Electrical Data Communications

[ramollari]

What is the best way of viewing data sent by a modem through a telephone line: as a changing voltage in terms of time or as moving electrical signals? In my Networking course exchanged bits, bytes, and packets, are portrayed as waves (current changing with distance) that propagate through the wires.

 

[pervect]

What is the best way of viewing data sent by a modem through a telephone line: as a changing voltage in terms of time or as moving electrical signals? In my Networking course exchanged bits, bytes, and packets, are portrayed as waves (of changing current) that propagate through the wires.

You can do either one. I assume the intent is to model the phone line as a transmission line.

 

[ramollari]

Well, are the electrical signals 'waves'? Do they propagate from one point to another in a long cable or set the voltage throughout its length?

 

[NoTime]

Well, are the electrical signals 'waves'? Do they propagate from one point to another in a long cable or set the voltage throughout its length?

Modem data is encoded on a carrier. The modulation is both in frequency and amplitude. Old modems just used frequency modulation.

As far as your phone connection being a "long" cable, most likely not.
Often it is digitized then reassembled near the destination.

Also it is probably better to think of a phone connection in terms of current rather than voltage.

 

[ramollari]

Yeah now I have a better view of how it works. But I've been confused a lot about the electrical details and I bet that most theorists on computer networking provide contradictory or incomplete explanations, which they don't understand very well themselves.