Driving Bits Across a Wire

Driving Bits Across a Wire

To send one binary code from one device to another, the sending device puts some electricity on the wire. Electrical signals have many characteristics that a NIC can control and vary. By varying one of these features to two different values, with one value meaning binary 1 and one meaning binary 0, you can transfer data over the wire.

For example, imagine that both PC1 and PC2 have a NIC, and there is a single wire connecting the two cards. The wire is just a skinny, long piece of copper, and copper conducts electricity very well. Now, imagine that the encoding standard used by the company that made the NIC defines that a binary 0 is represented by a voltage of ±5 volts, and a binary 1 is represented with ±10 volts. Encoding is the term that refers to a set of rules that defines what a sender should make the electrical signal look like to imply a binary 0 or a binary 1. Figure 4-3 depicts the general idea.