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Global Standardization Activities

Vol. 20, No. 1, pp. 96–101, Jan. 2022.

Report on ITU-T SG2 Standardization of Telecommunication Numbering

Koji Isshiki


The Working Party (WP) 1 of the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Study Group 2 has been engaged in the allocation and management of international telecommunication numbering, naming, addressing, and identification resources. Due to the recent migration to Internet Protocol networks and the rapid development and globalization of Internet-of-Things services and over-the-top services, the issues have been diversified. Since the problems of fraud by spoofing by telecommunication number misuse have increased, it has become an urgent topic for discussion. In the WP2, they discuss the issues concerning network management.

This article mainly reports on the telecommunication numbering and identifications studied in WP1, subjected by the World Telecommunication Standardization Assembly Resolutions.

Keywords: telecommunication numbering, IoT numbering, number spoofing


1. WTSA Resolutions on telecommunication numbering and identification

World Telecommunication Standardization Assembly (WTSA) is the primary meeting of the International Telecommunication Union Telecommunication Standardization Sector ( ITU-T), and its output, WTSA Resolutions, give direction of the activities of ITU-T. Resolution 2 defines the responsibilities and obligations of each Study Group (SG) and the other Resolutions are materialized further and mapped to the studies in each SG. The following are the WTSA Resolutions relevant to telecommunication numbering and identifications discussed in SG2 Working Party (WP) 1 [1].

Extraction of WTSA Resolutions relevant to telecommunication numbering and identifications
  • Resolution 20: Procedures for allocation and management of international telecommunication numbering, naming, addressing, and identification resources
  • Resolution 29: Alternative calling procedures on international telecommunication networks
  • Resolution 49: ENUM*
  • Resolution 60: Responding to the challenges concerning the evolution of the identification/numbering system and its convergence with Internet Protocol (IP)-based systems/networks
  • Resolution 61: Countering and combating misappropriation and misuse of international telecommunication numbering resources
  • Resolution 64: IP address allocation and facilitating the transition to and deployment of IPv6
  • Resolution 65: Calling party number delivery, calling line identification, and origin identification information
  • Resolution 70: Telecommunication/information and communication technology accessibility for persons with disabilities
  • Resolution 88: International mobile roaming
  • Resolution 91: Enhancing access to an electronic repository of information on numbering plans published by the ITU-T
  • Resolution 98: Enhancing the standardization of Internet of Things (IoT) and smart cities and communities for global development
* ENUM: E.164 Number Mapping; the framework of mapping of IP address and telecommunication number.

2. Issues under study in SG2 WP1

Issues with telecommunication numbers and identifications under study in ITU-T SG2 WP1 are diversifying and categorized into items (1) to (15) listed in the next subsection. Figure 1 shows the subdivision of these individual issues and their relation to the WTSA Resolutions. The issues concerning (1) the allocation of international numbers for IoT and (4) the status of optimizing the use of numbers that are actively discussed are introduced in Section 3. Section 4 presents a list of the recommendations, including some drafts, based on the studies of the issues.

Categorization of the studies in SG2

(1) Allocation of IoT international numbers, (2) Allocation of international mobile subscriber identity (IMSI) for mobile subscriber identification, (3) Global number for humanitarian services, (4) Optimization of number usage, (5) Maintenance of existing ITU-T E-series numbering-related Recommendations, (6) Efficient procedure of international numbers, (7) Number portability, (8) International interworking, (9) ENUM, (10) Issues with national numbering, (11) Revenue from International Numbering Resources (INR), (12) Input to WTSA20, (13) IPv6, (14) Disaster recovery, (15) Coordination with regional organization.

Fig. 1. Mapping of SG2 studies and WTSA Resolutions.

3. Active issues

Even though the issues are diversifying due to the recent migration to IP networks and the rapid development and globalization of IoT and over-the-top (OTT) services, the items actively discussed most for standardization are the studies on the proper use of telecommunication numbers. The issues with IoT numbering have also been high priority for discussion. The status of the two studies are introduced on the basis of the results from the 9th meeting held from May 31 to June 11, 2021.

3.1 Optimization of number usage

The items being actively discussed most for standardization are the studies on the proper use of telecommunication numbers.

3.1.1 Approval of the revised recommendation (E.157): International calling party number delivery

Since the background has enhanced to include the services on the Internet and OTT, which are beyond the current basis of public switched telephone networks and public land mobile networks, the discussion regarding the revised E.157: International calling party number delivery in the meeting has diversified due to the opinions regarding scope, level of details, degree of obligation, etc. The editor of the UK then elaborated to coordinate the group and brought the solution with agreement to edit the recommendation, i.e., removing the section of preventing individual cases of spoofing to the separate technical report based on the general principles.

3.1.2 Consent of TR.spoofing

As mentioned in 3.1.1, countering spoofing is a new item separated from E.157 describing the methods of preventing individual cases of spoofing. It covers the mechanism of number spoofing caused by SIM (subscriber identification module) boxes etc., internationally carried out by OTT operators, and STIR/SHAKEN (Secure Telephony Identity Revisited/Signature-based Handling of Asserted Information Using Tokens), which is being introduced in the United States as a countermeasure against number spoofing, including comparison with blockchain technology etc. Figure 2 shows an example of number spoofing in international communications.

Fig. 2. Example of number spoofing during an international call (referred from TR.spoofing).

3.1.3 Discussion on creation of technical report on Wangiri

Sudan proposed a new Work Item to create a technical report on methodologies to mitigate Wangiri fraud (i.e., a callback scam). The proposal was approved to create a new Work Item of TR.MMWF (methodologies to mitigate Wangiri fraud). Interactive voice response facility, using artificial intelligence technology, number blocking, and sharing of blacklists are being introduced for the technological method to mitigate Wangiri and number administration.

3.1.4 Discussion on OTT

As a fraudulent case associated with the use of E.164 numbers for OTT services that are deployed on the Internet, the UAE proposed to start studying countermeasures for cases in which mobile numbers and fixed numbers are used to authenticate and launch apps such as WhatsApp. It was agreed to contact the OTT application provider through the ITU Telecommunication Standardization Bureau (TSB) regarding this issue. In addition, the United States proposed to encourage WhatsApp to participate in future discussions on this matter.

3.2 Standardization of allocation of IoT international numbers

3.2.1 Background of studies on IoT numbering recommendation: E.IoT-NNAI (naming numbering addressing and identifiers)

This issue started with the UK editor as one of the major issues for this study period for the study to assign appropriate international numbers in response to the rapid increase in global IoT services.

Initially, the eCall service, which is standardizing emergency calls within Europe, is specified as a use case, and it was decided to be used as part of the international service number (E.164-number for global services) applied to universal personal telecommunication (UPT) services. It is regarded that the 878 number allocated for the global mobility services as UPT services will be appropriate usage for IoT since the usage of the number is currently still low. However, the roaming of the existing national mobile number (E.164-number for geographic areas) and international network numbers (E.164-number for networks), such as 883, have been applied for currently deployed eCall and other various global IoT services, while the studies of IoT numbers continue. Such difference in number usage also needs discussion. Figure 3 illustrates the IoT international numbers.

Fig. 3. International numbers for IoT services.

3.2.2 Draft recommendation of E.IoT-NNAI at the 9th meeting

At the 9th meeting, the following contributions were input, and the discussion will continue on the basis of the draft reflecting the inputs.

  • NTT proposed Annex-A in the draft recommendation describing the number portability of IoT services. The proposal was agreed, and the studies of carrier switching of service providers will start with this draft for the next meeting.
  • Malta proposed to include that the IoT number 878 should not be used for existing voice and short messaging services in the E.IoT-NNAI Recommendation, and it was decided to proceed with further studies.
  • Russia proposed a list of issues such as definition of terms, regulation of each field of IoT numberings, number portability, and global/domestic role of number management, and it was decided to proceed with further examination.

4. Recommendation of the output of the studies

Table 1 lists the recommendations that will be the output of the examination of various issues introduced in Section 2. The WTSA Resolutions associated with each recommendation are also listed.

Table 1. ITU-T SG2 Recommendations and relevant WTSA Resolutions.

5. Conclusion

Along with the development of telecommunication services and changes in network formats, the roles of numbers and identifiers are changing, and SG2 has a variety of activities from short-term issues that require immediate response to medium- to long-term issues. While observing these trends, we will continue to engage actively in activities such as standardization activities related to numbers and identifiers with discussions at the TTC (Telecommunication Technology Committee) Numbering Planning Expert Committee in Japan.


[1] WTSA Resolutions of ITU-T,
Koji Isshiki
Professional Staff, Network Innovation Business Headquarters, NTT Advanced Technology Corporation.
He joined NTT Advanced Technology Corporation in 2001 after he had engaged in the research and development of voice and data switching systems at research section, business section, and international business section in NTT. Since then he has been engaged in the investigation and standardization of telecommunication numbers and related technologies by attending ITU-T SG2, Internet Engineering Task Force, European Telecommunications Standards Institute (ETSI), Third Generation Partnership Project (3GPP), and CEPT ECC Working Group Numbering and Networks, and by visiting number NRAs (national regulatory authorities) in the US and European countries every year.