Fundamentals of Communications and Networking, 3rd Edition

From Analog to Digital to IP

The common experience of always being connected to the rest of the world is fairly recent. Until about 1990, almost all electronic communication used analog media. Analog devices transmit data using continuously variable signals. The analog devices had limitations that made it difficult to do much more than engage in voice conversations and slowly transmit other types of data. Of course, before telephones, most communication occurred through either face-to-face interaction or written documents. Letters were the primary method for communicating when face-to-face meetings were not practical. At that time, the transmission speed depended entirely on how fast the sender could deliver a letter to the recipient. This ...