ENUM (Electronic Numbering) is a protocol developed by the Internet Engineering Task Force's (IETF) Telephone Number Mapping Working Group, which used the Domain Name System (DNS) architecture and protocol to identify available services associated with E.164. ENUM involves the process of creating a domain name from a telephone number and resolving it to an Internet address or Uniform Resource Identifier (URI) using DNS technology and the hosting of ENUM domain names on the E.164 ARPA domain.  ENUM is defined in RFC 3761.
The International Engineering Task Force created the the Telephone Number Mapping Working Group in 1999. The working group was tasked with determining a DNS-based architecture and protocol for mapping a telephone number to a set of characteristics, such as a URL, that could be utilized to associate a resource to that particular number. In 2000, the working group published RFC 2916, which discussed ways of using the DNS to determine available services connected to a E.164 number. E.164 is an international telecommunications numbering plan. E.164 numbers are globally unique, language independent identifiers for resources on Public Telecommunication Networks capable of supporting numerous services and protocols.
In 2001, several International Telecommunications Standardization Sector (ITU-T) workshops were conducted in Asia, Europe and North America regarding the administrative issues in implementing ENUM.
By 2002, ITU-T and the Internet Architecture Board approved interim procedures for ENUM, subject to national authorities and end-users approval. ENUM protocols allowed consumers to use one number to access numerous terminals and services, which included phone, fax, e-mail, pager, mobile telephones, websites or any other services available through an Internet addressing scheme. Subsequently, the European Telecommunications Standards Institute (ETSI) published its technical specifications for ENUM Administration in Europe. The IAB also assigned the responsibility of delegating the E.164 ARPA domains to Reseaux IP Européens Network Coordination Centre (RIPE NCC). RIPE NCC assigned the ENUM TLD, 9.4.e164.arpa to the German Interne Community DENIC, which started the ENUM trial on May 21, 2002.
In 2003, ETSI published its technical specifications for Minimum Requirements for Interoperability of European ENUM Trials while the IETF issued final procedures for the ENUM domain and opened the registration of ENUM services through the Internet Assigned Numbers Authority (IANA). In 2004, IETF RFC 3761 was released, which specifies ENUM services registration, commercial private ENUM services and public ENUM (E.164.arpa).. The Asia Pacific ENUM Engineering Team (APEET) was established due to the growing interest of the use of ENUM in the region. Its members include JPRS, CNNIC, KRNIC, SGNIC and TWNIC. In 2005, APEET coordinated the ENUM/SIP live trial in Kyoto during the APRICOT Conference.
In 2006, the Public User ENUM trial was conducted in the United States for six months between n March 2006 and June 2007. It was sponsored by the Country Code 1 ENUM Limited Liability Company (LLC).
ENUM Working Group
The ENUM Working Group is responsible in monitoring and promoting discussions and initiatives to develop the advancement of ENUM, the internet resource mapping technology using the E.164 telephone numbers identifiers.
Types of ENUM
There are three types of ENUM:
- Public User ENUM, which allows an end user to enter his or her own records in the ENUM registry under the public dumaine164.arpa;
- Private Infrastructure ENUM, which is used by a closed group without using the e164.arpa public domain; instead they opt to use the process of creating a domain name from a telephone number and resolving it to a URI to exchange IP traffic;
- Public Infrastructure ENUM is assigned by a National Number Administrator, which normally delegates a telephone number to a carrier, which in turn assigns the telephone number to an end-user. The carrier maps telephone numbers to internal network addresses to enable call routing features that are not publicly available, it is highly secure and access is restricted to other service providers.
Uses of ENUM
- It serves as single number point of contact wherein a single ENUM number facilitates the routing of telephone calls to the internet instead of the regular telephone sytem, meaning it allows numerous access points to different types of communication such as fax, cellular phones, and many others.
- It facilitates the transition away from the Public Switch Telephone Network (PSTN) to the Internet as the main carrier of voice communication.
- It can be used as an internal routing within a telephone company's network, for example major telecommunication companies in the United States convert voice calls using VoIP.
- It serves as a dial access to new internet service providers that allows users to simply dial a telephone number which can be translated using ENUM to a desired internet address for them to be able to access Internet services via cellphone.
The International Telecommunication Union (ITU) is responsible for designating which organization will administer or control the implementation of ENUM based on the regulations of a certain country. Every country sets their own rules that govern the establishment and control of ENUM records, this means that "called party control" of ENUM is administered by each country.
ENUM Deployment Status
Since its establishment, ENUM has become commercially available worldwide. ENUM trials began in 2003 in different countries such as Australia, Austria, China, France, Germany, Korea, Netherlands, Sweden, Switzerland, and the United States. Prior to the implementation of ENUM in the United States, the Department of Commerce (DoC) issued an endorsement regarding the participation of the U.S. in the official ENUM trial and sought to create guidelines to protect users' privacy and security.
- RFC 3761
- ENUM Working Group
- RFC 2916
- E.164 Definition
- ITU-T Workshops
- ITU Press Release
- RFC 3761
- APRICOT 2005 Conference
- ENUM administration ad interim
- Types of ENUM
- ENUM:Mapping Telephone Numbers Onto The Internet
- ENUM Admiistration
- Deployment Status