posted by David Adams on Fri 19th Jun 1998 11:39 UTC, submitted by John Renyolds
IconHaving determined at the time we began the experiment that ISDN was the only viable form of high speed internet access available in our area, we set out to get wired with ISDN.

The promise of ubiquitous high speed data transmission has coaxed us into dreams of a bright future. Increased productivity, telecommuting, interactive entertainment, and cheap videotelephone communication seems to be just around the corner. The internet has exploded onto the world scene, altering the way that many of us work and play. Networking is central to computing, more now than ever. There are several emerging technologies for high speed internet access to homes and businesses. How well do they work, where and when will they be available, and are they compatible with the computer systems we want to use?

Several years ago, experts studied the world telecommunications infrastructure and decreed that it would be many years before this dream came to fruition. They were half right. The infrastructure isn't there. It would take billions of dollars to run fiber optic cable all over the world, to every household. However, few people could have guessed at the advances that would be made allowing increasing transmission rates over existing lines.

Surprisingly, the existing lines are not always phone lines. Though several digital solutions over copper phone systems are available, there is also cable TV wires, the digital satellite TV infrastructure, and even the electric company's wires, not to mention wireless networking.

This article will cover technologies that are widely available now, those that should achieve wide availability in the next years, and those that are on the horizon.

About analog modems

The modem, whose name comes from MODulator/DEModulator, is a device which converts data into an analog signal which can be transmitted over a standard voice phone line. Various standards exist which allow a modem on one side of the line to understand and translate the noise coming from the other modem. Though they seem to keep getting faster, modem technology is extremely limited because there is only so much noise that can be emitted and then decoded over a regular phone line. A bad phone line will reduce the quality of the data connection, because the two computers may have to send the same information over and over. If you have a 56k modem, you may have noticed that it's not much faster than your older 33.6 modem. That's because it isn't much faster, no matter what US Robotics says. We have just about hit the analog ceiling.

Analog vs. Digital

Analog transmission of data transmits an analogy of the data. When you play an old LP record, what you are hearing is not the original music but something that sounds very much like the original music because the original sounds were used to make grooves in the record, and the record player creates a reproduction of those sounds based on the grooves. Just like that old game where you tell a detailed story to people down the line and with each retelling it becomes slightly changed, analog transmission loses quality quickly and it subject to severe degradation if the medium is low quality. A good artist can make an amazing likeness of a person's face with canvas and paints. But if all they have to work with is bark and a charred stick, it won't look that real. In technospeak, if the signal to noise ratio becomes too low, the data will not be transmitted properly.

When information is transmitted digitally, it is translated into ones and zeroes, transmitted, then translated back. This process can be repeated infinite times, and as long as the method of translation is the same, the data will not lose quality. Digital transmission can also use a lower quality medium and remain true. Whether using paint and canvas or bark and charcoal the ones and zeroes still look like ones and zeroes. Clearly, now that we have the technology to encode our communications digitally, it is most efficient to transmit them digitally too.

Analog's Last Gasp Efforts: 56k and Bonding

Nobody knows how to make hoopla like the computer industry. Constant fast paced innovation has made high tech companies masters of rolling out new products, and the 56k frenzy is no exception. In creating a new 56k standard, modem companies have the chance to sell new modems to both the end users and the ISPs, so it served their purposes to exaggerate the benefits of the 56k technology. Nevertheless, 56k modems are faster, and the reason is simple: application of digital technology.

Most ISPs have digital connections to the phone company's main switches. A 56k compatible ISP connects to the phone company digitally, while the end user's 56k modem connects just like an analog modem. The result is a slightly faster connection, because half of the connection is digital. So if you need to buy a new modem anyway, you can't get or can't afford higher speed access, and there is a 56k compatible ISP in your area, go ahead and get a 56k modem. It will cost slightly more than an older 33.6 modem, and it will be faster

The analog "pipe" that can carry information can only be so big, but if you use multiple pipes and bond them together, you can get more information. Using this theory, many modem manufacturers are starting to market "bonding" modems, rightly called inverse multiplexing modems. Bonding has been used for years in digital ISDN lines (we'll cover ISDN later); it essentially allows a bunch of data to be split into parts and then reassembled into a whole. For those many people who can not get or afford any other type of high speed access, bonded modems could be a real opportunity. However, most ISPs do not support bonding, multiple phone lines are still expensive, and bonded modems still have a large problem with latency, which we'll cover soon.

See Also: More information about bonding

A Word About Speed

When talking about networking, we usually talk about the "speed" of a connection. That's not entirely accurate. The speed is not really a factor, because all electronic transmission travels at near the speed of light. The difference between different methods of transmission is the bandwidth, or the capacity of the connection. How much information can fit "through the pipe," so to speak.

Analog's Secret Shame: Latency

If the "speed" of the connection should rightly be though of as the size of the pipe, another important consideration is how many bursts of information can travel through that pipe in a given time. Latency is the speed between the transfer of a packet of information and the transfer of the next packet. It has a huge effect on the perceived speed of a network connection. Analog modem connections have especially poor latency.

To give you an idea of where the modem fits in, the minimum latency for modem is 100ms, or a 100 millisecond delay between transmitted packets. Ironically, the more data the modem crams in, the worse the latency. A 14.4kb/s modem has a theoretical latency of 40ms, and a 33.6 is 64ms. These numbers are theoretical, but tests have shown that all modems score more than 100ms in the real world. To compare, ethernet has a latency of .3 ms and ISDN, 10ms. A hard drive's "seek time" is also very similar.

During our evaluations of the rest of the types of high speed networking we will be examining latency along with bandwidth when determining speed.

See Also: More about latency

Currently Available technologies: ISDN

Integrated Services Digital Network is a method for transmitting digital data over telephone lines. Its big advantage is that it has been around for a long time and it's widely available in urban and suburban areas. Its primary disadvantage is that in many areas it's quite expensive and is rather difficult to set up.

ISDN allows for data transmission at 56 or 64 kb/s. You might say, "well that's not any better than my 56k modem." Well there you go mistaking bandwidth for speed again. With a latency of less than one tenth of your average analog modem connection, ISDN "feels" a lot faster than a modem, even at 64k. By packing all the packets closer together, ISDN can bring the information to you a lot faster. However, if you need more bandwidth, you can easily bond two 64k lines together for a 128k line. Most telephone companies, ISPs, and hardware manufacturers support two channel ISDN bonding. In fact, for years, businesses who have required high bandwidth have bonded two, four, sixteen or more ISDN lines together.

Since ISDN is a digital signal, it is cleaner than analog, and data can be compressed more. Modems try to compress data in order to fit more in the pipe, but ISDN allows for more compression. Another advantage is that an ISDN connection takes only about two seconds to initiate. Anyone who's sick of listening to their modem screech then sit and wait for it to make the connection will be happy to know that from the moment you type your URL into your browser and when the page comes up is so quick you might think that your connection had never hung up at all.

With ISDN, depending on your type of hardware, you can also transmit analog signals over your line. A typical ISDN terminal adapter, often erroneously called an ISDN modem, has two analog phone ports on the back, where a fax machine, phone line, or analog modem can be plugged in. If you are using both channels for data and a phone call comes in, it will drop one channel and ring the phone. Very handy.

See Also: More about ISDN

OS News Labs

We tested three terminal adapters of different types, using three types of computers: A Windows 95 box, a Mac laptop, and a Linux box. We tried single channel ISDN and bonding. We wrestled and wrangled with our phone company to get the line installed correctly, and we shopped around for the best price. In next week's installment of this article, we'll tell you all about it.

We'll also cover one other widely available high speed data method, Hughes' satellite-based DirecPC, along with DSL and cable modem technology, which is starting to become available to large numbers of people. In our third installment, we'll cover those technologies that may be just over the horizon, like wireless networking and data over other wires.

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