This supplement was originally printed
in the June 2000 issue of MacOS monthly.

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My name is Corby Stephens and I am a Macophile. I have been using Macs since 1991 when I started college with my Mac Plus, two megs of RAM, and two 800K floppy drives (no hard disk!) that my dad paid $600 for. I have been working on Macs since 1994. Back in those days I was networking Mac Classics and Mac II computers with PhoneNet LocaTalk wiring and System 7.1. These days I'm using my iMacDV, OS 9, and 128 megs of RAM. How did I learn? Mostly by failing. How else do you learn, right? As time marched on I got to tackle an all Mac10BaseT network with fiber optic cables going between buildings on the campus. My how quickly things change! It seems like only yesterday everyone was rushing out to get the latest 56K modem so that they could upgrade from their 33.6, only to find that, for the most part, they still only connected at around 33.6. Well kids, not anymore! Enter DSL.

Digital Subscriber Line

DSL has been around for about a year now, to the joy and frustration of thousands of users. When it works, it's fabulous. When it doesn't work, it's a stone drag. Here's the deal: DSL gives you 144KBps to 7MBps (it's possible!) download speeds compared to your 56Kbps analog modem using the same exact phone lines. But how? It's time to use our imagination's boys and girls.

Imagine a piece of pipe 10 inches in diameter, which is used to move water. The water flowing through this pipe flows through the bottom inch. Not very much, right? Now imagine that our pipe is your telephone line. Your voice, your 56K modem, and your fax machine only use the bottom one inch of your telephone "pipe". There is only so much information you can cram through one inch of pipe, which is why modem development has reached its end. When the telephone system was first developed they had to weigh how good the fidelity, or quality, of the sound being transmitted could be with how much they could spend (and therefore charge) to implement it. The developers decided that the bottom one inch was good enough, leaving the other 9 inches wide open and unused.

DSL uses those other 9 inches to bring us the speed that we can enjoy. The technical term is "broadband". This is also the reason that you can talk on your phone and be on the internet using DSL at the same time. Your voice is using the bottom one inch and the DSL is using the other 9.

You might wonder what you have to do to get DSL. It isn't what you must do, it's what you have control over. There are more factors out of your control that determine if you can get it at all. You either qualify for DSL or you don't. First of all you must live no more that 18,000 feet (typically) from your Central Office (CO). A CO is where all of the phone lines in your neighborhood run to and connect into the telephone system. That 18,000 feet is line feet, not physical distance. You may be 12,000 feet in a straight line from your CO but the phone lines go up and down poles, take indirect routes around buildings, and eventually end up at your house. By that time it's about 18,001 feet; you don't qualify. Second, your CO has to have the right equipment. Namely, it has to have a DSLAM (Digital Subscriber Line Access Multiplexer). This fancy piece of equipment takes all of the DSL lines coming into it and puts them all into one connection, out to your Internet Service Provider (ISP). Thirdly, if you are within 18,000 feet and your CO does have a DSLAM, there has to be an empty slot in that DSLAM for your connection. If it is full, you are out of luck until someone decides to drop the service or the phone company (or the company who is leasing space from the phone company for their own DSLAM) decides to add more DSLAMs. There are some other potential problems your line specifically might have on it, but these are the three big factors.

What kind of hardware do you use? You don't use a modem that you can go to the store and buy. The company that is providing the DSL line to you provides a special piece of hardware, usually a router or a bridge. This connects to your computer through an ethernet cable. Don't worry, chances are your Mac has ethernet built in. Can you share your connection with more than one computer? Yes! Depending on who your ISP is and how they handle giving out addresses, you may or may not need special software to do this. Can you use it with your AirPort? Absolutely! Connecting and sharing your DSL with your other Macs will be covered in a future article. For more information, I've set up a web page with all kinds of information regarding DSL and your Mac. Until then, surfs up!

Bits per seconds vs. bytes per second

So you have a 56K modem. What does that mean? How come I only download at 2-4KBps? Why not 56K? It's all in the lingo. In a previous article, Shop Talk discussed binary. Binary consists of zeros and ones. A "bit" of data is a single binary digit, either zero or one. A "byte" of data is a grouping of 8 bits. Your 56K modem can potentially move data at a rate of 56,000 bits per second (though the FCC has limited the rate to 53,300). When you watch your browser (slowly) display the speed at which it is downloading a file or graphics, it displays the speed in bytes. Your 56K modem could potentially do 7,000 bytes per second (7KBps). The deal is that no one ever really connects at 56K. The speed is usually around 33-44,000. That's 4-5KBps, which doesn't take into account how backed up traffic is out on the internet. This is why you see 2-4KBps speeds on your analog modem. With DSL you can expect 20-30KBps, depending on the speed of line you signed up for.

Word of the month: broadband

Basically, this means that there is more than one kind of signal going over the wires. In the ethernet world you commonly see 100BaseT. The "Base" means that there is only one kind of signal being passed over the ethernet wiring. There is such a thing as 100BroadX, which means that there is more than one kind of signal being passed at any given time. With DSL, your phone lines can carry your voice and your DSL connection at the same time.

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I hope this has been helpful. If you have any questions, comments, or snide remarks, please send them on in to corby@macosjournal.com and I'd be happy to help you out.

Corby Stephens - corby@macosjournal.com
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