What's it really like?

To get a better understanding of what it's like to do something, many people want to talk to someone who has already done it. We have a staff member who's in a good position to offer a comparison because that staffer's home has both cable modem and DSL service. Read on for a quick comparison and a personal perspective.

I am now in a bizarre position of living with both sorts of services. Yes, I really have two independent broad-band connections into my house right now... this means I'm well covered if one provider's service has problems, but so far both have been quite reliable. That I am continuing to use both services is a good illustration of the differences between DSL and cable (and how much we use the Internet at my house).

How did it all begin? That I started with DSL service was partly a function of what was available in my neighborhood and what I wanted to do with the connection.

Location is important because the distance of your home from the telephone company's central office plays a crucial role in what DSL services are available. For my house, Qwest is not currently providing DSL services because I am more than 3 miles from the nearest Qwest central office. However, even in the dark ages of DSL Qwest was not the only game in town. Other companies provide DSL service using different technologies, and it was possible to purchase a somewhat slower form of DSL service (called iDSL) from Onvoy, which I did.

DSL: sharing and speed

However, even given the limitations of iDSL, buying DSL was one of the best computer investments I have ever made. Why? First, the connection is always live, so you don't have to wait to be connected. Second, even though iDSL is the slowest form of DSL available, at 144 Kbps upstream and downstream, it is much faster than the fastest reliable modem connections I could get. Working at home feels almost as fast as the network connection at work for most things other than large file uploads and downloads. Even though moving a large file is not quite as fast as in my office at the University, it is at least feasible.

Note that most DSL service today is much faster than iDSL: you can expect to see downstream data rates around 600 kbps with upstream data rates of around 128 Kbps. These sorts of asymetric data rates are fine if what you're primarily interested in is visiting Websites. If you are thinking of sending large amounts of data (like running a server), then you want to look into a service that provides fast upstream and downstream connections.

Another thing I like about my DSL service is that it is possible to share the connection among a couple of computers using a technique called NAT (Network Address Translation). The iDSL router that was installed in my house supports NAT, so after spending some time reading the manual, I figured out how to share the DSL connection among all computers in my house. So, not only was the connection to the Internet faster than via modem, but by setting up a small network inside my house, everyone at home (except the cat) could share the connection and the telephone was not always busy.

Since I was interested in running a server, I was very interested in a service that would provide at least one static IP address. Some services are designed primarily for browsing the Web; and for this sort of use, it does not matter what IP address your computer gets when you connect. However, if you are running a server, you want the server to be at a known address, and a service that provides static IP addresses is important.

Installation in the dark ages

The actual installation of the iDSL circuit was an exercise in frustration since back in the dark ages (2000), Qwest was not doing very well with installing phone lines for competing DSL providers. Things should have improved since then, given the change that allows for DSL providers to share existing phone lines in many cases. To be fair, I was a worst-case installation since a new phone line was needed (unusual), and the phone box is located inside my house, so someone had to be home on a couple occasions as Qwest brought in the new phone line, and then Covad's tech visited to install their equipment. On the other hand, I did end up with a nice router installed on the wall in the basement, and I can work from home a lot more effectively. In spite of the hassles involved in getting the service installed, I would not willingly give up DSL service. Once the DSL router was in place, using the service was a simple matter: connect the Ethernet interface of my computer to the Ethernet connector on the DSL router. My DSL router even came with a couple spare Ethernet spigots, so until the number of computers at home went over 4, I didn't have to buy an Ethernet hub. More computers at home is an unintended consequence of a DSL connection.

What about a cable modem?

So, if DSL is so great, why would you consider getting broadband Internet access via cable modem? In my case, the answer is to get much faster downloads.

So, several months ago, I got a cable modem connection from the cable company called MediaOne, but now called Comcast. Over the last year and a half at the time, MediaOne replaced its old cable system so that they would be able to offer better TV, phone service, and high speed Internet access. While the wiring infrastructure MediaOne used is different from DSL, what you see in your home is an Ethernet connection (just like my DSL service). Once the cable modem is installed, you connect the Ethernet interface of you Mac, PC, or Linux machine to the cable modem's Ethernet port, configure your PC's network connection, and you are set.

Speed and dynamic addresses

The most dramatic difference between cable modem and DSL is speed. On good days I can see speeds in the range of 380 kpbs upstream and 1100 kbps downstream. However, these speeds are somewhat variable because the cable system is set up so that you share bandwidth with others in your area. If someone else is doing a lot of downloading at the same time you are, you may see the speed decrease. You can also see some broadcast traffic from other computers on your segment of the cable system. This is a consequence of how the cable people have built their system. Rather than having a router filtering traffic in the basement (which is what I have with my iDSL service), the router is located somewhere upstream of me in MediaOne's world. In any case, the speed difference is significant, especially when viewing videos and downloading audio (such as MP3 files). I make it a point to use the cable modem connection whenever I plan to do large downloads.

The downside to the cable modem service is that it is set up with a dynamic address, and the dynamic address is not tied to a specific computer. That is, whenever the computer configured for use with the cable modem is turned on, it asks MediaOne's server's for the IP address to be used for the session. This is a drawback if you are planning on running a server, since the server needs to be at a predictable address. If you change your computer, you need to call MediaOne to tell them the Ethernet hardware address of you new computer, since they use Ethernet hardware addresses to control who gets IP addresses (and limit access to specific machines).

Another downside to the cable modem service is that the cable modem does not have the built-in firewall and NAT capability that my iDSL router has. MediaOne did offer relatively inexpensive additional network addresses so you can share the network connection with other computers in the house. On the other hand, the built-in NAT and firewall in my DSL service was one less thing to sort out. Firewall capability is a consideration for the security it can provide. If you have an always-on connection to the Internet, you also have an always-on avenue for the curious to probe how secure your computer is.

Installation of the cable modem went fairly smoothly, although the cable tech had to climb the pole in my backyard and tighten the connections for the cable feed to my house (which had the side effect of improving the TV signal). The tech also replaced the filters in the coaxial cable feeding into the house. This was necessary because the Internet access uses frequencies that are not used by the cable TV service. So, my Jurassic home cable plant was slightly upgraded. Since the coaxial cable inside the house did not run all the way to the basement where I have my local area network hub, I ended up making an Ethernet cable to run from the cable modem to the hub that serves the house's local area net.

Home network infrastructure

Whichever sort of broadband connection you get, high-speed network access at home will raise the issue of network infrastructure in the house. This becomes a real issue if there is more than one computer user who wants to share the connection. At a minimum, you may end up connecting the computer with a local area network. I ultimately ended up buying a 24-port Ethernet hub and running Ethernet cable up the laundry chute. I am gradually pulling Ethernet into each room of the house. I know other people who have purchased wireless Ethernet hubs so that they could share the network connection without pulling cables through the house.

You do want to give some thought to securing your computer from the inevitable probes by script kiddies. Visit the Broadband Reports Website for some pointers on network tuning and security; this site also has tools to measure the speed of you network connection.

For many people, the DSL vs. cable modem decision is already made because of where you are located or what sort of service you want. For others, speed or the availability of static IP addresses are considerations that will influence your decision. In either case, you should get more reliable service than dial-up modem over analog phone lines. There are no busy signals, and you have a fast enough connection that streaming media (audio and video) is feasible to access from home.

- Office of Information Technology