Network Working Group R. Brandner
Request for Comments: 4415 Siemens AG
Category: Standards Track L. Conroy
Siemens Roke Manor Research
R. Stastny
Oefeg
February 2006
IANA Registration for Enumservice Voice
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document registers the Enumservice "voice" (which has a defined
subtype "tel"), as per the IANA registration process defined in the
ENUM specification RFC 3761. This service indicates that the contact
held in the generated Uniform Resource Identifier (URI) can be used
to initiate an interactive voice (audio) call.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Voice Service Registration . . . . . . . . . . . . . . . . . . 3
4. Example of voice:tel Enumservice . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Brandner, et al. Standards Track [Page 1]RFC 4415 IANA Voice Enumservice Registration February 2006
1. Introduction
ENUM (E.164 Number Mapping, RFC 3761 [1]) is a system that transforms
E.164 numbers [2] into domain names and then uses DNS (RFC 1034 [3])
features such as delegation through NS records, and the use of Naming
Authority Pointer (NAPTR) records, to look up the communication
services available for a specific domain name.
This document registers an Enumservice according to the guidelines
given in RFC 3761 to be used for provisioning in the services field
of a NAPTR [4] resource record to indicate what class of
functionality a given endpoint offers. The registration is defined
within the Dynamic Delegation Discovery System (DDDS, [5] [6] [4] [7]
[8]) hierarchy, for use with the "E2U" DDDS application defined in
RFC 3761.
Enumservices have a type and subtype. This latter is optional, as it
may be implicit in the service type. The type defines the kind of
communication session that can be initiated using the contact
indicated by the URI generated by the enclosing NAPTR. In
telecommunications engineering terms, it reflects the "teleservice".
The subtype defines the subsystem that is to be used to initiate the
communication session. Note that the subtype definition is usually
associated with the URI scheme that is to be used.
Both the type and subtype (where present) must be supported for the
NAPTR to be used by a potential correspondent.
There are a number of DDDS applications in addition to ENUM (for
example, see [7] and [8]). However, an Enumservice indication
operates only within the context of the "E2U" (ENUM) DDDS
Application.
Whilst the protocol elements that make up ENUM are defined in the
above documents and in this one, further examples of the use to which
these may be put are given in other documents, for example, in ETSI
TS 102 172 [11].
This document registers the Enumservice "voice" (which has a defined
subtype "tel"), as per the IANA registration process defined in the
ENUM specification RFC 3761. This service indicates that the contact
held in the generated URI can be used to initiate an interactive
voice (audio) call.
Brandner, et al. Standards Track [Page 2]
RFC 4415 IANA Voice Enumservice Registration February 2006
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119 [9].
3. Voice Service Registration
Enumservice Name: "voice"
Enumservice Type: "voice"
Enumservice Subtype: "tel"
URI Scheme: 'tel:'
Functional Specification:
The kind of communication indicated by this Enumservice is
"Interactive Voice". From a protocol perspective, this
communication is expected to involve bidirectional media streams
carrying audio data.
A client may imply that the person controlling population of a
NAPTR holding this Enumservice indicates his capability to engage
in an interactive voice session when contacted using the URI
generated by this NAPTR.
Security Considerations:
See Section 5.
Intended Usage: COMMON
Authors:
Rudolf Brandner, Lawrence Conroy, and Richard Stastny (for author
contact detail, see Authors' Addresses section)
Any other information the author deems interesting:
This Enumservice indicates that the person responsible for the
NAPTR is accessible via the Public Switched Telephone Network
(PSTN) or Public Land Mobile Network (PLMN) using the value of the
generated URI.
The kind of subsystem required to initiate a Voice Enumservice
with this subtype is a "Dialer". This is a subsystem that either
Brandner, et al. Standards Track [Page 3]RFC 4415 IANA Voice Enumservice Registration February 2006
provides a local connection to the PSTN or PLMN or provides an
indirect connection to those networks. The subsystem will use the
telephone number held in the generated URI to place a voice call.
The voice call is placed to a network that uses E.164 numbers to
route calls to an appropriate destination.
Note that the PSTN/PLMN connection may be indirect. The end user
receiving this NAPTR may have a relationship with a Communications
Service Provider that accepts call initiation requests from that
subsystem using an IP-based protocol such as SIP or H.323, and
places the call to the PSTN using a remote gateway service. In
this case, the provider either may accept requests using "tel:"
URIs or has a defined mechanism to convert "tel:" URI values into
a "protocol-native" form.
The "tel:" URI value SHOULD be fully qualified (using the "global
phone number" form of RFC 3966 [10]). A "local phone number" as
defined in that document SHOULD NOT be used unless the controller
of the zone in which the NAPTR appears is sure that it can be
distinguished unambiguously by all clients that can access the
resource record and that a call from their network access points
can be routed to that destination.
4. Example of voice:tel Enumservice
The following is an example of the use of the Enumservice registered
by this document in a NAPTR resource record.
$ORIGIN 0.6.9.2.3.6.1.4.4.e164.arpa.
3.8.0 NAPTR 10 100 "u" "E2U+voice:tel"
"!^.*$!tel:+441414960000!" .
5. Security Considerations
DNS, as used by ENUM, is a global, distributed database. Thus, any
information stored there is visible to anyone anonymously. Whilst
this is not qualitatively different from publication in a telephone
directory, it does open the data subjects to having "their"
information collected automatically without any indication that this
has been done or by whom.
Such data harvesting by third parties is often used to generate lists
of targets for unrequested information; in short, they are used to
address "spam". Anyone who uses a Web-archived mailing list is aware
that the volume of "spam" email sent increases when he or she posts
to the mailing list; publication of a telephone number in ENUM is no
different, and may be used for attempts to send "junk faxes" or "junk
SMS", for example.
Brandner, et al. Standards Track [Page 4]RFC 4415 IANA Voice Enumservice Registration February 2006
Many mailing list users have more than one email address and use
"sacrificial" email accounts when posting to such lists to help
filter out unrequested emails sent to them. This is not so easy with
published telephone numbers; the PSTN E.164 number assignment process
is much more involved and usually a single E.164 number (or a fixed
range of numbers) is associated with each PSTN access. Thus,
providing a "sacrificial" phone number in any publication is not
possible.
Due to the implications of publishing data on a globally accessible
database, as a principle the data subjects MUST give their explicit
informed consent to data being published in ENUM.
In addition, they should be made aware that, due to storage of such
data during harvesting by third parties, removal of the data from
publication will not remove any copies that have been taken; in
effect, any publication may be permanent.
However, regulations in many regions will require that the data
subjects can at any time request that the data be removed from
publication and that their consent for its publication be explicitly
confirmed at regular intervals.
When placing a voice call via the PSTN (or from the Public Land
Mobile Network), the sender may be charged for this action. In both
kinds of networks, calling some numbers is more expensive than
sending to others; both kinds of networks have "premium rate"
services that can be charged at a rate considerably more than a
"normal" call. As such, it is important that end users be asked to
confirm placing the call and that the destination number be presented
to them. It is the originating user's choice whether or not to place
a call to this destination number, but the originating user SHOULD be
shown the destination number so that he or she can make this
decision.
In addition to the specific security considerations given above, all
security considerations given in RFC 3761 apply, as well as the
DNS-specific threats covered in RFC 3833 [12].
6. IANA Considerations
The IANA has registered the Enumservice "voice" with a single subtype
"tel" according to the framework defined in RFC 3761. The current
document defines this Enumservice and the expected behaviour of
clients.
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RFC 4415 IANA Voice Enumservice Registration February 2006
7. References
7.1. Normative References
[1] Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
Application (ENUM)", RFC 3761, April 2004.
[2] ITU-T, "The International Public Telecommunication Number
Plan", Recommendation E.164, May 1997.
[3] Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES",
RFC 1034, November 1987.
[4] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Three: The Domain Name System (DNS) Database", RFC 3403,
October 2002.
[5] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
One: The Comprehensive DDDS", RFC 3401, October 2002.
[6] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Two: The Algorithm", RFC 3402, October 2002.
[7] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Four: The Uniform Resource Identifiers (URI)", RFC 3404,
October 2002.
[8] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Five: URI.ARPA Assignment Procedures", RFC 3405, October 2002.
[9] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, March 1997.
[10] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
December 2004.
7.2. Informative References
[11] ETSI, "Minimum Requirements for Interoperability of ENUM
Implementations", ETSI TS 102 172, January 2005.
[12] Atkins, D. and R. Austein, "Threat Analysis of the Domain Name
System (DNS)", RFC 3833, August 2004.
Brandner, et al. Standards Track [Page 6]RFC 4415 IANA Voice Enumservice Registration February 2006
Authors' Addresses
Rudolf Brandner
Siemens AG
Hofmannstr. 51
81359 Munich
Germany
Phone: +49-89-722-51003
EMail: rudolf.brandner@siemens.com
Lawrence Conroy
Siemens Roke Manor Research
Roke Manor
Romsey
United Kingdom
Phone: +44-1794-833666
EMail: lwc@roke.co.uk
Richard Stastny
Oefeg
Postbox 147
1103 Vienna
Austria
Phone: +43-664-420-4100
EMail: Richard.stastny@oefeg.at
Brandner, et al. Standards Track [Page 7]
RFC 4415 IANA Voice Enumservice Registration February 2006
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Brandner, et al. Standards Track [Page 8]
