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Cable Modem Basics
Questions and Answers
- What is a cable modem?
- Why would I want a cable modem?
- How does a cable modem work?
- How fast are cable modem connections?
- What does "always-on" mean?
- Who manufacturers cable modems?
- Where can I buy a cable modem?
- What do "DOCSIS" and "CableLabs Certified" mean?
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What is a cable modem?
Traditional dial-up modems provide online access through the public telephone network at up to 56,000 bits per second (kbps). A cable modem, on the other hand, provides high-speed Internet access through a cable television network at more than 1 million bits per second (mbps). Cable modems are typically external devices placed next to your computer.
Why would I want a cable modem?
The No. 1 reason is speed. Cable modems can offer download speeds from the Internet in excess of 1 mbps -- at least 20 times as fast as a traditional telephone modem. Web pages that take minutes to paint in with a dial-up connection pop up instantly with a cable modem. If you frequently download large files, such as video clips, audio clips or software, cable modems will make life much easier.
The second reason is "always-on" connectivity. With a cable modem, there's no need to dial in to an Internet service provider (ISP). Simply click on your browser and you're on the Internet. No more waiting, no more busy signals.
How does a cable modem work?
A cable television system typically has 60 or more channels, and most of them are used for programming services like CNN, ESPN and HBO. These channels also can be used to offer high-speed Internet access service. Cable modems connect to the cable network with a standard coaxial cable, just like the wiring that's plugged into your television set to receive cable TV service. The cable modem then connects to your PC through a standard Ethernet interface.
How fast are cable modem connections?
Many cable companies and Internet providers tout cable modems as 100 times faster than a dial-up Internet connection, or the equivalent of more than 5 mbps. That, however, is a slight exaggeration. Theoretically, it can be done. But realistically, it rarely happens for a number of technological reasons. A more accurate figure would be 1 mbps -- about 20 times faster than a 56-kbps dial-up connection.
Another note: Cable modems are typically asymmetric, meaning that download speeds are faster than upload speeds.
When calculating Internet-access speeds, it's important to recognize the difference between bits and bytes. Web browsers, such as Netscape Navigator, often report download speeds in kilobytes per second (KB/s). Modems report speeds in kilobits per second (kbps). There are eight bits in each byte. So, if your browser is downloading a file at 100 KB/s over a cable modem connection, that's equal to 800 Kbps.
What does "always on" mean?
It means that the cable modem is continuously connected to the Internet whenever your computer is turned on. When you want surf the Web, all you need to do is type in a site's address. There's no need to "dial up" an Internet service provider, as you must do with traditional telephone modems.
Who manufactures cable modems?
More than 20 companies, including 3Com, Cisco Systems, Com21, Motorola, Nortel Networks, Philips, Terayon, Thomson, Toshiba, Samsung and Sony.
Where can I buy a cable modem?
Cable modems are starting to become available to consumers who'd like to buy their own units. Cable companies also lease modems to subscribers so that they won't have to deal with obsolescence issues as the technology evolves.
It may save you money in the long run to purchase your own modem. As DOCSIS becomes the industry standard you shouldn't have to worry about the modem being incompatible with another system if you move. Make sure when you are buying a modem that it will be compatible with your system. There are still a few non-DOCSIS networks out there.
Cable modems range in price from $120 to $200, though a sale can knock quite a bit off that price. They can be found at retail outlets specializing in home electronics and at various online stores.
What do "DOCSIS" and "CableLabs Certified" mean?
DOCSIS, which stands for Data Over Cable Service Interface Specification, is the North American standard for cable modem products. CableLabs, an industry technology organization, developed the DOCSIS standard to ensure that cable modem equipment built by a variety of manufacturers is compatible.
CableLabs is managing a rigorous testing process for DOCSIS cable modems. Products that pass the tests are deemed "CableLabs Certified." So far, DOCSIS modems from 12 manufacturers have won approval.
