How International Calling Works

With mobile phones, the internet and other forms of modern communication, the world seems a lot smaller than a decade or two ago: we can get in touch with someone on the other side of the  globe, and do so more or less instantly.

Because of such speed and ease of service, we probably don't give a second's thought to making a long distance or international call. We just do it and it happens - as it by magic. It's easier than ever before to make an international call and the figures reflect this: 20 years ago, around 200 million international calls were made annually from the USA. That's changed now to over six billion.

But how does international calling actually work?

Well, it's certainly changed from how it used to be. Once upon a time, human operators manning the local phone company's office would manage a switchboard, which was essentially a collection of sockets. There was one socket for each phone in town. When a call was placed the light above your phone's socket would turn on, the operator would plug a jack into the socket and ask the caller who you wanted to talk to. The operator would then plug the jack into the receiving party's socket and talk to the person who answered. A wire between the two jacks would connect the caller and recipient together.

For long distance calls via the same system the phone company would add lines to enable connection to a long distance office.

The next stage in development was to remove the physical operator with a mechanical switch; computers would create the connections and also the billing records. Physical wires still made the connections between towns. Area codes were used and the computers were able to use these numbers to identify where the calls needed to go.

Basically, that system is still in place today but there is a fundamental change. Offices are no longer connected by physical wires - fibre-optic cables are used instead. These are long, thin strands of very pure glass, around the diameter of a human hair, and they carry a digitised version of your voice.

When a long distance call is placed the switch in the local office (now automated, of course, no longer monitored by a person) accesses a database that has a record of every phone number. The database contains a PIC code (Primary Interchange Carrier) which shows which long distance carrier the caller has chosen. The switch looks up the PIC code, connects to a long distance switch for your long distance carrier, and that routes the call to the local carrier for the person you are calling. That person's local carrier completes the call.

The reason international dialling codes are so lengthy is that each set of digits is required to route the call correctly. You need your country's exit code, plus the country code of the country you wish to call, plus the area code and then the local telephone number. For example, if you're in the UK and calling LA, in California, USA, you first dial 00, which is the UK's exit code. Then 1, which is the country code for the USA, then 323, the area code for Los Angeles. Then the personal phone number of whoever you are calling.

It might sound a long-winded process, but of course, it is not. It all happens within a second - an amazing journey of technology which allows us to speak to anyone in the world as if they were standing right next to us.