For the uninitiated, even the very thought of buying a modem is a little like exploring the back side of the computer black arts. Their are more initials here than most people will ever see in an entire lifetime, and when you add new telephone services like ISDN that use something like a modem (but that isn't) it gets even worst.
Almost every computer store offers a range of modems from about $49.95 to several hundred dollars. How is it that there is such a range and how do you know that what you buy will work with what you have and will also work with the services you want to use?
First let's see what a modem does, then we will go into how to specify the right kind of communications tool for you. After that we will touch on some of the new technologies that are coming along, like ISDN and the Terminal Adapters (TA) they use.
The term modem is derived from the two words MODulator, dEModulator. You see, the computer is digital (values represented by zeros and ones), and the phone lines we all have used for many years are designed to carry voice signals (tones) and these are called Analog signals. Try as it might, the computer world doesn't "speak" analog, so it is the modem's job to convert you computer's voice into one the phone lines can carry and then change it back so the computer on the other end can understand.
The computer sends the modem a series of zeros and ones (in a code called ASCII) via a serial port and a cable. The modem is then charged with the job of making the zeros and ones into tones or sounds that can then be spoken on the wires of the phone company. The originating modem "calls" the answering modem and this second modem reverses the process.
Over the years the speed at which this is done has steadily risen to the point today that modems can actually work at the speeds of the first high speed supercomputers that formed the "backbone" of the Internet. Twenty years ago the first modems worked at a speed limit of 110 bits per second (BPS). About eighteen years ago a small company called Hayes Microcomputers developed a set of rules that would let modems work together. Now modems made by one manufacture could speak to modems of another manufacture. This was called the AT command set because all of the commands sent to the modem started with AT, (which stands for ATTENTION).
Hayes also got the speed up to 300 BPS, about six words per second) and this was fast enough to promote the use of computers in remote locations as information terminals. This caused an explosion of activity as computer "Bulletin Boards" sprang up to let people share programs, ideas and information. In a few years the modem engineers figured out a new way of sending signals that allowed speeds to increase to 1,200 BPS (about 24 words per second).
Suddenly private national information services were possible, and companies like CompuServe and The Source were formed. These companies have lead to the online giants of today, like America Online. AOL and Prodigy put the money into advertising to make online service a well-recognized term. Combined with the growth of the Internet there was a sudden need for even faster modems to make graphics work with these services (so we can transmit pictures in addition to words).
Modem manufactures have obliged us with ever faster modems at speeds of 9600, 14,400 and 28,800 BPS. Using various compression techniques we can get occasional speeds up to 115,200 BPS out of the devices of today. We are, however, reaching the end of the amount of speed gains that "plain old telephone service" (POTS) wires can carry. Because of this, new standards like ISDN (Integrated Services Digital Networks) have started to be deployed.
While modems and ISDN Terminal Adapters (TAs) can cost several hundred dollars if you are going after state-of-the-art features, it is possible to have speed up to 57,600 BPS for under $ 100.00.
Today the minimum speed of the modem you are considering should be no less than 14,400 bits per second. At this speed (almost 300 words per second) data communications are quite usable, painting words is fast and painting pictures is reasonable. When I use the term "painting" I am refiring to the speed at which a page of text or pictures displays on the screen. Basic 14,400 modems like the Zoom and Practical Perifferals (and more clones than you can shake a stick at) are very suitable to use BBSs or the online services. However if you are planning to cruise the "net" please consider these devices points of entry only.
I say this in that the so called "Information Superhighway" that we have today is really just an improved country road, some of it gravel, some of it paved, and all with potholes! The better modems have compression at the hardware level, and a lot of error correction built in. Even better ones use standards that make their basic rates of operation twice this 14,400 speed. The so-called 28,800 modems are the key if you are trying to transfer files or use the World Wide Web, one of the most popular and promoted services on the Internet.
I say "so-called" speed of 28,800 BPS in that we now start coming up against the speed limits of the phone companies wires. While both modems on both sides can speak 28,800, the wires (roadway) that carry the signals often can't. Many times your 28,800, modem will only do 24,000 or 26,400 BPS again due to the quality of the phone wires and their condition. To get faster speeds we have to resort to other tricks.
The most often used trick is to compress the signals before the modem has to deal with them. This is actually an extension of how the modem has itself gained speed advantages over 2400 BPS. Compression works like this. If I have a picture of a lake with blue sky, a lot of the information in the picture repeats. One way to send the picture would use a code for every spot or dot on it, the way color copiers work. But if I examine the picture I can see that much of the sky is the same color.
If I see a section of the sky that is all the same color I can say to the modem, "Send blue, and then tell the receiving system to use this same value of blue 57 times in this area of the sky." That takes a lot less time than saying, "Send blue, send blue, send blues...," 57 times.
So when you get your 14,400 modem be sure it does compression. You will most often see that compression figure listed as a faster figure than the 14,400 base speed of the modem. This base speed in the alphabet soup of computer lingo is called the DCE rate, and the compression speed possible is called the DTE rate. All better modems do this in hardware, not software. If you see the initials RIP on the modem it is a software compression modem and will put a strain on your computer to do the work. I don't recommend them.
One other thing to be aware of: the party you are calling also needs to have this hardware compression on, and poll their modems at this rate or higher. If they don't you won't get all the performance out of your machine unless the files are precompressed and stored in that form on their system. This is one of the compelling reasons not to use the online services like AOL. In order to bring more lines back to their central sites, most do not implement hardware compression and high speed polling, although most do precompress their files.
To determine this, ask your Internet service at what rate they poll their modems. Most of the online services poll their modems at the DCE rate, the better ones poll at the higher DTE rates of 57,600 or more. So what kind of modems manage these higher speeds? Almost all of the best known names, like U.S. Robotics, Motorola, Hayes, Boca and TDK qualify. Any of these modems are well worth the money. Modem prices from these name brand manufactures have fallen more than 30% in the last year.
Other good quality modems, like Practical Perifferals, GVC, and Supra offer discount prices and good quality without some of the additional features of the name brands above. Many of these are made using the same chipsets (the basic building blocks) of the modems. Others like Zoom and some of the clones will provide basic services, but may not manage long-term duty cycles. Most modems will get three or more years service with average use. If you buy a modem for Windows 95 use, be sure to ask if it is "Plug and Play".
Almost as important as the modem is the quality of the serial port connecting it to the computer and the quality of the communications software that makes it run. Be sure that your serial port is a 16550 UART type. Internal modems will have their own UART; it also should be a 16550 type. If you only have a 16450 UART, your speed will be limited to about 19,200 BPS. Internal modems, which are placed inside the computer, are less expensive than external models because they use the computer's power supply and case.
When you buy your modem you will also get some software. Unfortunately most of it is poorly documented and most is bundled with the expectation it will be replaced. It is best to use the better communications packages, like Telix, Procomm Plus, Delrena, and Qmodem. All of these in Windows or Dos flavors can be found at several area software stores.
If you need even more speed, the next step is ISDN. This service is now available throughout the metropolitan area, and although the installation cost is still quite high the data rates available go up to 128,000 BPS without compression. With compression, these rates can approach the speed of connections most Internet providers have coming into them. ISDN is complicated and beyond the scope of this story, but more information can be had by calling via modem to my BBS (One Crossroads Place) at (913) 663-1100. Type /go ISDN from any menu to learn more. Our ISDN number is (913) 664-5082.
Finally, I often get asked what I use. For the fastest connections, I use U.S. Robotics or Hayes Optima; that is what I have on my desk. For low cost I use Supra and GVC. For ISDN I use the Motorola Bitsurfer. I have had very good luck with these and highly recommend them. For software I like Telix and a small program called BananaComm. Despite the funny name it is a great terminal program and many BBSs, including ours, give it away free.
If you would like to have computer questions answered, please send them to me by e-mail at Kansas City Mail Online or by the Internet: graeme@kcmo.com. The e-mail impaired can reach me by fax at 816-252-5545 or phone at 816-252-4080.
Graeme Gibson is the director of Computer Training Corporation and author of ``How to Build a Clone Computer'' and ``The Computer Repair Handbook.'' His weekly TV show ``Computers Today'' is distributed locally by American Cablevision and Tele-Cable.
copyright Graeme Gibson, C.D.P. 1996
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