Distinguished colleagues of ITU-SG2,


 The IETF ENUM working group (WG), with the assistance of SG2
 participants, defined a DNS-based architecture and protocol [RFC 3761] by which an
 E.164 number, as defined in ITU-T Recommendation E.164, can be expressed
 as a Fully Qualified Domain Name (FQDN) in a specific Internet domain
defined for this purpose (e164.arpa). Recently, the scope of the ENUM WG was
expanded to include the investigation of “infrastructure” ENUM, a proposed
system for providing information of specific interest to service providers
(e.g., call routing and service data) via ENUM technology, as initially
described in the infrastructure ENUM requirements [RFC 5067]. The ENUM WG
study of infrastructure ENUM has now concluded.

After a thorough investigation of the problem space, the IETF was unable
to reach a consensus to advance any proposal for infrastructure ENUM to
the IETF Standards Track. The ENUM WG has, however, documented some of the
considerations and proposals it examined in two Informational RFCs:
[RFC5526], which discusses the introduction of a new branch off of the
e164.arpa tree for infrastructure ENUM; and [RFC5527], which explores
transition mechanisms for allowing “infrastructure” records to integrate
with existing e164.arpa ENUM deployments. While the IETF has no plans to
pursue this work further, this conclusion obviously does not preclude ITU-T SG2 from 
further consideration of infrastructure ENUM, nor from using these Informational products 
of the ENUM WG as a basis for ongoing work. The IAB would however like to note that 
splitting the root of ENUM into multiple branches, such that the resolution of a particular 
E.164 number yields a different result depending on the branch consulted, gives
 rise to the concerns mentioned in Section 2.2 of [RFC 3245] (which in turn
 references [RFC 2826]).

The IAB and the ITU-T reached several agreements on how the domains
within e164.arpa should be delegated. These agreements and associated
operational considerations were documented in 2002 in the IETF in RFC 3245
and in SG2 in COM 2-10-E, COM 2-11-E, and COM 2-12-E. Those agreements
clearly define administration of ENUM at and below the country level as
national matters (See Section 4.5 of RFC 3245 and COM 2-10-E). Should
>TU-T SG2 decide to pursue an apex for infrastructure ENUM beneath
e164.arpa, the IAB recognizes that this might entail amendments to the
previous agreements or the creation of entirely new ones, and we invite
the ITU-T to initiate those discussions as necessary. The IAB continues to
be responsible for decisions related to the namespace in the DNS according
 to the existing exchange of letters between IAB, ITU-T, ITU-T TSB and the
registry for ENUM (as appointed by the IAB, currently RIPE NCC).


Respectfully,

 For The Internet Architecture Board
 Olaf Kolkman
 IAB Chair.