Digital Regulation Platform

Technical regulation: Numbering, naming, addressing, and identification (NNAI)


Why do numbering, naming, and addressing matter?

Telephone numbers were devised well over a century ago to provide a way of identifying destinations of telephone calls uniquely. They then became used to identify sources of telephone calls, in calling line identification (CLI). They could contain information about tariffs and value-added contents. They are now used much more generally as unique identifiers, in money transfers, over-the-top (OTT) messages, Internet of Things (IoT) devices, and so on. In effect “destination” has been expanded to refer to people and things generally.

The rotary dials originally used to input numbers have long since disappeared (though “dialling” is still used for the input of a telephone number). People now often send messages by touching screens or speaking commands; in doing so, they do not usually see or say telephone numbers, but the numbers might still be there in their contact lists.

Since the 1960s, numbering, naming, addressing, and identification (NNAI) resources have evolved to meet emerging requirements and technological innovation. The digital age is no different. In fact, the evolution of the uses to which NNAI resources are being put in the digital age could not occur were it not for the early evolutionary steps.

What are NNAI resources?

The term “NNAI resources” is a generic reference to resources that are described in ITU-T Recommendations and that are used to provide telecommunication services. Of those that are specified, three are considered in this section because of their usefulness in the digital age:

Telephone numbers were originally used by the network to identify the destination of a call, and to route the call across the network between two fixed points. Each of the fixed points were known to the operator, and based on these fixed points that operator could charge the customer. The introduction of mobility required other mechanisms to be developed that would identify that connection could be established, and that charges could be made. International mobile subscription identifiers (IMSIs) are the means by which a user can be provided with service outside of their national network of choice to make and receive calls. An Issuer Identifier Number (IIN) is used to identify the charges that accrue from a call in a mobile scenario. The focus of the following sections is on the telephone number as it is the most visible resource.

NNAI management

NNAI management falls generally under the responsibility of the numbering plan administrator. Such administration can occur within a designated ministry, or within the mandate of a regulator. The scope of the responsibilities of the entity that has the responsibility is a national matter. In some cases, an official national authority might take the role, or agents might do so on behalf of the authority (as happens with some countries in the North American Numbering Plan). NNAI management by the regulator can fulfil the following objectives:

Although customers are allocated individual numbers by operators and service providers, operators and service providers are allocated numbers in blocks by the numbering plan administrator. The numbering plan administrator is the entity responsible for the assignment of numbers. Originally this was the incumbent operator, but with the introduction of regulation and competition this responsibility has passed to the relevant ministry or the independent regulator, or their agent (as is the case for some members of the North American Numbering Plan). The size of the block varies according to the use to be made of numbers within that block.

The association of individuals with the telephone number and the reluctance to change telephone numbers to take an alternative service was identified in the early introduction of competition as a barrier to the take up of alternative services. The introduction of number portability, the ability of consumers to change service providers but retain their telephone numbers, did much to remove that barrier. The governance of, and the mechanisms to implement, number portability do vary between countries. ITU-T Recommendation E.164 Supplement 2 (ITU-T 2010) [2] that is continuously updated in ITU-T Study Group 2 (SG2), responsible for operational aspects, including NNAI, defines standard terminology for a common understanding of the different aspects of number portability within an ITU-T E.164 numbering scheme. It identifies numbering and addressing formats, call flows, network architectures, and routing approaches that will provide alternative methods of implementation. It also proposes some examples of the administrative and operational processes required for the successful implementation of number portability.

Global NNAI resources

The NNAI resources being used to support the provision of services until the 1990s focused on the national environment. The resources identified thus far were allocated and assigned to operators indirectly by the International Telecommunication Union (ITU), that is, the ITU allocated the resources to member states, based on rules agreed to by those member states. As a consequence, the rules governing these resources were a national matter. However, during the 1990s this changed with the introduction of global (or directly assigned) resources.

Directly assigned NNAI resources are specified in ITU-T Recommendations. They were originally used for services, such as toll-free, shared revenue, and premium rate services, but for customers that were global in nature, e.g. major hotel chains, helplines, and so on. Such global services had their own country codes allocated and to this day are directly administered by the ITU to service providers and operators. For example, the global, or International Freephone Service (IFS) (Recommendation ITU-T E.152) (ITU-T 2006b) was assigned the country code +800. The use of directly assigned resources has continued to evolve.

The digital age emerges

The relevance of NNAI resources remains even as the nature of telecommunications itself is evolving. The traditional model of communications, which used technology to support voice (known generically as circuit switched), has changed to one where other types of communication, besides voice, exist (known generically as packet switched). The change of the model of communication has also meant changes in the use of NNAI resources.

The environment in which such NNAI resources exist has changed to reflect what is understood by the term telecommunications. The environment is becoming more complex and diverse. There are some national environments where telecommunications are operated by the government; there are other national environments that are fully competitive, with multiple service providers and an independent regulator, or are on the transition towards such an environment. Even the approach to setting the rules that govern the use of NNAI resources varies, with some governments vetting the entities wishing to operate telecommunication services, and so be allocated NNAI resources, while other governments only require such operators to agree to abide by the rules. The former is a licensing regime, and the latter is a general authorization regime.

It is in the context of the transition of national environments, of the changes to telecommunications itself as well as to emergence of new technologies, that the use of NNAI resources continues to evolve in the digital age. The evolution of the uses to which NNAI resources are being put in the digital age exploits previous evolutionary steps in the use made of NNAI resources.

Impact of new technologies

The emergence of new technologies has allowed new services and capabilities to also emerge that in turn has placed new requirements on the availability and deployment of NNAI resources, not only to meet these new demands but also for use by new providers. Such evolution has also impacted the evolution of the environment in which NNAI resources exist and the way in which consumers communicate.

The trends that have emerged in recent years, and that continue to drive the evolution of NNAI resources, are based on the greater use of technology in all aspects of people’s lives. The greater use of technology in this way is reflected in the continued need for NNAI resources. That said, the predominant use of telecommunications has changed from one that was wholly voice based to the situation today where the predominant use is based on data associated with digital services.

One such area that has emerged has been over-the-top (OTT) services. These services have emerged as an alternative to traditional voice communication. Some OTT services make use of the telephone number for direct communication within the OTT service. This is allowed for within the terms and conditions to which a consumer agrees (but often does not read) when initially signing up to the OTT service. Some OTT service providers utilize alpha characters and therefore do not need to make use of telephone numbers for direct communication within an OTT service.

The decision as to how the telephone number is used is often taken out of the hands of the users in the call, and determined by the software of the OTT service as covered in the terms and conditions that the user has agreed to on taking the service. This can result in a caller dialing a telephone number and the called user receiving the call via an OTT service. This and similar issues related are under discussion in ITU-T SG2.

The reuse of telephone numbers in an OTT service is as identifiers rather than telephone numbers, and such identifiers map often to IP addresses within the application. One issue that emerges from the use of telephone numbers as identifiers is if the telephone number is reassigned to a new customer who then registers with the same OTT service. In such circumstances, it has been possible for the new customer to get access to the original customer’s data.

The characteristics of communications are evolving and this has consequences beyond the use of NNAI resources in terms of commercial arrangements. Communications for digital services, such as machine-to-machine (M2M) communications and the IoT, are becoming characterized by very short duration connectivity, that are low latency and perhaps less infrequent than the duration and occurrence of voice or human-to-human calls. Also, digital services are being used as an alternative to traditional telecommunications. OTT applications are readily available and are being used by consumers at a fraction of the cost, sometimes at the expense of quality.

Digital service communications are impacting the revenues that can be expected by operators for call-by-call charges associated with voice communication. Many operators are changing the commercial arrangements for traditional voice services, moving to add value to calls rather than just for the communication. For example, one business development that has emerged is that providers of machine-to-machine (M2M)/IoT connectivity are more likely to offer a complete management solution to a business rather than just the communication element. Another example of evolving business development is the manner by which service providers of traditional voice communications, in order to compete with OTT services, have sought to counter the introduction of OTT procedures by moving to a monthly fee rather than call-by-call charges.

The trend to interconnection between the old and new worlds of communications for consumers has given rise to many discussions. These discussions include the extent to which such interconnection might contribute to bypass fraud, or might be seen as an evolution of telecommunications. In some countries, OTT voice services, whether they interconnect with the traditional voice implementation or not, are considered to be network bypass. From an NNAI aspect, whichever view is taken of such interconnection, there have to be commercial arrangements in place and legal and regulatory permissibility for the interconnection to exist. This interconnection represents an evolution of the context in which NNAI resources are being used. Calls from the new services utilize the telephone numbers that are already in use. Calls to the new services require the new and emerging operators to be able to be allocated NNAI resources, which has occurred in many jurisdictions.

What instruments can the regulator use?

The regulator acts by maintaining, and changing as required, three main instruments. With these instruments the regulator can manage numbering effectively and efficiently. They are:

New uses bring new Issues

The use of telecommunications to manage technology, for example in vehicles, is a clear example of the trends that are impacting NNAI. However, these continuing trends bring new issues associated with the use of NNAI. One example is driven by car manufacturers that have deployed the capability to remotely monitor and, if necessary, manage the performance of an individual’s car. This capability requires remote access for data collection. Also being deployed is in-car emergency calling, that is, the ability to communicate from, and sometime to, the vehicle in the case of an emergency. This requires an element of voice communication between the vehicle and the public safety access point (PSAP). However, both capabilities are using NNAI resources.

An additional issue associated with in-car emergency calling is one of routing. It is questionable whether the continued use of NNAI resources from the country of a car manufacturer used in a third country would always facilitate access to a PSAP.

In some uses of in-car emergency calling, such as eCall voice calls in the European Union, these can be initiated from either the vehicle or an emergency service centre. However, the most that can be required is that eCall voice calls can be initiated from cars only to closed user groups. Of course, other IoT services, as yet unimplemented, might require calls broadcast to anonymous groups (all users within 1 kilometre, for example). M2M numbers might be intended primarily for data traffic (in domestic alarm systems, for example). For OTT calls, the use of NNAI should be governed by the same rules as the use of other similar numbers where a regulator has chosen to permit the use of similar numbers for OTT services, or specific rules can apply where the regulator chooses to use a specific number range dedicated to OTT services.

However, unlike mobile telecommunications, where the use of the NNAI resources outside of a geographic jurisdiction may be temporary, the use of such NNAI resources when associated with a vehicle may be permanent when the car is permanently exported to a third country. To ensure that the use of NNAI resources for such capabilities is possible, national regulators are becoming aware of the issues and are adapting the regulations accordingly.

The example of the permanently exported car is but one example. Other examples could include management of shipping containers, or M2M/IoT devices that would require wireless connection in order to communicate, such as alarm systems. There are two issues for originating countries whose NNAI resources may be permanently exported. The first is to ensure that, as the NNAI resources are deployed permanently overseas, that there are sufficient NNAI resources for their own national use. The second is to ensure that, where their resources are used overseas, such use complies with the national regulation of overseas countries.

For those countries that require cessation of permanent roaming of NNAI resources within their jurisdiction after a period of time, then other issues emerge. One such issue is requiring the replacement of the NNAI resources from the originating country with NNAI resources from the national environment. A further issue is then “returning” the original NNAI resources to the originating country. It is possible to replace the NNAI resources but currently there is no solution for returning the original countries’ resources.

The means of managing NNAI resources has also evolved and has contributed to the changing use of NNAI. The evolution of the mobile communications device that originally required a physical Subscriber Identification Module (SIM) now allows for an electronic, or virtual, version of the SIM. This has its own issues. For example, a car manufacturer that exports vehicles to an overseas market, and that uses physical SIMs, may incur costs to replace those SIMs if required by national regulation. Industry has developed the ability to update eSIMs over the airwaves (OTA) but this has its own associated costs. That said, regulators may see the implementation of eSIMs and the use of OTA technology as a means of promoting competition in those markets that would otherwise encounter barriers to competition with the need to physically replace SIMs. Such a circumstance may be faced by enterprises using smart meters for their customers and who use mobility NNAI resources to communicate if such enterprises wish to switch communications providers.

Global NNAI resources

One avenue to avoid some of these emerging issues is to avoid the use of national NNAI resources. There has been an increase in the past few years of operators and service providers, both old and new, wanting a direct allocation of NNAI resources from the ITU. While global allocations of NNAI resources address some of the issues of permanent deployment of national resources overseas, direct assignment brings its own set of challenges. The main challenge associated with global numbers for operators and service providers is getting recognition of the directly assigned NNAI resources, that exist behind the country code, to allow for routing and charging. For regulators, the use of global resources in a national context raises the issue of ensuring compliance with national regulation. Ensuring that use of such global resources comply with national regulation and does not, for example, offer competitive advantage, is challenging as the use of such resources is governed by ITU-T Recommendations not by national regulations. Nevertheless, allowing the use of a global resource in a national context may avoid unnecessary depletion of national NNAI resources and as such ensure a ready supply of national resources for the future. For an entity that has global NNAI resource to be used in multiple jurisdictions, there is the benefit of, for example, just one numbering range to be administered rather than a potential myriad of such resources. The rules governing the use of such resources is enshrined in ITU-T Recommendations that have been approved by member states.

Future challenges for NNAI

The evolution of NNAI for use in new services is a continuation of events that started over 60 years ago. As new services and new technologies emerge, existing NNAI resources are continuing to play a role. This is because of the history of flexibility and evolution that started in the 1960s, both in terms of the use of the NNAI resources and the regulatory and legal environment in which the NNAI resources have existed. This means that the emergence of the digital age does not represent a step change for the use of NNAI resources but is, rather, a continuation of the evolution. The manner by which NNAI resources have been specified, managed. and that have evolved provide a sound foundation for their continued use in the digital age.

What can the regulator do to address these NNAI challenges?

For instance, to help people to use numbers, the regulator can:

In addition, to avoid future shortages of numbers, the regulator can:

The demand for NNAI resources to support new and emerging services and technologies is unlikely to abate in the short to medium term. The challenges that are to be faced in managing the NNAI resources are likely to become more complicated. The challenges include having sufficient resources available, being able to adapt the rules governing the assignment of NNAI resources to meet the needs of the market (as part of the responsibility of promoting competition) but doing so in a manner that ensures consumer protection and meets national legal regulation.

The rules governing the use of national NNAI resources have evolved to meet requirements that have emerged. While those requirements have been the same in many jurisdictions, the manner by which the use of NNAI resources have been deployed (and governed) have reflected different national environments. This is also true of the digital age.


  1. The limitation is 15 digits and is specified in Recommendation ITU-T E.164.
  2. Supplement 2 to Recommendation ITU-T E.164 defines standard terminology for a common understanding of the different aspects of number portability within an ITU-T E.164 numbering scheme. It identifies numbering and addressing formats, call flows, network architectures and routing approaches that will provide alternative methods of implementation. It also proposes some examples of the administrative and operational processes required for the successful implementation of number portability.


ITU-T. 1996. Home Country Direct. Recommendation ITU-T E.153.

ITU-T. 2001. Notation for National and International Telephone Numbers, E-Mail Addresses and Web Addresses. Recommendation ITU-T E.123.

ITU-T. 2006a. The International Telecommunication Charge Card. Recommendation ITU-T E.118.

ITU-T. 2006b. International Freephone Service. Recommendation ITU-T E.152.

ITU-T. 2010. The International Public Telecommunication Numbering Plan. Recommendation ITU-T E.164.

ITU-T. 2013. Presentation of National Numbering Plans. Recommendation ITU-T E.129.

ITU-T. 2016. The International Identification Plan for Public Networks and Subscriptions. Recommendation ITU-T E.212.

Last updated on: 19.01.2022
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