On Tue, 11 Jun 2002, Pete Resnick wrote: > 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. You're confusing your physical and data-link layers. There is no communication on the physical layer; only transmission... > 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. You're confusing your modems and your acoustic couplers. An electrical transmission in the ~3.5kHz bandpass range that equates to the dominant frequencies used by the human voice, which the phone system was engineered to convert and carry easily, is not a sound. Modulating an electrical signal into said electrical transmission does not involve sound. > >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.) buttons on a touch-tone phone connected to a traditional analogue line cause electrical signals in that 3.5kHz bandpass range to be produced. > >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). I can't hear my gigabit ethernet. L. It's at times like this I think the IETF needs actual engineers. > pr > -- > Pete Resnick <mailto:presnick@qualcomm.com> > QUALCOMM Incorporated - Direct phone: (858)651-4478, Fax: (858)651-1102 <http://www.ee.surrey.ac.uk/Personal/L.Wood/><L.Wood@surrey.ac.uk>