How does a voice travel over a wire?
Date: Around 1993
How does a voice travel over a wire? How can a picture or picture
with sound do the same? How does ISDN allow multiple independent
transmissions to occur at high speed over normal copper wires?
Basically, a phone is analog (from your house to the local
switching station). Analog means that the air patterns (pulses of air) from
your mouth are transformed to analog signal. The analog signal is a electric
'wave' that represent the sound in electric form. Actually, this electric
form is a varying voltage that can duplicate your voice by moving a diaphragm
connected to magnet in the receiver on the other end. It can be thought of as
when you talk you move a magnet in a coil which produces a signal. This
signal cause a similar action on a coil in the receiver on the other end. Now
let us cover ISDN next: I said your current phone is analog to the local
switching station (in many cases anyway). From the switching station, to
other switching stations, is digital. This means that analog (wave pattern)
is translated to digital and transmitted. Well, the digital signal is much
more efficient. WHY? Well, the digital signal is translated and packaged in
a "Packet". This packet has a header that has an address. This address is
then pushed out on a high speed network (like an expressway). The expressway
is full of many signals. All actually going lets say single file, but since
each signal is en capsuled in its own packet or envelope, special devices can
grab the packets and route them to the correct destination (like exit ramps).
So, in essence, you call can share the same road as many other calls. When
you talk, your words are packaged and sent out on this busy network. ISDN
means that the whole process is digital. Your "voice" never gets transmitted
in analog. So, to send a video or voice signal, all that is needed is to
convert them to digital. Then package them and send them along. On the other
end they are unpackaged, converted back (in some cases like CD or other
digital technology this is not needed), and displayed or played.
The key to the process is bandwidth. In other words, how much data can flow at one time. You need very high speed data paths to allow the rate of video to travel
across this network. Fiber optics have a much greater potential of carrying
large amounts of data than do copper cables. Soon (some are experimenting
with it today) it will be possible to transmit voice, data (computer stuff),
and video all over a single connection at your house. That is when ISDN comes
to the house.
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Update: June 2012