[Cable Modems...]
From what I've read, and my (basic) knowledge of Local Area Networks (LANs) and TCP/IP, cable modems have a very basic problem which I believe doom them to failure.
My understanding of how cable modems work is that they are like a typical office LAN - they dump the data traffic out onto a service loop (in this case the CATV coaxial cable running up and down the street). What this means is that the available throughput for any individual, although THEORETICALLY very high, quickly degrades as other concurrent users are added. An easy way to think about how this works is this: imagine two people on opposite sides of a big, empty room. They can communicate quite quickly and easily just calling back and forth to each other. Add another pair simultaneously talking to each other, and there's some interference: the two pairs sometime drown each other out, and must repeat the the "lost" words. Add another pair, and another, and it quickly becomes a din, and no data is exchanged between ANYBODY.
There's acutally a term for this; it's called a "data storm".
I've experienced (and even triggered a few) data storms in my Ham radio activities. We have what is essentially a vhf/uhf TCP/IP network covering various areas of the country. If there's a lot of stations trying to communicate with the central node (nodes are distributed all over the country, and they are usually connected to each other over a backbone frequency), there are more and more "retries", which causes more traffic on the network, which causes more interference and hence more retries. It pretty awsome to see this physically manifested when you have a radio trying like the "Little Engine that Could", clicking frantically between transmit and receive modes in a futile attempt to transfer data.
I've read reviews praising the performance of cable modems, but I've not seen the results of any network stress tests. Has anyone else seen any info on this?
The network topology with ADSL is more that of a "star" model - each node communicates with a central point via its own physical connection. This ensures that you have adequate bandwith available to you, at least until it gets to the Central Office.
Another concern I have, and have never read anything about, concerns the issue of security; if you have a loop with all this network traffic on it, and you have a box inside the house to direct your data to your device (such as a PC), I believe that means that if someone slaps a network analyzer on the back side of the box, you get to see ALL the traffic flowing by. Now, I'll admit, most folks don't have network analyzers sitting in the closet next to the vacuum cleaner, but still - my data's MY data! I don't want anyone ELSE looking at it. Does anyone know if my concern is a valid one? As I said, I've never seen the subject brought up anywhere.
If the security issue is in fact true, that could make two good reasons to "Just Say ADSL" to cable modems.
Thoughts?
Steve |
