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Internet Service Provider

Internet service provider

An Internet service provider (ISP, also called Internet access provider) is a business or organization that offers users access to the Internet and related services. Many but not all ISPs are telephone companies. They provide services such as Internet transit, domain name registration and hosting, dial-up access, leased line access and colocation.

ISP connection options

Generally, an ISP charges a monthly access fee to the consumer. The consumer then has access to the Internet, although the speed at which this data is transferred varies widely. Internet connection speed can generally be divided into two categories: dialup and broadband. Dialup connections require the use of a phone line, and usually have connections of 56Kbs or less. Broadband connections can be either ISDN, Broadband wireless access, Cable modem, DSL, Satellite or Ethernet. Broadband is always on (except ISDN that is a circuit switching technology), and varies in speed between 64Kb and 20+Mb per second. In the early 2000s, ISPs in the United States faced serious challenges. Telecommunications and IT-related stocks fell sharply, and many ISPs were forced to close, restructure, sell, or merge. Some telcos like Worldcom were spectacular collapses. The slower-than-expected growth of broadband services and key decisions on broadband open access matters all added to the industry's problems. By late 2005 a 1Mb connection was being described as slow within the United Kingdom. Many modern software add ons demand minimum speeds of 256K or 512K. With the increasing popularity of file sharing and downloading music and the general demand for faster page loads, higher bandwidth connections are becoming more popular.

Virtual ISP

A Virtual ISP (vISP) re-sells to the general public Internet access purchased from a wholesale ISP. The vISP's role is to provide any services beyond Internet connectivity, such as e-mail, web hosting, and technical support. The vISP must perform all authentication and accounting functions necessary to provide access and then bill their users for it. This model allows for larger ISPs to increase returns on their investment into what is generally a geographically large, high capacity network, a network which smaller ISPs, as customers of the larger ISP, can use to serve customers in locations that would previously have been unavailable to them.

Other relevant acronyms

- IAP (Internet Access Provider)
- NSP (Network Service Provider)

Related services

- Broadband access
- Digital Subscriber Line
- Fixed wireless access
- Cable
- Triple play
- Web hosting services
- Usenet servers
- Email services
- DNS
- Dynamic DNS

Internet

:For the more general networking concept, see internetworking. The Internet, or simply the Net, is the worldwide system of interconnected computer networks which makes information stored on it accessible. This information is transmitted by packet switching using a standardized Internet Protocol (IP) and many other protocols. It is made up of thousands of smaller commercial, academic, domestic and government networks. It carries various information and services, such as electronic mail, online chat, and the interlinked web pages and other documents of the World Wide Web.

Creation of the Internet

During the 1950s, several communications researchers realized that there was a need to allow general communication between users of various computers and communications networks. This led to research into decentralized networks, queuing theory, and packet switching. The subsequent creation of ARPANET in the United States in turn catalyzed a wave of technical developments that made it the basis for the development of the Internet. Contrary to popular myth, the DoD did not create the ARPANET so that they could communicate to the US Government after a nuclear war. The first TCP/IP wide area network was operational in 1984 when the United States' National Science Foundation (NSF) constructed a university network backbone that would later become the NSFNet. It was then followed by the opening of the network to commercial interests in 1995. Important separate networks that offered gateways into, then later merged into the Internet include Usenet, Bitnet and the various commercial and educational X.25 networks such as Compuserve and JANET. The ability of TCP/IP to work over these pre-existing communication networks allowed for a great ease of growth. Use of Internet as a phrase to describe a single global TCP/IP network originated around this time. The collective network gained a public face in the 1990s. In August 1991 CERN in Switzerland publicized the new World Wide Web project, two years after Tim Berners-Lee had begun creating HTML, HTTP and the first few web pages at CERN in Switzerland. In 1993 the Mosaic web browser version 1.0 was released, and by late 1994 there was growing public interest in the previously academic/technical Internet. By 1996 the word "Internet" was common public currency, but it referred almost entirely to the World Wide Web. Meanwhile, over the course of the decade, the Internet successfully accommodated the majority of previously existing public computer networks (although some networks such as FidoNet have remained separate). This growth is often attributed to the lack of central administration, which allows organic growth of the network, as well as the non-proprietary open nature of the Internet protocols, which encourages vendor interoperability and prevents any one company from exerting too much control over the network.

Today's Internet

FidoNets, FTP client, and Telnet client]] Apart from the complex physical connections that make up its infrastructure, the Internet is held together by bi- or multi-lateral commercial contracts (for example peering agreements) and by technical specifications or protocols that describe how to exchange data over the network. Indeed, the Internet is essentially defined by its interconnections and routing policies. In an often-cited, if perhaps gratuitously mathematical definition, Seth Breidbart once described the Internet as "the largest equivalence class in the reflexive, transitive, symmetric closure of the relationship 'can be reached by an IP packet from'". Unlike older communications systems, the Internet protocol suite was deliberately designed to be independent of the underlying physical medium. Any communications network, wired or wireless, that can carry two-way digital data can carry Internet traffic. Thus, Internet packets flow through wired networks like copper wire, coaxial cable, and fiber optic; and through wireless networks like Wi-Fi. Together, all these networks, sharing the same high-level protocols, form the Internet. The Internet protocols originate from discussions within the Internet Engineering Task Force (IETF) and its working groups, which are open to public participation and review. These committees produce documents that are known as Request for Comments documents (RFCs). Some RFCs are raised to the status of Internet Standard by the Internet Architecture Board (IAB). Some of the most used protocols in the Internet protocol suite are IP, TCP, UDP, DNS, PPP, SLIP, ICMP, POP3, IMAP, SMTP, HTTP, HTTPS, SSH, Telnet, FTP, LDAP, SSL, and TLS. Some of the popular services on the Internet that make use of these protocols are e-mail, Usenet newsgroups, file sharing, Instant Messenger, the World Wide Web, Gopher, session access, WAIS, finger, IRC, MUDs, and MUSHs. Of these, e-mail and the World Wide Web are clearly the most used, and many other services are built upon them, such as mailing lists and blogs. The Internet makes it possible to provide real-time services such as Internet radio and webcasts that can be accessed from anywhere in the world. Some other popular services of the Internet were not created this way, but were originally based on proprietary systems. These include IRC, ICQ, AIM, and Gnutella. There have been many analyses of the Internet and its structure. For example, it has been determined that the Internet IP routing structure and hypertext links of the World Wide Web are examples of scale-free networks. Similar to how the commercial Internet providers connect via Internet exchange points, research networks tend to interconnect into large subnetworks such as:
- GEANT
- Internet2
- GLORIAD These in turn are built around relatively smaller networks. See also the list of academic computer network organizations In network schematic diagrams, the Internet is often represented by a cloud symbol, into and out of which network communications can pass.

Internet culture

The Internet is also having a profound impact on work, leisure, knowledge and worldviews. worldviews]]

ICANN

The Internet Corporation for Assigned Names and Numbers (ICANN) is the authority that coordinates the assignment of unique identifiers on the Internet, including domain names, Internet protocol addresses, and protocol port and parameter numbers. A globally unified namespace (i.e., a system of names in which there is one and only one holder of each name) is essential for the Internet to function. ICANN is headquartered in Marina del Rey, California, but is overseen by an international board of directors drawn from across the Internet technical, business, academic, and non-commercial communities. The US government continues to have a privileged role in approving changes to the root zone file that lies at the heart of the domain name system. Because the Internet is a distributed network comprising many voluntarily interconnected networks, the Internet, as such, has no governing body. ICANN's role in coordinating the assignment of unique identifiers distinguishes it as perhaps the only central coordinating body on the global Internet, but the scope of its authority extends only to the Internet's systems of domain names, Internet protocol addresses, and protocol port and parameter numbers.

The World Wide Web

Through keyword-driven Internet research using search engines like Google, millions worldwide have easy, instant access to a vast and diverse amount of online information. Compared to encyclopedias and traditional libraries, the World Wide Web has enabled a sudden and extreme decentralization of information and data. Some companies and individuals have adopted the use of 'weblogs' or blogs, which are largely used as easily-updatable online diaries. Some commercial organizations encourage staff to fill them with advice on their areas of specialization in the hope that visitors will be impressed by the expert knowledge and free information, and be attracted to the corporation as a result. One example of this practice is Microsoft, via whose product developers publish their personal blogs in order to pique the public's interest in their work. For more information on the distinction between the World Wide Web and the Internet itself — as in everyday use the two are sometimes confused — see Dark internet where this is discussed in more detail.

Remote access

The Internet allows computer users to connect to other computers and information stores easily, wherever they may be across the world. They may do this with or without the use of security, authentication and encryption technologies, depending on the requirements. This is encouraging new ways of working from home, collaboration and information sharing in many industries. An accountant sitting at home can audit the books of a company based in another country, on a server situated in a third country that is remotely maintained by IT specialists in a fourth. These accounts could have been created by home-working book-keepers, in other remote locations, based on information e-mailed to them from offices all over the world. Some of these things were possible before the widespread use of the Internet, but the cost of private, leased lines would have made many of them infeasible in practice. An office worker away from his or her desk, perhaps the other side of the world on a business trip or a holiday, can open a remote desktop session into his or her normal office PC using a secure Virtual Private Network (VPN) connection via the Internet. This gives him or her complete access to all their normal files and data, including e-mail and other applications, while they are away.

Collaboration

This low-cost and nearly instantaneous sharing of ideas, knowledge and skills has revolutionized some, and given rise to whole new, areas of human activity. One example of this is the collaborative development and distribution of Free/Libre/Open-Source Software (FLOSS) such as Linux, Mozilla and OpenOffice.org. See Collaborative software.

File-sharing

A computer file can be e-mailed to customers, colleagues and friends as an attachment. It can be uploaded to a website or FTP server for easy download by others. It can be put into a "shared location" or onto a file server for instant use by colleagues. The load of bulk downloads to many users can be eased by the use of "mirror" servers or peer-to-peer networking. In any of these cases, access to the file may be controlled by user authentication; the transit of the file over the Internet may be obscured by encryption and money may change hands before or after access to the file is given. The price can be paid by the remote charging of funds from, for example a credit card whose details are also passed - hopefully fully encrypted - across the Internet. The origin and authenticity of the file received may be checked by digital signatures or by MD5 message digests. These simple features of the Internet, over a world-wide basis, are changing the basis for the production, sale and distribution of many types of product, wherever they can be reduced to a computer file for transmission. This includes all manner of office documents, publications, software products, music, photography, video, animations, graphics and the other arts. This in turn is causing seismic shifts in each of the existing industry associations, such as the RIAA and MPAA, that previously controlled the production and distribution of these products.

Streaming media and VoIP

Many existing radio and television broadcasters have provided Internet 'feeds' of their live audio and video streams (for example, the BBC). They have been joined by a range of pure Internet 'broadcasters' who never had on-air licences. This means that an Internet-connected device, such as a computer or something more specific, can be used to access on-line media in much the same way as was previously possible only with a TV or radio receiver. The range of material is much wider, from pornography to highly specialised technical web-casts. The simplest equipment can allow anybody, with little censorship or licencing control, to broadcast on a worldwide basis. Time-shift viewing or listening is not a problem as the BBC have shown with their Preview, Classic Clips and Listen Again features. Web-cams can be seen as an even lower-budget extension of this phenomenon. In this case the picture may update only slowly - perhaps once every few seconds or slower, but Internet users can watch animals around an African waterhole, ships in the Panama Canal or the traffic at a local roundabout live and in real time. Video chat rooms, video conferencing, and remote controllable webcams have become popular. Some people install webcams in their bedrooms that can be accessed by other voyeurs, often with two-way sound. VoIP stands for Voice over IP, where IP refers to the Internet Protocol that underlies all Internet communication. This phenomenon began as an optional two-way voice extension to some of the Instant Messaging systems that took off around the turn of the millennium. In recent years many people and organizations have made VoIP systems as easy to use and as convenient as a normal telephone. The benefit is that, as the actual voice traffic is carried by the Internet, VoIP is free or costs much less than an actual telephone call, especially over long distances and especially for those with always-on ADSL or DSL Internet connections anyway. The disadvantages are that it is still difficult to initiate a call with someone, unless they also have a VoIP phone or are at their computer and that there are still several competing standards that are mitigating against universal acceptance. In all of these cases, existing large organisations, that have grown accustomed to regular incomes for their services, are finding increased competition in their service areas, coming directly from the Internet. While newcomers strive to make these inroads, the traditional industries are having to adapt, adopt, complain or suffer. Meanwhile the consumer in each case most probably benefits from the increased range of services and possible price reductions. Some worry about censorship and control while others see a continuing globalisation of culture and norms.

Language

Main article: English on the Internet The most prevalent language for communication on the Internet is English. This may be due to the Internet's origins or to the growing role of English as an international language. It may also be related to the poor capability of early computers to handle characters other than those in the basic Latin alphabet (see Unicode). After English (32 % of web visitors) the most-requested languages on the world wide web are Chinese 13 %, Japanese 8 %, Spanish 6 %, German 6 % and French 4 %. (From [http://www.internetworldstats.com/stats7.htm Internet World Stats]) By continent, 33 % of the world's Internet users are based in Asia, 29 % in Europe and 23 % in North America.[http://www.internetworldstats.com/stats.htm] The Internet's technologies have developed enough in recent years that good facilities are available for development and communication in most widely used languages. However, some glitches such as mojibake still remain.

Cultural awareness

From a cultural awareness perspective, the Internet has been both an advantage and a liability. For people who are interested in other cultures it provides a significant amount of information and an interactivity that would be unavailable otherwise. However, for people who are not interested in other cultures there is some evidence indicating that the Internet enables them to avoid contact to a greater degree than ever before.

Censorship

Some countries, such as Iran and the People's Republic of China, restrict what people in their countries can see on the Internet, especially unwanted political and religious content. In the Western world, it is Germany that has the highest rate of censorship. Internet Service Providers are required by law to block some sites that contain child pornography or Nazi or Islamist propaganda. Censorship is sometimes done through government sponsored censoring filters, or by means of law or culture, making the propagation of targeted materials extremely hard. At the moment most Internet content is available regardless of where one is in the world, so long as one has the means of connecting to it.

Internet access

Germany Common methods of home access include dial-up, landline broadband (over coaxial cable, fiber optic or copper wires), Wi-Fi, satellite and cell phones. Public places to use the Internet include libraries and Internet cafes, where computers with Internet connections are available. There are also Internet access points in many public places like airport halls, in some cases just for brief use while standing. Various terms are used, such as "public Internet kiosk", "public access terminal", and "Web payphone". Many hotels now also have public terminals, though these are usually fee based. Wi-Fi provides wireless access to computer networks, and therefore can do so to the Internet itself. Hotspots providing such access include Wi-Fi-cafes, where a would-be user needs to bring their own wireless-enabled devices such as a laptop or PDA. These services may be free to all, free to customers only, or fee-based. A hotspot need not be limited to a confined location. The whole campus or park, or even the entire city can be enabled. Grassroots efforts have led to wireless community networks. Apart from Wi-Fi, there have been experiments with proprietary mobile wireless networks like Ricochet, various high-speed data services over cellular or mobile phone networks, and fixed wireless services. These services have not enjoyed widespread success due to their high cost of deployment, which is passed on to users in high usage fees. New wireless technologies such as WiMAX have the potential to alleviate these concerns and enable simple and cost effective deployment of metropolitan area networks covering large, urban areas. There is a growing trend towards wireless mesh networks, which offer a decentralized and redundant infrastructure and are often considered the future of the Internet. Broadband access over power lines was approved in 2004 in the United States in the face of stiff resistance from the amateur radio community. The problem with modulating a carrier signal onto power lines is that an above-ground power line can act as a giant antenna and jam long-distance radio frequencies used by amateurs, seafarers and others. Countries where Internet access is available to a majority of the population include Germany, India, China, Chile, Iceland, Finland, Sweden, Greece, Italy, Australia, Denmark, the United States, Canada, the United Kingdom, The Netherlands, Japan, Singapore, Taiwan, Thailand, South Korea and Norway. The use of the Internet around the world has been growing rapidly over the last decade, although the growth rate seems to have slowed somewhat after 2000. The phase of rapid growth is ending in industrialized countries, as usage becomes ubiquitous there, but the spread continues in Africa, Latin America, the Caribbean and the Middle East. However, there are still problems for many. ADSL and other broadband access are rare or nonexistent in most developing countries. Even in developed countries, high prices, mediocre performance and access restrictions often limit its uptake. Within individual countries, wide differences may exist between larger cities (often having multiple providers of broadband access) and some rural areas, where no broadband access may be available at all. The expansion of the availability of Internet access is a way to bridge the so-called digital divide.

Capitalization conventions

In formal usage, Internet is traditionally written with a capital first letter. The Internet Society, the Internet Engineering Task Force, the Internet Corporation for Assigned Names and Numbers, the World Wide Web Consortium, and several other Internet-related organizations all use this convention in their publications. In English grammar, proper nouns are capitalized. Most newspapers, newswires, periodicals, and technical journals also capitalize the term. Examples include the New York Times, the Associated Press, Time, The Times of India, Hindustan Times and Communications of the ACM. In other cases, the first letter is often written small (internet), and many people are not aware of any convention of using a capital letter. Some argue that internet is the correct form. Since 2000, a significant number of publications have switched to using internet. Among them are The Economist, the Financial Times, the London Times, and the Sydney Morning Herald. As of 2005, most publications using internet appear to be located outside of North America although one American news source, Wired News, has adopted the lowercase spelling.

Leisure

The Internet has been a major source of leisure since before the World Wide Web, with entertaining social experiments such as MOOs being conducted on university servers, and humor-related USENET groups receiving much of the main traffic. Today, many Internet forums have sections devoted to neta; short cartoons in the form of Flash movies are also popular. The pornography and gambling industries have both taken full advantage of the World Wide Web, and often provide a significant source of advertising revenue for other Web sites. Although many governments have attempted to put restrictions on both industries' use of the Internet, this has generally failed to stop their widespread popularity. One main area of leisure on the Internet is multiplayer gaming. This form of leisure creates communities, bringing people of all ages and origins to enjoy the fast-paced world of multiplayer games. These range from MMORPG to first-person shooters, from role-playing games to online gambling. This has revolutionized the way many people interact and spend their free time on the Internet. Online gaming began with services such as GameSpy and MPlayer, which players of games would typically subscribe to. Non-subscribers were limited to certain types of gameplay or certain games. With the release of Diablo by Blizzard Entertainment, gamers were treated to a built in online game service that was free of charge. With Blizzard's next game, StarCraft, the gaming world saw an explosion in the numbers of players using the Internet to play multi-player games. StarCraft may have been the first non-MMO game in which most players utilized the online gameplay as opposed to the single-player gameplay. Online gaming has progressed so much in the last 10 years that gamers earn a living from being a professional at the subject by winning tournaments and prizes as well as signing sponsor deals. Because there is a large support for certain online games, a new community has been born for people modding games, where users edit games to add a whole new element to it. This is how games such as Counter-Strike were born from the Half-Life Gaming Engine. Cyberslacking has become a serious drain on corporate resources; the average UK employee spends 57 minutes a day surfing, according to a study by Peninsula Business Services[http://news.scotsman.com/topics.cfm?tid=914&id=1001802003].

A complex system

Many computer scientists see the Internet as a "prime example of a large-scale, highly engineered, yet highly complex system" (Willinger, et al). The Internet is extremely heterogeneous. (For instance, data transfer rates and physical characteristics of connections vary widely.) The Internet exhibits "emergent phenomena" that depend on its large-scale organization. For example, data transfer rates exhibit temporal self-similarity.

Marketing

The Internet has also become a big market, and the biggest companies today have grown by taking advantage of the efficient low-cost advertising and commerce through the Internet. It is the fastest way to spread information to a vast community of people all at once. The Internet has revolutionized shopping –– a person can order a CD online and receive it in the mail within a couple of days, or download it directly in some cases.

Criticism

Many hyperlinks are outdated as time takes its toll on the existence of URL weblinks. These weblinks are often times defunct and are retained as hyperlinks for extended timeframes as a result of laziness or being busy enough to be sidetracked away from updating webpages. This is a common hoax for people who are fans in the field of what those links provide them with/to.

External links

General

- [http://www.channel101.com/ Internet TV Stations]
- [http://www.isoc.org/ The Internet Society (ISOC)]
- [http://www.techterms.org/internet.php Internet Dictionary] - Definitions of Internet-related terms
- [http://www.experienced-people.co.uk/1099-webmaster-glossary/ The Alternate Internet Glossary] (Humor)
- A [http://www.illusivecreations.com Calgary Web Design] company that has put together over 300 articles about the internet and web development. You can view them by going [http://www.illusivecreations.com/articles/ here].
- [http://www.clickz.com/stats/sectors/geographics/article.php/5911_151151 Internet access stats]
- [http://www.sharpened.net/glossary/ Glossary of Computer and Internet Terms]
- [http://scoreboard.keynote.com/scoreboard/Main.aspx?Login=Y&Username=public&Password=public Internet Health Report] from Keynote
- [http://www.internetworldstats.com/stats.htm Internet World Stats]

Articles

- [http://www.iht.com/articles/2005/09/29/business/net.php "EU and U.S. clash over control of the Net" - International Herald Tribune article by Tom Wright]
- [http://www.wired.com/wired/archive/13.08/intro.html "10 Years that changed the world" - WiReD looks back at the evolution of the Internet over last 10 years]
- [http://www.fourmilab.ch/documents/digital-imprimatur/ John Walker: The Digital Imprimatur]
- [http://www.addressingtheworld.info addressingtheworld.info] - website accompanying a book (ISBN 0742528103) on the history of DNS
- [http://computer.howstuffworks.com/internet-infrastructure.htm How Stuff Works explanation of the Infrastructure of the Internet]
- [http://www.searchandgo.com/articles/internet/net-explained-1.php Internet Explained] Seven part article explaining the origins to the present and a future look at the Internet.
- [http://www.wired.com/news/culture/0,1284,64596,00.html?tw=wn_tophead_7 "It's Just the 'internet' Now" - Wired.com article by Tony Long]

History

- [http://www.isoc.org/internet/history/brief.shtml The Internet Society History Page]
- [http://www.internetvalley.com/archives/mirrors/cerf-how-inet.txt How the Internet Came to Be]
- [http://www.zakon.org/robert/internet/timeline/ Hobbes' Internet Timeline v7.0]
- [http://www.ciolek.com/PAPERS/e-scholarship2000.html Futures and Non-futures for Scholarly Internet. ]
- [http://www.lk.cs.ucla.edu/internet_history.html History of the Internet links]
- [http://www.ietf.org/rfc/rfc801.txt RFC 801, planning the TCP/IP switchover]
- [http://www.archive.org/ Internet Archive] - A searchable database of old cached versions of websites dating back to 1996
- A list of lectures, some of which relate to the Internet, from the Massachusetts Institute of Technology is available [http://ocw.mit.edu/OcwWeb/Comparative-Media-Studies/CMS-930Media--Education--and-the-MarketplaceFall2001/VideoLectures/index.htm here]. Of particular interest is lecture #3 The Next Big Thing: Video Internet which is delivered in Real Player format. The lecture gives a brief history of networking; discusses convergence between the internet/telephone/television networks; the expansion of broadband access; makes predictions about the future of delivery of video over the internet.

References

- Walter Willinger, Ramesh Govindan, Sugih Jamin, Vern Paxson, and Scott Shenker. (2002). Scaling phenomena in the Internet. In Proceedings of the National Academy of Sciences, 99, suppl. 1, 2573 – 2580. Category:Communication Category:Digital media Category:Internet Category:Digital Revolution Category:Technology Category:Computer networks Category:Networks ko:인터넷 ms:Internet ja:インターネット simple:Internet th:อินเทอร์เน็ต fiu-vro:Internet

Transit (internet)

Internet transit is the provision of a dedicted connection to the internet that works at an extremely high speed. The most common use of internet transit is when a customer has a large number of machines, and wants to put them all on the same connection.

Domain name

The term domain name has multiple meanings, all related to the Domain Name System (main article).
- a name that is entered into a computer (e.g. as part of a website or other URL, or an email address) and then looked up in the global [Domain Name System] which informs the computer of the IP address(es) with that name.
- the product that registrars provide to their customers.
- a name looked up in the DNS for other purposes. They are sometimes colloquially (and incorrectly) referred to by marketers as "web addresses". Domain names are Hostnames that provide rememberable names to stand in for numeric IP addresses. They allow for any service to move to a different location in the topology of the Internet (or another internet), which would then have a different IP address. Each string of letters, digits and hyphens between the dots is called a label in the parlance of the domain name system (DNS). Valid labels are subject to certain rules, which have relaxed over the course of time. Originally labels must start with a letter, and end with a letter or digit; any intervening characters may be letters, digits, or hyphens. Labels must be between 1 and 63 characters long (inclusive). Letters are ASCII A–Z and a–z; domain names are compared case-insensitively. Later it became permissible for labels to commence with a digit (but not for domain names to be entirely numeric), and for labels to contain internal underscores, but support for such domain names is uneven. These are the rules imposed by the way names are looked up ("resolved") by DNS. Some top level domains (see below) impose more rules, such as a longer minimum length, on some labels. Fully qualified names (FQDNs) are sometimes written with a final dot. Translating numeric addresses to alphabetical ones, domain names allow Internet users to localize and visit websites. Additionally since more than one IP address can be assigned to a domain name, and more than one domain name assigned to an IP address, one server can have multiple roles, and one role can be spread among multiple servers. One IP address can even be assigned to several servers, such as with anycast and hijacked IP space.

Examples

The following examples illustrates the difference between a URL (Uniform Resource Locator) and a domain name: : URL: http://www.example.com/ : Domain name: www.example.com As a general rule, the IP address and the server name are interchangeable. For most internet services, the server will not have any way to know which was used. However, the explosion of interest in the web means that there are far more websites than servers. To accommodate this, the hypertext transfer protocol (HTTP) specifies that the client tells the server which name is being used. This way, one server with one IP address can provide different sites for different domain names. This feature is goes under the name virtual hosting and is commonly used by web hosts. For example, the server at 192.0.34.166 handles all of the following sites: : www.example.com : www.example.net : www.example.org

Top-level domains

Every domain name ends in a top-level domain (TLD) name, which is always either one of a small list of generic names (three or more characters), or a two characters territory code based on ISO-3166 (there are few exceptions and new codes are integrated case by case). Examples of (gTLD) extensions are:
- .com
- .net
- .org
- .biz
- .info
- .name
- .museum
- .travel
- .pro
- .aero
- .xxx (disapproved by ICANN) Examples of country code top-level domain (ccTLD) extensions are:
- .au
- .eu (not an ISO-3166 code, and not a country, but used anyway for the European Union. Scheduled to be launched December 7, 2005)
- .us
- .uk (not an ISO-3166 code, but used anyway)
- .br
- .fr
- .es
- .de
- .in
- .it
- .jp
- .ca
- .nz
- .su (not an existing country at the moment - Soviet Union, but used anyway)

Official assignment

ICANN (Internet Corporation for Assigned Names and Numbers) has overall responsibility for managing the DNS. It controls the root domain, delegating control over each top-level domain to a domain name registry. For ccTLDs, the domain registry is typically controlled by the government of that country. ICANN has a consultation role in these domain registries but is in no position to regulate the terms and conditions of how a domain name is allocated or who allocates it in each of these country level domain registries. On the other hand, generic top-level domains (gTLDs) are governed directly under ICANN which means all terms and conditions are defined by ICANN with the cooperation of the gTLD registries. Domain names which are theoretically leased can be considered in the same way as real estate, due to a significant impact on online brand building, advertising, search engine optimization, etc.

Uses and abuses

As domain names became attractive to marketers, rather than just the technical audience for which they were originally intended, they began to be used in manners that in many cases did not fit in their intended structure. As originally planned, the structure of domain names followed a strict hierarchy in which the top level domain indicated the type of organization (commercial, governmental, etc.), and addresses would be nested down to third, fourth, or further levels to express complex structures, where, for instance, branches, departments, and subsidiaries of a parent organization would have addresses which were subdomains of the parent domain. Also, hostnames were intended to correspond to actual physical machines on the network, generally with only one name per machine. However, once the World Wide Web became popular, site operators frequently wished to have memorable addresses, regardless of whether they fit properly in the structure; thus, since the .com domain was the most popular and memorable, even noncommercial sites would often get addresses under it, and sites of all sorts wished to have second-level domain registrations even if they were parts of a larger entity where a logical subdomain would have made sense (e.g., abcnews.com instead of news.abc.com). A website found at http://www.example.org will often be advertised without the "http://", and in most cases can be reached by just typing "example.org" into a web browser. In the case of a .com, the website can sometimes be reached by just typing "example" (depending on browser versions and configuration settings, which vary in how they interpret incomplete addresses). With "virtual hosting", often many domain names would point to the same physical server. The popularity of domain names also led to uses which were regarded as abusive by established companies with trademark rights; this was known as cybersquatting, in which somebody took a name that resembled a trademark in order to profit from traffic to that address. To combat this, various laws and policies were enacted to allow abusive registrations to be forcibly transferred, but these were sometimes themselves abused by overzealous companies committing reverse domain hijacking against domain users who had legitimate grounds to hold their names, such as their being generic words as well as trademarks in a particular context, or their use in the context of fan or protest sites with free speech rights of their own.

Generic domain names — problems arising out of unregulated name selection

Within a particular top-level domain, parties are generally free to select an unallocated domain name as their own on a first come, first served basis. For generic or commonly used names, this may sometimes lead to the use of a domain name which is inaccurate or misleading. This problem can be seen with regard to the ownership or control of domain names for a generic product or service. By way of illustration, there has been tremendous growth in the number and size of literary festivals around the world in recent years. In this context, currently a generic domain name such as literary.org is available to the first literary festival organisation which is able to obtain registration, even if the festival in question is very young or obscure. Some critics would argue that there is greater amenity in reserving such domain names for the use of, for example, a regional or umbrella grouping of festivals. Related issues may also arise in relation to non-commercial domain names.

Unconventional domain names

Due to the rarity of one-word dot-com domain names, many unconventional domain names, domain hacks, have been gaining popularity. They make use of the top-level domain as an integral part of the website's title. Two of the most visited domain hack websites are del.icio.us and blo.gs, which spell out 'delicious' and 'blogs', respectively. Some unconventional domain names are also used to create email hacks. Non-working examples that spell 'James' are j@m.es and j@mes.com, which use the domain names m.es (of Spain's .es) and mes.com.

Commercial resale of domain names

An economic effect of the widespread usage of domain names has been the resale market for generic domain names that has sprung up in the last decade. Certain domains, especially those related to business, gambling, pornography, and other commercially lucrative fields have become very much in demand to corporations and entrepreneurs due to their intrinsic value in attracting clients. In fact, the most expensive internet domain name to date, according to Guinness World Records, is business.com which was resold in 1999 for $7.5 million. Another high value domain name, sex.com, was stolen from its rightful owner by means of a forged transfer instruction via fax. During the height of the dot-com era, the domain was earning millions of dollars per month in advertising revenue from the large influx of visitors that arrived daily. Two long-running US lawsuits resulted, one against the thief and one against the domain registrar VeriSign[http://www.wired.com/news/business/0,1367,63142,00.html]. In one of the cases, the judge found in favor of the plaintiff, leading to an unprecendented ruling that classified domain names as property, granting them the same legal protections. In 1999, Microsoft traded the valuable name Bob.com for the name Windows2000.com which was the name of their new operating system.[http://www.theregister.com/1999/11/11/windows2000_com_owner_sells_domain/] One of the reasons for the value of domain names is that even without advertising or marketing, they attract clients seeking services and products who simply type in the generic name. Furthermore, generic domain names such as Rent.com or Books.com are extremely easy for potential customers to remember, increasing the probability that they become repeat customers or regular clients. Although the current domain market is nowhere as strong as it was during the dot-com heyday, it remains strong and is currently experiencing solid growth again. Annually tens of millions of dollars change hands due to the resale of domains. Large numbers of registered domain names lapse and are deleted each year. On average 25,000 domain names drop (are deleted) every day.

Caveat Emptor

Care should always be exercised when registering a domain name: DNS is case-insensitive and the modern trend of words run together with intercapping can be misinterpreted when converted to lowercase. Who Represents, a database of artists and agents, chose http://www.whorepresents.com; Experts Exchange, the programmers' site, famously had http://www.expertsexchange.com; Pen Island unwisely chose http://www.penisland.net; a therapists' network thought http://www.therapistfinder.com looked good and of course the Italian power company PowerGen Italia became http://www.powergenitalia.com. Fortunately the dash is allowable in DNS, a fact possibly unknown to those organisations listed above. DNS is case-insensitive, so CAMFT's website can be advertised as http://www.TherapistFinder.com (instead of http://www.therapistfinder.com).

External links

- [http://www.dnjournal.com/ Domain Name Journal] - Covering the Domain Name Industry with Profiles and News.
- [http://www.domainnamewire.com/ Domain Name Wire] - Latest news about Domain Name Industry, domain sales, and legal issues.
- [http://www.gobin.info/domainname/ Domain Name Universe] - List of all existing Domain Name Registries, global Domain Name Search, Latest news.
- [http://www.faqs.org/rfcs/std/std13.html STD 13/RFC 1034], Domain Names—Concepts and Facilities, an Internet Protocol Standard.
- [http://www.icann.org/ ICANN] - Internet Corporation for Assigned Names and Numbers.
- [http://www.icann.org/udrp/udrp.htm UDRP], Uniform Domain-Name Dispute-Resolution Policy.
- [http://www.internic.net/ Internic.net], public information regarding Internet domain name registration services.
- [http://lifeofawebsite.com/begin/country-specific-domains.php List of Country Specific Domains]
- [http://www.circleid.com/ CircleID], Community discussions on TLDs and Internet infrastructure.
- [http://xona.com/domainhacks/ Domain Hacks] - unconventional domain name search utility
- The authoritative definition is that given in
- RFC 1032 - Domain administrators guide
- RFC 1033 - Domain administrators operations guide
- RFC 1034 - Domain names - concepts and facilities
- RFC 1035 - Domain names - implementation and specification Category:Domain Name System Category:Internet Category:Information technology Category:Identifiers als:Domäne (Internet) ja:ドメイン名

Leased line

A leased line is a (usually) symmetric telecommunications line connecting two locations together. Unlike traditional PSTN lines they do not have a telephone number, each side of the line being permanently connected to the other. They can be used for telephone, data or Internet services. In the UK, leased lines are usually available at speeds of 64k, 128k, 256k, 512k, 2Mb and provided to the customer on X.21 presentation. Higher speeds are available on alternative interfaces. In the US, leased lines are usually presented on a T1 bearer circuit in a number 56k or 64k timeslots. This has advantages over the UK - more than one logical connection can be provided on a single bearer, and upgrades can take place relatively easily. However, the customer must manage their own network termination equipment - Data Service Unit or Channel Service Unit (CSU/DSU).

Colocation

.]] A colocation centre ("colo") or carrier hotel is a type of data centre where multiple telecommunications network or service providers, such as telcos or internet service providers, site their connections to one another's networks (points of presence). Increasingly organizations are recognizing the benefits of colocating their mission-critical equipment within a data centre. Colocation is becoming popular because of the time and cost savings a company can realize as result of using shared data centre infrastructure. With IT and communications facilities in safe, secure hands, telecommunications, internet, ASP and content providers, as well as enterprises, enjoy less latency and the freedom to focus on their core business. Additionally, customers reduce their traffic back-haul costs and free up their internal networks for other uses. Moreover, by outsourcing network traffic to a colocation service provider with greater bandwidth capacity, web site access speeds should improve considerably. Major types of colocation customers are:
- Web commerce companies, who use the facilities for a safe environment and cost-effective, redundant connections to the Internet
- Major enterprises, who use the facility for disaster avoidance
- Telecommunication companies, who use the facilities to interexchange traffic with other telecommunications companies and access to potential clients Most Network Access Point facilities provide colocation.

Trivia

Some colocation centres feature a "meet-me-room" where the different carriers housed in the centre can efficiently exchange data. Most peering points are sited in colocation centres. These sites are often used for web hosting. Most colocation centres have high levels of physical security and multiple redundant power and humidity / air-conditioning systems. A typical Colocation centre setup would consist of the following hardware and services: Building:
- Usually built near a GlassFibre ring.
- Fibre has multiple access points into building to prevent back hoe cuts.
- Guarded 24/7 and secured with closed circuit cameras.
- "Clean" rooms to ensure optimal running conditions for computer and network hardware.
- Empty pipe fire suppression of some sort.
- Relay racks, cabinets or cages to mount servers into. Power:
- Connected to two or more different power stations/grids.
- Inline power backup using a system of UPS batteries (often with a diesel standby generator).
- Possibility to connect two different grids of power distribution to one server.
- Most also have Backup Diesel generators standby to support power delivery. Connections:
- Because of the high concentration of servers inside a colocation centre most carriers will be interested in bringing direct connections to such buildings.
- In most cases there will be a larger Internet-Exchange hosted inside a colocation centre, on which customers can connect for peering. Confusingly, one company can operate a colocation centre, another can provide the bandwidth, whereas a third company would rent a cage inside the centre, renting out racks to hosting providers which would rent the servers themselves to actual clients. Any and all of those companies will claim ownership of the facility and will feature photos and descriptions of it on their web sites. At the actual physical location various ID cards with various logos will be present, including those of the company that built/rents/owns the actual building.

Services offered

Most colocation centres offer different types of services to customers ranging from dedicated suites/rooms or cages to smaller racks or partial racks. Some colocation centres also offer some degree of SLAs (service level agreements) to support a wide range of computer and network related services, for example server reboots, hardware replacements, software updates etc. There are a few key differences between a dedicated server and colocation servers. Dedicated servers tend to be owned and rented out, while a colocation server is one that you own. Category:Internet hosting

Dialup

Dial-up access is an inexpensive but slow form of Internet access in which the client uses a modem to dial the Internet service provider's (ISP) node, a dial-up server type such as the Point-to-Point Protocol and TCP/IP protocols to establish a modem-to-modem link, which is then routed to the Internet. It is currently regarded as legacy technology given the advent of widely available broadband Internet access in the Western world, though many people worldwide still use it simply because they do not have access to a faster connection technology.

Availability

Dial-up requires no additional infrastructure on top of the telephone network. As telephone points are available throughout the world, dial-up remains useful to travellers. Dial-up is usually the only choice available for most rural or remote areas where getting a broadband connection is impossible due to low population and demand. Sometimes, dial-up access may also be an alternative to people who have limited budgets, though broadband is now increasingly available at lower prices due to market competition. Dial-up requires time to establish a telephone connection and perform handshaking before data transfers can take place, potentially a source of frustration. In locales with telephone connection charges, each connection incurs an incremental cost. If calls are time-charged, the duration of the connection incurs costs. Dial-up access is a transient connection, because either the user or the ISP terminates the connection. Internet service providers will often set a limit on connection durations to prevent hogging of access, and will disconnect the user — requiring reconnection and the costs and delays associated with that.

Performance

Dial-up modems typically have a maximum theoretical speed of 56 kbps (using the V.92 protocol), although in most cases only up to 53 kbps is possible due to overhead. Also, these speeds are the maximum possible; in almost all cases transfer speeds will be lower, averaging about 32 kbps. Other factors such as line noise further reduce achieved transfer rates. Dial-up connections usually have high latency that can be as high as 200ms or even more, which can make online gaming or videoconferencing difficult, if not impossible. Some games, such as Star Wars Galaxies and The Sims Online are capable of runnning on 56K dial-up. Broadband Internet access (mostly via cable and ADSL) have been replacing dial-up connections in the last five years. The reason for this replacement is mostly because broadband connections usually have speeds which far exceed the capacity of dial-up, in some cases up to 15,360 kbps. An increasing amount of Internet content such as Macromedia Flash, online gaming and streaming media require large amounts of bandwidth. Many computer games released in 2005 (such as Battlefield 2 or Star Wars Battlefront) are not compatible for online play with dial-up modems. It is likely that this trend will continue into the future.

External links

- [http://www.itu.int/TIES/services/connect/appendix_c.html Installing Dial Up Networking] Category:Network access ja:ダイヤルアップ接続

ISDN

:ISDN is also short for isosorbide dinitrate isosorbide dinitrate Integrated Services Digital Network (ISDN) is a type of circuit switched telephone network system, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in better quality and higher speeds than available with analog systems. More broadly, ISDN is a set of protocols for establishing and breaking circuit switched connections, and for advanced call features for the user. The English term is a "backronym", thought better for English-language advertisements than the original, "Integriertes Sprach- und Datennetz" (German for "integrated voice and data net"). In a videoconference, ISDN provides simultaneous voice, video, and text transmission between individual desktop videoconferencing systems and group (room) videoconferencing systems.

Configurations

In ISDN, there are two types of channels, B (for "Bearer") and D (for "Delta"). B channels are used for data (which may include voice), and D channels are intended for signalling and control (but can also be used for data). There are two kinds of access to ISDN. Basic rate interface (BRI) — also Basic rate access (BRA) — consists of two B channels, each with bandwidth of 64 kbit/s, and one D channel with a bandwidth of 16 kbit/s. Together these three channels can be designated as 2B+D. Primary rate interface (PRI) — also Primary rate access (PRA) — contains a greater number of B channels and a D channel with a bandwidth of 64 kbit/s. The number of B channels for PRI varies according to the nation: in North America and Japan it is 23B+1D, with an aggregate bit rate of 1.544 Mbit/s (T1); in Europe and Australia it is 30B+1D, with an aggregate bit rate of 2.048 Mbit/s (E1). Using a variation of the alternate mark inversion encoding technique, call data is transmitted over the data (B) channels, with the signalling (D) channels used for call setup and management. Once a call is set up, there is a simple 64 kbit/s synchronous bidirectional data channel between the end parties, lasting until the call is terminated. There can be as many calls as there are data channels, to the same or different end-points. Bearer channels may also be multiplexed into what may be considered single, higher-bandwidth channels via a process called B channel bonding. The D channel can also be used for sending and receiving X.25 data packets, and connection to X.25 packet network, this is specified in X.31. In practice, X.31 was only commerically implemented in France and Japan.

Reference points

A set of reference points are defined in the ISDN standard to refer to certain points between the telco and the end user ISDN equipment.
- R - defines the point between a non-ISDN device and a terminal adapter (TA) which provides translation to and from such a device
- S - defines the point between the ISDN equipment (or TA) and a Network Termination Type 2 (NT-2) device
- T - defines the point between the NT-2 and NT-1 devices¹
- U - defines the point between the NT-1 and the telco switch² ¹ Most NT-1 devices can perform the functions of the NT-2 as well, and so the S and T reference points are generally collapsed into the S/T reference point.
² Inside North America, the NT-1 device is considered customer premises equipment and must be maintained by the customer, thus, the U interface is provided to the customer. In other locations, the NT-1 device is maintained by the telco, and the S/T interface is provided to the customer.

Types of communications handled

Among the kinds of data that can be moved over the 64 kbit/s channels are pulse-code modulated voice calls, providing access to the traditional voice PSTN. This information can be passed between the network and the user end-point at call set-up time. In North America, ISDN is nowadays mostly used as an alternative to analog connection, most commonly for Internet access. Some of the services envisaged as being delivered over ISDN are now delivered over the Internet instead. In Europe, and in Germany in particular, ISDN has been successfully marketed as a phone with features, as opposed to a POTS phone (Plain Old Telephone Service) with few or no features. However meanwhile features that were first available with ISDN (such as Three-Way Call, Call Forwarding, Caller ID, etc.) are now commonly available for ordinary analog phones as well, eliminating this advantage of ISDN. Another advantage of ISDN was the possibilty of multiple simultaneous calls (one call per B channel), e.g. for big families, but with the increased popularity and reduced prices of mobile telephony this has become less interesting as well, making ISDN rather unappealing to the private customer. Where an analog connection requires a modem, an ISDN connection requires a terminal adapter (TA).

A sample ISDN call

The following is an example of a Primary Rate (PRI) ISDN call showing the Q.921/LAPD and the Q.931/Network message intermixed (i.e. exactly what was exchanged on the D-channel). The call is originating from the switch where the trace was taken and goes out to some other switch, possibly an end-office LEC, who terminates the call. The first line format is <time> <D-channel> <Transmitted/Received> <LAPD/ISDN message ID>. If the message is an ISDN level message, then a decoding of the message is attempted showing the various Information Elements that make up the message. All ISDN messages are tagged with an ID number relative to the switch that started the call (local/remote). Following this optional decoding is a dump of the bytes of the message in <offset> <hex> ... <hex> <ascii> ... <ascii> format. The RR messages at the beginning prior to the call are the keep alive messages. Then you will see a SETUP message that starts the call. Each message is acknowledged by the other side with a RR.

10:49:47.33  21/1/24  R  RR
0000  02 01 01 a5                                          ....

10:49:47.34  21/1/24  T  RR
0000  02 01 01 b9                                          ....

10:50:17.57  21/1/24  R  RR
0000  02 01 01 a5                                          ....

10:50:17.58  21/1/24  T  RR
0000  02 01 01 b9                                          ....

10:50:24.37  21/1/24  T  SETUP
    Call Reference       : 000062-local
    Bearer Capability    : CCITT, Speech, Circuit mode, 64 kbit/s 
    Channel ID           : Implicit Interface ID implies current span, 21/1/5, Exclusive
    Calling Party Number : 8018023000 National number  User-provided, not screened  Presentation allowed
    Called Party Number  : 3739120 Type: SUBSCRB
0000  00 01 a4 b8  08 02 00 3e  05 04 03 80  90 a2 18 03   .......>........
0010  a9 83 85 6c  0c 21 80 38  30 31 38 30  32 33 30 30   ...l.!.801802300
0020  30 70 08 c1  33 37 33 39  31 32 30                   0p..3739120

10:50:24.37  21/1/24  R  RR
0000  00 01 01 a6                                          ....

10:50:24.77  21/1/24  R  CALL PROCEEDING
    Call Reference       : 000062-local
    Channel ID           : Implicit Interface ID implies current span, 21/1/5, Exclusive
0000  02 01 b8 a6  08 02 80 3e  02 18 03 a9  83 85         .......>......

10:50:24.77  21/1/24  T  RR
0000  02 01 01 ba                                          ....

10:50:25.02  21/1/24  R  ALERTING
    Call Reference       : 000062-local
    Progress Indicator   : CCITT, Public network serving local user, In-band information or an appropriate pattern is now available
0000  02 01 ba a6  08 02 80 3e  01 1e 02 82  88            .......>.....

10:50:25.02  21/1/24  T  RR
0000  02 01 01 bc                                          ....

10:50:28.43  21/1/24  R  CONNECT
    Call Reference       : 000062-local
0000  02 01 bc a6  08 02 80 3e  07                         .......>.

10:50:28.43  21/1/24  T  RR
0000  02 01 01 be                                          ....

10:50:28.43  21/1/24  T  CONNECT_ACK
    Call Reference       : 000062-local
0000  00 01 a6 be  08 02 00 3e  0f                         .......>.

10:50:28.44  21/1/24  R  RR
0000  00 01 01 a8                                          ....

10:50:35.69  21/1/24  T  DISCONNECT
    Call Reference       : 000062-local
    Cause                : 16, Normal call clearing.
0000  00 01 a8 be  08 02 00 3e  45 08 02 8a  90            .......>E....

10:50:35.70  21/1/24  R  RR
0000  00 01 01 aa                                          ....

10:50:36.98  21/1/24  R  RELEASE
    Call Reference       : 000062-local
0000  02 01 be aa  08 02 80 3e  4d                         .......>M

10:50:36.98  21/1/24  T  RR
0000  02 01 01 c0                                          ....

10:50:36.99  21/1/24  T  RELEASE COMPLETE
    Call Reference       : 000062-local
0000  00 01 aa c0  08 02 00 3e  5a                         .......>Z

10:50:36.00  21/1/24  R  RR
0000  00 01 01 ac                                          ....

10:51:06.10  21/1/24  R  RR
0000  02 01 01 ad                                          ....

10:51:06.10  21/1/24  T  RR
0000  02 01 01 c1                                          ....

10:51:36.37  21/1/24  R  RR
0000  02 01 01 ad                                          ....

10:51:36.37  21/1/24  T  RR
0000  02 01 01 c1                                          ....

External links

- http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/isdn.htm
- http://hea-www.harvard.edu/~fine/ISDN/
- http://www.itu.org
- http://www.ralphb.net/ISDN/
- http://www.concito.net/isdn.php Category:ITU-T recommendations category: telephony Category:Network access ko:ISDN ja:ISDN

Cable modem

A cable modem is a special type of modem that is designed to modulate a data signal over cable television infrastructure. Cable modems are primarily used to deliver broadband Internet access, taking advantage of unused bandwidth on a cable television network. There were 22.5 million cable modem users in the United States during Q1 2005. That's up from 17.4 million in Q1 2004. It is also commonly found in Latin America. Cable modems should not be confused with older LAN systems such as 10base2 or 10base5 that used coaxial cables — and especially not with 10broad36, which actually utilized the same sort of cable as CATV systems. 10broad36]

Cable Internet Access

The term cable Internet access (or simply cable) refers to the delivery of Internet service over this infrastucture. Along with DSL technology, cable modems ushered in the age of broadband Internet access in developed countries. Cable modems usually delivery faster speed than DSL does. Prior to the availability of such systems, Internet access involved slow dial-up access over a public switched telephone network. Three often cited disadvantages of cable Internet are: #Users in a neighborhood share the available bandwidth provided by a single coaxial cable line. Therefore, connection speed can vary depending on how many people are using the service at the same time. Often the idea of a shared line is seen as a weak point of cable Internet access. From a technical point of view, all networks, including DSL services, are sharing a fixed amount of bandwidth between a multitude of users — but because cable networks tend to be spread over larger areas than DSL services, more care must be taken to ensure good network performance. #A more significant weakness of cable networks using a shared line is the risk of loss of privacy, especially considering the availability of hacking tools for cable modems. This issue is addressed by encryption and other privacy features specified in the DOCSIS (Data Over Cable Service Interface Specification) standard used by most cable modems. #Many cable Internet providers are reluctant to offer cable modem access without tying it to a cable television subscription. This has ramifications similar to those of the lack of naked DSL.

CDLP

CDLP is a proprietary standard made by Motorola. CDLP CPE was capable of both RF (Cable Network) and PSTN return paths. The standard is more or less defunct now with new providers using DOCSIS and existing providers changing. [http://broadband.motorola.com/catalog/productdetail.asp?image=large&productID=221 Sample Motorola CDLP Modem] The Australian ISP BigPond employed this system when it started Cable Modem trials in 1996. For a number of years cable Internet access was only available to Sydney, Melbourne and Brisbane via CDLP. This network ran parallel to the newer DOCSIS system for a number of years. In 2004 the CDLP network was switched off and now is exclusively DOCSIS.

Cable Modems and VoIP

With the advent of Voice over IP telephony, cable modems can also be used to provide telephone service. Many people who have cable modems have opted to eliminate their Plain Old Telephone Service (POTS). Because most telephone companies do not offer naked DSL (DSL service without a POTS line), many VoIP users prefer cable modems. VoIP and other new data services that require broadband Internet access are driving demand for increased bandwidth delivery via cable modems. As of 2005, several national cable systems in the United States have announced plans to upgrade their networks to meet this demand.

Cable modem manufacturers

- 3Com
- Cisco Systems
- D-Link
- Ericsson
- Linksys
- Motorola
- Nortel Networks
- RCA
- Scientific Atlanta
- Terayon
- Toshiba

External links

- [http://www.cable-modem.net/ Cable Modem Information Network]
- [http://electronics.howstuffworks.com/cable-modem.htm/printable Cable modem]
- [http://www.cablemodem.com/ DOCSIS standard]
- [http://www.cable-modems.org/ The Cable Modem Reference Guide]
- [http://www.cablemodem.ch/ The Swiss Cable Modem webpage] Category:Broadband Category:Networking hardware Category:Internet

Digital Subscriber Line

Digital Subscriber Line, or DSL, is a family of technologies that provide digital data transmission over the wires used in the "last mile" of a local telephone network. Typically, the download speed of DSL ranges from 128 kilobits per second (Kb/s) to 6000 Kb/s depending on DSL technology and service level implemented. Upload speed is lower than download speed for ADSL and symetrical for SDSL.

History

The origin of Digital Subscriber Line technology dates back to 1988, when engineers at Bell Labs devised a way to carry a digital signal over the unused frequency spectrum available on the twisted pair cables running between the telephone company's telephone exchange and the customer premises. Implementation of DSL could permit an ordinary telephone line to provide digital communication without interfering with voice services. However, the management of incumbent local exchange carriers (ILEC) were not enthusiastic about it, since DSL was not as profitable as installing a second phone line for consumers who preferred simultaneous dial-up internet and voice connections, and the broadband data connection would cannibalize existing ISDN customers. This changed in the late 1990s when cable television companies began marketing broadband Internet access. Realizing that most consumers would prefer broadband Internet to dial-up Internet, ILECs rushed out the DSL technology, which they had delayed implementing, as an attempt to win market share from the broadband Internet access offered by cable television operators. As of 2005, DSL is the principal competition of cable modems for providing high speed Internet access to home consumers in Europe and North America. Older ADSL standards can deliver 8 Mbit/s over about 2 km (1.24 miles) of unshielded twisted pair copper wire. The latest standard ADSL2+ can deliver more than 20 Mbit/s over similar distances. Many customers, however, are located farther than 2 km (1.24 miles) from the telephone exchange, which reduces the amount of bandwidth available (thereby reducing the data rate) on the wires. On average, cable is faster than DSL in most commercial situations. Modern cable systems can provide 30 Mbit/s downstream, but this bandwidth is shared between all the users on the cable segment (which could be from 100 to 200 households).

Operation

The local loop of the Public Switched Telephone Network was initially designed to carry POTS voice communication and signaling, since the concept of data communications as we know it today did not exist. For reasons of economy, the phone system nominally passes audio between 300 and 3,400 Hz, which is regarded as the range required for human speech to be clearly intelligible. This is known as commercial bandwidth. Dial-up services using modems are constrained by the Shannon capacity of the POTS channel. At the local telephone exchange (UK terminology) or central office (US terminology) the speech is generally digitized into a 64 kbit/s data stream in the form of an 8 bit signal using a sampling rate of 8,000 Hz, therefore – according to the Nyquist theorem – any signal above 4,000 Hz is not passed by the phone network (and has to be blocked by a filter to prevent aliasing effects). The local loop connecting the telephone exchange to most subscribers is capable of carrying frequencies well beyond the 3.4 kHz upper limit of POTS. Depending on the length and quality of the loop, the upper limit can be tens of megahertz. DSL takes advantage of this unused bandwidth of the local loop by creating 4312.5 Hz wide channels starting between 10 and 100 kHz, depending on how the system is configured. Allocation of channels continues at higher and higher frequencies (up to 1.1 MHz for ADSL) until new channels are deemed unusable. Each channel is evaluated for usability in much the same way an analog modem would on a POTS connection. More usable channels equates to more available bandwidth, which is why distance and line quality are a factor. The pool of usable channels is then split into two groups for upstream and downstream traffic based on a preconfigured ratio. Once the channel groups have been established, the individual channels are bonded into a pair of virtual circuits, one in each direction. Like analog modems, DSL transceivers constantly monitor the quality of each channel and will add or remove them from service depending on whether or not they are usable. The commercial success of DSL and similar technologies largely reflects the fact that in recent decades, while electronics have been getting faster and cheaper, the cost of digging trenches in the ground for new wires remains expensive. All flavors of DSL employ highly complex digital signal processing algorithms to overcome the inherent limitations of the existing twisted pair wires. Not long ago, the cost of such signal processing would have been prohibitive but because of VLSI technology, the cost of installing DSL on an existing local loop, with a DSLAM at one end and a DSL modem at the other end is orders of magnitude less than would be the cost of installing a new, high-bandwidth fiber-optic cable over the same route and distance. Most residential and small-office DSL implementations reserve low frequencies for POTS service, so that with suitable filters and/or splitters the existing voice service continues to operate independent of the DSL service. Thus POTS-based communications, including fax machines and analog modems, can share the wires with DSL. Only one DSL modem can use the subscriber line at a time. The standard way to let multiple computers share a DSL connection is to use a router that establishes a connection between the DSL modem and a local Ethernet or Wi-Fi network on the customer's premises. Once upstream and downstream channels are established, they are used to connect the subscriber to a service such as an Internet service provider.

Equipment

The subscriber end of the connection consists of a DSL modem. This converts data from the digital signals used by computers into a voltage signal of a suitable frequency range which is then applied to the phone line. In the early days of DSL, installation required a technician to visit the premises. A "splitter" was installed near the demarcation point, from which a dedicated data line was installed. Today, many DSL vendors offer a self-install option, in which they ship equipment and instructions to the customer. In this case, since no changes are made to the cable plant on the customer premises, all the phone wires are carrying both POTS and DSL signal frequencies; therefore the customer generally needs to plug a DSL filter into each telephone outlet. However, this can sometimes cause degradation of the DSL signal (especially if more than 5 analogue devices are connected to the line) because the DSL signal is present on all telephone wiring in the building. A way to circumvent this is to install one filter upstream from all telephone jacks in the building, except for the jack to which the DSL modem will be connected. Since this requires wiring changes by the customer and may not work on some (poorly designed) household telephone wiring, it is rarely done. It is usually much easier to install filters at each telephone jack that is in use. Establishing new cable modem or satellite broadband service generally does require a visit by a technician to the premises, even when there is existing cable television service to this customer; this constitutes one of the major competitive advantages of DSL over cable broadband service. At the exchange a digital subscriber line access multiplexer (DSLAM) terminates the DSL circuits and aggregates them, where they are handed off onto other networking transports. It also separates out the voice component.

Protocols and configurations

Many DSL technologies implement an ATM layer over the low-level bitstream layer to enable the adaptation of a number of different technologies over the same link. DSL implementations may create bridged or routed networks. In a bridged configuration, the group of subscriber computers effectively connect into a single subnet. The earliest implementations used DHCP to provide network details such as the IP address to the subscriber equipment, with authentication via MAC address or an assigned host name. Later implementations often use PPP over Ethernet or ATM (PPPoE or PPPoA), while authenticating with a userid and password and using PPP mechanisms to provide network details. DSL also has contention ratios which need to be taken into consideration when deciding between broadband technologies.

DSL technologies

The line length limitations from telephone exchange to subscriber are more restrictive for higher data transmission rates. Technologies such as VDSL provide very high speed, short-range links as a method of delivering "triple play" services (typically implemented in fiber to the curb network architectures). Example DSL technologies (sometimes called xDSL) include:
- High-bit-rate Digital Subscriber Line (HDSL), covered in this article
- Symmetric Digital Subscriber Line (SDSL), a standardised version of HDSL
- Asymmetric Digital Subscriber Line (ADSL), a version of DSL with a slower upload speed
- Rate-Adaptive Digital Subscriber Line (RADSL)
- Very-high-bit-rate Digital Subscriber Line (VDSL)
- Very-high-bit-rate Digital Subscriber Line 2 (VDSL2), an improved version of VDSL
- G. Symmetric High-speed Digital Subscriber Line (G.SHDSL), a standardised replacement for early proprietary SDSL by the International Telecommunication Union Telecommunication Standardization Sector

Transmission methods

Transmission methods vary by market, region, carrier, and equipment.
- CAP: Carrierless Amplitude Phase Modulation - deprecated in 1996
- DMT: discrete multitone modulation, otherwise known as OFDM
- OFDM: Orthogonal frequency-division multiplexing

External links

- [http://www.iol.unh.edu/training/dsl/ The UNH-IOL DSL Knowledgebase (advanced tutorials)]
- [http://www.uk-bug.net The UK Broadband Usergroup]
- [http://www.howstuffworks.com/ Howstuffworks.com] - [http://electronics.howstuffworks.com/dsl.htm "How DSL Works"]
- [http://tldp.org/HOWTO/DSL-HOWTO/ DSL HOWTO for Linux]
- [http://www.t1.org/t1e1/_e14home.htm ANSI Working Group T1E1.4, a standards group for DSL]
- [http://www.dslforum.org/ DSL Forum, a promotional trade organization for the ADSL industry] Category:Telephony Category:Broadband ja:デジタル加入者線

Satellite internet

Satellite internet services are used in locations where terrestrial Internet access is not available and in locations which move frequently. Internet access via satellite is available globally, including vessels at sea. There are three types of satellite Internet service:
- one-way multicast,
- one-way with terrestrial return, and
- two-way satellite access.

One-way multicast

One-way multicast satellite Internet systems are used for IP multicast-based data, audio and video distribution. In the U.S., an FCC license is required only for the uplink station and no license is required for users. Note that most Internet protocols will not work correctly over one-way access, since they require a return channel. However, Internet content such as web pages can still be distributed over a one-way system by "pushing" them out to local storage at end user sites, though full interactivity is not possible. This much like a TV or radio content which offers little user interface.

System hardware components

Similar to one-way terrestrial return, satellite Internet may include interfaces to the Public Switched Telephone Network for squawk box applications. An Internet connection is not required, but many applications include an FTP server to queue data for broadcast.

System software components

Most one-way multicast applications require custom programming at the remote sites. The software at the remote site must filter, store, present a selection interface to and display the data. The software at the Teleport must provide access control, priority queueing, sending, and encapsulating of the data.

One-way with terrestrial return

One-way terrestrial return satellite Internet systems are used with traditional dial-up access to the Internet, with outbound data travelling through a telephone modem, but downloads are sent via satellite at a speed near that of broadband Internet access. In the U.S., a FCC license is only required for the uplink station, no license is required for the users.

System hardware components

The transmitting station is called the Teleport (also called "Head End", "Uplink Facility", or "Hub"). It has two components:
- Internet Connection: The ISP's routers connect to proxy servers which can enforce QoS (Quality of Service) bandwidth limits and guarantees for user traffic. These are then connected to a DVB Encapsulator which is then connected to a DVB-S modem. The RF signal from the DVB-S modem is connected to an up convertor which is connected via feedline, to the outdoor unit.
- Satellite uplink: The Block Up Converter (BUC) and Low Noise Block (LNB) connects to the splitter which uses a wave guide (optional) to connect to the OMT which

Internet service provider

ISP connection options

Virtual ISP

Other relevant acronyms

Related services

See also

Internet

Creation of the Internet

Today's Internet

Internet culture

ICANN

The World Wide Web

Remote access

Collaboration

File-sharing

Streaming media and VoIP

Language

Cultural awareness

Censorship

Internet access

Capitalization conventions

Leisure

A complex system

Marketing

Criticism

See also

External links

General

Articles

History

References

Transit (internet)

Domain name

Examples

Top-level domains

Official assignment

Uses and abuses

Generic domain names — problems arising out of unregulated name selection

Unconventional domain names

Commercial resale of domain names

Caveat Emptor

See also

External links

Leased line

See also

Colocation

Trivia

Services offered

Dialup

Availability

Performance

External links

ISDN

Configurations

Reference points

Types of communications handled

A sample ISDN call

Related topics

Protocols

Other

External links

Cable modem

Cable Internet Access

CDLP

Cable Modems and VoIP

See also

Cable modem manufacturers

External links

Digital Subscriber Line

History

Operation

Equipment

Protocols and configurations

DSL technologies

Transmission methods

See also

External links

Satellite internet

One-way multicast

System hardware components