MODEMS

The word modem comes from "MOdulate-DEModulate" which is sort of engineer shortcut language for a device that sends and receives digital signals over analog phone lines. The first modems had two little rubber cups where you could insert the handset of your telephone and it would squeal into the mouthpiece and listen at the earpiece. That was back when all desk phones were the same (and all owned by Ma Bell!) and possible speeds were pretty slow - by todays standards.

Modern modems are plugged into the expansion slot of your computer and have a normal phone line that connects to the phone jack in your wall. Actually, your modem will probably have 2 phone jacks on the back of it - one will be labeled Line (or Wall) which is where the phone line connects between the modem and the wall, and the other is usually labeled Phone and gives you a place to plug in your telephone.

External modems were common not so very long ago and are still used in the Apple world. They would connect to the serial port of a PC, and some people still prefer them because they have status lights so you can keep track of the action of the modem and the phone lines. Also, it's easy to use an external modem with several different type computers - for instance, the same external modem could be used by an old IBM-PC, an Apple IIe and your modern PC (not at the same time!). Another favorable point for an external modem is that it doesn't use any more of your mainboard resources (IRQs or I/O memory locations) since it uses a serial port. The reason external modems are not more popular is because they take up desk space, they are a lot more expensive to build (since they are in their own seperate little case with their own power supply) and they do use up a serial port. Also, as modem speeds have gotten faster and faster, the extra cables used by an external modem offer another place to get interferrence and possibly degrade performance.

O.K., now lets get a little technical and talk about speed.

There are two (at least!) ways to describe the speed of data transmission over the phone lines. Originally people talked about "baud rate" and now about all you hear is "bit rate", or "bits per second".

Baud rate (named for an inventor, Frenchman Emile Baudot, who invented the asynchronous telegraph pointer) is the rate at which a signal between two devices changes in one second. For instance, if a phone line is capable of changing frequency (or phase) 300 times in one second, then you can communicate at 300 baud.

On the other hand, bit rate is determined by how many bits you can send with each baud. So baud describes signaling rate and bit rate talks about the actual data transmission rate, or how many bits per second (bps) you can send. Nowadays bit rate is usually described in Kbps, or Kilo-bits-per-second.

The interesting part about data transmission starts here: normal analog phone lines are only capable of about 3200 baud (that would be a GOOD phone line, a noisy phone line would probably be limited to 2400 baud). So, if you can change at a rate of 3,200 time per second, how can you transmit 56,000 bits per second? Well, as it turns out, you can't. Using different methods of modulation and error correction, it's possible to send (and receive) approximately 33,600 bits per second over good analog phone lines and about 28,800 bps over average phone lines. The 56K modems that most of us have in our computers today have a special protocol that allow us to receive signals at 56 Kbps, IF our ISP is capable of sending at that rate, and IF most of our local Phone Company's lines are fiberoptic (rather than analog). But our 56K modems will still transmit data at 33.6 Kbps - on good phone lines, less on average ones. So, if your computer (with a 56K modem) connects to a friend's computer (through their 56K modem), about the best rate of communication you might expect woukd be 33.6 Kbps. Sounds like a rip-off doesn't it? It's just modern marketing hype; 56K describes the maximum, one-way, data transmission rate that is possible under ideal conditions.

In the real world better is not always better. Where we live, for instance, anything over a 28.8 Kbps modem is wasted - our normal hook-up to our local ISP varies from 24 Kbps to 28 Kbps, with 26.6 Kbps being usual - because of our lousy phone lines. Almost everyone reading this will have better service that that! .

Where do you go from here? There are choices out there - more for those of you living in (or near) major cities than those of us living in the hinterlands.

Direct-PC, for instance, uses satellite linkage (similar to, but not compatible with, satellite TV) to download data to your PC at a very high rate of speed. Your computer still uses your local ISP to connect with Direct-PC and tell them what to send to your computer via satellite.

Cable Modems are becoming more and more available. They connect your computer to your local Cable TV Network using a Network Interface Card (NIC) rather than a modem and, if available, are usually the best deal you can get for your money. They don't tie up a phone line, they're "on" 24 hours a day, they're extremely fast compared to a modem/phone line/ISP and they are not nearly as expensive as some of the alternatives. Check with your local Cable TV Company to see if it's available in your area.

DSLs (Digital Subscriber Lines) are a fast growing option in some parts of the country. They use your local phone lines and a special external modem in your home/office to obtain high speed data tranfers. They are not available everywhere and you get the best performance when the Phone Company uses mainly fiberoptic lines - something that is usually common only in the larger cities, so far.

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