Your choice between the other pathways is likewise determined by which ones are available in your area. DSL over cable is pretty much the same as DSL over a phone line in terms of speed. Cable may even be a bit faster if their system is new or well maintained. But the carrier signal is radio frequency (RF) and subject to interference.

The infrastructure has to be re-tuned periodically. Cable companies are tempted to put off this maintenance to save money at the expense of signal quality. This can affect cable data more than video. Cable providers don’t give ironclad guarantees concerning consistency of speed or latency.

Cable TV companies are in the “land rush” to sign up new customers, but few of them have completely overhauled their infrastructure to accommodate two-way data. This requires a cable modem on the customer end and a cable modem termination system (CMTS) at the cable provider’s end, plus a lot of equipment in between.

Because of its great bandwidth, coaxial cable can carry many TV channels, each getting a 6 MHz slice of the total available. Internet data is encoded to look just like one of those TV channels, and occupies the same bandwidth. As with telephone DSL, cable upstream data links have a slower data rate.

They fit into a smaller 2 Mhz frequency slice. Unfortunately, these uplinks ride on the low end of the cable frequency spectrum and are therefore more subject to interference.

Most systems are upgrading to fiber-optic cables. Their bandwidth is even more enormous. They carry digitized TV and data channels far out to the neighborhoods without distortion, and there it is then broken out onto coaxial lines for the short hop into residences.

You may be able to get Internet service even if you are not a subscriber to the cable video, but if so, it will cost more than if you were getting the TV channels. A typical monthly fee is $40 to $50, but you may get a discount if you subscribe to cable TV service at the same time or if you buy your own modem (which will cost you from $100 to $300).

One advantage over the other pathways is that cable DSL is usually faster to get going, assuming that you already have a cable TV line into your house. The hardware requirements are simpler because the cable modem will probably adhere to the DOCSIS standard. If so, the modem can be purchased off the shelf.

This is almost always a better deal than leasing one from the cable company, because if you do, you will be charged month after month, regardless of how often you actually use it. Buying a non-DOCSIS or proprietary cable modem is a bad idea, assuming you can find one that matches your system’s specifications.

They can become obsolete and it may be hard to find someone to repair them. Before buying a proprietary cable modem, ask the cable company if the device will remain useable in the future. The cable franchise may be planning infrastructure upgrades that will render it obsolete.

And ask yourself if you plan to be staying in your present area, because the operator in the next town may use something else. A common complaint about Internet service in general and cable DSL in particular is that providers sometimes underestimate the demand for service and fail to provide adequately for it.

The term for this sometimes premeditated practice is the same one used at the airlines: overbooking. If too many subscribers are riding the same cable, the service may bog down. Users may have to avoid cable Internet rush hours, such as Sunday evenings and weekdays at 6 P.M. when users arrive home from work and check their email.

Users who play interactive games or do video conferencing may get frustrated at those times. You may not have to purchase cable TV service and cable Internet service as a bundled package, but if you do so, you can watch TV and surf the Net at the same time.

If you are already a cable TV subscriber, your existing cable may have to be replaced because the cable modem needs a higherquality signal than your TV set. Also, if you are using a splitter or amplifier to drive multiple television sets, make sure the cable modem is connected ahead of it, because multitap devices will not pass bidirectional signals.

With telephone DSL, an unshared telephone line carries your data back to a central office. But a cable line is shared with many other users, which makes security measures for your home network more important. When you share your PC’s hard drives one to another, be sure that you are not sharing them with the world as well.

To summarize, cable and Telco DSL are usually equivalent in terms of price and performance. Telco DSL promises to function more quickly in the future, however, and offers an exclusive upstream link to the Internet. If you hope to upgrade to an SDSL business-grade service, Telco DSL gives you a path.