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November 05, 2008

International Calling: Under the Hood

International Calling

By Mae Kowalke, TMCnet Senior Editor


Most people give little or no thought to what happens behind the scenes during an international call. Long distance calling has been around in more-or-less its current form since the early 1980s. International calling is now a simple process of picking up a phone, dialing some digits, and being connected nearly instantaneously in a voice call featuring clear audio quality.
It wasn’t always that way. In its article, “How does long-distance call work?,” notes that making long distance calls once required humans to perform manual routing procedures. Back then, each town had a phone company central office, manned by one or more operators. Physical phone lines ran from each house to this central office.
At the central office, an operator sat in front of a switchboard — a collection of sockets. Each phone in the town had its own socket. If someone wanted to call someone else in the town, the operator would have to physically connect the call by attaching a special wire between the two sockets — caller and receiver.
Things got more complicated when it came to connecting long distance calls. In this case, says in its article, one or more special lines were added at the central office to a long distance office. The operator would still have to physically connect the two calls, but now this process was longer because he or she had to first connect to the long distance office, which acted as an intermediary. This extra step introduced more complexity and meant calls were not connected nearly as quickly.
For today’s phone users, the process of waiting for a call to connect — and having to first speak with an operator — probably seems incredibly cumbersome. At certain points in the history of telephone systems innovations were introduced that, at the time, must have seemed very significant. Even these improvements, though, would be unlikely to impress today’s phone users.
An example of just such an innovation, described in’s article, was the mechanical switch. Once this was added, local calls were connected automatically — no operators needed. For long distance calls, it was still necessary to speak with an operator, and the caller would dial “0” to initiate that process.
Today, all phone call connections — local and long-distance — are connected automatically, with no human operators involved. This is thanks to computerized switches. In the early days of computerized switches, physical wires still connected calls, and the familiar 11-digit long distance number format (area 1 + area code + local exchange + number) was used. Now, although long distance numbers still typically involve dialing 11 digits, physical wires are no longer used for connections; instead, voice signal is digitized and sent over fiber optic lines. This system is much less expensive to build and maintain than traditional copper wires.
To learn more about how long distance telephony works, please visit the International Calling channel on, brought to you by Packetel (News - Alert).
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Mae Kowalke is senior editor for TMCnet, covering VoIP, CRM, call center and wireless technologies. To read more of Mae's articles, please visit her columnist page. She also blogs for TMCnet here.

Edited by Mae Kowalke


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