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Introdution to ISDN
In most parts of the US and in many European countries, you can connect your computer to the world with a super-fast technology called ISDN (Integrated Services Digital Network). It lets you work with more information faster and more efficiently than you'd ever dream a traditional phone line and modem connection could. But there's more. ISDN opens a whole world of possibilities, including video conferencing, the ability to let two people in remote locations work on the same project, digital audio transmission, and a multitude of other opportunities as well as providing traditional voice phone service. In this article, we'll introduce you to ISDN technology and give you some idea of its power. We'll also compare ISDN to traditional modems and phone service and list some of the hardware that will enable you to use ISDN in your home or office. Let's begin by exploring why you might want ISDN. Mighty "morphing" ISDN power Speed is one distinct advantage ISDN has over traditional modem connections. Documents that once took hours to send with regular modems can transfer in minutes with ISDN. Graphic designers and engineers can collaborate on designs without waiting for overnight delivery service. Telecommuters, advertising agents, lawyers, students, writers, and business people can take advantage of this technology to manage tasks from home or remote offices rather than scheduling trips to do so. Another advantage is ISDN's practically noiseless connection. Digital signals are far less likely to suffer from line problems than traditional analog connections. What's more, ISDN can work over the same wires that currently drive your regular telephone. ISDN can even replace your current phone line. If your local phone company can provide you with ISDN service, you can easily upgrade to--or add--an ISDN phone in your home or office. How ISDN works ISDN is a completely digital connection--all the way from the phone company to you. This is a big improvement over today's phone service. To see the advantages of ISDN's digital connection, you need to know a bit about how traditional phone service works. The average phone requires an analog connection. That is, the sound gets pumped through a phone (or out of a modem) in a series of electrical currents similar to the signals that drive speakers and microphones on a stereo. As you might imagine, this analog signal isn't very efficient, can be difficult to transmit clearly over long distances, and takes more time to reach a destination than its digital counterpart. The phone companies once used only analog equipment to transmit sound, as shown in Figure A. After a while, they discovered that if they converted sound to a digital format at the central office, they could transfer that audio information from place to place faster and more efficiently. Today, most phone services use a hybrid of analog and digital technologies. Your phones and modems send out a raw, inefficient analog signal. As shown in Figure B, the phone company converts the analog signal into digital form once it reaches the switching equipment at the central office. The phone service converts the signal back to analog before the connection reaches the destination phone or modem. The advantage to this analog-to-digital-to-analog conversion is that it's cheap to implement and easy to maintain. The disadvantage is mediocre sound quality because the audio doesn't need to be exact. Modems are severely limited by this poor sound quality as well. The human ear and mind can easily handle inconsistencies in signal quality. Your modem, however, isn't quite as smart as you are and requires more clarity. Computers just can't process information like humans can. Even the slightest noise or a momentary interruption can cause critical errors in a computer signal that will cause your modem to disconnect. That's one of the problems with using modems in conjunction with analog phone lines. Because the phone company restricts the audio quality an analog phone connection can produce, it also limits the amount of data a modem can squeeze into those analog lines. Since moving data is what the Internet is all about, your modem is often the tightest bottleneck in your Internet connection. And this bottleneck can turn your surf through cyberspace into a slow canoe trip. Your computer can move much more information than a standard modem can fit into the archaic analog phone line. ISDN completely eliminates the analog-to-digital and digital-to-analog (AD/DA) conversions, thus providing your computer with the capability to handle more data than a standard modem. The ISDN connection is completely digital. Your signal isn't limited to the narrow constraints of an analog phone line's "last mile" from the central office to your home or business. Also, your connec-tion doesn't lag as a result of the AD/DA conversions, which impose their own costs and inefficiencies. For your Internet surf sessions, ISDN's digital connection means more dependable Internet connec-tions at much higher speeds. ISDN's completely digital
connection allows your computer
Zero to 64 in seconds Since ISDN provides a completely digital connection from one point to another, your connection is very fast. As a matter of fact, a basic-rate ISDN, or BRI (basic rate interface), line provides a multichannel digital connection that consists of three separate channels: two 64-Kbps (kilobits per second) B (bearer) channels and one 16-Kbps D (Delta) channel, commonly referred to as 2B+D. (Another word for the amount of information measured in Kbps is bandwidth.) The B channels in an ISDN line move data at transmission rates of up to 64,000 Bps per channel--before any sort of data compression. ISDN's smaller D channel manages the B channel connections, all control information such as a busy signal, and connection information. Since the D channel demands only 16 Bps to check to see if a line is busy, the connection is much more efficient for the phone companies to handle and, therefore, faster. As a result, ISDN's digital communication lets your computer create nearly instant connections to other ISDN services, such as your Internet provider. ISDN provides two B channels
for data and one D channel,
An ISDN line to your home or office costs a little bit more than traditional analog phone lines do right now. However, the advantages over basic analog phone service far outweigh the costs. Special features ISDN's multichannel lines provide the ability to make more than one connection at a time. For example, with ISDN, you can talk on the phone with one of the B channels while simultaneously looking up information on the Internet with another. By using equipment designed to do so, you could also bond both B channels to produce a 128-Kbps signal, thus creating a very fast Internet connection from your home or office. What you need for an ISDN Internet connection Since ISDN uses technology different from standard modems to transmit information, you'll need some new hardware to take advantage of this digital technology. Your Internet service provider must also have the hardware to support ISDN. In addition, you'll need to ask your local phone company to install an ISDN line in your home or office. When your phone company installs the ISDN line, you'll need a network termination device--called an NT or an NT-1--to convert the ISDN signal into something your computer can use. An NT-1 will also let you attach other devices to the ISDN line. To make the connection from your computer to the NT-1, you need an ISDN terminal adapter (TA)--the digital equivalent of a modem. This TA will connect to the NT-1. Many of the newer TAs include a built-in NT-1. This is a good feature to look for in TAs--especially if you plan to use ISDN for digital communication between computers and the Internet. You might want to rush out and buy ISDN equipment right away. However, there are a few options you should consider before making your purchases. Choosing ISDN equipment There are several configurations you can choose from when you look for ISDN equipment. For the single user, you can connect your computer directly to a TA with a built-in NT-1 for the easiest and least-expensive solution. For small offices, a TA with an Ethernet connection may provide the best way for more than one computer to connect to the Internet. Figure E illustrates just a few of the possible combinations of ISDN-based Internet connections. ISDN equipment needs to interact closely with your local phone company's and Internet provider's hardware. Although most newer ISDN equipment should support a wide variety of standard phone equipment, you should consult your Internet provider before making your final purchase. An Internet provider will most likely have experience with a variety of ISDN options and can guide you to those vendors whose products the provider can support. Your Internet service provider can also give you an idea of how much your ISDN hardware and connection should cost. The price of technology All this technology does come at some cost. However, that cost isn't as high as you might think. Currently, an ISDN line can cost anywhere from $40 to $200 for installation if your local phone company provides the service in your area. Connection fees can run anywhere from $25 to $100 per month for a single BRI 2B+D line. Your Internet service provider may also charge an increased rate for ISDN access. Finally, expect to pay around $495 and up for a TA with a built-in NT-1. To offset the cost, you can attach regular phones to your ISDN line if you use the right equipment. Some TAs include an analog phone-line connector and the circuitry to convert an analog signal to a digital signal. This allows you to plug a standard desk phone into your TA and use it as you would on an analog line. Again, your Internet service provider can help you in these matters. Conclusion ISDN is an inexpensive way to get a fast Internet connection. With the information we've presented in this article, you'll have a good understanding of what makes ISDN work, what ISDN does, and what you'll need to get started with ISDN. Ali
hussain(c 1999)
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