ENUM Working Group J. Livingood
Internet-Draft Comcast Cable Communications
Expires: February 16, 2008 T. Zhou
Comcast Cable Communications
R. Ferrise
Comcast Cable Communications
C. Harvey
Comcast Cable Communications
D. Troshynski
Acme Packet
H. Kaplan
Acme Packet
August 2007
IANA Registration for an Enumservice
for Voice Messaging
draft-livingood-enum-voicemsg-00
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Abstract
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This document registers the Enumservice type "voicemsg" and subtype
"sip" using the URI scheme sip, as well as the subtype "tel" using
the URI scheme 'tel' as per the IANA registration process defined in
the ENUM specification, RFC 3761. This Enumservice is used to
facilitate the real-time routing of voice communications to a voice
messaging system.
Table of Contents
1. Terminology....................................................2
2. Introduction...................................................2
3. Distribution of Data...........................................4
4. ENUM Service Registration for voicemsg.........................4
4.1 ENUM Service Registration for "voicemsg" with Subtype "sip"4
4.2 ENUM Service Registration for "voicemsg" with Subtype "tel"5
5. Examples.......................................................6
5.1 Example of a calling party send to a voice messaging system,
Using a 'sip' URI Scheme.......................................6
5.2 Example of a calling party send to a voice messaging system,
Using a 'tel' URI Scheme.......................................6
5.3 Example Using a Regular Expression.........................6
6. Implementation Recommendations.................................7
6.1 Call Processing When Multiple Records Are Returned.........7
6.2 NAPTR Configuration issues.................................7
7. Security Considerations........................................7
8. IANA Considerations............................................8
9. Acknowledgements...............................................8
10. References....................................................8
10.1 Normative References......................................8
10.2 Informative References....................................9
Authors' Addresses................................................9
Intellectual Property and Copyright Statements...................11
1. 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].
2. Introduction
ENUM (E.164 Number Mapping, RFC 3761 [1]) is a technology that
transforms E.164 numbers (The International Public Telecommunication
Numbering Plan, ITU-T Recommendation E.164 [2]) into domain names and
then uses DNS (Domain Name System, RFC 1034 [3]) delegation through
NS records and NAPTR records (Dynamic Delegation Discovery System
(DDDS) Part Three: The Domain Name System (DNS) Database, RFC 3403
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[4]) to look up what services are available for a specific domain
name.
This document registers Enumservices according to the guidelines
given in RFC 3761 [1] to be used for provisioning in the services
field of a NAPTR [4] resource record to indicate the types of
functionality associated with an end point and/or telephone number.
The registration is defined within the DDDS (Dynamic Delegation
Discovery System [4][5][6][7][8]) hierarchy, for use with the "E2U"
DDDS Application defined in RFC 3761.
Voice messaging systems are used widely with telephony and voice
communication services. The need for a voice messaging service type
has become clear in order to provide certain applications with direct
access to various voice messaging services, for example voicemail,
most typically via the use of SIP.
The authors considered the use of VPIM [11] but found that VPIM was
best suited to the non-real-time and non-session-based routing of a
voice message once it had been deposited into a voice messaging
system. Thus, VPIM was a good solution for the non-real-time and
non-session-based routing of voice messages between and within
domains, but it did not enable real-time interaction with a voice
messaging system.
Thus, a need has been identified for this voice messaging service
type that would enable, for example some of the following use cases:
* A called party is busy or does not answer a call. A client or
server then determines that a voice messaging service should be used
and sends the calling party’s session to such a service. The client
or server needs to be able to determine which server to direct this
real-time session to, whether that is within or outside of the called
party’s domain.
* Similar to the above use case, a real-time session is attempted to
a voice messaging system, but that system is currently unavailable.
Since multiple voice messaging service type records may be returned
by the original ENUM query, the client or server could then attempt
to initiate a session with one or more backup voice messaging servers
in a manner which is transparent to the calling party, and which
supports better overall availability of a voice messaging service.
* Similar to the above use case, this voice message service type
could be used to balance load across multiple voice messaging
servers, whether those are in the same or in different physical
locations.
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* A user with an account on a voice messaging service needs to
connect to a voice messaging service in order to retrieve voice
messages. They initiate a real-time session and an ENUM query is
performed to discover the voice messaging server that holds their
mailbox.
The authors considered whether this service type could simply use the
SIP Enumservice type [16], but found that it does not satisfy their
voice messaging requirements. For example, a request for access to
such a service could be extended to the requesting SIP client, or
User Agent Client (UAC), rather than relying upon the local policy of
a SIP server, or User Agent Server (UAS), which means that special
routing logic within a UAS cannot be relied upon to solve this
problem. More importantly, however, the authors have found that
without this service type, a UAC or UAS will be presented with
multiple SIP URIs, with no ability other than in non-standards-based
routing rules or application logic to recognize which one is related
to a voice messaging service. This is due in part to the fact that
the IANA registration for the SIP Enumservice does not register any
subtypes.
3. Distribution of Data
The authors believe that it is more likely that these records will be
distributed on a purely private basis, but they may also be
distributed in public ENUM trees. Distribution of this NAPTR data
could be either (a) on a private basis (within a service provider's
internal network, or on a private basis between one or more parties
using a variety of security mechanisms to prohibit general public
access) or (b) openly available.
4. ENUM Service Registration for voicemsg
4.1 ENUM Service Registration for "voicemsg" with Subtype "sip"
Enumservice Name: "voicemsg"
Enumservice Type: "voicemsg"
Enumservice Subtypes: "sip"
URI Schemes: 'sip:'
Functional Specification:
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This Enumservice indicates that the remote resource identified can be
addressed by the associated URI scheme in order to initiate a voice
communication session to a voice messaging system.
Security Considerations: See Section 9.
Intended Usage: COMMON
Authors:
Jason Livingood (jason_livingood@cable.comcast.com)
Tong Zhou (tong_zhou@cable.comcast.com)
Richard Ferrise (rich_ferrise@cable.comcast.com)
Chris Harvey (chris_harvey@cable.comcast.com)
Don Troshynski (dtroshynski@acmepacket.com)
Hadriel Kaplan (hkaplan@acmepacket.com)
Any other information the author deems interesting:
Implementers should review a non-exclusive list of examples below in
Section 5.
4.2 ENUM Service Registration for "voicemsg" with Subtype "tel"
Enumservice Name: "voicemsg"
Enumservice Type: "voicemsg"
Enumservice Subtype: "tel"
URI Schemes: 'tel:'
Functional Specification:
This Enumservice indicates that the remote resource identified can be
addressed by the associated URI scheme in order to initiate a voice
communication session to a voice messaging system.
Security Considerations: See Section 9.
Intended Usage: COMMON
Authors:
Jason Livingood (jason_livingood@cable.comcast.com)
Tong Zhou (tong_zhou@cable.comcast.com)
Richard Ferrise (rich_ferrise@cable.comcast.com)
Chris Harvey (chris_harvey@cable.comcast.com)
Don Troshynski (dtroshynski@acmepacket.com)
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Hadriel Kaplan (hkaplan@acmepacket.com)
Any other information the author deems interesting:
Implementers should review a non-exclusive list of examples below in
Section 5.
5. Examples
The following sub-sections document several examples for illustrative
purposes. These examples shall in no way limit the various forms
that this Enumservice may take.
5.1 Example of a calling party send to a voice messaging system, Using a
'sip' URI Scheme
$ORIGIN 3.2.1.0.5.5.5.5.1.2.1.e164.arpa.
NAPTR 10 100 "u" "E2U+voicemsg:sip"
"!^.*$!sip:12155550123@gw.example.com!".
In this example, a calling party has attempted a session which has
gone unanswered after a certain period of time. The calling party’s
session is sent to the appropriate voice messaging server, a
personalized greeting is played to the calling party, after which
they record a voice message to the called party.
5.2 Example of a calling party send to a voice messaging system, Using a
'tel' URI Scheme
$ORIGIN 3.2.1.0.5.5.5.5.1.2.1.e164.arpa.
NAPTR 10 100 "u" "E2U+voicemsg:tel"
"!^.*$!tel:1-215-555-0123!".
In this example, a calling party has attempted a session which has
gone unanswered after a certain period of time. The calling party’s
session is sent to the appropriate voice messaging server, a
personalized greeting is played to the calling party, after which
they record a voice message to the called party.
5.3 Example Using a Regular Expression
$ORIGIN 3.2.1.0.5.5.5.5.1.2.1.e164.arpa.
NAPTR 10 100 "u" "E2U+voicemsg:sip"
"!(^.*)$!sip:\1!".
In this example, a regular expression replacement function is used to
reduce the size of the NAPTR record. The sip URI uses "\1" which
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would dynamically replace the expression with the TN, in this case
+12155550123.
6. Implementation Recommendations
6.1 Call Processing When Multiple Records Are Returned
It is likely that that both E2U+sip and E2U+voicemsg Enumservice type
records will be returned for a given query. In this case, this could
result in what is essentially E2U+sip records for real-time
communications with an end user, while the E2U+voicemsg records will
be used for real-time communications with a voice messaging service,
when the called party is not available or does not wish to be
disturbed. Therefore, the network element that receives the results
of this ENUM query will need to know enough information in order to
select the voicemsg service type, rather than the sip service type.
In addition, it is likely that multiple E2U+voicemsg Enumservice type
records will be returned for a given query. In this case, multiple
records may include order and preference to allow recursion or load
balancing. Order could be used to designate a primary and a backup
voice messaging service. Preference could be used to load balance
across multiple voice messaging servers by weight.
Finally, as with multiple records resulting from a typical ENUM query
of the e164.arpa tree, it is up to the application using an ENUM
resolver to determine which record(s) to use and which record(s) to
ignore. Implementers should take this into consideration and build
logic into their applications that can select appropriately from
multiple records based on business, network, or other rules.
6.2 NAPTR Configuration issues
Implementers may wish to consider using regular expressions in order
to reduce the size of individual NAPTRs. This will have a
significant effect on the overall size of the database involved.
7. Security Considerations
DNS, as used by ENUM, is a global, distributed database. Should
implementers of this specification use e164.arpa or any other
publicly available domain as the tree for maintaining voicemsg
Enumservice data, this information would be visible to anyone
anonymously. While this is not qualitatively different from
publication in a Telephone Directory, it does open or ease access to
such data without any indication that such data has been accessed or
by whom it has been accessed.
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Such data harvesting by third parties is often used to generate lists
of targets for unsolicited information. Thus, a third party could use
this to generate a list that they can use to make unsolicited
"telemarketing" phone calls, or so-called SPAM over Internet
Telephony (SPIT). Many countries have do-not-call registries or other
legal or regulatory mechanisms in place to deal with such abuses.
As noted earlier carriers, service providers, and other users may
simply choose not to publish such information in the public e164.arpa
tree, but may instead simply publish this in their internal ENUM
routing database that is only able to be queried by trusted elements
of their network and/or partner networks, such as softswitches and
SIP proxy servers. They may also choose to publish such information
in a carrier-only branch of the e164.arpa tree, should one be
created.
Although an E.164 telephone number does not appear to reveal as much
identity information about a user as a name in the format
sip:username@hostname or email:username@hostname, 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 [13] to this is provided in RFC 3761
[1]. A thorough analysis of threats to the DNS itself is covered in
RFC 3833 [14].
8. IANA Considerations
This document registers the 'voicemsg' Enumservice type and the
subtype "tel" and "sip" under the Enumservice registry described in
the IANA considerations in RFC 3761. Details of this registration
are provided in Section 4 of this document.
9. Acknowledgements
TBD
10. References
10.1 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.
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[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] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
December 2004.
[10] Rosenberg, J., et al., "SIP: Session Initiation Protocol", RFC
3261, June 2002.
10.2 Informative References
[11] Vaudreuil, G., "Voice Message Routing Service", RFC 4238,
October 2005.
[12] Bradner, et al., "IANA Registration for Enumservices email, fax,
mms, ems and sms", RFC 4355, January 2006.
[13] Arends, R. and et al., "Protocol Modifications for the DNS
Security Extensions", RFC 4035, March 2005.
[14] Atkins, D. and Austein, R., "Threat Analysis of the Domain Name
System (DNS)", RFC 3833, August 2004.
[15] Foster, M., McGarry, T., and Yu, J., "Number Portability in the
GSTN: An Overview", RFC 3482, February 2003.
[16] Peterson, J., "enumservice Registration for Session Initiation
Protocol (SIP) Addresses-of-Record", RFC 3764, April 2004.
Authors' Addresses
Jason Livingood
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Comcast Cable Communications
1500 Market Street
Philadelphia, PA 19102
USA
Phone: +1-215-981-7813
Email: jason_livingood@cable.comcast.com
Tong Zhou
Comcast Cable Communications
1500 Market Street
Philadelphia, PA 19102
USA
Phone: +1-215-286-7301
Email: tong_zhou@cable.comcast.com
Richard Ferrise
Comcast Cable Communications
1500 Market Street
Philadelphia, PA 19102
USA
Phone: +1-215-320-8880
Email: rich_ferrise@cable.comcast.com
Chris Harvey
Comcast Cable Communications
1500 Market Street
Philadelphia, PA 19102
USA
Phone: +1-215-981-7813
Email: chris_harvey@cable.comcast.com
Donald Troshynski
Acme Packet
Email: dtroshynski@acmepacket.com
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Hadriel Kaplan
Acme Packet
Email: hkaplan@acmepacket.com
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