Eli5: How are phone numbers generated and assigned ? Why do different countries have different phone number lengths ?
In: Technology
In North America, there is the NANPA (North American Numbering Plan Administrator) which … administers the numbering plan.
The general format is country code, 3 digit area code, 3 digit central office code, then 4 digits for the subscriber.There are rules for what can be valid in each field. For example, 555-0100 thru 555-0199 in any area code is not assignable. 555-1212 is typically directory assistance.
Switching was generally done by routing the call to the proper area code, then to the proper CO (think of this as a neighbourhood) and the CO signals the subscriber at the last 4 digits.
Mobile phones have confounded that, generally speaking, since the number isn’t tied to a physical location. There are CO blocks that are usually used for mobile operators though.
Other countries are free to assign numbers based on their own scheme, but for the most part the same principles apply, parts of the phone number describe more and more precise targets for the call, until it ultimately reaches the subscriber.
It’s basically up to each country to decide how they want to organize the phone system based on states, counties, cities, or just “areas” (area codes). Basically, each country’s government can decide what they want to do.
It’s typically based on how the population is distributed / where people live. Taking a US number as an example, (800) 555 – 1212, the 800 would be an “area” code (only in this case it’s just the code reserved for collect calls), the 555 used to be a “region” code, and the 1212 was part of the 9999 possible numbers within that region. So obviously a large city may have more than 999 – 9999 (basically, 10 million) people, and may need multiple area codes to cover everyone.
Otherwise, each country has an international code. For example, any call that starts with 041 will be sent to Switzerland, and then it’s up to them to figure out where to route it / what to do with it.
Different countries have different country codes, i.e. US has the code “1”, while UK has “44”. The length of the compete phone number with the country code is usually the same – 11 digits. Smaller countries have longer country code and shorter internal numbers for use within the country. At least that’s how it was supposed to be, I guess, in practice it’s somewhat more complicated, so phone number lengths may vary due to convenience.
Every country can allocate phone numbers however they decide. Countries with more people naturally need more phone numbers, so they have more digits. For example my country (Israel) added a digit in the early 90s because they we started running out.
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