How is a Landline Phone Call Made?

by : Gloria Moore



Though most of us don't even think about phones these days - they're just a part of our very nature, the way we live - the telephone is an integral part of our lives, and very few of us actually know how they work. How does a landline call from your home or office connect you to the intended recipient? If you think about it, it is pretty amazing that if you want to talk to someone, all you need to do is pick up a very simplistic, readily available device - of which you likely own several - and dial a few short digits. The connection is virtually instant.

Furthermore, this network of telephones extends around the globe, so that pretty much anyone on the planet can be reached as long as they also own a phone and are connected to that network.

It wasn't really that long ago that the only way to communicate with someone on the other side of the world was to write a letter - one that might take many weeks to reach its intended recipient.

For a land line call to work, the telephone must be connected to wires which then link to the rest of the phone network. The network itself begins in your own home, where a pair of copper wires for every phone line that you have runs in from a box somewhere at the roadside (frequently referred to as the entrance bridge) into your house. Those wires go to your phone jacks, to which your telephones are connected.

The entrance bridge is connected to a thick cable which runs along your road, and either goes directly to the phone company's switch, or to another, larger box which acts as a digital concentrator.

The digital concentrator is a device which digitizes your voice (at an 8-bit resolution and at a rate of 8,000 samples per second). Your voice is then combined with dozens of other voices which are all sent along one wire (often a coax cable or a fiber-optic cable) to the phone company's office. There, your line is connected to a line card at a switch (which is what provides you with the dial tone when you pick up your phone).

When you call someone local, the switch simply crates a loop between your phone and the telephone of the person you are calling. On the other hand, if you are calling long-distance, then your digitized voice is then passed on to the long distance network, where it must travel further until it reaches the office of the recipient. Microwave towers may also send your signal, depending where you are calling.