Saturday, August 1, 2009

Basics Of How Your Home Phone Works

By Tammy Simpson

We take our telephones - and the technology upon which they're designed - for granted. Without giving the process a second thought, we pick up the receiver, punch a few numbers (or, select a name), and expect to reach the other person. It matters little whether that person is located in the next town or halfway around the world. Consider that a century ago, it took a few weeks just to get a letter to someone and you'll appreciate how far we've come.

Many people still fail to realize how their phone calls are completed. Below, we'll explain the entire process, from the moment you lift the receiver to sending your voice to a recipient who may live across the globe.

Placing The Call

With a residential landline service, a connection exists between your line and your provider. The provider will maintain a central office and oversee a telephone exchange (sometimes called a switch) that is responsible for connecting calls. When you lift your receiver, you'll hear a dial tone. That tone signifies that the connection between your landline and your provider's exchange is live.

In the old days, most people had telephones with rotary dials. You would select numbers by "dialing" them. If you were you to listen in the receiver, you would have heard a series of clicking noises with each number dialed. Those were pulses. They interrupted the connection between your line and your provider's switch and in doing so, identified the phone number you wanted to call. Hardly anyone uses rotary dials today; most people now have telephones that have replaced pulse dialing with dual-tone multi-frequency dialing. The local switch identifies the desired phone number through the tones.

In order to route your call properly, the local switch needs to establish a connection between your landline and the line of the person you're calling. Long ago, operators would make these connections manually. They would unplug and plug wires into one of dozens of sockets in order to connect callers with each other. This responsibility is now handled automatically by computerized exchanges. However, the underlying principle (making connections between callers) is still at work.

Transmitting The Signal

Your receiver contains an internal diaphragm. When you speak, your voice creates vibrations in this diaphragm which in turn, converts the sound into electricity. As an electrical signal, it travels across the line until emerging through the recipient's earpiece speaker. As it emerges, the signal is converted back into sound (in this case, your voice). Telephone technology has evolved to the point that the entire process can happen in reverse simultaneously. That is, you and the person you've called can talk at the same time while the sound of your respective voices travel to the other person.

Telephony has expanded in ways that Alexander Graham Bell likely never predicted. By transmitting signals through fiber-optic cables, we can now enjoy long-distance and international calls with the same clarity and speed as local connections. Though most of us take the technology for granted, it has arguably changed the manner in which we live.

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