IANA Registration of Enumservices for Voice and Video Messaging
draft-ietf-enum-vmsg-02

ENUM Working Group                                         J. Livingood 
Internet-Draft                             Comcast Cable Communications 
Expires: October 2008                                     D. Troshynski 
Intended Status: Proposed Standard                          Acme Packet 
                                                         April 16, 2008 
    
    
                     IANA Registration of Enumservices 
                       for Voice and Video Messaging 
                          draft-ietf-enum-vmsg-02 
    
    
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   This Internet-Draft will expire on October 18, 2008.  
    
Copyright Notice 
    
   Copyright (C) The IETF Trust (2008). 
    
    
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. 
 
 
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Table of Contents 
    
   1. Terminology....................................................2 
   2. Introduction...................................................3 
      2.1 Selected Use Cases for Illustrative Purposes...............4 
      2.2 Consideration of Other Existing Enumservices...............4 
   3. Distribution of Data...........................................5 
   4. Security Considerations........................................5 
   5. ENUM Service Registration for voicemsg.........................6 
      5.1 Registration for "voicemsg" with Subtype "sip".............6 
      5.2 Registration for "voicemsg" with Subtype "sips"............6 
      5.3 Registration for "voicemsg" with Subtype "tel".............7 
      5.4 Registration for "voicemsg" with Subtype "http"............8 
      5.5 Registration for "voicemsg" with Subtype "https"...........8 
   6. ENUM Service Registration for videomsg.........................9 
      6.1 Registration for "videomsg" with Subtype "sip".............9 
      6.2 Registration for "videomsg" with Subtype "sips"...........10 
      6.3 Registration for "videomsg" with Subtype "http"...........10 
      6.4 Registration for "videomsg" with Subtype "https"..........11 
   7. ENUM Service Registration for unifmsg.........................12 
      7.1 Registration for "unifmsg" with Subtype "sip".............12 
      7.2 Registration for "unifmsg" with Subtype "sips"............13 
      7.3 Registration for "unifmsg" with Subtype "http"............13 
      7.4 Registration for "unifmsg" with Subtype "https"...........14 
   8. Selected Examples for Illustrative Purposes...................15 
      8.1 Example Using a 'sip' URI.................................15 
      8.2 Example Using a 'tel' URI.................................15 
      8.3 Example Using a Backreference.............................15 
      8.4 Example Using a 'sip' URI Without a Telephone Number......16 
      8.5 Example of Failover Using E2U+videomsg:sip................16 
   9. Implementation Recommendations................................16 
      9.1 Call Processing When Multiple Records Are Returned........16 
      9.2 NAPTR Configuration issues................................17 
   10. IANA Considerations..........................................17 
   11. Acknowledgements.............................................17 
   12. Contributors.................................................18 
   13. References...................................................18 
      13.1 Normative References.....................................18 
      13.2 Informative References...................................19 
   Authors' Addresses...............................................19 
   Intellectual Property and Copyright Statements...................20 
    
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]. 
    

 
 
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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 
   [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 [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. 
    
   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 
 
 
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   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. 
    
2.1 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 which is 
   transparent to the calling party, and which 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 their 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.  
   
2.2 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, 
 
 
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   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.   
 
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, (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. 
    
4. 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 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. 
    

 
 
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   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]. 
    
5. ENUM Service Registration for voicemsg 
 
5.1 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 4. 
    
   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 8. 
 
5.2 Registration for "voicemsg" with Subtype "sips" 
    
   Enumservice Name: "voicemsg" 
    
   Enumservice Type: "voicemsg" 
    
 
 
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   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 4. 
    
   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 8. 
    
5.3 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 4. 
    
   Intended Usage: COMMON 
    
   Authors: 
    
   Jason Livingood (jason_livingood@cable.comcast.com) 
   Don Troshynski (dtroshynski@acmepacket.com) 
    
 
 
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   Any other information the author deems interesting: 
    
   Implementers should review a non-exclusive list of examples below in 
   Section 8. 
    
5.4 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 4. 
    
   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 8. 
    
5.5 Registration for "voicemsg" with Subtype "https" 
    
   Enumservice Name: "voicemsg" 
    
   Enumservice Type: "voicemsg" 
    
   Enumservice Subtype: "https" 
 
 
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   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 4. 
    
   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 8. 
    
    
6. ENUM Service Registration for videomsg 
 
6.1 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. 
 
 
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   Security Considerations: See Section 4. 
    
   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 8. 
    
6.2 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. 
    
   Security Considerations: See Section 4. 
    
   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 8. 
    
6.3 Registration for "videomsg" with Subtype "http" 
    
   Enumservice Name: "videomsg" 
    
 
 
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   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 4. 
    
   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 8. 
    
6.4 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.   
    
 
 
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   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 4. 
    
   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 8. 
 
7. ENUM Service Registration for unifmsg 
 
7.1 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 4. 
    
   Intended Usage: COMMON 
    
   Authors: 
    
   Jason Livingood (jason_livingood@cable.comcast.com) 
   Don Troshynski (dtroshynski@acmepacket.com) 
    
 
 
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   Any other information the author deems interesting: 
    
   Implementers should review a non-exclusive list of examples below in 
   Section 8. 
    
7.2 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. 
    
   Security Considerations: See Section 4. 
    
   Intended Usage: COMMON 
    
   Authors: 
    
   Jason Livingood (jason_livingood@cable.comcast.com) 
    
   Any other information the author deems interesting: 
    
   Implementers should review a non-exclusive list of examples below in 
   Section 8. 
    
7.3 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.   
    
 
 
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   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 4. 
    
   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 8. 
    
7.4 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 4. 
    
   Intended Usage: COMMON 
 
 
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   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 8. 
    
8. 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. 
    
8.1 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 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. 
    
8.2 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 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. 
    
8.3 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!". 
    

 
 
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   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. 
    
8.4 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 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.  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. 
    
8.5 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.   
    
9. Implementation Recommendations  
 
9.1 Call Processing When Multiple Records Are Returned 
    
   It is likely that 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 
 
 
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   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, 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.   
    
9.2 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.   
    
    
10. 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 5 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 6 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 7 of this document. 
    
11. 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 
 
 
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   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. 
    
    
12. 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 
    
13. References 
    
13.1 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. 
    

 
 
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   [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. 
    
   [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. 
    
13.2 Informative References 
    
   [13] Peterson, J., et al., "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] Bradner, et al., "IANA Registration for Enumservices email, fax, 
   mms, ems and sms", RFC 4355, January 2006. 
    
   [16] Arends, R. and et al., "Protocol Modifications for the DNS 
   Security Extensions", RFC 4035, March 2005. 
    
   [17] Atkins, D. and Austein, R., "Threat Analysis of the Domain Name 
   System (DNS)", RFC 3833, August 2004. 
    
   [18] Foster, M., McGarry, T., and Yu, J., "Number Portability in the 
   GSTN: An Overview", RFC 3482, February 2003. 
 
   [19] Peterson, J., "enumservice Registration for Session Initiation 
   Protocol (SIP) Addresses-of-Record", RFC 3764, April 2004. 
    
   [20] Bradner, et al., "IANA Registration for Enumservice 'web' and 
   'ft', RFC 4022, February 2005. 
    
Authors' Addresses 
    
   Jason Livingood 
   Comcast Cable Communications 
 
 
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   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 
     
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