Recently on thelist, Jason B. asked if the rumors about cable modems being slower and slower as more and more people use them are true. He also wondered aloud if cable modems were here to stay, or just a passing fad.

Realizing that this could very well be a question that many fellow Web developers were asking themselves, I set out with a six pack of Brown Ale from Capital Brewery (America's #1 rated micro!) to cut through the BS and try to provide a helpful explanation  about cable modems and how they compare to DSL. (This is pretty much a cut-and-paste of my post to thelist, excuse the casual writing style :)

Part of the theory that cable modems will get slower with more and more people in the 'hood using them is true, part isn't.

Around 4-6 years ago, when cable modems first started becoming a bit more mainstream, one of the big knocks against them - as the PacBell commercial points out - is that the more people in your neighborhood that use them, the slower overall they get.

Typically this was true because the infrastructure (the physical wires, cables, switches, etc.)  that the cable companies were using to deliver Internet access was (and still is in many areas) very outdated. Most of the infrastructure in place when the cable modem explosion hit 4-6 years ago was equipment that had been deployed in the early-to-mid 80's when the cable TV boom hit. Cable companies tried to push too much data across this somewhat primitive infrastructure, and the result was poor service and slow download times as the number of people using it increased.

So that explains part of the perception that cable modems are slow(we'll get to more in a bit). DSL, on the other hand, uses plain old telephone wires (more or less, for the sake of this discussion :) to give you service to your ISP. Here is my big thing with DSL: They'll promise you 'Near T-1 speed to the ISP!!' which is right on the money. You will always have that near T-1 speed to your ISP - no matter how many of your neighbors get the service and download pr0n mpegs. They'll get T-1 speeds to the ISP as well. It sounds great untill you've got 50 people(on the low end) with DSL at 'near T-1 speeds' connecting to an ISP that only has one T-1 to the Internet to start with.

So while you're getting T-1 speed - typically 1.5 Mps - from your computer to the ISP you get DSL from, you only can connect/download as fast as the highest amount of bandwidth your ISP has. If your ISP has a T-1 line, the maximum you can download at is T-1 speed.

Now, if your neighbor next door, or even a person on the other side of town, also has DSL and is trying to download at the same time you are, and you both have the same DSL provider, you're going to have to share bandwidth. Not bandwidth between you or them and the ISP, but between the ISP and the Internet. Also, most ISPs don't have a direct connection to the Internet as I suggest above.

Rather, most ISPs have an ISP that they connect to, typically these are called "tier two" ISPs. These "tier two" ISPs then connect to the Internet through "tier one" ISPs such as MCI Worldcom, UUNet, Sprint, and Cable & Wireless -- the companies that provide the backbone infrastructure of the Internet. Each of these connections to an upstream provider is referred to as a "hop." The more "hops" you have, the more lateny (lag) you'll notice, and the slower your Internet connection will seem. The point to all this is that with every "hop" to the Internet the ISP is selling bandwidth to an unknown number of customers -- which isn't bad in itself. It is bad when the ISPs starts overselling its bandwidth so that its pipe is full of data to the next "hop." Once the pipe to the next "hop" is full, you're in the slow lane. In short, the less of these "hops" you have to traverse to get to the Internet backbone, the faster and more reliable your Internet service will be. (This is why you almost always host Web sites with tier 1 or 2 providers.) At any rate, back to DSL and cable modems. :)

Now, most any decent DSL ISP would have more than a T-1 connection, of course. But even with a pretty fast T-3 connection(45 Mps) to the Internet, it can get crowded (and slow!) in a hurry.

So the real question is, "What's worse?" Sharing bandwith between you and the ISP (cable modems), or sharing it from the ISP to the Internet (DSL)? Naturally, the less you have to share is better, which is why DSL providers have enjoyed a lot of success in the last two years -- they've capitalized on the mistakes that cable companies were making, and the slow speeds they typically provided.

Now, this brings us back to the whole infrastructure issue. The cable companies aren't stupid. They've been seeing cable modem users move to DSL because of some of the slowness issues. They've also seen eroding market share from their TV service because people have continued to buy satellite dishes. So they've responded over the last one and a half years by spending a boatload of money on their infrastrucutre to kill two birds with one stone.

Time Warner has been out there like a banshee laying down high speed networks to pump both digital quality TV and Internet access to the home. Wisconsin is a good example of what they're doing nationwide: Laying down the biggest, fastest pipes between their offices and customer homes in order to pump as many services as they can to you. They've also been putting down fiber optic ATM(asynchronis transer mode) networks for the last two years in order to get all these services to the home user.

These ATM networks are capable of 155 Mps (and will have the power to scale higher with better compression technology) and towns are split into nodes of seperate 155 Mps networks. Milwaukee, for example, has about 50 of these nodes that are independent of each other. (Joe across town downloading porn won't affect your speed -- your immediate neighbors will, though). These networks then converge to a central point where it connects to the Internet. (This would typically be considered the ISP for a DSL customer). Again, in Oshkosh, Wis., and Milwaukee, they have massive bandwidth to the Internet. I've been told they have between an OC-12 (622 Mps) and OC-48 (2.5 Gps) connection in areas like Chicago and Los Angeles.

So to sum up:

Yes, cable modems are affected by your neighbors. So are DSL customers, although just a bit further down the pipe. In the future, its all going to be about who has the most bandwidth and best infrastructure to offer its customers. DSL is stuck using POTS (plain old telephone system), which as regular modems have proved over the last 15 years, can only be stretched so far. The cable companies like AOL/Time Warner are in much better position to provide quality service to their customers in the future.

Although you'll never really see breakneck speeds with a cable modem(or DSL or analog modems) between 6 p.m. and 10 p.m., cable is most definitely is not a passing fad -- and, in my opinion, will be the one that wins in the end.

Tomorrow we'll get into part two of Battle of the Bandwidth and explain the alphabet soup of DSL service and what it can do for you.
Comments about your cable/DSL service? Post them below!