Re: modems

[Pete Resnick <presnick at qualcomm.com>]

On 6/11/02 at 3:22 AM -0400, Bill Cunningham wrote:

> I know modems communicate on the physical layer by electrical pulses 
> or binaries sent on copper wires.

No, not at all. Modems communicate by sound. They MODulate the 
electrical pulses they get from the computer into sound, and the 
other end DEModulates the sounds back into electrical pulses to hand 
to the computer.

> Is that screeching you hear electrical communication?

The sound you hear is a sonic representation of the data. Changes in 
the frequency and amplitude of that sound represent the data. 
(Similarly, buttons on a touch-tone phone produce a sound that 
represent data.)

> Computers don't communicate by screeching...or do they?

They sure do. Back in the days of slower modems, it sounded more like 
a base-line "beep" sound with little "blip" sounds interspersed. 
Today it goes so fast that it just sounds like screeching (or 
hissing).

pr
--
Pete Resnick <mailto:presnick at qualcomm.com>
QUALCOMM Incorporated - Direct phone: (858)651-4478, Fax: (858)651-1102