Newer, digital phone lines are coming into use, but that's the topic of another presentation. So, for all practical purposes, we can assume that the phone lines you use at home, work, and school are analog in nature. The kind of connection we are talking about now is termed asynchronous . This simply means that the communication is not synchronized. Everyone synchronized their watches, and from then on, everything happened according to a predetermined plan.
Synchronous communication is like that.
To make use of an analog phone line you need a device called a modem . Modem is shorthand for modulator- demodulator . It's called this because it massages digital data coming from a computer and changes it to an analog form on one end of a connection, and vice-versa on the other. These services all have computers connected to the internet 24 hours per day. Here's a picture of what a dial-up connection looks like.