Types of Digital Modems

Digital Modems

A digital modem does not have to convert between analog and digital signals. Technically it's not a "modem" at all since it is not modulating and demodulating. A digital modem is faster than an analog modem.

To get the increase in speed you will have to pay extra (of course!). Digital modems are more expensive and so are digital data lines from the phone company. The phone company has to install additional equipment for some kinds of digital modems.

Normally a digital modem can receive data at a much higher rate than it can send it out. That works out fine for most people because they are only sending out a few responses instead of whole web pages or data files.

Warning: Once you have used a high speed device, you will be spoiled forever!

ISDN modem:

(I ntegrated S ervices D igital N etwork) - a digital device using a digital phone line. It actually should be called a terminal adapter, but the name modem has stuck. An ISDN device is capable of higher rates than an normal modem, 64 Kbps for a single line and 128 Kbps for a bonded dual line. ISDN adapters cost more than normal modems and also require special arrangements with the phone company (and more $$ for them, of course!). Fiber optic line is best for the highest ISDN transmission rate, but the copper wires used in most homes and offices will work also.
Note: To get the highest speeds out of your ISDN modem, you may need a high speed I/O (input/output) card in the computer to which to connect the modem.

DSL (commonly used for ASDL):

(A symmetric D igital S ubscriber L ine) - a new technology that allows a single regular telephone line to serve for normal phone calls and digital data at the same time.

An ADSL modem receives data (downloading) at rates ranging from 384 Kbps to 8Mbps, depending on the particular kind of service. Even the slowest type is 4 times faster than the best ISDN!

The sending (uploading) rate is much slower, thus the "asymmetric" part of the full name for this kind of service. That is not a problem for most people since they do not need to upload much data at a time.

Besides great speed, ADSL does not require a separate phone line and you are connected all of the time. No more dialing up! You can use a regular phone on the same line and at the same time that you are surfing the Internet. No more busy signals to your friends and relatives!

Another plus is that you can easily hook up all of the new parts yourself. This saves a LOT of aggravation since you won't have to wait on the phone company or the cable TV guy to show up.

Cable modem:

Hooks up to your cable TV line and can receive up to 1.5 Mbps or more. You must have an account with a cable company that also provides data service. You may need a special cable box to which you connect your TV and your computer. You will be sharing the line with all of the cable customers hooked up to your particular cable line. The actual transfer rate you get will depend on how many people are using the cable at the same time. Once cable modems become popular in your neighborhood, your speed will slow down noticeably. Most companies now restrict the top speed level and balance the load better than they used to do. A cable modem connection is certainly faster than ISDN. Most cable accounts are faster than most DSL accounts.

Дата добавления: 2014-12-23