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rfc:rfc5278

Network Working Group J. Livingood Request for Comments: 5278 Comcast Cable Communications Category: Standards Track D. Troshynski

                                                          Acme Packet
                                                            July 2008
  IANA Registration of Enumservices for Voice and Video Messaging

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.

Abstract

 This document registers the Enumservice named "vmsg", which is used
 to facilitate the real-time routing of voice, video, and unified
 communications to a messaging system.  This vmsg Enumservice
 registers three Enumservice types: "voicemsg", "videomsg", and
 "unifmsg".  Each type also registers the subtypes "sip", "sips",
 "http", and "https", as well as the subtype "tel" for the "voicemsg"
 type.

Livingood & Troshynski Standards Track [Page 1] RFC 5278 VMSG Enumservice July 2008

Table of Contents

 1. Introduction ....................................................3
    1.1. Selected Use Cases for Illustrative Purposes ...............4
    1.2. Consideration of Other Existing Enumservices ...............5
 2. Distribution of Data ............................................5
 3. Security Considerations .........................................5
 4. ENUM Service Registration for voicemsg ..........................6
    4.1. Registration for "voicemsg" with Subtype "sip" .............6
    4.2. Registration for "voicemsg" with Subtype "sips" ............7
    4.3. Registration for "voicemsg" with Subtype "tel" .............7
    4.4. Registration for "voicemsg" with Subtype "http" ............8
    4.5. Registration for "voicemsg" with Subtype "https" ...........9
 5. ENUM Service Registration for videomsg .........................10
    5.1. Registration for "videomsg" with Subtype "sip" ............10
    5.2. Registration for "videomsg" with Subtype "sips" ...........10
    5.3. Registration for "videomsg" with Subtype "http" ...........11
    5.4. Registration for "videomsg" with Subtype "https" ..........12
 6. ENUM Service Registration for unifmsg ..........................13
    6.1. Registration for "unifmsg" with Subtype "sip" .............13
    6.2. Registration for "unifmsg" with Subtype "sips" ............13
    6.3. Registration for "unifmsg" with Subtype "http" ............14
    6.4. Registration for "unifmsg" with Subtype "https" ...........15
 7. Selected Examples for Illustrative Purposes ....................16
    7.1. Example Using a 'sip' URI .................................16
    7.2. Example Using a 'tel' URI .................................16
    7.3. Example Using a Backreference .............................16
    7.4. Example Using a 'sip' URI without a Telephone Number ......17
    7.5. Example of Failover Using E2U+videomsg:sip ................17
 8. Implementation Recommendations .................................17
    8.1. Call Processing When Multiple Records Are Returned ........17
    8.2. NAPTR Configuration Issues ................................18
 9. IANA Considerations ............................................18
 10. Acknowledgements ..............................................18
 11. Contributors ..................................................19
 12. References ....................................................19
    12.1. Normative References .....................................19
    12.2. Informative References ...................................20

Livingood & Troshynski Standards Track [Page 2] RFC 5278 VMSG Enumservice July 2008

1. 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 Naming Authority Pointer (NAPTR) records (Dynamic
 Delegation Discovery System (DDDS) Part Three: The Domain Name System
 (DNS) Database, RFC 3403 [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 Voice Profile for Internet Mail
 (VPIM) [14] 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 use cases listed in
 this section.
 Video messaging systems, sometimes called visual voice messaging
 systems, are beginning to be used with real-time communication
 services.  The need for a video messaging service type has become
 clear in order to provide certain applications with direct access to
 various video messaging services, most typically via the use of SIP.
 Thus, a need has been identified for this video messaging service
 type that would enable, for example, some of the use cases listed in
 this section.

Livingood & Troshynski Standards Track [Page 3] RFC 5278 VMSG Enumservice July 2008

 Finally, several service providers and software developers have
 indicated that their system for voice messaging and video messaging
 either have been or soon will be unified into a single system.  As
 such, they desired to have the option of using an Enumservice type
 that represents a subscriber's mailbox as being a so-called unified
 messaging repository.  Thus, a need has been identified for this
 unified voice and video messaging service type that would enable, for
 example, some of the use cases listed in this section.

1.1. Selected Use Cases for Illustrative Purposes

 The following is a partial, non-exclusive list of use cases that the
 vmsg Enumservice could address:
  • A called party is busy or does not answer a call. A client or

server then determines that a 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 messaging system, but that system is currently unavailable.

   Since multiple 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 messaging servers in a manner that
   is transparent to the calling party and that supports better
   overall availability of a messaging service.
  • Similar to the above use case, this service type could be used to

balance load across multiple messaging servers, whether those are

   in the same or in different physical locations.
  • A user with an account on a messaging service needs to connect to

the messaging service in order to retrieve messages. They initiate

   a real-time session, and an ENUM query is performed to discover the
   messaging server that holds its mailbox.
  • In the process of invoking and supporting a real-time, automated

and interactive session with a user, whether for message deposit or

   retrieval, VoiceXML files are referenced and utilized, via either
   HTTP or HTTPS.  Multiple VoiceXML servers could be associated with
   a user and returned via ENUM query, for the purposes of load
   balancing, for example.

Livingood & Troshynski Standards Track [Page 4] RFC 5278 VMSG Enumservice July 2008

1.2. Consideration of Other Existing Enumservices

 The authors considered whether this service type could simply use the
 SIP Enumservice type [19], but found that it does not satisfy their
 voice messaging requirements, particularly given the non-SIP URI sub-
 types specified herein.  Even with sub-types for SIP URIs, however,
 there are challenges to using the SIP Enumservice type.  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, video messaging, or
 unified voice and video messaging service.

2. 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, (b) on a private basis between one or more parties
 using a variety of security mechanisms to prohibit general public
 access, or (c) openly available.

3. 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.
 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 it 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.

Livingood & Troshynski Standards Track [Page 5] RFC 5278 VMSG Enumservice July 2008

 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 [16] to this is provided in RFC 3761
 [1].  A thorough analysis of threats to the DNS itself is covered in
 RFC 3833 [17].

4. ENUM Service Registration for voicemsg

4.1. Registration for "voicemsg" with Subtype "sip"

 Enumservice Name: "voicemsg"
 Enumservice Type: "voicemsg"
 Enumservice Subtypes: "sip"
 URI Schemes: 'sip:'
 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 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)

Livingood & Troshynski Standards Track [Page 6] RFC 5278 VMSG Enumservice July 2008

 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

4.2. Registration for "voicemsg" with Subtype "sips"

 Enumservice Name: "voicemsg"
 Enumservice Type: "voicemsg"
 Enumservice Subtypes: "sips"
 URI Schemes: 'sips:'
 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 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)
 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

4.3. Registration for "voicemsg" with Subtype "tel"

 Enumservice Name: "voicemsg"
 Enumservice Type: "voicemsg"
 Enumservice Subtype: "tel"
 URI Schemes: 'tel:'

Livingood & Troshynski Standards Track [Page 7] RFC 5278 VMSG Enumservice July 2008

 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 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)
 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

4.4. Registration for "voicemsg" with Subtype "http"

 Enumservice Name: "voicemsg"
 Enumservice Type: "voicemsg"
 Enumservice Subtype: "http"
 URI Schemes: 'http:'
 Functional Specification:
 This Enumservice indicates that the remote resource identified by the
 associated URI scheme is capable of being a source of information.
 Note that the kind of information retrieved can be manifold. Usually,
 contacting a resource by an 'http:' [11] URI provides a document.
 This document can contain references that will trigger the download
 of many different kinds of information, such as text, audio, video,
 executable code, or even voice message files.  Thus, one cannot be
 more specific about the kind of information expected when contacting
 the resource.
 Security Considerations: See Section 3.
 Intended Usage: COMMON

Livingood & Troshynski Standards Track [Page 8] RFC 5278 VMSG Enumservice July 2008

 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)
 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

4.5. Registration for "voicemsg" with Subtype "https"

 Enumservice Name: "voicemsg"
 Enumservice Type: "voicemsg"
 Enumservice Subtype: "https"
 URI Schemes: 'https:'
 Functional Specification:
 This Enumservice indicates that the remote resource identified by the
 associated URI scheme is capable of being a source of information,
 which can be contacted using TLS or the Secure Socket Layer protocol.
 Note that the kind of information retrieved can be manifold. Usually,
 contacting a resource by an 'https:' [12] URI provides a document.
 This document can contain references that will trigger the download
 of many different kinds of information, such as text, audio, video,
 executable code, or even voice message files.  Thus, one cannot be
 more specific about the kind of information expected when contacting
 the resource.
 Security Considerations: See Section 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)
 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

Livingood & Troshynski Standards Track [Page 9] RFC 5278 VMSG Enumservice July 2008

5. ENUM Service Registration for videomsg

5.1. Registration for "videomsg" with Subtype "sip"

 Enumservice Name: "videomsg"
 Enumservice Type: "videomsg"
 Enumservice Subtypes: "sip"
 URI Schemes: 'sip:'
 Functional Specification:
 This Enumservice indicates that the remote resource identified can be
 addressed by the associated URI scheme in order to initiate a video
 communication session to a video messaging system.
 Security Considerations: See Section 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)
 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

5.2. Registration for "videomsg" with Subtype "sips"

 Enumservice Name: "videomsg"
 Enumservice Type: "videomsg"
 Enumservice Subtypes: "sips"
 URI Schemes: 'sips:'
 Functional Specification:
 This Enumservice indicates that the remote resource identified can be
 addressed by the associated URI scheme in order to initiate a video
 communication session to a video messaging system.

Livingood & Troshynski Standards Track [Page 10] RFC 5278 VMSG Enumservice July 2008

 Security Considerations: See Section 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)
 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

5.3. Registration for "videomsg" with Subtype "http"

 Enumservice Name: "videomsg"
 Enumservice Type: "videomsg"
 Enumservice Subtype: "http"
 URI Schemes: 'http:'
 Functional Specification:
 This Enumservice indicates that the remote resource identified by the
 associated URI scheme is capable of being a source of information.
 Note that the kind of information retrieved can be manifold. Usually,
 contacting a resource by an 'http:' [11] URI provides a document.
 This document can contain references that will trigger the download
 of many different kinds of information, such as text, audio, video,
 executable code, or even video message files.  Thus, one cannot be
 more specific about the kind of information expected when contacting
 the resource.
 Security Considerations: See Section 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)

Livingood & Troshynski Standards Track [Page 11] RFC 5278 VMSG Enumservice July 2008

 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

5.4. Registration for "videomsg" with Subtype "https"

 Enumservice Name: "videomsg"
 Enumservice Type: "videomsg"
 Enumservice Subtype: "https"
 URI Schemes: 'https:'
 Functional Specification:
 This Enumservice indicates that the remote resource identified by the
 associated URI scheme is capable of being a source of information,
 which can be contacted using TLS or the Secure Socket Layer protocol.
 Note that the kind of information retrieved can be manifold. Usually,
 contacting a resource by an 'https:' [12] URI provides a document.
 This document can contain references that will trigger the download
 of many different kinds of information, such as text, audio, video,
 executable code, or even video message files.  Thus, one cannot be
 more specific about the kind of information expected when contacting
 the resource.
 Security Considerations: See Section 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)
 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

Livingood & Troshynski Standards Track [Page 12] RFC 5278 VMSG Enumservice July 2008

6. ENUM Service Registration for unifmsg

6.1. Registration for "unifmsg" with Subtype "sip"

 Enumservice Name: "unifmsg"
 Enumservice Type: "unifmsg"
 Enumservice Subtypes: "sip"
 URI Schemes: 'sip:'
 Functional Specification:
 This Enumservice indicates that the remote resource identified can be
 addressed by the associated URI scheme in order to initiate a unified
 communication session to a unified messaging system.
 Security Considerations: See Section 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)
 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

6.2. Registration for "unifmsg" with Subtype "sips"

 Enumservice Name: "unifmsg"
 Enumservice Type: "unifmsg"
 Enumservice Subtypes: "sips"
 URI Schemes: 'sips:'
 Functional Specification:
 This Enumservice indicates that the remote resource identified can be
 addressed by the associated URI scheme in order to initiate a unified
 communication session to a unified messaging system.

Livingood & Troshynski Standards Track [Page 13] RFC 5278 VMSG Enumservice July 2008

 Security Considerations: See Section 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)
 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

6.3. Registration for "unifmsg" with Subtype "http"

 Enumservice Name: "unifmsg"
 Enumservice Type: "unifmsg"
 Enumservice Subtype: "http"
 URI Schemes: 'http:'
 Functional Specification:
 This Enumservice indicates that the remote resource identified by the
 associated URI scheme is capable of being a source of information.
 Note that the kind of information retrieved can be manifold. Usually,
 contacting a resource by an 'http:' [11] URI provides a document.
 This document can contain references that will trigger the download
 of many different kinds of information, such as text, audio, video,
 executable code, or even video message files.  Thus, one cannot be
 more specific about the kind of information expected when contacting
 the resource.
 Security Considerations: See Section 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)

Livingood & Troshynski Standards Track [Page 14] RFC 5278 VMSG Enumservice July 2008

 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

6.4. Registration for "unifmsg" with Subtype "https"

 Enumservice Name: "unifmsg"
 Enumservice Type: "unifmsg"
 Enumservice Subtype: "https"
 URI Schemes: 'https:'
 Functional Specification:
 This Enumservice indicates that the remote resource identified by the
 associated URI scheme is capable of being a source of information,
 which can be contacted using TLS or the Secure Socket Layer protocol.
 Note that the kind of information retrieved can be manifold. Usually,
 contacting a resource by an 'https:' [12] URI provides a document.
 This document can contain references that will trigger the download
 of many different kinds of information, such as text, audio, video,
 executable code, or even video message files.  Thus, one cannot be
 more specific about the kind of information expected when contacting
 the resource.
 Security Considerations: See Section 3.
 Intended Usage: COMMON
 Authors:
 Jason Livingood (jason_livingood@cable.comcast.com)
 Don Troshynski (dtroshynski@acmepacket.com)
 Any other information the author deems interesting:
 Implementers should review a non-exclusive list of examples below in
 Section 7.

Livingood & Troshynski Standards Track [Page 15] RFC 5278 VMSG Enumservice July 2008

7. Selected Examples for Illustrative Purposes

 The following sub-sections document several examples that
 implementers may find informative.  These examples shall in no way
 limit the various forms that this Enumservice may take.

7.1. Example Using a 'sip' URI

    $ORIGIN 3.2.1.0.5.5.5.5.1.2.1.e164.arpa.
       NAPTR 10 100 "u" "E2U+voicemsg:sip"
       "!^.*$!sip:12155550123@gw.example.com!".
 In this example, a calling party has attempted a session that 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 it
 records a voice message to the called party.

7.2. Example Using a 'tel' URI

    $ORIGIN 3.2.1.0.5.5.5.5.1.2.1.e164.arpa.
       NAPTR 10 100 "u" "E2U+voicemsg:tel"
       "!^.*$!tel:1-215-555-0123!".
 In this example, a calling party has attempted a session that 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 it
 records a voice message to the called party.

7.3. Example Using a Backreference

    $ORIGIN 3.2.1.0.5.5.5.5.1.2.1.e164.arpa.
       NAPTR 10 100 "u" "E2U+voicemsg:sip"
       "!(^.*)$!sip:\1@example.net!".
 In this example, a backreference is used to reduce the size of the
 NAPTR record.  The sip URI uses "\1", which would dynamically replace
 the expression with the TN, in this case +12155550123.

Livingood & Troshynski Standards Track [Page 16] RFC 5278 VMSG Enumservice July 2008

7.4. Example Using a 'sip' URI without a Telephone Number

    $ORIGIN 3.2.1.0.5.5.5.5.1.2.1.e164.arpa.
       NAPTR 10 100 "u" "E2U+voicemsg:sip"
       "!^.*$!sip:johndoe@gw.example.com!".
 In this example, a calling party has attempted a session that 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 it
 records a voice message to the called party.  The URI that this
 session is directed to does not include a telephone number, as this
 user has multiple service that are not particularly tied to telephone
 numbers whereby text, audio, video and other multimedia messages can
 be received and accessed.

7.5. Example of Failover Using E2U+videomsg:sip

    $ORIGIN 3.2.1.0.5.5.5.5.1.2.1.e164.arpa.
       NAPTR 10 100 "u" "E2U+videomsg:sip"
       "!^.*$!sip:12155550123@gw1.example.com!".
    $ORIGIN 3.2.1.0.5.5.5.5.1.2.1.e164.arpa.
       NAPTR 10 200 "u" "E2U+videomsg:sip"
       "!^.*$!sip:12155550123@gw2.example.com!".
 In this example, the preference indicates that gw1.example.com is
 used first (100), and if this is unreachable, then the next higher
 preference (200) is used and gw2.example.com is contacted.  While out
 of scope for this document, a service provider could thus mirror or
 cluster a message store and fail from the primary to secondary using
 the DNS in an active-standby mode.

8. Implementation Recommendations

8.1. Call Processing When Multiple Records Are Returned

 It is likely that both E2U+sip and E2U+voicemsg, E2U+videomsg, and/or
 E2U+unifmsg 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,
 for example, 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.

Livingood & Troshynski Standards Track [Page 17] RFC 5278 VMSG Enumservice July 2008

 In addition, it is likely that multiple E2U+voicemsg, E2U+videomsg,
 and/or E2U+unifmsg 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, video, or unified voice
 and video messaging service.  Preference could be used to load
 balance across multiple voice, video, and/or unified voice and video
 messaging servers by weight, for example.
 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.

8.2. 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.

9. IANA Considerations

 This document registers the 'voicemsg' Enumservice type and the
 subtype "tel", "sip", "sips", "http", and "https" under the
 Enumservice registry described in the IANA considerations in RFC
 3761.  Details of this registration are provided in Section 4 of this
 document.
 This document registers the 'videomsg' Enumservice type and the
 subtype "sip", "sips", "http", and "https" under the Enumservice
 registry described in the IANA considerations in RFC 3761.  Details
 of this registration are provided in Section 5 of this document.
 This document registers the 'unifmsg' Enumservice type and the
 subtype "sip", "sips", "http", and "https" under the Enumservice
 registry described in the IANA considerations in RFC 3761.  Details
 of this registration are provided in Section 6 of this document.

10. Acknowledgements

 The authors thank Rich Ferrise, Chris Harvey, Tong Zhou, and Hadriel
 Kaplan for their detailed assistance in developing the ideas behind
 this document in numerous brainstorming sessions, with information
 gleaned from their work to solve real application architecture
 issues.  The authors also thank Lawrence Conroy and Jean-Francois
 Mule for their feedback in developing this document.

Livingood & Troshynski Standards Track [Page 18] RFC 5278 VMSG Enumservice July 2008

11. Contributors

 Tong Zhou
 Comcast Cable Communications
 Email: tong_zhou@cable.comcast.com
 Richard Ferrise
 Comcast Cable Communications
 Email: rich_ferrise@cable.comcast.com
 Chris Harvey
 Comcast Cable Communications
 Email: chris_harvey@cable.comcast.com
 Hadriel Kaplan
 Acme Packet
 Email: hkaplan@acmepacket.com

12. References

12.1. 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 Numbering
       Plan", Recommendation E.164, May 1997.
 [3]   Mockapetris, P., "Domain names - concepts and facilities", STD
       13, 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.

Livingood & Troshynski Standards Track [Page 19] RFC 5278 VMSG Enumservice July 2008

 [8]   Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
       Five: URI.ARPA Assignment Procedures", BCP 65, RFC 3405,
       October 2002.
 [9]   Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
       December 2004.
 [10]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
       Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
       Session Initiation Protocol", RFC 3261, June 2002.
 [11]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
       Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
       HTTP/1.1", RFC 2616, June 1999.
 [12]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

12.2. Informative References

 [13]  Peterson, J., Liu, H., Yu, J., and B. Campbell, "Using E.164
       numbers with the Session Initiation Protocol (SIP)", RFC 3824,
       June 2004.
 [14]  Vaudreuil, G., "Voice Message Routing Service", RFC 4238,
       October 2005.
 [15]  Brandner, R., Conroy, L., and R. Stastny, "IANA Registration
       for Enumservices email, fax, mms, ems, and sms", RFC 4355,
       January 2006.
 [16]  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
       "Protocol Modifications for the DNS Security Extensions", RFC
       4035, March 2005.
 [17]  Atkins, D. and R. Austein, "Threat Analysis of the Domain Name
       System (DNS)", RFC 3833, August 2004.
 [18]  Foster, M., McGarry, T., and J. Yu, "Number Portability in the
       Global Switched Telephone Network (GSTN): An Overview", RFC
       3482, February 2003.
 [19]  Peterson, J., "enumservice registration for Session Initiation
       Protocol (SIP) Addresses-of-Record", RFC 3764, April 2004.

Livingood & Troshynski Standards Track [Page 20] RFC 5278 VMSG Enumservice July 2008

Authors' Addresses

 Jason Livingood
 Comcast Cable Communications
 One Comcast Center
 1701 John F. Kennedy Boulevard
 Philadelphia, PA 19103
 USA
 EMail: jason_livingood@cable.comcast.com
 Donald Troshynski
 Acme Packet
 EMail: dtroshynski@acmepacket.com

Livingood & Troshynski Standards Track [Page 21] RFC 5278 VMSG Enumservice July 2008

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 contained in BCP 78, and except as set forth therein, the authors
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Livingood & Troshynski Standards Track [Page 22]

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