September 2012 - "Having gained partners from North America, Latin America and Asia Pacific, has grown to a global production-grade community service in recent years. As one of the key building blocks of global unified communications, it is our mission to coordinate and continuously enhance the service for the benefit of the entire research and education community, in a sustainable manner."
- Michael Nowlan, (former) Chief Techincal Officer, GÉANT

What is ENUM?

E.164 Telephone Number Mapping (ENUM) is a standard protocol that is the result of work of the Internet Engineering Task Force's (IETF's) Telephone Number Mapping working group. ENUM translates a telephone number into a domain name. This allows users to continue to use the existing phone number formats they are familiar with, whilst allowing the call to be routed using DNS. This makes ENUM a quick, stable and cheap link between telecommunications systems and the Internet.

IETF RFC 3761 discusses the use of the Domain Name System (DNS) for storage of E.164 numbers. More specifically, how DNS can be used for identifying available services connected to one E.164 number. The RIPE NCC provides DNS operations for "" (known as Golden ENUM tree) in accordance with the Instructions from the Internet Architecture Board.

What is

The Service is an end-user ENUM service run by GÉANT and the participating NRENs (National Research and Education Networking organisations). It is aimed primarily at academia. is considered as a complementary service and a valid alternative to the Golden ENUM tree. The domain "" is being populated in order to provide the infrastructure in DNS for storage of E.164 numbers. The Service includes the operation of the Tier-0 root DNS(s) and the delegation of county codes to Registries. "" is a registered community trademark of GÉANT. tree refers to the DNS tree structure where:

  • Tier-0 root DNSs (technically one master and several secondary servers ensuring the reliability) are run by the hosting organisations (see the actual list of hosts on the Service homepage) and coordinated by the Operations Team.
  • Tier-1 DNSs are run by the (national or regional) Registries responsible for the country code(s) delegated.
  • Tier-2 and lower DNS sub-delegations may be implemented and regulated by the national service policies.
DNS tree

An Registry is an entity that is authorised by the Operations Team to operate the national or regional Tier-1 DNS and be responsible for the county code(s) delegated. In many countries there is a National Research and Education Networking organisation (NREN) that acts as the Registry of the country.

An Registrar is responsible for the number/block registration in the Tier-1 DNS and a number Validation Entity is responsible for the validation of the E.164 telephone numbers to be registered (see valid vs. virtual numbers). Note that the NREN may at the same time have the role of the Registry, Registrar, and Validation Entity for the country code(s) delegated.

A Registrant (end user) is an E.164 telephone number holder. Holders of E.164 numbers who want to be listed in the service need to contact the appropriate Registrar.

Number (block) delegation is the technical process of assigning country codes (e.g., +36 for Hungary) to national registries (e.g., NIIF/HUNGARNET in Hungary) or number blocks under country codes to end users.

Number (block) registration is the technical process of configuring DNS and populating it with the appropriate ENUM records (i.e. adding NAPTR records to DNS) via registrars.

The ITU-T strictly regulates the number structure of valid E.164 telephone numbers and assigns number blocks to national authorities (telecom regulators) or recently to global entities directly. The national authorities can further delegate the number ranges to local operators within the country or region. A Virtual number has either a non-valid E.164 number structure (e.g., longer than 15 digits) or has a valid structure but is not assigned to any national authorities or operators. The number Validation Entity is responsible for checking the numbers to be registered to

Service operation procedures

Service architecture