format, and may provide navigation to other web pages via hypertextlinks.

Web pages may be retrieved from a local computer or from a remote web server. The

web server may restrict access only to a private network, e.g. a corporate intranet, or itmay publish pages on the World Wide Web. Web pages are requested and served from

web servers using Hypertext Transfer Protocol(HTTP).

Web pages may consist of files of static text stored within the web server's file system

(static web pages), or the web server may construct the (X)HTML for each web pagewhen it is requested by a browser (dynamic web pages).Client-side scriptingcan make

web pages more responsive to user input once in the client browser.

Web pages usually include instructions as to the colors of text and backgrounds and very

often also contain links to images and sometimes other media to be included in the final

view.

Layout, typographic and color-scheme information is provided by Cascading Style Sheet

(CSS) instructions, which can either be embedded in the HTML or can be provided by a

separate file, which is referenced from within the HTML. The latter case is especiallyrelevant where one lengthy stylesheet is relevant to a whole website: due to the way

HTTP works, the browser will only download it once from the web server and use the

cachedcopy for the whole site.(notepad)
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Images are stored on the web server as separate files, but again HTTP allows for the fact

that once a web page is downloaded to a browser, it is quite likely that related files such

as images and stylesheets will be requested as it is processed. An HTTP 1.1 web serverwill maintain a connection with the browser until all related resources have been

requested and provided. Browsers usually render images along with the text and other

material on the displayed web page.

Daynamic behavior:-

Client-side computer code such as JavaScriptor code implementing Ajax techniques can

be provided either embedded in the HTML of a web page or, like CSS stylesheets, asseparate, linked downloads specified in the HTML (using for example .js file extensions

for JavaScript files). These scripts may run on the client computer, if the user allows

them to, and can provide a degree of interactivity between the web page and the user afterthe page has downloaded.

Website:-

A website is a collection ofweb pages, images, videos or other digital assets that are

hosted on one or more web servers, usually accessible via the Internet.

A web page is a document, typically written in (X)HTML, that is almost always

accessible via HTTP, a protocol that transfers information from the web serverto display

in the user's web browser.

IEEE 802 :-

IEEE 802 refers to a family of IEEE standards dealing with local area networks and

metropolitan area networks. More specifically, the IEEE 802 standards are restricted to

networks carrying variable-size packets. (By contrast, in cell-based networks data istransmitted in short, uniformly sized units called cells. Isochronous networks, where data

is transmitted as a steady stream of octets, or groups of octets, at regular time intervals,

are also out of the scope of this standard.) The number 802 was simply the next free

number IEEE could assign, though 802 is sometimes associated with the date the firstmeeting was held February 1980.
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The services and protocols specified in IEEE 802 map to the lower two layers (Data Link

and Physical) of the seven-layerOSInetworking reference model. In fact, IEEE 802

splits the OSI Data Link Layer into two sub-layers named Logical Link Control (LLC)andMedia Access Control, so that the layers can be listed like this:

IEEE 802.2 :-

IEEE 802.2 is the IEEE 802 standard defining Logical Link Control (LLC), which is theupper portion of the data link layer of the OSI Model. The LLC sublayer presents a

uniform interface to the user of the data link service, usually the network layer. Beneath

the LLC sublayer is the Media Access Control (MAC) sublayer, which is dependent on

the particular medium being used (Ethernet,token ring,FDDI,802.11, etc.).

The IEEE standard adds this sublayer which adds the standard 8-bit DSAP (Destination

Service Access Point) and SSAP (SourceService Access Point) labels to a given packet

regardless of network type. There is also an 8 or 16 bit control field for use in auxiliary

functions such as flow control. There is room for 64 globally assigned SAP numbers, andthe IEEE does not assign them lightly. IP does not have an assigned SAP number,

because only international standards could be given globally assigned SAP numbers.

Protocols which are not international standards can use a SAP number from the locallyadministered SAP number space. The Subnetwork Access Protocol (SNAP) allows

EtherType values to be used to specify the protocol being transported atop IEEE 802.2,

and also allows vendors to define their own protocol value spaces

IEEE 802.3 :-

IEEE 802.3 is a collection of IEEE standards defining thephysical layer, and the media

access control (MAC) sublayerof the data link layer, of wired Ethernet. This is generally

aLAN technology with some WAN applications. Physical connections are made betweennodes and/or infrastructure devices (hubs, switches,routers) by various types of copper or

fiber cable.

802.3 is a technology that can support the IEEE 802.1 network architecture.

The maximumpacket size is 1518bytes, although to allow the Q-tag for Virtual LANand priority data in 802.3ac it is extended to 1522 bytes. If the upper layer protocol

submits a protocol data unit (PDU) less than 64 bytes, 802.3 will pad the data field to
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achieve the minimum 64 bytes. The minimum Frame size will then always be of 64

bytes.

Although it is not technically correct, the terms packet and frame are often usedinterchangeably. The ISO/IEC 8802-3 and ANSI/IEEE 802.3 standards refer to MAC

sub-layer frames consisting of the destination address, the source address, length/type,data payload, and frame check sequence (FCS) fields. The preamble and Start Frame

Delimiter (SFD) are (usually) together considered a header to the MAC frame. Thisheader and the MAC frame constitute a packet.

The original Ethernet is called Experimental Ethernet today. It was developed by Robert

Metcalfe in 1972 (patented in 1978) and was based in part on the wireless ALOHAnetprotocol. The first Ethernet that was generally used outside Xerox was DIX Ethernet,

followed by Ethernet II. IEEE defines a 802.3 standard where the Type field is replaced

by Length, and an 802.2 LLC header follows with the Type field. However, as DIXEthernet was derived from Experimental Ethernet, and as many standards have been

developed that are based on DIX Ethernet, the technical community has accepted the

term Ethernet for all of them. Therefore, the term Ethernet can be used to name networks

using any of the following standardized media and functions:

IEEE 802.4 :-

IEEE 802.4 defines the medium access control (MAC) layer forbus networks that use a

token-passing mechanism (token bus networks). This is an application of the conceptsused in token ring networks. The main difference is that the endpoints of the bus do not

meet to form a physical ring. The IEEE 802.4 Working Group is disbanded.

IEEE 802.5

Token ring

Introduction :-

Stations on a token ring LAN are logically organized in a ring topology with data being

transmitted sequentially from one ring station to the next with a control token circulating

around the ring controlling access. This token passing mechanism is shared by ARCNET,token bus, and FDDI, and has theoretical advantages over the stochasticCSMA/CD of

Ethernet.
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Physically, a token ring network is wired as a star, with 'hubs' and arms out to each

station and the loop going out-and-back through each.

IBM hermaphroditic connector with locking clip

Cabling is generally IBM "Type-1" shielded twisted pair, with unique hermaphroditic

connectors, commonly referred to as IBM data connectors. The connectors have thedisadvantage of being quite bulky, requiring at least 3 x 3 cm panel space, and, composed

of many complex plastic pieces, being quite fragile.

Initially (in 1985) token ring ran at 4 Mbit/s, but in 1989 IBM introduced the first 16

Mbit/s token ring products and the 802.5 standard was extended to support this. In 1981,Apollo Computer introduced their proprietary 12 Mbit/s Apollo token ring (ATR) and

Proteon introduced their 10 Mbit/s ProNet-10 token ring network in 1984. However, IBM

token ring was not compatible with ATR or ProNet-10.

Each station passes or repeats the special token frame around the ring to its nearestdownstream neighbor. This token-passing process is used to arbitrate access to the shared

ring media. Stations that have data frames to transmit must first acquire the token before

they can transmit them. Token ring LANs normally use differential Manchester encodingof bits on the LAN media.

IBM popularized the use of token ring LANs in the mid 1980s when it released its IBM

token ring architecture based on active multi-station access units (MSAUs or MAUs) and

the IBM Structured Cabling System. The Institute of Electrical and Electronics Engineers(IEEE) later standardized a token ring LAN system as IEEE 802.5.[1]

Token ring LAN speeds of 4 Mbit/s and 16 Mbit/s have been standardized by the IEEE

802.5 working group. An increase to 100 Mbit/s was standardized and marketed during
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the wane of token ring's existence while a 1000 Mbit/s speed was actually approved in

2001, but no products were ever brought to market.[1]

When token ring LANs were first introduced, there were widely circulated claims thatthey were superior to Ethernet.[2] These claims did not hold up when tested.[3]

With the development ofswitched Ethernet and faster variants of Ethernet, token ring

architectures lagged badly behind Ethernet in both performance and reliability. Thehigher sales of Ethernet allowed economies of scale which drove down prices further, and

added a compelling price advantage to its other advantages over token ring.

Token ring networks have since declined in usage and the standards activity has since

come to a standstill as switched Ethernet has dominated the LAN/layer 2 networkingmarket.

Token frame :-

When no station is transmitting a data frame, a special token frame circles the loop. This

special token frame is repeated from station to station until arriving at a station that needs

to transmit data. When a station needs to transmit data, it converts the token frame into adata frame for transmission. Once the sending station receives its own data frame, it

converts the frame back into a token. If a transmission error occurs and no token frame,or more than one, is present, a special station referred to as the Active Monitor detects theproblem and removes and/or reinserts tokens as necessary (see Active and standby

monitors). On 4 Mbit/s Token Ring, only one token may circulate; on 16 Mbit/s Token

Ring, there may be multiple tokens.

The special token frame consists of three bytes as described below (J and K are specialnon-data characters, referred to as code violations

IEEE 802.6 :-

IEEE 802.6 is a standard governed by the ANSI forMetropolitan Area Networks (MAN).

It is an improvement of an older standard (also created by ANSI) which used the Fiberdistributed data interface(FDDI) network structure. The FDDI-based standard failed due

to its expensive implementation and lack of compatibility with current LANstandards.

The IEEE 802.6 standard uses the Distributed Queue Dual Bus (DQDB) network form.This form supports 150 Mbit/s transfer rates. It consists of two
http://en.wikipedia.org/wiki/IEEE_802.5#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/IEEE_802.5#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/IEEE_802.5#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/IEEE_802.5#cite_note-Boggs1995-2%23cite_note-Boggs1995-2http://en.wikipedia.org/wiki/Network_switchhttp://en.wikipedia.org/wiki/Network_switchhttp://en.wikipedia.org/wiki/Economies_of_scalehttp://en.wikipedia.org/wiki/Token_ring#Active_and_standby_monitorshttp://en.wikipedia.org/wiki/Token_ring#Active_and_standby_monitorshttp://en.wikipedia.org/wiki/American_National_Standards_Institutehttp://en.wikipedia.org/wiki/Metropolitan_Area_Networkshttp://en.wikipedia.org/wiki/Fiber_distributed_data_interfacehttp://en.wikipedia.org/wiki/Fiber_distributed_data_interfacehttp://en.wikipedia.org/wiki/Fiber_distributed_data_interfacehttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Distributed-queue_dual-bus_networkhttp://en.wikipedia.org/wiki/IEEE_802.5#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/IEEE_802.5#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/IEEE_802.5#cite_note-Boggs1995-2%23cite_note-Boggs1995-2http://en.wikipedia.org/wiki/Network_switchhttp://en.wikipedia.org/wiki/Economies_of_scalehttp://en.wikipedia.org/wiki/Token_ring#Active_and_standby_monitorshttp://en.wikipedia.org/wiki/Token_ring#Active_and_standby_monitorshttp://en.wikipedia.org/wiki/American_National_Standards_Institutehttp://en.wikipedia.org/wiki/Metropolitan_Area_Networkshttp://en.wikipedia.org/wiki/Fiber_distributed_data_interfacehttp://en.wikipedia.org/wiki/Fiber_distributed_data_interfacehttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Distributed-queue_dual-bus_network


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unconnected unidirectional buses. DQDB is rated for a maximum of 160 km before

significant signal degradation over fiberoptic cable with an optical wavelength of 1310

nm.

This standard has also failed, mostly due to the same reasons that the FDDI standard

failed. Most MANs now use Synchronous Optical Network(SONET).
http://en.wikipedia.org/wiki/Synchronous_optical_networkinghttp://en.wikipedia.org/wiki/Synchronous_optical_networkinghttp://en.wikipedia.org/wiki/Synchronous_optical_networking

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