1. What is ENUM?
ENUM is a protocol that is the result of
work of the Internet Engineering Task Force's (IETF's) Telephone
Number Mapping working group. The charter of this
working group was to define a Domain Name System
(DNS)-based architecture and protocols for mapping a
telephone number to a Uniform Resource Identifier (URI)
which can be used to contact a resource associated with
that number. The protocol itself is defined in
to URI DDDS Application (ENUM) which obsoletes
The protocol provides facilities to resolve E.164
telephone numbers into other resources or services on the
Recommendation E.164 is the international public
telecommunication telephone numbering plan and
ENUM delegations can be found
here. The syntax of
Uniform Resource Identifiers (URIs) is defined in RFC 2396
(1998). ENUM makes extensive use of Naming Authority
Pointer records defined in RFC 2915
in order to identify available ways or services for
contacting a specific node identified through the E.164
number. Other related Internet drafts and RFCs can be
2. What is ITU-T E.164? Are there
E.164 describes the international public
telecommunication numbering plan. Recommendation
E.190 describes the general principles to be utilized
in the assignment of ITU-T E-Series international
numbering resources. Recommendation
E.164.1 describes the procedures and criteria for the
reservation, assignment, and reclamation of E.164 country
codes and associated Identification Code (IC) assignments.
The criteria and procedures are provided as a basis for
the effective and efficient utilization of the available
E.164 numbering resources.
is the related domain name system (DNS) zone under which a
parallel E.164 name space will be administered?
The Internet Architecture Board has
recommended the use of the e164.arpa zone. The IAB has
issued a related statement Infrastructure
Domain and Subdomains. ITU Member States are currently
discussing the responsibility, delegation and authority
for the ENUM "root zone". While discussions have
been initiated on this topic at the recent ITU-T SG2
meeting in January/February 2001, they have yet to be
concluded and the international resolution of these
concerns could have an eventual impact on the IAB
selection of e164.arpa.
4. How is the related DNS zone constructed?
For example, lets construct the related
DNS zone to look up resources associated with the
information desk of the Louvre Museum in Paris, France,
which can be found at the telephone number +33 1 40 20 51
Write the E.164 number is written in its
full form, including the countrycode.
Example: +33 1 40 20 51 51
Remove all non-digit characters with the
exception of the leading '+'.
Remove all characters with the exception
of the digits.
Put dots (".") between each
Reverse the order of the digits.
Considering the recommendation of the
Internet Architecture Board, append the string
".e164.arpa" to the end.
5. What is the operational, administration
and delegation model?
Architecture Board (IAB)
Study Group 2 are discussing collaboration on the operational,
administration and delegation issues related to deployment
of ENUM protocol-based services. This requires extensive
consultation with administrators of resources derived from
the international E.164 numbering plan including national
and integrated numbering plan administrators.
The ITU-T has defined
Interim procedures for Geographic Country Codes and
Interim procedures for shared Country Codes for Networks
and Groups of Countries.