



Network Working Group                                        P. Robinson
Internet-Draft                                             29 April 2026
Intended status: Informational                                          
Expires: 31 October 2026


A Proposal for Long-Term Expansion of the North American Numbering Plan
                          (NANP) to 11 Digits
                    draft-robinson-nanp-expansion-01

Abstract

   The North American Numbering Plan (NANP) is projected to exhaust
   available telephone numbering resources within the coming decades
   under current allocation and utilization trends.  Existing mitigation
   strategies, including area code overlays and number pooling, extend
   the usable life of the NANP but introduce increasing operational
   complexity and user confusion.

   This document proposes a long-term, uniform expansion of NANP
   telephone numbers from 10 to 11 digits through extension of the area
   code or Numbering Plan Area (NPA) from 3 to 4 digits.  The proposal
   emphasizes backward compatibility, fixed-length numbering, and a
   multi-phase transition strategy designed to minimize disruption.
   This document is intended to stimulate discussion and does not
   represent the position of any standards body or regulatory authority.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-robinson-nanp-expansion/.

   Source for this draft and an issue tracker can be found at
   https://github.com/electric-socket/11digitdialing.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.





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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 31 October 2026.

Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Design Goals  . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Non-Goals . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Proposed Expansion Model  . . . . . . . . . . . . . . . . . .   6
   8.  Human Factors . . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  Routing Considerations  . . . . . . . . . . . . . . . . . . .   8
   10. Transition Strategy . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Phase 0: Infrastructure Readiness  . . . . . . . . . . .   8
     10.2.  Phase 1: Dual-Format Acceptance  . . . . . . . . . . . .   9
     10.3.  Phase 2: User Notification . . . . . . . . . . . . . . .   9
       10.3.1.  Segment 1  . . . . . . . . . . . . . . . . . . . . .   9
       10.3.2.  Segment 2  . . . . . . . . . . . . . . . . . . . . .   9
     10.4.  Phase 3: Mandatory Expansion . . . . . . . . . . . . . .   9
     10.5.  Phase 4: Full Expansion  . . . . . . . . . . . . . . . .   9
   11. Alternatives Considered . . . . . . . . . . . . . . . . . . .  10
     11.1.  Further subdivision of number pooling blocks . . . . . .  10
     11.2.  Expansion using only reserved NPA ranges (e.g., N9X) . .  10
     11.3.  Overlay NPAs . . . . . . . . . . . . . . . . . . . . . .  10
     11.4.  Variable-length numbering schemes  . . . . . . . . . . .  10
     11.5.  Expansion Of NXX To NXXX . . . . . . . . . . . . . . . .  11
     11.6.  Expansion Of XXXX To XXXXX . . . . . . . . . . . . . . .  11
   12. Operational Considerations  . . . . . . . . . . . . . . . . .  11
   13. Backwards Compatibility Risks . . . . . . . . . . . . . . . .  12
   14. Benefits  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
   15. Economic Considerations . . . . . . . . . . . . . . . . . . .  14



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     15.1.  Cost Considerations Of Methods Used  . . . . . . . . . .  14
     15.2.  Billing and Rating Impact  . . . . . . . . . . . . . . .  14
   16. Security Considerations . . . . . . . . . . . . . . . . . . .  15
   17. Transition Governance . . . . . . . . . . . . . . . . . . . .  15
   18. Transition Difficulties . . . . . . . . . . . . . . . . . . .  15
   19. International Considerations  . . . . . . . . . . . . . . . .  16
   20. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   21. Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  16
   22. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     22.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     22.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Appendix A.  Changelog  . . . . . . . . . . . . . . . . . . . . .  17
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   The NANP currently utilizes a fixed-length 10-digit numbering format
   (NPA-NXX-XXXX).  Growth in telecommunications services, device
   proliferation, and number portability has steadily increased demand
   for numbering resources.

   Mitigation strategies such as overlays and thousands-block number
   pooling have delayed exhaustion but introduce increasing complexity
   in routing, administration, and user experience.

   This document explores a uniform expansion of NANP numbers to 11
   digits as a long-term solution.

   This proposal preserves fixed-position digit parsing, avoiding
   variable-length interpretation and timing-based ambiguity.  This
   property is a primary design objective, as it minimizes required
   changes to existing switching and routing infrastructure.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Definitions

   CP:  is Cellular Provider, the service provider for a caller using
      cellular telephony.

   IXC:  Interexchange Carrier - the organization that carries a call




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      between the caller's service provider and the called party's
      service provider where the caller's service provider does not
      serve the area of the called party.

   Jeopardy:   Jeopardy is the condition where an NPA is in danger of
      running out of available NXXs to use for new telephone
      subscribers, requiring a freeze on the issuance of further
      subscriber numbers in that NPA until more NXXs become available.

   LEC:  Local Exchange Carrier, the service provider for a caller using
      a landline or VoIP service, the organization that provides dial
      tone and carries a call to the called party where they are within
      the service area of the LEC, or transfers the call to an IXC when
      the called party is outside its service area.

   N versus X:  In the context of a telephone number, N is used to
      indicate a digit that is restricted to values of 2 through 9,
      while X indicates an unrestricted digit with values 0 through 9.

   NPA:  The area code, or first three digits of the 10-digit telephone
      number.  This document will use both 'area code' and 'NPA'
      interchangeably, generally with NPA used when discussing technical
      and implementation issues, and area code being used when
      discussing issues faced by subscribers and the public.

   NPAX:  The new area code, or first four digits of the new 11-digit
      telephone number.  This proposal recommends expansion of the NPA
      field by 1 digit and provides an expansion of the entire telephone
      number to 11 digits.

   NXX:  The prefix, or digits four through six of the 10-digit
      telephone number, or first three digits of the subscriber number.
      This field is to remain unchanged, but is moved to digits five
      through seven of the new 11-digit telephone number.

   SIT tone:  A Special Information Tone (SIT) is a standardized, three-
      beep audio signal (typically 950/1400/1800 Hz) played before a
      recorded announcement to indicate a telephone call has failed.

   Subscriber number:  The portion of the telephone number following the
      NPA or NPAX.  It remains unchanged at seven digits, but is moved
      from positions four through ten of the telephone number, to
      positions five through eleven.

   Telephone number:  The entire number of the party to be called,
      consisting of either





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   *  On 10-digit systems, the three-digit NPA, three-digit NXX, and
      four-digit XXXX.

   *  On 11-digit systems, the four-digit NPAX, three-digit NXX, and
      four-digit XXXX.

   VoIP:  Voice Over IP, or telephone service where the call initiates
      from or terminates via the Internet.

   XXXX:  The last four digits of the subscriber number, or line number,
      digits seven through ten of the 10-digit telephone number.  This
      field is also to remain unchanged, but is moved to digits eight
      through eleven of the new 11-digit telephone number.

4.  Problem Statement

   The current NANP faces several challenges:

   *  Finite NPA capacity under existing numbering rules

   *  Fragmentation of numbering resources due to allocation practices

   *  Growing operational complexity in routing and database systems

   *  Long lead times required for major numbering plan changes

   A long-term solution should address these challenges while minimizing
   disruption to existing systems and users.

   All feasible approaches to expanding NANP numbering capacity
   introduce some degree of disruption.  The proposed expansion of the
   NPA is considered the least disruptive option, as it preserves the
   existing hierarchical structure of the numbering plan and minimizes
   changes to subscriber numbering and routing semantics.

5.  Design Goals

   The proposed solution is guided by the following goals:

   *  Maintain fixed-length numbering

   *  Minimize changes to existing routing logic

   *  Preserve compatibility with existing numbering structures







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6.  Non-Goals

   The following approaches are explicitly not considered desirable:

   *  Variable-length telephone numbers

   *  Region-specific numbering formats

   *  Frequent or repeated structural changes to the numbering plan

   *  Solutions requiring rapid or "flash cut" transitions

7.  Proposed Expansion Model

   This document is a proposal to expand NANP numbers from 10 to 11
   digits by extending the NPA from three digits to four digits.  This
   ensures that existing fixed-position digit parsing logic can be
   extended with minimal modification, avoiding the need for timing-
   based or variable-length interpretation.

   Existing numbers:

     NPA-NXX-XXXX

   Expanded format:

     NPAX-NXX-XXXX

   During initial deployment, the fourth digit added to the NPA to form
   the NPAX MUST be selected such that it does not conflict with
   existing digit patterns used to identify the first digit of NXX
   codes.  Under current NANP rules, the first digit of an NXX is
   restricted to values 2 through 9.

   By selecting 0 or 1 for the additional NPA digit, the boundary
   between the expanded NPAX and the following NXX remains unambiguous.
   This allows existing digit analysis algorithms to distinguish between
   legacy 10-digit and expanded 11-digit numbers using a simple
   examination of the fourth digit.

   Restricting the fourth digit initially to a single value minimizes
   required changes to routing logic and reduces deployment cost.

   This property allows existing fixed-position digit analysis logic to
   be extended with minimal modification, avoiding the need for timing-
   based disambiguation, interdigit timeout adjustments, or variable-
   length parsing mechanisms.




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   A single value (0 or 1) SHALL be used consistently across all NPAs
   during the initial deployment phase to ensure uniform behavior across
   networks.  Uniformity avoids user confusion, simplifies parsing, and
   prevents mixed national behavior during migration.

   Example:

     213-555-1234  (legacy)

     2130-555-1234 (expanded)

   Or:

     303-555-1234  (legacy)

     3031-555-1234 (expanded)

   A telephone switching system processes a telephone number using the
   following logic:

   1.  Scan fourth digit of number.

   2.  If 0 or 1, process as NPAX.

   3.  Else, process as NXX.

   This proposal preserves the semantic structure of the number.

   *  NPAX is still geographic.

   *  NXX is still used as the routing block.

   *  XXXX is still the subscriber line number.

   The widespread adoption of overlay area codes has fundamentally
   altered the NANP environment.  A return to strictly geographic, non-
   overlapping area codes is no longer practical.  The proposed approach
   assumes the continued existence of overlays and does not attempt to
   reverse this trend.

   The designation of 988 as a nationwide service code required the
   elimination of 7-digit dialing in affected areas, accelerating the
   transition to uniform 10-digit dialing across the NANP.  As a result,
   this proposal does not impact legacy 7-digit dialing, as that
   capability has already been largely eliminated.






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   This approach ensures that numbering expansion occurs at the highest
   level of the NANP hierarchy, avoiding disruption to lower-level
   components such as routing prefixes and subscriber numbers.

   This method preserves fixed-field positional parsing, avoiding the
   need for timing-based digit collection or variable-length
   interpretation, which are known sources of complexity and error
   in telephony systems.

8.  Human Factors

   During and after transition, published numbers SHOULD be displayed in
   hyphenated 4-3-4 form (e.g., 2130-555-1234).  Users will find this
   format similar to the existing 3-3-4 format, and are expected to
   adapt to the new format following the patterns observed during the
   transition to mandatory 10-digit dialing.  Contact storage systems,
   dialing interfaces, and automated dialing features are expected to
   adapt with minimal modification due to the preserved fixed-length
   structure.

9.  Routing Considerations

   Existing routing systems rely on fixed field positions within the
   NANP number.  The proposed expansion preserves the relative position
   of the NXX and subscriber line number fields, allowing for minimal
   modification to routing logic.

   Systems that perform digit analysis MUST be updated to recognize the
   NPAX format.  This includes SS7-based switching systems, SIP routing
   platforms, and number portability databases.

   These updates are limited to recognition of the fourth digit as a
   format discriminator and do not require changes to downstream routing
   logic based on NXX or subscriber number.

10.  Transition Strategy

   A phased transition is recommended:

10.1.  Phase 0: Infrastructure Readiness

   Networks and systems are updated to support 11-digit numbers without
   public announcement.  Switching systems MUST be updated to recognize
   and correctly route NPAX-based numbers during Phase 0.

   There SHOULD be some cross-network communication system such as a
   website, a mailing list, a help desk, and/or other method for parties
   involved in the conversion to report progress and to obtain



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   information helpful in diagnosing problems, issues and events that
   may require special attention or otherwise require additional
   resources for resolution.  This SHOULD be provided or operated by a
   neutral third-party.

10.2.  Phase 1: Dual-Format Acceptance

   Both 10-digit and 11-digit dialing are accepted by all CPs, IXCs, and
   LECs.  All originating and terminating networks MUST accept both
   formats.

10.3.  Phase 2: User Notification

   Phase 2 is implemented as two segments.

10.3.1.  Segment 1

   In Segment 1 of Phase 2, LECs, CPs, IXCs, and regulatory authorities
   MUST publicize the implementation of the expansion of the NPA to an
   NPAX, where the area code is expanded to four digits, and the
   telephone number to eleven digits.  An important highlight of the
   announcement SHOULD emphasize that there will be no change to the
   subscriber number.  It SHOULD also state the date Segment 2 will
   begin and the date that phase 3 will begin.

10.3.2.  Segment 2

   In Segment 2 of Phase 2, Intercept messages SHALL be imposed on
   callers dialing a 10-digit phone number, and such message SHALL
   inform callers dialing telephone numbers using the current 10-digit
   format of upcoming requirements, MAY inform them of the digit they
   need to append to the area code, and SHOULD state the date when
   dialing the new 11-digit number will be required.  The call SHALL
   still complete.

10.4.  Phase 3: Mandatory Expansion

   11-digit dialing becomes required.  Callers dialing the old format
   10-digit number SHALL be presented with an intercept message
   beginning with a SIT tone and an announcement that they must dial the
   new 4-digit area code.  The message MAY announce the additional digit
   that MUST be dialed.  The call SHALL NOT complete, and SHALL be
   treated equivalently to dialing an invalid number.

10.5.  Phase 4: Full Expansion

   The fourth digit of the NPA is opened to all values 0 through 9,
   increasing numbering capacity.



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11.  Alternatives Considered

   The following alternatives were evaluated:

11.1.  Further subdivision of number pooling blocks

   Further subdivision of pooling blocks provides only limited extension
   while increasing database and administrative complexity.

11.2.  Expansion using only reserved NPA ranges (e.g., N9X)

   If the rest of the available NPAs are exhausted, this becomes a stop-
   gap measure until this or some other planned expansion of the
   telephone number to 11 digits.

11.3.  Overlay NPAs

   Originally each NPA covered one region exclusively.  As more
   telephone numbers were needed, more NXXs were added until no more
   were available.  The answer at that point is to split the NPA, take
   about half the NXXs that were geographically adjacent to each other,
   and assign them to the new NPA.  The advantage was the subscriber
   number did not change, so local seven-digit dialing was unaffected,
   and the subscriber simply had to advise people that their area code
   had changed.  This practice worked when regions were large and the
   remaining regions after the split are of a reasonable size.  When
   they are city-sized or smaller, splitting NPAs produces a point of
   diminishing returns, where an NPA might only be part of a city.

   The switch to overlays alleviated this problem as now the combined
   number pool of both NPAs is available for the entire region.  It also
   ends the dilemma of an NPA in jeopardy status being split, with one
   NPA having more than sufficient available NXXs and the other
   remaining in jeopardy.  Overlays were inevitable and solved the
   problem of an NXX surplus/starvation NPA split result dilemma.

   While overlays are useful, and it is very likely new NPAs will be
   added as overlays to existing regions, they won't be enough to solve
   the problem when it is not NXXs that are in jeopardy, but NPAs.

11.4.  Variable-length numbering schemes

   These approaches introduce significant implementation complexity,
   increase validation burden across systems, and may negatively affect
   user perception of numbering uniformity.

   These approaches either provide limited long-term benefit or
   introduce undesirable complexity.



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11.5.  Expansion Of NXX To NXXX

   The expansion of the subscriber number to 8 digits by increasing the
   size of the NXX to four digits was considered, but it creates an even
   larger disruption:

   *  The number of NXXs in an NPA rises from slightly under 800 to
      nearly 8,000.  It would vastly increase the size and complexity of
      local number portability databases

   *  It would also increase the number and size of call routing tables

   *  Third parties would have to update software for holding much
      larger number ranges

   *  The number of potential telephone numbers in an area code rises
      from around 7,000,000 to nearly 70,000,000

   *  In most regions this would cause each area code in the state to be
      many times greater than the entire population of the region served
      by that NPA.  Much of the additional capacity would be unusable or
      wasted.

11.6.  Expansion Of XXXX To XXXXX

   The expansion of the line number to 5 digits adds even more
   complexity and potentially even greater added costs than expanding
   the NXX to 4 digits:

   *  Even larger number portability databases, as each NXX expands by a
      factor of 10

   *  Local switches have to handle not potentially 10,000 lines for
      each NXX they service, but 100,000

   It is entirely possible switch hardware cannot support this large a
   number pool, either rewiring replacement or upgrading expensive
   switching equipment.  It may require splitting NXXs onto multiple
   switches and require even more routing changes to accommodate.  In
   heavily populated urban areas it might require acquisition of 
   additional expensive switches, real estate, and buildings.

12.  Operational Considerations

   The proposed expansion is designed to minimize impact on:

   *  Call routing systems




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   *  Number portability databases

   *  Inter-carrier signaling

   However, significant updates would be required in:

   *  Customer-facing systems

   *  Validation logic

   *  Legacy equipment and embedded systems

   A question that may arise is "Why not allow the full number range of
   0-9 in the fourth digit of the telephone number to be activated
   immediately, rather than the current proposal to initially only
   permit a single digit?"

   The rationale is cost and complexity.  Initial deployment using a
   single digit minimizes required routing changes.  This proposal
   acknowledges \ that significant costs would be involved in moving to
   an 11-digit telephone number.  Eventually, the change must happen.
   The fact remains, initially implementing only one digit generates the
   least amount of cost increase, as only the routing logic of the
   fourth digit of the telephone number is required to be changed.
   Later, when digits 2-9 are enabled, the code required to check the
   fourth digit can then be eliminated.  Thus, this also reduces the
   complexity involved in making this change.

13.  Backwards Compatibility Risks

   There will need to be lead time to account for, and attention placed
   on informing owners of systems that may need to be replaced because
   of incapacity to update them to use the new format telephone number,
   such as systems using:

   *  Hard-coded 10-digit fields

   *  Regular expression validation failure

   *  Embedded devices

   Emergency equipment that sends "final warnings" or notifications need
   to be considered:

   *  Elevator telephones

   *  Audible Burglar alarms




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   *  Silent alarms

   *  Credit/debit card processing terminals in places where Internet
      connections are unavailable

   *  Roadside motorist assistance telephones

   Civil emergency response centers will have critical need to make
   certain proper expansion and adjustment is done for:

   *  911/E-911 routing

   *  PSAP systems

   *  ALI/ANI databases

   Number portability and carrier identification databases must be
   adjusted to compensate for this change:

   *  LNP databases are massive, and may require updates to database
      schemas and query logic in both SQL and NoSQL implementations

   *  Key lookup structures are dependent on current NPA-NXX format

   One advantage this proposal provides is it requires no change to NXX
   format, preserving existing LNP granularity.

14.  Benefits

   The current NPA format allows a maximum of 800 NPAs to be implemented
   (200-999).  However, practical considerations reduce this in several
   ways:

   *  X11 codes (211, 311, 911 etc.) are unavailable

   *  988 as an additional N11-style number (and possibly others in the
      future) will reduce the supply further

   *  N9X was reserved for future expansion.

   Given these constraints, the maximum number of NPAs is probably more
   like 700.  While this is a large number, it eventually will be
   exhausted, possibly within the foreseeable future.

   Expansion of area codes to add an extra digit, and later full
   expansion to 11-digits expands the numbering range by a full factor
   of magnitude, to 8000 possible NPAXs.  Assuming similar carve-outs
   are used:



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   *  N11X is reserved to prevent confusion

   *  988X is also reserved

   *  Other similar service codes to 988 (200, 766, 322, 433 etc) are
      created, and those code ranges are restricted, e.g. 200X, 322X,
      433X

   *  N9XX is reserved for future expansion

   It still leaves a huge pool of available NPAXs.  If the X11X, 988X,
   and 10 additional service code code blocks are reserved, in addition
   to N9XX, we have

   *  72 NPAXs restricted for N11X protection

   *  110 NPAXs restricted for 988X protection and 10 additional service
      code blocks

   *  800 NPAXs reserved for N9XX expansion

   Leaves more than 7,000 potential NPAXs available for assignment.
   This represents an approximate order-of-magnitude increase in
   addressable numbering capacity compared to the current NANP
   structure.

15.  Economic Considerations

15.1.  Cost Considerations Of Methods Used

   Incremental approaches distribute cost over time but increase long-
   term complexity.  A planned expansion incurs higher initial cost but
   may reduce cumulative cost and operational burden.

   Early planning enables gradual transition and reduces the risk of
   emergency implementation.

15.2.  Billing and Rating Impact

   Carriers price call charges (including call origination and
   termination payments) on

   *  NPA-NXX

   *  LATA boundaries






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   Other than increasing the length of the NPA and temporarily carrying
   duplicate records (one for the old 3-digit NPA, and one for its
   replacement NPAX during phases 1 through 3 (much of which can be
   automated) these impacts are expected to be minimal due to
   preservation of the NPA-NXX structure used in existing billing and
   rating systems.

16.  Security Considerations

   Changes to numbering formats may impact fraud detection systems, call
   validation mechanisms, and authentication processes.  These impacts
   SHOULD be evaluated during implementation planning.

   Number spoofing detection systems, including but not limited to STIR/
   SHAKEN authentication to take into account both the current, and
   replacement numbers.

   Call authentication assumptions MUST be reviewed and updated to
   ensure compatibility with both legacy and expanded numbering formats.
   This represents an approximate order-of-magnitude increase in
   addressable numbering capacity compared to the current NANP
   structure.

17.  Transition Governance

   One or more coordinating authorities MUST be designated to manage key
   aspects of the transition.  These include:

   *  Whether the NPAX flag digit in position 4 of the telephone number
      is 0 or 1

   *  Timeline for start and implementation of each phase and segment of
      the upgrade plan

   *  Who will be responsible for enforcing compliance with all
      mandates?

18.  Transition Difficulties

   Not all parties involved in the transition will necessarily act as
   expeditiously as possible.  Concerns over depreciation or
   amortization of existing equipment and/or  software will be a serious
   concern to various organizations and responsible  individuals.  This
   may result in compatibility problems with respect to

   *  "Long tail" legacy systems

   *  Private Branch Exchange (PBX) systems



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   *  International interoperability lag

   As a result, partial deployment conditions may persist long after
   others are fully ready for the changes as a result of the
   implementation of 11-digit telephone numbers.

19.  International Considerations

   The proposed 11-digit format remains compatible with the E.164 [ITU]
   maximum length of 15 digits.  Coordination with international
   carriers and regulatory bodies is required.

   *  This change poses no impact to global numbering compatibility

   *  It fits into the existing +1 country code model

   No changes to the E.164 country code (+1) are required.

20.  IANA Considerations

   This document has no IANA actions.

21.  Conclusion

   Expansion of the NANP to 11 digits represents a viable long-term
   solution to numbering exhaustion.  Early evaluation and planning are
   recommended to enable a controlled and gradual transition.

   Given the long lead times required for numbering plan changes, early
   evaluation is necessary to avoid time-constrained or emergency
   implementation.

22.  References

22.1.  Normative References

   [ITU]      International Telecommunications Union, "The international
              public telecommunication numbering plan Recommendation
              ITU-T E.164", November 2010, <https://www.itu.int/rec/
              dologin_pub.asp?lang=e&id=T-REC-E.164-201011-I!!PDF-
              E&type=items>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.





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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

22.2.  Informative References

   [RFC1394]  Robinson, P., "Relationship of Telex Answerback Codes to
              Internet Domains", RFC 1394, DOI 10.17487/RFC1394, January
              1993, <https://www.rfc-editor.org/rfc/rfc1394>.

Appendix A.  Changelog

   draft-00:

   *  Initial Release

   draft-01:

   *  correct misspelling: allowsexisting -> allows existing
   *  Explain drawbacks of some alternative strategies
   *  Adjust line lengths to improve ease if editing, to take
      advantage of kramdown-rfc and xml2rfc automatic reformatting

Author's Address

   Paul Robinson
   Email: comments@11digitdialing.com
























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