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ICANN Yokohama Meeting Topic -Introduction of New Top-Level Domains: Expression of Interest #8

Posted: 9 July 2000

NetNumber Statement of Interest

".tel" gTLD

Top Level Domain For Internet-Telephony Applications

Table of Contents

1. Abstract

2. Self-Identification

3. Purpose for the new gTLD

4. System Description

4.1 Directory Locator Service (DLS / gTLD)

4.2 The TEL Domain Name Space

4.3 TEL Domain Name Resolution

4.4 Authoritative Directory Service (ADS)

5. TEL Domain Name Registration

5.1 gTLD Registration Process

6. Conflict Resolution Process

7. Formal Proposal

1. Abstract

This document is to declare NetNumbers Interest in becoming the Registry for a special purpose gTLD called tel. A holistic directory system is described which translates a standard telephone number into the Internet address information required to support IP-enabled communications applications such as real-time voice, voice-messaging, fax or unified-messaging. Described herein is the architecture of a Global Internet-Telephony Directory (GITD) system positioned as a new gTLD called "tel". The GITD is the outgrowth of a three-year technology development, intellectual property and standards body effort launched by the NetNumber team in early 1997. The GITD has been deployed and is fully operational today under the sub-domain Integration discussions and joint development activities are underway with multiple Internet-Telephony technology vendors interested in leveraging the GITD to translate telephone numbers into Internet addresses. For more information see For questions regarding this document please send email to .

2. Self-Identification

NetNumber is a Delaware corporation with corporate offices located in Lowell, Massachusetts. Network based directory services provided by NetNumber include the "Global Internet-Telephony Directory" and the "Virtual Private LDAP Directory"    

3. Purpose for the new gTLD

The purpose of the "tel" gTLD is to provide a global system for translating telephone numbers into the Internet address information necessary to support all forms in Internet-Telephony applications. A serious impediment to the development and acceptance of Internet-Telephony services is the different addressing schemes employed by the Public Switched Telephone Network (PSTN) and the Internet. A global directory service that enables the translation of a PSTN telephone number into a corresponding Internet address eliminates this impediment. The precise nature and structure of such a directory has been the object of considerable speculation, research and discussion. A number of companies, technical groups, industry organizations and standards bodies have made contributions to this effort.

Telephone numbers follow a well-defined format. Therefore, translating a telephone number into an Internet address is a rather straightforward task. However, complexities emerge as the concept is expanded globally and extended to include multiple Internet-Telephony service providers, each providing different services tied to the same telephone number.

The Global Internet-Telephony Directory (GITD) system proposed herein utilizes the Internet Domain Name System within a two-tier logical control model to translate a telephone number into an application specific Internet Address.

4. System Description

The system proposed herein utilizes DNS within a two-tier control model to translate a telephone number into an application specific Internet Address. The first-tier is a "Directory Locator Service" (DLS) that maps a telephone number into the IP address of a second-tier authoritative directory. The second-tier is an "Authoritative Directory Service" (ADS) that translates a number into an application specific Internet address.

4.1 Directory Locator Service (DLS / gTLD)

The DLS provides the high-level function of referring a requesting Internet-Telephony application to the Authoritative Directory Service (ADS) containing the desired Internet address information associated with a telephone number. The DLS has been designed as a global resource for the entire Internet-Telephony industry and as such, is an ideal candidate for an Internet Domain Name System "Top Level Domain" (gTLD).

Following conventions observed with all existing top-level domains, (i.e., .com, .net, .org, etc.) the DLS utilizes Name Server (NS) records and associated A records to delegate authority to subordinate Name Servers. This system allows an Internet-Telephony application or platform to iteratively access a hierarchy of DNS name servers until the desired resource record information is found or until the search is exhausted.

A Directory Locator Service defined as a DNS top-level domain offers several advantages:

1.      A top-level Internet domain is a global resource that operates under a well-defined regulatory and operational structure.

2.      Through the use of standard DNS resolution, a single query is sufficient to locate the desired Internet address information.

4.2 The TEL Domain Name Space

The "tel" domain name space is a special purpose domain that follows a well-defined structure regarding ownership/control of names and a well-defined structure regarding valid sub-domains. Sub-domains of "tel" may not be arbitrarily defined; rather they are defined in accordance with the ITU E.164/I.331 standard that defines the global standard for valid telephone numbers.

A standard telephone number consists of a country code and a nationally specific part. For reasons of scalability, reliability and flexibility, the "tel" domain name space will be partitioned into a number of zones distributed across multiple name servers. The segmentation of a telephone number into a country code and a nationally specific part, with the latter further segmented by area-code/city-code, presents natural boundaries for such partitioning.

4.3 TEL Domain Name Resolution

Internet-Telephony applications query the DLS (gTLD) using a DNS query based on an application specific telephone number domain name. The following steps define its formulation:

1. Start with a complete telephone number.

Example: +1-603-362-4315

2. Remove all characters other than digits.

Example: 16033624315

3. Reverse the order of the phone number.

Example: 51342633061

4. Insert a "." between each digit and at the end.


5. Append, as a suffix, the "tel" top-level domain.


6. Append, as a Prefix, a "Service Protocol" name indicative of the desired service. (Examples: sip, h323, smtp, vpim, etc.)


When a client DNS resolver queries the gTLD, the DLS returns the NS- and A-records which define the IP address of the next DNS name server. Upon receipt of the NS and A records from the DLS, the client resolver reissues the query to the newly discovered name server.

The following illustrates a sample zone file fragment containing NS and A records: IN NS



4.4 Authoritative Directory Service(ADS)

The ADS provides authoritative Internet address information in support of one or more Internet-Telephony applications associated with a subset of numbers. The ADS is a delegated DNS name server that must be properly registered with the gTLD.

The ADS will return one of the following results based on a query using an application specific "tel" domain name.

1.      An end-point address in the form of a URI. For example, real-time voice applications using the SIP protocol or unified-messaging applications using the SMTP protocol would receive the following:





2.      A referral to a non-DNS service in the form of a URI. For example, voice messaging applications requiring spoken name will utilize a referral to an LDAP directory:


Result: ldap://,dc=tel

3.      The NS-records and associated A-records for a delegated ADS that contains the URI for the requested application. This ADS delegation feature enables control over various Internet-Telephony applications tied to the same telephone number to be delegated out to different service providers.

4.      A negative response. Indicates that no Internet address information exists for the specific application queried.

Note: An effort is underway within the IETF to define a standard for a generic DNS query based on a telephone number that will return a full list of supported Internet addresses tied to that particular number. (SIP, H323, SMTP, VPIM, etc.). NetNumber is an active participant in the IETF process. The GITD will be updated to incorporate this additional generic query capability once a standard has been defined.

5. TEL Domain Name Registration

The creation and eventual assignment of telephone numbers to end-users "Subscribers" (individuals or corporations) is a well-defined process that exists within the PSTN today. The registration of numbers in the Global Internet-Telephony Directory is complimentary to this existing process and takes place only after a PSTN Carrier has assigned a telephone number to a Subscriber.

Following the current practice with all Internet top-level domains, a single trusted "Registry" will manage the registration of telephone numbers in the DLS. It is assumed that this exclusive Registry function will fall under the regulatory control of ICANN and operated by NetNumber. The actors involved in the registration process are as follows:

DLS Registry (NetNumber):

        Deploys and operates the globally distributed DLS service.

        Builds, deploys and maintains the DLS registration service for use by all ADS Registrars.

        Manages the DLS "Conflict Resolution Process".

ADS Registrar (Corporation, Service Provider or existing ICANN Registrar)

        Deploys and operates an ADS as a service to Registrants who want to register their telephone numbers and associated Internet address information.

        Registers telephone numbers in the DLS via a secure DLS Registry update service.

Registrant: (Telephone Number Subscriber)

        Telephone number Subscriber or designated representative that claims day-to-day control over a number and registers that number in the "tel" gTLD through a Registrar.

5.1 gTLD Registration Process

1.      A Registrant (telephone number subscriber or designated service provider representative) registers one or more telephone numbers and associated Internet addresses with a Registrar. Registrant is responsible for having day-to-day control over the telephone numbers registered.

2.      The Registrar updates the top-level DLS via a secure update service operated by the Registry. (A bulk load DLS update API and a real-time DLS update API have already been developed and deployed for the GITD)

3.      The Registry checks the Registrants numbers against the list of existing registered numbers to determine if a conflict exists over control of the number(s). If no conflict exists, the registration is approved. If a conflict exists, the DLS Registry contacts the two parties that have both claimed to be the valid Subscribers for the same number to resolve the conflict.

4.      DLS Registry makes Registrant name, address, and contact information freely available via an on-line Who-is database.

6. Conflict Resolution Process:

Conflict over the registration of telephone numbers in the top-level DLS (gTLD) can occur for one of three general reasons:

        Data Entry Error: Registrant makes a data entry error during the registration process and inadvertently registers a wrong number with a Registrar.

        Old Data Error: Registrant returns day-to-day control over one or more numbers to the originating PSTN carrier that issued the numbers but fails to update their Registrar. Example: A corporation shuts down an office, terminates its phone service but fails to un-register the numbers with their Registrar.

        Intentional Error: Registrant intentionally claims to be the Subscriber that has day-to-day control over a number when in fact they are not.

Conflict occurs when two Registrants both claim to be the valid Subscriber for the same number. Conflict over ownership of a name or number in the Internet naming space is not a new problem. In the domain name space conflict occurs when one entity registers a name like "McDonalds" in a top-level-domain ( and then another entity claims trademark control over the name "McDonalds". In the case of the "tel" domain name space, conflict can be easily resolved because it is clear how the day-to-day control of a number is defined:

        PSTN Service Provider Control: A PSTN Service Provider (telephone company) that has registered a number on behalf of a customer can certainly validate the identity of the Subscriber.

        Telephone Number Subscriber Control: A corporation or individual that has been assigned a number through the normal PSTN provisioning process is the only valid Registrant for that number. Confirmation of such assignment can be obtained through reviewing PSTN billing records.

Conflict is identified when an entity attempts to register a number that has already been registered by another Registrant. The burden of maintaining a system for resolving conflict in an orderly process falls on the DLS Registry. The current GITD conflict resolution process operates under the following principles:

        Cost of resolution should be born by the mistaken party: Registrants are expected to take responsibility for their own mistakes. If the DLS Registry is required to take action to correct a registration mistake made by a Registrant then the mistaken party is expected to pay the direct costs associated with the resolution process.

        Cost of conflict resolution should be zero: In most cases, conflict will be the result of a simple human error. NetNumber operates under the theory that Registrants that make a data entry mistake should be given an opportunity to correct the mistake at zero cost. As a result, NetNumber operates an on-line system to identify conflicts, notify the appropriate Registrant/Registrar, and enable on-line corrections. In the event that the entire process can be managed via an automated on-line process and resolved in a reasonable period of time then the cost to all parties is zero.

        Billing records can be used to clarify difficult conflicts: In the most difficult case where two entities claim control over a number and the conflict cannot be resolved through an automated system, billing records can be used to clarify day to day control over a number. Extended conflict like this is likely to be rare, particularly in light of the provision that the mistaken party is required to pay the direct cost of conflict resolution under this model.

7. Formal Proposal

NetNumber has already deployed assets and is currently operating the Global Internet-Telephony Directory system described herein under the sub-domain NetNumbers likelihood of creating a formal proposal to ICANN for this TEL gTLD is 100%.

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