Network Working Group R. Brandner
Request for Comments: 4355 Siemens AG
Category: Standards Track L. Conroy
Siemens Roke Manor Research
R. Stastny
Oefeg
January 2006
IANA Registration for Enumservices email, fax, mms, ems, and sms
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 Enumservices "email", "fax", "sms",
"ems", and "mms" using the URI schemes 'tel:' and 'mailto:' as per
the IANA registration process defined in the ENUM specification RFC
3761.
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Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................3
3. Email Service Registration ......................................4
4. Fax Service Registration ........................................4
5. MMS, EMS, SMS Service ...........................................5
5.1. Introduction ...............................................5
5.2. SMS Service Registrations ..................................6
5.2.1. SMS Service Registration with tel: URI ..............6
5.2.2. SMS Service Registration with mailto: URI ...........6
5.3. EMS Service Registrations ..................................7
5.3.1. EMS Service Registration with tel: URI ..............7
5.3.2. EMS Service Registration with mailto: URI ...........8
5.4. MMS Service Registrations ..................................9
5.4.1. MMS Service Registration with tel: URI ..............9
5.4.2. MMS Service Registration with mailto: URI ..........10
6. Security Considerations ........................................11
7. Acknowledgements ...............................................13
8. References .....................................................13
8.1. Normative References ......................................13
8.2. Informative References ....................................14
1. Introduction
ENUM (E.164 Number Mapping, RFC 3761 [2]) is a system that transforms
E.164 numbers [3] into domain names and then uses DNS (Domain Name
Service, RFC 1034 [4]) services like delegation through NS records
and NAPTR records to look up what services are available for a
specific domain name.
This document registers Enumservices according to the guidelines
given in RFC 3761 to be used for provisioning in the services field
of a NAPTR [5] resource record to indicate what class of
functionality a given endpoint offers. The registration is defined
within the DDDS (Dynamic Delegation Discovery System [6][7][5][8][9])
hierarchy, for use with the "E2U" DDDS Application defined in RFC
3761.
The following Enumservices are registered with this document:
"email", "fax", "sms", "ems", and "mms". These share a common
feature in that they each indicate that the functionality of the
given endpoints and the associated resources are capable of receiving
discrete messages, albeit of different types.
According to RFC 3761, the Enumservice registered must be able to
function as a selection mechanism when choosing one NAPTR resource
record from another. That means that the registration MUST specify
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what is expected when using that very NAPTR record, and the Uniform
Resource Identifier (URI) scheme that is the outcome of the use of
it.
Therefore, an Enumservice acts as a hint, indicating the kind of
service with which the URI constructed using the regexp field is
associated. There can be more than one Enumservice included within a
single NAPTR; this indicates that there is more than one service that
can be achieved using the associated URI scheme.
The common thread with this set of definitions is that they reflect
the kind of service that the end-user will hope to achieve with the
communication using the associated URI.
The services specified here are intended not to specify the protocol
or even method of connection that must be used to achieve each
service. Instead they define the kind of interactive behaviour that
an end-user will expect, leaving the end system to decide (based on
policies outside the remit of this specification) how to execute the
service.
Since the same URI scheme may be used for different services (e.g.,
'tel:'), and the same kind of service may use different URI schemes
(e.g., for VoIP 'h323:' and 'tel:' may be used), it is necessary in
some cases to specify the service and the URI scheme used.
The service parameters defined in RFC 3761 allow, therefore, a "type"
and a "subtype" to be specified. Within this set of specifications,
the convention is assumed that the "type" (being the more generic
term) defines the service and the "subtype" defines the URI scheme.
Even where currently only one URI scheme is associated with a given
service, it should be considered that an additional URI scheme to be
used with this service may be added later. Thus, the subtype is
needed to identify the specific Enumservice intended.
In this document, there are two URI schemes that are used within the
various services. These are 'tel:', as specified in RFC 3966 [10]
and 'mailto:', as specified in RFC 2368 [11].
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 [1].
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3. Email Service Registration
Enumservice Name: "email"
Enumservice Type: "email"
Enumservice Subtypes: "mailto"
URI Scheme: 'mailto:'
Functional Specification:
This Enumservice indicates that the remote resource can be
addressed by the associated URI scheme in order to send an email.
Security Considerations:
See Section 6.
Intended Usage: COMMON
Authors:
Rudolf Brandner, Lawrence Conroy, Richard Stastny (for author
contact detail, see Authors' Addresses section)
Any other information the author deems interesting:
None
4. Fax Service Registration
Enumservice Name: "fax"
Enumservice Type: "fax"
Enumservice Subtype: "tel"
URI Scheme: 'tel:'
Functional Specification:
This Enumservice indicates that the resource identified by the
associated URI scheme is capable of being contacted to provide a
communication session during which facsimile documents can be
sent.
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Clients selecting this NAPTR will have support for generating and
sending facsimile documents to the recipient using the Public
Switched Telephone Network (PSTN) session and transfer protocols
specified in [12] and [13]. In short, they will have a fax
program with a local or shared PSTN access over which they can
send faxes.
Security Considerations:
See Section 6.
Intended Usage: COMMON
Authors:
Rudolf Brandner, Lawrence Conroy, Richard Stastny (for author
contact detail see Authors' Addresses section)
Any other information the author deems interesting:
None
5. MMS, EMS, SMS Service
5.1. Introduction
An ENUM NAPTR indicates ability on the part of the Subscriber to
receive specified communication service (or services) provided via
the contact address (shown in the generated URI).
In the case of MMS, EMS, and SMS services, the capability of these
services is a nested superset; thus, a service supporting MMS can
support also delivery of EMS or SMS message content to a recipient
that is receiving a Multimedia Message, whilst a service supporting
EMS can also deliver SMS message content to a recipient that can
accept receipt of EMS Messages.
Thus, even if a client wants only to generate and send content that
could be carried in an SMS message, the client MAY choose to consider
also NAPTRs holding EMS and/or MMS Enumservices, as these indicate
that the destination can accept EMS and/or MMS messages. These
services will be able to deliver SMS content to the recipient
address.
Conversely, a client capable of sending MMS messages may choose to
consider also NAPTRs indicating support for EMS or SMS messages
(assuming that the network to which it is connected provides these
services as well, or is capable of providing a gateway to systems
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that do provide these services). In taking this choice, it would
have to "downgrade" its User Interface to allow only generation of
content that conforms to SMS or EMS standards.
These behaviours on the part of the client are purely optional and
are NOT the subject of any protocol standardisation.
5.2. SMS Service Registrations
5.2.1. SMS Service Registration with tel: URI
Enumservice Name: "sms"
Enumservice Type: "sms"
Enumservice Subtypes: "tel"
URI Scheme: 'tel:'
Functional Specification:
This Enumservice indicates that the resource identified by the
associated URI scheme is capable of receiving a message using the
Short Message Service (SMS) [14].
Security Considerations:
There are no specific security issues with this Enumservice.
However, the general considerations of Section 6 apply.
Intended Usage: COMMON
Authors:
Rudolf Brandner, Lawrence Conroy, Richard Stastny (for author
contact detail, see Authors' Addresses section)
Any other information the author deems interesting:
None
5.2.2. SMS Service Registration with mailto: URI
Enumservice Name: "sms"
Enumservice Type: "sms"
Enumservice Subtypes: "mailto"
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URI Scheme: 'mailto:'
Functional Specification:
This Enumservice indicates that the resource identified by the
associated URI scheme is capable of receiving a message using an
email protocol.
SMS content is sent over SMTP using the format specified by TS
23.140 [15] Section 8.4.4 and TS 26.140 [16] Section 4, as an MMS
message. Within such a message, SMS content is carried as either
a text or application/octet-stream MIME sub-part (see TS 26.140
[16] Section 4.1).
Security Considerations:
There are no specific security issues with this Enumservice.
However, the general considerations of Section 6 apply.
Intended Usage: COMMON
Authors:
Rudolf Brandner, Lawrence Conroy, Richard Stastny (for author
contact detail, see Authors' Addresses section)
Any other information the author deems interesting:
None
5.3. EMS Service Registrations
5.3.1. EMS Service Registration with tel: URI
Enumservice Name: "ems"
Enumservice Type: "ems"
Enumservice Subtype: "tel"
URI Scheme: 'tel:'
Functional Specification:
This Enumservice indicates that the resource identified by the
associated URI scheme is capable of receiving a message using the
Enhanced Message Service (EMS) [14].
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Security Considerations:
There are no specific security issues with this Enumservice.
However, the general considerations of Section 6 apply.
Intended Usage: COMMON
Authors:
Rudolf Brandner, Lawrence Conroy, Richard Stastny (for author
contact detail, see Authors' Addresses section)
Any other information the author deems interesting:
Note that an indication of EMS can be taken as implying that the
recipient is capable of receiving SMS messages at this address as
well.
5.3.2. EMS Service Registration with mailto: URI
Enumservice Name: "ems"
Enumservice Type: "ems"
Enumservice Subtypes: "mailto"
URI Scheme: 'mailto:'
Functional Specification:
This Enumservice indicates that the resource identified by the
associated URI scheme is capable of receiving a message using an
email protocol.
EMS content is sent over SMTP using the format specified by TS
23.140 [15] Section 8.4.4 and TS 26.140 [16] Section 4, as an MMS
message. Within such a message, EMS content is carried as either
a text or application/octet-stream MIME sub-part (see TS 26.140
[16] section 4.1).
Security Considerations:
There are no specific security issues with this Enumservice.
However, the general considerations of Section 6 apply.
Intended Usage: COMMON
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Authors:
Rudolf Brandner, Lawrence Conroy, Richard Stastny (for author
contact detail, see Authors' Addresses section)
Any other information the author deems interesting:
None
5.4. MMS Service Registrations
5.4.1. MMS Service Registration with tel: URI
Enumservice Name: "mms"
Enumservice Type: "mms"
Enumservice Subtype: "tel"
URI Scheme: 'tel:'
Functional Specification:
This Enumservice indicates that the resource identified by the
associated URI scheme is capable of receiving a message using the
Multimedia Messaging Service (MMS) [15].
Security Considerations:
There are no specific security issues with this Enumservice.
However, the general considerations of Section 6 apply.
Intended Usage: COMMON
Authors:
Rudolf Brandner, Lawrence Conroy, Richard Stastny (for author
contact detail, see Authors' Addresses section)
Any other information the author deems interesting:
Note that MMS can be used as an alternative to deliver an SMS
RP-DATA RPDU if, for example, the SMS bearer is not supported. If
an entry includes this Enumservice, then in effect this can be
taken as implying that the recipient is capable of receiving EMS
or SMS messages at this address. Such choices on the end system
design do have two small caveats; whilst in practice all terminals
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supporting MMS today support SMS as well, it might not necessarily
be the case in the future, and there may be tariff differences in
using the MMS rather than using the SMS or EMS.
5.4.2. MMS Service Registration with mailto: URI
Enumservice Name: "mms"
Enumservice Type: "mms"
Enumservice Subtypes: "mailto"
URI Scheme: 'mailto:'
Functional Specification:
This Enumservice indicates that the resource identified by the
associated URI scheme is capable of receiving a message using an
email protocol.
MMS messages are sent over SMTP using the format specified by TS
23.140 [15] Section 8.4.4 and TS 26.140 [16] Section 4.
Within and between MMS Environments (MMSE, network infrastructures
that support the MultiMedia Service), other pieces of state data
(for example, charging-significant information) are exchanged
between MMS Relay Servers. Thus, although these servers use SMTP
as the "bearer" for their application exchanges, they map their
internal state to specialised headers carried in the SMTP message
exchanges. The headers used in such MMSE are described in detail
in [17].
Security Considerations:
There are no specific security issues with this Enumservice.
However, the general considerations of Section 6 apply.
Intended Usage: COMMON
Authors:
Rudolf Brandner, Lawrence Conroy, Richard Stastny (for author
contact detail see Authors' Addresses section)
Any other information the author deems interesting:
The MMS Architecture describes an interface between the MMSE and
"legacy messaging systems" (labelled as MM3) that accepts
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"standard" SMTP messages. Thus, although the MMS Relay Server
that supports this interface appears as a standard SMTP server
from the perspective of an Internet-based mail server, it acts as
a gateway and translator, adding the internal state data that is
used within and between the MMS Environments. This mechanism is
described in [17], which also includes references to the
specifications agreed by those bodies responsible for the design
of the MMS.
6. 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 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 they are sent increases when they
post to the mailing list. Publication of a telephone number in ENUM
is no different, and may be used to send "junk faxes" or "junk SMS",
for example.
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, 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 data subjects
can at any time request that the data is removed from publication and
that their consent for its publication is explicitly confirmed at
regular intervals.
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When placing a fax call via the PSTN or a sending a message via the
Public Land Mobile Network, the sender may be charged for this
action. In both kinds of network, calling or messaging to some
numbers is more expensive than sending to others; both networks have
"premium rate" services that can charge considerably more than a
"normal" call or message destination. As such, it is important that
end-users be asked to confirm sending the message and that the
destination number be presented to them. It is the originating
user's choice on whether or not to send a message to this destination
number, but end-users SHOULD be shown the destination number so that
they can make this decision.
Although a fax number, like other E.164 numbers, doesn't appear to
reveal as much identity information about a user as a name in the
format user@host (e.g., an email or SIP address), the information is
still publicly available; thus, there is still the risk of unwanted
communication.
An analysis of threats specific to the dependence of ENUM on the DNS,
and the applicability of DNSSEC [18] to these, is provided in RFC
3761 [2]. A thorough analysis of threats to the DNS itself is
covered in RFC 3833 [19].
An email address is a canonical address by which a user is known.
Placing this address in ENUM is comparable to placing a SIP or H.323
address in the DNS.
DNS does not make any policy decisions about the records that it
shares with an inquirer. All DNS records must be assumed to be
available to all inquirers at all times. The information provided
within an ENUM NAPTR resource record must, therefore, be considered
to be open to the public, which is a cause for some privacy
considerations.
Therefore, ENUM Subscribers should be made aware of this risk. Since
it is within the responsibility of the ENUM Subscriber which data is
entered in ENUM, it is within the ENUM Subscriber's control if he
enters email addresses:
1. allowing inference of private data, e.g., his first and last name
2. at all
It should also be considered that it is the purpose of public
communication identifiers to be publicly known. To reduce spam and
other unwanted communication, other means should be made available,
such as incoming message filtering.
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Some Value Added Service Providers use receipt of a short message to
a given special service telephone number as a trigger to start
delivery of data messages to the calling number. By sending an SMS
(or, in principle, an EMS or MMS) to one of these special service
numbers, one is entering into a contract to pay for receipt of a set
of messages containing information (e.g., news, sports results, "ring
tones").
Thus, it is very important that the end terminal presents the
destination number to which any message is to be sent using the "sms:
tel", "ems:tel", or "mms:tel" Enumservices, to allow the end-user to
cancel any message before it is sent to one of these numbers.
At present, these systems use the circuit switched network trusted
calling line identifier to identify the destination for the
subsequent charged information messages, and so it is believed that
sending using the "sms:mailto", "ems:mailto", or "mms:mailto"
Enumservices does not have this risk currently.
7. Acknowledgements
Many thanks to Ville Warsta for his close reading of the document and
extracting the right references. Thanks also to those who are
involved in the parallel effort to specify the requirements for "real
world" ENUM trials resulting in TS 102 172 [20], in which this and
other Enumservices are referenced.
8. References
8.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, 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] ITU-T, "The International Public Telecommunication Number
Plan", Recommendation E.164, May 1997.
[4] Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES",
RFC 1034, November 1987.
[5] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Three: The Domain Name System (DNS) Database", RFC 3403,
October 2002.
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[6] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
One: The Comprehensive DDDS", RFC 3401, October 2002.
[7] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Two: The Algorithm", RFC 3402, October 2002.
[8] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Four: The Uniform Resource Identifiers (URI)", RFC 3404,
October 2002.
[9] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Five: URI.ARPA Assignment Procedures", RFC 3405, October 2002.
[10] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
December 2004.
[11] Hoffman, P., Masinter, L., and J. Zawinski, "The mailto URL
scheme", RFC 2368, July 1998.
[12] ITU-T, "Standardization of Group 3 facsimile terminals for
document transmission", Recommendation T.4, April 1999.
[13] ITU-T, "Procedures for document facsimile transmission in the
general switched telephone network", Recommendation T.30,
April 1999.
[14] 3GPP, "Technical realization of the Short Message Service
(SMS); (Release5)", 3GPP TS 23.040.
[15] 3GPP, "Multimedia Messaging Service (MMS); Functional
description; Stage 2 (Release 5)", 3GPP TS 23.140.
[16] 3GPP, "Multimedia Messaging Service (MMS); Media formats and
codecs; (Release 5)", 3GPP TS 26.140.
[17] Gellens, R., "Mapping Between the Multimedia Messaging Service
(MMS) and Internet Mail", RFC 4356, January 2006.
8.2. Informative References
[18] Arends, R. and et al. , "Protocol Modifications for the DNS
Security Extensions", RFC 4035, March 2005.
[19] Atkins, D. and R. Austein, "Threat Analysis of the Domain Name
System (DNS)", RFC 3833, August 2004.
[20] ETSI, "Minimum Requirements for Interoperability of ENUM
Implementations", ETSI TS 102 172, January 2005.
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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
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Full Copyright Statement
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This document is subject to the rights, licenses and restrictions
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RFC, FYI, BCP