About Modem

Telephone lines were designed to carry the human voice， not electronic data from a puter. Modems were invented to convert digital puter signals into a form that allows them to trel over the phone lines. Those are the scratchy sounds you hear from a modem's speaker. A modem on the other end of the line can understand it and convert the sounds back into digital information that the puter can understand. By the way， the word modem stands for MOdulator/DEModulator.

Buying and using a modem used to be relatively easy. Not too long ago， almost all modems transferred data at a rate of 2400 Bps （bits per second）。 Today， modems not only run faster， they are also loaded with features like error control and data pression. So， in addition to converting and interpreting signals， modems also act like traffic cops， monitoring and regulating the flow of information. That way， one puter doesn't send information until the receiving puter is ready for it. Each of these features， modulation， error control， and data pression， requires a separate kind of protocol and that's what some of those terms you see like V.32， V.32bis， V.42bis and MNP5 refer to.

If your puter didn't e with an internal modem， consider buying an external one， because it is much easier to install and operate. For example， when your modem gets stuck （not an unusual occurrence）， you need to turn it off and on to get it working properly. With an internal modem， that means restarting your puter——a waste of time. With an external modem it's as easy as flipping a switch.

Here's a tip for you： in most areas， if you he Call Waiting， you can disable it by inserting *70 in front of the number you dial to connect to the Inter （or any online service）。 This will prevent an ining call from accidentally kicking you off the line.

This table illustrates the relative difference in data transmission speeds for different types of files. A modem's speed is measured in bits per second （bps）。 A 14.4 modem sends data at 14，400 bits per second. A 28.8 modem is twice as fast， sending and receiving data at a rate of 28，800 bits per second.

Until nearly the end of 1995， the conventional wisdom was that 28.8 Kbps was about the fastest speed you could squeeze out of a regular copper telephone line. Today， you can buy 33.6 Kbps modems， and modems that are capable of 56 Kbps. The key question for you， is knowing what speed modems your Inter service provider （ISP） has. If your ISP has only 28.8 Kbps modems on its end of the line， you could he the fastest modem in the world， and only be able to connect at 28.8 Kbps. Before you invest in a 33.6 Kbps or a 56 Kbps modem， make sure your ISP supports them.

Speed It Up

There are faster ways to transmit data by using an ISDN or leased line. In many parts of the U.S.， phone panies are offering home ISDN at less than  30 a month. ISDN requires a so-called ISDN adapter instead of a modem， and a phone line with a special connection that allows it to send and receive digital signals. You he to arrange with your phone pany to he this equipment installed. For more about ISDN， visit Dan Kegel's ISDN Page.

An ISDN line has a data transfer ra

te of between 57，600 bits per second and 128，000 bits per second， which is at least double the rate of a 28.8 Kbps modem. Leased lines e in two configurations： T1 and T3. A T1 line offers a data transfer rate of 1.54 million bits per second. Unlike ISDN， a T-1 line is a dedicated connection， meaning that it is permanently connected to the Inter. This is useful for web servers or other puters than need to be connected to the Inter all the time. It is possible to lease only a portion of a T-1 line using one of two systems： fractional T-1 or Frame Relay. You can lease them in blocks ranging from 128 Kbps to 1.5 Mbps. The differences are not worth going into in detail， but fractional T-1 will be more expensive at the slower ailable speeds and Frame Relay will be slightly more expensive as you approach the full T-1 speed of 1.5 Mbps. A T-3 line is significantly faster， at 45 million bits per second. The backbone of the Inter consists of T-3 lines.

Leased lines are very expensive and are generally only used by panies whose business is built around the Inter or need to transfer massive amounts of data. ISDN， on the other hand， is ailable in some cities for a very reasonable price. Not all phone panies offer residential ISDN service. Check with your local phone pany for ailability in your area.

Cable Modems

A relatively new development is a device that provides high-speed Inter access via a cable TV work. With speeds of up to 36 Mbps， cable modems can download data in seconds that might take fifty times longer with a dial-up connection. Because it works with your TV cable， it doesn't tie up a telephone line. Best of all， it's always on， so there is no need to connect——no more busy signals！ This service is now ailable in some cities in the United States and Europe.

The download times in the table above are relative and are meant to give you a general idea of how long it would take to download different sized files at different connection speeds， under the best of circumstances. Many things can interfere with the speed of your file transfer. These can range from excessive line noise on your telephone line and the speed of the web server from which you are downloading files， to the number of other people who are simultaneously trying to access the same file or other files in the same directory.

DSL

DSL （Digital Subscriber Line） is another high-speed technology that is being increasingly popular. DSL lines are always connected to the Inter， so you don't need to dial-up. Typically， data can be transferred at rates up to 1.544 Mbps downstream and about 128 Kbps upstream over ordinary telephone lines. Since a DSL line carries both voice and data， you don't he to install another phone line. You can use your existing line to establish DSL service， provided service is ailable in your area and you are within the specified distance from the telephone pany's central switching office.

DSL service requires a special modem. Prices for equipment， DSL installation and monthly service can vary considerably， so check with your local phone pany and Inter service provider. The good news is that prices are ing down as petition heats up.