VoIP Numbering Issues
VoIP Numbering Issues
1) Purpose and Format
The purpose of this paper is to examine, from a numbering perspective only, the impact of Voice
over Internet Protocol (VoIP). This paper will provide background information on VoIP service but
the primary focus is intended to examine how the service uses telephone numbers from the PSTN
and how this use potentially impacts the life and present assignment and administration of NANP
2) Description of Service
i) Many companies who provide VoIP service will and already are competing with service
providers in the PSTN. In the October 2002 issue, of ISPWORLD the CEO of one VoIP
provider, states that his company is not selling their specific brand of service to customers as
VoIP phone service, but they “are selling it to them as a replacement to their existing phone
ii) VoIP service is described as a way for end users to get local, regional, and long distance
nationwide calling. Many VoIP service providers offer features such as Call Waiting Caller ID,
Personalized Voice Mail, Call Forwarding, Caller ID Block (*67), Repeat Dialing.
The specific feature offerings that directly impact numbering are the ability of the customer to
A telephone number in any area code of their choice;
The ability to take their telephone number with them when they move outside of their
current rate center.
iii) Many VoIP providers’ services are based on Internet Session Initiation Protocol (SIP)2.
iv) A high-speed Internet connection, such as a Cable Modem or DSL connection is required. In
addition, a phone adaptor is required. One such VoIP service provider provides the customer
with a Cisco ATA 186 Analog Telephone Adaptor, which converts the traditional analog phone
into a SIP VoIP phone The adaptor converts analog voice into digitized voice signals and then
into IP data packets. The adaptor is installed at the customer’s premise(s).3
3) Conceptual Diagram
Figure 1 is a conceptual diagram of architecture used to support VoIP service. The diagram
illustrates when a customer is assigned a TN from a non-home rate center. In this diagram, the
customer who resides in the Atlanta rate center is assigned a number from a New York NPA/NXX.
A call that originates from the PSTN to this Atlanta customer would be routed via the PSTN to New
York. The call then is placed on the Internet via a Gateway server. The call is routed to the Atlanta
1 Erickson, Todd Judd, “VoIP Finally Flexes Some Market Muscle”, :ISPWORLD, October 2002
2 The Session Initiation Protocol (SIP) is based on the protocols used for emails and web pages, which follow a client-host model.
Users in a SIP network are identified by unique SIP addresses. A SIP address is similar to an e-mail address and is in the format of
sip:userID@gateway.com. The user ID can be either a user name or an E.164 address.
3 The Cisco ATA 186 Analog Telephone Adaptor is a handset-to-Ethernet adaptor that interfaces regular analog phones with IP-based
telephony networks. The ATA 186 has two voice ports that can only support legacy analog touchtone telephones.
customer via the Internet. It should be noted that the customer can subscribe to this service without
changing their existing NPA or rate center.
Class 5 End Partner
Office Or Tandem
New York Atlanta Customer with
4) Examples of Numbering Selection Currently Offered by Two VoIP Providers
a) VoIP providers do not obtain numbers directly from NANPA. It appears they obtain numbers
from LECs that have received numbers from NANPA. Today, the LEC service provider that
provides the numbers to VoIP providers must report these numbers on NRUF as “Intermediate”
numbers. The VoIP provider in turn re-assigns these numbers to their VoIP customers.
In the previously cited example of service, the VoIP service provider allows customers to obtain
and keep telephone numbers from any of the area codes where the VoIP service provider has
received Intermediate numbers as long as they remain with that VoIP company. The following
list includes some of the area codes served by one VoIP service provider:
California: 213 310 323 408 510 619 626 650 707 714 760 805 818 831 858 909
Florida: 305 561 786 954
Georgia: 404 678 706
Illinois: 312 630 708 773 815 847
Massachusetts: 508 617 781 978
New Jersey: 201 609 732 856 908 973
New York: 212 347 516 631 646 718 845 914 917
Pennsylvania: 215 267 412 484 610
Texas: 409 832 936 979 214 254 469 817 903 940
At least one VoIP provider advertises that by subscribing to their service the customer is no
longer tied to their "local area code". The customer can select any area code they want from the
list of available area codes where they operate. For example if a subscriber lives in New York,
they can have a telephone number in a California Area Code. Their advertisement goes on to
state their service gives an appearance of a local presence without having to be physically
located in that area.
Two features that one VoIP provider presents as unique features of their service include
allowing customers to keep their telephone number as long as they want and allowing customers
to keep their numbers even if the customer changes location regardless of the their new location.
Their website explains these features as follows:
“Keep your ________telephone number for as long as you’d like. As long as you are a
________customer, you can keep your telephone number. Even if you move across the state,
or across the country, you never have to change your telephone number again.”
“Never before have you had the ability to take your home phone with you wherever you go.
With _________, you can travel with your home phone or even move (emphasis added)
without skipping a beat. Whether you’re traveling across the United States or anywhere else
or you’re moving into a dorm, or another town; all you need is a high speed internet
connection and the phone adapter (that we provide for free). It’s home phone service that
goes with you.” This, in fact, is the same as maintaining a wireless telephone number and
service when moving.
It should be noted however that in this VoIP providers Terms and Conditions, they state that
the “Customer has no proprietary or ownership rights to or interest in a specific phone
number or phone numbers ("Number") assigned to you by _______, and the number is not
portable to any other service provider.
b) A second VoIP service provider allows a customer to get a personal number based on the area
code of the customer’s choice. Also, each account includes voicemail that can be accessed from
a telephone or from the web. This particular VoIP service provider advertises that customers
can select any available area code from the list below, no matter where they live in the world.
Their number is not constrained by the city that they live in.
They currently offer numbers from the following area codes:
California: 213 415 510
New York: 347 646 718 917
Texas: 214 281
The company advertises that the customer should contact them if the above list does not contain
the area code from which a customer wishes to request a telephone number.
5) Numbering Issues
Shown below are excerpts from industry guidelines established by the Industry Numbering
Committee, which is sponsored by ATIS. The FCC has plenary authority over the INC’s guidelines.
This section contains identified numbering issues with VoIP type service and is divided into three
sections: General Issues, Specific Numbering Guideline Issues and Technical Issues.
a) General Issues
i) Rate Center Assignment Principle
An assignment principle in the both the Industry Numbering Committee’s (INC) CO-NXX
Assignment Guidelines and the Industry Numbering Committee’s Thousands-Block
Number Pooling Assignment Guidelines is that service providers are assigned resources on
a rate center basis4. This principle applies whether the service provider is applying for
initial numbering resources in a rate center or additional numbering resources in a rate
center. For initial resources in a rate center, a service provider must show proof of
readiness and certification for providing service. For growth numbering resources, the
service provider must show proof of need, and must show the months to exhaust and
utilization requirement have been met.
Entities that receive “intermediate” numbers do not have to meet utilization criteria today
per the FCC. Many service providers, including VoIP service providers, can obtain any
quantity of numbers from LECs anywhere in the country without meeting the requirements
applicable to other certified service providers. This is in contrast to current requirements for
the more conventional service providers who must track and report their quantities of
intermediate numbers and use them in demonstrating their ability to meet the current
Months-to-Exhaust requirements for growth numbering resources on a per rate center basis.
Since VoIP service providers are interconnecting with the existing PSTN and using PSTN
numbering resources, the primary question is: Should the number assignment rules that
apply to conventional service providers apply to VoIP providers?
ii) Impact on NPA Relief & NANP Exhaust
VoIP provider’s current use of telephone numbers will expand the need for telephone
numbers, which could advance the exhaust of the NPAs. Assigning telephone numbers
from a particular NPA in one area of the country to customers that do not reside in that
NPA (i.e. they may actually reside in another state) may accelerate the need for NPA relief.
As VoIP service providers begin to obtain and assign numbers in this fashion, it creates
additional demand. This issue also arose with the deployment of E-fax services and will
continue to be an issue as new technologies are deployed offering alternatives to the
traditional use of numbers.
The impacts on NPA relief and NANP exhaust will no doubt cause concern with some state
public utility commissions since NPA exhaust may be accelerated because telephone
numbers are assigned to customers outside the NPA or even outside their respective state.
For example, New York City residents can potentially be burdened with additional area
code relief because subscribers not under New York regulatory jurisdiction could end up
taking a large quantity of their numbers for use outside of the state. On the other hand,
there is an impact on customers who keep their existing numbers when they move. In the
past these numbers went back into a carriers inventory for reassignment to other customers.
One other concern stems from the situation where a typical subscriber may already have a
wireline phone, fax, cell phone etc., where they preside. VoIP service may encourage
subscribers to add additional numbers from any number of cities. This scenario could lead
to a single customer obtaining multiple sets of numbers from multiple cities. Should this
concept become popular it could result in an acceleration of the demand for numbers.
4 The Industry Numbering Committee (INC) is an ATIS forum provides and provides a forum for customers and providers in the
telecommunications industry to identify, discuss and resolve national issues that affect numbering.
iii) Number Resource Utilization and Forecasting (NRUF) Reporting
The definition of Intermediate numbers and how they are treated in utilization calculations
and in NRUF reporting is currently under review by the NANC. Numbers obtained and
used by VoIP service providers may impact NRUF reporting.
Should VoIP service providers be accountable for how they use NANPA resources?
The current arrangement requires VoIP providers to obtain individual telephone numbers
from existing code holders.
Also, should numbers given to VoIP service providers be reported and tracked using a new
FCC numbering category?
b) Specific Numbering Guidelines Issues
i) Assumptions of the Industry Numbering Committee (INC) on Use of Numbers
This section will review INC’s assumptions from the Central Office Code (NXX)
Assignment Guidelines and the Thousands Block Number (NXX-X) Pooling Assignment
Guidelines as adopted by the FCC. The issues address the use of NANPA resources and
identify those assumptions, which appear to conflict with existing VoIP use of numbers.
(1) Central Office Code Assignment Guidelines dated September 27, 2002
(a) Assumptions 2.1:
The NANP resources are considered a public resource and are not owned by the
assignees. Consequently, the resources cannot be sold, brokered, bartered, or
leased by the assignee for a fee or other consideration. Transfer of code(s) due to
merger/acquisition is permitted.
If a resource is sold, brokered, bartered, or leased for a fee, the resource is subject
It should be clear to customers when purchasing service from any service provider
that the customer is not purchasing the number and does not own the number.
(b) Assumption 2.2
NANP numbering resources shall be assigned to permit the most effective and
efficient use of a finite numbering resource in order to prevent premature exhaust
of the NANP and delay the need to develop and implement costly new numbering
The existing numbering resources have historically been allocated for specific
geographic areas. By assigning New York telephone numbers to Georgia residents
this geographic association is impacted.
(c) Assumption 2.10:
SPs and numbering resource administrators are responsible for managing
numbering resources in accordance with these guidelines and the orders of
applicable regulatory authorities.
INC numbering guidelines will have to be revised to incorporate VoIP applications
that use NANP numbers. Is it time for resellers and VoIP service providers to be
recognized as service providers subject to the accountability for their use of TNs?
Furthermore, the impacts of area code relief measures such as NPA splits must be
addressed as this may require changes to the numbers used by VoIP providers.
(d) Assumption 2.14:
It is assumed from a wireline perspective that CO codes/blocks allocated to a
wireline service provider are to be utilized to provide service to a customer’s
premise physically located in the same rate center that the CO codes/blocks are
assigned. Exceptions exist, for example tariffed services such as with the exception
of foreign exchange service.5
Should all providers be afforded the opportunity to be excluded from this existing
assumption, permitting the use of numbers beyond rate centers? This is a large
issue since existing number assignment guidelines and regulations for the request,
use, and reporting of numbers are all rate center based.
c) Technical Issues
i) Number Portability
According to the October 2002 issue of ISPWORLD, in September 2002, a VoIP provider
planned to introduce number portability using partnerships with local exchange carriers (LECs).
As VoIP service providers begin to offer local service, the impact of VoIP service on number
portability requires examination.
As background there are three types of portability. They are:
(1) Service Provider Portability
Service provider portability, as defined in the Telecommunications Act of 1996, is “the
ability of end users to retain, at the same location, existing telephone numbers as they
change from one service provider to another”.
This is the type of portability that has been ordered by the FCC and implemented by LECs
and will soon be implemented by wireless service providers.
(2) Location Portability
Location portability, as defined in the First Report & Order, Docket No. 95-116, is “the
ability of users of telecommunications services to retain existing telephone numbers without
impairment of quality, reliability, or convenience when moving from one physical location
Location portability allows customers to take their telephone when they move to another
geographic location outside of the original rate center.6
(3) Service Portability
5 Foreign Exchange differs in that it uses a dedicated facility from the customer premise located in a foreign rate center to a switch of a code
holder in the serving rate center.
6 In the Second Memorandum Opinion and Order on Reconsideration in CC Docket 95-116, the FCC concluded that nothing in the Act
precludes them from mandating location portability; however, they had plans to address location portability.
Service portability, as defined in the First Report & Order in Docket No. 95-116, is “the
ability of users of telecommunications services to retain existing telephone numbers
without impairment of quality, reliability, or convenience when switching from one service
to another service provided by the same telecommunications carrier7.
The implementation of service provider portability was very complex and time consuming. The
technical requirements and standards ordered by the FCC and adopted by the industry were
developed by the industry after lengthy periods of analysis and discussion. The FCC adopted
the industry recommendations and standards.
From a service provider portability viewpoint, some questions that arise are:
How will “porting” be done with a VoIP service provider? For example:
If VoIP service providers are going to complete calls to and from the PSTN, should
they also be required to have to implement LNP using LRN?
If VoIP service providers offer number portability will they need to interact with the
Will a new subscriber that is assigned a PSTN telephone number from a VoIP provider be
able to port their number to a PSTN service provider if requested? If so, will that port be
limited to a specific geographic area? Should compatible system interfaces be developed to
port numbers between VoIP providers and PSTN providers?
Does the definition or the role of N-1 carrier apply or change?
Should the process of “snap back” be used when a number is ported from a PSTN service
provider to a VoIP service provider or is it correct to leave it with the VoIP provider who
has obtained the number form another type of carrier?
These are just some of the portability issues that should be addressed when VoIP service
providers begin to offer local service. In the end, the concept of location portability as it is
known today may need to be revisited. For example, as other VoIP providers enter the market
and offer limited location portability, an issue of standards may arise.8 Do standard bodies need
to ensure that location portability is developed in a consistent manner and is compatible with the
PSTN? Will location probability need to be offered by traditional LECs? Should there be a
limitation to the geographic area for which location portability applies? These are just some of
the issues that require examination.
d) Other Issues
i) Number Jurisdictional Issues
With VoIP service providers offering local service with NANP resources, concerns regarding
jurisdictional authority over numbering resources become a key issue. The FCC has plenary
jurisdiction over the use of NANP resources. Specific aspects of that jurisdiction have been
7 The FCC is not addressing service portability at this time and requirements for service portability are still undefined
8 Limited location portability in IP telephony is implemented by the use of redirect servers and proxy servers. It is similar to call forwarding in
delegated to state regulatory bodies. As such, any concerns as to the ability of VoIP providers
to use NANP numbers are to be guided by the intentions of the FCC. As technology continues
to advance and the integration of IP telephony and the existing PSTN develops, it becomes
necessary for the industry as a whole, (wireline, wireless, VoIP, CLEC, DLEC, etc.) to provide
the FCC with solid data and facts to permit the FCC to make its decision on the appropriate use
and applications for NANP numbering resources.
Embedded within the jurisdictional issue is the matter of how the cost of NANP number
administration is paid and prorated. With VoIP service offerings, VoIP is obtaining numbers
that were originally allocated to LECs. Therefore the LEC pays for the administration of that
number. In the future, the question will become should the VoIP providers also pay for the
numbering resources administration under the required guidelines. These administrative issues
should be dealt with, once the jurisdiction issues are addressed.
Finally, 911 and other N11 dialing capabilities and requirements may vary from State to State.
These must be clearly evaluated as a to if and how VoIP will support these dialing capabilities
One of the major challenges resulting from the integration of the PSTN and Internet is the status of
calls that pass from one network service provider to another service provider between the PSTN and
the Internet. Due to multiple architectural configurations for VoIP, a lack of existing all-
encompassing industry standards, and an indeterminate regulatory landscape, the current numbering
paradigm as applied to numbering responsibilities and obligations needs to change in this
developing environment. The change is a complex problem to solve. Today’s rules and regulations
address number assignment, number use and the responsibilities of both regulators and Industry
only in a PSTN environment. These rules and regulations have been formulated to maximize the use
and life of the existing NANP numbering resources. VoIP service represents a new element and
application that will have an impact on the life of the NANP. In the past the introduction of cell
phones, CLEC entry, pagers and other services have impacted NANP numbering resources and
consequently changes were adopted.
It will be necessary to address the constraints that PSTN service providers must operate under in
order to obtain and use NANP resources when incorporating the VoIP service providers use of
numbers into the rules and regulations.
In order to support PSTN and Internet integration it is necessary that all numbering issues be
thoroughly examined. Thus, as new implementations of VoIP are introduced (e.g. ENUM), or for
that matter any future use of the numbering resources, issues involving numbering in VoIP
environments need to be identified and examined to determine their impact on the North American
Numbering Plan (NANP).
It’s recommended that the NANC assist the FCC in addressing these numbering issues to prevent
any disparities that are arising based on existing regulations to achieve true NANP resource