2021-09-10
Telephone numbers in the United States and Canada are in the format of 1-NPA-NXX-XXXX. The “1” is the “country code” for both the United States and Canada. The “NPA” refers to a “Numbering Plan Area” more commonly known as an “area code”. The “NXX” refers to a central office, exchange, or rate center. The “XXXX” refers to a local subscriber number.
Number assignments for area codes and central office codes are made by the North American Numbering Plan Administrator (NANPA) following guidelines produced by an industry organization known as the Alliance for Telecommunications Industry Solutions (ATIS).
Blocks of 10,000 or 1,000 subscriber numbers (“XXXX”) are issued by NANPA to service providers which are interconnected on the Public Switched Telephone Network (PSTN). Service providers assign individual subscriber numbers to their customers.
NANPA maintains a database of its NPA-NXX assignments.
For subscriber telephone numbers that have been ported outside of the NPA-NXX assignment a separate Local Number Portability (LNP) database is maintained by the Number Portability Administration Center (NPAC). NPAC is currently operated by a company called iconectiv (previously Telcordia Technologies and Bellcore prior to that).
When a call is placed on the PSTN the originating switch will query the LNP database to see if the number has been ported. (Usually this is done with SS7 signaling.) If it has been ported, then the query results will provide a Location Routing Number (LRN) along with various other pieces of information (such as whether the provider is wireless, wireline, or VoIP). The originating switch then would place the call to the switch identified by the resulting LRN if the destination number was ported – or to the switch identified by the NPA-NXX assignment if the destination number was not ported.
Initially telephone numbers were not portable. Consequently, prior to 1997 telephone customers would need to change their phone numbers if they changed their telephone service provider. The transition to full number portability (also called “National Number Portability” or “NNP”) is a slow-moving process that is not yet complete and does not have an expected date for completion.
The first instances of available LNP were limited to major metropolitan areas beginning in 1997 and became available elsewhere the following year. Wireless Local Number Portability (WLNP) began in 2003. However, both LNP and WLNP are local portability only, meaning the number can only be ported between service providers within the same local access and transport area (LATA).
But wait, how can that be? There are plenty of people who move across the country and keep their same wireless number – even if they switch providers in their new location. The answer is that WLNP works just fine for that situation as long as the new wireless service provider has a business location in the LATA where the original phone number was assigned. So, WLNP works for most situations where major wireless providers (or their subsidiaries) are involved; it may not work for some situations in some rural LATAs or with some smaller wireless service providers who may not have business locations in the LATA where the original phone number was assigned.
What about all of those on-line fax service providers who port numbers to their service from all across the country? The answer is basically the same. In those cases the on-line fax service provider is actually porting the number to a VoIP provider doing business in the same LATA as the number’s origin with whom they have contracted services and then routing the received calls to their datacenters elsewhere, wherever they may be. Consequently, the call transits a VoIP call path from the original LATA to the fax service provider’s datacenter.
Why can’t telephone numbers be ported to outside of their LATA? Couldn’t the NPAC simply use the LNP database to point a number to somewhere outside of the assigned LATA? Yes, technically it could, but it can’t because that’s the policy established by the FCC and other organizations mentioned earlier. Things like the difference between local calling and long-distance calling would become quite complicated for ported numbers. Some entity bears the burden for carrying local calls outside of the LATA, and decisions need to be made regarding how that entity will be compensated.
So, why doesn’t Mainpine do the same as some other on-line fax service providers and use VoIP to get numbers ported? Because VoIP is not reliable enough for our customers’ fax use. Our customers depend on high-reliability fax services, and that’s just not consistently possible with the likelihood of jitter on VoIP networks over the course of the entire fax call. (That’s not to mention the meddlesome nuisance that T.38 can easily become in that environment.) Other service providers may be willing to accept the usual failure rate that accompanies faxing over VoIP networks; however, Mainpine customers find such failure rates to be unacceptable. Consequently, Mainpine strongly recommends that its on-line fax service customers have fax traffic sent directly to the fax numbers that Mainpine assigns.
If customers have a local number that they wish to retain and thus are unwilling to follow the recommendation above, then Mainpine recommends that the local number be forwarded over a TDM network (not VoIP) to the number Mainpine assigns and that the service provider be capable of forwarding multiple concurrent calls. (The service provider should consider enabling Two B-Channel Transfers (2BCT) in order to get the call path of forwarded calls from out of their network.) By forwarding incoming calls the consumer is consenting to the cost burden of carrying local calls outside of the LATA. Ideally the customer has an unlimited long distance plan which can be utilized by the forwarded calls, otherwise the monthly fees for the tolls for forwarded calls could get expensive.
If the local number is already being serviced by a VoIP provider then the best course of action for the customer to retain the number and also facilitate reliable fax operations for incoming fax calls to that number is to port that number to the local incumbent service provider (ILEC) or another local provider (CLEC) with TDM services, and to have the number forwarded from there. However, this can be a tedious process, and the monthly tolls or contract fees could be expensive.
The North American Numbering Council (NANC), a federal advisory committee for the FCC, is currently evaluating and determining a course of action for NNP, which would allow telephone numbers to be ported outside of their originally-designated LATAs. However, this process is already decades old and is likely to not be completed for many more years. The proposed National Local Routing Number (NLRN) solution would be suitable for reliable fax use.
However, even when it is eventually completed, it’s quite possible that NNP would be made available only via an alternative Internet Protocol Local Routing Number (IPLRN) solution, so only through VoIP. This isn’t an extremely reliable option for fax applications as it is basically the same as what some fax service providers do today. There is no guarantee that NNP via NLRN would ever be implemented.
IPLRN proponents tout T.38 (Fax over Internet Protocol or “FoIP”) as the remedy for reliable fax operations on IP networks, but we already know that is not the case. In some regions of the United States, local governments have permitted TDM infrastructure to be removed entirely from the PSTN, leaving only VoIP networks. Consumers in these regions already have a practically impossible task of acquiring telephone services which are reliable for fax use. In such situations consumers have no other immediate, practical, and reliable fax option than to outsource their faxing operations to an on-line fax service provider, for example.
In conclusion, Mainpine continues to strongly recommend to its on-line fax service customers that they request faxes to be sent directly to the fax number that Mainpine provides. If a local fax number must be used, then that fax number should be forwarded using a TDM service provider that is capable of forwarding multiple concurrent calls and ideally utilizing 2BCT. For future progress Mainpine recommends the adoption of the NLRN solution for NNP, and the proliferation of features such as SSL Fax for reliable fax integration with IP networks.
Mainpine encourages all fax receiving endpoints (in particular fax service providers) to utilize CSID to advertise the direct inbound number. This, then, enables a fax sender who is struggling to deliver fax documents through a forwarded number to subsequently attempt the fax operation to the direct number and thereby avoid complications caused by problematic carriers involved in the call forwarding.
See Also:
Number Portability FAQ for Marketers
ATIS PTSC: Packet Technologies and Systems Committee