National Pooling Administration
Tools - Glossary




Administrative Operating Company Number. The term "AOCN" also refers to the company that updates rating and routing information associated with central office code assignments.


Automatic Number Identification


American National Standards Institute


Alliance for Telecommunications Industry Solutions (


Business Integrated Routing and Rating System




Contract Data Requirements List


Carrier Identification Code


Common Interest Group on Rating and Routing


Competitive Local Exchange Carrier


COMMON LANGUAGE® Location Identification


Central Location ON-line Entry System


Central Office


Central Office Code Assignment Guidelines


Disaster Recovery Plan


Emergency Service Query Key


Federal Communications Commission


First Implementation Meeting


Future of Numbering Working Group


Internet Access NXX


Incumbent Local Exchange Carrier


Issue Management Group


Industry Numbering Committee


Interexchange Carrier


Local Access and Transport Area


Local Exchange Carrier


Local Exchange Routing Guide


Limited Liability Corporation


Local Number Portability


Location Routing Number


Mandatory Rate Center


Mandatory Rate Center with only One SP


State Designated Mandatory Rate Center


State Designated Mandatory Rate Center with One SP


Metropolitan Statistical Area


Months to Exhaust


Mean Time to Repair


North American Numbering Council


North American Numbering Plan


North American Numbering Plan Administration


National Association of Regulatory Utility Commissioners


Number Administration Service Center (Toll-Free 800/866/877/888 database)


Network Interconnection and Interoperability Forum


Numbering Oversight Working Group, a subgroup of the NANC


Numbering Plan Area (Area Code)


Number Portability Administration Center


Number Resource Optimization


Network Rating and Routing Information Committee


Numbering Resource Utilization Forecast


The format of an NPA code or a central office code (N=2-9, X=0-9)


Optional Rate Center


Ordering and Billing Forum


Operating Company Number


Pooling Administrator


Pseudo Automatic Number Identification


Pooling Administration System


Personal Communications Service


Public Safety Answering Point


Public Service Commission


Public Switched Telephone Network


Public Utility Commission


Rate Area


Rate Center


Service Access Code


Supplemental Implementation Meeting


Service Provider


Signaling Transfer Point


Thousands Block Pooling Administration Guidelines


Telephone Number


Terminating Point Master


TELCORDIA™ Routing Administration


Excluded Rate Center


Vertical & Horizontal (Coordinates)


Virtual NXX


Voice Over Internet Protocol


Vertical Service Code



Activation Deadline

Six months from the original effective date returned on the Part 3 and entered on the BCR/BCD screen in BIRRDS.  A Part 4 should be returned to the Pooling Administrator by this date.


Active Block

A thousands-block assigned by the PA and implemented in the PSTN for specific routing requirements as of the block effective date.


Administrative Constraint/Reason

A limitation of the Point of Interconnection or Switching Entity where an existing block and/or TNs cannot be used for designated network routing and/or rating of PSTN calls.  An example of a constraint would be the limitation in the administration of a thousands-block across multiple switches in a rate area and would require a waiver from the FCC Commission.


Administrative Numbers

Administrative numbers are numbers used by telecommunications carriers to perform internal administrative or operational functions necessary to maintain reasonable quality of service standards.  FCC 00-104 §52.15 (f)(1) (i).

Subcategories of administrative numbers are: test numbers, employee/official numbers, Location Routing Numbers, Temporary Local Directory Numbers (TLDN), soft dial tone numbers and wireless E911 emergency service routing digit/key (ESRD/ESRK) numbers. (FCC 00-104 ¶ 36).


Administrative Operating Company Number (AOCN)

A four character numeric or alphanumeric that identifies the administrator of one (or more) data record contained in Telcordia’s Business Integrated Rating and Routing Database System BIRRDS. Numeric/alphanumeric AOCNs are determined by Operating Company Number (OCN) assignment. The AOCN further identifies the entity authorized by the code holder to input and maintain data into BIRRDS.


Affected Parties

Affected parties are a) those entities that have applied for and/or received thousands-block (NXX-X) assignments within the NXX code b) administrative entities involved in number administration, number portability or number pooling.


Aging Numbers

Aging numbers are disconnected numbers that are not available for assignment to another end user or customer for a specified period of time. Numbers previously assigned to residential customers may be aged for no more than 90 calendar days.  Numbers previously assigned to business customers may be aged for no more than 365 calendar days. (FCC 00-104 §52.15 (f)(1) (ii) See Erratum in CC Docket 99-200, released July 11, 2000).

An aging interval includes any announcement treatment period, as well as the vacant telephone number intercept period.  A number is disconnected when it is no longer used to route calls to equipment owned or leased by the disconnecting subscriber of record.


Allocated/Assigned Block

A thousands-block is allocated/assigned to an SP when the block information has been entered into BIRRDS by the PA.


Allocation Date

The Allocation Date is the date established by the PA when the PA officially makes the block assignment to an SP.



SPs who submit a block request to the PA for the purpose of being assigned a thousands-block for their use.


Assigned Numbers

Assigned numbers are numbers working in the PSTN under an agreement such as a contract or tariff at the request of specific end users or customers for their use, or numbers not yet working but having a customer service order pending.  Numbers that are not yet working and have a service order pending for more than five calendar days shall not be classified as assigned numbers. (FCC 00-104 §52.15 (f)(1) (iii))

Ported-out numbers should be included as a subcategory of assigned numbers. (FCC 00-104 ¶ 36).



The accumulation and evaluation of evidence about documented information of an auditee to determine and report on the degree of compliance with INC industry guidelines.



The SP/NANPA/PA that is the subject of an audit.


The FCC Common Carrier Bureau’s Audits Branch of the Accounting Safeguards Division or its other designated agents perform audits of US numbering resources. (FCC 00-429 ¶ 90). State Commissions also may conduct audits. (FCC 01-362 ¶101.


Authorized Representative of an Applicant

A person from an applicant's organization or its agent that has the legal authority to take action on behalf of the applicant.


Available Numbers

Available numbers are numbers that are available for assignment to subscriber access lines, or their equivalents, within a rate area and are not classified as assigned, intermediate, administrative, aging, or reserved.  Available numbers is a residual category that can be calculated by subtracting a sum of numbers in the assigned, reserved, intermediate, aged, and administrative primary categories from the total of numbers in the inventory of a code or block holder  (FCC 00-104 §52.15 (f)(1) (iv)).


Block Applicant

See “Applicant.”


Blocks Available for Assignment

Thousands-blocks (NXX-X) within the industry inventory pool rate center which are within an NPA/NXX that is flagged as LNP capable in the LERG Routing Guide and the NPAC, and which are available for assignment within the SP’s rate center.



Block Code Record/Block Code Data

Block Donation Date

The deadline for SPs to donate their thousands-block(s).


Block Donation Identification Date

The deadline for SPs to report their surplus of thousands-blocks to the PA.  This is also the date when SPs may begin to port all TNs in contaminated thousand blocks that they are donating to the pool. All blocks to be donated must be portable in the NPAC and LERG Routing Guide.


Block Exhaust

a) When used by the Block Holder in applying for additional thousands-blocks, a point in time at which the quantity of TN's within existing thousands-block(s) which have been assigned to the Block Holder equals zero for a rate area.

b) When used by the PA in applying for additional NXX codes, block exhaust is defined as a point in time at which the quantity of thousands-blocks within the rate area which are “available for assignment” equals zero. 


Block Holder

The entity to which a thousands-block (NXX-X) has been assigned for use.


Block Protection Date

The deadline for SPs to donate their thousands-blocks. This is also the date by which all providers participating in thousands-block number pooling in the NPA must have all their Intra Service provider ports completed. Five business days later, Telcordia will update the LERG Routing Guide with thousands-blocks SPs are retaining.



The Telcordia™ Business Integrated Routing and Rating Database System contains data in the routing and rating of calls.  Contains a complete description of all Local Exchange Companies’ networks in the NANP Area and pertinent information relating to the networks of other code holders.  This provides information for, (1) message routing, (2) common channel signaling call setup routing, and (3) operator service access routing.  Data supports all CO Codes assigned through these Guidelines, as well as all CO Codes in place prior to the existence of these Guidelines, and covers all Numbering Plan Areas (NPAs) administered under the North American Numbering Plan (NANP). 


Central Office (CO) Code

The sub-NPA code in a TN, i.e., digits D-E-F of a 10-digit NANP Area address.  Central office codes are in the form "NXX", where N is a number from 2 to 9 and X is a number from 0 to 9.  Central office codes may also be referred to as "NXX codes" (47 C.F.R. § 52.7(c)).



The authorization of a carrier by a regulator to provide a telecommunications service in the relevant geographic area. 47 CFR § 52.15 (g) (2) (i) requires that applications for initial numbering resources include evidence that the applicant is authorized to provide service in the area for which numbering resources are being requested.



A CLLI Location Identification Code is an eleven-character alphanumeric descriptor used to identify switches, points of interconnection, and other categories of telephony network elements and their locations.  Companies that are licensees of Telcordia™ COMMON LANGUAGE® Products can refer questions to their company's COMMON LANGUAGE Coordinator.  If you do not know if you are a licensee, do not know your Coordinator, or are a licensee with questions regarding CLLIs, call the COMMON LANGUAGE Hotline, 877-699-5577.  Alternatively, or if you are not a licensee, obtain further information at  (COMMON LANGUAGE is a registered trademark and CLLI is a trademark of Telcordia Technologies, Inc.)


CO Code Administrator

Entity(ies) responsible for the administration of the NXX codes within an NPA. In the United States and its territories, this is currently the NANPA. See also 47 CFR § 52.7 (d).


Code Holder

An assignee of a pooled or non-pooled NXX that is assigned by the CO Code Administrator. The responsibilities of an assignee for a pooled NXX are defined in Section 4.2.1 of the Thousands Block Number (NXX-X) Pooling Administration Guidelines (TBPAG) and for a non pooled NXX are defined in Section 6.3 of the Central Office Code (NXX) Assignment Guidelines (COCAG). A given Code Holder is identified in the LERG Routing Guide as the NPA-NXX-A (Assignee) OCN record holder.


Contamination occurs when at least one telephone number within a thousands-block of telephone numbers is not available for assignment to end users or customers. Blocks contaminated up to and including 10 percent are eligible for donation. For purposes of this provision, a telephone number is “not available for assignment” if it is classified as administrative, aging, assigned, intermediate, or reserved as defined in FCC rules (47 CFR § 52.7 (h)).


Critical Industry Inventory Insufficiency

Critical industry inventory insufficiency exists for a rate area when the available resources in the industry inventory pool for a particular rate area fall below the actual and/or forecasted demand for the next 66 calendar days.


Dealer Numbering Pools

Numbers allocated by a service provider to a retail dealer for use in the sale and establishment of service on behalf of that service provider.  See the definition of “Intermediate Numbers” below. (FCC 00-104 ¶20)



The term “donation” refers to the process by which carriers are required to contribute telephone numbers to a thousands-block number pool (47 CFR § 52.7(i)).

Effective Date

The date by which routing and rating changes within the PSTN must be complete for the assigned thousands-block or the assigned CO Code.  Also, the date by which the thousands-block becomes an active block. (Also referred to as “the LERG Routing Guide effective date.”)


Forecast Report

All thousands-block number pooling service providers shall provide a Thousands-Block Forecast Report, on a semi-annual basis, by rate area to the Pooling Administrator. The Thousands-Block Forecast Report is based on a 12-month interval.  A Thousands-Block Forecast Report will be sent by service providers to the PA for all number resource requirements in thousands-block number pooling rate areas, including full NXX Codes as well as thousands-blocks. The forecast submitted is incremental above the quantity of thousands-blocks already allocated in the service provider's inventory. 



Industry Numbering Committee (INC) provides an open forum to address and resolve industry-wide issues associated with the planning, administration, allocation, assignment and use of numbering resources and related dialing considerations for public telecommunications within the North American Numbering Plan (NANP) area.


Initial Block

An initial block or “footprint” block is the first NXX-X block that a service provider receives in a rate center where the SP has no other assigned resources (FCC 00-104, ¶ 86 and 191).

In Service

A code or block for which local routing information appears in the LERG Routing Guide, and one or more telephone numbers within the NXX code or NXX-X block has been Assigned to an end user (FCC 00-104, ¶240). Numbers that are categorized as Administrative, Aging, Intermediate, Reserved, or Available cannot also be Assigned and do not satisfy the In Service requirement.


Intermediate Numbers

Intermediate numbers are numbers that are made available for use by another telecommunications carrier or non-carrier entity for the purpose of providing telecommunications service to an end user or customer. Numbers ported for the purpose of transferring an established customer’s service to another service provider shall not be classified as intermediate numbers (47 CFR § 52.15 (f) (1) (v)).Numbers such as dealer number pools should be included as a subcategory of intermediate numbers. (FCC 00-104 ¶ 36).


Intra-service Provider Port

An intra-service provider port allows an SP to retain unavailable TNs in contaminated thousands-blocks that are being donated to an industry inventory pool.  Specifically, numbers assigned to customers from donated thousands-blocks that are contaminated will be ported back to the donating carrier to enable it to continue to provide service to those customers.  An intra-service provider port can also be used to move a TN(s) from one switch serving a rate area to another switch serving the same rate area where LRN-LNP technology is in use. 



The term “inventory” refers to all telephone numbers distributed, assigned or allocated:

(1) To a service provider, or
(2) To a Pooling Administrator for the purpose of establishing or maintaining a thousands-block number pool (47 CFR § 52.7 (j)).

(Industry) Inventory Pool

Used in thousands-block number pooling to describe a reservoir of unallocated thousands-blocks administered by the PA for purposes of assignment to SPs participating in thousands-block number pooling.



A jeopardy condition exists when the forecasted and/or actual demand for NXX code resources will exceed the known supply during the planning/implementation interval for relief. 


LATA (Local Access and Transport Area)

Also referred to as service areas by some BOCs, a LATA serves two basic purposes:  to provide a method for delineating the area within which the BOCs may offer services and, to provide a basis for determining how the assets of the former Bell System were to be divided between the BOCs and AT&T at divestiture.


LERG™ Routing Guide

The Telcordia™ LERG™ Routing Guide contains information about the local routing data obtained from the BIRRDS.  This information reflects the current network configuration and scheduled network changes for all entities originating or terminating PSTN calls within the NANP.

Contact Information:
Telcordia Routing Administration (TRA)
8 Corporate Pl. 3N141
Piscataway, NJ  08854-4156

LNP Port

The process of moving a TN from one SP to another SP using LRN-LNP technology.  See also “Intra-Service Provider Port” definition.


Location Routing Number (LRN)

The ten-digit (NPA-NXX-XXXX) number assigned to a switch/POI used for routing in a permanent local number portability environment.  See “Administrative Numbers” definition.


Mandated Implementation Date

The date identified by the appropriate regulatory body by which thousands-block number pooling is to be implemented.


Months to Exhaust

When used by SPs to document the need for an additional block:

=               TNs Available for Assignment


                Average Monthly Growth Rate


When used by the PA to document the need for an additional CO Code:

=                Blocks Available for Assignment


                  Average Monthly Growth Rate


NANP (North American Numbering Plan)

A numbering architecture in which every station in the NANP area is identified by a unique ten-digit address consisting of a three-digit NPA code, a three digit central office code of the form NXX, and a four-digit line number of the form XXXX, where N represents the digits 2-9 and X represents the digits 0-9.

It is the basic numbering scheme for the telecommunications networks located in American Samoa, Anguilla, Antigua, Bahamas, Barbados, Bermuda, British Virgin Islands, Canada, Cayman Islands, Dominica, Dominican Republic, Grenada, Jamaica, Montserrat, St. Kitts & Nevis, St. Lucia, St. Vincent, Turks & Caicos Islands, Trinidad & Tobago, and the United States (including Puerto Rico, the U.S. Virgin Islands, Guam, the Commonwealth of the Northern Mariana Islands) [47 CFR § 52.5 (c)].

NANPA (North American Numbering Plan Administration)

The NANPA is responsible for the neutral administration of NANP numbering resources, subject to directives from regulatory authorities in the NANP member countries (see also 47 CFR § 52.7 (e)). The NANPA is an impartial non-governmental entity that is not aligned with any particular telecommunications industry segment.[1] Under contract to the FCC, NANPA's responsibilities include assignment of NANP resources, and, in the U.S. and its territories, coordination of area code relief planning and collection of utilization and forecast data. See also 47 CFR § 52.13.


North American Numbering Plan, Numbering Resource Utilization/Forecasting Report (NRUF Report)

The NANPA gathers forecast and utilization information to monitor and project exhaust in individual NPAs/area codes as well as in the NANP overall.   This semi-annual report includes number utilization information as well as a five year forecast of demand by year.  Pooling carriers report at the thousands-block level per rate center.  Non-pooling carriers report at the Central Office Code level per rate center.  For more detailed information, see the NRUF Report Guidelines.



Numbering Plan Area (NPA), also called area code. An NPA is the 3-digit code that occupies the A, B, and C positions in the 10-digit North American Numbering Plan (NANP) format that applies throughout the NANP Area. NPAs are of the form NXX, where N represents the digits 2-9 and X represents any digit 0-9. In the NANP, NPAs are classified as either geographic or non-geographic.

a) Geographic NPAs are NPAs which correspond to discrete geographic areas within the NANP Area.

b) Non-geographic NPAs are NPAs that do not correspond to discrete geographic areas, but which are instead assigned for services with attributes, functionalities, or requirements that transcend specific geographic boundaries. The common examples are NPAs in the N00 format, e.g., 800.



The NPAC Service Management System is a database which contains all necessary routing information on ported TNs and facilitates the updating of the routing databases of all subtending SPs in the portability area.


OCN (Operating Company Number)

An Operating Company Number (OCN) is a four place alphanumeric code that uniquely identifies providers of local telecommunications service. OCN assignments are required of all SPs in their submission of utilization and forecast data (FCC 00-104, ¶ 41 and Public Notice DA 00-1549). Relative to CO Code assignments, NECA assigned Company Codes may be used as OCNs. Companies with no prior CO Code or Company Code assignments contact NECA (; 800-228-8597) to be assigned a Company Code(s). Since multiple OCNs and/or Company Codes may be associated with a given company, companies with prior assignments should direct questions regarding appropriate OCN usage to the Telcordia™ Routing Administration (TRA) (; 866-672-6997).


Point of Interconnection (POI)

The physical location where an SP's connecting circuits interconnect for the purpose of interchanging traffic on the PSTN.


Pooling Administrator

The term Pooling Administrator refers to the entity or entities responsible for administering a thousands-block number pool (47 CFR § 52.7 (g)). The Pooling Administrator is responsible for the neutral administration of thousands-blocks from Central Office (CO) Codes in areas where thousands-block number pooling has been ordered or implemented. The PA is an impartial non-governmental entity that is not aligned with any particular telecommunications industry segment and is under contract to the FCC.

Pooling Administration System (PAS)

The term Pooling Administrator refers to the entity or entities responsible for administering a thousands-block number pool (47 CFR § 52.7 (g)). The Pooling Administrator is responsible for the neutral administration of thousands-blocks from Central Office (CO) Codes in areas where thousands-block number pooling has been ordered or implemented. The PA is an impartial non-governmental entity that is not aligned with any particular telecommunications industry segment and is under contract to the FCC.


Pool Start/Allocation Date

The date the PA may start allocating thousands-blocks from the industry inventory pool to SPs.  This is also the start date for SPs to send requests for thousands-blocks to the PA.


Public Switched Telephone Network (PSTN)

Public Switched Telephone Network.  The PSTN is composed of all transmission and switching facilities and signal processors supplied and operated by all telecommunications common carriers for use by the public.  Every station on the PSTN is capable of being accessed from every other station on the PSTN via the use of NANP E.164 numbers.


Rate Center

Rate Center is used for numbering resource applications and reports to associate telephone numbers with a geographic area, as defined by the relevant regulatory agency. A Rate Center is also a uniquely defined point (Vertical & Horizontal Coordinates) located within an exchange area from which mileage measurements are determined. These measurements can be used with the tariffs in the message rating processes.



The process of reestablishing the assignment of a thousands-block, which was previously assigned to another SP or to a new SP.


Reporting Carrier

Refers to a telecommunications carrier that receives numbering resources from the NANPA, a Pooling Administrator or another telecommunications carrier. 


Reserved Numbers

Reserved numbers are numbers that are held by service providers at the request of specific end users or customers for their future use. Numbers held for specific end users or customers for more than 180 calendar days shall not be classified as reserved numbers (47 CFR § 52.15 (f) (1) (vi).


Service Provider (SP)

The term “service provider” refers to a telecommunications carrier or other entity that receives numbering resources from the NANPA, a Pooling Administrator or a telecommunications carrier for the purpose of providing or establishing telecommunications service (47 CFR § 52.5 (i)).


Service Provider Inventory

The inventory of all geographic NANP TNs allocated by the CO Code Administrator/PA to a Code/Block Holder.


Switching Entity

An electromechanical, electronic, or digital system for connecting lines to lines, lines to trunks, or trunks to trunks for the purpose of originating/terminating PSTN calls. A single switching system may handle several Central Office (CO) codes.

Technical Requirement, Reason, Limitation or

A limitation of the Point of Interconnection or Switching Entity where an existing thousands-block and/or TNs cannot be used for designated network routing and/or rating of PSTN calls.   Examples that constitute “technical constraint” include limitations on a switch, network element or planning constraint, CPE limitations or unique AIN Triggers.



A range of one thousand TNs within an NPA-NXX beginning with X000 and ending with X999, where X is a value from 0 to 9.


Thousands-Block Number Pooling

Thousands-block number pooling is a process by which the 10,000 numbers in a central office code (NXX) are separated into ten sequential blocks of 1,000 numbers each (thousands-blocks), and allocated separately within a rate center (47 CFR § 52.20 (a)).


Type 1 Interconnection Service Provider

A wireless SP that utilizes Type 1 (trunk side with line treatment) interconnection with another SP’s end office switch.


Utilization Threshold/Utilization Level or Threshold

The Service Provider’s current numbering resource utilization level for the rate center in which it is seeking growth numbering resources.

The numbering resource utilization level shall be calculated by dividing all assigned numbers by the total numbering resources in the applicant’s inventory and multiplying the result by 100. Numbering resources activated in the LERG Routing Guide (within the preceding 90 calendar days of reporting utilization levels may be excluded from the utilization threshold calculation.

All applicants for growth numbering resources shall achieve a 60% utilization threshold, calculated in accordance with 47 CFR § 52.15 (h), for the rate center in which they are requesting growth numbering resources.

The initial utilization threshold of 60% was effective May 2001. The utilization threshold was increased by 5% on June 30, 2002, and annually thereafter until the utilization threshold reached 75% (47 CFR § 52.15 (h)).

Wireless E911 ESRD/ESRK Number

A 10-digit number used for the purpose of routing an E911 call to the appropriate Public Service Answering Point (PSAP) when that call is originating from wireless equipment.  The Emergency Services Routing Digit (ESRD) identifies the cell site and sector of the call origination in a wireless call scenario.  The Emergency Services Routing Key (ESRK) uniquely identifies the call in a given cell site/sector and correlates data that is provided to a PSAP by different paths, such as the voice path and the Automatic Location Identification (ALI) data path.  Both the ESRD and ESRK define a route to the proper PSAP.  The ESRK alone, or the ESRD and/or Mobile Identification Number (MIN), is signaled to the PSAP where it can be used to retrieve from the ALI database, the mobile caller’s call-back number, position and the emergency service agencies (e.g., police, fire, medical, etc.) associated with the caller’s location.  If a NANP TN is used as an ESRD or ESRK, this number cannot be assigned to a customer.  See “Administrative Numbers” definition.


These definitions are informational, and have been gathered from multiple sources including the FCC, ATIS, NANPA, NPAC and industry forums. Please do not cite them as primary source material.