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Wired for Speed
Exploring the possibilities of the Integrated Services Digital Network
Having just recently written a two-part mini-series of columns on personal communication services (PCS), the wave of the wireless future, I decided to initiate something of a trend by offering another two-parter, of which this column is the first. The topic this time around, however, deals with a telecommunication service that is distinctly wired.
The concept of the Integrated Services Digital Network was touted as the wave of the future when I was an undergraduate Telecommunications student. At that time, the first experimental ISDN call had yet to be placed. It eventually did take place, in 1986, and what was once hailed as the blueprint for public networks in the 1990s is now an almost-readily available service. It's not exactly what you would call the dominant feature of the telecommunications landscape, however. Ask yourself this: How many people do I know who have an ISDN line? The answer is likely to be precious and few, as the old song goes.
Yet, the ISDN technology is sound, its benefits are substantial, and its presence is a reality. Unlike some European countries, however, the United States has been slow to adopt the technology due to a variety of factors, the explanation of which warrants more space than we have here. Suffice to say that a combination of market forces and a perhaps slower-than-expected transition from analog to digital switches on the part of the RBOCs and others has led to ISDN being the service of which most people have never heard, despite its substantial benefits.
What is it about ISDN that makes it undeserving of its relative obscurity? Well, if you're the average Internet junkie, frustrated with download speeds that seem to age you beyond your years, it could well be your salvation -- if you can afford it. If you are an Information Systems manager, ISDN could well be the most economical and efficient way to meet some or all of your business voice and data needs.
Let's look at it from the consumer point of view. The copper twisted pair phone line coming into your house is an analog line with 9600 bps of bandwidth. An ISDN line, making use of that very same twisted pair wire, will provide you with 144 kbps of bandwidth -- that's 144,000 bps vs. 9,600 bps -- and will do it in a way that gives you maximum flexibility in using your bandwidth.
ISDN manages this feat by dividing the bandwidth into two 64 kbps "bearer" channels and one 16 kbps "delta" channel, commonly abbreviated as "2B+D." The two "B" channels can be used for simultaneous two-way voice and data traffic, while the "D" channel is used for signaling and calling independently of the other two channels. Moreover, ISDN provides a standard universal interface for switched voice, data, and video services. Using your one-line-does-it-all service, you could establish a direct digital link to circuit switched networks, packet switched networks, information service providers, and other value-added networks.
Business users, of course, would need considerably more bandwidth than the garden-variety ISDN can muster. Primary access ISDN ups the ante to the tune of 23 64 kbps "B" channels accompanied by a 64 kbps "D" channel for a total bandwidth that is essentially the same as a T1 line. On the horizon is BISDN (B as in broadband, as in gigabits), which may actually develop into the service that one day provides us with on-demand, real-time, switched distribution of informational and entertainment programming to the home or office.
Next month's column answers the burning question: What kinds of ISDN services are available in the Bluegrass and how much do they cost?