I spent all day yesterday trying to find the answer to this without success. I know it must be out there, perhaps I just don't know the correct terminology to use in order to find it. My question is this: When I transfer data from one computer to another, the network card in the first computer does something, which causes the electrons in the cat5 to do something, and the network card in the second computer is able to understand this something as data which is displayed to the user. What I want to know is what those somethings are, especially what actually goes on inside the cat5. For example, if I were to graph the current/voltage of the cat5 over time, what would it look like? How would it differ between one piece of data and another? And how does the computer that is receiving the data interpret these currents as being data? All I have been able to find are higher level explanations (e.g. "The computer sends a packet..."), nothing that explains what is happening on the physical level. If anybody could help me with this that would be awesome! Thanks!