How Does a Cable Modem Work?

Cable modems are among the fastest methods of connecting to the Internet. They were designed to compete directly with the Digital Subscriber Line (DSL) services offered by telephone companies. By using a cable modem, speeds well in excess of 10Mbps can be achieved. They work on the same principle as cable television, and use basically the same type of signal, carried in the same lines, as the signal for television broadcasts.

Cable signals operate by compressing data into a 6 megahertz electronic "stream" that travels along a dedicated portion of the cable line. The signals, contrary to popular belief, don't take up much space at all, and a typical coaxial cable from the cable company can carry hundreds of these signals at a time. A cable modem works by decoding the signal as it reaches to modem, thereby translating that electronic signal into data that the computer can decode.

All cable modems, whether part of your computer or part of your television cable box, contain a few specific parts. The first is a tuner, which ensures that only the data stream on a specific portion of the coaxial line is intercepted by the modem. The tuner then passes that signal along to the demodulator, whose purpose it is to change the phase and amplitude of the signal, converting it to a form that can be recognized by the A/D converter. The A/D, or Analog/Digital Converter, is the part of the cable modem which coverts the signal from its transmission form into a series of 1s and 0s, which allows the computer to understand the data.

One of the biggest disadvantages to cable modems is that the data that you request from the Internet isn't just sent to your modem. Any data sent from the server is sent to every user on the cable channel that you're on. It's left up to the customer's network connection to decide which data is meant for each customer. This means that, theoretically, a user's data could be co-opted and viewed by a third party. The sheer amount of data means that this is unlikely, but many people find that an unacceptable risk.

The biggest advantage that cable modems have over DSL connections is that the customer receives the maximum available connection speed, regardless of distance from the signal source. DSL customers see massive speed decreases the further they are from the switching station. Cable signals are designed to travel large distances, and aren't attenuated by distance to the same extent as DSL signals.