See CN.


Emergency telephone service where the calling party is connected to a local, Public Service Answering Point (PSAP), commonly located at public, law enforcement or emergency services offices. The called PSAP will receive your telephone number and physical address so as to aid in dispatch of emergency personnel.


Charge Number, is the billable telephone number associated with the calling party. Often this number is different from CPN which provides the basis for CID which is displayed as the calling party on the called party’s telephone. CN is the basis for toll billing and should never be changed or manipulated by any transit or the terminating carrier. ANI is a term referring to CN.


Caller ID, is based on CPN and is what is displayed as the calling party telephone number on the called party’s telephone.


Competitive Local Exchange Carrier, a business entity that is certified and licensed to operate by a state Public Utilities Commission to provide local telephone service.


Calling Name Delivery Service provides alpha numeric information or “plain text” identifying the calling party.


Calling Party Number is the basis for CID which is the referenced telephone number of the calling party and what is displayed on the called party’s telephone. CPN/CID can be manipulated if accompanied with a valid CN as CN will provide the first basis for billing jurisdiction.


Direct Inward Dialing, A service feature that allows inward-directed calls to a “trunk connected” customer switch or PBX to reach a specific PBX or telephone number and end subscriber served by the customer switch without human intervention.


is an ITU-T recommendation which defines the international public telecommunication numbering plan used in the PSTN and some other data networks. It also defines the format of telephone numbers. E.164 numbers can have a maximum of fifteen digits and are usually written with a + prefix. To actually dial such numbers from a normal fixed line phone, the appropriate international call prefix must be used.


ISDN User Part, the portion of the SS7 protocol stack that is used to connect and disconnect a call between physically interconnected telephones switches in the NANP area.


Telecommunication Standardization Sector, coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland.


Inter-exchange Carrier, commonly referred to as a “Long Distance Company”. The IXC switches and transport calls between LATA and state jurisdiction areas.


Local Access Transport Area., the geographic region set up to differentiate local and long distance telephone calls within the U.S. Telephone calls between parties within a LATA (intraLATA) are handled by the local telephone companies and are under the jurisdiction of the state’s public tility commission. Calls between LATAs are handled by interexchange carriers (IXCs) and are governed by the FCC.


Line Information Database, used for various purposes and commonly the basis for White Page, telephone book listings and 411 directory assistance database entries.

NANP (Area)



North American Numbering Plan Administration, NANPA holds overall responsibility for the neutral administration of NANP numbering resources, subject to directives from regulatory authorities in the countries that share the NANP. 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.

NANPA (format)

The numbering format adhered to in the NANP areas, i.e. NPA-NXX-XXXX or 702-553-3007.


Plain Old Telephone System or Service, the most rudimentary telephony service such a s single business or residential line.


Public Safety Answering Point, a physical location where 911 emergency telephone calls are received and then routed to the proper emergency services.


Public Switched Telephone Network, is the network of the world’s public circuit-switched telephone networks, in much the same way that the Internet is the network of the world’s public IP-based packet-switched networks. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital, and now includes mobile as well as fixed telephones.


Responsible Organization, the entity that manages and, or administrates SMS/800 database information and routing data for a given toll free telephone number.


The database that provides per call routing for all Toll Free Telephone Numbers in the NANP Area. Commonly, the CLEC’s originating switch will query the SMS database to identify a POTS number and, or CIC code and then pass same information to a regional Access Tandem for proper routing to the IXC that supplies intrastate and interstate transport of the toll free call.




Time Division Multiplexing, A technology that transmits multiple signals simultaneously over a single transmission path. Each lower-speed signal is time sliced into one high-speed transmission. In the simplest example, three incoming 1,000 bps signals (A, B and C) can be interleaved into one outgoing 3,000 bps signal as ABCABCABCABC. The receiving end divides the single stream back into its original signals.