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Toeing the Telcos' Party Line: Do Cable Modems Suffer From Success?
Toeing the Telcos' Party Line: Do Cable Modems Suffer From Success? |
With nearly seven million users installed, cable modems are today's No. 1 consumer choice for high-speed Internet access. Little wonder, then, that telephone companies, whose Digital Subscriber Line (DSL) subscribership stands at about three million, are quick to knock cable modems.
At the top of the list of supposed cable modem deficiencies: Users share them, which cuts down their speed. That compares to a "dedicated," or sole user, technology like DSL, whose boosters contend delivers better performance and tighter security. Those claims, however, demand a closer look.
Shared-Access Issues
Yes, cable modems are based on "shared-access" technology, not unlike the Internet or local area networks (LANs) operated by large companies. But that's not necessarily a disadvantage.
Cable households in a limited geographic area -- say, a few thousand homes -- share a downstream 30-million-bits-per-second (mbps) data channel. According to DSL advocates, logic dictates that 200 cable modem subscribers sharing a 30-mbps connection would each get about 150 thousand bits per second (kbps) of throughput. That would only be a bit more than a 128-kbps integrated services digital network (ISDN) connection, right? Well, not quite.
While circuit-switched telephone networks allocate each caller a dedicated connection, cable modem users don't occupy a fixed amount of bandwidth during an online session. They share the network with other users, just as they would share an LAN at work. In other words, a cable modem subscriber uses a network's resources only when he or she actually sends or receives data in quick bursts. So instead of 200 cable online users each being allocated 150 kbps, each can grab all the bandwidth available during the millisecond they need to download their data packets -- up to many megabits per second. While a DSL modem can offer a dedicated 256 kbps, a cable modem can burst to speeds a lot higher than that when data must be sent or retrieved.
Think of it this way: Would you prefer a dedicated lane on a highway that guaranteed you could drive at 25 mph, but no faster? Or, would you rather share the highway with other drivers if the speed limit were 100 mph? If you'd prefer the latter, a cable modem is for you.
Something else to consider: DSL modems offer a dedicated connection only if your household or office is within three miles of a telephone company switching station. From there, DSL traffic is routed onto a shared data network backbone, and then to the Internet, which is itself a shared network. In other words, a dedicated DSL modem doesn't improve the performance of a Web site sitting on a server 2,000 miles away, because you still have to cover the shared Internet network to reach it.
Security Considerations
Another cable modem concern raised by DSL advocates centers on security. If cable modems are shared, they can't be secure, right? The idea is that users on the network can eavesdrop on data transmissions.
While some older cable modem products were "leaky," so to speak, that's not true with newer cable modems, particularly units built to the DOCSIS standard.
According to Jim Forster, an engineer with Cisco Systems, a leading manufacturer of both cable modem and ADSL equipment, cable security concerns are overblown.
"With DOCSIS, each cable modem uses a separate 56-bit DES [digital encryption standard] encryption key to ensure privacy. Dial-up and ADSL modems rely on the physical security of the entire copper loop path, which is not guaranteed," he says. "Given the very strong privacy that DOCSIS has, unencrypted dial-up and ADSL modems can leave users more vulnerable to snooping."
There is one area of vulnerability for cable and DSL modems tied to network settings on Windows or Macintosh computers: They let several computers share files and printers, which can leave your system vulnerable to hackers. To keep attackers out, disable those file- and printer-sharing capabilities before connecting a cable or DSL modem.
If you need that functionality, we highly recommend that you install a router or Internet-sharing device with a firewall between the cable modem and your local area network.
