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ENUM Domain – What Is It?

ENUM is derived from the term telephone number mapping. ENUM domains make Internet and telecommunication services available under a single telephone number. Under a single ENUM domain, a person's business and home phone, mobile phone, fax, business and private e-mail addresses, video conference addresses or websites may be addressed. The application that is being used at a given moment to get into contact with someone identifies the destination address that corresponds to the ENUM domain. Thus, ENUM automatically ensures that the message is sent to the appropriate device.

Examples:

  • E-mail program: e-mail address
  • Telephone call: fixed-line phone, mobile phone or IP phone

ENUM Domain – How Does it Work?

ENUM makes use of the Domain Name System (DNS). The linking of telecommunication resources and the Internet is achieved by registering an ENUM domain for a telephone number. For example: The telephone number +49 12345678 is assigned to the ENUM domain 8.7.6.5.4.3.2.1.9.4.arpa, including the domain holder's various communication services.

Since 2006, ENUM domains of the German number space have been registered by DENIC. The ENUM domains administered by DENIC under the German country code +49 are under 9.4.e164.arpa.

As opposed to .de domains, ENUM domains cannot give rise to conflicts about names, since registration is linked to the corresponding telephone number. In the ENUM context, questions are thus more likely to arise in relation to whether the holder of the ENUM domain and the legitimate holder of the telephone number are indeed identical: An ENUM domain for a particular telephone number can only be registered by the person holding that number. For ENUM domain registrations, DENIC's ENUM Domain Terms and Conditions and ENUM Guidelines apply. In order to ensure that an ENUM domain is actually registered by the legitimate holder of the corresponding telephone number, DENIC provides a Complaint Procedure.

Registering an ENUM Domain

If you wish to register an ENUM domain, please proceed as follows:

Request a provider who offers ENUM domains to handle your registration. 

The name service, through which the communication entries are determined, may either be requested from a DENIC memberor any other provider, or you can do this job yourself.

Registration as an ENUM domain is only possible for those domains that correspond to geographic telephone numbers (all numbers with German area dialling codes), mobile numbers within the (0)15, (0)16 and (0)17 ranges, national numbers ((0)32), national free phone (toll-free) numbers ((0)800), personal telephone numbers ((0)700) or service numbers ((0)18).

Before you place your domain registration request, you should be familiar with the ENUM Domain Guidelines. These contain the rules that apply for ENUM domains under 9.4.e164.arpa. A domain contract with DENIC can only be concluded if all the conditions laid down there have been fulfilled. The provisions applicable to the domain contract are summarised in the ENUM Domain Terms and Conditions. These describe and explain the rights and obligations of domain holders and DENIC.

Technical Background Information

The ENUM protocol was developed by the ENUM Working Group of the IETF (Internet Engineering Task Force) and documented in the Internet standard RFC3761. There are some other Internet standards for future RFCs in this field. Access to the ENUM services on the Internet's existing Domain Name System (DNS) is via a subdomain reserved for ENUM. The IAB (Internet Architecture Board ) proposed .e164.arpa for this purpose, since E.164 is the standard in which the ITU (International Telecommunications Union) describes the international telecommunications number plan and .arpa is a specific Top Level Domain used as "Address and Routing Parameter Area" for infrastructure services. It is RIPE NCC in Amsterdam that acts as the international registry for .e164.arpa. Under this subdomain, an ENUM domain is then formed according to the following rule: the digits from the telephone number are placed before the .e164.arpa ending in reverse order and separated from one another by dots. To give an example, DENIC's telephone number is +49 69 27 2350 and it is linked to the domain 0.5.3.2.7.2.9.6.9.4.e164.arpa.

As far as the German part of the ENUM name tree is concerned (i.e. .9.4.e164.arpa), it was agreed with the relevant decision-making bodies to delegate it to DENIC. The lower levels can then be administered by the providers or by the customers themselves.

Requesting an ENUM

Technically, an ENUM request functions like this: once the user has entered the desired call number, the ENUM client accesses the so-called Naming Authority Pointer (NAPTR) records via the .e164.arpa name server on the ENUM name server. These records contain information about the available services that are combined with a particular E.164 call number. The result of this ENUM request may be just one or several URIs (uniform resource identifier), including the sequence in which they are to be processed. These URIs are now used to address resources or services that are associated with the E.164 call number.

ENUM Domain Request

[Translate to English:] ENUM Domainabfrage

  1. Input of the fax number (+49 1234) of the subscriber at the sending device.

  2. Request of the sending device to the ENUM DNS server using the ENUM domain (4.3.2.1.9.4.e164.arpa) of the dialled number.

  3. Answer of the ENUM DNS server delivers a list of possible communication items, among them the information to which URL (ifax:fax@denic.de) an incoming fax message has to be sent.

  4. Establishing a connection via the Internet between the sending and the receiving fax device.