I need to explain a few things first here, so bear with me. A sine wave is a basic type of wave. Sound can be divided into sine waves. Sound waves, or sine waves, are measured by the number of cycles they make in one second. The number of sine wave cycles sound waves make in one second is measured in hertz. The symbol for hertz is Hz. The sine waves created by human voices average 0 to 4,000 Hz. That means the sound of your voice produces from 0 to 4,000 sine waves made of sound in a single second. That 0 to 4,000 is considered your voice's range or frequency. OK. Now that we've gotten that out of the way: Telephone wiring is made of copper. That wiring is capable of transporting much higher frequencies, or more hertz, than just the frequencies your voice can produce. To put it another way, there's a lot more room on the wiring that's not being used. So the phone companies divide up the wiring to use it for other things as well, namely Internet usage. This may seem like common knowledge. But if you think about it, you download from the Internet more than you upload. You're downloading this article right now! But how often are you uploading? Maybe you send lots of emails, which aren't very wieldy, or a big attachment once in awhile. That's nothing compared to the website and programs you probably download. So the phone company makes lots room on the copper wire for frequencies dedicated to downloading from the Internet, and less for uploading. The phone companies uses higher frequencies on the wiring for both this internet uploading and downloading.. And by the way, the frequencies are higher than those used for both voice and faxes. This is how you're able to surf the web and talk on the computer at the same time! Have you ever wondered why you need to install filters on all your phones and fax machines when you install DSL? Well, the filters are to keep out those higher frequencies reserved for your internet data out of your phone and fax lines, and keep the frequencies you need to talk and fax with in. You can thank your DSL modem for helping the process. Transmission to and from the Internet is all data transmission. The modem is the tool that sends the data coming to and from your computer over the phone line to your phone company, while voice or fax signals may be coming at the same time. At the phone company a contraption called a multiplexed divides up the voice or fax from the data. Next it sends the data part to your Internet service provider, which takes care of the rest!