Telephone Number 1.0
Telephone numbers were created early in the 20th century as a way for people with telephones to call other people with telephones without having to go through an operator. Telephone numbers were administered by Ma Bell and served two primary purposes – addressing and billing. They served these purposes for much of the 20th century.
The telephone number was the address (An address is information communications networks use to route messages and establish sessions, e.g., telephone numbers, IP address.) The first six digits (area code and central office code) identified the specific telephone switch in the network that served a particular customer.
Switches in the network were configured to route calls to the switch associated with those six digits. The last four digits identified four copper wires on something called the main distributing frame (MDF) in that switching office. These copper wires ran all the way to the customer’s house and to their phone. The serving switch would connect the call to the four copper wires on the MDF and ring the customer’s telephone.
Billing for much of the 20th century, and even today in some cases, was based on the distance that the call traveled. Because the first six digits of the telephone number identified a specific switch and a specific location, the calling and called telephone numbers could be used to generate distance and therefore the rate for the call. The country was divided into regions called rate centers based on the first six digits of the customer’s telephone number. Rate centers were determined by a particular switch’s serving area. Basically they cover a town or a collection of towns.
Your Number, Your Identity
To some extent telephone numbers came to serve as part of a person’s identity. Where I grew up, if your central office code was 791, I knew you lived in Valley Stream, Long Island. This persists today, but much less so for central office codes than for area codes; 212, 310, 312, etc.
Competition in the telephone industry forced some changes in telephone numbers towards the end of the 20th century. This affected telephone number administration and addressing.
Telephone Number 2.0.
Since Ma Bell was no longer the only provider of telephone service it was not appropriate that she should administer such an important resource as telephone numbers. Access to telephone numbers meant the ability to provide telephone service. So telephone number administration was transferred to an entity that was restricted from providing telephone service. Carriers would now go to this entity to get telephone numbers for their inventory. Blocks of 10,000 telephone numbers identified by a specific area code and central office code (typically called the NPA-NXX) were distributed to service providers. States would also go to this same entity to get a new area code when their existing area code was exhausted.
Telephone users are very closely tied to their telephone numbers. They would not change service providers if it meant they had to change their telephone number. Since new service providers had their own switches, it was necessary to figure out a way to move existing telephone numbers, with an NPA-NXX associated with a specific switch, to a different switch. This meant that the telephone number could no longer be used as the address as had been done for so many years.
The Intelligent Network & Number Portability
A technology called Intelligent Network enabled the telephone network to stop a call in midstream and query a database to find an address for a specific telephone number. Then the call could be routed to the new address and a different switch than the one associated with the NPA-NXX. The new address is called a routing number and is in the form of a telephone number. The network uses the NPA-NXX of the routing number to complete the call to the new switch. This is called number portability.
With number portability a person’s telephone number became a name and no longer an address. (A name does not provide routable information for communications networks, e.g., ported telephone numbers, domain names.) It identifies the person you are trying to contact, not the address on the network associated with that person’s telephone.
The Internet had to solve this problem very early in its evolution. They created the domain name system (DNS) because they realized that IP addresses, e.g., 172.16.254.1, were not very useful as names. The DNS translates the domain name that you put in email addresses and web browsers into an IP address to connect you with that name. Separating the name from the address was a significant change for telephone numbers. They can now be moved within and between networks and service providers.
Along with competition came a great demand for NPA-NXXs from the new competitive service providers. To maintain parity with Ma Bell the new service providers were able to obtain an inventory of NPA-NXXs in each rate center. There are over 20,000 rate centers. If one service provider requested one NPA-NXX in every rate center it would be an inventory of over 200M telephone numbers. At one time there were over 4,000 service providers. There are only 300M people in the US.
While service providers were more selective about acquiring NPA-NXX this still created a great deal of stress on NANPA’s supply of telephone numbers. Area codes quickly exhausted and new ones had to be put into service. And much of the new inventory was not being used. While there were many new service providers they were all going after the same 300M people.
The industry quickly realized this was not sustainable and instituted various conservation measures. One of these measures utilized the new capabilities that came with number portability. Telephone numbers were no longer given out in blocks of 10,000 associated with an NPA-NXX, but in blocks of 1,000 associated with an NPA-NXX-X (a thousands block or 1KB). This is called telephone number pooling because an NPA-NXX could be pooled among 10 service providers.
Numbering in the Internet Age?
While TN 2.0 created significant changes in telephone numbers, much still remains the same as it was in the early 20th century. Blocks of telephone numbers are still given out based on rate centers. This contributes to the fact that over 40% of all telephone numbers distributed to service providers are unused. Area codes can exhaust with a large percentage of telephone numbers unused.
And while customers are greatly tied to telephone numbers they are mostly powerless when it comes to managing them. They cannot pick their telephone number. While they can move their existing telephone number to a new service provider there are many obscure rules and overly complex back-office processes that limit porting and therefore discourage it. They cannot transfer their telephone number. These are all capabilities available to domain name holders.
Download the PDF of the paper, “The Future of Telephone Numbers-TN 3.0″
How then can we move telephone numbers into the Internet age? Check back next week for our final installment of our series on the Future of Numbering to find out.