I often train new employees trying to learn telephony, and especially international telephony, on the routing and multiple carriers, networks and equipment involved in a single international telephone call. Many find it interesting (or at least they pretend to) so I thought I’d share it here so you can appreciate what’s involved when you call your friend in a different continent.
Let’s say you live in Detroit and your friend Pat lives in Paris (lucky Pat). Your outbound call to Paris would go from your telephone through copper cable to your local telephone carrier (who may be a telephone company or an internet service provider). The local carrier will realize you’ve dialed not only a long distance call but also an international call and ‘switch’ that call from their network to a long distance carrier like AT&T or Verizon. That long distance carrier (called an Inter-Exchange Carrier) would then carry your call across your network as far as they could and normally hand that call off to an international carrier to transit the call across the Atlantic. However this carrier is likely to convert the signal to a Voice over IP (VoIP) transmission as technology makes it more efficient to transit long distances by using a data network like the internet or their own private data network.
The international carrier may hand off to other international carriers with service into France, but then finally the last international carrier will likely convert the signal back into a standard protocol from VoIP and deliver the call to Pat’s local exchange carrier who will deliver the call to Pat’s telephone handset so that you two can catch up.
So from the time your voice starts in your telephone until Pat hears it on the other end, there are up to 5 different companies, thousands of miles of fiber optic cables (even under the ocean), and dozens of pieces of hardware your call is being transmitted through to make a single international telephone call. And this happens in a matter of a few seconds! That gives a whole new appreciation for the speed of light, which is how the call is sent through fiber optic cables. Essentially "light goes on, light goes off" becomes zeros and ones in a digital transmission.
Just be glad you don’t have to think about or keep track of all of those hops. You just get to dial the digits and enjoy the conversation. Let us do all that nasty detail work for you.