How do long distance calls actually work?
When calling a friend thousands of miles away, there is a lot going on between your mouth and their ear. It is pretty amazing to think that 150 years ago it would have taken weeks to get correspondence from California to New York and now it can happen almost instantaneously. Let's consider what happens in those microseconds it takes to get the sound of your voice to your friends phone receiver.
There is a lot of computer technology that has gone into making your call happen. A historical overview of how modern phone systems have evolved over the past few decades will help us to understand how they currently function.
At one point, long distance calls were routed through a very simple system by a human being sitting in a town's central office normally located in the middle of town. From here a set of copper wires was run to every phone, connecting to each individual's telephone receiver.
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An operator would work in the central office on what was known as a switchboard. This switchboard would have a "socket" for each of the phones in town. When you wanted to make a call, you would pick up your phone and the operator would see the light above your phone's socket turn on. The operator would then plug a jack into your socket and ask who you would like to talk to. They would then plug their jack into the receiving party's socket, send a ring signal down the line, and talk to the person who answered. At that point the operator could plug a wire into your jack and the other party's jack to make the connection. When your conversation was over, your lights would go out and the operator would remove the wire connecting your sockets.
To make long-distance calls using this simple system, the local phone company would add a line or more to connect to a long distance office. To make a long-distance call to your friend in this system, you would pick up your phone and tell the operator the long distance number for your friend. The operator would then connect to one of the lines going to the long-distance office, speak to the operator in the long-distance office, and then the long-distance operator would connect the operator to the long distance office for the area code of your friend. Your operator would talk to the long-distance operator and eventually get connected to the operator in the central office for the town that your friend lives in who would make a connection to your friend.
This system was effective, but slow and required actual people to operate. Your call would be patched together using physical wires going from one office to the next. This eventually evolved into using a mechanical switch in place of the live operator. To make local calls, the mechanical switch would connect you and to make a long distance call you would dial zero to speak to an operator who would connect the call as before.
Computers soon replaced the long-distance operators with computerized switches. The computers could create the connections and the billing records just like the human operator. Physical wires still connected you to the receiving party on each call, but the computer connected them together at each office. For example, when dialing a long distance number 1-234-567-8910, the following is communicated:
- 1= long distance call
- 234= the switch needs to grab this long distance line
- 567= the receiving long distance office needs to connect to this local office
- 8910= connect with your friend
The computers in each office would pass the numbers along as digital data through data lines connected between the switches. However, this system too had its drawbacks. Running copper lines was extremely expensive.
Nowadays, there are two major characteristics of phone systems that make them different than the ones previously described. These are:
- Physical wires no longer connect the offices together for each phone call. Rather, a fiber-optic line carries a digitized version of your voice and thousands of others' voices in a stream of bytes. The cost difference is huge between "a pair of copper wires carrying a single conversation" and "a single fiber carrying thousands and thousands of conversations".
- Any single phone company is no longer a monopoly. Instead, there are many different long-distance carriers.
Now, when you go to make a long-distance call, a switch in the local phone office accesses a database that contains a record for each phone number connected to the switch. The database contains a code that indicates which long-distance carrier you have chosen. This is the code that will change if you decide to switch long-distance carriers.
At this point, the switch looks up the code for your number and then connects to a long-distance switch for your long-distance carrier. Your long-distance carrier's switches route the call to the local carrier for your friend, and the local carrier completes the call to your friend. This complicated process using computers, switches, wire and fiber-optic cable all takes place in seconds.
