ENUM Working Group J. Livingood Internet-Draft Comcast Cable Communications Expires: July 21, 2006 R. Shockey NeuStar January 2006 IANA Registration for an Enumservice Containing PSTN Signaling Information draft-ietf-enum-pstn-03 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on July 21, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document registers the Enumservice type "pstn" and subtype "tel" using the URI scheme 'tel', as well as the subtype " sip" using the URI scheme 'sip' as per the IANA registration process defined in the ENUM specification, RFC 3761. This Enumservice is used to facilitate the routing of telephone calls in those countries where Number Portability exists. Livingood & Shockey Expires July 21, 2006 [Page 1] Internet-Draft PSTN Enumservice January 2006 Table of Contents 1. Terminology....................................................2 2. Introduction...................................................2 3. Distribution of Data...........................................4 4. ENUM Service Registration for PSTN.............................4 4.1 ENUM Service Registration for PSTN with Subtype "tel"......4 4.2 ENUM Service Registration for PSTN with Subtype "sip"......5 5. Examples.......................................................6 5.1 Example of a Ported Number, Using a 'tel' URI Scheme.......6 5.2 Example of a Ported Number, Using a 'sip' URI Scheme.......6 5.3 Example of a Non-Ported Number, Using a 'tel' URI Scheme...6 5.4 Example of a Non-Ported Number, Using a 'sip' URI Scheme...6 5.5 Example Using a Regular Expression.........................7 6. Implementation Recommendations.................................7 6.1 Call Processing When Multiple Records Are Returned.........7 6.2 NAPTR Configuration issues.................................7 7. Example of E2U+pstn in Call Processing.........................8 7.1 Dialed Number Not Available On-Net.........................8 7.2 Dialed Number Available On-Net and on the PSTN.............8 8. Security Considerations........................................8 9. IANA Considerations............................................9 10. Acknowledgements..............................................9 11. References....................................................9 11.1 Normative References......................................9 11.2 Informative References...................................10 Authors' Addresses...............................................11 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 [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 Livingood & Shockey Expires July 21, 2006 [Page 2] Internet-Draft PSTN Enumservice January 2006 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. Number Portability allows telephone subscribers to keep their telephone numbers when they change service provider, move to a new location, or change the subscribed services [15]. In many countries, such as the United States and Canada, the functions of naming and addressing on the Public Switched Telephone Network (PSTN) have been abstracted. In the case of a ported number, the dialed number is not directly routable on the PSTN and must be translated into a routing number for call completion. Other numbers, which are not ported, and which can be routed directly on the PSTN based on the dialed number, are typically assigned to carriers and other entities in large blocks or pools. Number Portability and other numbering information is distributed in a variety of methods and formats around the world. The Enumservices described here could enable service providers to place ported, pooled, and blocks of numbers and their associated PSTN contact information, into externally available or highly locally cached ENUM databases. This, in turn, could enable such parties to consolidate all telephone number lookups in their networks into a single ENUM lookup, thereby simplifying call routing and network operations, which would then result in either an on-net, or IP-based response, or off-net, PSTN-based response. It is conceivable that being able to query for this information in ENUM databases could significantly reduce or eliminate the need for these parties to maintain traditional query gateways, applications, and protocols in their networks, such as those Signaling System 7 (SS7), Transaction Capabilities Application Part (TCAP), and Signaling Transport(SIGTRAN). The following Enumservice is registered with this document: "pstn" to indicate PSTN routing data, including number portability data, non- ported telephone number data (individually or in number blocks), and other PSTN-oriented data that is associated with E.164 telephone numbers. The purpose of this Enumservice is to describe information about telephone numbers which cannot be used on the public Internet or a private/peered Internet Protocol (IP) network. Thus, these are numbers which are only reachable via the traditional PSTN. The service parameters defined in RFC 3761 dictate that a "type" and a "subtype" should 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. Livingood & Shockey Expires July 21, 2006 [Page 3] Internet-Draft PSTN Enumservice January 2006 When only one URI scheme is associated with a given service, it should be assumed that an additional URI scheme to be used with this service may be added at a later time. Thus, the subtype is needed to identify the specific Enumservice intended. In this document, two URI schemes are specified. The first is 'tel:', as specified in RFC 3966 [9], and as further specified with number portability data in Number Portability Parameters for the "tel" URI, draft-ietf-iptel-tel-np-08 [10] and 'sip:', as specified in RFC 3261 [11]. 3. Distribution of Data The distribution of number portability data is often highly restricted either by contract or regulation of a National Regulatory Authority (NRA), therefore NAPTR records specified herein may or may not be part of the e164.arpa DNS tree. The authors believe that it is more likely that these records will be distributed on a purely private basis. 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), (b) openly available or, (c) distributed by the relevant number portability organization or other industry organization, but possibly on a national basis and subject to or in accordance with national regulatory policy. If such data was distributed nationally, the national telephone numbering authority, or some other regulatory body or numbering organization, may have jurisdiction. Such a body may choose to restrict distribution of the data in such a way that it may not pass over that country's national borders. How number portability data is collected and distributed is out of scope of this document. 4. ENUM Service Registration for PSTN 4.1 ENUM Service Registration for PSTN with Subtype "tel" Enumservice Name: "pstn" Enumservice Type: "pstn" Enumservice Subtype: "tel" URI Schemes: 'tel:' Functional Specification: Livingood & Shockey Expires July 21, 2006 [Page 4] Internet-Draft PSTN Enumservice January 2006 These Enumservices indicate that the remote resource identified can be addressed by the associated URI scheme in order to initiate a telecommunication session, which may include two-way voice or other communications, to the PSTN. Security Considerations: See Section 9. Intended Usage: COMMON Authors: Jason Livingood and Richard Shockey (for author contact detail see Authors' Addresses section) Any other information the author deems interesting: None 4.2 ENUM Service Registration for PSTN with Subtype "sip" Enumservice Name: "pstn" Enumservice Type: "pstn" Enumservice Subtypes: "sip" URI Schemes: 'sip:' Functional Specification: These Enumservices indicate that the remote resource identified can be addressed by the associated URI scheme in order to initiate a telecommunication session, which may include two-way voice or other communications, to the PSTN. Security Considerations: See Section 9. Intended Usage: COMMON Authors: Jason Livingood and Richard Shockey (for author contact detail see Authors' Addresses section) Any other information the author deems interesting: None Livingood & Shockey Expires July 21, 2006 [Page 5] Internet-Draft PSTN Enumservice January 2006 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 Ported Number, Using a 'tel' URI Scheme $ORIGIN 3.1.8.7.1.8.9.5.1.2.1.e164.arpa. NAPTR 10 100 "u" "E2U+pstn:tel" "!^.*$!tel:+1-215-981-7813;npdi;rn=+1-215-555-1212!". In this example, a Routing Number (rn) and a Number Portability Dip Indicator (npdi) are used as shown in draft-ietf-iptel-tel-np-08 [10]. The 'npdi' field is included in order to prevent subsequent lookups in legacy-style PSTN databases. 5.2 Example of a Ported Number, Using a 'sip' URI Scheme $ORIGIN 3.1.8.7.1.8.9.5.1.2.1.e164.arpa. NAPTR 10 100 "u" "E2U+pstn:sip" "!^.*$!sip:+1-215-981-7813;npdi;rn=+1-215-555-1212 @gw.example.com;user=phone!". In this example, a Routing Number (rn) and a Number Portability Dip Indicator (npdi) are used as shown in draft-ietf-iptel-tel-np-08 [10]. The 'npdi' field is included in order to prevent subsequent lookups in legacy-style PSTN databases. The method of conversion from a tel to a SIP URI is as demonstrated in RFC 3261, Section 19.1.6 [11], as well as in , draft-ietf-iptel-tel-np-08 Section 6 [10]. 5.3 Example of a Non-Ported Number, Using a 'tel' URI Scheme $ORIGIN 3.1.8.7.1.8.9.5.1.2.1.e164.arpa. NAPTR 10 100 "u" "E2U+pstn:tel" "!^.*$!tel:+1-215-981-7813;npdi!". In this example, a Number Portability Dip Indicator (npdi) is used [10]. The 'npdi' field is included in order to prevent subsequent lookups in legacy-style PSTN databases. 5.4 Example of a Non-Ported Number, Using a 'sip' URI Scheme $ORIGIN 3.1.8.7.1.8.9.5.1.2.1.e164.arpa. NAPTR 10 100 "u" "E2U+pstn:sip" "!^.*$!sip:+1-215-981-7813;npdi@gw.example.com;user=phone!". Livingood & Shockey Expires July 21, 2006 [Page 6] Internet-Draft PSTN Enumservice January 2006 In this example, a Number Portability Dip Indicator (npdi) is used [10]. The 'npdi' field is included in order to prevent subsequent lookups in legacy-style PSTN databases. The method of conversion from a tel to a SIP URI is as demonstrated in RFC 3261, Section 19.1.6 [11], as well as in , draft-ietf-iptel-tel-np-08 Section 6 [10]. 5.5 Example Using a Regular Expression $ORIGIN 3.1.8.7.1.8.9.5.1.2.1.e164.arpa. NAPTR 10 100 "u" "E2U+pstn:tel" "!(^.*)$!tel:\1;npdi!". In this example, a regular expression replacement function is used to reduce the size of the NAPTR record. The tel URI uses "\1" which would dynamically replace the expression with the TN plus the leading "+", in this case +1-215-981-7813. 6. Implementation Recommendations 6.1 Call Processing When Multiple Records Are Returned It is likely that that both E2U+sip and E2U+pstn Enumservice type records will be returned for a given query. In this case, this could result in what is essentially an on-net and off-net pstn record. Thus, one record gives the associated address on an IP network, while the other gives the associated address on the PSTN. 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. For example, such a resolver could be configured to grant preference to the on-net record, or execute other logic as required by the application. 6.2 NAPTR Configuration issues It has been suggested that tel URIs may be easier and more efficient to use in practice than SIP URIs. In addition, the use of tel URIs may result in somewhat smaller NAPTR records which, when considering adding hundreds of millions of these records to the DNS, could have a substantial impact on the processing and storage requirements for service providers or other entities making use of this Enumservice type. 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. Livingood & Shockey Expires July 21, 2006 [Page 7] Internet-Draft PSTN Enumservice January 2006 Using the Section 5.5 example from above, this is 11 bytes per record. 7. Example of E2U+pstn in Call Processing This is an example of how a switch, proxy, or other calling application may make use of this Enumservice type during the call initiation process. 7.1 Dialed Number Not Available On-Net a) A user, which is connected to a calling application, dials an E.164 telephone number: +1-215-981-7813. b) The calling application uses the dialed number to form a NAPTR record: 3.1.8.7.1.8.9.5.1.2.1.e164.arpa. c) The DNS finds an E2U+pstn:tel record and returns a tel URI for processing by the calling application: tel:+1-215-981- 7813;npdi. d) The calling application uses routing logic to determine which media gateway is the closest to this number and routes the call appropriately. 7.2 Dialed Number Available On-Net and on the PSTN a) A user, which is connected to a calling application, dials an E.164 telephone number: 1-215-981-7813. b) The calling application uses the dialed number to form a NAPTR record: 3.1.8.7.1.8.9.5.1.2.1.e164.arpa. c) The DNS finds both an E2U+pstn record, as well as an E2U+sip record, since this number happens to be on the IP network of a connected network. d) The calling application prioritizes the on-net record first: sip:+1-215-981-7813;npdi@gw.example.com;user=phone. e) The calling application sets up the SIP call to gw.example.com. f) Should the IP call route fail for whatever reason, the calling application may be able to utilize the E2U+pstn record to invoke a fallback route to a media gateway that is connected to the PSTN. 8. 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 PSTN 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. Livingood & Shockey Expires July 21, 2006 [Page 8] Internet-Draft PSTN Enumservice January 2006 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. 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, 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]. 9. IANA Considerations This document registers the 'pstn' 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 sections 3 and 4 of this document. 10. Acknowledgements The authors wish to thank Lawrence Conroy, Tom Creighton, Jason Gaedtke, Jaime Jimenez, Chris Kennedy, Alexander Mayrhofer, Doug Ranalli, Jonathan Rosenberg, Bob Walter, and James Yu for their helpful discussions of this topic, and detailed reviews of this document. The authors also wish to thank the IETF's ENUM Working Group for helpful feedback in refining and developing this draft. 11. References 11.1 Normative References Livingood & Shockey Expires July 21, 2006 [Page 9] Internet-Draft PSTN Enumservice January 2006 [1] Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)", RFC 3761, April 2004. [2] ITU-T, "The International Public Telecommunication Number Plan", Recommendation E.164, May 1997. [3] Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES", RFC 1034, November 1987. [4] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Three: The Domain Name System (DNS) Database", RFC 3403, October 2002. [5] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part One: The Comprehensive DDDS", RFC 3401, October 2002. [6] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Two: The Algorithm", RFC 3402, October 2002. [7] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Four: The Uniform Resource Identifiers (URI)", RFC 3404, October 2002. [8] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Five: URI.ARPA Assignment Procedures", RFC 3405, October 2002. [9] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966, December 2004. [10] Yu, J., "Number Portability Parameters for the "tel" URI", draft-ietf-iptel-tel-np-08, December 2005. [11] Rosenberg, J., et al., "SIP: Session Initiation Protocol", RFC 3261, June 2002. 11.2 Informative References [12] Bradner, et al., "IANA Registration for Enumservices email, fax, mms, ems and sms", draft-ietf-enum-msg-05.txt, May 2005. [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. Livingood & Shockey Expires July 21, 2006 [Page 10] Internet-Draft PSTN Enumservice January 2006 [16] Peterson, J., "enumservice Registration for Session Initiation Protocol (SIP) Addresses-of-Record", RFC 3764, April 2004. Authors' Addresses Jason Livingood Comcast Cable Communications 1500 Market Street Philadelphia, PA 19102 USA Phone: +1-215-981-7813 Email: jason_livingood@cable.comcast.com Richard Shockey NeuStar 46000 Center Oak Plaza Sterling, VA 20166 USA Phone: +1-571-434-5651 Email: richard.shockey@neustar.biz Intellectual Property and Copyright Statements Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary Livingood & Shockey Expires July 21, 2006 [Page 11] Internet-Draft PSTN Enumservice January 2006 rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Livingood & Shockey Expires July 21, 2006 [Page 12]