Classic Computer Magazine Archive CREATIVE COMPUTING VOL. 11, NO. 2 / FEBRUARY 1985 / PAGE 30

Telecommunications talk; modem speed: what does it mean to you? Corey Sandler.

Is twice as fast twice as good? Will half the price end up costing you double? And while we're on the subject, just how high is up?

These are some of the very real questions facing modem users and buyers these days, as the telecommunications hardware industry speeds into 1985, a period that seems to have unofficially designated as the Year of the 2400 Baud Modem. Seven modem manufacturers were first out of the gate with introduction of new models last fall. If the recent history of manufacturing in microcomputerdom is any gauge, those models should just be arriving in computer stores about now. The early participants are: Cermetek Microelectronics, Hayes Microcomputer Products, Multi-Tech Systems, Novation, Racal-Vadic, Telenetics, U.S Robotics and Micom.

A modem changes the digital pulses of a microcomputer into an analog warble that can be sent over a telephone line. The act of changing a digital pulse into an analog waveform is called modulation; the translating the other way is called demodulation. Hence, the phrase modem from a concatenation of the two words. A modem rated at 1200 baud is theoretically capable of sending or receiving 1200 bits of information per second; the 2400 baud modem can send 2400 bits per second.

Most computers store data in the form of 8-bit words, or bytes. Each computer "Word" is equivalent to an ASCII character. Typically, there are about 5.5 characters in the average English language word. Therefore, the 2400 baud modem's 2400 bits a second speed is equal to about 300 characters, which translates to approximately 55 words a second. A 10,000 word data file should take approximately 184 seconds, or just over three minutes to send.

At 1200 baud, the throughput is theoretically half--about 150 characters or 27 words a second. A 10,000 word data file should take approximately 368 seconds, or just over six minutes to transmit.

Many microcomputer owners, especially those with simpler or less expensive machines, use modems rates at 300 baud. The equivalent numbers: 300 bits per second, equivalent to 37.5 characters per second, or 6.8 words per second. The 10,000 word file would crawl across the phone lines in 1470 seconds, or 24.5 minutes of warbling.

Obviously, the faster the modem the more theoretical speed for your transmissions. But let's go back to the questions posed at the start of this column. The answers appear to be: 1) Sometimes but not always: 2) It could, in certain situations; and 3) Up seems to sit somewhere around 9600 baud. More Baud for the Buck

The cost of a 2400 baud modem now seems to have settled in a range of 15 to 25% above that of its half-as-fast 1200 baud cousins. For that extra $100 to $200 or so, you get the theoretical saving of 50% on telephone charges, plus the value of the time of the human operators or users at each of the line. On that basis, going to a 2400 baud modem represents a real bargain.

To determine the most efficient and economical speed for you and your particular microcomputer use, you'll have to give some consideration to several other factors related to the nature and amount of use, and the characteristics of the human and electronic equipment at each end.

To begin with, remember that the modem speed (and a few other protocols of communication) must be the same at both ends of the phone line. If the party or service you will be communicating with is limited to 1200 baud, that is the fastest setting you may use. (Almost all of the new 2400 baud modems also allow use at 1200 and 300 baud speeds, so you could lay out the extra cash now in expectation of future payoffs. Then again, prices are heading inexorably downward.)

Next, bear in mind that not all telecommunications public networks have established 2400 baud input lines. At the time of writing, Tymnet has hooked up a handful of high speed links around the country, but Uninet, MCI, and others had not yet joined the group. Count on this to be a short-term problem, though.

And then there is the unpleasant and unrealistic attitude of some public networks that have decided that if they charge a 1200 baud user $1.50 per minute, they should charge a 2400 baud user $3 per minute. Not only does this negate the theoretical cost saving of high speed transmission, in some instances it could end up making such communications considerably more expensive.

Anyone who has used a public network like The Source or the Dow Jones News Retrieval Service knows that you can end up spending a good part of your time tapping your fingers on the desktop instead of the keyboard while you wait for the mainframe computer at the other end of the line to get around to responding to your request or delivering the information you have requested. It is not that the mainframes are slow--hardly--it is that you are just one of perhaps dozens of users vying for split seconds of CPU, disk storage, or input/output switching. Your message to the mainframe zips along the lines at high speed, and the response of the mainframe comes back to you at the same speed, but in between you're just another fish on the line. And the meter keeps ticking away, at double charge for transmission and receipt of nothing at all.

A more reasonable approach for billing by public networks might involve a structure that charges for use of the telephone line, regardless of the speed of characters sent over it, and a charge for the amount of CPU time grabbed by your microcomputer. Is anyone out there listening? Signal Quality

And finally there is the question of the quality of the signal and the nature of the error-checking system used by the computers at each end--elements not directly related to the modem hardware. A particularly bad telephone connection can result in the modems transmitting and retransmitting blocks of data-several times before a successful exchange is made. A 2400 baud modem might end up being slightly more choosy about the quality of phone line it will accept. And certain software protocols require extra levels of checking before data are accepted.

Nevertheless, you will notice a significant increase in speed whenever you up the potential raw speed of your modem. If you or your company does a lot of telecommunication directly between offices--dumping data or retrieval from a database or heavy use of electronic mail, the higher speed will pay for itself in phone charge savings in days or weeks. If, on the other hand, you use your modem to "chat" on a CB simulator on CompuServe, you will not notice much of a change--you type considerably slower than 300 characters per second, as does the person with whom you are communicating.

Years ago, when some modems spoke to each other at 110 baud and 300 baud was considered zippy, it appeared that the speed limit would reside somewhere around 1200 baud. This was in part due to limitations presented by the microcomputer hardware and in part to limitations of the telephone lines. The problems with microcomputers have been dealt with by speedier microprocessors, input/output controllers, and improved circuitry in the modem itself.

The problem with the telephone lines has been dealt with by some very creative engineering by modem designers.

Going from 1200 baud to 2400 is simply a matter of cramming more signals closer together in a particular moment of time. Poor phone lines, though, can rob the signal of its strength or introduce noise that will distort the message. One solution chosen by U.S. Robotics and a few other manufacturers, involves a step away from the present technology, called "compromise equalizers," toward circuitry called "automatic adaptive equalizers."

This new technology in effects has the modem constantly checking the changing nature of the telephone line and making adjustments in the amplitude and other characteristics of the signal being sent. This circuitry is also available when the modem is being used at a slower speed, improving communications there as well. How High is Up?

The next step up may be 4800 baud or a leap to 9600 baud, using technologies called "echo cancellers," and "channel coding." Right now, modems operating at those speeds are available, but the price premium puts them out of reach for all but very high volume telecommunications users.

But consider this: sales of modems for microcomputers have been growing at a phenomenal rate recently; some estimate one million units were sold in the last year, with the curve still headed upward. Economies of scale and the increased use of LSI and VLSI (Large Scale Integration and Very Large Scale Integration) chips is expected to bring the price of modems way down, perhaps to the $100 level for 1200 or even 2400 baud devices. When that happens, your wrist computer can reach out and touch someone with speed and efficiency Dick Tracy only dreamed of.