ENUM S. Lind
Internet-Draft AT&T Labs
Expires: August 26, 2006 P. Pfautz
AT&T
February 22, 2006
Infrastrucure ENUM Requirements
draft-ietf-enum-infrastructure-enum-reqs-00
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Abstract
This document provides requirements for "infrastructure" or "carrier"
ENUM, defined as the use of RFC 3761 technology to facilitate
interconnection of networks for E.164 number addressed services, in
particular but not restricted to VoIP.
Conventions used in this document
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RFC2119 [1] provides the interpretations for the key words "MUST",
"MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" found in this document.
1. Infrastructure ENUM
1.1. Definition
Infrastructure ENUM is defined as the use of the technology in
RFC3761 [2] by the carrier-of-record for a specific E.164 number [3]
to map a telephone number into a URI that identifies a specific point
of interconnection to that service provider's network that could
enable the originating party to establish communication with the
associated terminating party. It is separate from any URIs that the
end-user, who registers their E.164 number, may wish to associate
with that E.164 number.
In User ENUM, the entity or person having the right-to-use in a
number has the sole discretion about the content of the associated
domain and thus the zone content. From a domain registration
perspective, the end user number assignee is thus the registrant.
Within the infrastructure ENUM namespace, we use the term "carrier of
record" for the entity having discretion over the domain and zone
content and acting as the registrant. The "carrier of record" will
typically be a service provider authorized to issue E.164 numbers for
the provisioning of PSTN service under the authority of a National
Regulatory Authority (NRA), but generally exhibits one or more of the
following properties:
o it has been assigned one or more national number ranges by an NRA.
o it has been assigned a number range directly by the ITU, for
instance a code under "International Networks" (+882) or "Universal
Personal Telecommunications (UPT)" (+878).
o it can be the recipient of a number porting operation.
o it provides a PSTN point-of-interconnect for the number.
It is understood that definition of carrier or record is ultimately a
matter for national authorities to determine.
1.2. Background
Voice service providers use E.164 numbers currently as their main
naming and routing vehicle. infrastructure ENUM in e164.arpa or
another publicly available tree allows service providers to link
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Internet based resources such as URIs to E.164 numbers (Note: this is
the other way round then User ENUM). This allows service providers
in addition to interconnecting via the PSTN (or exclusively) to peer
via IP-based protocols. Service providers may announce all E.164
numbers or number ranges they host, regardless of whether the final
end-user device is on the Internet, on IP-based closed NGNs or on the
PSTN, provided an access (e.g. SBC or gateway) to the destination
service provider's network is available on the Internet. There is
also no guarantee that the originating service provider querying
infrastructure ENUM is able to access the ingress network element of
the destination provider's network. Additional peering and
accounting agreements requiring authentication may be necessary. The
access provided may also be to a shared network of a group of
providers, resolving the final destination network within the shared
network.
2. Requirements for Infrastructure ENUM
2.1.
Infrastructure ENUM SHALL provide a means for a provider to populate
DNS RRs in a common publicly accessible namespace for the E.164
numbering resources for which it is the carrier-of-record.
2.2.
Queries of infrastructure ENUM FQDNs MUST return a result, even if
the result is NXDOMAIN. Queries must not be rejected, e.g. based on
ACLs.
2.3.
Infrastructure ENUM SHALL support RRs providing a URI that can
identify a point of interconnection for delivery of communications
addressed to the E.164 number.
2.4.
Infrastructure ENUM SHALL support an IRIS capability that allows
qualified parties to obtain information regarding the E.164 numbering
resources and the corresponding carrier-of-record.
2.5.
Implementation of Infrastructure ENUM MUST NOT restrict the ability
of an end-user, in a competitive environment, to choose a Registrar
and/or Tier 2 name server provider for end-user ENUM registrations.
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2.6.
Infrastructure ENUM SHALL be implemented under a TLD that can support
reliability and performance suitable for PSTN applications.
2.7.
Infrastructure ENUM MUST meet all reasonable privacy concerns about
visibility of information an end user has no control over, for
example discovery of unlisted numbers, or inadvertent disclosure of
user identity.
2.8.
Proposed implementations of Infrastructure ENUM SHOULD
a. Minimize changes required to existing requirements that are part
of RFC 3761
b. Work with open numbering plans
c. Restrict additional functionality to service provider resolvers.
d. Minimize the number of lookups required to obtain as many NAPTR
records (end-user and infrastructure) as possible.
e. Minimize the client knowledge of the numbering plan required.
f. Maximize synergies with end-user ENUM
g. Support interworking with private ENUM trees.
3. Security Considerations
Existing security considerations for ENUM detailed in [2] still
apply. Note that some registration validation issues concerning end
user ENUM may not apply to infrastructure ENUM. Where the Tier 1
registry is able to identify the provider serving a number e.g.,
based on industry data for number block assignments and number
portability, registration might be more easily automated and a
separate registrar not required.
Some parties have expressed concern that an infrastructure ENUM could
compromise end user privacy by making it possible for others to
identify unlisted or unpublished numbers based on their registration
in ENUM. This can be avoided if providers register all of the their
allocated (as opposed to assigned) numbers. Unassigned numbers
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should be provisioned to route to the provider's network in the same
fashion as assigned numbers and only then provide an indication that
they are unassigned. In that way, provider registration of a number
in ENUM provides no more information about status of a number than
could be obtained by dialing it.
4. IANA Considerations
IANA considerations will depend on the architecture ultimately chosen
to meet the requirements.
5. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
Application (ENUM)", RFC 3761, April 2004.
[3] International Telecommunications Union-T, "The International
Public Telecommunication Number Plan", Recommendation E.164",
May 1997.
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Authors' Addresses
Steven Lind
AT&T Labs
180 Park Ave
Florham Park, NJ 07932-0971
USA
Email: slind@att.com
Penn Pfautz
AT&T
200 S. Laurel Ave
Middletown, NJ 07748
USA
Email: ppfautz@att.com
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