ITU - Telecommunication Standardization Sector        Temporary Document 1/2-32

WORKING PARTY 1/2    Original :  English

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Berlin, 19 - 26 October 2000

                       

Question(s)1/2

 

SOURCE*:              ITU General Secretariat

TITLE:                   Proposed course of collaboration between IETF and ITU regarding ENUM

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Contribution to Study Group 2 on ENUM

ITU Strategies and Policy Unit

October 2000

1     INTRODUCTION

This contribution discusses the recently finalized ENUM protocol and summarizes discussions between the Chairman of Study Group 2, ITU Secretariat staff and the Internet Architecture Board (IAB) concerning a proposed course of collaboration between the IETF and the ITU, specifically with ITU-T Study Group 2, to facilitate deployment of ENUM services.

2         THE ENUM PROTOCOL

The ENUM protocol is the result of work of the Internet Engineering Task Force's (“IETF's”) Telephone Number Mapping working group^[1]. The charter of the ENUM group was to define a Domain Name System (“DNS”)-based architecture and protocol for mapping an E.164 telephone number^[2] to what are known as Uniform Resource Identifiers (“URIs”).^[3] A relatively stable standards-track version of the ENUM protocol has recently been published as RFC 2916^[4]. URIs are strings of characters that identify resources such as documents, images, files, databases, email addresses or other resources or services in a common structured format. The most commonly known types of URIs are Uniform Resource Locators (“URLs”) which are used to locate resources using the World Wide Web. For example, http://www.itu.int/infocom/enum/ is the URL for the ITU web site providing an overview of ENUM activities. The Internet Assigned Numbers Authority (“IANA”) , now part of the Internet Corporation for Assigned Names and Numbers (“ICANN”), maintains a list of standardized URL prefix schemes such as ‘http’, ‘ftp’, and ‘mailto’.^[5]

The ENUM protocol uses Naming Authority Pointer (“NAPTR”) DNS resource records defined in RFC 2915^[6] in order to identify available methods or services for contacting a specific node identified through an E.164 number. The ENUM protocol defines and uses a specific type of NAPTR service with the mnemonic “E2U” (E.164 to URI resolution).

The result of a query can be one or more URIs with their order of processing and preference indicated though NAPTR record fields. These URIs can be used to reference resources or services associated with the E.164 number (e.g., associated fax number, mail address, GPS coordinates, mobile number, phone redirection services, unified messaging services, voice mail, user’s public key for asymmetric encryption applications, etc.). Indeed, one of the exciting possibilities of ENUM is the potential for creative E.164-based lookup services.

3     How are E.164 numbers mapped into the DNS?

ENUM services are looked up through a one-to-one corresponding reverse mapping of digits in an E.164 number into separate DNS “zones”. The user interface to this reverse mapping and lookup are performed through application software.

The IAB has recommended that the top level of the corresponding DNS structure for ENUM be “e164.arpa”.^[7] The justification cited is that .arpa (Address and Routing Parameters Area) is a top level domain to be used for Internet infrastructure purposes.

As an example, lets construct the related DNS zone to look up NAPTR resource records associated with the E.164 number +33 1 40 20 51 51 that corresponds to the information desk at the Louvre Museum in Paris, France:

Write the E.164 number in its full form, including the country code, then remove all non-digit characters with the exception of the leading “+”.

Example: +33140205151

Remove all characters with the exception of the digits and put dots (“.”) between each digit. 

Example: 3.3.1.4.0.2.0.5.1.5.1

Reverse the order of the digits and, considering the recommendation of the IAB, append the string “.e164.arpa” to the end. 

Example: 1.5.1.5.0.2.0.4.1.3.3.e164.arpa

The client application can now perform the lookup and, as an example, retrieve a corresponding fax number, email address, or voice mail redirection service for +33 1 40 20 51 51.

4     Implications for IP Telephony

One particular application of ENUM deserves special mention: IP telephony.^[8] Although much technical Voice over IP (“VoIP”) standards work has been done in the ITU-T and IETF on voice gateways (e.g., H.323, SIP) and call agents (e.g., media gateway controllers such as H.248/Megaco, MGCP), one of the remaining challenges is integration of addressing systems between E.164 numbers used in the PSTN and DNS or IP addresses. ENUM can potentially provide this mapping between distinct addressing systems (e.g., mapping an E.164 number to a SIP URI). However, a global administrative framework is necessary to secure consistency of mapping between the E.164 dial plan and the parallel DNS structure needed in ENUM.

In discussions with the IAB and IESG, there is common agreement that it is of fundamental importance that an integrated global dialing plan exists. Therefore, the same E.164 number would reach a subscriber regardless of whether VoIP or PSTN network technology is used. Indeed, the concept of “technology neutrality” suggests that any global numbering plan should be abstracted as much as possible from underlying lower layer technologies.

5         The Historical DNS and Numbering Plan Context

The ITU Secretariat has had a multi-year involvement in issues related to the management of Internet domain names and addresses. The role of the ITU Secretariat staff is to represent the ITU Secretary-General, who is instructed to take an active part in the international discussions and initiatives on the management of Internet domain names and addresses according to ITU Plenipotentiary Resolution 102 (Minneapolis 1998).^[9] Since then, the ITU Secretary-General has reported yearly on its activities to the ITU Council, principally with regard to its roles in ICANN. His most recent report to Council 2000^[10] briefly outlines some of the contentious history  related to the DNS and indicates some of the issues that remain outstanding. Historically, especially because of the economic stakes involved, one of the most problematic issues has been numerous claims to rights or ownership over various zones in the DNS. These include various claims of private rights or ownership over both generic and geopolitical “country code” top level domains (i.e., based on the ISO 3166-1 Standard). Debates over the latter have been one of the focus activities of ICANN’s Government Advisory Committee (“GAC”) and have still eluded satisfactory resolution.

To those involved in regulatory or policy making initiatives related to telecommunications liberalization and its implications in changes to numbering or addressing schemes, these problems may sound somewhat familiar. Once regarded as an obscure and rather uninteresting technical aspect of networks, naming, numbering and addressing have now emerged as an important aspect of telecommunications policy. There is good reason: control of the issuing of the names and addresses effectively is often control of communications systems.

In general, policy makers are concerned with balancing the needs of the consumers with the needs of the industry. In a liberalized environment they must also serve as an intermediary between competing industry interests for control over addressing resources. Recent regulatory trends (e.g., number portability, the establishment of independent regulators as called for in the WTO telecoms agreements) have forced numbering into the public consciousness and required policy makers to make much more difficult decisions. As the strategic importance of numbering and addressing grows, policy makers have responded by taking control away from service providers and administering it directly or contracting it out under neutral regulatory oversight. The 1999 ITU Regulatory Survey among its Member States showed that responsibility for numbering plans is now distributed rather evenly across Ministries, Regulators, and Operators. However, countries with privatized telecommunication operators, almost always give regulatory bodies control of numbering plans, especially in liberalized countries. In these situations, the regulator is expected to play a coordinating role and to guarantee equity and transparency in number and addressing allocation procedures.

Because E.164 numbers typically start with “country codes”, they implicitly or explicitly have implications of sovereignty which, in turn, is often associated with national legislation related to telecommunications market liberalization. A few examples include consumer protection (e.g., anti-slamming), public interest (e.g., emergency services) and pro-competitive initiatives (e.g., number portability). Therefore, it seems appropriate that national or integrated numbering plan policy makers at a “country code” level decide how ENUM services shall be handled or delegated in their corresponding DNS zones. It should be pointed out that the DNS zone structure makes it possible to further sub-delegate administrative or operational responsibilities for ENUM zones at lower levels (e.g., at the area code level for regions with integrated numbering plans).

At the e164.arpa level, a global administrative framework is also necessary to assure global consistency of mapping between the E.164 dial plan and the parallel DNS structures. This suggests that the principles defined in ITU-T Recommendations such as E.164, E.164.1 and E.190 also be applied to reservation and assignment of DNS zones at the “country code” level and that there be close coordination with the actual operation of these DNS zones to maintain synchronization. In fact, RFC 2916 (defining the ENUM protocol) explicitly suggests this and states that ENUM zones should be allocated hierarchically and assigned in accordance with E.164. The corresponding procedures are likely to require additional standardization work developed in cooperation with parties responsible for E.164 resource management. Finally, it should be mentioned that in the case of some E.164 numbering resources at a global level (e.g., UIFNs), ITU as a registrar of these numbering plans is directly concerned.

6         The Joint View Forward

Recognizing that the intersection of the E.164 dial plan and the DNS could result in difficult administrative, policy and operational issues, the Chairman of Study Group 2 and ITU Secretariat staff have had extensive discussions with the Internet Architecture Board (IAB) and the Internet Engineering Steering Group (IESG) related to deployment of ENUM protocol-based services and how further collaboration can be accomplished. These discussions have resulted in the following base set of common understandings that they suggest guide further work involving Study Group 2, namely:

a)      that it is fundamentally important that an integrated dialing plan exist whether VoIP or the PSTN networks technology is used;

b)      that conflicts over claims to ownership or rights over DNS zones that result from the mapping of E.164 to the DNS, as envisioned in ENUM, should be avoided;

c)      that sovereignty concerns, as reflected in ITU-T Recommendations E.164, E.164.1 and E.190 be fully recognized in assignment of related top level ENUM DNS zones;

d)      that ENUM service providers cooperate with public numbering plan administrative and policy frameworks;

e)      that ENUM zone allocation and assignment at the “country code” level parallel ITU’s policy and administrative framework for current E.164 reservations and assignments;

f)        that operational matters for e164.arpa and immediate zones under e164.arpa be separated from policy or administrative oversight;

g)      that the current cooperation between the IETF and ITU with regard to the administrative,  policy and operational issues for ENUM be continued;

h)      that a division of responsibilities between the IETF and ITU with regard to ENUM be developed in cooperation with Study Group 2 and defined in a written agreement between the IAB and ITU;

i)        that the ITU cooperate with the IAB on mutually satisfactory operational responsibilities for the e164.arpa and immediate zones under e164.arpa respecting the common understandings above.

 

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