NPA.NXX
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What is it?
The term NPA.NXX refers to the first six digits of a phone number, or prefix, as derived from the North American Number Plan (NANP). The area code is the first three digits and delineates a toll area in the US, Canada, and Mexico. The area code is also referred to as a Number Plan Area or NPA. NXX refers to the exchange, which is the three digits following the area code. Together, they form a number unique to a specific Central Office (CO). There are 24,000 COs in the US and Canada.
Is an NPA.NXX a unique location identifier?
In order for an ISP to generate a quote for transit across its backbone, it must calculate the distance from the CO serving the installation premise to the nearest POP. Since the NPA.NXX is unique and no two COs can have the same NPA.NXX, carriers use this number to verify the CO from which the premise is served and they measure the local access loop distance from this point. It also tells them what Regional Bell Operating Company (RBOC) is providing the loop. Often, carriers will have different rates for local access for each RBOC depending on volume of lines in use with that particular company and corporately negotiated discounts in effect.
Why is it so important?
The NPA.NXX must be correct before the quoting process takes place in order for the local access loop to be calculated correctly. Often, an incorrect NPA.NXX can lead to a faulty quote which may not be caught until the circuit order is placed with the RBOC or even after the circuit is installed. In each case, the results can be detrimental since much consideration is placed on selecting a provider and price is always a determining factor.
What NPA.NXX will return errors?
Cellular NPA.NXX, while they may have been assigned in the same metro area, are not served from traditional COs and will not return an accurate telecom quote.
Non Geographic NPA such as 800 or 900 are Service Access Codes (SAC) and are not specific to a certain area, and therefore will not suffice.
CLEC assigned NPA.NXX will cause malfunction seventy-five percent of the time. CLECs are often assigned a group of exchange numbers to cover an entire metropolitan area and may span multiple COs. A NPA.NXX must resolve to a specific CO to be accurate. If you have service from a CLEC and were assigned numbers from them as new or original service as opposed to porting existing numbers over to them, the chances are that they will not be accurate.
Port Forwarded NPA.NXX such as when a business moves location and is served out of a new CO but maintains original numbers will not work. When this occurs, the business is actually assigned new numbers but the old number stays in service. When the old number is dialed, the call is automatically transferred to the new numbers. A new telecom quote however, will resolve to the old CO and therefore will be invalid.
DID associated NPA.NXX; if the NPA.NXX is part of a Direct Inbound Dialing (DID) block, it is most likely unique to the serving CO, but may not be part of the universally accepted number list of that CO. The reason being that the CO may generate phone numbers for a DID block that are outside of its actual NPA.NXX list to serve large allotments of DIDs when they may be low on numbers. These numbers may not resolve to any CO by a carrier pricing system and may therefore be invalid.
What to do if you don't have an accurate NPA.NXX
Should you be in a situation where you have no existing NPA.NXX at the installation premise such as with new office situations or if your NPA.NXX matches one of the descriptions listed above as invalid, consult with the rep of the quoting telecom company and inform them ahead of time. As a tip, make sure you have in writing (or as an e-mail response) that you pointed out the NPA.NXX discrepancy. That way if a mistake is made in the quoting process it won’t be your fault. This could be key in a costly legal situation should the difference between quoted and actual price be tens of thousands of dollars. A telecom rep should have many tools beyond the NPA.NXX at their disposal to confirm the serving CO.
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