telephone number mapping (IP/IETF) (ENUM)
Telephone Number Mapping (ENUM) is a technique for unifying the various communications and telephone numbers for home and business telephone, fax and cell phone numbers, Web pages, short message services, instant messaging and e-mail. The Enum protocol links resources from telecommunications networks and the Internet and translates the telephone numbering scheme specified in ITU RecommendationE.164 into IP addresses.
With Enum, users access their own directory in their name server, which covers all forms of communication via fixed networks, mobile networks and the Internet and which they can maintain themselves. In addition to address and service management, priorities can be set so that certain services are given priority at certain times. Address management for certain communications services such as e-mail is supported by special e-mail clients that convert the telephone number into the e-mail address.
Integration of traditional telephone networks and Internet telephony
Enum technology brings together the switching technologies for Internet telephony and classic telephony, resulting in cost advantages for carriers and providers. However, when converting telephone numbers to Fully Qualified Domain Name( FQDN), it is important to note that domain names are read from back to front. The Internet Engineering Task Force( IETF) has developed the enum domain e164.arpa for this conversion.
The telephone numbers are integrated into the Domain Name System( DNS). To ensure that telephone numbers comply with the international telephone numbering plan, there is the ITU standard E.164. The conversion of a telephone number and its mapping as a domain address are subject to standardized rules. For example, an Enum-capable terminal converts the telephone number +49 221 1234567 into the Enum domain 7.6.5.4.3.2.1.1.2.2.9.4.e164.arpa and sends a request for this number to the DNS system. This returns a list of corresponding resources to the enum end device, the Naming Authority Pointer Record (NAPTR). The terminal selects the appropriate resource from this list and establishes a telephone connection for Internet telephony ( VoIP) via the Session Initiation Protocol( SIP).
Enum technology allows telecommunications devices to access Internet services using their numeric keypad; on the other hand, Internet telephony can be performed using normal telephone numbers. The Enum specifications originate from the Internet Engineering Task Force (IETF) and are described in RFC 3761.