I've been beta testing a cable modem since mid-January. I confess, I love it. When it works, that is. I get enormous data rates; Web pages SNAP! onto the screen. Huge documents download in seconds.
But it doesn't always work. Remember the old rap against cable system reliability, that cable systems aren't reliable enough to compete against the telephone companies? It's still true.Installing my cable modem
I'm testing a downstream-only cable modem; my existing telephone modem is used for upstream transmissions. I think this is a smart way for cable companies to get into the Internet access business without first spending the big bucks for full two-way capability.
Installing the modem took two people more than two hours. One person ran the cable from its entrance point in my home to the room with the computer. Remember that the computer is never in the same room as the TV. That took a lot of time.
The other person opened up my computer, installed the card, and configured the Windows 95 software. That took awhile, too. When they were there, I asked whether they were going to test the signal strength. The installer said, "No, if you can get a picture on y our TV, the signal is strong enough." Wrong.
After a few days, I started having problems connecting. Normally when I connect, the Web browser comes up on the screen and displays the cable system's home page. But perhaps a third of the time, the browser would come up, but there would be no Web page. I would call and leave a message on the installer's voicemail at the cable company to say that the system was down. She would call me back and say, "No, the system wasn't down at the time you called." (No, they don't have a pre-recorded status line where I could call to check the status.)
Eventually, the installer called and said that they had learned some things about cable modem performance. She scheduled another visit, came out and tested the signal strength. Much too low. Installed an amplifier. Much better pictures on my TV. Now I can connect successfully about 90 percent of the time. But there are evidently still some mysterious problems in the server at the cable headend.Speed issues
The industry has agreed on parts of a standard for cable modems, including the use of 64 QAM modulation downstream. That's a data rate of about 27 Mbps. And that's what my cable modem delivers.
But it doesn't deliver data to my computer at that rate. There are several reasons. First, the server at the cable headend is connected to the Internet with a T-1 line. That has a data rate of 1.5 Mbps. So that's a bottleneck, at least for now. I was told they will replace that with one or more T-3 lines (44 Mbps ) when they migrate from a beta test to commercial operations.
And I can actually achieve a 1.5 Mbps data rate on downloads at some times. I get the whole T-1 pipe. A 4 megabyte file takes about 20 seconds to download. (At 28.8 kbps, it would take about 20 minutes.)
How do I know the data rate I'm getting? I'm using a neat little program called Net Medic. You can download a 30-day free trial from www.vitalsigns.com.
Once the cable company installs a T-3, can I expect to get downloads at the full 27 Mbps data rate? No, according to several Internet experts I talked with. First, of course, the downstream 64 QAM channel is shared among all the cable modems in town, or at least, all that are fed from the same hub. So as more customers sign up, there will be contention for the capacity.Round trip delay
In addition, the http protocol for downloading Web pages requires acknowledgement messages from my modem back to the server, and has limitations on the number of data packets that can be sent before an acknowledgement is needed. So there is a speed limitation imposed by the round trip time delay. With current http specifications, this is in the 3 Mbps range, I was told. You can learn more about Internet protocols and performance at www.w3.org/pub/www.
And finally, of course, there are delays in the Internet itself. Hosts that carry "popular" Web pages are often overloaded, or the speed of their connection to the Internet is too low to satisfy their demand. And there are other causes of congestion in the Internet.
But for now, I'm sometimes getting 1.5 Mbps data rates, and usually getting 400 kbps rates or more. I love it.Satellite Internet access
I also plan to check out a product called DirecPC, which is similar to the downstream-only cable modem, but it uses satellite delivery instead of cable delivery. The data rate in that product is limited to 400 kbps, still plenty fast. It requires installing a small dish antenna.
This would be for my office — that's where I really need the high data rates, for downloading huge documents from the FCC's Web page. But I can't get a cable modem for my office. The cable system doesn't provide service in business areas. That's the other rap against cable systems. And like reliability, it's also still a problem.