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Gentle Readers, Been over three months since I have done an update on this for you, but my previous posts are in the Archive. By the very nature of this forum, many have seen none of them. To review: ADSL - Asynchronous Digital Subscriber Line is the "darling" of the industry and a hot technology; but there are problems that surfaced during trials with all the major telcos. The idea behind the technology was to off-load digital traffic from the voice lines at the Central Office (CO) and thereby ease congestion. But there is roughly a three mile transmission limit to all xDSL technologies. Also, the telcos, who have contracted with vendors already, must install DSLAMs (Digital Subscriber Line Access Multiplexers) in their COs to off-load that traffic. The *rub* is that there are still two competing technologies with proponents of each fighting for competitive advantage with IEEE and ANSI and the solution will probably only come with third and fourth generation products that will detect and use either. We are now only at the end of the first generation with the second out in testing. CAP - Carrierless Amplitude Modulation has its backers and is *said* to be slightly more *mature* but suffers greatly in the presence of older phone lines; it is "destroyed" by the load coils. DMT - Discrete Multi-Tone Modulation has its proponents also and is technologically more sound but suffers the throes of patent licensing and some arcane business practices by the patent holders. Of note is the fact that three companies that have licensed it are Nortel (Northern Telcom, a big CO switch maker), Lucent (another CO switch maker) and Motorola. The last two have single chip DMT solutions. Other xDSL technologies are:
The second one is now being sold as ISDN by many of the telcos in various metropolitan areas. And, the last one, hold on to your hats here, is being sold as T1 in some areas. Both at a premium!!! Got T1??? How do I know how it is done??? If it comes in on 24 wires (12 pairs) then it is traditional; but if it comes in on 4 wires (2 pairs) then it is going into a DSLAM at the CO and you are being overbilled, probably. Why??? They can sell six times as many lines that way!!! The problems that have surfaced, especially with ADSL, is cross-talk between different lines when too many of them are on a copper trunk. DMT handles it better and fiber optics do not have the problem. Well, I brought you into May with this, and I intend to take into July by the end of the weekend. There is a *light* at the end of the tunnel that just went before ANSI at the beginning of July, watch for the next two volumes, if it interests you, and URLs are: http://www.adsl.org/, now adsl.com
The first has tutorials, hope to add these to my site soon!!! Enjoy, and as always, Peace,
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Revised: 07/07/98 Copyright © 1997, 1998