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Now, let’s finish up with a high-level look at phone numbers.

The standard phone number is made up of 13 numbers. Most people forget that every number in the United States has a national identifier for the US. It is 001. Then there is a three digit area code, let’s say 603, then a three digit prefix, let’s say 740, and finally the extension 5555. This makes a 13-digit number. Within the US, we do not need to dial the 001, and in most states, if you’re within the local area you do not need to dial the area code. But these numbers are still part of the addressing scheme.

So let’s dial the call. When you dial a 7-digit number, the local switch may be able to complete the call. You may be calling your neighbor, and since you are both located on the same switch, the connection can be made locally.

If you are calling someone a couple miles away, it is still a local call, but the connection may need to go through several switches. If you are calling long distance, your call will definitely need to go through multiple switches. When this is the case, the number you dial will tell the switches how to forward your call.

You can think of the number as an address. The area code tells the switch the state and region, the prefix tells it the city, and the extension identifies the phone you are calling.

Furthermore, if a special type of call is being made, such as to 911 or an 800 number, the local switch consults a database to determine where to forward your call.

Strange as it may seem, just because you are dialing a 1-800 number does not really mean the call is going long distances. That 1-800 number has to be located someplace, so it might even be connected to the same local switch you are connected to. When you dial an 800 number, your local switch contacts a database to determine where the phone you are calling is located and then sets up the call as required.

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