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A field of first level (in English signal level domain , shortened TLD ), is a Domain name Domain Name System (DNS) which is at the top of the hierarchy of the fields; it is the part according to the last point in a domain name (e.g.: fr.wikipedia. org ). The most known fields of first level are those used on Internet: .com , .fr , .de , etc

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On Internet

Each field of first level is managed by an organization which is charged to manage and to allocate (possibly in a commercial way) its under-fields. The List of the fields of first level of Internet account approximately 300 fields. One distinguishes the generic fields from the geographical fields . Moreover, at the beginning of the 21e century, TLDs active appeared.

The special TLD

A special TLD exists:

.arpa : exploited for technical reasons.

TLDs credits ( gTLDs )

It is known and the most used on Internet. They are of two types:

Restricted gTLDs

.edu: education institutions accredited with the the United States (e.g.: web.mit. ''' edu ''', the Massachusetts Institute off Technology) as well as the education institutions of other countries whose formations were approved in the United States such as polytechnic. ''' edu ''', the Polytechnic school in France.
.int : international agencies (e.g.: www.coe. ''' int ''', the the Council of Europe)
.mil: American military organizations (e.g.: www.navy. ''' millet ''', US Navy)
.gov: American government organizations (e.g.: www.whitehouse. ''' gov ''', the White House)

gTLDs opened with all

.com: organizations with the purpose lucrative (e.g.: Microsoft. ''' COM ''', Microsoft)
.net: organisms in charge of the administration of the network (e.g.: www.gandi. ''' Net ''', GANDI)
.org: non-profit organizations (e.g.: fr.wikipedia. ''' org ''', Wikipédia)

New gTLDs appeared in 2001 and 2002:

.biz: businesses ( business )
.name: individuals (with a charter of naming)
.pro: accountants, lawyers, doctors and other professionals (with a charter of naming)
.info: services of information (unlimited use)

TLDs geographical ( ccTLDs )

The geographical TLD (with two letters) are intended for the countries and dependences territorial, and coded in accordance with the standard ISO 3166-1 which defines them. On the whole 246 ccTLDs are envisaged. E.g.: .be for the Belgium, .ca for the Canada, .ch for the Swiss , .fr for the France, .sn for the Senegal, .mq for the Martinique, .gp for the Guadeloupe, .in for the India.
The ccTLD " .gb" because " is not active; .uk" was used historically (ISO 3166-1 was updated to add code the U.K. in an exceptional way). The ccTLD " .kp" is not active because of the embargo on the North Korea and the absence of will of the North Korea to connect itself to the Internet). The ccTLD " .eu " (European Union) with the public the April 7th 2006 was opened.

TLDs active ( sTLDs )

New TLDs active appeared in 2001 and 2002. They are intended to characterize the activity of the organization which manages them. Contrary to the gTLDs, they are not opened with all but fix access terms at the applicants, or technical requirements of use concerning their contents:

.aero : industries of air transport
.coop: Co-operative S
.museum: museums

Then in 2005:

.jobs : for the RH, managed by an american company Employ Media LLC (www.employmedia.com)
.travel: for the voyage, managed by an american company Tralliance Corporation (www.tralliance.info)

and finally in 2006:

.cat : for the culture and the Catalan language
.mobi: for the Mobile Internet (profile XHTML-MP)
.tel: for telephony on IP (VoIP) (opening in 2007)

Other projects of sTLDs are subjected to the ICANN (.asia, .mail, .post). Others were rejected for financial technical reasons or (.kids, .xxx) and insufficiencies of justification of the need and system effectiveness designed to support the project indeed.

On a private Data-processing network

The preceding TLD are in force on Internet, but are the result of an arbitrary choice.

On a Lan, one can completely create TLD as much, and give them the semantics which one wants. One frequently uses the TLD .lan ( L ocal has rea N etwork in English = lan) or .local or .localnet .

Others are used locally according to the needs, but their use is not recommended, because there exists a collision risk de with of TLDs Internet, and thus of fragmentation of the network. E.g.: “.achat” for the service purchase, “.prod” for the production machine tools, “.fact” for the services invoicings…

Pseudo-TLDs

For needs for documentation, or preconfiguration of software or hardware, one is often brought to give examples of domain names. Rather than to use an actual address (which would be likely to be used such as it is since another site), one uses pseudos-TLDs which do not correspond to any existing TLD (their use such as it is will turn over an error or any contents or accessible service).

Pseudo-TLD was defined explicitly for that in the standards, the TLD .example (with the English orthography). But one finds also .tld (not standard but enough running because that indicates the type of value awaited to the place).

See too

Domain Name System
List of the fields of first level of Internet
Domain name
Resolution of names
Field of second level

External bond

TLD, by ICANN.

Simple: Signal-level domain

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