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.
Will a cable modem interfere with my cable TV service?
No. High-speed cable modem services are delivered within dedicated cable channels and don't affect other TV programming.
I've heard cable modems offer shared access. How does this impact performance?
Cable households in a limited geographic area -- usually a few thousand homes -- share a downstream 30-million-bits-per-second (mbps) data channel. Common sense dictates that 200 cable data subscribers sharing a 30-mbps connection would each get only 150 kbps of throughput, right? Not quite.
Unlike circuit-switched telephone networks in which a caller is allocated a dedicated connection, cable modem users don't occupy a fixed amount of bandwidth during their online sessions. Instead, they share the network with other active users, like an office LAN or the Internet, and only use the network's resources when they actually send or receive data in quick bursts. So, instead of 200 cable online users each being allocated 150 kbps, they can grab all the bandwidth available -- say, a lot of megabits per second -- during the millisecond they need to download their data packets.
Some telephone companies argue that ADSL is superior to cable modems because it offers a "dedicated" connection, albeit at lower bandwidth. For example, while an ADSL modem may offer a dedicated 256 kbps, a cable modem can burst to speeds many times higher than that.
Think of it this way: Would you like to have a dedicated lane on a highway where you can go a guaranteed 25 mph, but no faster? Or would you prefer to share the highway with other users if there's a 100-mph speed limit? If you prefer the latter, go with a cable modem.
Are cable modem connections secure?
Newer cable modems, particularly those built to the industry's DOCSIS standard, use heavy-duty DES encryption to make sure that other users on the network can't eavesdrop on private data transmissions.
The one area of vulnerability for both cable and ADSL modems is tied to the network settings for file- and printer-sharing options on your Windows or Macintosh computers. To keep hackers out of your files, be sure to disable those settings before connecting your cable modem. If you plan to use those functions, install a router or Internet-sharing device with a firewall between the cable modem and your local area network (LAN).
I've heard about some cable modem service problems. Are cable modems reliable?
There have been a few isolated, but well-publicized, cable modem service glitches, including AT&T's problems in the San Francisco Bay area. But for the most part, the majority of cable modem subscribers get reliable service. Indeed, most cable modem customer surveys show satisfaction levels above 90%.
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